Monsoons are complex phenomena involving coupled atmosphere-ocean-land interactions and remain notoriously difficult to forecast at NWP, subseasonal and seasonal scales, casting doubt also on our future climate projections. A better understanding of monsoon physics and dynamics and their response to forcing, with more accurate simulation, prediction and projection of monsoon systems is therefore of great importance.
This session invites presentations on any aspects of monsoon research in present-day, future and palaeoclimate periods, involving observations, modelling, attribution, prediction and climate projection. Topics ranging from theoretical works based on idealized planets and ITCZ frameworks to the latest field campaign results are equally welcomed, as is work on impacts, extremes and compound weather events, NWP modelling, S2S and decadal forecasting, and the latest CMIP findings to help inform the IPCC AR7.
In the future, monsoon rainfall over densely populated South Asia is expected to increase, even as monsoon circulation weakens. In contrast, past warm intervals were marked by both increased rainfall and a strengthening of monsoon circulation, posing a challenge to understanding the response of the South Asian summer monsoon (SASM) to warming. Here we show consistent SASM changes in the mid-Pliocene, Last Interglacial, mid-Holocene, and future scenarios, characterized by an overall increase in monsoon rainfall, a weakening of the monsoon trough-like circulation over the Bay of Bengal, and a strengthening of the monsoon circulation over the northern Arabian Sea, as revealed by a compilation of proxy records and climate simulations. Increased monsoon rainfall is thermodynamically dominated by atmospheric moisture following the rich-get-richer paradigm, and dynamically dominated by the monsoon circulation driven by the enhanced land warming in the subtropical western Eurasia and northern Africa. The coherent response of monsoon dynamics across warm climates reconciles past strengthening with future weakening, reinforcing confidence in future projections. Further prediction of SASM circulation and rainfall by physics-based regression models using past information agrees well with climate model projections, with spatial correlation coefficients of approximately 0.8 and 0.7 under the high-emissions scenario. These findings underscore the promising potential of past analogs, bolstered by paleoclimate reconstruction, in improving future SASM projections.
How to cite: Zhou, T., He, L., and Guo, Z.: Past warm intervals inform the future South Asian summer monsoon, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6649, https://doi.org/10.5194/egusphere-egu26-6649, 2026.
The Himalaya hosts some of the world’s richest biodiversity and affects climate globally. However, the environmental impacts, in particular on the Asian monsoon, of a rising Himalaya are still intensely debated. Dated and analyzed proxy-observations, from a location at ~5,800 m elevation on Mt. Shishapangma, central Himalaya, the world’s highest fossil baring site, reveal a lush mid-Miocene forest, where today cool arid conditions persist. Together with data from surrounding regions, a major vegetation transition from mixed forest to alpine meadow occurred on the northern slopes of the Himalaya at approximately 11 million years ago, but why? New high-resolution paleoclimate model simulations show significant climate and vegetation transition occurred when the Himalaya passed through a critical height tipping point of 6,000–6,500 m over by pushing out monsoonal conditions from the Tibetan region, yet this rapid uplift of the Himalaya had little impact on the wider monsoon in Asia, contrary to previous interpretations.
How to cite: Farnsworth, A., Jia, L., Valdes, P., Spicer, R., and Tao, S.: The height of the Himalaya exceeded a climate tipping point 11 million years ago, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12911, https://doi.org/10.5194/egusphere-egu26-12911, 2026.
Within Earth’s climate system, the ocean, cryosphere, and vegetation exhibit hysteresis behavior such that their state depends on their past and not merely on their current boundary conditions. The atmosphere’s fast mixing time scales were thought to inhibit the necessary memory effect for such multistability. Here, we show that moisture accumulation within the atmospheric column generates hysteresis in monsoon circulation independent of oceanic heat storage and yields two stable atmospheric states for the same solar insolation. The dynamics of monsoon rainfall is thus that of a seasonal
transition between two stable states. The resulting hysteresis is shown in observational data and reproduced in a general circulation model where it increases with decreasing oceanic memory and exhibits the two distinct states that persist for more than 60 y. They are stabilized by moisture accumulation within the atmospheric column that carries information across time scales much longer than those typical for mixing. We discuss possible implication of an observed seasonal tipping of monsoon systems for the analysis of a future Arctic winter sea ice threshold.
How to cite: Levermann, A. and Katzenberger, A.: Monsoon hysteresis reveals atmospheric memory: implications for Arctic winter sea ice, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11139, https://doi.org/10.5194/egusphere-egu26-11139, 2026.
The Earth’s monsoon systems are closely linked to seasonal migration of the Intertropical Convergence Zone (ITCZ) while the Atlantic Meridional Overturning Circulation (AMOC) acts as a major control on the ITCZ’s latitudinal position through cross-equatorial heat transport. Under sustained global warming, climate models consistently predict a weakening of the AMOC, with some recent studies suggesting a potential tipping, i.e. an irreversible and substantial decline to approximately 3–5 Sv. Such an AMOC collapse is associated with significant cooling and drying in the Northern Hemisphere and a southward shift of the ITCZ.
To assess the impact of a potential AMOC shutdown on the South American Monsoon System (SAMS), we conducted an atmosphere-only simulation using the ICON model at 10 km horizontal resolution. At this resolution, convection is explicitly resolved, and no convective parameterization is required. Sea surface temperatures (SSTs) were taken from an existing AMOC shutdown experiment conducted with a coupled climate model.
Our results broadly reproduce the large-scale precipitation and temperature anomalies observed in lower-resolution coupled model experiments. The southward displacement of the ITCZ produces a zonally elongated dipole precipitation anomaly over the Atlantic Ocean. However, over the South American continent, this signal is attenuated in the high-resolution simulation compared to the lower resolution coupled simulations, where the dipole extends much further inland. This is consistent with previous research indicating that land–atmosphere interactions differ in convection-resolving models compared to CMIP-type models, potentially altering the precipitation response to large-scale perturbations.
In particular, precipitation associated with the SAMS is remarkably robust to the ITCZ shift. Key features such as the Bolivian High, the South Atlantic Convergence Zone, and the South American Low-Level Jet remain qualitatively unchanged despite the AMOC shutdown. This suggests that other drivers—such as the seasonal solar cycle, the orography and geometry of South America, and moisture recycling from the Amazon rainforest—may dominate the spatiotemporal structure of the SAMS, outweighing the influence of large-scale AMOC-driven changes.
How to cite: Riechers, K., Schmidt, H., Hohenegger, C., and Stevens, B.: Robustness of the South American monsoon system to an AMOC collapse in a kilometer-scale atmosphere-only model, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14438, https://doi.org/10.5194/egusphere-egu26-14438, 2026.
Projections of the Asian–Australian, African, and American monsoons are currently challenged by considerable levels of uncertainty, which influences the effectiveness of climate change adaptation strategies. Clarifying the uncertainty sources is essential to reduce this uncertainty. Most previous studies have addressed this issue based on limited members in individual models, which cannot strictly isolate the forced model response from the internal variability. Here, we first employ the latest multi-model large ensemble (MMLE), with a total of 550 members from eight models, under very-high emission scenarios. The results show that model uncertainty (internal variability) increases (decreases) with time for all monsoon regions, but with notably regional disparities in their relative contributions. On the grid scale, internal variability dominates the total uncertainty of summer precipitation changes during the near-term (2020–2039) and mid-term (2040–2059) periods in most monsoon regions. For monsoon circulation, internal variability exerts an even greater influence over the Asian–Australian monsoon region. Compared with the MMLE results, a conventional approach to isolate the forced signal based on polynomial fitting tends to underestimate the fraction of internal variability, particularly when and where that fraction is large. Consequently, the conventional approach overestimates the forced signal of monsoon precipitation relative to internal noise, leading to an earlier time of emergence by about 10 years compared with that derived from the MMLE, which is before 2050 for most monsoon regions. The results highlight the necessity of using MMLEs to quantify sources of uncertainty in climate projections, providing important implications for improving the robustness of future climate assessments.
How to cite: Wang, L., Chen, X., and Lin, P.: Disentangling Internal Variability and Forced Response in Global Land Monsoon Projection Uncertainty: Insights from Multi-Model Large Ensembles, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19186, https://doi.org/10.5194/egusphere-egu26-19186, 2026.
Climate model projections reveal zonally asymmetric changes in monsoon rainfall under global warming. American Monsoon rainfall decreases substantially, primarily due to a pronounced weakening of upward air motion, whereas Asian monsoon rainfall generally increases as a result of enhanced atmospheric moisture and minor changes in vertical motion.
Using abrupt CO2-quadrupling experiments, we separate the impacts of direct radiative forcing from those mediated by sea surface temperature (SST) changes. First, because the Eastern Hemisphere is dominated by large landmasses while the Western Hemisphere is dominated by oceans, an increase in atmospheric CO2 can alter large-scale circulation and suppress upward air motion over tropical America, in particular the North American monsoon region. Second, SST warming exhibits a characteristic pattern with amplified warming over the equatorial Pacific relative to the tropical mean warming, and the increase of latent heating over equatorial Pacific induces a Gill-type atmospheric circulation response, suppressing convection and rainfall over tropical American sector. Third, global warming substantially strengthens summertime latent heating over the Tibetan Plateau, and the enhanced heating counteracts the weakening tendency of the Asian monsoon circulation. Therefore, Asian monsoon rainfall changes are dominated by increasing moisture content, while American monsoon rainfall changes are dominated by weakening monsoon circulation.
These three mechanisms exhibit distinct spatial controls: the first operates at planetary scale and affects both the Asian and American monsoon regions, while the second and third primarily govern changes in the American and Asian monsoons, respectively. The magnitude of equatorial Pacific warming is strongly linked to the historical zonal SST gradient in the tropical Pacific; however, the systematic model bias toward a too-weak historical SST gradient may lead to an underestimation of future drying over the American monsoon regions. Observation-constrained projections suggest that the magnitude of tropical American drying could be up to 1.6 times larger than indicated by raw model projections.
References
[1] He C, Wang Z, Zhou T, Li T (2019) Enhanced Latent Heating over the Tibetan Plateau as a Key to the Enhanced East Asian Summer Monsoon Circulation under a Warming Climate. J Climate 32 (11):3373-3388.
[2] He C, Li T, Zhou W (2020) Drier North American Monsoon in Contrast to Asian–African Monsoon under Global Warming. J Climate 33 (22):9801-9816.
[3] He C, Zhou W (2020) Different Enhancement of the East Asian Summer Monsoon under Global Warming and Interglacial Epochs Simulated by CMIP6 Models: Role of the Subtropical High. J Climate 33 (22):9721-9733.
[4] He C, Zhou T (2022) Distinct Responses of North Pacific and North Atlantic Summertime Subtropical Anticyclones to Global Warming. J Climate 35 (24):4517-4532.
[5] He C, Chen X, Zhou T, Kucharski F, Song F (2025) Drying tropical America under global warming: Mechanism and emergent constraint. Geophys Res Lett. (Under 2nd round review)
How to cite: He, C., Zhou, T., Li, T., Zhou, W., Chen, X., Kucharski, F., Wang, Z., and Song, F.: Wetting Asian monsoon and drying American monsoon under global warming: Mechanism of zonal asymmetric responses, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-683, https://doi.org/10.5194/egusphere-egu26-683, 2026.
Anthropogenic aerosol emissions have significantly shaped historical monsoon precipitation, yet uncertainties persist in the projected response to future emissions. This study employs models contributing at least ten ensemble members to the Detection and Attribution Model Intercomparison Project—MIROC6 and CanESM5—to examine the mid-century response of the Northern Hemisphere (NH) summer monsoons to changes in aerosol burdens. We focus on a scenario characterized by an increase in aerosol burdens over South Asia, but strong reductions over the NH extra-tropical continents (i.e., over United States, Europe, and East Asia), since this is consistent with observed trends. These anomalous reductions induce an inter-hemispheric energy imbalance, prompting a large-scale response in the atmospheric meridional overturning circulation. The upper-tropospheric levels of the overturning circulation enhance heat transport towards the Southern Hemisphere, while the lower levels bring enhanced moisture convergence into the NH, leading to more rainfall across NH monsoon regions. Our findings highlight that global aerosol pollution control measures may have wide-ranging impacts well beyond the aerosol source regions. For South Asia, these findings suggest that widespread remote aerosol reductions could offset the precipitation suppression from rising local aerosols.
How to cite: Kallikkal Puthiyaveettil, S., Dhara, C., Dey Choudhury, A., Vishisth, K., Kumar Mukherjee, S., Turner, A., and Raghavan, K.: Future intensification of Northern Hemisphere Monsoons due to Declining Remote Aerosols, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16309, https://doi.org/10.5194/egusphere-egu26-16309, 2026.
Beyond future emission pathways, projections of precipitation in a changing climate are still showing a large spread among CMIP's Global Circulation Models (GCMs), especially at the regional scale. This is mainly arising from the so-called model uncertainty, i.e. from our limited knowledge in but also from the plural representation of climate system's complex mechanisms. Those uncertainties represent a point of great concern for the design of responsible regional adaptation policies, and it is urgent to reduce these uncertainties to better assess future change in regional precipitation. While ongoing and future improvement of GCMs will surely allow for precision of climate change trajectory, here we suggest to make the best use of already existing information for uncertainty reduction now.
We will focus on the example of the Indian summer monsoon, being a regional phenomenon of importance for the livelihood of billions of people; yet its evolution under climate change is largely uncertain. Using the two latest generations of GCMs (CMIP5 and CMIP6), we suggest an original method for constraining models' projections of Indian summer precipitation change based on observations and using an inter-model Maximum Covariance Analysis (MCA) technique. Our method is compared to a straightforward emergent constraint approach and shows promising and robust results, both in terms of reduction in uncertainty and in the explanation of underlying physical mechanisms. Additionally, a robustness assessment is done through a perfect model validation i.e. by checking the ability of our method to reliably predict a left one out model. We believe robustness-checks are a needed procedure for an honest and trustworthy reduction in uncertainty of future change.
How to cite: Whittle, G., Douville, H., and Terray, P.: A novel constraining method for a better description of the Indian monsoon precipitation change, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7065, https://doi.org/10.5194/egusphere-egu26-7065, 2026.
Heat lows are key components of monsoon systems, forming as areas of low pressure in response to strong surface heating. Heat lows can affect the intensity, timing and location of monsoon rainfall by altering horizontal pressure gradients, encouraging low-level convergence and generating mid-level dry air outflow. It may be expected that heat lows will strengthen in response to surface warming, particularly as they form in arid regions which are heating faster than the global average. Despite this, trends in heat lows globally have neither been fully investigated nor compared, and the role of heat lows in monsoon change remains uncertain.
Here we analyse trends across the planet’s five strongest heat lows in reanalysis data spanning the last 45 years. We demonstrate that heat lows have increased in average size (50,000–120,000 km2 per decade) and frequency of occurrence (3.2–12.7 heat low days per decade) in North America, the Sahara, the Arabian Peninsula and southern Africa. Between regions, however, we note diversity in the spatial and seasonal characteristics of heat low trends. For example, trends in the Southern African heat low are uniquely concentrated in the pre-monsoon period, consistent with delayed regional rainfall onset. Moreover, we point to regionally variable mechanisms of heat low change, whereby trends are either driven by increased downward longwave radiation associated with increased atmospheric moisture (the Sahara, West Asia, Australia), or by increased downward shortwave radiation caused by reductions in cloud cover (North America, southern Africa).
Results point to rapid changes to heat lows which are likely to have significant impacts on adjacent monsoon systems, particularly during the pre-onset period. Critically, we show that heat low trends and their respective driving mechanisms are not globally uniform, hence their impact on monsoons is likely to be regionally dependent, motivating further research into heat-low–monsoon interactions at the regional scale.
How to cite: Attwood, K., Washington, R., and Munday, C.: Increasing heat low size and frequency in major monsoon regions., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10243, https://doi.org/10.5194/egusphere-egu26-10243, 2026.
Sea surface temperature (SST) patterns strongly influence tropical convection, large-scale circulation, and the global energy balance. Yet, the physical mechanisms linking SST patterns to monsoon variability remain insufficiently understood, particularly from an energetic perspective. This study aims to understand how SST patterns, particularly those related to the El Niño Southern Oscillation (ENSO), have influenced Northern Hemisphere monsoons using a subcloud moist static energy (MSE) framework. Utilising 6-hourly ERA5 reanalysis and GPCP precipitation data, we find that Northern Hemisphere monsoon systems exhibit significant negative regressions with boreal summer SST anomalies in the eastern equatorial Pacific, consistent with ENSO-driven variability. Removing the ENSO signal strengthens relationships with other SST patterns, including those over the Mediterranean and tropical North Atlantic for the West African monsoon. Findings also reveal that the theoretical monsoon extent, defined by the latitude of peak subcloud MSE, remains relatively stable interannually, independent of ENSO conditions. ENSO phases instead modulate the distribution and local gradient of subcloud MSE, producing a dipole structure in MSE anomalies. In El Niño years, reduced subcloud MSE poleward of the climatological MSE maximum corresponds to suppressed precipitation, consistent with the upped-ante mechanism in which enhanced tropospheric warming increases the energetic threshold for deep convection at the northern edge of the monsoon where moisture is limited. These results highlight that ENSO-driven SST patterns primarily alter the energetics of monsoon systems remotely through a top-down mechanism that modulates atmospheric stability and local MSE gradients. They also underscore the importance of region-specific processes in mediating SST–monsoon interactions.
How to cite: Garcia Valencia, J. P., Holloway, C., Turner, A., and Tomassini, L.: Explaining how SST patterns influence monsoon interannual variability using a moist static energy framework, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3819, https://doi.org/10.5194/egusphere-egu26-3819, 2026.
This study examines how the summertime Indian Ocean (IO) SST anomalies (SSTAs) affect the Indian Summer Monsoon (ISM) and its predictability in the El Niño developing years from the perspective of seasonal predictions for the years 1997 and 1972. The CFSv2-COLA ensemble seasonal reforecasts successfully predicted the ISM in 1972 but failed in 1997, as those years exhibited drastically different ISM states. Our sensitivity experiments, in which the ocean and atmosphere are decoupled in the tropical IO with the prescribed SST, reveal that the erroneous prediction of cold IO SSTAs in 1997 exacerbates an El Niño-induced ISM drought and “correcting” these SST errors improves the ISM prediction substantially, whereas a good prediction of the summertime IO SSTAs contributes positively to the skillful ISM reforecast in 1972.
It is also demonstrated that the warm IO SSTAs centered in the Arabian Sea in 1997 reduce sea-level pressures locally and steer the low-level anomalous winds to transport water vapor into the India. This regional process counters the El Niño-induced drought tendency and results in a nearly normal ISM that defies the historical El Niño-ISM relation. However, the warm SSTAs centered at the western equatorial IO in 1972 strengthen the anomalous Walker circulations originally set up by the developing El Niño in the Indo-Pacific domain, which further enhance the El Niño evolution and its teleconnection to the ISM. This inter-basin feedback process intensifies the typical El Niño-ISM relation. The spatial structure of the summer IO SSTAs may determine whether the IO regional process or the inter-basin process prevails.
Our study shows that reexamination of current reforecasts on how realistically they predict the key elements of specific historical events in a case-by-case fashion is a useful approach in making progress on exploring physical mechanisms and evaluating model qualities. This synoptic-style examination, combined with modeling experiments and diagnostic analysis, can also help us to identify more regional, delicate, or event-specific sources of seasonal predictability beyond conventional assessment of prediction skill and statistical patterns.
How to cite: Shin, C.-S.: Understanding the sources of the Indian Summer Monsoon Predictability in the El Niño developing years , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7884, https://doi.org/10.5194/egusphere-egu26-7884, 2026.
ENSO typically reaches its peak during the boreal winter but can exert a lasting influence on the East Asian summer monsoon (EASM) for up to six months. The remarkably prolonged impact of ENSO establishes it as a valuable precursor for predicting the EASM, which is beneficial to approximately 1.6 billion people. Over the past three decades, scientists have made significant strides in understanding this relationship, benefiting not only from their own efforts but also from the heightened role of ENSO on the EASM since the late 1970s.
However, our present study discovered that the influence of ENSO on the EASM has been diminishing in the last two decades. Moreover, we revealed that this interdecadal weakening of ENSO's impact is linked to changes in ENSO's decaying rate around the early 2000s. From 1977 to 1999, ENSO events peaking in the boreal winter frequently displayed a gradual decay, which triggered robust positive feedback in the tropical Indian Ocean and the western North Pacific, resulting in pronounced EASM anomalies. In contrast, during the period of 2000 to 2022, ENSO events exhibited a faster decay, leading to a substantial decrease in the ENSO-induced anomalies in the Indo-western Pacific and the associated EASM anomalies. These findings are well supported by model simulations.
The recent decline in ENSO's impact on EASM anomalies poses a significant challenge for predicting EASM in the coming decades. At a time when global warming is causing severe heatwaves and droughts in the EASM region, the changing role of ENSO in influencing the EASM introduces new uncertainties in our efforts to adapt to the global warming crisis.
How to cite: Chen, W. and Yu, T.: Weakened influence of ENSO on the East Asian summer monsoon since the early 2000s, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9006, https://doi.org/10.5194/egusphere-egu26-9006, 2026.
Monsoons are historically understood as continental-scale land-ocean Breeze. Modern studies, however, link monsoons to seasonal migrations of the inter-tropical convergence zone (ITCZ) -- a band of intense precipitation that lies along the rising limb of the tropical overturning circulation. Here, we explore in reanalysis data the relative role of zonal vs. meridional migrations of tropical convergence zones in the Asian-Australian monsoon, employing energetic constraints. Both seasonal ITCZ shifts and seasonal land-ocean energetic contrasts are shown to have a critical influence on monsoons. Energetic constraints, therefore, merge the Breeze and ITCZ interpretations of monsoons and provide a simple analytic framework for understanding monsoon variations. Specifically, we provide energetic constraints on South Asian Summer Monsoon (SASM) onset, retreat, and strength, which yield a mechanism explaining the known tendency for enhanced SASM during La Niña episodes. Similarly, the tendency for enhanced Australian monsoon during La Niña episodes is shown to be related to energetically constrained zonal shifts of the Indo-Pacific regional overturning circulation. Moreover, we show that meridional and zonal energetic contrasts in the Indo-Pacific sector are both statistically independent and precede SASM variations by up to two months. Regional energetic contrasts may therefore be used for predictive applications of seasonal SASM variability.
How to cite: Adam, O., Bhattacharyya, S., and Chakraborty, A.: Energetic constraints unify the Breeze and ITCZ interpretations of monsoons and explain regional monsoon variability, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21203, https://doi.org/10.5194/egusphere-egu26-21203, 2026.
Successive CMIP model generations have indicated a future delay in the onset of the rainy season in some monsoonal regions worldwide, driven mostly by the reduction in the onset phase precipitation. These projections are in agreement with the observed drying trend in these regions, coupled with an increased likelihood of recurring drought-like conditions resulting from rising temperatures. Here, we use a novel methodology to characterise the present-day and future rainy season onset in monsoonal regions over Southern Africa (SAfr) and South America (SAm). The Dry-to-Wet Transition Period (DWTP) expands the current use single date onset methods to consider a period, incorporating more information about the transition, such as duration, precipitation intensity, and dry spells. The DWTP starts with the first significant rains of the season and ends when the rain becomes regular and sustained. The DWTP starts in the southeastern and northwestern SAfr regions between August and September and progresses towards central SAfr by mid-October. Over SAm, the DWTP starts in late August in the western Amazon progressing eastward to reach eastern Brazil in late October. In both regions, the onset date defined using established methodologies occurs within the DWTP. Future projections, based on global parameterised and regional convection-permitting simulations, confirm a delay in the DWTP of about 20 days over SAfr and 20-30 days over SAm. Future scenarios project a later start of the rains in both monsoon areas, resulting in a shorter DWTP. Over SAfr, the DWTP will see more dry days over the Congo basin while over eastern SAfr, the fraction of dry days will increase, resulting in a more abrupt start of the rainy season. Over SAm, the DWTP is projected to have lower rain rates and more dry days over the Amazon, resulting in a shorter but more abrupt transition into the rainy season. These results exemplify the advantages of using a period to better characterise the transition into the rainy season and identify observed and future trends in its characteristics. It provides a novel framework to better quantifying the diverse response to global warming that can modulate regional hydrological cycles and water availability. The methodology can be further expanded to account for different variables, such as temperature and soil moisture, and can be easily implemented in the seasonal forecast system as a tool to improve the overlook into the dry-to-wet transition periods.
How to cite: Zilli, M., Samuel, J., Morris, F., and Hart, N.: Future changes in the characteristics of the dry-to-wet transition period in the monsoonal regions of Southern Africa and South America , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18928, https://doi.org/10.5194/egusphere-egu26-18928, 2026.
During the 2025 Indian summer monsoon, north India was impacted by 17 western disturbances (WDs) – extratropical storms whose impacts over this region are more typically felt in winter months. WD-monsoon interactions often lead to high impact weather as strong synoptic forcing from the WD meets the monsoon's abundant moisture supply. In 2025, this led to, among others, flash flooding in Mandi (killing 3), the devastating Dharali floods in early August (killing at least 5), and the Kishtwar floods several weeks later (killing at least 50). The total number of WDs, 17, was claimed by the media as record-breaking and unprecedented.
In fact, despite the extraordinary number of high-impact weather events, 2025 was comparable to previous years in terms of WD frequency (2024 had 17 WDs as well; 2023 had 15; 2019 had 22). In this talk, I will identify the large-scale atmospheric conditions present during the 2025 monsoon that led to these WDs being so impactful over north India, and discuss how atypical they were compared to the last 80 years. I will explore the relative roles of climate change and internal variability and ask whether such an unusual season is likely to happen again.
How to cite: Hunt, K.: The 2025 Indian summer monsoon and its 17 western disturbances – beyond unprecedented?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7402, https://doi.org/10.5194/egusphere-egu26-7402, 2026.
Monsoon low pressure systems (LPS) are synoptic scale disturbances that form over South Asia during the summer monsoon season and often produce extreme precipitation events, causing disastrous floods. Numerous modelling and observational studies have confirmed the role of convection as a major energy provider for the propagation of LPS. Here, using NCAR’s Community Earth System Model (CESM1.2.2), we investigate the major energy providers for LPS propagation under a reduced mean monsoon precipitation. Four simulations are performed in which the height of the Tibetan and Himalayan Orography (THO) is altered by 1.5, 1.0, 0.5, and 0.0 times its original height. Earlier studies have found a decrease in mean monsoon precipitation with a decrease in the height of THO. However, even with reduced precipitation and convective activity, the number, intensity, and lifetime of LPS are higher when the height of THO is decreased. Barotropic instability associated with the horizontal shear of mean meridional wind is found to increase with a decrease in height of THO, providing energy for LPS formation. However, in the later stages, horizontal advection of dry static energy (DSE) is found as the major energy source for LPS propagation. The decrease in height of THO leads to an increase in dry air intrusion into the Indian mainland and an increase in surface temperature. This leads to an increase in horizontal DSE advection, which in turn induces vertical motion and moistens the atmosphere to the west of LPS. The moist ascent over the west of LPS maintains the precipitation and leads to the intensification of LPS. This idealized study suggests that monsoon LPS can form and propagate in scenarios of reduced mean monsoon precipitation, potentially leading to extreme precipitation events even in drought years.
How to cite: Thomas, T. M. and Sivaprasad, M.: Can monsoon low pressure systems propagate even under reduced mean monsoon precipitation?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2763, https://doi.org/10.5194/egusphere-egu26-2763, 2026.
Moist heat impairs the human body’s ability to cool through sweat-based evaporative cooling, posing a serious health risk. In India, this risk is especially acute, since the Indian summer monsoon (ISM) brings abundant moisture, and socio-economic conditions significantly increase the exposure and vulnerability to moist heat. However, there is a limited understanding of the characteristics and large-scale drivers of moist heatwaves during the ISM. This study uses the ERA5 reanalysis to analyse moist heatwaves and their relationship with active and break periods of the ISM during 1940–2023. An empirical orthogonal function analysis of daily maximum wet-bulb temperature (Tw) anomalies reveals that the first two principal components (PCs) explain key patterns of variability of moist heatwaves, with PC1 controlling their occurrence and PC2 controlling their spatial extent. Whilst breaks in the monsoon favour moist heatwaves in eastern and peninsular India, active rainfall events, corresponding to phases 5–7 of the Boreal Summer Intraseasonal Oscillation, favour moist heatwaves in northern and northwestern India. Specific humidity plays a larger role than dry-bulb temperature in controlling Tw variability in India. The results of this study reveal important characteristics of moist heatwaves during the ISM and offer potential for developing forecasting tools, which could ultimately benefit stakeholders in India.
How to cite: Deoras, A., Turner, A., Lekshmi S, D., Birch, C., Volonté, A., Menon, A., Schiemann, R., and Wilcox, L.: Anatomy of moist heatwaves in India during the summer monsoon season, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2941, https://doi.org/10.5194/egusphere-egu26-2941, 2026.
We propose a novel diagnostic framework within a unified monsoon coordinate system to quantify the variability of the East Asian Summer Monsoon (EASM). This framework introduces two new concepts: Monsoon Vector Projection (MVP), which quantifies monsoon intensity, and Directed Angle (DA), which captures directional variability. The newly developed MVP and DA indices exhibit highly significant correlations with summer precipitation over the middle–lower Yangtze River basin and outperform traditional EASM indices. Moreover, they offer a clearer and more comprehensive representation of the spatial pattern of the Meiyu–Changma–Baiu rainbelt.
Strong EASM years are characterized by pronounced convergence along the Meiyu front, as indicated by enhanced MVP, and are accompanied by anomalous cyclonic shear reflected in DA deflection. This circulation pattern is associated with enhanced rainfall in the Meiyu region, a westward extension and southward shift of the Western Pacific Subtropical High, and suppressed precipitation over northern China, collectively forming a north–south dipole in rainfall anomalies. In contrast, weak EASM years display the opposite pattern. These circulation features are closely linked to the Indo–Asian–Pacific (IAP) teleconnection, as revealed by horizontal Rossby wave ray trajectories and the newly introduced Rossby wave ray flux (Li-Yang WRF). Furthermore, the monsoon coordinate framework is extendable to other monsoon regions, offering a promising tool for better capturing monsoon variability and improving our understanding of its relationship with broader climate dynamics.
How to cite: Yang, Y. and Li, J.: Novel monsoon indices based on vector projection and directed angle for measuring the East Asian summer monsoon, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4466, https://doi.org/10.5194/egusphere-egu26-4466, 2026.
Understanding how high-level clouds shape the global energy balance is critical for characterizing the physical processes driving monsoon systems, which serve as a primary engine of the global water cycle and support billions of people. High-level clouds significantly influence Earth’s energy balance, not only by modulating top-of-atmosphere fluxes, but also their radiative interactions within the atmosphere itself. This high-level cloud radiative effect (HCRE) represents the internal atmospheric heating or cooling caused by high-level clouds. By modifying temperature gradients, the HCRE serves as a key component of the global energy balance and has been shown to influence circulation patterns and precipitation. While such findings suggest that the HCRE also modulates monsoon systems, its specific impact has not yet been investigated. The impact of the HCRE on monsoons involves two pathways: a pathway linked to changes in atmospheric temperatures, and a surface pathway linked to changes in surface temperatures. To date, research has primarily focused on the atmospheric pathway, and has neglected interactions with the ocean surface that are known to be central to monsoon dynamics.
In this study, we aim to quantify how the HCRE modulates monsoon systems when the temperature of the surface layer of the ocean responds to changes in the atmosphere. Specifically, we address how HCRE impacts the seasonal thermodynamic structure of the troposphere, circulation patterns, and the spatial extent and magnitude of monsoon rainfall. To achieve this, we use the Icosahedral Non-hydrostatic Earth System Model (ICON-ESM). Simulations are performed using both prescribed sea surface temperatures and an interactive slab ocean that allows sea surface temperatures to adjust to cloud-driven surface flux changes. For each ocean setup, a control simulation is compared to a simulation in which high-level clouds are made radiatively transparent but remain physically present. Simulations with prescribed sea surface temperatures, are used to isolate the atmospheric pathway. We then identify the surface pathway by subtracting the atmospheric pathway from the total impact of the slab ocean setup. We anticipate stronger and more spatially coherent shifts in the Intertropical Convergence Zone and Hadley-circulation, when the surface pathway is included. This is hypothesized to drive a northward expansion of the northern hemisphere monsoon, even as increased atmospheric stability suppresses mean tropical precipitation.
How to cite: Trogrlić, M., Gasparini, B., and Voigt, A.: Impact of high-cloud radiative effects on monsoons, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13558, https://doi.org/10.5194/egusphere-egu26-13558, 2026.
The monsoon plays a very important role in controlling water availability over land, especially in regions like South Asia. While monsoon rainfall is often studied as a seasonal event, it is also influenced by what happens before and after the monsoon season. In this work, we study the idea that the monsoon system behaves like a **hydrological capacitor**, where land water storage accumulates during the monsoon and slowly releases afterward, affecting future conditions.
In this framework, soil moisture and subsurface water storage act as a memory of past rainfall. During the monsoon, rainfall adds water to the land surface, similar to charging a capacitor. During the dry season, this stored water is lost through evaporation, transpiration, and runoff, which is like discharging the capacitor. Because this discharge happens slowly, the land retains memory of past monsoon conditions over several months or even years.
We develop a simple mathematical model to describe how water storage changes from year to year under monsoon rainfall forcing. The model shows that the amount of storage before the monsoon can strongly influence surface dryness and land–atmosphere interactions in the following season. Even small changes in monsoon duration or intensity can lead to large differences in pre-monsoon dryness, especially when the storage decay timescale is long.
Using idealized stochastic rainfall forcing, we derive expressions for the variability and persistence of land water storage. The results show that interannual variability in monsoon rainfall naturally produces correlations across years because of this storage memory. The model also suggests that a shift in monsoon onset or withdrawal by about 10–20 days can significantly change the amount of water stored in the land system.
As part of the ongoing work, observational data from reanalysis and gridded precipitation products will be used to estimate realistic storage timescales and to test whether the predicted relationships are seen in real monsoon regions. The model will also be extended to study how large-scale climate variability influences the monsoon through changes in rainfall statistics.
Overall, this study shows that viewing the monsoon as a capacitor-like system provides a simple and useful way to understand monsoon memory, interannual variability, and the persistence of dry and wet conditions.
How to cite: Raju, S. and Gunturu, U. B.: The Monsoon as a Hydrological Capacitor: Memory Effects and Interannual Variability, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13241, https://doi.org/10.5194/egusphere-egu26-13241, 2026.
Recent decades have seen major advances in monsoon theory, shifting from the traditional “large-scale land-sea breeze” view towards the understanding that the world’s monsoons are partly local manifestations of the seasonal migration of the ITCZ. There are a handful of frameworks which explain different aspects of the monsoons through energy or momentum conservation approaches. For example, the “Energy Flux Equator” – a proxy for the tropical rainband latitude at seasonal or longer timescales – is located where the meridional column-integrated moist static energy transport is zero. While furthering our understanding of the monsoons, these frameworks have typically used a zonal-mean approach. Here we explore a recent approach using the energy flux potential which allows the study of zonal asymmetries in combination with the moist static energy budget to shine a light on regional monsoon dynamics in present-day and future CMIP6 simulations, for the Asian and West African Monsoons.
How to cite: Pietschnig, M., Geen, R., and Chadwick, R.: Investigating monsoon dynamics in CMIP6 models using a combination of novel and classic energetic frameworks, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10366, https://doi.org/10.5194/egusphere-egu26-10366, 2026.
The Hadley circulation (HC) is an important atmospheric circulation system connecting the tropics and subtropics, and variabilities of regional HC exhibit significant impacts on tropical cyclones (TC). However, the potential feedback of TC on the regional HC remains unclear. Here, we reveal that western North Pacific TC (WNPTC) activity exerts a significant 1-month lagged negative effect on the western Pacific HC intensity (WPHCI), and this relationship is independent of the influence of El Niño–Southern Oscillation (ENSO). We show that WNPTC activity can influence variations in environmental fields through modulating the variations of sea surface temperature over WP, thereby altering the thermal conditions and energy conversion, ultimately contributing to the weakening of the WPHC. The mechanism is further validated by sensitivity experiments. Our results demonstrate the significant effect of WNPTC activity on its adjacent meridional circulation, and illustrate the unignorable cumulative effect of extreme weather systems on the climate systems, which is especially important for that more frequent extreme events are projected under global warming.
How to cite: Xu, F., Feng, J., Li, J., Ji, X., and Wang, Y.: Western North Pacific Tropical cyclones act to suppress its adjacent Hadley circulation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7201, https://doi.org/10.5194/egusphere-egu26-7201, 2026.
Atmospheric aerosols play a pivotal role in impacting the global energy budget and public health. Meteorological conditions significantly affect PM2.5 concentrations at regional scales, while the potential influence of circulation on PM2.5 concentrations in the entire latitude belt from a hemispheric scale remains unknown. Here, we focused on the impact of interannual variations of northern Hadley circulation (HC) edge (NHCE) on PM2.5 concentrations variations during boreal summer on the hemispheric scale. We determined that a northward (southward) shift in the NHCE leads to increased (decreased) PM2.5 concentrations over the northern subtropics within 20°–30°N, mainly through circulation processes. Variations in the latitude of the NHCE explain about 30% of the PM2.5 concentrations averaged over 20°–30°N, with the strongest impacts over North Africa, where NHCE-regulated anomalies of local PM2.5 concentrations reach 36%. The northwards shift of NHCE is accompanied by an overall migration of the northern cell of HC, corresponding to anomalous rising as well as divergence (convergence) in the upper (lower) troposphere over northern subtropics, resulting in enhanced PM2.5 concentrations. Our results are verified by numerical model with fixed anthropogenic emissions. Besides, the amplitude of poleward HC over the past four decades is comparable to the interannual NHCE variation, indicating that the risk of increased PM2.5 concentrations over the northern subtropics may increase. This study highlights the significant modulation of interannual variation of NHCE latitude on PM2.5 concentrations, implying that the effects of circulation may be essential for environmental policy formulation in the northern subtropics.
How to cite: Wang, S., Feng, J., Lou, S., Li, J., Ji, X., and Xu, F.: Summer PM2.5 concentrations in the northern subtropics modulated by the Hadley circulation edge location, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7070, https://doi.org/10.5194/egusphere-egu26-7070, 2026.
Subseasonal variability strongly influences the seasonal mean and spatial distribution of rainfall in the Indian Summer Monsoon (ISM). While the late-twentieth-century weakening of ISM precipitation has been widely attributed to anthropogenic aerosols, their effects on subseasonal variability remain less well understood. Using single-forcing and all-forcing simulations from the Coupled Model Intercomparison Project Phase 6 (CMIP6) Detection and Attribution Model Intercomparison Project (DAMIP), this study investigates how aerosol and greenhouse gas (GHG) forcings modify monsoon variability across synoptic and intraseasonal timescales. Results show that aerosols and GHGs exert opposing influences: aerosol forcing suppresses convection, reduces low pressure system (LPS) rainfall intensity by about eight percent, and weakens the 25–90-day monsoon intraseasonal oscillation (MISO), whereas GHG forcing enhances moisture availability and amplifies both LPS-related and intraseasonal rainfall by roughly six percent. These contrasting effects are consistent with associated changes in vertically integrated moisture flux convergence, with aerosols diminishing oceanic moisture inflow and GHGs strengthening it. The combined historical forcing produces a nonlinear response, indicating interactions between radiative and dynamic feedback that cannot be explained by a linear superposition of individual forcings. The findings suggest that aerosols suppress subseasonal rainfall variability, while GHGs amplify it through thermodynamic and moisture feedback. Understanding these competing influences is critical for interpreting past monsoon trends and projecting future variability under evolving aerosol mitigation and greenhouse gas emission pathways.
How to cite: Narbar, S., Sukumaran, S., and Ganguly, D.: Contrasting Effects of Aerosols and Greenhouse Gases on Subseasonal Variability of the Indian Summer Monsoon, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1399, https://doi.org/10.5194/egusphere-egu26-1399, 2026.
This study employs Coupled Model Intercomparison Project Phase 6 (CMIP6) simulations to assess how large-scale semi-permanent systems of Indian Summer Monsoon (ISM) change in future under varying greenhouse gas emission scenarios. Eight CMIP6 models are analyzed for three Shared Socioeconomic Pathways (SSP1-2.6, SSP2-4.5, and SSP5-8.5) across two future periods: near future (2031-2060) and far future (2071-2100). Model evaluation shows that MCM-UA-1-0 and MIROC-ES2L capture ISMR variability more realistically, whereas ACCESS-CM2 and CanESM5-CanOE exhibit dry biases. Projections indicate an overall intensification of ISMR with increasing emissions, most pronounced under SSP5-8.5. Dynamic responses reveal a strengthening and equatorward shift of the Subtropical Westerly Jet (SWJ), a weakening and southward displacement of the Tropical Easterly Jet (TEJ), and a poleward shift of the Low-Level Jet (LLJ) from the near- to far-future period. Thus, the meridional wind shear weakens while zonal shear strengthens, modifying monsoon dynamics in higher emission scenarios. Teleconnection analysis indicates a persistently negative ENSO-ISMR relationship, while DMI-ISMR and NAO-ISMR linkages intensify under higher emission scenarios. In accordance with these changes, the Central and South Peninsular India would be experiencing more rainfall, particularly in September, but a noticeable decrease is noted in Northeast India rainfall. These findings highlight the future changes in synoptic conditions and rainfall of the ISM over homogeneous regions.
How to cite: Gollapalli, S., Osuri, K. K., Kundeti, K., and Anguluri, S. R.: Understanding Future changes in Semi-Permanent Systems and associated Rainfall during the Indian Summer Monsoon, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-172, https://doi.org/10.5194/egusphere-egu26-172, 2026.
The East Asian summer monsoon (EASM) has undergone two distinct decadal transitions recently: a weakening in the late 1970s that established the “southern-flood-northern-drought” pattern, followed by a recovery around the late 1990s that shifted the rain belt northward. Yet, why the summer monsoon exhibits such changes in a warmer climate remains debated. Identifying the mechanisms controlling recent monsoon changes is a demanding task, with great societal and economic value across this densely populated region.
Here we examine the relative roles of internal climate variability and external forcing using eight large ensemble simulations, finding that recent observed EASM variations are largely governed by internal variability, whereas external forcing exerts a limited positive effect. Pacemaker model experiments further show that the out-of-phase shifts of Atlantic Multidecadal Oscillation and Interdecadal Pacific Oscillation play a dominant role in these monsoon changes, through both tropical and midlatitude pathways.
How to cite: Yu, T., Collins, M., Huang, P., and Chen, W.: Atlantic-Pacific constructive interference drives decadal East Asian Summer Monsoon variations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14692, https://doi.org/10.5194/egusphere-egu26-14692, 2026.
Over the past century, East Asian land monsoon rainfall (EALMR) has exhibited significant decadal variations, primarily linking to sea surface temperature anomalies (SSTAs) in the tropical and North Pacific (TNP). However, how will the decadal variability of EALMR change and the role of TNP SSTAs in a warming world remain uncertain. Projections from the Coupled Model Intercomparison Project Phase 6 (CMIP6) indicate that the leading mode of decadal EALMR will retain its near-uniform spatial pattern, but no significant change in the intensity of decadal EALMR compared to the historical period, which may attribute to the insignificant change in intensity of TNP SSTAs and its relationship with the decadal EALMR. It hints that TNP SSTAs may continue to serve as a key predictability source for decadal EALMR. Comparisons with different external forcings and pre-industrial control experiments indicate that the unchanged property and the role of TNP SSTAs are primarily influenced by the internal variability, which possibly results in the insignificant intensity changes of decadal EALMR under various future scenarios.
How to cite: Li, J.: Insignificant future changes in decadal variability of East Asian summer monsoon rainfall, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9416, https://doi.org/10.5194/egusphere-egu26-9416, 2026.
The monsoon plays a major role in the Asian and African climate. Its variability exerts a strong control of water resources in lots of countries and its future evolution is of concern. While there is extensive knowledge of its mean-state evolution during the Holocene, its centennial variability has remained little explored. Such variability scale cannot be explored from the too short instrumental observation period, but high-resolution paleoclimate archives, such as speleothems, allows to access to indirect measurements of monsoon variability over long time scales.
In this work, we use data from an IPSL-CM6A-LR simulation to investigate this range of variability, both in spatial domains, using ordination techniques derived from Principal Component Analysis, and in frequency domains, using spectral analysis.
To assess the model correspondence to climate reconstructions, we first compare the simulated precipitation with speleothems δ¹⁸O records from the SISALv2 database1, considering the long-term trends. The speleothems δ¹⁸O records constitute a composite proxy of temperature and precipitation. Following Parker et al. 20212, we applied a principal coordinate analysis (PCoA) to the δ¹⁸O and precipitation datasets in order to explore their spatial similarities. In both cases, a strongly predominant first coordinate is found. However, it explains more variance in the precipitation data (about 90%) than in the δ¹⁸O data (about 70%). This ordination technique also makes it possible to discuss similarities between regions by performing a clustering in the reduced PCoA space. A strong coherence is found in Asian monsoon variability, while the African monsoon is shown to be closer to the South American monsoon.
We then explore the centennial band of variability in the Fourier spectrum of precipitation time series (from simulation) for each tropical monsoon region. In this centennial band, most regions exhibit a white-noise spectrum, indicating that monsoon variability on these timescales has no memory. Significant peaks are identified in the East Asian monsoon.
References
1 Comas-Bru, L., Atsawawaranunt, K., Harrison, S., and SISALworking group members: SISAL (Speleothem Isotopes Synthesis and AnaLysis Working Group) database version 2.0, University of Reading [data set], https://doi.org/10.17864/1947.256, 2020a.
2 Parker, S. E., Harrison, S. P., Comas-Bru, L., Kaushal, N., LeGrande, A. N., & Werner, M. (2021). A data–model approach to interpreting speleothem oxygen isotope records from monsoon regions. Climate of the Past, 17(3), 1119-1138.
How to cite: Bouguemari, R., Braconnot, P., and Marti, O.: Centennial variability of the Afro-Asian monsoon during the Holocene, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18476, https://doi.org/10.5194/egusphere-egu26-18476, 2026.
The Indian Summer Monsoon (ISM) is a critical driver of global water availability, agriculture, and food security, yet future climate projections rely largely on instrumental records that are insufficient to capture its long-term, non-linear variability. The Holocene epoch (~11.7 ka to present) provides a crucial framework for resolving these dynamics and evaluating climate models under near-modern boundary conditions, as well as constraining nonlinear monsoon behaviour and large-scale teleconnections through the investigation of abrupt events. The margins of the Thar Desert represent a highly sensitive archive of ISM variability, where monsoon weakening and abrupt climatic events have been linked to the decline of the Bronze Age Indus Civilisation. Despite this significance, continuous high-resolution Holocene records and a clear understanding of seasonal precipitation dynamics remain absent from this region.
Here, we reconstruct Holocene ISM variability and its impacts along the margins of the Thar Desert using an integrated proxy-model approach. Multi-proxy lake sediment records are compared with Paleoclimate Modelling Intercomparison Project (PMIP) and transient TraCE-21ka climate simulations. Results indicate an early Holocene shift from arid to wetter conditions. PMIP results indicate significant mid-Holocene seasonality changes. Furthermore, lake water mass balance modelling is employed to quantify seasonal precipitation–evaporation dynamics during abrupt climatic events captured in proxy records. By resolving the mechanisms driving Holocene monsoon variability and non-linear responses, this work offers insights for refining regional climate projections and assessing future climate risks.
How to cite: Kumari, A., Defliese, W. F., AchutaRao, K., and Dixit, Y.: Proxy-Model Constraints on Holocene Indian Summer Monsoon Variability and Seasonality in Northwest India, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16982, https://doi.org/10.5194/egusphere-egu26-16982, 2026.
In this study, we investigate how the Indian summer monsoon, its water vapor sources, and isotopic signature of precipitation (δ¹⁸Oprecip) responded to the Last Glacial Maximum (LGM, ~21 ka BP) boundary conditions using an isotope-enabled general circulation model with water-vapor source tagging (iCESM1). The LGM presents a valuable case study for understanding the Indian monsoon responses to reduced CO₂, the presence of Laurentide ice sheets and ice-sheet topography, and orbital forcing.
The simulations show a pronounced weakening of Indian summer monsoon precipitation (~15%) during the LGM, in agreement with available proxy records. The drying reflects both thermodynamic and dynamic controls: lower temperatures reduce atmospheric water vapor content, while enhanced zonal temperature gradients between the relatively warm western Pacific and the cooler Indian subcontinent lead to anomalous subsidence over India, further suppressing rainfall.
Moisture source tagging indicates that the dominant source regions to monsoon rainfall-the South Indian Ocean, Arabian Sea, Central Indian Ocean, and continental recycling-remain the same between the pre-industrial control and the LGM, but their relative contributions are reduced under glacial conditions. The δ¹⁸Oprecip values over the Indian monsoon region are enriched by approximately 1‰ in the LGM simulation. A decomposition analysis shows that the enrichment is driven primarily by reduced contributions from distant, isotopically depleted water vapor sources and secondarily by weaker rainout during moisture transport from the Indian Ocean. These results suggest that glacial changes in Indian monsoon δ¹⁸Oprecip primarily reflect large-scale circulation and moisture-source shifts rather than local rainfall amount ("Amount Effect"), highlighting the importance of atmospheric dynamics when interpreting monsoon isotope records.
How to cite: Tharammal, T., Bala, G., and Nusbaumer, J.: Glacial Changes in Indian Summer Monsoon δ¹⁸O Driven by Circulation and Moisture-Source Shifts, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8197, https://doi.org/10.5194/egusphere-egu26-8197, 2026.
The early Eocene represents one of the warmest periods in Earth’s history, with atmospheric CO₂ concentrations and global temperatures far higher than today. Studying this period offers a useful way to explore how monsoon systems behave under extreme greenhouse conditions. However, the markedly different paleogeography, including altered land–sea distributions and the absence of the Himalayas, makes direct comparison with the modern monsoon challenging. Here, we examine the behavior of low-level monsoonal circulation over the Indian Ocean during the early Eocene using five climate model simulations from the Deep-time Model Intercomparison Project (DeepMIP). All simulations show a coherent monsoon-like circulation, indicating that a proto-monsoon system existed during this warm climate state. We further identify low-level jet structures aligned with paleotopographic features over the Eastern African Rift and the Deccan Plateau, which we refer to as the Proto-LLJ. Despite enhanced land–sea temperature contrasts under elevated CO₂, the strength of the Proto-LLJ weakens across the simulations. This contrasts with present-day behavior, where a stronger land–sea contrast is often linked to intensified or poleward-shifted monsoon jets. Our results indicate that CO₂-driven warming leads to increased tropical atmospheric stability, reduced vertical temperature gradients, and weaker convective overturning. As a result, the vertical motion needed to sustain strong low-level monsoon winds is suppressed. These findings suggest that in very warm climates, increased atmospheric stability can outweigh thermal forcing and lead to weaker monsoonal circulation, highlighting a key control on paleo-monsoon dynamics under extreme greenhouse conditions.
How to cite: Ha, K.-J., Kad, P., Steinig, S., Boer, A. D., Chan, W.-L., Hutchinson, D., Thirumalai, K., Lunt, D., Niezgodzki, I., Parekh, A., and Saini, H.: Atmospheric Stabilization Weakened Proto-Low-Level Jet over the IndianOcean during the Eocene Hothouse, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3634, https://doi.org/10.5194/egusphere-egu26-3634, 2026.
Monsoon depressions (MD) are synoptic-scale cyclonic vortices that form over the Bay of Bengal and propagate north-westward through the monsoon trough onto the Indian subcontinent, bringing substantial amounts of rainfall to central and northern India.
Despite their importance, key questions on the mechanisms driving their generation and development are still open. Motivated by aircraft and ground-based observations made during the INCOMPASS field campaign in India in 2016, here we inspect the structure and dynamics of a MD case study (1-10 July 2016) using a variety of Met Office model simulations (1.5 km, 4.4 km and 17 km horizontal resolutions).
The 1.5 km simulation proves effective at resolving intense rainfall caused by deep convection, convergence lines, and kilometre-scale orographic interactions. The evolution of the case-study MD can be divided into two stages: initially the MD is completely embedded in a near-saturated environment up to the mid-troposphere. Then, an intrusion of low-potential-temperature dry air from the west at low and mid-levels starts interacting with the MD.
Using Lagrangian trajectory analysis, we find that during the initial stage of the MD, high-θe air from mesoscale convective systems in the vicinity of the MD reaches its centre at low and mid-levels, enabling its growth. During the second stage, the intrusions of stable and subsiding dry air bring low-θe, low-PV air at low and mid-levels towards the centre of the depression, hindering its development.
The 1.5-km simulation enables us to highlight the presence of individual vorticity towers or filaments embedded within the MD that were not otherwise resolved at coarser (17km) resolution. We use analysis with Stokes' theorem to explore the aggregation of these filaments and their contribution to central vorticity as the MD develops. The work paves new directions for theoretical understanding of growth of monsoon depressions.
How to cite: Turner, A., Menon, A., Volonte, A., Hunt, K., and Deoras, A.: Dynamics and evolution of a case study monsoon depression in a high-resolution simulation of the Met Office Unified Model, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17955, https://doi.org/10.5194/egusphere-egu26-17955, 2026.
Previous studies have extensively examined the intraseasonal and synoptic-scale variability of the Indian summer monsoon, but the Quasi-Biweekly (QBW) mode remains less explored. This study investigates the key modes of subseasonal variability in the homogeneous rainfall regions of India over the past 73 summer monsoon seasons, with a particular focus on the QBW scale. By analysing scale energetics in the frequency domain, the study finds that QBW variability over Northeast India is mainly driven by Rossby wave-like atmospheric disturbances from the Western North Pacific (WNP), which are triggered by diabatic heating and the resulting generation of available potential energy. The strength of QBW variability varies significantly between different monsoon years, with stronger variability during deficit monsoons and weaker variability during excess monsoons. The enhanced (or reduced) available potential energy over the WNP during deficit (or excess) monsoons is responsible for the stronger (or weaker) QBW activity. Wave–wave interactions are identified as the primary mechanism for the formation and propagation of QBW oscillations, while mean–wave interactions play a secondary role, though with contrasting effects over the Indian monsoon region. The interaction between QBW, intraseasonal oscillations, and synoptic systems reveals a multiscale exchange of kinetic energy that impacts the formation and clustering of low-pressure systems over the Bay of Bengal. These findings underscore the significant role of QBW-scale dynamics in shaping the variability and extremes of the Indian summer monsoon.
How to cite: Jeeva P J, A., Dubey, S. K., and Sandeep, S.: QBW Dynamics and Multiscale Interactions in Contrasting Indian Summer Monsoon Years, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1105, https://doi.org/10.5194/egusphere-egu26-1105, 2026.
Extreme rainfall events (EREs) over India are strongly influenced by the Boreal Summer Intraseasonal Oscillation (BSISO), yet how this relationship
has evolved in recent decades remains poorly understood. Using observational datasets and reanalysis from the past four decades, we examine the changes in BSISO characteristics in the recent past and their role in modulating EREs over the Indian monsoon region. We find a marked strengthening of BSISO-associated rainfall over central India (15N–25N), along with a spatially coherent increase in rainfall accumulation from EREs as well as in seasonal mean monsoon rainfall.
Our results suggest that these trends mainly stem from an increase in the number of active BSISO days. Increased BSISO activity creates a more favourable environment, which supports the occurrence and persistence of extreme rainfall. A dynamic-thermodynamic decomposition of the BSISO precipitation shows that the dynamic component, associated with the BSISO circulation, dominates the changes in precipitation. However, increased vertical velocity is limited to areas with increased background moisture, indicating a strong connection between dynamic forcing and thermodynamic conditions.
In summary, our findings highlight a linkage between BSISO variability and extreme rainfall in India over recent decades. The mechanisms we identified provide a physical framework for understanding observed changes in monsoon rainfall and offer insights into how intraseasonal variability might impact future monsoon extremes in the warming climate.
How to cite: Kottapalli, A., Pn, V., and Adam, O.: Strengthening linkage between the Boreal Summer Intraseasonal Oscillation and extreme rainfall events over India, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3603, https://doi.org/10.5194/egusphere-egu26-3603, 2026.
The monsoon intraseasonal oscillation (ISO), marked by alternating active and break phases, plays a crucial role in modulating water resources and high-impact weather events in the tropics. The tropical ISO comprises of two distinct seasonal modes: the Madden-Julian Oscillation (MJO), which is active during boreal winter (December to February), and the boreal summer intraseasonal oscillation (BSISO), which dominates during boreal summer (May to October). While the dependence of the MJO on interannual variations associated with the El Niño-Southern Oscillation (ENSO) has received considerable attention, the corresponding influence of ENSO phases on the BSISO remains poorly understood. Mechanisms controlling the BSISO may be made more complex since it operates on a sheared mean state arising from the monsoon. In this study, we investigate the nonlinear interaction between ENSO and the BSISO, focusing on how the slowly varying, seasonally persistent ENSO signal modulates the background mean state through which the BSISO propagates. Using 43 years (1979–2021) of observational and reanalysis data during the summer monsoon period (June-September), we examine how the frequency, amplitude, phase speed, and spatial extent of BSISO-related convection vary between El Niño and La Niña years by performing simple compositing and statistical analysis. Results reveal the following notable features: (1) Overall, El Niño years support a greater number of active BSISO days than La Niña years. (2) El Niño years tend to produce zonally extended stronger BSISO convection anomalies over the west and central Pacific (during BSISO phase 6), whereas La Niña years form a more conducive environment for convective activity over the Indian Ocean basin (in phase 3). (3) The northward propagation of the BSISO is stronger during El Niño than La Niña, both over the Bay of Bengal and the western North Pacific. The findings are statistically robust based on Welch’s t-test and bootstrapping. To investigate the physical mechanisms, we analyse the meridional structures of key atmospheric variables and conduct vorticity budget analyses for each phase of BSISO under El Niño and La Niña conditions to assess how ENSO induced changes in the background mean state influence the vertical shear mechanism governing BSISO propagation. The findings in this study potentially pave the way for conditional forecasts of BSISO based on ENSO mean state.
How to cite: Mukherjee, I., Turner, A. G., Hunt, K. M. R., Lee, R. W., Volonté, A., and Johnson, S. J.: How ENSO modifies the Boreal summer intraseasonal oscillation (BSISO) in the Asian monsoon region, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15250, https://doi.org/10.5194/egusphere-egu26-15250, 2026.
The Western Pacific (WP) pattern is a crucial driver of mid-latitude teleconnections in the Northern Hemisphere, strongly influencing East Asian winter temperatures. While its seasonal impacts are well established, its subseasonal variability and long-term changes remain less understood. This study identifies significant changes in the subseasonal influence of the WP pattern on surface temperature over South Korea since the mid-1990s using observational and reanalysis datasets. Our analysis reveals a significant shift in the WP teleconnection, with its influence strengthening in December but weakening in January and February. These changes are associated with an anomalous displacement of the WP-associated anticyclone and modulated by interactions with the Arctic Oscillation. Furthermore, seasonal forecast models from the Asia–Pacific Economic Cooperation Climate Center multi-model ensemble capture the WP-induced temperature variations in December; however, strong modulation by El Nino–Southern Oscillation inhibits the independent effect of the WP teleconnection. These findings highlight important deficiencies in current seasonal forecast models and emphasize the need for improved representations of WP teleconnections at subseasonal timescales. A refined understanding of winter temperature variability is essential for enhancing climate predictions, supporting climate adaptation strategies, and mitigating societal risks associated with increasing winter temperature variability in South Korea.
How to cite: Moon, S., Im, S.-H., Kim, O., and Lee, W.-S.: Evolving subseasonal impacts of the Western Pacific pattern on winter temperature over South Korea, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2136, https://doi.org/10.5194/egusphere-egu26-2136, 2026.
The Indian Summer Monsoon (ISM) supplies nearly 80% of annual rainfall over the Indian mainland during June–September and exhibits variability across multiple timescales. Intraseasonal variations, especially the timing and intensity of active and break spells, are critical for water resources and agriculture. However, how well CMIP6 models capture the observed link between the seasonally persistent background state and intraseasonal variability remains unexamined.
We apply Multichannel Singular Spectrum Analysis (MSSA) to IMD rainfall observations (1979–2014) and CMIP6 historical simulations over the Indian mainland to evaluate how well models represent the observed spatial structure and amplitude of the dominant intraseasonal oscillation (ISO) modes: a low-frequency mode (20–60 days) with poleward propagation from the equatorial Indian Ocean and a high-frequency mode (10–20 days) with northwestward propagation from the Bay of Bengal. Across CMIP6 models, systematic biases are evident in both the spatial structure and amplitudes of these modes. Most models also fail to reproduce the observed relationship between seasonal rainfall and ISO intensity: observations show a negative correlation between all-India summer monsoon rainfall and the low-frequency ISO and a positive correlation with the high-frequency ISO, whereas many models simulate the opposite. These errors suggest that widely reported JJAS rainfall biases, particularly dry biases over the monsoon core region, may be closely linked to deficiencies in simulated intraseasonal variability.
To investigate further and diagnose processes, we introduce a moisture budget framework that decomposes the total variability into contributions from the daily climatology, daily anomalies, and a seasonally persistent component defined as the seasonal mean of daily anomalies. By combining this persistent component with the daily climatology to construct an augmented mean state, we quantify interannual variability embedded within the mean advection terms, which incorporates the seasonally persistent component of daily anomalies, and isolate residual transient anomalies upon subtracting both the daily climatology and the seasonally averaged daily anomalies. The seasonally persistent component of both wind and moisture anomalies emerges as the key term differentiating flood and drought years with respect to both horizontal and vertical moisture advection.
We extend the same framework to analysis of vorticity budgets and examine biases in moisture and vorticity budget terms to understand biases in the rainfall-weighted latitude of precipitation (ITCZ) i.e. assess the ability of a model to realistically simulate this parameter vis-a-vis observations. Some models simulate a northward-displaced ITCZ, while others show a southward bias relative to the climatological mean ITCZ position of 23.8° N derived from IMD data. These analyses help elucidate mechanisms governing intraseasonal ITCZ migration. Finally, phase composites of budget terms conditioned on low- and high-frequency ISO phases identify the dominant dynamical and thermodynamical contributions to northward and westward propagation, respectively, and highlight the processes CMIP6 models fail to represent accurately.
Overall, the analysis provides a systematic assessment of intraseasonal variability dynamics and their biases in CMIP6. By linking ISO dynamics to persistent large-scale circulation and background moisture fields, this study advances diagnostics of interannual variations in active and break spell occurrence across models.
How to cite: Jha, R., Nanjundiah, R., and Seshadri, A.: Seasonal-Intraseasonal Coupling and Systematic CMIP6 Biases in the Indian Summer Monsoon , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15994, https://doi.org/10.5194/egusphere-egu26-15994, 2026.
The Indian Ocean dipole (IOD) has been proven to be synergistically influenced by the South China Sea summer monsoon (SCSSM) and El Niño-Southern Oscillation (ENSO) through the regional Hadley and Walker circulations. However, the atmosphere circulation variations are essentially controlled by the atmosphere energetics changes, this study investigates the energetic processes of the synergistic effect of the SCSSM and ENSO on the IOD development from the perspective of the perturbation potential energy (PPE). An anomalous meridional PPE dipole over the western North Pacific (WNP) and southern Maritime Continent (SMC) associated with the independent SCSSM events induces the regional Hadley circulation through energy conversion, leading to the strong east and weak west poles of IOD. Response to the independent ENSO events, the Walker circulation is reinforced by an anomalous zonal PPE dipole over the central-eastern Pacific and SMC. Meanwhile, the significantly uniform troposphere PPE anomalies (in line with troposphere temperature mechanism) over the central-eastern Pacific can extend eastward to the tropical eastern Indian Ocean as the form of Kelvin wave and further stabilize the local environment. These two mechanisms cooperate over the western Indian Ocean and offset over the eastern Indian Ocean, resulting in the strong west and weak east poles of IOD. As the SCSSM and ENSO events coexist, the east and west poles of IOD are both strengthened, much larger than that induced by the isolated SCSSM or ENSO events, demonstrating the synergistic effect of the SCSSM and ENSO on the IOD development. This situation can persist from boreal summer to autumn with the increase of the zonal gradient over the tropical Indian Ocean, contributing to the culminated IOD. In addition, the PPE anomalies are distinctly different in vertical profile, which is mainly contributed by the heat source in the upper troposphere and heat sink in the lower troposphere. Consequently, the PPE serves as the atmosphere bridge in the synergistic effect of the SCSSM and ENSO on the IOD development.
How to cite: Li, J., Zhang, Y., Fu, Y., Zuo, B., Diao, Y., Liu, T., Qi, X., and Wang, H.: On the perturbation potential energy in the synergistic effect of ENSO and South China Sea summer monsoon on the Indian Ocean dipole development, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8493, https://doi.org/10.5194/egusphere-egu26-8493, 2026.
The accurate attribution of summer precipitation in the middle and lower reaches of the Yangtze River (MLYR) is essential for operational forecasting and disaster prevention. However, traditional linear correlation methods are insufficient for capturing reliable causal linkages, making causal discovery algorithms a more appropriate solution. Causal effect measures suggest that tropical climate anomalies exert strong driving and mediating influences during boreal summer, while the Asian climate anomalies exhibit greater sensitivity. Causal analysis identifies seven direct drivers of MLYR precipitation: pressure anomalies over northwest Pacific, Northeast Asia, mid-latitude eastern Pacific, Ural Mountains, southwest Pacific, Scandinavia and Greenland. Additionally, we uncovered the further causal pathways linking MLYR precipitation with tropical Pacific and Antarctic Oscillation signals. These results identify the detailed mediations through the direct drivers of MLYR precipitation, which are crucial to capture its remote precursors. Our findings reveal the physical attributions of MLYR precipitation from the global climate, which may improve its operational prediction skills, and even broaden the precursors of East Asian summer monsoon.
How to cite: Tang, Y., Hu, W., Duan, A., and Hu, D.: Causal inference and mediation for summer precipitation over middle and lower reaches of the Yangtze River, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11, https://doi.org/10.5194/egusphere-egu26-11, 2026.
This study reveals that the linkage between the El Niño-Southern Oscillation (ENSO) and the northern boundary of the East Asian summer monsoon (EASM) has experienced a marked interdecadal weakening since the late 1980s. We further explore the underlying mechanisms of this interdecadal transition, emphasizing the role of Indian Ocean sea surface temperature (SST) anomalies. Before the late-1980s, ENSO-induced warming of the Indian Ocean—driven by atmospheric teleconnections and ocean-atmosphere interaction—suppressed Indian summer monsoon rainfall (ISMR) via enhanced convective heating and a strengthened Hadley circulation. The resulting decrease in ISMR triggered a negative-phase Silk Road Pattern (SRP), leading to a southward shift of the EASM northern boundary and a decline in precipitation over the monsoon transition zone. After the late 1980s, concurrent cold SST anomalies in the tropical North Atlantic suppressed the ENSO-driven Indian Ocean warming by enhancing easterly winds, increasing cloud cover, and reducing downward shortwave radiation. This weakened the associated Hadley circulation and SRP response, thereby diminishing the influence of ENSO on the monsoon boundary. The proposed mechanism is further supported by numerical experiments conducted with the atmospheric general circulation model.
How to cite: Ren, Z., Chen, W., Chen, S., Wang, Z., and Wang, L.: Fading influence of El Niño-Southern Oscillation on East Asian Summer Monsoon Northern Boundary after the late-1980s, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2130, https://doi.org/10.5194/egusphere-egu26-2130, 2026.
Monsoons, although embedded within the large-scale Intertropical Convergence Zone, exhibit distinct regional dynamics. Two major components viz Indian Summer Monsoon and Sahelian Summer Monsoons display substantial interannual variability that affects a significant part of the world’s population. Thus, understanding how these systems interact is essential for the predictability both at the intraseasonal and interannual timescales.
In this study, we combine observational datasets and reanalysis products to investigate a dynamical pathway that couples the two Monsoon systems. We also analyze the strength of this coupling in a changing climate. Our analysis suggests that the Indian Monsoon Rainfall (IMR) and Sahelian Monsoon Rainfall (SMR) have become coupled in recent decades (1985–2020), showing a much stronger interannual relationship than during 1950–1984. This enhanced coupling is closely linked to large-scale dynamical changes, particularly those associated with the African Easterly Jet (AEJ).
The coupling between the two systems is governed by the intraseasonal convective disturbances that originate over Northern India and propagate westwards and reach Sahel roughly two weeks later, enhancing moist convection and rainfall anomalies. A defining feature of these westward-propagating intraseasonal disturbances is their coherent potential vorticity (PV) core in the mid-troposphere, which collocates with the core of the AEJ in the mid-troposphere. This alignment of the PV core with the AEJ core dynamically traps these waves along the AEJ and thus results in a coherent wave propagation.
In the recent decades, the AEJ has strengthened due to an increased meridional temperature gradient, thus the propagation of these waves from Indian region to Sahel have become more effective thereby contributing to the observed strengthening of the two large scales Monsoons.
How to cite: Bordoloi, A., Chakraborty, A., and Nanjundiah, R. S.: A Monsoon Bridge Across Continents: Untangling the Strengthening Link Between Indian and Sahel Rainfall, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1289, https://doi.org/10.5194/egusphere-egu26-1289, 2026.
Uncovering predictability sources of Northern Hemisphere land monsoon rainfall (NHLMR) is a vital importance for disaster prevention and mitigation as well as sustainable economic development. Using observations from 1971 to 2020, the present study reveals a regime shift of the tropical oceanic drivers of the interannual variation of NHLMR. We show that the interannual variation of NHLMR is dominated by a zonal sea surface temperature (SST) contrast in the tropical Pacific and a uniform SST pattern in tropical Atlantic, and accompanied by a dipole SST pattern in the tropical Indian Ocean. While the relationship of NHLMR with tropical Pacific remains stable over the past five decades, the relationship with tropical Atlantic is strengthened around the mid-1990s. Observations and numerical experiments demonstrate that decadal warming of the tropical Indian Ocean and Atlantic Ocean, associated with the phase transition of the Atlantic multidecadal oscillation, is the main contributor to the enhanced influence of the tropical Atlantic on NHLMR after mid-1990s by modulating the pantropical Walker circulation.
How to cite: Zhu, Z.: Stronger Influence of the Tropical Atlantic on Interannual Variability of Northern Hemisphere Land Monsoon Rainfall since the Mid-1990s, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10575, https://doi.org/10.5194/egusphere-egu26-10575, 2026.
The Arctic climate system exhibits dramatic changes in autumn, yet its connection to the tropics remains unclear. This study leverages inter-basin/region teleconnectivity (IB(R)T) analysis to unveil the key teleconnected regions responsible for the connection between autumn Arctic temperature and tropical sea surface temperature (SST). A robust positive correlation is identified between North American Arctic (NAA) temperatures and North Tropical Atlantic (NTA) SST, with the NTA SST leading by one season. Observational evidence reveals that western Pacific (WP) subtropical high (WPSH) and SST play an intermediary role in this cross-seasonal tropical-Arctic connection. Summertime NTA warming triggers an intensification of the WPSH, subsequently inducing autumnal warming of WP SST via inter-basin interactions. This intensified WP convection generates a Rossby wave train propagating from the Northern WP eastward towards the NAA, ultimately leading to an anomalous high over the NAA. The increased atmospheric thickness and air temperature enhances downward longwave radiation, further contributing to surface warming over the NAA. The linear baroclinic model experiments, forced with thermal anomalies corresponding to WP SST warming, successfully reproduce the observed atmospheric circulation response and the associated air temperature changes over the NAA. Our findings provide insights into the role of inter-basin connections in Tropical-Arctic linkages.
How to cite: Lou, W., Sun, C., and Li, J.: Summer tropical Atlantic drives autumn North American Arctic warming through western Pacific Bridge, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7218, https://doi.org/10.5194/egusphere-egu26-7218, 2026.
Posters virtual: Mon, 4 May, 14:00–18:00 | vPoster spot 5
EGU26-4971 | ECS | Posters virtual | VPS2
Synoptic-Scale Mechanisms And Climate Oscillation Influences On The Monsoon Breaks Of The Indian Summer Monsoon SystemMon, 04 May, 14:39–14:42 (CEST) vPoster spot 5
The Indian Summer Monsoon Rainfall (ISMR), occurring from the month of June to September, is characterized by intraseasonal variability in the form of active and break spells. Monsoon breaks are periods of sparse to no rainfall, marked by positive outgoing longwave radiation anomalies, above-normal pressures, and clear-sky conditions. These monsoon breaks can have socioeconomic impacts due to their effect on crop growth stages, irrigation planning, and water management. This study aims to investigate the synoptic-scale systems responsible for the onset and sustenance of monsoon breaks over the Western Ghats and other parts of India to improve future predictability of the same. Rainfall data from 1901 to 2025 is used to identify break spells and classify them into short, moderate, and long-duration events. Subsequently, decadal rainfall composites are constructed. These composites reveal patterns of rainfall suppression and enhancement over the Indian subcontinent, equatorial Indian Ocean and West Pacific. Although the spatial structure of rainfall anomalies remains consistent, slight decadal variabilities are observed. Composite analyses of outgoing longwave radiation, and upper and lower tropospheric winds are used to diagnose the synoptic features associated with monsoon breaks. Case studies of recent drought years, 2002 and 2015, highlight the role of upper tropospheric anticyclones, northward displacement of the monsoon trough, and dry air intrusion from West Asia in sustaining and prolonging the breaks, confirming previous studies. The influence of large scale climate oscillations such as ENSO, EQUINOO, and the Boreal Summer Intraseasonal Oscillation (BSISO) on monsoon break frequency and duration is investigated using statistical and machine learning tools, with the aim of informing the development of improved predictive frameworks for monsoon breaks.
How to cite: Aboobaker, J. and Singh, Dr. S.: Synoptic-Scale Mechanisms And Climate Oscillation Influences On The Monsoon Breaks Of The Indian Summer Monsoon System, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4971, https://doi.org/10.5194/egusphere-egu26-4971, 2026.
EGU26-731 | ECS | Posters virtual | VPS2
Evolving Characteristics in Western Disturbances over the Hindu Kush HimalayasMon, 04 May, 14:54–14:57 (CEST) vPoster spot 5
Western Disturbances (WD) are key atmospheric phenomena over northern India, Pakistan, and the Western Himalayas, especially during winter months (December to February). In recent years, increasing variability in these systems has been observed across all seasons, notably pre-monsoonal months (March to May), although thorough investigation remains underexplored. The study evaluates the shifting behaviour and structure in WDs across two climatologically distinct periods – 1950 to 1976 and 1977 to 2022, corresponding to the well-documented 1976-1977 climate shift. In this study, vorticity-based WD track data, coupled with the ERA5 reanalysis dataset, have been utilised to analyse the shift. Behavioural changes are quantified through frequency trends, maximum vorticity distribution and mean track, while structural evolution is examined through composite vertical profiles of key atmospheric variables. The study unravels notable increase in WD frequency during the pre-monsoon season in recent decades, accompanied by a westward shift in WD origins and longer track durations, thereby enhancing the potential for moisture transport. Furthermore, substantial strengthening of upper-level zonal winds, intensified mid-tropospheric convection, and atmospheric moisture availability have been observed through structural analysis. Such transformations indicate a transition of WD towards hybrid systems with enhanced convective features, thereby elevating the potential for extreme precipitation events during the pre-monsoon period. This improved understanding of the evolving WD dynamics is critical for hydrological planning, climate action, strategies and disaster preparedness in the highly vulnerable Himalayan and adjoining regions.
How to cite: Mitra, S., Sardana, D., and Agarwal, A.: Evolving Characteristics in Western Disturbances over the Hindu Kush Himalayas, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-731, https://doi.org/10.5194/egusphere-egu26-731, 2026.
