This session invites contributions that advance process understanding and prediction of weather and climate with a particular focus on the subtropics. We welcome studies based on observations, theory, numerical models, and machine learning. Topics of interest include, but are not limited to:
• Atmospheric processes shaping clouds, circulation patterns, dust and air pollution transport, and surface weather such as tropical–extratropical interactions, subtropical jet fluctuations, Rossby wave dynamics, transient eddies, monsoon circulations, and convergence zones.
• Weather, climate, and compound extremes – droughts, heatwaves, wildfires, heavy precipitation, flooding, dust storms, and windstorms – spanning their drivers, future changes, and impacts on society and ecosystems.
• The water cycle – rainfall, evapotranspiration, and moisture transport – modulated by weather systems such as cyclones, cutoff lows, cold air outbreaks, mesoscale convective systems, easterly waves, and atmospheric rivers.
• Coupled interactions between Earth system components, including land-atmosphere and ocean-atmosphere feedbacks, and the role of sea surface temperature patterns in shaping subtropical climate.
• Climate variability and remote linkages with ENSO, the Madden-Julian Oscillation (MJO), and the Hadley circulation.
• Observations and climate model simulations addressing past and future changes in regional circulation patterns and surface weather, and novel approaches for identifying model biases and for reducing uncertainties in projections.
Orals: Mon, 4 May, 08:30–10:15 | Room 1.61/62
Large-scale tropical and extratropical responses to anthropogenic warming are well studied. These include mean poleward shifts of the extratropical jet streams and expansion of Hadley cells. Debate about the interaction between the two in changing the poleward limit of the Hadley cell continues. However, this literature has limited focus on subtropical drying. Hadley cell expansion does appear a leading candidate for the observed and projected winter drying across the mediterranean climates of the Southern Hemisphere. But the most unambiguous drying signal in climate model projections is in the southern monsoons and their extensions during austral spring (September-November). In this contribution, we argue that understanding this drying requires new climate theory developed with a specific subtropical dynamics lens.
Subtropical westerly flow on the edge of tropical convective hotspots allows the propagation of synoptic-scale Rossby waves into low latitudes. The propagation of these extatropical upper-level westerly waves towards the tropics is known to modulate rainfall across subtropical deserts, monsoons, and monsoon extensions.
The unique geographic distribution of ocean and land in the Southern Hemisphere preferentially supports such wave propagation and absorption into three well-defined subtropical convergence zones in the South Pacific, Atlantic, and Indian Oceans. While the subtropical belt is a zone of mean subsidence, hence the large deserts, frequent synoptic-scale interaction between upper-level westerly waves and tropically-sourced warm humid air intermittently overcomes this mean subsidence in these subtropical convergence zones. The resulting tropical-extratropical cloud bands produce much of the rainfall supporting the water resources and agro-economies across southern Africa, the South Pacific Islands, and South America.
Here, we present contemporary trends of decline in these cloud bands which are projected to continue under planetary warming. These trends are most robust in austral spring (October-November), coinciding with delays to the onset of southern monsoons. Declines in cloud bands are partially associated with poleward shifts of the eddy-driven jet, however, analysis of the annual cycle shows that across the CMIP model ensembles the equinoctial switch of the Hadley cell from the southern into the northern hemisphere is delayed about one month. This delayed switch explains a relative enhancement of subtropical subsidence during austral spring which is reflected in monsoonal dynamics, especially over South America and Southern Africa.
How to cite: Hart, N.: Subtropical dynamics and change and their influence on the monsoons, especially in the Southern Hemisphere., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19926, https://doi.org/10.5194/egusphere-egu26-19926, 2026.
Summer rainfall over eastern China is shaped by interactions between the East Asian monsoon and mid–high latitude circulation regimes. The Northeast China Cold Vortex (NCCV), a cut-off low over East Asia and the western Pacific, plays a central yet poorly understood role in modulating large-scale rainfall patterns and the timing and meridional position of summer rain belts. Here, we investigate the summer manifestation of NCCV activity using long-term reanalysis and gridded precipitation datasets from a circulation-regime perspective.
NCCVs are identified from 500-hPa geopotential height and temperature minima using a set of simplified, consistently applied detection schemes formulated under different constraint conditions across ERA5, NCEP/NCAR, and CRA reanalyses, yielding an ensemble NCCV dataset. Summer precipitation characteristics of the three major rain belts—Meiyu, North China, and Northeast China—are objectively quantified using five independent precipitation datasets (MSWEP, ERA5, NCEP/NCAR, CRA, and CPC), including onset, withdrawal, duration, accumulated precipitation, and a composite precipitation index.
Composite differences between years of exceptionally high and low NCCV activity, selected using strict criteria based on NCCV frequency and rain-belt precipitation indices, reveal a robust, recurring three-dimensional circulation regime. A pronounced dry–wet boundary emerges between 30°–40°N, accompanied by a meridional dipole in 500-hPa geopotential height and temperature, with positive anomalies to the south and negative anomalies to the north. This pattern persists throughout June–August but exhibits systematic seasonal migration, with the latitude of maximum upper-tropospheric westerly anomalies shifting northward from ~30°N in June to ~40°N in August.
Vertical cross-sections of the same composite differences further reveal pronounced meridional asymmetry, characterized by upper-tropospheric westerly wind anomalies near 40°N and deep-tropospheric easterly wind anomalies near 55°N. These anomalies are collocated with sharply tilted extrema in potential temperature and geopotential height, with a sign reversal in potential temperature across ~200 hPa and a coincident geopotential height anomaly maximum, indicating the dominance of meridional dynamical processes rather than purely zonal adjustments. Convergent meridional flow emerges as a preferred environment for NCCV development and precipitation enhancement, while thermal anomalies in the tropical upper atmosphere (10–100 hPa) may play a role in modulating the background westerly strength and the excitation of NCCV-related precipitation over eastern China.
Across datasets, NCCV activity primarily regulates summer rainfall over eastern China by shifting the timing and meridional position of regional rain belts rather than uniformly intensifying precipitation. Significant linkages are identified with Meiyu rainfall amount, the onset and withdrawal of North China rainfall, and the duration of Northeast China rainfall. Together, these results establish a physically interpretable circulation regime through which mid–high latitude systems interact with the monsoon to shape East Asian summer rainfall, offering robust observational constraints for future dynamical studies.
How to cite: Zhang, N.: When Mid–High Latitude Systems Meet the Monsoon:How the Northeast China Cold Vortex Regulates Summer Rain-Belt Timing and Meridional Shifts, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8760, https://doi.org/10.5194/egusphere-egu26-8760, 2026.
Extreme precipitation in the subtropical regions is often influenced by a combination of tropical and extratropical processes. In this work, we examine two-way feedbacks between the tropical moist margin, which is a proxy for heavy rainfall, and extratropical Rossby waves, defined by upper-level potential vorticity (PV). Firstly, cyclonic PV anomalies that approach the moist margin induce strong poleward moisture transport resulting in heavy rainfall, but only if the PV anomaly extends into the low- to mid-troposphere. The enhanced convection and associated upper-level divergence then feeds back onto the upper-level PV field by contributing to ridge building, potentially having downstream impacts. These processes are highlighted in composite analysis and a case study of a subtropical cyclone affecting New Zealand in January 2018. Experiments with modified latent heating in the ACCESS-rAM3 model reveal the critical role of moist processes in such events.
How to cite: Robinson, C., Narsey, S., Jakob, C., and White, B.: Interactions between the tropical moist margin and extratropical Rossby waves for rainfall extremes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1551, https://doi.org/10.5194/egusphere-egu26-1551, 2026.
Brazilian spring (SON) of 2023 was marked by the occurrence of heatwaves and droughts in the tropics as well as extreme daily rainfall produced by a series of extratropical cyclones in subtropical latitudes. These events were (partially) attributed to a persistent ridge over western subtropical South Atlantic which blocked the propagation of extratropical disturbances further equatorward over Brazil. El Niño conditions further intensified the tropical subsidence, contributing to the tropical drought. Here, we assess whether this combination of extreme events was just only a coincidence or could be attributed to a new emerging trend. We compared two periods (1979-1993 and 2009-2024) using ERA5 upper-level (300hPa) circulation during austral spring (SON), we identify a strengthening of the polar jet over South Pacific and the weakening (strengthening) of the subtropical jet over South Pacific (South America) that favours (hinders) the propagation of synoptic-scale (planetary scale) RW towards subtropical South America. We evaluate the extent to which some of these changes may emerge from the displacement and change of intensity of the tropical and subtropical convection, which is the dominant diabatic control on the intensity and location of the Rossby Wave Sources over the (sub)tropical Pacific. Finally, we evaluate the connection between the seasonal changes in large-scale circulation and the synoptic-scale events throught changes in the activity of Rossby Wave Packets (RWPs) and Rossby Wave Breaking (RWB) events over the region. These provisional results provide insight about changes in the interaction between diabatic forcing, Rossby waves, and synoptic-scale circulation contributing to compound extreme events like those observed over South America in 2023.
How to cite: Perez, I. and Zilli, M.: Seasonal and synoptic scale circulation linked to dry spring conditions in Brazil, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13880, https://doi.org/10.5194/egusphere-egu26-13880, 2026.
Future climate change is projected to substantially alter the precipitation patterns across subtropical regions of the planet. These precipitation changes are largely attributed to modifications of upper-tropospheric dynamics. Idealized climate simulations with stabilized global warming levels (GWLs) provide a controlled framework to investigate these responses in detail. In this study, we focus on the MENA region, a pronounced climate change hotspot, which is expected to be extensively affected by the shifting precipitation patterns. We identify the changes in the precipitation patterns and extremes for different global warming levels, and we link these changes to changes in the upper tropospheric dynamics. Specifically, we diagnose shifts in convergence regions and their associated changes in the large-scale vertical motion in the troposphere. In addition, we study changes in the Rossby wave patterns and amplitude, and the associated transient eddy activity. Finally, we explore how these dynamical changes modulate extreme precipitation events over MENA, thereby clarifying the physical drivers of the region’s emerging hydroclimatic risks under warming.
How to cite: Karpasitis, A., Hadjinicolaou, P., and Zittis, G.: Linking upper-tropospheric dynamics to precipitation changes and extremes in the MENA region: insights from idealized experiments, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3378, https://doi.org/10.5194/egusphere-egu26-3378, 2026.
Located in the subtropics, the record-breaking extreme rainfall (ER) that struck Dubai on April 16, 2024, provides a high-impact case for diagnosing subtropical jet–moist-convection coupling from an energetics perspective. This study applies the perturbation potential energy (PPE) framework to diagnose the energetics of this event. We develop an energetically closed, self-reinforcing energy-pump feedback mechanism, identify extreme conditions using the Rank Attribution Method relative to the 1979–2024 baseline, and quantify moisture source contributions using the Water Accounting Model (WAM). The energetics exhibit clear precursors, with stratospheric PPE and upper-tropospheric perturbation kinetic energy (PKE) becoming significantly anomalous 24–48 h before rainfall onset. Critically, as the bridge between PPE and PKE, the perturbation conversion from PPE to PKE term (PCK) leads to rainfall by about 2 h and effectively anchors both subsequent intensity and the primary rainband. When PCK intensifies, PKE increases in both the upper and lower troposphere, enhancing upper-tropospheric divergence and lower-tropospheric convergence; ascent then accelerates and rainfall amplifies. Latent heating (LH) further warms the column, increases PPE, and strengthens conversion, closing the positive energy-pump feedback loop (LH–PPE–PCK–PKE–LH) that sustains deep convection. Two distinct episodes in this event share this mechanism but differ dynamically: Process I is upper-level dominated and primarily jet-divergence forced, whereas Process II is lower-tropospheric dominated with stronger moisture transport, producing a more rapid rise to peak intensity. Moisture sourcing is dominated by the northwestern Arabian Sea (50.4%), with secondary contributions from the Red Sea (8.2%), the Gulf of Aden (6.7%), and the eastern Mediterranean (4.5%). These results deepen understanding of the energetics of ER over the Arabian Peninsula and highlight PCK as a physically based early-warning indicator for forecasting and risk assessment.
How to cite: Liu, Y., Li, J., Zhao, Y., Zhao, H., and DeLarmea, E.: The Energy-Pump Mechanism Behind Dubai ‘16•4’ Record-Breaking Rainfall, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4642, https://doi.org/10.5194/egusphere-egu26-4642, 2026.
The Southern Hemisphere polar vortex provides a key pathway for stratosphere–troposphere coupling and can influence Australian spring and summer climate, including extreme heat, drought, and fire weather. However, the extent to which this coupling depends on the phase of the Quasi-Biennial Oscillation (QBO) remains unclear. Here, we assess how the QBO modulates the influence of polar-vortex variability on Australian spring and summer climate.
Using ERA5 reanalysis, we define a weak-vortex index based on polar-cap temperature at 100 hPa (Temp100; 65–90°S), where anomalously warm Temp100 indicates weak-vortex conditions. Associated circulation and surface anomalies are diagnosed using regression and composite analyses, conducted separately for easterly (EQBO) and westerly (WQBO) QBO phases. Downward propagation of stratospheric anomalies is examined using height–time regressions of polar-cap geopotential height and temperature. Tropospheric coupling is quantified through correlations with the Southern Annular Mode (SAM) index and Australian near-surface temperature.
Weak-vortex events are characterised by anomalous polar-cap warming and coherent stratospheric height anomalies that descend toward the lower stratosphere. The timing of this downward influence exhibits a pronounced dependence on the QBO phase. During EQBO, the tropospheric response is delayed, emerging in November and persisting into mid-December, whereas under WQBO the surface response is largely confined to October. Temp100 is negatively correlated with the SAM index in both QBO phases, but peak coupling occurs in November–December during EQBO and in October during WQBO. Australian near-surface temperature shows corresponding seasonality and distinct spatial patterns. Under EQBO, warming is strongest over southeastern Australia in November and shifts toward northeastern regions in December. Under WQBO, warming emerges over northern Australia in October, while cooling dominates southern regions.
These results highlight the QBO as a key modulator of Southern Hemisphere polar-vortex variability and its downward influence, identifying a potential source of extended-range predictability for regional Australian climate. Ongoing work will quantify impacts on heat and fire-weather extremes, test sensitivity to event definitions, and assess whether subseasonal forecast systems reproduce the observed QBO dependence.
How to cite: Jiang, X., Love, P., and Marshall, A.: Weak Polar Vortex Events and QBO Modulation: Pathways Linking Stratospheric Variability to Australian Heat and Fire Risk, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7086, https://doi.org/10.5194/egusphere-egu26-7086, 2026.
The South Pacific Convergence Zone (SPCZ) is the dominant perennial rainfall feature of the Southern Hemisphere, yet the physical mechanisms driving its variability on decadal to multi-decadal timescales remain poorly constrained. Using prescribed sea-surface temperature (SST) perturbations in the atmosphere-only IGCM4 model, we investigate how three major modes of low-frequency climate variability – the Inter-decadal Pacific Oscillation (IPO), Atlantic Multi-decadal Variability (AMV), and Southern Ocean SST-driven mid-latitude jet shifts – modulate South Pacific hydroclimate. IPO forcing produces the most substantial and spatially coherent SPCZ response: a positive (negative) IPO anomaly drives a north-eastward (south-westward) shift in the SPCZ. This behaviour arises from coupled dynamic and thermodynamic dynamic changes, with anomalous moisture convergence – rather than altered Rossby wave refraction – emerging as the dominant control on SPCZ position. By contrast, AMV-forced atmospheric tele-connections exert only weak and statistically insignificant impacts on South Pacific precipitation; any apparent signal is best interpreted as an alias of IPO-like SST anomalies in the Pacific. Southern Ocean SST anomalies induce significant shifts in the Southern Hemisphere mid-latitude jet and associated Hadley–Ferrel cell structure, but these changes do not generate a coherent SPCZ displacement. Instead, precipitation anomalies reflect large-scale regions of anomalous ascent and descent, driven by Hadley and Ferrel cell shifts, rather than modifications to SPCZ dynamics.
How to cite: Robbins, C., Skinner, D., Inglis, G., Joshi, M., Langdon, P., Matthews, A., Peaple, M., Osborn, T., and Sear, D.: Mechanisms of South Pacific hydroclimate variability on decadal to multi-decadal time scales, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13690, https://doi.org/10.5194/egusphere-egu26-13690, 2026.
Given the critical role of the Madden–Julian Oscillation (MJO) in modulating global climate variability and subseasonal-to-seasonal (S2S) predictability, this study evaluates its simulation in the Korea Meteorological Administration’s Global Seasonal Forecasting System version 6 (GloSea6) and compares it with version 5 (GloSea5), focusing on prediction skill and key physical processes over the Maritime Continent (MC). Both models exhibit systematic biases, including weaker amplitudes and a tendency for the MJO to stall over the MC. Nevertheless, GloSea6 shows enhanced propagation across the MC, consistent with improved thermodynamic processes. The eastward-to-westward spectral power ratio increases from 1.52 in GloSea5 to 1.93 in GloSea6, closer to the observed 2.79, reflecting a more realistic dominance of eastward propagation. Process-based diagnostics reveal region-dependent improvements: more pronounced over the MC but limited over the Indian Ocean (IO). MC improvements are linked to better simulation of lower-level moisture convergence, equivalent potential temperature, and available potential energy, supported by reduced SST biases and a steeper meridional moisture gradient. These background-state changes strengthen moistening processes that precondition convection and sustain eastward propagation over the MC. These findings highlight that thermodynamic and mean-state improvements in GloSea6 are process- and region-dependent, and play a key role in shaping MJO-driven variability relevant to subtropical climate, emphasizing the importance of reducing systematic biases for improving S2S prediction system. However, improvements in spatial pattern similarity did not always translate into propagation skill gains, particularly over the IO, underscoring the complexity of dynaical responses.
How to cite: Kim, G., Shin, S.-H., and Lee, K.-J.: Process-based understanding of improved MJO propagation across the Maritime Continent in GloSea6, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3247, https://doi.org/10.5194/egusphere-egu26-3247, 2026.
The current El Niño-Southern Oscillation (ENSO) indices are defined based on the sea surface temperature anomalies (SSTAs) in different regions of the equatorial Pacific. Considering that the impact of ENSO on the large-scale atmospheric circulation is mainly through the release of latent heat associated with convection anomalies, we found a zonal dipole distribution of convection anomalies expressed by outgoing long wave radiation anomalies (OLRAs) over the central-western tropical Pacific, which links well with both the ENSO and the East Asian winter monsoon (EAWM). A new index (ITC) based on the anomalous tropical Pacific convection dipole is thus defined to measure ENSO and its impact on EAWM. It is illustrated that the new index ITC can well represent ENSO events. Detailed comparisons are made for the differences in the connections of each ENSO index with the EAWM indices, precipitation and atmospheric circulation over East Asia in winter. It is demonstrated that the ITC is more closely related to the EAWM and can better depict the impact of ENSO on the precipitation and atmospheric circulation over East Asia than the ENSO indices defined by SSTAs .The new ENSO index ITC can act as a single representative among the numerous existing ENSO indices in understanding, monitoring and predicting the impact of ENSO on the EAWM,eliminating the uncertainty and inconvenience that numerous existing ENSO indices defined by SSTAs may have caused.
How to cite: Huang, J., Zhang, R., and Tan, Y.: A tropical Pacific convection ENSO index suitable for measuring the impact of ENSO on the East Asian winter monsoon, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11724, https://doi.org/10.5194/egusphere-egu26-11724, 2026.
Tropical cyclones (TCs) that move into the midlatitudes undergo changes in their structure and transition into extratropical cyclones. The process is known as extratropical transition (ET), which can affect the weather further downstream.
The current study conducts a comprehensive synoptic-climatological analysis of the downstream development of the midlatitude flow associated with ET over the Southern Hemisphere. We use a state-of-the-art low-pressure system detection and classification scheme to objectively track tropical cyclones and detect those that undergo ET based on ERA5 data. Case-to-case variability of the TC structural changes and downstream influence during ET is examined by clustering ET events into four clusters.
We found that the transitioning cyclones in clusters 2 and 3 lead to a pronounced downstream ridge development. Mechanisms of the interaction between the cyclone and midlatitude flow are investigated using potential vorticity and eddy kinetic energy diagnostics. In the potential vorticity framework, the diabatically-driven divergent TC outflow anchors the eastward-propagating upstream trough and contributes substantially to downstream ridge amplification. The nonlinear interaction between the cyclone and midlatitude flow serves as a secondary important factor for the ridge building. From the eddy kinetic energy viewpoint, the downstream development occurs because the transitioning cyclone injects additional energy into the midlatitude flow, which is redistributed by the ageostrophic wind and thus enhances downstream energy.
Clusters 2 and 3 highlight two pathways of the interaction between the cyclone and midlatitude flow. In Cluster 2, the transitioning cyclone deforms an initially zonally-oriented jet anticyclonically and excites Rossby wave development downstream. This is characterised by the development of a notable downstream trough and associated surface cyclone development. Conversely, in Cluster 3, a preexisting upstream Rossby wave captures the cyclone during ET, and while the downstream ridge amplifies, no downstream trough development is observed.
How to cite: Jin, C., Ritchie, E. A., and Holbrook, N. J.: Downstream development of the extratropical transition of tropical cyclones in the Southern Hemisphere, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2900, https://doi.org/10.5194/egusphere-egu26-2900, 2026.
Heavy precipitation events (HPEs) are a precious source of water in the Sahara, but they also trigger potentially devastating flooding. Saharan HPEs are strongly associated with surface cyclones, making accurate cyclone forecasting crucial for predicting hydrometeorological hazards and their impacts. In this study, we investigate the predictability of HPE-associated cyclones across the Sahara and its drivers. We use ERA5 reanalysis between December 2000 and November 2020 to evaluate ensemble ECMWF reforecasts and to identify the atmospheric conditions controlling forecast skill. Short-, medium-, and extended-range forecast skill is evaluated based on the overlapping areas of observed and forecasted cyclones over the Sahara. Results show that the lead time of skilful prediction is up to about 10 days. On short-range lead times, forecast skill is higher in winter, whereas on medium to extended lead times, skill is higher in summer and fall. In winter, when cyclones are mainly located in the northern Sahara, forecast skill is higher for deeper cyclones. In summer, skill is higher for cyclones located in the southwestern Sahara. Rossby wave patterns extending over the North Atlantic are associated with both high and low skill forecasts, highlighting a flow-dependent control on predictability over the Sahara and underscoring the need for more detailed investigation. These findings show key characteristics of skilful HPE-associated cyclone forecasts on timescales of a few days to two weeks in advance. Understanding these variations across regions and seasons is key to improving the predictability of HPEs and their related impacts.
How to cite: Armon, M., Ling, G., and Afargan-Gerstman, H.: Sub-seasonal predictability of heavy precipitation–associated cyclones in the Sahara, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9468, https://doi.org/10.5194/egusphere-egu26-9468, 2026.
Extreme heat events in the Middle East have become increasingly frequent and intense due to human-driven climate change. During the Hajj pilgrimage in Mecca, Saudi Arabia, in June 2024, temperatures soared to a record-breaking 51.8°C, resulting in the tragic deaths of at least 1,300 pilgrims and over 2,700 non-fatal injuries on 16 June alone. Considering that the intensity and persistence of this heatwave exceed all recorded analogues in the available historical record, it may be considered statistically unprecedented within the context of the observed climate. Our analysis of future projections, tailored for the region, indicates that in a warmer climate, we can expect such devastating events to become a regular occurrence, potentially happening every year. In the hottest scenarios, the absolute maximum temperatures in Mecca are projected to reach or exceed 57°C. Addressing these challenges through effective climate mitigation and adaptation is essential to building resilience against future extreme heat risks.
How to cite: Zittis, G., Alberti, T., Almazroui, M., Driouech, F., Faranda, D., Francis, D., Hadjinicolaou, P., Kurnaz, M. L., Lazoglou, G., Nikulin, G., Osipov, S., Ozturk, T., Stenchikov, G., Tanarhte, M., Zaaboul, R., and Lelieveld, J.: The 2024 Hajj heat disaster: a glimpse into the future, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3922, https://doi.org/10.5194/egusphere-egu26-3922, 2026.
The Arabian Peninsula (AP) has an arid climate with the whole annual precipitation falling in non-summer months, high levels of ambient dust, and extreme surface temperatures. The characteristics of the climate of the AP changed comprehensively since the late 1990s. The climate of the region is closely tied to the baroclinic activity mediated by the subtropical jet stream flowing over the northern region of the Peninsula. Synoptic disturbances on the Subtropical Jet over the Arabian Peninsula create and regulate most of the weather patterns in the region. The STJ has a high Ertel's potential vorticity gradient that acts as a restoring force for disturbances. Rossby waves formed by these disturbances create mid- and upper-level vortices downstream of the STJ exit, causing precipitation, deep convection, dust storms, and turbulent winds at the surface as they travel south. Changes in the STJ can cause significant variations in the frequency and strength of these disturbances, altering the region's climate. Here I show that there have been significant changes in the baroclinic activity after 1998: (a) the magnitude of the PV gradient in the region of the maximum PV gradient (MGPV) has decreased, and (b) the mean location of the latitude of the MGPV has generally moved north,. These changes resulted in lowered convection an increased stability of the region. CRU data shows that there have been abrupt changes in several climate variables in 1998: the mean and variance before and after 1998 are different. Thus, the distributions of climate variables changed before and after 1998. Abrupt changes in climate variables cannot be explained in a slowly changing climate. Here we decompose the mean meridional temperature gradient into its intrinsic constituent frequency components using Empirical Mode Decomposition, and show that: (a) the high frequency components gain strength after 1998, and (b) the low frequency components have a reduced magnitude after 1998. These time-frequency changes in terms of frequency and amplitude result in abrupt changes in almost all the climate variables.
These changes are likely to destabilize the sustainability of the region. Further, I will also discuss the implications of such an abrupt comprehensive climate change in the Arabian Peninsula, and keep the results in the context of global climate change.
How to cite: Gunturu, U. B.: Abrupt climate change in the Arabian Peninsula mediated by the subtropical jet stream dynamics, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6352, https://doi.org/10.5194/egusphere-egu26-6352, 2026.
Interannual variability in precipitation across the arid Middle East has profound societal and environmental importance. While previous studies have identified a linkage between El Niño-Southern Oscillation (ENSO) and interannual precipitation variability in this region, this relationship and the underlying mechanisms are not fully understood. Using observation-based datasets and a range of diagnostics, this study quantifies the influence of ENSO on Middle Eastern precipitation variability during the extended cool season (October-May) and explores the underlying atmospheric drivers. Consistent with previous studies, we find that El Niño is associated with increased precipitation, whereas La Niña is associated with decreased precipitation. This relationship varies substantially within the cool season with a strong precipitation increase during autumn and a modest increase in spring under El Niño conditions, and a persistent precipitation decrease throughout the cool season under La Niña conditions. These precipitation anomalies during El Niño (La Niña) are associated with an equatorward (poleward) displacement of the subtropical jet along with increased (decreased) Rossby wave breaking frequencies at the poleward flank of the jet and underneath the jet core. Simultaneously, a mid-tropospheric cyclonic (anticyclonic) circulation anomaly over the Middle East promotes strengthened (weakened) atmospheric moisture transport into the region leading to enhanced (reduced) atmospheric moisture content across the region. From a global perspective, these regional circulation patterns result from (1) a zonally symmetric shift in the meridional position of the subtropical jet, (2) a barotropic Rossby wave response reaching from the tropical Pacific toward the Middle East via the extratropics, and (3) a baroclinic response in the tropical circulation extending westwards over the Indian Ocean and South Asia consistent with the Gill-Matsuno model. Co-varying circulation patterns over the Indian Ocean, linked to the Indian Ocean Dipole, contribute to the intraseasonally varying and asymmetric influence of ENSO on Middle Eastern precipitation. Our findings advance process understanding of precipitation variability in the water-scarce Middle East, having implications for seasonal predictions, flood and drought warnings, and the evaluation of climate model projections.
How to cite: De Vries, A. J., Feldstein, S. B., Casselman, J. W., Fragkoulidis, G., Lelieveld, J., and Domeisen, D. I. V.: The influence of El Niño-Southern Oscillation on cool-season precipitation variability in the arid Middle East, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9909, https://doi.org/10.5194/egusphere-egu26-9909, 2026.
Tropical-extratropical cloud bands are elongated cloud structures bridging tropical and midlatitude regions, and play an important role in the hydrological cycle. While the role of Rossby wave breaking in the formation of cloud bands is established, the extent to which this dynamic precursor governs their formation, duration, spatial distribution, and seasonality has not yet been systematically quantified. In this study, we use an object-based approach applied to reanalysis data to investigate how stratospheric potential vorticity (PV) intrusions, as indicators of Rossby wave breaking, influence cloud band formation and persistence over the South Pacific region. Our climatological analysis confirms a robust statistical link, in which cyclonic PV anomalies steer tropical moisture poleward and eastward and shape the diagonal orientation of the cloud bands. We also reveal that the longevity of cloud bands is modulated by the properties of PV structures: long-lived cloud bands are sustained by persistent PV intrusions that penetrate significantly farther equatorward than those associated with transient events. These findings highlight that equatorward-breaking Rossby waves create a tropospheric environment not only favouring the formation but also the maintenance of tropical-extratropical cloud bands. Consequently, accurately resolving PV intrusion forcing is critical for improving the predictability of cloud band duration and associated precipitation.
How to cite: Pilon, R., de Vries, A., and Domeisen, D.: The Link Between Rossby Wave Breaking and the Maintenance of Tropical-Extratropical Cloud Bands over the South Pacific, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20465, https://doi.org/10.5194/egusphere-egu26-20465, 2026.
