We invite studies
* focusing on the understanding and impacts of features of the atmospheric water cycle related to weather systems, with a special focus on the role of Atmospheric Rivers, Cold-Air Outbreaks, Warm Conveyor Belts, Tropical Moisture Exports, and the global Monsoon systems;
* investigating the large-scale drivers behind the past, ongoing and future variability and trends within the atmospheric water cycle, from field campaigns (CAESAR, NAWDIC, (AC)3, ISLAS, etc.), long-term observations, reanalysis data, regional to global model simulations, or (isotopic) data assimilation;
* reconstructing past hydroclimates based on paleo-proxy records from archives such as ice cores, lake sediments, tree-rings or speleothems;
* applying methods such as tagged water tracers and Lagrangian moisture source diagnostics to identify source-sink relationships and to evaluate model simulations of the water cycle;
* using the isotopic fingerprint of atmospheric processes and weather systems to obtain new mechanistic insights into changes in the water cycle;
* describing the global and regional state of the atmospheric water cycle (e.g. monsoon systems) with characteristics such as the recycling ratio, life time of water vapour, and moisture transport properties.
We particularly encourage contributions linking across neighbouring disciplines, such as atmospheric science, climate, paleoclimate, glaciology, and hydrology.
Orals: Thu, 7 May, 10:45–12:30 | Room 1.61/62
Mid-latitude weather systems play a significant role in causing floods, wind damage, and related societal impacts. Advances in numerical modeling and observational methods have led to the development of numerous conceptual models in mid-latitude synoptic and dynamical research. As these models proliferate, integrating new insights into a cohesive understanding can be challenging. This study uses a kinematic perspective to interpret mid-latitude research in a way that synthesises various concepts and create a schematic diagram of an atmospheric river lifecycle. Our analysis demonstrates that, despite varying methods, definitions, and terminology used to describe extratropical cyclones, warm conveyor belt airflows, and atmospheric rivers, the underlying mechanisms driving their formation and development are consistent. Thus, while studying these features independently is valuable, it is important to recognise that they are all part of a larger atmospheric flow pattern. We hope this kinematic approach will serve as a bridge to link research on these phenomena.
How to cite: Dacre, H. and Clark, P.: A kinematic analysis of extratropical cyclones, warm conveyor belts and atmospheric rivers, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1858, https://doi.org/10.5194/egusphere-egu26-1858, 2026.
Marine Cold Air Outbreaks (MCAOs) along the western boundary currents trigger strong air-sea interactions in the entrance region of the storm tracks and act as an important moisture source for cyclones developing within the northern hemispheric storm tracks. Changes in MCAO intensity with climate change, however, are complex to evaluate because of the competing effects of the expected increase in air temperature (which would reduce MCAO intensity) and in sea surface temperatures (which would increase MCAO intensity). This study aims to achieve a detailed understanding of MCAO intensity changes in relation to these opposing effects, by comparing present and future MCAOs along the northern hemispheric western boundary currents as simulated by the Community Earth System Model 2 (CESM2) forced by the SSP3-7.0 radiative forcing scenario. Lagrangian, three-dimensional air parceltrajectories initialized from within the MCAOs are computed directly from the 6-hourly climate model output, allowing to gain insights into the processes responsible for changes in MCAO intensity.
We find that in the considered scenario the increase in air temperature outweighs the increase in SSTs, leading to weakening of future MCAOs along western boundary currents. Backward trajectories initiated from the MCAOs show that the increase in air temperature in the MCAOs results from substantially higher initial potential temperature and slightly weaker diabatic cooling experienced by the air parcels on their way towards the MCAOs. For future MCAOs along the Gulf Stream specifically, the permanently sea ice-free Hudson Bay additionally acts as a new warming source on the trajectories, prior to reaching the Gulf Stream region. Despite the decrease in intensity, future MCAOs are associated with increased net evaporation, suggesting that MCAOs are expected to remain an important contributor to the water cycle of the northern hemispheric storm tracks.
How to cite: Fieldhouse, N., Schnyder, F., and Riboldi, J.: Drivers of marine cold air outbreak intensity along the Gulf Stream and Kuroshio Current in a warmer climate, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13555, https://doi.org/10.5194/egusphere-egu26-13555, 2026.
Atmospheric rivers (ARs) are thought to be the main driver of extreme precipitation events in the North Atlantic and Pacific, and are responsible for most of the total extratropical poleward moisture transport. They are associated with violent weather and high precipitation that can lead to floods in populous coastal areas. Moreover, the frequency and intensity of ARs is expected to increase with climate change, driven by the rise in atmospheric moisture and precipitation. An important question about ARs is whether they are being supplied primarily from remote subtropical regions, or whether they are recycling water vapor by evaporating and precipitating as they travel northward.
In a previous paper, we implemented water vapor (WV) age tracers in a global circulation model to resolve the WV age spectrum and the age of precipitation in both space and time, which allowed us to study the dynamics of WV age. In this study, we use our novel tracers to test how the mean WV age and the mean age of precipitation can be used to identify and investigate the dynamics behind ARs. We use column integrated water vapor (CWV) wave activity and precipitation (Lu et al., 2017) to track AR features, and show that the mean WV age at the surface and the mean age of precipitation is well correlated to CWV wave activity in wintertime extreme precipitation events over the North Atlantic and Pacific.
From composite images of our WV age tracers and climatological diagnostics, we show how during winter, surface WV age and the age of precipitation are higher than the seasonal average, supporting long range moisture transport by ARs, while in summer, they are lower than average, meaning local sources of water vapor is feeding into convective storms. During winter, tropical WV lifts up and travels poleward via extra tropical cyclones, with convective precipitation removing WV from the lower levels along the way. In the midlatitudes, large scale condensation precipitates most of the subtropical WV. As a result, the age of precipitation and surface WV age are about 2 days over seasonal average at the end of the storm track, matching our estimated advective time scale from the subtropics. Also, the large amount of precipitation reduces the WV age in the upper levels of the atmosphere.
During summer on the other hand, there are high values of CWV wave activity which could be interpreted to also indicate long range transport. But, lower surface WV age and age of precipitation than average, among other results, indicates that it is due to local evaporation and convective storms recycling the locally available WV along the storm tracks.
In summary, our results show how our tracers of WV age, which could be implemented relatively simply into more complex climate models, give us a new straightforward tool to analyse the lengthscale WV travels in the atmosphere, helping us understand the dynamics behind WV transport, and its impact on the water cycle with climate change.
How to cite: Boulanger, P. and Fajber, R.: Atmospheric River Dynamics: What Can Water Vapor Age Tell Us About the Moisture Transport Leading to Extreme Precipitation?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8447, https://doi.org/10.5194/egusphere-egu26-8447, 2026.
To better understand the mechanisms behind precipitation extremes, one can determine the origin of the precipitation, i.e. its moisture sources. The time and spatial distribution of these sources provide insights into the importance of land-ocean–atmosphere interactions and moisture recycling and the synoptic situation of an extreme event. This allows for better prediction and improved disaster preparedness.
However, the moisture sources of extreme precipitation cannot be measured directly. Therefore, a variety of moisture tracking methods have been developed over recent decades, but the uncertainties associated with these methods remain poorly quantified. Here, we present the IdentificatioN of Sources of Precipitation through an International Research Effort (INSPIRE), a coordinated intercomparison of moisture tracking methods. Within this initiative, the moisture tracking community gathered to compare moisture sources of three extreme precipitation events across 14 different methods. The events occurred under different meteorological conditions: monsoon precipitation in Pakistan, convective precipitation in Australia, and atmospheric river-associated precipitation over Scotland. Our findings show that, in all cases, the different moisture tracking methods qualitatively agree on moisture source patterns, although there are regional and quantitative differences. For example, for the Pakistan case, the recycling ratio shows a multi-method spread of 2–20%. We also find that groups of methods behaved similarly across events. This study provides a first quantitative benchmark of inter-method uncertainty and establishes a reference framework for future moisture tracking studies.
How to cite: Benedict, I., Keune, J., Weijenborg, C., van der Ent, R., Kalverla, P., and Koren, G. and the Moisture tracking intercomparison team: Intercomparison of moisture tracking methods simulating sources of extreme precipitation events, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14175, https://doi.org/10.5194/egusphere-egu26-14175, 2026.
For several decades, the comparison of climate data with results from water isotope-enabled Atmosphere General Circulation Models (AGCMs) significantly helped to a better understanding of the processes ruling the water cycle, which is one of the main drivers of the climate variability. For the modern period, the use of AGCMs nudged with weather forecasts reanalyses is a powerful way to obtain model outputs under the same weather conditions than at the sampling time of the observations.
In this regard, Cauquoin and Werner (2021) [1] produced a simulation at T127 horizontal resolution (~0.9°) with the ECHAM6-wiso model nudged to the ERA5 reanalyses [2, 3] for the period from 1979 to present time. The simulation results have been used extensively in many studies focusing on, for example, snow-vapor interactions in polar regions, processes controlling isotopic content of water vapor and precipitation in the Asian monsoon area, or the use of isotope information to reconstruct past cyclone frequency.
To go further and considering that one limitation for isotope model-data comparisons is the spatial resolution, we present here new ECHAM6-wiso nudged simulation at 0.5° horizontal resolution for the extended period 1940-2024. This higher resolution will be very useful to improve the interpretation of various water isotope records. Also, the extended data period from 1950 to present time is an opportunity to enhance statistical analyses related to interannual changes in isotopes and climate under global warming. An example of application (EGU26-12139) is presented in the same session as the present abstract.
[1] Cauquoin and Werner (2021). Journal of Advances in Modeling Earth Systems, https://doi.org/10.1029/2021MS002532.
[2] Hersbach al. (2020). Quarterly Journal of the Royal Meteorological Society, https://doi.org/10.1002/qj.3803.
[3] Soci et al. (2024). Quarterly Journal of the Royal Meteorological Society, https://doi.org/10.1002/qj.4803.
How to cite: Cauquoin, A. and Werner, M.: Very high-resolution simulation with ECHAM6-wiso nudged to ERA5 reanalyses for the period 1940-2024, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15201, https://doi.org/10.5194/egusphere-egu26-15201, 2026.
In-cloud conversion efficiency, defined as the fraction of water vapor converted into precipitation during ascent, is a key but weakly constrained variable of the atmospheric water cycle. It summarizes the combination of microphysical and dynamical processes that control precipitation formation. We present a methodology to retrieve observation-derived estimates of the conversion efficiency globally using paired H2O–HDO measurements from the Infrared Atmospheric Sounding Interferometer (IASI) aboard the MetOp satellites for the period 2014–2020.
IASI δD retrievals from mid-tropospheric clear-sky regions are combined with 15-day backward Lagrangian trajectories calculated using three-dimensional wind data from the ERA5 reanalysis to identify last saturation events along air-parcel histories. These events are diagnosed using specific hydrometeor content thresholds, while precipitation-contaminated and humidity-non-conserving cases are excluded. To link isotope signals to conversion efficiency, a simple Rayleigh condensation box model is applied along the diagnosed ascent pathways. For convective ascent, the model follows pseudo-adiabatic vertical motion from cloud base to the diagnosed last saturation locations associated with the IASI observations; for slantwise ascent, the box model is applied along 48-hour Lagrangian trajectories. Modeled δD profiles are then combined with IASI observations to derive in-cloud conversion efficiencies constrained by the observed water isotope signals, within the uncertainty range of the remote sensing observations and the trajectory calculation.
The resulting dataset will provide the first global satellite-derived estimates of in-cloud conversion efficiency for both convective and slantwise ascents. Case studies ranging from mesoscale convective systems in the tropics to warm conveyor belts in the midlatitudes demonstrate the methodology and illustrate distinct efficiency regimes, offering a new observational constraint on moist process representations in the atmosphere.
How to cite: Brennan, K. P., Fieldhouse, N., and Aemisegger, F.: Retrieval of global in-cloud conversion efficiency estimates based on satellite-measured H2O–HDO pairs, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7162, https://doi.org/10.5194/egusphere-egu26-7162, 2026.
The Arctic is warming at more than twice the global average, a phenomenon known as Arctic amplification. In consistency with this rapid warming, a pronounced moistening trend is observed over the past 30-40 years. While the region's atmospheric humidity is increasing, it remains unclear whether this increased moisture originates primarily from local sources such as enhanced evaporation from ice-free ocean surfaces or is transported from lower latitudes. Atmospheric rivers (ARs) play a central role in the poleward moisture transport and play a critical role in Arctic climate processes.
During phase change processes, such as evaporation and condensation, the heavy stable isotopes of water accumulate in the condensed phase. As a result, the isotopic composition of water vapour act as an integrated tracer of an air parcel’s condensation (or phase change) history, providing information on moisture sources and transport pathway that can help to improve our understanding of moisture processes during transport into and within the Arctic.
In this study, we investigate the isotopic composition of water vapour during an event that occurred in March 2021 where an AR made landfall in Northern Scandinavia. We analyse data from the isotope-enabled COSMO model (COSMO-iso) and evaluate them against observations from the TROPOMI satellite instrument and TCCON ground based stations to diagnose the isotopic signals associated with the AR. The comparison indicates that TROPOMI observations capture more detailed spatial structures and more distinct features than COSMO-Iso model output. Histogram analyses further show systematic differences in isotope abundances in the model compared to TROPOMI. Ground-based TCCON observations provide an independent reference to assess the consistency of both the model simulations and satellite retrievals during the event.
How to cite: Ignatious, A., Bösch, H., Sodemann, H., and Buschmann, M.: Water Vapour Isotope Signals during an Atmospheric River Event: Model Simulations and Observations from TROPOMI and TCCON, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11973, https://doi.org/10.5194/egusphere-egu26-11973, 2026.
Rapid Arctic warming and sea ice retreat have increased atmospheric humidity, yet the relative contributions of local evaporation and advected lower-latitude moisture remain poorly quantified. Here, we present high-resolution, ship-based in-situ measurements of near-surface water vapor isotopes across diverse Arctic sea ice regimes. By integrating isotope fractionation models with multi-source meteorological data, we show that sea ice changes act as a key modulator of Arctic water vapor isotopic variations. Under ice-covered conditions, water vapor isotopes are controlled by Rayleigh distillation, producing depleted δ18O with a strong temperature dependence and elevated d-excess from ice-phase processes. As sea ice retreats, kinetic fractionation from local evaporation becomes increasingly important, particularly at temperatures above ~ 5 °C, generating enriched δ18O, elevated d-excess, and a characteristic "anti-temperature" effect. A Bayesian isotope mixing model quantifies the resulting moisture source shift, showing local evaporation contributions rise from 9.3 % in ice-covered regions to 22.7 % in melt regions, despite advected moisture remaining predominant. These findings establish a process-based isotope framework for the Arctic hydrological cycle, complementing conventional meteorological diagnostics and offering a robust benchmark for interpreting paleo-isotope archives.
How to cite: Zhang, Y., Liu, Z., Li, D., Li, Z., and Shao, H.: Arctic Sea Ice Loss Amplifies Local Evaporation Influence on Water Vapor Isotopes: Insights from Cruise Observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3379, https://doi.org/10.5194/egusphere-egu26-3379, 2026.
Moisture transport of Earth’s monsoon systems into the upper troposphere and lower stratosphere is poorly constrained, with implications for stratospheric chemistry and radiative budget. Water isotopes provide information on moisture transport pathways in Earth’s atmosphere, and both satellite and in situ measurements of ẟD show enhancements of up to 50 per mille in the 15-19 km range above the North American monsoon relative to the Asian monsoon. This is indicative of differences in the life cycle and fate of convectively lofted ice in the monsoon system. Here we use data from the Chicago Water Isotope Spectrometer (ChiWIS), which flew aboard high-altitude aircraft in the Asian Monsoon center during the StratoClim (2017) campaign out of Nepal, in monsoon outflow during ACCLIP (2022) out of South Korea, and in the North American Monsoon in 2021 and 2022 out of Houston, to show that in situ measurements of the HDO/H2O isotopic ratio in these systems trace strong convective activity, which is processed differently between the monsoon systems after detrainment. Both campaigns sampled a broad range of convective and post-convective conditions, letting us trace how convective ice sublimates, reforms, and leaves behind characteristic isotopic signatures. We additionally use other tracers, isotopic models, along with TRACZILLA backtrajectories and convective interactions derived from radar and cloud-top products, to follow the evolving isotopic composition along flight paths in both campaigns and to asses the origins of the difference in isotopic signature.
How to cite: Clouser, B., KleinStern, C., Singer, C., Desmoulin, A., Khaykin, S., Lykov, A., Viciani, S., Bianchini, G., D'Amato, F., Bucci, S., Legras, B., Homeyer, C., Thornberry, T., and Moyer, E.: Water isotopic composition above the North American and Asian Summer Monsoons provides a tracer of strong convective activity, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19779, https://doi.org/10.5194/egusphere-egu26-19779, 2026.
Moisture availability is a fundamental prerequisite for precipitation. Within the water cycle, moisture contributing to precipitation originates from evapotranspiration (ET) in both local and remote regions. This moisture is transported through the atmosphere and may be progressively depleted during transit through precipitation. Consequently, the moisture supply to a region can vary in response to changes in evapotranspiration, atmospheric circulation, and environmental conditions that influence moisture transport and precipitation efficiency. Here we use a Lagrangian moisture source identification model BTrIMS1.1, in combination with analysis of weather systems, ET, and convective environment to understand the mechanisms of precipitation variability during two extreme events that lead to drought and floods in Australia.
The Tinderbox Drought (January 2017–December 2019) in Australia severely threatened urban water supplies including Sydney, caused substantial agricultural losses and contributed to the devastating Black Summer bushfires. This drought was associated with a ~50% reduction in precipitation compared with climatology. In stark contrast, the following triple La Niña period (September 2020– August 2023) brought persistent heavy precipitation to eastern Australia, resulting in widespread flooding and storm-related damage. Despite their opposite hydrological impacts, both events were characterized by pronounced precipitation anomalies.
We focus on the Murray-Darling Basin, Australia, because of its critical importance to agricultural production. Our analysis indicates that oceanic moisture contributions were substantially reduced during the Tinderbox Drought, driven primarily by changes in atmospheric circulation. Altered weather systems diverted climatological moisture sources away from the Basin, shifting dominant moisture sources towards regions with lower ET. This shift resulted in a pronounced moisture deficit, which was further exacerbated by reduced local ET.
In contrast, during the triple La Niña period, there was an increased occurrence of slow-moving cyclone and anticyclone pairs, enhancing easterly flow and oceanic moisture transport towards eastern Australia. In addition, moisture contribution from inland Australia increased, driven by a substantially higher land ET during this period. By the third year, precipitation was further amplified by enhanced local moisture recycling due to wetter land surfaces. The persistence of slow-moving low-pressure systems also provided a more favourable environment for precipitation over extended periods, consistent with the higher mean convective available potential energy observed during triple La Niña period. Together, circulation anomalies and enhanced convective conditions combined to produce anomalously high precipitation and widespread flooding during this period.
Key words: precipitation, moisture sources, Lagrangian, weather systems, evapotranspiration, ENSO, extreme events
How to cite: Mu, Y., Evans, J., Taschetto, A., and Holgate, C.: Understanding the Driving Mechanisms of two Extreme Precipitation and Drought Events in Australia from a Moisture Source Perspective, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2011, https://doi.org/10.5194/egusphere-egu26-2011, 2026.
While first estimates of the importance of below-cloud evaporation for reducing precipitation exist, the impact of this process on the atmospheric water vapour budget and on the downstream dynamics is largely unknown. Previous modeling work has indicated that below-cloud rain evaporation can account for about one-third of the moisture uptakes when a dry intrusion penetrates the subtropical boundary layer, emphasizing the importance of this process for re-moistening the atmosphere. Such internal moisture recycling plays a key role in feeding subsequent storm systems with moisture, particularly in dry regions.
We present an extension to an existing trajectory-based moisture source diagnostic (MSD), incorporating the moisture sources of precipitation and cloud evaporation. The extended MSD identifies increases in specific humidity along Lagrangian trajectories, categorizing the uptakes occurring in the presence of rain or snow as precipitation evaporation and the uptakes occurring in the presence of cloud liquid or ice water as cloud evaporation. In total, the methodology defines six uptake categories based on these hydrometeor types, mixing and the surface evaporation flux.
The extended MSD is evaluated for a 13-day test case in January/February 2018 over the North Atlantic, including three types of airstreams: a dry intrusion, a warm conveyor belt, and an adiabatic flow segment along the jet stream in the mid-latitudes. Physical consistency is then analysed from the model perspective using moisture tendency outputs from the microphysical, convective, and turbulent parameterisations of the Integrated Forecasting System (IFS) of the European Centre for Medium-Range Weather Forecasts (ECMWF). Since the moisture tendencies indicate which physical processes influenced the moisture budget, comparing them with moisture uptakes from the extended MSD allows verification of whether the MSD identifies these processes in a consistent way within the modeling framework. Potential discrepancies are addressed by defining physically meaningful thresholds for moisture uptake and rainout, constrained by multi-platform observations from the North Atlantic Waveguide, Dry Intrusion, and Downstream Impact Campaign (NAWDIC). Furthermore, different approaches for attributing moisture uptake to the newly introduced source categories are tested. These include methods based on the relative rain, snow, cloud liquid, and cloud ice water contents along the trajectories, as well as approaches that additionally account for Lagrangian changes in hydrometeor contents.
This analysis enables an assessment of the diagnostic’s ability to attribute moisture uptakes to specific processes, even when several act simultaneously. Ultimately, this development provides a necessary framework for quantifying the role of internal recycling processes in the atmosphere and assessing its role for downstream intensification of strongly precipitating airmasses such as in extratropical cyclones or mesoscale convective systems.
How to cite: Fasnacht, L., Brennan, K. P., and Aemisegger, F.: Quantifying precipitation and cloud re-evaporation: a novel Lagrangian diagnostic evaluated with field observations and moisture tendency outputs from numerical simulations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18920, https://doi.org/10.5194/egusphere-egu26-18920, 2026.
Global warming is causing changes in atmospheric dynamics that directly influence the hydrological cycle and its components. Moisture sources in the Central American region are not exempt from these changes. The research objective is to study future changes, by the middle and end of the 21st century, in moisture sources in three regions: Central America, Northwest South America, and the Orinoco region. For this purpose, a computational framework based on the regional models WRF-ARW and FLEXPART-WRF is used, and the outputs of the global model CESM2 are used as initial and boundary conditions (forcers). The periods used were: historical (1985 to 2014), mid-(2036 to 2065) and end-century (2071 to 2100), under the climate scenario SSP5-8.5. A Lagrangian methodology was used for the calculation of moisture sources and the analysis was carried out by seasons and annually. The moisture sources from Central America will increase, by the end-century, over that region and in the Caribbean Sea, with a greater increase in autumn, with a slight decrease to the west, over the Pacific coasts. In the North South American region, the greatest changes are also observed at the end-century, with a predominant increase in moisture sources over the region in winter and spring, which extends over the western Atlantic in summer and autumn. In the Orinoco region, the increase is observed, over the region itself in winter, while in the remaining seasons, extending towards the Central Atlantic.
How to cite: Alvarez Socorro, G., Fernández Alvarez, J. C., Nieto, R., Gimeno, L., and Sorí, R.: Future changes in moisture sources in Central American region using high-resolution numerical simulations., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6722, https://doi.org/10.5194/egusphere-egu26-6722, 2026.
Extratropical cyclones (ETCs) play a pivotal role in hydrological processes of the atmosphere, such as evaporation, moisture transport and precipitation. Long-term changes in the hydrological contribution of ETCs will therefore have important impacts on shifts in precipitation patterns, droughts, and extreme events. ETCs are projected to decrease in frequency and increase in intensity under global warming—maintaining a near balance in their net contribution to moisture fluxes. However, hydrological cycle changes associated with cyclonic fronts may exhibit stronger signals and are more uncertain, because these frontal systems are often under-resolved in coarse grid simulations.
In this study, we investigate how higher resolution modeling affects the impacts that ETCs will have on atmospheric moisture fluxes under global warming, while also accounting for the contribution of cyclonic fronts. We analyze long-term MESACLIP historical and future simulations at varying resolutions (up to ~25 km). Using cyclone and front tracking algorithms, we quantify long-term changes in ETC-induced freshwater fluxes and compare results across model resolutions. Because small-scale processes are crucial for cyclogenesis and associated fluxes, we expect stronger air–sea coupling and enhanced vertical motions along cyclonic fronts in higher-resolution models, potentially amplifying the overall imprint of ETCs on important hydrological processes of the atmosphere. Our work highlights the need to adequately account for frontal processes when assessing future changes in atmospheric moisture fluxes.
How to cite: Mäder Arrabali, D., Givon, Y., Noyelle, R., and Jnglin Wills, R. C.: Moisture Transport by Extratropical Cyclones and Fronts in High-Resolution Climate Change Simulations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14557, https://doi.org/10.5194/egusphere-egu26-14557, 2026.
We have implemented fractionation, tracing and dispersion processes for water stable isotopes in a protoptype version of the Norwegian Earth-System Model (NorESM) based on the numerical schemes of iCESM (Nussbaumer et al., 2017).
Current capabilities include land-atmosphere-ice coupled integrations following the AMIP protocol, and 3-D nudging to observed reanalysis data.
Work on the ocean component (BLOM) is on-going.
We discuss preliminary results from a comparison with iCESM integrations, and from simulations intended to contribute to the WisoMIP effort (Bong et al. 2025).
How to cite: Dietrich, L., Sodemann, H., Steen-Larsen, H.-C., and Toniazzo, T.: A prototype WISO-enabled version of NorESM, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12654, https://doi.org/10.5194/egusphere-egu26-12654, 2026.
The stable oxygen isotope ratio (δ18O) measured in ice cores is widely used to reconstruct past climate variability on short and long timescales. Among synoptic processes, atmospheric rivers (ARs) play a key role in the poleward transport of moisture. ARs are long, narrow corridors of intense horizontal water vapour transport, typically associated with extratropical cyclones. They convey large amounts of moisture from distant, often low-latitude source regions together with warm air advection, thereby introducing a distinct isotopic signature into precipitation. Through snowfall, the isotopic composition of atmospheric water vapour is recorded in snow and ultimately preserved in ice cores.
While several studies have examined the influence of ARs on δ18O variability in Antarctic ice cores, a comparable assessment for Greenland remains more limited until now.
Here, we investigate the imprint of ARs on δ18O variability in Greenland ice cores using virtual firn cores (VFCs) derived from a new high-resolution (0.5°) simulation performed with the isotope-enabled atmospheric general circulation model ECHAM6-wiso nudged to ERA5 reanalyses. VFCs are generated for the Renland Ice Cap (RECAP) and Southeastern Dome (SED) sites and evaluated against their corresponding very high-resolution measured δ18O records.
Our results show that ARs do not fundamentally change the δ18O variability. However, they exert a pronounced influence on seasonal and subseasonal δ18O variations during periods when AR-related snowfall contributes a substantial fraction of total precipitation. On the subseasonal timescale, individual AR events are found to increase δ18O values by approximately 3‰ on average, with extreme cases reaching up to 5‰.
How to cite: Gagliardi, A., Leroy-Dos Santos, C., Rimbu, N., Casado, M., Cauquoin, A., Landais, A., Werner, M., Lohmann, G., and Ionita, M.: Imprint of atmospheric rivers on stable-oxygen isotopes ratio in Greenland ice cores: an assessment, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12139, https://doi.org/10.5194/egusphere-egu26-12139, 2026.
Understanding the phase-change history of atmospheric water is essential for constraining the physical parameterizations of the hydrological cycle in general circulation and regional climate models, ultimately improving the accuracy of their predictions. Stable water isotopes are natural tracers of these processes, as they record the integrated effects of phase changes along atmospheric transport pathways and therefore provide constraints for atmospheric models. However, obtaining observations of the stable isotopic composition of water vapor throughout the troposphere remains challenging because of the high costs associated with aircraft-based measurements. In this study, we present the latest results from the Water Vapor Isotopologue Flask sampling for the Validation Of Satellite data (WIFVOS) project, including both recent field observations and the technical developments of the balloon-borne flask sampling system achieved over the past three years, aimed at providing a cost-effective platform for retrieving water vapor mixing ratio (w, ppm) and isotopic composition (δ¹⁸O and δD, ‰ VSMOW). During the 2024 WIFVOS field campaign in Sodankylä (northern Finland), four successful balloon launches were conducted using a newly designed flask sampler. During the descent phase of each flight, four flasks were filled at different altitudes, providing water vapor concentration and isotopic composition at predefined pressure levels up to 3000 m ASL. A Vaisala RS92-SGP radiosonde was attached to the sampler to independently assess the quality of the humidity measurements obtained from the flask samples. Flask analyses were performed offline using a Picarro L2120-i analyzer within a few hours after balloon recovery. The retrieved humidity showed excellent agreement with radiosonde measurements (mean absolute error = 484 ppm), and clear isotopic gradients were observed within the boundary layer and the lower troposphere. To extend the vertical coverage of the profiles, AirCore samples were collected within a few hours of the flask sampling. The flask sample reproducibility was evaluated through two additional low-altitude flights conducted with a hexacopter drone equipped with a modified, lightweight version of the sampler: one flight at a fixed altitude and one sampling the lowest few hundred meters of the atmospheric column. These flights yielded standard deviations fully comparable with uncertainties estimated from dedicated laboratory tests performed prior to field deployment (±0.2 ‰ for δ¹⁸O and ±1.0 ‰ for δD). During the campaign, simulations were performed with the isotope-enabled regional weather prediction model COSMOiso, providing a highly resolved representation of the vertical distribution of atmospheric water vapor isotopic composition. We demonstrate the applicability of WIFVOS data for satellite validation by comparing the flask-based measurements with observations from the nearby Total Carbon Column Observing Network (TCCON) spectrometer in Sodankylä. Finally, we discuss the potential of the lightweight sampler for measuring additional trace gases, such as CH4, in the lower atmosphere using conventional drones. The vertically resolved isotopic observations obtained with the complementary techniques presented here provide key constraints for Earth System Models in the Arctic, supporting improved representation of atmospheric moisture processes.
How to cite: Kivi, R., Zannoni, D., Heikkinen, P., Räty, V., Steen-Larsen, H. C., Kristensen, T. O., Röckmann, T., Leuenberger, M., Nyfeler, P., and Aemisegger, F.: Following the Isotopic Fingerprints of Atmospheric Water Vapor with Balloon-Borne Sampling, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14048, https://doi.org/10.5194/egusphere-egu26-14048, 2026.
The Himalayan region, a major source of freshwater for downstream river basins, exhibits strong sensitivity to climate variability due to its complex terrain and the interplay of multiple moisture sources, primarily the Indian Summer Monsoon and western disturbances. This complexity limits the interpretations of rainfall variability and underscores the need for direct constraints on moisture sources and precipitation processes. Continuous monitoring of atmospheric water vapor isotopes (δ²H, δ¹⁸O, and δ¹⁷O), together with meteorological observations, has been instrumental in investigating the moisture transport, condensation processes, and evaporative source characteristics over the region. In this study, we analyze high-resolution atmospheric water vapor isotope measurements obtained using a Picarro L2140-i along with event-based precipitation isotope measurements during the JJAS 2024 season from Manali to assess below cloud rain-vapor interaction, and associated fractionation processes. Distinct intraseasonal variability is evident in the vapor isotope signals. Variations in local and regional meteorology, moisture recycling and the relative contributions of distinct moisture sources are investigated to account for the pronounced isotopic depletion observed during extreme rainfall and cloudburst events. A Lagrangian back-trajectory analysis is used to trace moisture sources associated with precipitation over Manali. We used the specific humidity–δ18O diagnostic diagrams, constrained by theoretical Rayleigh distillation curves and two-component mixing hyperbolas, to interpret the drivers of intraseasonal isotopic variability. Overall, this contribution highlights the utility of stable isotope analyses for improving process-based understanding of moisture sources, hydrological dynamics, and climate variability across the Himalayan region.
How to cite: Singh, A., Kumar, G., Ranjan, S., Leuenberger, M., and Dixit, Y.: Insights into Northwest Himalayan water cycle from continuous atmospheric water vapor and event-based rainwater isotopes , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18510, https://doi.org/10.5194/egusphere-egu26-18510, 2026.
The stable isotopic composition of precipitation at any given site is strongly influenced by global, regional and local factors. Among these, geographic position (latitude, altitude, distance form moisture sources) and climatic conditions (air temperature; precipitation types, patterns and amount; relative humidity) are considered as being the most important. However, mounting evidence points towards larges-scale atmospheric circulation patterns as having a role that offsets and/or masks some (or most) of these factors. In this paper, we use modern and palaeo data to show that in regions with complex interactions between climatic influences and thus highly variable moisture sources, such patterns are the main controlling factors on the distribution of δ18O and δ2H in precipitation. Our study area is SE Europe, where interactions between the North Atlantic Oscillation, the Siberian High, the Scandinavian Pattern (and several other, regional patterns) results in advection of moisture from the Atlantic and Arctic Oceans; the Mediterranean, Black and Caspian Seas; and interior Asia, all with distinctive δ18O and δ2H values, that are strongly imprinted in that of local precipitation. In turn, these are registered by paleoarchives (cave ice, speleothems, tree ring cellulose) resulting in ambiguous signals that can be interpreted as changes in local/regional climatic conditions, rather than changes in the source of moisture. We discuss how δ18O and δ2H (and the secondary d-excess parameter) values in precipitation are linked to the varying strength of the main atmospheric circulation patterns and how regional sedimentary archives register them and further, how we can reconstruct past changes in their dynamics.
How to cite: Perşoiu, A.: Large-scale atmospheric circulation patterns control the stable isotopic composition of precipitation in SE Europe, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19432, https://doi.org/10.5194/egusphere-egu26-19432, 2026.
