A 25-year record from the United States Network for Isotopes in Precipitation (USNIP) using data from seventy-three sampling sites reveals the dynamic role of moisture sources and storm tracks in controlling the precipitation geochemistry at a continental scale. Our study provides a fresh perspective on processes governing the water isotope cycle beyond the classic role of temperature. We report that Climate Oscillations (COs) combine to influence synoptic climatology and atmospheric transport patterns, thereby driving spatiotemporal distribution of precipitation ¹⁸O, ²H and d-excess values. The relationship between the individual COs and the isotopic composition of precipitation is spatially, temporally, and geographically inconsistent with varying time periods of linear (positive/negative), non-linear, or no coherence. The interactions between COs drive variations in isotope fractionation associated with evaporation (moisture source dynamics) and transport (storm track pathways and degree of rainout) of moisture. These are mirrored in the spatiotemporal precipitation isotope patterns across contiguous USA and supported by airmass trajectory analysis. We use the USNIP observational dataset to validate and test process representation in the variable-resolution isotope-enabled Community Earth System Model-version 2 (VR-iCESM2) with regional grid refinement to ~12.5 km over the contiguous US. To explore the relative influences of origin, transport, and condensation of water vapor on precipitation isotope patterns, we use process-oriented water tags in the VR-iCESM2 that track physical properties at the evaporation source locations, Rayleigh rainout effect, and precipitation condensation temperature. We find the model prediction to be deficient in coastal regions which improves in the continental interior, but ‘nudging’ the model with atmospheric thermodynamic properties and grid refinement leads to an overall enhancement in model performance relative to low resolution (~100 km) iCESM simulations. Evaluating and improving water cycling processes in climate models using spatially dense, long-term observational datasets of water isotopes, such as USNIP, will improve interpretations of paleoclimate records and predictions of future changes.

How to cite: Dar, S. S., Macarewich, S., Klein, E., and Welker, J.: 25 years of precipitation isotopic composition across the USA: Assessment of non-linearities associated with moisture source dynamics and storm track variations in the Community Earth System Model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7663, https://doi.org/10.5194/egusphere-egu24-7663, 2024.

One of the challenges in climate change studies is understanding the moisture source, oceanic or terrestrial, responsible for the recent increase in global land precipitation evident by ERA-5 reanalysis data.  To explain the moisture source responsible for increase in the land precipitation we have used the d-excess value of precipitation which distinctly inherits the signature of various processes in the hydrological cycle and has been widely used for the validation of general circulation models. We created a global monthly time series of d-excess value (1978-2021) using precipitation isotope data (n= 62,665) from 913 sites. Since 1996, the enigmatic surge in the d-excess value aligns with the rise in the global land precipitation which cannot be explained by the already known moisture source of the global water cycle. Such a huge spike in d-exces value suggests an increase in contribution from the terrestrial moisture, especially from the evaporation of irrigated groundwater, a component which was not considered in the global hydrologic cycle. To feed the growing population, introduction of multiple cropping seasons and a decrease in the frequency of global land precipitation led to an increase in the groundwater-dependent agricultural practice. Previous studies have shown that the extraction of groundwater for irrigation is so huge and significant that it has been held responsible for global sea level rise  and drift of Earth’s rotation axis. In Spite of that, the remotely sensed data and land surface models partition the moisture sources of water cycle in the various components; such as transpiration, open water evaporation,  canopy interception, bare soil evaporation and  snow sublimation, however, never considered the coupling of groundwater with atmosphere. Therefore, to understand the global hydrological cycle, the moisture and energy exchange between groundwater and atmosphere, via evaporation of irrigated water, should be considered. Here, the enigmatic rise in d-excess value, equivalent to glacial-interglacial scale variation, signifies human domination in the global hydrological cycle.

How to cite: Ajay, A. and Sanyal, P.: Coupling of Groundwater with Atmosphere: A New Anthropogenic Component in the Global Hydrological Cycle, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-963, https://doi.org/10.5194/egusphere-egu24-963, 2024.

Water-stable isotopic compositions of snow or ice (here δ¹⁸O and δD) represent the main way to reconstruct past temperature in Antarctica, and one way to interpret these isotopic signals is through the use of isotope-enabled atmospheric general circulation models. In this study, we combine isotopic observations from surface snow samples, daily precipitation and water vapour to evaluate the LMDZ6iso model in Antarctica from climatic to seasonal and sub-daily time scale. Time-averaged δ¹⁸O in precipitation from LMDZ6iso for the period 1980-2022 is in excellent agreement with δ¹⁸O of surface snow samples across the continent, but there is a strong disagreement for d-excess at cold temperature sites. For sub-annual time scale analyses, we focus on two sites in East Antarctica: the coastal station Dumont d'Urville and the continental station Concordia. The model accurately reproduces the seasonal isotopic cycle of daily precipitation at both stations, with better performances at Concordia. Moving from statistical evaluation to process analyses, we use water vapour isotopes to study water exchanges in the boundary layer. LMDZ6iso performs well in representing the observed diurnal isotope cycle at both sites. However, the model simulates a larger vapour δ¹⁸O depletion than observed during the night at Concordia. We analyse the contribution of each physical process affecting isotope concentrations in LMDZ6iso to show what controls the vapour isotope signal. At Concordia, surface sublimation during the day is the main driver of the diurnal cycle of vapour isotopes, whereas at Dumont d'Urville, daily isotope variations are driven by surface sublimation and turbulence during the day and by air advection from the katabatic flow during the night.

How to cite: Dutrievoz, N., Agosta, C., Risi, C., Vignon, É., Nguyen, S., Landais, A., Fourré, E., Leroy-Dos Santos, C., Casado, M., Ollivier, I., Jouzel, J., Roche, D., Minster, B., and Prié, F.: Antarctic water stable isotopes in the global atmospheric model LMDZ6: from climatology to boundary layer processes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19539, https://doi.org/10.5194/egusphere-egu24-19539, 2024.

The northwest China (NWC) is situated in an arid and semi-arid inland, rendering its ecosystem highly susceptible to precipitation changes. Previous studies have revealed the wetting trend and potential moisture sources of the NWC, while not clearly quantified the moisture (water vapor and precipitation) sources and its interannual variability. Here, by performing and analyzing CAM5.1 simulation for 40 years, with a coupled atmospheric water tracer algorithm (AWT), we find that the dominant sources of summer moisture over NWC are from terrestrial sources (81.8% of vapor and 77.4% of precipitation), i.e. from the North Asia (NA), Europe (EUP), southern Tibetan Plateau (STP), and southeastern China (SEC), rather than the oceanic sources. Due to the influence of synoptic patterns, the precipitation-conversion efficiency of water vapor from the southwest airflow (STP and SEC) is higher than that from the northwest airflow (NA and EUP). We also find that despite a general increasing trend in humidification, the fluctuation from relatively dry to wet years still persists in the NWC influenced by the increased transport of moisture from terrestrial sources (NA and STP).

How to cite: Qian, P.: Quantifying the moisture and precipitation sources over Northwest China and investigating the source differences in dry and wet summer seasons, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1515, https://doi.org/10.5194/egusphere-egu24-1515, 2024.

The main philosophy in building a climate model is to represent the most possible number of phenomena, with the purpose of answering the most possible number of questions, with one unique perfect model. For this purpose, climate models have historically evolved from energy balance models, to radiative-convective models, to general circulation models, to the earth system model, with growing complexity. While this approach is relevant in some domains (e.g. climate services), more simple models could answer simple questions (e.g. calculate the mean temperature or precipitations for paleoclimates). Moreover, all climate models use parameterizations to represent the processes with unknown or not numerically solvable physical laws. Moreover, to make them accurate, all climate models tune their parameters. For example, in the atmosphere in the vertical direction, the energy flux often obeys a Fourier-like law with a "conductivity" coefficient tuned to fit observations. The approach we use is entirely different, and because of that, we need to rebuild everything from scratch. We want to construct a simple atmospheric model with no parameterizations (the ultimate goal could be to couple it to a vegetation or an ice model and run long simulations).

We use the MEP hypothesis (maximum entropy production) to do so. This hypothesis has been used in realistic cases with parameterizations, or without parameterizations in more theoretical cases (like 2-box models). However, we aim to construct a full climate model with the MEP hypothesis. First, we restrict ourselves to a vertical tropical atmosphere: a radiative-convective model. Only stationary states are considered. Also, the relative humidity is fixed at 100%. A realistic radiative code is used, and convection is computed with the MEP hypothesis. The computed temperatures fit well with the observations. Also, precipitations can be computed and are coherent with observations. This means that almost only the knowledge of radiative transfer is needed to obtain a good order of magnitude of precipitations. In recent developments, the model has allowed deep convection, leading to slightly different precipitations. When relative humidity is allowed to vary; in the simple convection case, the MEP solution gives a 100% relative humidity almost everywhere; and the deep convection case gives a non-trivial relative humidity profile.

Because MEP is only a hypothesis, we still need to find out if the MEP solution is the exact solution. However, it must represent some upper bound in the system because it corresponds to a maximum. It is already interesting to explore what this upper bound is.

How to cite: Pikeroen, Q. and Paillard, D.: Computing precipitations with a 1D vertical (radiative-convective) model using zero parameterizations., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18906, https://doi.org/10.5194/egusphere-egu24-18906, 2024.

The EUREC4A-OA experiment (January - February 2020. Bony et al., 2017) took place in the Northwest Tropical Atlantic. Atmospheric simulations were performed at kilometric scale during the EUREC4A-OA experiment (47 days) in order to estimate the sensitivity of the Marine Atmospheric Boundary-Layer (MABL) thermodynamics and circulation to the SST front associated with the North Brazil Current (NBC) and to the SST diurnal cycle. It will be shown that the NBC SST front and associated eddies «Couloir des Tourbillons» strongly control the MABL properties (Surface Pressure, Surface Heat Fluxes, Temperature, Wind, Vertical Shear, Precipitable Water, Liquid Water Content ...), while the diurnal cycle of the SST alters these properties by 5 to 10%.

A full MABL water budget has shown that the precipitable water (PW) results of the balance between the total Advection and entraiment at the MABL top, which drains water out the MABL, and surface evaporation that fills in the MABL. It will be shown that the NBC increases the loss of water by advection and by entrainment and increases the gain of water by surface evaporation, by 80 mm in 47 days. The diurnal cycle of SST amplifies these responses by 30 mm in the NBC.

Some components of the MABL energy budget will be also presented.

How to cite: Giordani, H., Conejero, C., and Renault, L.: Adjustment of the Marine Atmospheric Boundary-Layer to the North Brazil Current during the EUREC4A-OA Experiment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11548, https://doi.org/10.5194/egusphere-egu24-11548, 2024.

The loss of Arctic sea ice is conducive to more Arctic evaporation, which can alter precipitation through moisture cycling and transport. However, the extent of this influence remains uncertain. Our work focuses on Arctic seas where seasonal sea ice has retreated significantly. The Arctic evaporation was tracked to establish a link between changes in both sea ice and precipitation over land during the cold season (October to March). Our results show a significant one-third increase in Arctic moisture contribution to land precipitation. Despite Arctic moisture comprising a relatively small proportion of land precipitation, its heightened contribution significantly influenced the precipitation, especially over lands adjacent to the Arctic. Our findings highlight that the progressively ice-free Arctic tends to contribute to a gradual yet discernible shift in the climatological land precipitation, which may lead to an elevated risk of extreme disasters.

How to cite: Liu, Y. and Tang, Q.: Impact of increased evaporation from an increasingly ice-free Arctic on land precipitation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16667, https://doi.org/10.5194/egusphere-egu24-16667, 2024.

The explosive development of extratropical cyclones and the presence of atmospheric rivers play a crucial role in driving some types of extreme weather in the mid-latitudes, like compound flood-windstorm events. Although these phenomena are individually well-established and their relationship has been studied previously, there is still a gap in our understanding of how a warmer climate may affect their concurrence. Here, we focus on evaluating the current climatology and assessing changes in the future climate of the concurrence between atmospheric rivers and explosive cyclones in the North Atlantic.

We use both the ERA5 and ERA-Interim reanalysis between 1980 to 2009 from October to March to evaluate the concurrence of atmospheric rivers and explosive cyclones in the current climate. To accomplish this, we first independently detect and track atmospheric rivers and extratropical cyclones. Next, we classify each cyclone as either explosive or non-explosive and define concurrence with an atmospheric river if the latter is detected within 1500 km of the minimum sea level pressure of the cyclone. We further analyse several CMIP6 climate models for the historical scenario (1980-2009) and for the future scenarios SSP1-2.6, SSP2-4.5 and SSP5-8.5 at the end of the century (2070-2099).

Our findings reveal that atmospheric rivers are more often detected in the vicinity of explosive cyclones than non-explosive cyclones in all datasets. Moreover, we identified a significant increase in the concurrences and the atmospheric river intensity in all the future scenarios analysed. As such, our work provides a novel statistical relation between explosive cyclones and atmospheric rivers in climate projections, a characterization of both in future climates and a new climatology of the concurrences for a higher-resolution reanalysis.

How to cite: Lopez-Marti, F., Ginesta, M., Faranda, D., Rutgersson, A., Yiou, P., Wu, L., and Messori, G.: Changes in the concurrence of atmospheric rivers and explosive cyclones in the North Atlantic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18497, https://doi.org/10.5194/egusphere-egu24-18497, 2024.

Extreme precipitation over western Iberia is mostly concentrated in the winter half-year. While relatively rare, intense precipitation events can disrupt and are often associated with major human, social and economic damages. Most of the time these extreme precipitation events are triggered by intense extratropical cyclones and associated frontal systems. However, in the last decade a number of studies have shown the important role played by Atmospheric Rivers (ARs) in the occurrence of extreme precipitation events in western Europe, particularly in the Iberia Peninsula.

In this study we analyse the all-time 24h record-breaking precipitation values recorded in Lisbon, Portugal between the 12 and 13 December 2022 in terms of the synoptic background. We obtained a comprehensive synoptic characterization of the atmospheric circulation between the 1^st and 15^th of December, considering a wide range of meteorological fields, such as vertically integrated water vapor flux, sea level pressure, geopotential height and divergence at the 850 hPa isobar, divergence at the 200 hPa, vertical velocity at the 500 hPa and temperature and specific humidity at 900 and 600 hPa.

Results show that on the 8 December by 06 UTC an extratropical cyclone was present in the middle of the North Atlantic, with a high moisture content and that by 18 UTC on the following day a cut-off low was formed in the northwest Atlantic. This cut-off system was well characterized by relatively high vertical velocities and convergence at the low levels, combined with high rates of evaporation acquired over the Gulf Stream, intensifying the moisture content to its south side. Both systems converged on 10 December by 12 UTC and by the 18 UTC the algorithm detected an AR located southward of the extratropical cyclone. The combination between high IVT values, with maxima ranging between 947 kg m^-1 s^-1 and 1227 kg m^-1 s^-1, with a dynamical component characterised by winds above 20 m/s, as well as a suitable vertical motion, allowed the system to evolve and maintain the AR characteristics for 72 h. The AR progressed towards Iberia, affecting Portugal and central Spain as an extreme AR event, leading to the 24h precipitation record of 134.6 mm measured at the Geophysical Institute in Lisbon, the highest value since continuous measurements started in the 1860. The previous record was registered on the 18 February 2008, with a value of 118.4 mm.

This work was supported by the Portuguese Science Foundation (FCT) through the project AMOTHEC (DRI/India/0098/2020) with DOI 10.54499/DRI/India/0098/2020 and also through national funds (PIDDAC) – UIDB/50019/2020. Tiago Ferreira was supported by FCT through PhD grant UI/BD/154496/2022.

How to cite: Ferreira, T., M. Trigo, R., M. Ramos, A., Gaspar, T., and G. Pinto, J.: The Record-Breaking Precipitation Event of December 2022 in Portugal: Synoptic Background, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-778, https://doi.org/10.5194/egusphere-egu24-778, 2024.

The diversity of water vapor content in the air is crucial for the regional analysis of atmospheric precipitation occurrences. The amount of water vapor carried by the air mass over a specific area can vary significantly depending on the current characteristics of air circulation, with a key role played by atmospheric rivers. These rivers originate from the meridional transport of water vapor and have a significant impact on Europe through the interaction with extratropical cyclones.
The aim of the work is to assess the intensity of water vapor transport over Europe and the extent of its inland penetration.
Atmospheric rivers/streams will be identified based on ECMWF ERA5 reanalyses data from 1991 to 2023 and CMIP6 future projections until the year 2100.
Selected cases of intense water vapor transport over the European region, especially Central Europe, will be compared with the occurrence of atmospheric precipitation.

How to cite: Wypych, A.: Atmospheric moisture transport in Central Europe – rivers or streams, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14310, https://doi.org/10.5194/egusphere-egu24-14310, 2024.

Extra-tropical storms over the North Atlantic often leads to socio-economic impacts over Western Europe, associated with strong winds and precipitation. Such storms can be associated with so-called Atmospheric Rivers (ARs) which are relatively narrow regions of concentrated water vapor (WV) and strong winds where intense horizontal moisture transport can take place. In turn, the moisture availability along the cyclone path and the ARs lifetime can be impacted by boundary layer processes. For example, the occurrence of Dry Intrusions (DI) associated with previous cyclones can strongly destabilize the planetary boundary layer (PBL) leading to enhanced moisture uptake over the ocean. This can support the formation and/or intensification of the ARs themselves.

The objective of this study is to understand the influence of DI on the moisture uptake in the PBL and transport associated with ARs impacting France.

With this aim, an adapted version of the detection algorithm developed by Ramos et al. (2015), was applied to ERA-5 reanalysis targeting events impacting the Atlantic coast of France. A total of 300 AR-events were detected over the extended winter (ONDJFM) spanning the years 1979 to 2023. Indeed, the most intense landfalling ARs are associated with intense precipitation and high wind speeds over western France.

For a subset of these AR-events, occurring between 1992 and 2022, the Lagrangian FLEXPART model using ERA5-data was applied to calculate the moisture sources for these events. This approach allows for the tracking of air masses 10 days backward in time from the target region (5°W to 0.5°E and 43.75°N to 50°N). 

Additionally, the occurrence of DI outflows (from 1979 onward) was based on its Lagrangian detection in ERA5 to assign possible DI outflows overlapping with the source regions of moisture uptake.

Our results suggest a relationship between the areas of DIs and moisture uptake, indicating the possibility of the DI exerting influence on the formation and intensification of ARs. Overall, this work serves as a preliminary investigation for the upcoming North Atlantic Waveguide, Dry Intrusion, and Downstream Impact Campaign (NAWDIC) recently endorsed by the World Weather Research Programme (WWRP).

How to cite: Weiss, K. A., Gaspar, T., Pérez-Alarcón, A., Raveh-Rubin, S., Pinto, J. G., and Ramos, A. M.: The role of Dry Intrusions in the formation and intensification of Atmospheric Rivers impacting France, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19562, https://doi.org/10.5194/egusphere-egu24-19562, 2024.