AS1.21
Orals: Mon, 24 Apr | Room 0.11/12
Precipitation is the largest freshwater flux that enables life on land. However, climate change is projected to increase the frequency and intensity of extreme precipitation events, which often culminate in droughts and floods with devastating impacts on humanity and the environment. To better understand the dynamics of precipitation in a changing climate, recent studies aimed to unravel the interaction between evaporation and precipitation. To do so, atmospheric moisture tracking models have often been employed to determine the origins of precipitation and establish source–sink relationships. However, due to the lack of sufficient and accurate observations to evaluate these models, their estimated source regions of precipitation often remain unvalidated. Nonetheless, the number of studies using such models is increasing, even if only a few have addressed associated uncertainties and even fewer employed multiple models.
Here, we advocate the need for moisture tracking model intercomparisons to advance this field of study. Therefore, we provide an overview of models and methods that track moisture through the atmosphere and determine the origins of precipitation. Further, we highlight conceptual differences between these models and demystify assumptions hidden in the analysis of source regions. Using selected case studies, we illustrate the uncertainty associated with the origin of precipitation and highlight the need for coordinated model comparisons using multiple models. Finally, we present our plans to engage with the entire moisture tracking community to collaborate on prospective model intercomparison studies. Through these efforts, we wish to raise awareness about the uncertainties inherent in moisture tracking approaches and achieve a better understanding of the drivers of precipitation in a changing climate.
How to cite: Keune, J., Benedict, I., Weijenborg, C., Schumacher, D. L., Koppa, A., and Miralles, D. G.: Estimating the origin of precipitation: uncertainties associated with atmospheric moisture tracking models, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-3606, https://doi.org/10.5194/egusphere-egu23-3606, 2023.
Moisture transport within atmospheric rivers (ARs) is a complex combination of processes, with convergence of moisture with different origin and its changes over the life cycle of an AR. The water vapour budget in an AR enables us to understand the contribution of the different moisture sources and sinks (horizontal transport, local evaporation and precipitation). Here, we focus on how these contributed to the formation and development of the exceptional AR associated with storm Denis that occurred in February 2020 leading to the 3rd highest UK average daily rainfall since 18911.
We use the WRF-ARW numerical limited-area atmospheric model to simulate the life-cycle of the AR in the North Atlantic basin. We use a resolution of 0.09º, and a domain covering both the AR’s formation region close to the Gulf of Mexico to the landfall region in northern and central Europe. Moreover, we performed two sets of sensitivity experiments by reducing the tropical moisture transport, and the sensible heat flux in specific areas of the oceanic basin to assess how these two main components affect the water vapour balance within the AR. We also defined a threshold to map the AR and used a centroid-based method to track its path in order to measure the shift of its location and intensity through time in the different experiments.
Our findings reveal significant relationships between the reduction of tropical moisture and a change of the location of the AR. The analysis also detected regional and temporal changes in the water vapour budget due to the perturbations done in the sensitivity experiments. In addition, relative importance of moisture sources are assessed. As such, our work provides a new case study to unravel feedback processes and the influence to the AR characteristics when perturbing the water vapour balance.
1 Davies, Paul A., et al. "The wet and stormy UK winter of 2019/2020." Weather 76.12 (2021): 396-402.
How to cite: Lopez-Marti, F., Wu, L., Messori, G., and Rutgersson, A.: Sources of Moisture to Extreme Atmospheric Rivers: a storm Denis case study, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-1553, https://doi.org/10.5194/egusphere-egu23-1553, 2023.
Atmospheric rivers (ARs) are filaments of extensive water vapor transport in the lower troposphere. They play a crucial role in the global water cycle and are a main source of fresh water for the mid-latitudes. However, very intense and persistent ARs are important triggers of heavy rainfall events and have been associated with natural and economical damage. Further motivated by their high impacts, in the last decade occurrences of ARs have been intensively studied, detection algorithms have been developed, and multiple AR catalogs have been produced. As a common approach, the detection of ARs is based on localizing anomalous atmospheric transport of moisture, usually by setting an absolute threshold on vertically integrated vapor transport (IVT) and/or vertically integrated water vapor (IWV) fields. Behind this methodology, there is the implicit assumption of stationary atmospheric moisture levels, which is not necessarily true for long periods under the context of a warming atmosphere. Also, these thresholds have proven to vary regionally which results in often excluded low-level ARs.
Here, we introduce AR-tracks, a global, high-resolution catalog of atmospheric rivers that we have developed based on the Image-Processing-based Atmospheric River Tracking (IPART) algorithm, using IVT estimates of the ERA5 reanalysis data set. As opposed to conventional detection methods, IPART calculates anomalies of the IVT field at the synoptical spatiotemporal scale of ARs and is, therefore, free from magnitude thresholds and stationarity assumptions. The resulting catalog displays a list of AR events, with a spatial resolution of 0.75° x 0.75° and a temporal resolution of 6 hours, covering the period between 1979 and 2019. For each AR, we provide common parameters such as the time and location of the landfall, the respective IVT value, the area, the width, and the length of the AR. Moreover, we also track the contour and the axis of each AR, the position of the centroid, and the proportion of the AR that is located over ocean and land, and over the different continents.
To show the potential of this new catalog, we study the spatiotemporal variability of European ARs between 1979-2019, analyzing the robustness of our results for distinct parameter choices in the definition of AR-tracks. We also use a novel power spectral measure to identify periodic cycles in the occurrence of European ARs, revealing spatially heterogeneous seasonal and multi-annual periodicities. Finally, we discuss the role of land-falling ARs as a trigger of heavy precipitation events in the regional domain.
With the extensive data we provide in this new catalog, we aim at contributing to the further understanding of the role of ARs in global climate dynamics, as long-lived ARs having cross-continent tracks can be reliably traced through their tropical/subtropical origins to high-latitude landfall, and novel topics such as inland penetration of ARs can be studied.
How to cite: Vallejo-Bernal, S. M., Braun, T., Marwan, N., and Kurths, J.: AR-tracks: A new comprehensive global catalog of atmospheric rivers, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-9251, https://doi.org/10.5194/egusphere-egu23-9251, 2023.
Global warming has resulted in frequent occurrences of hydrological extremes, especially floods, across the globe. Flooding may lead to significant loss of life and economic damage. The increase in these flood events is due to the short intense rainfall events. Finding the geographical sources of the moisture that causes these short intense rainfall events is an important step toward predicting extreme events. The present research intends to investigate moisture sources for precipitation events over the flood-prone Indian Basin. Using the lagrangian moisture diagnostic, the research will look at moisture sources below the boundary layer as well as variations above the boundary layer from 1980 to 2018 during the Indian Summer Monsoon season. The study will also look at how the contribution from various sources varies over the course of the Indian Summer Monsoon Rainfall season. This work will enhance our understanding of the hydrological cycle and assist with a variety of related issues, including water resource planning, weather forecasting, land and water management, and more.
How to cite: Choudhary, R., Dhanya, C. T., and Gosain, A. K.: Unravelling the sources of moisture for precipitation events in a flood-prone Indian basin, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-9436, https://doi.org/10.5194/egusphere-egu23-9436, 2023.
The sensitivity of coarse-grained daily extreme precipitation to sea surface temperature is analyzed using satellite precipitation estimates over the 300–302.5 K range. A theoretical scaling is proposed, linking changes in coarse-grained precipitation to changes in fine-scale hourly precipitation area fraction and changes in conditional fine-scale precipitation rates. The analysis reveals that the extreme coarse-grained precipitation scaling with temperature (∼7%/K) is dominated by the fine-scale precipitating fraction scaling (∼6.5%/K) when using a 3 mm/h fine-scale threshold to delineate the precipitating fraction. These results are shown to be robust to the selection of the precipitation product and to the percentile used to characterize the extreme. This new coarse-grained scaling is further related to the well-known scaling for fine-scale precipitation extremes, and suggests a compensation between thermodynamic and dynamic contributions or that both contributions are small with respect to that of fractional coverage. These results suggest that processes responsible for the changes in fractional coverage are to be accounted for to assess the sensitivity of coarse-grained extreme daily precipitation to surface temperature.
How to cite: Muller, C., Roca, R., and De Meyer, V.: Precipitating Fraction, Not Intensity, Explains Extreme Coarse-Grained Precipitation Clausius-Clapeyron Scaling With Sea Surface Temperature Over Tropical Oceans, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-16367, https://doi.org/10.5194/egusphere-egu23-16367, 2023.
Understanding rainfall and its extremes is essential for quantifying weather and climate related risks, and the management of water resources. However, climate projections of rainfall have large uncertainties because of differing sensitivities to changes in dynamic, thermodynamic and microphysical factors. Emergent statistical constraints derived from observations and high resolution simulations can be used to reduce these uncertainties, but must be based on process understanding to be robust.
Our recent work shows that clustering rainfall data into regions of similar wet day frequency, regardless of geographical separation, uncovers a strong correlation between wet day occurrence and daily rainfall accumulation distributions. This relationship is robust across a range of observational datasets with differing spatial resolutions.
We hypothesise that this relationship shows that the presence or absence of precipitation generating weather systems (atmospheric rivers, cyclones, fronts and mesoscale convective storms) rather than their individual intensities is critical for daily rainfall totals. In this presentation, we will first examine whether the probability of specific dynamic, thermodynamic and microphysical states drives wet day occurrence. We will also use feature analysis and tracking schemes to identify how the distribution of each of these dynamic, thermodynamic and microphysical states varies for each precipitation generating weather system. This potentially allows a quantification of the importance of different precipitation generating systems for different wet day occurrences and how each contributes to daily accumulation distributions. This expands on previous work which has shown that atmospheric rivers, cyclones, fronts and mesoscale convective storms have varying relationships to rainfall and their extremes. In particular, it allows us to identify their relative importance and explains their relative efficacy for precipitation generation.
How to cite: McDonald, A.: Understanding the relative importance of different precipitation generating weather systems and quantifying their efficiencies, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-10922, https://doi.org/10.5194/egusphere-egu23-10922, 2023.
Among all greenhouse gases (GHGs), atmospheric water vapour is the most abundant and has huge influence on the Earth’s radiation budget, and plays decisive role in regional weather processes. Unlike other GHGs, which are controlled by emissions, atmospheric water vapour is influenced by the surface temperature. Here, we examine the long-term changes in global and regional water vapour using satellite and reanalysis datasets. The annual mean water vapour shows very high values in tropics and low values in the polar and high terrain regions. A clear seasonal cycle is observed in the water vapour, with high values in summer (25–65 kg/m2) and small values in winter (5–20 kg/m2), except in the tropics. The high values in summer is maily due to the enhanced evapotranpiration driven by surface air temperature, and water vapour transport by winds. There is a significant rise in annual mean global water vapour, driven by global warming, about 0.025–0.1 kg/m2/yr for the period 1980–2020. Furthermore, higher positive trends in water vapour is also observed in arid regions (Sahara, Arabian and Thar desert), Indian subcontinent and the Arctic. The higher values of water vapour trends in the Arctic is due to the significant rise in temperature there. Similarly, the increase in water vapour in desert regions is due to water vapour transport from nearby oceans. The associated radiative effects on short-wave at the surface varies from -5 to -70 W/m2 over the tropical radiosonde stations, and the smallest of about -5– -10 W/m2 in the polar regions. This study, therefore, shows that there is significant rise in water vapour across the latitudes, which could further increase the global temperature through positive feedback mechamism and thus, change global and regional climate.
Keywords: Water Vapour, Evapotranspiration, Global Warming, Arctic, Desert; Radiative Effects
How to cite: Patel, V. K. and Kuttippurath, J.: Global warming triggers the notable rise in water vapour: implications for global climate change, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-3551, https://doi.org/10.5194/egusphere-egu23-3551, 2023.
Abstract
Summer (June to August) precipitation over the Three-River Headwaters’ (TRH) region has experienced a significant dry-to-wet transition during 1979-2020. The transition could have been caused by changed atmospheric circulations, which was modulated by oceanic forcings. This study intends to improve our understanding of the summer precipitation variability over the TRH region under the influence of oceanic modes. The combined effect of three interdecadal oceanic modes [Pacific decadal oscillation (PDO), Atlantic multidecadal oscillation (AMO), and Indian Ocean Basin mode (IOBM)] on the interdecadal dry-to-wet transition was examined, using composite analysis on HadISST and the fifth generation ECMWF reanalysis (ERA5) datasets. The results show that in positive AMO and negative PDO phases, a zonally oriented teleconnection wave train is generated across the Eurasian mid-to-high latitudes, propagating from the North Atlantic to northern East Asia along the westerly jet. This results in a weakened and northward-shifted westerly jet. Furthermore, the enhanced and northward-shifted Western Pacific Subtropical High (WPSH) brings water vapor from the Pacific Ocean, and cyclonic circulation over the Arabian Sea increases the amount of water vapor entering the TRH region. In positive IBOM phases, the warm Indian Ocean induces an anomalous anticyclone over the Bay of Bengal, and anomalous southwesterly delivers abundant water vapor from the Indian Ocean to the TRH region, which overlaps with the vapor transport caused by a positive AMO and PDO. As the Atlantic and Northern Pacific Oceans warm, the enhanced Walker circulation suppresses the ascending motion in the central Pacific and enhances the equatorial easterly, which in turn strengthens the anomalous anticyclone over the Bay of Bengal. As a result, the summer precipitation over the TRH is further increased. The analysis shows that the combined effect of the three oceanic modes played an important role in the dry-to-wet transition.
How to cite: Liu, X., Yang, M., Chen, D., and Wang, H.: The dry-to-wet transition of summer precipitation over the Three-River Headwaters’ region: the role played by three interdecadal oceanic modes, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-3316, https://doi.org/10.5194/egusphere-egu23-3316, 2023.
In 2019, a record-breaking drought happened in the middle reaches of the Lancang-Mekong River Basin (M-LMRB), which brings about 650 million dollars in economic loss and affected 17 million residences. As climate change evolute, the LMRB is suffering from increasingly frequent and intensive drought with the mechanisms remaining unclear. This study analyzed the water vapor circulation of the drought event in 2019 based on the land-atmosphere water budget and backward trajectory model. Results show that the precipitation of the M-LMRB from May to October 2019 was 71.9% of the climatological mean (1959-2021). The moisture transported from the Indian Ocean, Bay of Bengal, and Pacific Ocean, which are the main moisture sources of the region, was found to decrease through the backward trajectory model. From the comparison of the atmospheric circulation of 2019 and the climatology, the anomalous anticyclone in the BOB, the anomalous westerlies in the Northeast Indian Ocean, and the anomalous cyclone in the Western Pacific Ocean were found to facilitate the stronger export of water vapor jointly. Therefore, the dynamic processes should be more responsible for the extreme drought event of the LMRB in 2019 than the thermodynamics processes. The findings of this study provide new insights into understanding mechanisms of climate change affecting extreme drought events through the atmospheric circulation and are helpful to the risk management of droughts under climate change.
How to cite: Gong, G., Zhang, S., and Liu, J.: The anomalous water vapor circulation in an extreme drought event in the middle reaches of the Lancang-Mekong River Basin, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-6262, https://doi.org/10.5194/egusphere-egu23-6262, 2023.
Isotope ratios in water vapor record evaporation (E) and precipitation (P) along moisture transport paths. At low latitudes, the path-integrated E-P signal is dominated by local E and P, providing an indicator of tropical water balance. In contrast, at high latitudes, E and P patterns upstream overwhelm local signals, reflecting the dependence on remote moisture sources. This dependence defines the length scales of moisture transport.
In the zonal mean, moisture transport length scales can be represented visually in two dimensions by moist isentropic surfaces, along which poleward moisture transport occurs. These surfaces explain why Rayleigh distillation reasonably approximates meridional variations in high-latitude isotope ratios while also providing a physical basis for why polar isotope-temperature relationships are distinct in space and time.
Isotopically enabled GCM simulations and short-duration Antarctic ground-based observations both lend support for the isentropic view of moisture transport. They also suggest that this framework provides a simple means to predict changes in length scale in a warmer climate, assuming zonal-mean humidity changes follow Clausius-Clapeyron scaling. However, isotopic observations with the vertical resolution and temporal coverage necessary to easily evaluate recent and expected future variations in moist isentropic transport are lacking.
Here, we consider two possible alternative methods for testing predictions about long-term moisture length-scale changes with isotopic observations. Using the two-decade-long AIRS satellite record, we consider the extent to which mid-free tropospheric hydrogen isotope ratios, normalized by humidity, can provide a measure of length scale in a total-column sense. Second, we ask to what extent moist isentropic transport is set by episodic events, such as warm conveyor belts, that can be observed by infrequent but high-vertical-resolution airborne isotopic measurements. We discuss the implications of enhanced transport efficiency, expected in a warmer future, for increasing length scales and strengthening hydrological dependencies between remote locations.
How to cite: Bailey, A., Singh, H., Nusbaumer, J., Casado, M., Cauquoin, A., Heyblom, K., and Worden, J.: Changing length scales of moisture transport — their isotopic imprint and implications for remote moisture dependence, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-4543, https://doi.org/10.5194/egusphere-egu23-4543, 2023.
It still remains an intriguing question in weather and climate research on identifying the convective rainfall from stratiform. In a future warmer climate, this will be important to know to predict the changing pattern of rain intensity and distribution and to plan an efficient usage of water resources. Although quite a few methods have been proposed to address this question, such as cloud top temperature value, height-integrated ice and cloud water paths, brightness temperature, drop size distribution etc., the fidelity and validity of those vary widely, and hence their applicability remains limited. In this work, we propose a method to identify these two rainfall regimes using a combination of surface and remote sensing measurements. We collected the rainwater samples daily at Port Blair, Sagar and Tezpur in India as part of a project CRP F31006, funded by the International Atomic Energy Agency (IAEA). We measured the 18O content in these collected rainwater samples by measuring its fractionation (δ18O) using a Triple Isotope Water Analyzer by Los Gatos Research, USA. Among these sites, Port Blair is an island on the Bay of Bengal near the tropics, Sagar is an inland location in central India's dry, arid climate and Tezpur is located in the wet and heavily forested northeast India. Whereas Port Blair is situated very close to the tropics, Sagar and Tezpur are closer to the subtropics. The dual-frequency precipitation radar in the global precipitation measurement (GPM) program provides the convective and stratiform rainfall records by looking at radar reflectivities. We utilize these records to estimate the area-averaged stratiform rainfall fraction over each of these locations. We find that the relation between rain intensity and stratiform rainfall fraction can be represented by a logarithmic regression, whereas, the relation between δ18O and rain intensity can be represented by linear regression. However, the logarithmic regression weakens with latitude, and, the slope of the linear relation changes from slightly negative to slightly positive. The three sites considered here are located under different environmental conditions (oceanic to continental, semi-arid to forest, southwest to northeast monsoon zones, etc.) and house different vegetation types. To better understand the underlying processes governing such relations, we also study the impact of different meteorological variables in regulating these relations. Based on our study, the δ18O can be used as a proxy to identify the relative contributions of convective and stratiform rain types in the total rainfall over a region.
How to cite: Deb Burman, P. K., Chakraborty, S., Datye, A., Choudhury, A., Mujumdar, M., Mohan, P., Gogoi, N., Trivedi, R., Sarma, D., Bora, A., and Trivedi, N.: Identifying the convective and stratiform rainfall regimes using stable isotopic measurement , EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-14988, https://doi.org/10.5194/egusphere-egu23-14988, 2023.
Low-cloud feedbacks contribute large uncertainties to climate projections and estimated climate sensitivity. A key physical process modulating low-cloud feedbacks is shallow convective mixing between the boundary layer and the free troposphere. However, there are challenges in acquiring observational estimations of shallow convective mixing with global coverage. To this end, we propose a novel approach to constraining convective mixing using stable water vapor isotope profiles from satellite retrievals. We demonstrate that the vertical gradient of water vapor δD between the boundary layer and free troposphere can be used to track shallow convective mixing, especially over the trade-wind regions. We also evaluate this metric of shallow convective mixing against the EUREC4A experiment data. Analyzing isotopes in water vapor alongside low-cloud properties from satellite retrievals, we find that low-cloud fraction appears insensitive to convective mixing in trade cumulus regions. Our results suggest that satellite-derived observations of the relationship between shallow convective mixing and low-cloud are regionally-dependent, and strong shallow convective mixing is associated with moistening of the free troposphere in the tropics. The new estimations of low-cloud properties and their relationship with changes in convective mixing using water isotopes house potential to improve the simulation of low-cloud feedbacks in numerical simulations, refining estimates of climate sensitivity.
How to cite: Dee, S., Hu, J., Bailey, A., Nusbaumer, J., Sasser, C., and Worden, J.: Interrogating the influence of shallow convective mixing on low-level clouds with observations of stable water isotopes, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-9668, https://doi.org/10.5194/egusphere-egu23-9668, 2023.
Validation of gas exchange fluxes in models has been challenging due to the lack of ecosystem scale exchange fluxes partitioned into soil, plant and atmospheric components. One promising method to partition turbulent fluxes uses the exchange process dependent fractionation of molecules like CO2 and H2O. When applying this method to short spatiotemporal scales, an isotope flux (δ-flux) needs to be resolved. Few have attempted to measure this δ-flux as the required instrumentation only became available in recent years. In our presentation we will discuss observations made during the LIAISE 2021 field campaign using an EC system, Picarro L-2130i H2O isotope analyser, and Aerodyne TILDAS-CS CO2 isotope analyser. This campaign took place in the summer of 2021 in the heavily irrigated Ebro River basin near Lleida, Spain embedded in a semi-arid region.
We will present procedures to estimate and scrutinize the central δ-flux variable. To this end we calculated co-spectra of the relevant signals and compared their frequency dependent contributions. One relevant finding is that mole fractions and isotope ratios measured with the same instrument can be offset in time by more than a minute, thereby impacting the resulting δ-fluxes. Additionally, we found asymmetric signal loss between net ecosystem fluxes and δ-fluxes. We will show that such effects impact flux partitioning severely and indicate how they can be tackled using physically sound corrections. Only when such corrections and verifications are made, ecosystem flux partitioning can be applied to validate conceptual land-atmosphere exchange models. Such models will calculate the diurnal variability of CO2 and H2O isotopologue concentrations, and link local to regional scales, all with the purpose of better constraining current and future exchange fluxes.
How to cite: Moonen, R., Adnew, G., Hartogensis, O., Vila-Guerau de Arellano, J., and Röckmann, T.: Investigating diurnal ecosystem scale H2O and CO2 isotope fluxes in an irrigated semi-arid environment during the LIAISE 2021 field campaign, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-13348, https://doi.org/10.5194/egusphere-egu23-13348, 2023.
Changes in ice sheet size and configuration impact global moisture and heat transport, but few proxy records examine these impacts. High-latitude precipitation-isotope proxy records are often interpreted to reflect temperature change, but can also reflect changes in moisture source. We present independent sub-centennial-scale records of summer temperature and summer precipitation δ2H from the same lake sediment archive on northeastern Baffin Island. We also examine published TraCE-21k transient model simulation results. These records span from 12 to 7 ka, when the Laurentide Ice Sheet underwent major retreat. The correlation structure between summer temperature and precipitation δ2H on northeastern Baffin Island changed from negative to positive around 10 ka. We interpret this change in correlation structure to indicate a shift in moisture sources to northeastern Baffin Island. TraCE-21k results suggest that moisture sources in this region are controlled by the relative strength of the high pressure systems and associated anticyclonic circulation over the Greenland and Laurentide ice sheets. We therefore interpret the proxy records as follows: when the Laurentide high dominated prior to 10 ka, northerly winds brought cold, dry Arctic air to the region, allowing 2H-enriched local sea breezes to provide most of the moisture to Baffin Island. After 10 ka, the Greenland high dominated, causing southerly flow to carry warm, moist, 2H-depleted air masses to northeastern Baffin Island. Regional centennial-scale cooling events caused by periodic freshwater inputs to the Labrador Sea throughout the Early Holocene were also associated with intervals of 2H-enriched summer precipitation. This study provides evidence that atmospheric circulation was influenced by the waning continental ice sheets. Similar ice-sheet influences are critical to consider when interpreting precipitation isotope proxy records spanning periods of dramatic ice-sheet change. These results demonstrate that precipitation isotopes can reflect changes in atmospheric circulation in the geologic record.
How to cite: Thomas, E., Cluett, A., Erb, M., McKay, N., Briner, J., Castañeda, I., Corcoran, M., Cowling, O., Gorbey, D., Lindberg, K., and Salacup, J.: Early Holocene Laurentide Ice Sheet retreat influenced summer atmospheric circulation in the North American Arctic: Evidence from precipitation isotope and temperature proxy records and a climate model, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-12634, https://doi.org/10.5194/egusphere-egu23-12634, 2023.
Stable isotope ratios of oxygen (δ18Op) and hydrogen (δDp) record information about the hydrological cycle. These signals are preserved in natural archives, such as speleothems, stalagmites, ice cores, and pedogenic carbonates. Recent studies have used these proxy records of water isotopologues to reconstruct the evolution of paleoclimates, paleoenvironments, and even tectonic-related changes in surface elevations. However, such reconstructions require information about the atmospheric dynamics that drive the spatial variability of isotopic ratios. δ18Op and δDp are known to reflect the history of air masses, surface temperature, precipitation, and synoptic-scale atmospheric teleconnection patterns like the North Atlantic Oscillation (NAO). Climate-driven variations in these data can complicate their interpretation of geologic processes. The NAO is the predominant mode of inter-annual and seasonal variability that controls the weather and climate system across the North Atlantic region and continental Europe. The influence of the NAO on the Global Network of Isotopes in Precipitation (GNIP) stations records of δ18Op and δDp across Europe was previously studied in the winter season when the NAO impacts are well defined.
Here we build upon previous work by (1) investigating the present-day NAO-δ18Op and -δDp relationships and their associated atmospheric dynamics and causal mechanism in all seasons, and (2) studying the NAO’s influence on the δ18O and δD in precipitation in the late Cenozoic. We focus on the latter since many δ18Op- and δDp-based studies tackle problems in the Late Cenozoic. In addition, important characteristics of such pressure systems (e.g., the location of the centers of maximum and minimum pressures and axis of polarity) may change over longer (centennial to geological) time scales in response to different forcings such as atmospheric CO2, paleogeography, orbital changes, and land-surface cover. To achieve the study’s first goal, we explore the NAO-δ18Op and -δDp link by tracking the NAO in the ERA5 reanalysis data and relating its variability with GNIP observational data across Europe. For the second goal, we use the isotope-enabled Atmospheric General Circulation Model ECHAM5-wiso to perform time-specific, high spatial resolution (paleo)climate simulations with (paleo)environmental conditions of the middle Miocene (~14 Ma), the mid-Pliocene (~3 Ma), the Last Glacial Maximum (~21 ka), the mid-Holocene (~6.5 ka), the pre-industrial (the reference year 1850) and the present-day (1979-2000). We then transfer the analyses from the first step to our paleoclimate simulation output, using the present-day simulation for calibration. Our results help reconstruct the NAO from proxy archives and provide context for more refined interpretations of the isotopic ratios of rainwater in proxy archives.
How to cite: Boateng, D., G. Mutz, S., and A. Ehlers, T.: The influence of North Atlantic Oscillation on oxygen and hydrogen stable isotopes in precipitation of the Late Cenozoic: implications on paleoenvironment reconstructions, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-1752, https://doi.org/10.5194/egusphere-egu23-1752, 2023.
A continuous bi-weekly water isotope analysis (δ18O, δD, and d-excess) was done since 2015 from a subtropical reservoir (Feitsui Reservoir) in northern Taiwan. The Feitsui reservoir is an important national freshwater system, as it provides water for the large urban population of Taipei. The isotopic data reveals a multiyear pattern and it closely follows the rainfall isotopic composition. We made a simple mass-balance model using the rainfall isotopic composition, inflow and outflow volumes, and meteorological parameters that fit well (R2 = 0.55; p-value < 0.05) with the observed isotopic composition of the reservoir. Based on this model, we estimated reservoir isotopic composition for the previous 20 years (2001-2021). The model also well reproduced a few years of historical data reported in the literature. In the model, we noted two conspicuous patterns: (1) multiyear cyclicity in δ18O and d-excess, and (2) a long-term enriching trend in δ18O. These patterns were not so obvious in rainfall because of the strong seasonality, which gets diluted in the reservoir because of the longer water residence time (~6 months). However, these patterns became visible in rainfall isotopes after removing the seasonal cycles. The observed multiyear patterns do not resemble with the known multiyear global processes, such as ENSO, PDO, and the East Asian Monsoon Index. However, the role of these global processes cannot be ruled out completely. We believe that because of the unique geographical location of the island, multiple moisture sources (South China Sea and central/northern China), dual monsoons (summer and winter monsoons), and complex hydrometeorological processes, the signals of these multiyear global processes get modulated and modified. The long-term enriching trend in δ18O seems to be a consequence of climate change. The enriching trend is more vivid during the winters than summers. This indicates the possible role of global warming and the expansion of the tropics because the Tropics of Cancer passes through central Taiwan. There also remains a significant knowledge gap in understanding the role of winter monsoons in East Asia. This study highlights the importance and the need for rigorous climatic research in Taiwan because of its unique location which makes it highly sensitive to climate change. This study may also have implications for paleoclimatic studies because it highlights the complex hydrometeorology of the region.
How to cite: Oza, H., Wang, C.-H., and Liang, M.-C.: Enigmatic Multi-Year Oscillations in Water Isotopic Composition of East Asia: Insights from a Subtropical Reservoir , EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-13842, https://doi.org/10.5194/egusphere-egu23-13842, 2023.
Stable water isotope signals in inland Antarctic ice cores have provided wealth of information about past climates. This study investigated atmospheric circulation processes that influence precipitation isotopes in inland Antarctica associated with atmospheric circulations in the southern mid-latitudes during the Last Glacial Maximum (LGM, ~21 000 year ago). A couple of probable climates during this climate period were simulated using the isotope-enabled atmospheric general circulation model MIROC5-iso. Our results showed a steepened meridional sea surface temperature gradient in the southern mid-latitudes associated with a strengthening of the southern westerlies. This change in the atmospheric circulation enhanced the intrusion of warm and humid air from low latitudes that contributes to precipitation events, inducing heavy water isotope precipitation inland East Antarctica. Our results suggest that past southern westerlies can be constrained using water isotopic signals in Antarctic ice cores.
How to cite: Kino, K., Cauquoin, A., Okazaki, A., Oki, T., and Yoshimura, K.: Heavy Water Isotope Precipitation in Inland East Antarctica Accompanied by Strong Southern Westerly Winds during the Last Glacial Maximum, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-4775, https://doi.org/10.5194/egusphere-egu23-4775, 2023.
Posters on site: Tue, 25 Apr, 10:45–12:30 | Hall X5
From the 12th to the 15th of July 2021, Western Europe was confronted with an abnormal amount of precipitation leading to extreme floods and enormous damage in western Germany, Belgium, Luxembourg and the south of The Netherlands. Locally, almost thrice as much as the monthly precipitation amount was observed, culminating in 175 mm of rain in just two days. Dynamically, a stationary upper-level cut-off low was the driver of moisture transport to the region resulting in the extreme precipitation over a large area. A follow-up step to unravel the hydrometeorology of the event, is to understand the evaporative regions (moisture sources) that contributed to the event. In literature, these different source region contributions were presented, either indicating the importance of transpiration from vegetation over North America and Europe, or highlighting the role of the Baltic sea, which experienced a heatwave and high evaporation rates at the same time.
Here, we reconcile the moisture sources of the flood event in July 2021 and its uncertainties by comparing the results from three different moisture tracking models (WaterSip, HAMSTER & WAM-2layers) forced with ERA5. By further addressing model-internal sensitivities, we (can) provide a thorough estimate of the uncertainty of contributions from different regions to precipitation during the extreme event, and we ascertain the mechanisms that played a role. Our first results confirm that central Europe is the largest contributor of moisture for precipitation during the event (45 – 90%), whereas the Baltic contributed very little (0 – 5%), thereby contrasting results from recent single-model studies. However, substantial differences were found between the moisture tracking models indicating the need to better understand where those difference arise from and employ multi-model moisture tracking intercomparison studies in the future.
How to cite: Benedict, I., Weijenborg, C., Vermeulen, T., Keune, J., Sodemann, H., van der Ent, R., and Kalverla, P.: Reconciling the moisture sources of the extreme flood event in July 2021 over western Europe, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-9026, https://doi.org/10.5194/egusphere-egu23-9026, 2023.
Tropical cyclones (TCs) are one the principal natural hazards for coastal regions in tropical and subtropical latitudes. On a global scale, around 90 TCs form annually, and approximately 16% of them originated in the North Atlantic (NATL) basin. Heavy rainfall, one of the major hazards associated with TCs, can cause catastrophic flash flooding, landslide and related health and socio-economic problems. Therefore, understanding the precipitation origin during the passage of TCs is important to significantly aid in disaster mitigation and risk analysis. This work seeks to identify the origin of precipitation moisture within the TCs outer radius in the NATL basin from 1980 to 2018 by applying a Lagrangian moisture tracking method to air parcel trajectories. The TC information (intensity and position) was retrieved from the HURDAT2 database, while the outer radius was from the TCSize dataset. The pathways of air parcels that precipitated within the TC outer radius were obtained from the global outputs of the FLEXible PARTicle dispersion (FLEXPART) model fed by ERA-Interim reanalysis provided by the European Center for Medium-Range Weather Forecasts. The spatial moisture sources pattern exhibited a north-south split around 10ºN, coinciding with the mean position of the Intertropical Convergence Zone (ITCZ) during the boreal summer. The highest moisture contribution (~39%) during the genesis and peak of maximum intensification was from the tropical Atlantic Ocean north of ITCZ, including ~11% from the Caribbean Sean and ~6% from the Gulf of Mexico, followed by the western NATL (WNATL) with 23.8% and eastern NATL (ENATL) with 16.6%. Curiously, ~10% of moisture was from the Atlantic Ocean south of ITCZ and ~2% from the eastern Pacific Ocean. During the dissipation phase, the moisture sources shifted poleward as TCs moved, with the highest moisture support (~60.3%) from the subtropical north Atlantic Ocean (WNATL + ENATL) and ~11.2% from the NATL north of 50ºN. This behaviour shows that moisture sources for TCs precipitation are located circa to their positions. Indeed, by investigating the moisture uptake pattern along the TCs trajectories, we detected that the highest moisture uptake generally occurred within 3-5º from the TC track. Likewise, the moisture uptake within 2000 km from the TC centre was approximately two times higher during the rapid intensification than during the slow intensification process. Furthermore, the relative position of moisture sources to the TC centre changed from 24 hours before the extratropical transition (ET) process to 24 hours after. That is, before ET, the moisture sources were located in the southwest-south sector, while after ET appeared in the west-southwest sector. Overall, this work provides new insights into the TCs' climatology in the NATL basin. Additionally, these findings can be used as a reference to understand future changes in the origin of precipitation moisture for TCs precipitation under different climate changes scenarios.
How to cite: Pérez-Alarcón, A., Coll-Hidalgo, P., Fernández-Alvarez, J. C., Sorí, R., Trigo, R. M., Nieto, R., and Gimeno, L.: Identifying the origin of precipitation moisture within the tropical cyclones outer radius in the North Atlantic basin , EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-7569, https://doi.org/10.5194/egusphere-egu23-7569, 2023.
Atmospheric rivers (ARs) are filaments of enhanced moisture in the atmosphere, usually located in subtropical zones and mid-latitudes over oceanic areas. These structures are able to transport huge water vapor amounts, so that when they make landfall and the water vapor is forced upwards, they often cause heavy or even extreme rainfall, thus increasing the odds of catastrophic flooding. Given their potential effects on our daily lives, a better understanding of their physical properties is therefore needed.
One of the most studied and debated ARs properties in recent years is the origin of the moisture in them. Despite the numerous scholars dealing with this topic, moisture sources for precipitation in ARs have not yet been investigated from a global and climatological perspective. Here we present a first attempt to fill this gap by selecting different ARs events across the globe and subsequently simulating them with the FLEXPART model, enabled to calculate Lagrangian trajectories of individual air particles. In addition, we use state-of-the-art techniques to process and bias-correct FLEXPART outputs in other to accurately estimate precipitation origins. Our preliminary results reveal that ARs can tap from multiple moisture sources and that the contributions of the latter vary widely from case to case. Therefore, we conclude that moisture uptake in ARs is more complex and varied than previously known.
How to cite: Crespo-Otero, A., Insua-Costa, D., and Míguez-Macho, G.: Precipitation origin in atmospheric rivers from a global perspective: first steps , EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-12841, https://doi.org/10.5194/egusphere-egu23-12841, 2023.
In East Asia, summer monsoon rainbands usually stretch for thousands of kilometers in the east-west direction and are capable of producing heavy rainfall intensity of 20-40 mm day-1 on average, rendering them the culprit of many devastating historical floods. Despite the previous endeavor to understand their formation dynamics and hazards, the atmospheric water cycle of these rainband systems remains surprisingly poorly understood. In this study, we leverage backward moisture tracking to demystify the dominant moisture pathways and sources that feed the East Asian rain belt events during the warm season (April to September) from 1981 to 2018. The simulations were conducted using a semi-Lagrangian dynamical recycling model (DRM) forced by hourly-0.25˚ ERA5 reanalysis. In virtue of an Expectation-Maximization (EM)-based curve clustering, we classify up to 15 moisture pathways along four main corridors reaching the Somali Jet, South Asia, the Bay of Bengal and the Pacific basin. Long-range moisture pathways turn out to dominate high-impact monsoon rainbands, coinciding well with the role of planetary-scale atmospheric rivers in triggering extreme rainfall over East Asia. The result also highlights the importance of terrestrial moisture pathways and sources in supplying rain belts. Back-tracing the moisture pathways and atmospheric rivers unravels interesting couplings of pre-existing weather systems. The terrestrial moisture pathways over South Asia turn out to link to circumglobal wave trains at the upper levels up to a two-week lead time. The findings here bridge the knowledge gap in the regional hydrological cycle of the disastrous East Asian rain belts. The pre-existing weather systems uncovered by tracking the moisture and atmospheric rivers also provide potential predictability of heavy precipitation in East Asia.
How to cite: Lu, M., Cheng, T. F., and Dai, L.: Improved Understanding of the East Asian Monsoon Rainbands and Dynamics Via Lagrangian Moisture Tracking and Atmospheric Rivers Analysis, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-2474, https://doi.org/10.5194/egusphere-egu23-2474, 2023.
A combination of Flexpart-WRF simulations forced with ERA5 and the CESM2 model incorporated in the CMIP6 project to infer a series of changes over the present century in the behavior of the landfalling ARs arriving at the Iberian Peninsula was used. Potential changes in the strength and position of their main moisture sources are also studied first in the literature. In general terms, a gradual strengthening in the intensity of these events is expected, observable from an increase in the amount of moisture transported, while no significant changes in the net number of events are observed. A northward shift in the position of the centroids has also been detected. In relation to the moisture sources, an increase in the contribution of these sources to the moisture content is expected, compatible with Clausius-Clapeyron amplification.
How to cite: Fernández-Alvarez, J. C., Perez-Alarcon, A., Eiras-Barca, J., Ramos, A., Alvarez-Socorro, G., Rahimi, S., Nieto, R., and Gimeno, L.: Moisture sources projections under climate change for Atmospheric Rivers landfalling the Iberian Peninsula, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-9014, https://doi.org/10.5194/egusphere-egu23-9014, 2023.
When global temperature increases, the atmosphere will be able to hold more water,
as described by the Clausius-Clapeyron equation. It is thus hypothesised that the global
water cycle will intensify under a warming climate. This might lead to more intense and more
frequent extreme precipitation events and might also affect the atmospheric circulation.
This project investigates how moisture sources of precipitation over the European
continent will change under SSP1-2.6 and SSP3-7.0 warming, using the atmospheric
general circulation model ECHAM6-wiso. A present day simulation (1990-2020), nudged to
ERA5 reanalysis, and a future simulation for each investigated SSP (2070-2099), nudged to
respective CMIP6 coupled model output, are conducted. Using numerical water tracers, the
model is able to trace precipitation back to its point of evaporation, characterised by latitude
and longitude.
Our results suggest that, under warming, the source latitude and longitude of
precipitation in Europe will change across all seasons. The magnitude of change depends
on the strength of the warming. These changes in source latitude and longitude reflect
changes in the mid-latitude wind patterns and atmospheric circulation.
How to cite: Tschirschwitz, J., Werner, M., Gao, Q., Sime, L., and Brunello, C. F.: Moisture source changes of precipitation in Europe under SSP1-2.6 and SSP3-7.0 warming, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-17506, https://doi.org/10.5194/egusphere-egu23-17506, 2023.
Using the Lagrangian model FLEXPART and the quantitative method WaterSip, moisture sources of summer (June–July–August) precipitation over
eastern China are investigated for the period 1979–2009 in this study. It is found that the Indochinese Peninsula plus southern China, the South China
Sea, the northwestern Pacific Ocean, the Asian continent, and the Bay of Bengal are the major moisture sources in our results, and the moisture from eastern China, the Arabian Sea, and the Indian subcontinent also has minor contributions. Note that the contribution of the oceanic sources substantially surpasses that of the continental sources, and the contributions of sources exhibit interannual variations during 1979–2009, especially in the Indochinese Peninsula plus southern China, the South China Sea, the northwestern Pacific Ocean, the Asian continent, and the Bay of Bengal. Moreover, moisture sources have evident monthly variations and seasonal cycle features, which are responsible for supplying moisture to precipitating over eastern China in the different monsoonal periods. In addition, the major moisture sources for different intensities of precipitation over eastern China vary considerably; for light and moderate precipitation, a great amount of moisture originates from the local and northwestern continental regions and eastern oceanic regions adjacent to eastern China, while more moisture comes from southwestern oceanic sources and the surrounding continental regions of them for heavy precipitation.
How to cite: Hu, Q.: Moisture sources of summer precipitation over easternChina during 1979–2009: A Lagrangian transient simulation, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-16198, https://doi.org/10.5194/egusphere-egu23-16198, 2023.
Precipitation plays an important role in the global hydrological cycle, and its stable isotope ratio (δ2H, δ18O and δ17O) provides useful information for atmospheric circulation in forming precipitation. However, understanding of precipitation stable isotope ratio in mid-latitude is limited by an insufficient and restricted interpretation of hydrological and meteorological processes based on insufficient datasets. To improve domain knowledge, we monitored the water stable isotopes of rainwater and snowfall in Seoul, Korea, during the period of 2016-2022. The δ2H, δ18O and δ17O values varied from -120.3 to 3.9 ‰, from -16.58 to 1.21 ‰ and from -8.76 to 0.65 ‰, respectively with characteristic seasonal patterns. The prominent patterns were the isotopic depletion during winter (Dec-Feb; the mean δ2H of -9.39 ‰) under the influence of the Siberian High system and the isotopic enrichment during the spring (Mar-May; the mean δ2H of -2.6 ‰) affected by the Asia monsoon system. The summer season was characterized by the lowest deuterium excess (δ2H – 8 x δ18O; 7.4 ‰). As the interplay of the northeast Asia monsoon, and the Siberian High and the North Pacific High was the major cause of the seasonality of the isotope values, their covariance with temperature or the amount of precipitation was weak. The local meteoric water line had a lower slope and intercept (δ2H = 7.67 x δ18O + 9.28) compared to the global meteoric water line. Another local meteoric water line between δ17O and δ18O appeared to be δ17O = 0.5312 x δ18O + 0.0068 with a greater slope and intercept than its global meteoric line.
How to cite: Kim, S., Han, Y., Moon, J., Nyamgerel, Y., and Lee, J.: Stable isotope ratios (δ2H, δ18O and δ17O) of precipitation in Seoul, Korea, during 2016-2020, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-11452, https://doi.org/10.5194/egusphere-egu23-11452, 2023.
While studies of the spatial distribution of precipitation isotope contents is well known at large scale and for more or less homogeneous areas, regions with complex topography and aerology are more sparsely or not at all documented. The aim of this research is to understand the factors influencing spatial/temporal changes of isotopes content in rainfall over a heterogeneous region. The region presents strong topographic contrasts, an insular context with varied weather exposure and subsequent microclimates. The approach consists in building 'isotopes landscapes (isoscapes)' for different months taking advantage of the 7 year-long monthly monitoring survey of the Corsica Network for Isotopes in Precipitation (CNIP, Corsica, France). Isoscapes use linear predictions based on multiple regressions of station-based precipitation isotope, climatic and topographic data. These regressions reveal the controlling effect of altitude (with a dichotomous pattern observed between the winter and the summer periods) and slope, while meteorological settings partially influence isotope contents. By explaining 88% of the δ18O spatial variability, isoscapes highlight both a controlling effect of local-scale meteorological circulation, and a contribution of micro-scale dynamics (due to topographic forcing), on the precipitation isotopes content. The analysis of residual values revealed that these two effects are not sufficient to explain the depletion in heavy isotopes. The deuterium-excess was used to investigate the influence of large-scale meteorological systems. Taking into account previous meteorological investigation, it was possible for the first time to hypothesize an influence of types of precipitation (convective or stratiform) on the rainwater isotopic composition in the study region. Finally, these results appear as evidence of the climate complexity in areas with steep reliefs and a potential limitation for generating reliable isoscapes in Mediterranean regions. They also demonstrate the role that isoscapes can play in documenting the microclimate processes in the world.
– Nlend B., Huneau F., Garel E., Santoni S., Mattei A. (2023) : Precipitation isoscapes in areas with complex topography: influence of large-scale atmospheric dynamics versus microclimatic phenomena. Journal of Hydrology, 617, 128896. [ 10.1016/j.jhydrol.2022.128896 ]
How to cite: Huneau, F., Nlend, B., Garel, E., Santoni, S., and Mattei, A.: Precipitation isoscapes in areas with complex topography and Mediterranean conditions: Influence of large-scale atmospheric dynamics versus microclimatic phenomena, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-5718, https://doi.org/10.5194/egusphere-egu23-5718, 2023.
Shallow clouds, ubiquitous in the trade-wind region, substantially contribute to the cooling of the Earth's climate through their shortwave radiative effect. Their response to climate change is unclear, contributing to a large part of the uncertainty of climate projections. The cloud fraction at cloud base, in particular, has been identified as a key parameter for the spread of modelled feedback of these clouds to climate change. Therefore, understanding the processes controlling the variability of cloudiness at cloud base is of utmost importance. Stable water vapour isotopes reflect the integral of moist atmospheric processes encountered by the vapour since evaporation from the ocean surface. This study focuses on stable water isotopes variability from aircraft observations with the French ATR research aircraft and high-resolution isotope-enabled simulations in the winter trades near Barbados at cloud base. Nested convection resolving COSMOiso simulations at 10, 5 and 1 km grid spacing during the EUREC4A field experiment period are used, which have been thoroughly evaluated using observations from different platforms. The three main findings are: (i) contrasting isotope and humidity characteristics in clear-sky versus cloudy cloud base environments emerge due to vertical transport on time scales of 12 hours, which (ii) are associated with local, convective circulations, and show a clear diel cycle; (iii) the cloud base isotope signals are, in addition, sensitive to variations in the large-scale circulation on time scales of several days, which shows on average a Hadley-type subsidence but occasionally much stronger descent related to extratropical dry intrusions. This investigation, based on stable water isotopes in high-resolution simulations in combination with trajectory analyses reveals, in a physically plausible way, how dynamical processes at different scales act in concert to produce the observed humidity variations at the cloud base of trade wind cumuli.
How to cite: Aemisegger, F. and Villiger, L.: A process-oriented model evaluation using EURECA water isotope field observations in the North Atlantic trades reveals the imprint of the atmospheric circulation at different scales, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-12083, https://doi.org/10.5194/egusphere-egu23-12083, 2023.
The relationship between the isotopic composition of precipitation in the Mediterranean Sea, the atmospheric circulation patterns over the region and groundwater properties has been topic of investigation in recent years. Overall, the link between the isotopic composition of precipitation and the Mediterranean climate raises the question of how future climate change could affect the isotope ratios of precipitation and groundwater. Past and future atmospheric properties (i.e. humidity, evaporation, precipitation and winds) over the Mediterranean region can be used to investigate the past and possibly understand future characteristics of meteoric water isotope composition. In order to evaluate how the climate change will affect the isotope composition of meteoric water, we re-evaluated previous rain events in light of well-defined climate framework. The main objective is to retrieve information on the atmospheric circulation systems based on ERA5 reanalysis and relate climate features with the isotope composition of selected rain events. This will allow to identify the most appropriate parameters needed to constrain the circulation systems responsible for those events and their isotope composition. Preliminary results to infer scenario-based considerations on the evolution of the meteoric recharge will be shown and discussed.
How to cite: Liotta, M., Castorina, G., Simoncelli, S., and Cherchi, A.: How will climate change affect the isotope composition of meteoric water in the Mediterranean area?, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-8256, https://doi.org/10.5194/egusphere-egu23-8256, 2023.
Using the isotope-enabled atmospheric general circulation models iCAM5 and ECHAM6-wiso, we investigate the impact of relatively colder vs. warmer tropical sea-surface temperature on isotopes in precipitation during the Last Glacial Maximum. We forced the two models by the same sets of pre-industrial (PI) and Last Glacial Maximum (LGM) surface boundary conditions; the latter were taken from GLOMAP (Paul et al., 2021), which in turn were based on the MARGO project (MARGO Project Members, 2009) and recent estimates of Last Glacial Maximum sea-ice extent.
To test the sensitivity to changes in tropical sea-surface temperature, we deliberately increased respectively decreased the reconstructed tropical sea-surface temperature by about 1.5 °C. We compared our model results to reconstructions from ice cores (cf. Risi et al., 2010) and speleothems (cf. Comas-Bru et al., 2020). However, the resulting changes in water isotopes in precipitation were surprisingly small and difficult to detect, hence the sensitivity to changes in tropical sea-surface temperature is rather low. We discuss our results as well as the prospect of utilizing more sensitive proxy data that would allow to discriminate between the two sceanrios.
How to cite: Paul, A., Tharammal, T., Werner, M., Mulitza, S., and Cauquoin, A.: Impact of colder vs. warmer tropical sea-surface temperature on water isotopes in precipitation during the Last Glacial Maximum, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-4927, https://doi.org/10.5194/egusphere-egu23-4927, 2023.
Vapor from anthropogenic emissions accounted for a significant proportion of the urban atmospheric water due to the process of urbanization. Fossil fuel combustion-derived vapor (CDV) is one of the main sources of anthropogenic water. Due to the extremely low d-excess (δD - 8*δ18O) value of CDV (-206.7‰ weighted average from different kinds of fossil fuels), stable hydrogen and oxygen isotope can be a promising method to partition CDV from other natural sources. Considering several limitations of long-term in-situ measurement of water isotopes in the urban area, this study explored the possibility to use IsoRSM, an isotopic-enable regional spectral model to simulate the emission situation of CDV.
Two experiments were made respectively in Salt Lake City, USA for one month and in Beijing, China for one year. A fixed emitting rate of CDV with a fixed isotopic ratio was added to the evaporation process of the model in the urban domains (2°×2°) of these two cities, and the result indicated that the addition of CDV could significantly decrease the d-excess of water vapor, especially when the boundary layer was stable. The modified d-excess fitted better with the time series and diurnal variation of in-situ observation than the simulation without CDV in Salt Lake City and in the summer monsoon season of Beijing. Furthermore, the addition of CDV also resulted in an obvious negative correlation between vapor d-excess and specific humidity. In the simulations, the fraction of CDV in the total atmospheric water in January of Salt Lake City reached more than 20% with an average value of 3.4%, and the peak values mainly occurred when the stability of the atmosphere was relatively high. The mean CDV fraction in the monsoon season of Beijing would also be 2.3%. The CDV fraction calculated from vapor d-excess was slightly lower than moisture tracer method. In summary, the bias of d-excess simulation from IsoRSM in the stable boundary layer periods could be improved by adding CDV emission into the local evaporation process.
How to cite: Yang, Y. and Yoshimura, K.: Isotopic Simulation of Combustion-derived Vapor Emission in Urban Areas Using Regional Spectral Model, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-4656, https://doi.org/10.5194/egusphere-egu23-4656, 2023.
The evaporation isotope model proposed by Craig and Gordon (1965) is used in most atmospheric isotope models for the parameterization of fractionation during evaporation from the ocean. It describes the isotope ratios in the evaporation flux as a function of the isotope ratios in liquid water and the atmosphere, relative humidity, the equilibrium fractionation factor, and the nonequilibrium fractionation factor (kiso). Of these parameters, kiso is the most uncertain. Many isotope models use the formulation of Merlivat and Jouzel (1979), which parameterizes kiso as a function of wind speed and distinguishes between a smooth and a rough regime to account for the fact that waves act as roughness elements, inducing perturbations that significantly influence gas transfer rates. The resulting discontinuity in kiso and therefore isotope ratios, which usually occurs at around 7m/s wind speed, has been disputed by several empirical studies, based on measurements of deuterium excess and 17O-excess in the near-surface boundary layer. However, a theoretical framework, which would be in line with the measurements, is still lacking. Here, we present a new approach to parameterizing kiso by explicitly accounting for the influence of wave drag on the momentum flux near the surface. Following recent work by Cifuentes-Lorenzen et al. (2018), we add a third wave-induced component to the total momentum flux, in addition to the viscous and turbulent components, and extend the definition of the eddy viscosity to account for the loss of friction velocity due to ocean waves and the fall-off of turbulence close to the surface. The new scheme predicts a slight decrease of kiso with wind speed, similar to the values from Merlivat and Jouzel (1979) if the smooth-regime parameterization were used at all wind speeds. In a second step, we incorporate the new parameterization into the isotope-enabled Community Earth System Model, and run nudged simulations for the years 2000-2020, to analyze the effect on vapor and precipitation isotopes. While δD and δ18O remain nearly unaffected, the deuterium excess tends to be higher in the simulation with the new scheme than in the control simulation, especially in regions with high wind speeds.
References
Cifuentes-Lorenzen, A., Edson, J. B., and Zappa, C. J. (2018). Air–sea interaction in the southern ocean: Exploring the height of the wave boundary layer at the air–sea interface. Bound.-Layer Meteorol., 169(3), 461-482.
Craig, H. and Gordon, L. I. (1965). Deuterium and oxygen 18 variations in the ocean and the marine atmosphere. In Stable Isotopes in Oceanographic Studies and Paleo-Temperatures, pp. 9–130. Lab. Geol. Nucl., Pisa, Italy.
Merlivat, L. and Jouzel, J. (1979). Global climatic interpretation of the deuterium-oxygen 18 relationship for precipitation. J. Geophys. Res., 84(C8):5029–5033.
How to cite: Duetsch, M., Fairall, C. W., Blossey, P. N., and Fiorella, R. P.: A new theoretical framework for parameterizing nonequilibrium fractionation during evaporation from the ocean, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-13629, https://doi.org/10.5194/egusphere-egu23-13629, 2023.
Air-mass intrusions arriving from the mid-latitudes introduce moisture and heat into the Arctic and perturb cloud properties. These events have a strong impact on the water cycle as their frequency and intensity control the inter-annual variability of mean surface air temperature, humidity and energy budget. Warm air intrusions are all short-lived events related to blocking situations of the large-scale circulation, however, the characteristics of each individual air intrusion depend on the season, the sourcing of the air masses, the characteristics of the boundary layer and the surface conditions during the long-range transport.
In this study, we use atmospheric water vapour isotopes (H216O, H218O, HD16O) to trace the origin of the moisture and to gain insights into the exchange processes occurring during four distinct warm air intrusion events, recorded during a one-year expedition in the Central Arctic. Stable water isotopes can track feedback loops and exchange processes between the hydrological compartments of the Arctic, because evaporative sources, phase changes and interactions within hydrological compartments all have specific imprints on the isotopic compositions. Continuous observations of near-surface atmospheric vapour were obtained onboard RV Polarstern during the MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) drifting expedition in 2019-2020. By combining a moisture source diagnostic to the particle dispersion model FLEXPART, we constrain the magnitude and the location of the surface moisture uptake into the air masses.
We found that the moisture transported during the events originated from different locations, namely lower North Atlantic sector (<70°N), upper North Atlantic (>70°N), continental Siberia and sea-ice. The different evaporative conditions over these regions are key to determine the distinct isotopic signature of the sampled air masses. Further, we observe opposite sensitivity of d-excess to local temperature and humidity in the moisture sourced from the sea-ice. D-excess is a second order isotope parameter interpreted as a diagnostic of non-equilibrium fractionation. We further investigate the mechanisms leading to non-equilibrium phase changes and we examine the roles of: (i) mixed-phase cloud formation where water vapour is supersaturated with respect to ice, (ii) evaporation from leads and melt ponds, and (iii) changes in vapour isotopes with respect to snow on sea ice during sublimation/deposition regimes.
With this work we aim at better understanding the transport of mid-latitudes moisture into the Central Arctic region and identifying the moisture exchange processes with the Arctic cryosphere. In view of the projected increase of frequency and duration of warm air intrusions in the Arctic, our study contributes to understanding the mechanistic consequences of such short-lived events on the whole Arctic water cycle.
How to cite: Brunello, C. F., Gebhardt, F., Rinke, A., Meyer, H., Mellat, M., Bucci, S., Dütsch, M., Kopec, B. G., Welker, J. M., and Werner, M.: Stable water vapour isotopes as integrated tracers of moisture sources, transport and deposition during warm air intrusions in the Arctic, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-14175, https://doi.org/10.5194/egusphere-egu23-14175, 2023.
Posters virtual: Tue, 25 Apr, 10:45–12:30 | vHall AS
Stable water isotopes can be used as natural tracers of various physical processes in the atmospheric water cycle. The isotopic signal is modulated by several meteorological and cloud microphysical processes such as moisture recycling, advection, condensation, evaporation, etc. The interaction of these processes with water isotopes are often complex in tropical orographic regions especially in the lee side of the mountains which are, in general, rain shadow regions. Disentangling the roles of these process in the water isotope variability is very important considering these regions host a gamut of natural archieves from which decadal to centennial scale climate have been reconstructed earlier. Towards this, the current study presents daily rain and ground level vapour isotope observations in a tropical Indian rain-shadow region.The analyses shows that mesoscale convections affect both water isotope values significantly. A considerable isotopic exchange between rain and vapour is also noted in the sub cloud layer suggesting a strong control of sub cloud processes in the isotope values. Using an 1-D model, the role of all these process in the isotope values are further evaluated.
How to cite: Sheena Sunil, N. and Sengupta, S.: How meteorological and cloud processes affect water isotopes in a tropical rain shadow region? , EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-5260, https://doi.org/10.5194/egusphere-egu23-5260, 2023.
The primary component of the atmospheric branch of the water cycle is atmospheric moisture transport, and its amplitude has a strong influence on drought and precipitation extremes. Vertically integrated water vapor transport (IVT) is evaluated to assess atmospheric moisture transport (AMT) over the Indian Subcontinent. Linkages to flood-causing extreme precipitation events are understood using case studies that were in accordance with their intense rainfall conditions and flooding that resulted in huge losses over a specified region. Using a high-resolution daily gridded rainfall data set, an attempt has been made to analyze the spatiotemporal characteristics of atmospheric moisture transport (AMT) responsible for extreme events. The spatiotemporal characteristics of specific rainfall events associated with the occurrence of AMT show the existence of a strong relationship between the presence of high AMT and extreme precipitation events for the northwestern region where AMT penetrates inland and for the east coast region where AMT makes landfalls. Further analysis suggests that extreme precipitation events are predominantly influenced by the strong moisture convergence associated with the low-level pressure systems, wind speed, and wind direction developed in the vicinity of affected regions.
How to cite: Singh Raghuvanshi, A. and Agarwal, A.: Linking Atmospheric Moisture Transport to Extreme Precipitation Events Associated with Floods over India, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-336, https://doi.org/10.5194/egusphere-egu23-336, 2023.
The water isotope composition of snow precipitations, archived in the Antarctic ice sheet every year, is an important proxy of climatic conditions. This signal depends on several parameters such as local temperature, altitude, moisture source areas and air mass pathways.
However, especially in areas where snow accumulation is very low (as on the East Antarctic Plateau), the isotopic composition is affected by additional spatial variability induced by the interactions between the atmosphere and snow surface, and the pristine signal may be modified through isotopic exchanges, sublimation processes and mechanical mixing originated from wind action.
Here, we present the isotopic composition (δD and δ18O) and the second-order parameter d-excess of surface snow and snowpit samples collected during the Italian-French campaign in Antarctica (2019-2020). The sampling sites cover the area from Dumont D'Urville to Concordia Station and from Concordia Station towards the South Pole (EAIIST – East Antarctic International Ice Sheet Traverse). These data, compared with a previous dataset of Antarctic surface snow isotopic composition (Masson-Delmotte et al. 2008), are analyzed to determine the variability of the spatial relationship between precipitation isotopic composition and local temperature in relation to geographical parameters (latitude, distance from the coast and elevation). The interpretation of these factors determining the isotope signature is the base to better define the amount of the effects caused by subsequent interaction between atmosphere and surface snow, and by the wind action.
Understanding the spatial variability of this proxy, which strongly decreases the signal-to-noise ratio, could permit to improve the use of the “isotopic thermometer” to quantify past changes in temperature based on the stable isotopic record of deep ice cores.
How to cite: Petteni, A., Casado, M., Stenni, B., Dreossi, G., Fourré, E., Landais, A., Savarino, J., Spolaor, A., Delmonte, B., Becagli, S., and Frezzotti, M.: The spatial variability in isotopic composition of surface snow and snowpits on the East Antarctic Ice Sheet, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-1738, https://doi.org/10.5194/egusphere-egu23-1738, 2023.
