Andries-Jan De Vries

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De Vries

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Andries-Jan

ORCID

0000-0002-1175-6474

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Publications 1 - 8 of 8

Stable water isotope signals in tropical ice clouds in the West African monsoon simulated with a regional convection-permitting model
De Vries, Andries-Jan; Aemisegger, Franziska; Pfahl, Stephan; et al. (2022)
Atmospheric Chemistry and Physics
Tropical ice clouds have an important influence on the Earth's radiative balance. They often form as a result of tropical deep convection, which strongly affects the water budget of the tropical tropopause layer. Ice cloud formation involves complex interactions on various scales. These processes are not yet fully understood and lead to large uncertainties in climate projections. In this study, we investigate the formation of tropical ice clouds related to deep convection in the West African monsoon, using stable water isotopes as tracers of moist atmospheric processes. We perform convection-permitting simulations with the regional Consortium for Small-Scale Modelling isotope-enabled (COSMOiso) model for the period from June to July 2016. First, we evaluate our model simulations using space-borne observations of mid-tropospheric water vapour isotopes, monthly station data of precipitation isotopes, and satellite-based precipitation estimates. Next, we explore the isotope signatures of tropical deep convection in atmospheric water vapour and ice based on a case study of a mesoscale convective system (MCS) and a statistical analysis of a 1-month period. The following five key processes related to tropical ice clouds can be distinguished based on isotope information: (1) convective lofting of enriched ice into the upper troposphere, (2) cirrus clouds that form in situ from ambient vapour under equilibrium fractionation, (3) sedimentation and sublimation of ice in the mixed-phase cloud layer in the vicinity of convective systems and underneath cirrus shields, (4) sublimation of ice in convective downdraughts that enriches the environmental vapour, and (5) the freezing of liquid water just above the 0 °C isotherm in convective updraughts. Importantly, we note large variations in the isotopic composition of water vapour in the upper troposphere and lower tropical tropopause layer, ranging from below −800 ‰ to over −400 ‰, which are strongly related to vertical motion and the moist processes that take place in convective updraughts and downdraughts. In convective updraughts, the vapour is depleted by the preferential condensation and deposition of heavy isotopes, whereas the non-fractionating sublimation of ice in convective downdraughts enriches the environmental vapour. An opposite vapour isotope signature emerges in thin-cirrus cloud regions where the direct transport of enriched (depleted) vapour prevails in large-scale ascent (descent). Overall, this study demonstrates that isotopes can serve as useful tracers to disentangle the role of different processes in the West African monsoon water cycle, including convective transport, the formation of ice clouds, and their impact on the tropical tropopause layer.
Breaking Rossby waves drive extreme precipitation in the world’s arid regions
De Vries, Andries-Jan; Armon, Moshe; Klingmüller, Klaus; et al. (2024)
Communications Earth & Environment
More than a third of the world’s population lives in drylands and is disproportionately at risk from hydrometeorological hazards such as drought and flooding. While weather systems governing precipitation formation in humid regions have been widely explored, our understanding of the atmospheric processes generating precipitation in arid regions remains fragmented at best. Here we show, using a variety of precipitation datasets, that Rossby wave breaking is a key atmospheric driver of precipitation in arid regions worldwide. Rossby wave breaking contributes up to 90% of daily precipitation extremes and up to 80% of total precipitation amounts in arid regions equatorward and downstream of the midlatitude storm tracks. The relevance of Rossby wave breaking for precipitation increases with increasing land aridity. Contributions of wave breaking to precipitation dominate in the poleward and westward portions of arid subtropical regions during the cool season. Our findings imply that Rossby wave breaking plays a crucial role in projections and uncertainties of future precipitation changes in societally vulnerable regions that are exposed to both freshwater shortages and flood hazards. (Figure presented.)
A Lagrangian Perspective on Stable Water Isotopes During the West African Monsoon
Diekmann, Christopher J.; Schneider, Matthias; Knippertz, Peter; et al. (2021)
Journal of Geophysical Research: Atmospheres
We present a Lagrangian framework for identifying mechanisms that control the isotopic composition of mid-tropospheric water vapor in the Sahel region during the West African Monsoon 2016. In this region mixing between contrasting air masses, strong convective activity, as well as surface and rain evaporation lead to high variability in the distribution of stable water isotopologues. Using backward trajectories based on high-resolution isotope-enabled model data, we obtain information not only about the source regions of Sahelian air masses, but also about the evolution of (Formula presented.) O and its isotopologue HDO (expressed as (Formula presented.) D) along the pathways of individual air parcels. We sort the full trajectory ensemble into groups with similar transport pathways and hydro-meteorological properties, such as precipitation and relative humidity, and investigate the evolution of the corresponding paired { (Formula presented.) O, (Formula presented.) } distributions. The use of idealized process curves in the { (Formula presented.) O, (Formula presented.) } phase space allows us to attribute isotopic changes to contributions from (a) air mass mixing, (b) Rayleigh condensation during convection, and (c) microphysical processes depleting the vapor beyond the Rayleigh prediction, i.e., partial rain evaporation in unsaturated and isotopic equilibration in saturated conditions. Different combinations of these processes along the trajectory ensembles are found to determine the final isotopic composition in the Sahelian troposphere during the monsoon. The presented Lagrangian framework is a powerful tool for interpreting tropospheric water vapor distributions. In the future, it will be applied to satellite observations of { (Formula presented.) O, (Formula presented.) } over Africa and other regions in order to better quantify characteristics of the hydrological cycle.
Extreme weather in the Southern Hemisphere in early 2022
De Vries, Andries-Jan; Wicker, Wolfgang; Fragkoulidis, Georgios; et al. (2025)
Bulletin of the American Meteorological Society
In early 2022, several exceptionally extreme weather events struck the Southern Hemisphere. Deadly floods affected eastern Australia and South Africa, and an unprecedented heatwave in East Antarctica broke global temperature anomaly records. This study presents a multi-scale analysis of the atmospheric processes leading to these extreme events ranging from local to planetary scales. While the subtropical flood events were associated with slow-moving circulation patterns with moderate departures from climatology, the Antarctic heatwave was unprecedented with surface temperatures and atmospheric moisture content breaking records in observation-based data since 1979. Despite the variety in weather type and region, all three extreme events share the commonality that they result from extratropical Rossby wave breaking modulated by tropical variability on intraseasonal to interannual timescales. Equatorward wave breaking steered moisture transport from nearby oceans towards the subtropical flood regions favored by anticyclonic circulation anomalies in the midlatitudes and a poleward displaced midlatitude jet. Enhanced tropical convection over the Indian Ocean promoted poleward-eastward Rossby wave propagation eventuating in poleward wave breaking that forced an intrusion of exceptionally warm and moist air masses into the Antarctic continent. At seasonal timescales, large parts of the study regions experienced record-breaking surface weather associated with the influence of La Nina setting up favorable circulation patterns for heavy precipitation over the eastern Australian and South African coasts and heatwave occurrence over East Antarctica’s interior. This study contributes to an improved process-understanding of extreme weather events in the Southern Hemisphere with implications for weather and climate prediction of such events.
The role of cyclones and potential vorticity cutoffs for the occurrence of unusually long wet spells in Europe
Röthlisberger, Matthias; Scherrer, Barbara; De Vries, Andries-Jan; et al. (2022)
Weather and Climate Dynamics
The synoptic dynamics leading to the longest wet spells in Europe are so far poorly investigated despite these events' potentially large societal impacts. Here we examine the role of cyclones and potential vorticity (PV) cutoffs for unusually long wet spells in Europe, defined as the 20 longest uninterrupted periods with at least 5 mm daily accumulated precipitation at each ERA-Interim grid point in Europe (this set of spells is hereafter referred to as S20). The S20 occur predominantly in summer over the eastern continent, in winter over the North Atlantic, in winter or fall over the Atlantic coast, and in fall over the Mediterranean and European inland seas. Four case studies reveal distinct archetypal synoptic storylines for long wet spells: (a) a 7 d wet spell near Moscow, Russia, is associated with a single slow-moving cutoff-cyclone couple; (b) a 15 d wet spell in Norway features a total of nine rapidly passing extratropical cyclones and illustrates serial cyclone clustering as a second storyline; (c) a 12 d wet spell in Tuscany, Italy, is associated with a single but very large cutoff complex, which is replenished multiple times by a sequence of recurrent anticyclonic wave breaking events over the North Atlantic and western Europe; and (d) a 17 d wet spell in the Balkans features intermittent periods of diurnal convection in an environment of weak synoptic forcing and recurrent passages of cutoffs and thus also highlights the role of diurnal convection for long wet spells over land. A systematic analysis of cyclone and cutoff occurrences during the S20 across Europe reveals considerable spatial variability in their respective role for the S20. For instance, cyclones are present anywhere between 10 % and 90 % and cutoffs between 20 % and 70 % of the S20 time steps, depending on the geographical region. However, overall both cyclones and cutoffs appear in a larger number and at a higher rate during the S20 compared to climatology. Furthermore, in the Mediterranean, cutoffs and cyclones are significantly more persistent during the S20 compared to climatology. Our study thus documents for the first time the palette of synoptic storylines accompanying unusually long wet spells across Europe, which is a prerequisite for developing an understanding of how these events might change in a warming climate and for evaluating the ability of climate models to realistically simulate the synoptic processes relevant to these events.
Saharan rainfall climatology and its relationship with surface cyclones
Armon, Moshe; De Vries, Andries-Jan; Marra, Francesco; et al. (2024)
Weather and Climate Extremes
The Sahara is the largest and driest of the hot deserts on Earth, with regions where rainfall reaches the surface on average less than once a year. Water resources are scarce, and rainfall tends to occur sporadically in space and time. While rain is a precious resource in the Sahara, heavy precipitation events (HPEs) in the desert have the potential to trigger flash floods on the barren soil. Because of the sparse rainfall monitoring network and the relatively poor performance of global models in representing rainfall over the Sahara, the analysis of Saharan HPEs has primarily relied on case studies. Therefore, general rainfall characteristics of Saharan HPEs are unexplored, and the prevailing weather conditions enabling such rainfall are unknown. To tackle this problem, we utilised satellite-derived precipitation estimations (IMERG) spanning 21 years (2000–2021) to identify ∼42⋅103 small (>103km2) to large (<106km2) HPEs in the Sahara and to extract their rainfall properties, and atmospheric reanalyses (ERA5) to examine the corresponding meteorological conditions in which they develop. Three case studies illustrate the relevance of cyclones for exceptionally large HPEs, including one in the driest region of the Sahara. Saharan HPEs occur, on average, every second day. They are more common in summer than in the other seasons, occur most frequently in the southern Sahara, and exhibit a clear convectively-driven diurnal cycle. Winter events have, on average, larger spatial extent, longer duration, and are characterised by larger areas exhibiting more extreme rainfall in terms of return periods. Autumn HPEs are concentrated in the western Sahara, while events in the north of the desert and in its driest core in the northeast occur mainly in winter and spring. In these regions, north of the Tropic of Cancer, events are highly associated with surface cyclones. HPEs that were associated with cyclones are characterised by larger spatial extent and rainfall volume. Considering that weather and climate models often depict synoptic-scale weather systems more accurately than rainfall patterns, the association of Saharan HPEs with surface cyclones and other synoptic-scale systems can aid in comprehending the effects of climate change in the desert. Furthermore, it underscores the potential for higher predictability of these events.
A global climatological perspective on the importance of Rossby wave breaking and intense moisture transport for extreme precipitation events
De Vries, Andries-Jan (2021)
Weather and Climate Dynamics
Extreme precipitation events (EPEs) frequently cause flooding with dramatic socioeconomic impacts in many parts of the world. Previous studies considered two synoptic-scale processes, Rossby wave breaking and intense moisture transport, typically in isolation, and their linkage to such EPEs in several regions. This study presents for the first time a global and systematic climatological analysis of these two synoptic-scale processes, in tandem and in isolation, for the occurrence of EPEs. To this end, we use 40-year ERA-Interim reanalysis data (1979–2018) and apply object-based identification methods for (i) daily EPEs, (ii) stratospheric potential vorticity (PV) streamers as indicators of Rossby wave breaking, and (iii) structures of high vertically integrated horizontal water vapour transport (IVT). First, the importance of these two synoptic-scale processes is demonstrated by case studies of previously documented flood events that inflicted catastrophic impacts in different parts of the world. Next, a climatological quantification shows that Rossby wave breaking is associated with >90 % of EPEs over central North America and the Mediterranean, whereas intense moisture transport is linked to >95 % of EPEs over many coastal zones, consistent with findings of atmospheric river-related studies. Combined Rossby wave breaking and intense moisture transport contributes up to 70 % of EPEs in several subtropical and extratropical regions, including (semi)arid desert regions where tropical–extratropical interactions are of key importance for (heavy) rainfall. Odds ratios of EPEs linked to the two synoptic-scale processes suggest that intense moisture transport has a stronger association with the occurrence of EPEs than Rossby wave breaking. Furthermore, the relationship between the PV and IVT characteristics and the precipitation volumes shows that the depth of the wave breaking and moisture transport intensity are intimately connected with the extreme precipitation severity. Finally, composites reveal that subtropical and extratropical EPEs, linked to Rossby wave breaking, go along with the formation of upper-level troughs and cyclogenetic processes near the surface downstream, reduced static stability beneath the upper-level forcing (only over water), and dynamical lifting ahead (over water and land). This study concludes with a concept that reconciles well-established meteorological principles with the importance of Rossby wave breaking and intense moisture transport for the formation of EPEs. Another conclusion with major implications is that different combinations of Rossby wave breaking and intense moisture transport can reflect a large range of EPE-related weather systems across climate zones and can thus form the basis for a new classification of EPE regimes. The findings of this study may contribute to an improved understanding of the atmospheric processes that lead to EPEs and may find application in climatic studies on extreme precipitation changes in a warming climate.
Projections and uncertainties of winter windstorm damage in Europe in a changing climate
Severino, Luca G.; Kropf, Chahan M.; Afargan-Gerstman, Hilla; et al. (2024)
Natural Hazards and Earth System Sciences
Winter windstorms are among the most significant natural hazards in Europe linked to fatalities and substantial damage. However, projections of windstorm impact in Europe under climate change are highly uncertain. This study combines climate projections from 30 general circulation models participating in Phase 6 of the Coupled Model Intercomparison Project (CMIP6) with the climate risk assessment model CLIMADA to obtain projections of windstorm-induced damage over Europe in a changing climate. We conduct an uncertainty-sensitivity analysis and find large uncertainties in the projected changes in the damage, with climate model uncertainty being the dominant factor of uncertainty in the projections. We investigate the spatial patterns of the climate change-induced modifications in windstorm damage and find an increase in the damage in northwestern and northern central Europe and a decrease over the rest of Europe, in agreement with an eastward extension of the North Atlantic storm track into Europe. We combine all 30 available climate models in an ensemble-of-opportunity approach and find evidence for an intensification of future climate windstorm damage, in which damage with return periods of 100 years under current climate conditions becomes damage with return periods of 28 years under future SSP585 climate scenarios. Our findings demonstrate the importance of climate model uncertainty for the CMIP6 projections of windstorms in Europe and emphasize the increasing need for risk mitigation due to extreme weather in the future.

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