AS1.8

EDI
The Subtropics: Dynamics, variability, predictability and change in Past, Present and Future

The subtropics present unique regional hydroclimates across the globe, with strong influence from both tropical and mid-latitude dynamics and an extensive interplay between atmospheric thermodynamics, dynamics, and coupled ocean processes. With dependence on both tropical and extratropical processes, subtropical regions are emerging as hotspots of contemporary climate change. These hotspots reflect the paleoclimatological records of high climate sensitivity in subtropical climes (e.g. Green Sahara and Arabia, pluvials in the drylands of southern Africa, Australia). The complexity of subtropical climates present fundamental challenges to develop coherent theories of subtropical climate dynamics, resulting in large uncertainties in climate model simulations. To address these gaps in the understanding of the subtropical climate, we invite contributions focused on subtropical processes and their simulation including:
• diagonal convergence zones
• tropical-extratropical interactions
• subtropical jet fluctuations
• interplays between monsoons and mid-latitude transients
• weather and climate extremes in the subtropics
• analyses of climate simulations looking into past, present and future change in the subtropics
• development of bespoke climate services based on advances in subtropical theory and prediction

Co-organized by CL4
Convener: Neil Hart | Co-conveners: Marcia ZilliECSECS, Josephine Brown, Benjamin Lintner, Caio Coelho
Presentations
| Tue, 24 May, 17:00–18:30 (CEST)
 
Room 0.11/12

Session assets

Session materials

Presentations: Tue, 24 May | Room 0.11/12

Chairpersons: Marcia Zilli, Andries Jan De Vries, Neil Hart
17:00–17:05
17:05–17:10
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EGU22-12085
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Virtual presentation
Gabriel Martins Palma Perez, Pier Luigi Vidale, Helen Dacre, and Jorge Garcia-Franco

Large-scale mixing in the atmosphere redistributes moisture as organised bands or filaments. In some tropical and subtropical monsoon regions, a substantial part of rainfall happens under moisture and cloud bands commonly referred to as convergence zones. Recent regional studies have shown that such large-scale filaments or bands of moisture and rainfall form along or in the neighborhood of mixing features known as attracting ``Lagrangian Coherent Structure'' (LCSs) - material skeletons associated with strong attraction of air parcels. However, there are still no global climatologies to support more general conclusions about the spatiotemporal relationships between mixing and precipitation and the impact of large-scale mixing on monsoons. In this study, we investigate how mixing features determine the subseasonal and seasonal rainfall variability in tropical and subtropical regions around the globe. We characterise mixing by computing the Finite-time Lyapunov Exponent (FTLE), a measure of Lagrangian deformation among neighbouring parcels, on ERA5 reanalysis data between 1980 and 2009. Attracting LCSs are identified as ridges of the FLTE. We also employ diagnostic Eulerian variables such as mean sea level pressure and mass meridional streamfunction to associate mixing with general circulation features. On the seasonal scale, we show that the strength of mixing and the frequency of LCSs modulates rainfall under the African, American and Asian convergence zones and the ITCZ. On the subseasonal scale, we focus on the influence of the Madden-Julian oscillation and the North Atlantic oscillation on the mixing regime of the Atlantic and East Pacific; we show how these oscillations control horizontal mixing as to suppress or enhance precipitation variability over the American monsoons. This first long-term global climatology of mixing and LCSs quantifies the often overlooked role of Lagrangian kinematics on the hydrological cycle and provides a powerful process-based diagnostic to investigate mechanisms of rainfall variability that does not require region-specific considerations.

How to cite: Martins Palma Perez, G., Vidale, P. L., Dacre, H., and Garcia-Franco, J.: A global climatology of the kinematical skeletons organising subtropical and tropical convergence zones, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12085, https://doi.org/10.5194/egusphere-egu22-12085, 2022.

17:10–17:15
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EGU22-2824
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ECS
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On-site presentation
Hugo Braga and Tercio Ambrizzi

The South Atlantic Convergence Zone (SACZ), which extends from the Amazon to the southwestern South Atlantic, is one of the major precipitation systems in South America and has an important socioeconomic impact for Brazil. This study suggests the possibility of SACZ to act as a Rossby wave source using numerical simulations from a simple baroclinic model under strong El Niño basic state. Sixteen days after the perturbation, it is possible to observe wave propagation inside the subtropical latitudes of the northern hemisphere. The simulation is performed during the strong El Niño in 2015/16 austral summer, which has a intense westerly zonal flow and stationary wavenumbers 6-10 in the equatorial Atlantic region. The Rossby wave starts in the southeast Brazil, crosses the Atlantic Ocean and, embedded in the subtropical jet of the north hemisphere, extends to the subtropical latitudes over the African and Asian continents. According to the present analyses, SACZ may sometimes act as interhemispheric Rossby wave source, enabling a connection between South America and subtropical latitudes in north hemisphere over 16 days, providing there is westerly flow that allows wave propagation over the equatorial Atlantic Ocean.

How to cite: Braga, H. and Ambrizzi, T.: South Atlantic Convergence Zone as Rossby Wave Source During Strong El Niño, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2824, https://doi.org/10.5194/egusphere-egu22-2824, 2022.

17:15–17:20
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EGU22-10816
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Presentation form not yet defined
Irina Rudeva, Chiara Holgate, Acacia Pepler, Roseanna McKay, and Pandora Hope

A long-term reduction in southern Australian rainfall has been a focus of many studies. In south-eastern Australia it has been shown that after the Millennium Drought (1997 – 2009), the average precipitation has not recovered to the pre-drought values. Our analysis reveals a decline not only in the average precipitation but also in daily extreme rainfall amounts in the cold season. This study explores the physical processes leading to changes in extreme rainfall.  

High rainfall extremes are related, on the one hand, to a certain combination of weather systems at various height levels through the troposphere and, on the other hand, to moisture availability. We first identify which synoptic conditions lead to extreme rainfall events in south-eastern Australia and backtrack their development for a few days. Australia is believed to be affected by Rossby waves (RWs) propagating from the tropics. However, we show that extreme events in the southern part of the country are associated with breaking synoptic RWs propagating from the extratropical Indian Ocean. Interestingly, we find that the frequency of cut-off lows, that form following the breaking of RWs, have not declined over the recent decades.  This fact highlights that not all cut-off lows necessarily lead to extreme rainfall. We find that the strongest events occur in the presence of a Tasman High pressure system at the surface and a vertically developed low-pressure system to the west of it. We show that, despite little change in the frequency of cut-off lows in the upper troposphere, vertically developed lows have become less frequent after 1997 and when they occur, a larger moisture influxis required to produce an intense rainfall event. 

How to cite: Rudeva, I., Holgate, C., Pepler, A., McKay, R., and Hope, P.: Extreme subtropical precipitation in Australia: reasons for decline  , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10816, https://doi.org/10.5194/egusphere-egu22-10816, 2022.

17:20–17:25
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EGU22-8777
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ECS
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On-site presentation
Andries Jan De Vries, Moshe Armon, Klaus Klingmüller, and Raphael Portmann

Precipitation can have large dual societal impacts in regions with a dry climate. On the one hand, extreme precipitation can induce catastrophic floods, and on the other hand, replenish scarce fresh water resources. In contrast to wet extratropical regions, the atmospheric processes that lead to precipitation formation in the dry subtropics are often overlooked by the scientific community. In this study we address the role of Rossby wave breaking for annual and extreme precipitation in (semi)arid regions. To this end, we quantify the contribution of Rossby wave breaking to extreme precipitation days and annual precipitation amounts in regions with different degrees of aridity. Rossby wave breaking is represented by potential vorticity (PV) streamers and cutoffs on isentropic surfaces using ERA-Interim reanalysis data, while precipitation is used from the global precipitation measurement (GPM) integrated multi-satellite retrieval product IMERG for the period of 2001-2018. We show that the relevance of Rossby wave breaking for precipitation increases from humid to hyper arid regions. More specifically, equatorward breaking Rossby waves contribute to a large fraction of annual and extreme precipitation in regions on the pole-westward flanks of world’s most arid regions where most precipitation occurs in the cool season. In contrast, precipitation in the equator-eastward parts of these arid regions has a negative association with Rossby wave breaking, implying that the tropical forcing governs the precipitation formation which occurs in these regions predominantly in the warm season. The results suggest that breaking Rossby waves are of key importance for precipitation in (semi)arid regions that undergo a drying in a warming climate, underlining the need to better understand the response of wave breaking to global warming.

How to cite: De Vries, A. J., Armon, M., Klingmüller, K., and Portmann, R.: The role of Rossby wave breaking for annual and extreme precipitation in (semi)arid regions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8777, https://doi.org/10.5194/egusphere-egu22-8777, 2022.

17:25–17:30
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EGU22-4681
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ECS
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On-site presentation
José Vicencio, Christoph Böhm, Ulrich Löhnert, and Susanne Crewell

The Atacama and Namib Deserts are one of the driest places in the world. They are both located west coast of their respective continents (18-28ºS), under the effects of the east margin of the subtropical anticyclones, strong subsidence and cold ocean currents. However, they also differ in terms of topography, precipitation, and humidity, being the Atacama much higher and drier than the Namib. Our understanding of how water vapor is brought to these regions and interacts with the different local circulations and topography is still limited. The objective of this study is to investigate similarities and differences of the spatio-temporal variability of water vapor between both deserts in order to assess the impact of the distinctive local factors. To this end, we use state-of-the-art satellite observations and reanalysis for a long-term perspective on total column water vapor (TCWV) as well as on the vertical distribution of humidity, temperature and on cloud structure. The analysis is aided by a one-year measurement campaign at Iquique airport (22ºS).

We found a marked seasonal cycle in the total column water vapor (TCWV) in both offshore deserts areas. While both deserts share a similar timing of the annual TCWV peak between January and March, the values of the maxima differ. The Namib surpasses the Atacama by 30%. Our analysis suggests that at least two factors contribute to the common summer maxima of the TCWV. First, warmer sea surface temperatures (SSTs) along the west coasts produce a moistening of the marine boundary layer (MBL). Second, as a consequence of the southward displacement of the subtropical anticyclones, weaker southerly winds decrease the dry advection in the MBL. The excess of humidity in the Namib is associated with a strong moisture advection feature observed in the lower part of the free-troposphere (900-750 hPa). The easterlies also transport clouds and precipitation. In the Atacama, the presence of the Andes cordillera blocks most of the potential exchange of humidity with the continent, resulting in the Pacific Ocean being the main source of moisture.

While the respective driest period presents similar TCWV amounts (~12 Kg/m2) for both deserts, it is surprising to find that it occurs later in the Atacama (spring season) than in the Namib (winter). Potential causes for this shift, such as a stronger dependence of TCWV on the SST for the Atacama, are investigated and discussed.

Furthermore, we identified a recurring atmospheric feature for the summer which exhibits a strong northerly humidity advection above the MBL. This structure is only observed in the Atacama Desert and has not been described in the literature. However, it could be a major source of humidity for the inland region in Atacama.

How to cite: Vicencio, J., Böhm, C., Löhnert, U., and Crewell, S.: Understanding atmospheric differences in the water vapor transport for the Atacama and Namib deserts, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4681, https://doi.org/10.5194/egusphere-egu22-4681, 2022.

17:30–17:35
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EGU22-242
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ECS
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Virtual presentation
Chanil Park and Seok-Woo Son

Atmospheric rivers (ARs) are generally considered to be transient and concurrent with an extratropical cyclone (Ralph et al. 2018). However, this is not necessarily the case for the ARs in the East Asian summer monsoon (EASM). Despite several climatological surveys on the EASM ARs in recent years (e.g., Park et al. 2021a), through what processes they develop is still unclear because of the complex interplay between monsoonal and extratropical circulations in the region (Horinouchi 2014; Park et al. 2021b).

In this talk, we demonstrate that the EASM ARs have different “flavors” in terms of moisture transport characteristics. By quantifying the relative contribution of high- and low-frequency components of the integrated water vapor transport anomaly (IVTA) for each AR, it is found that both components are important in East Asia summer, in contrast to the ARs in the U.S. west coast where the high-frequency component is predominant.

To investigate the synoptic condition governing the high- and low-frequency IVTA, the EASM ARs are classified into the three categories—1) transient, 2) quasi-stationary and 3) intermediate ARs—depending on the fractional contribution of high-frequency IVTA to total IVTA. While the transient ARs are driven by an extratropical cyclone in an analogy of classical ARs, the quasi-stationary ARs are associated with an anomalously enhanced monsoon flow. The intermediate ARs, which are a majority of summertime ARs in East Asia, show the confounding features of the two types. We suggest that the concept of “transient” and “quasi-stationary” AR flavors offer an important foundation in understanding the EASM ARs with a variety of underlying dynamics. Further implications and possible future works will be also discussed.

References:

Horinouchi, T., 2014: Influence of upper tropospheric disturbances on the synoptic variability of precipitation and moisture transport over summertime East Asia and the northwestern Pacific. J. Meteor. Soc. Japan, 92, 519–541, https://doi.org/10.2151/jmsj.2014-602.

Park, C., S.-W. Son, and H. Kim, 2021a: Distinct features of atmospheric rivers in the early versus late EASM and their impacts on monsoon rainfall. J. Geophys. Res. Atmos., 126, e2020JD033537, https://doi.org/10.1029/2020JD033537.

Park, C., S.-W. Son, and J.-H. Kim, 2021b: Role of baroclinic trough in triggering vertical motion during summertime heavy rainfall events in Korea. J. Atmos. Sci., 78, 1687–1702, https://doi.org/10.1175/JAS-D-20-0216.1.

Ralph, F. M., M. D. Dettinger, M. M. Cairns, T. J. Galarneau, and J. Eylander, 2018: Defining “atmospheric river”: How the glossary of meteorology helped resolve a debate. Bull. Amer. Meteor. Soc., 99, 837–839. https://doi.org/10.1175/BAMS-D-17-0157.1.

How to cite: Park, C. and Son, S.-W.: Transient versus quasi-stationary flavors of atmospheric rivers during East Asian summer monsoon, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-242, https://doi.org/10.5194/egusphere-egu22-242, 2022.

17:35–17:40
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EGU22-1630
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Virtual presentation
Nabeela Sadaf, Yanluan Lin, and Wenhao Dong

In addition to various factors over the tropics, the interannual variability of northwest Indian summer monsoon (NWISM) rainfall is also regulated by extratropical signals. We defined a subtropical westerly jet index (SWJI) based on the meridional position and intensity of 200-hPa zonal wind within [25-55°N, 40-90°E]. It is found that SWJI exhibits a significant positive correlation with summer rainfall over the NWISM region during 1951-2015. During positive (negative) SWJI years, an upper-level anticyclonic (cyclonic) anomaly over Central Asia along with positive (negative) rainfall anomaly and low-level easterly (westerly) anomalies were observed over the NWISM region. The upper-level anticyclonic (cyclonic) anomaly was accompanied by the descending (ascending) motion and warm (cold) tropospheric temperature anomalies. The anticyclonic (cyclonic) anomaly increased (decreased) the land-ocean thermal contrast by warm (cold) air advection and modified the local meridional circulation. Interannual variability of rainfall over the NWISM region is associated with the meridional position and intensity of the jet that manifest in both upper- and low-level circulation anomalies. Further analysis showed that the interannual variability of SWJI is correlated with Arctic Oscillation (AO). During the positive phase of AO, an upper-level anticyclonic anomaly appeared over Central Asia and favored convection over the NWISM region.

How to cite: Sadaf, N., Lin, Y., and Dong, W.: Relationship between the Central Asian Subtropical Westerly and Northwest Indian Summer Monsoon rainfall, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1630, https://doi.org/10.5194/egusphere-egu22-1630, 2022.

17:40–17:45
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EGU22-1796
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ECS
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On-site presentation
Daniel Skinner, Adrian Matthews, and David Stevens

It is known that the Madden-Julian Oscillation (MJO) excites a response in the behaviour of many extratropical weather regimes at lag times of one to two weeks, acting as a key predictor in weather forecasting. Less well understood, however, is the robustness of these responses over long time scales. We begin by taking a statistical approach to assess the boreal winter response of a selection of key extratropical systems (e.g. North Atlantic Oscillation (NAO), Pacific North American (PNA) pattern) to the MJO, over two non-overlapping time periods (1974-1997 and 1997-2019). It is shown that there is significant change in both the magnitude and structure of the extratropical response signal, as a function of lag, between the two periods.

This is followed by a similar analysis applied to the 1100 year pre-industrial control run of the UKESM-1-0 coupled climate model. By breaking this period into separate 20 year segments and comparing the extratropical responses to the MJO in each segment, we show that although there is a predictable mean signal, it is overwhelmed by the internal variability in the system. Repeating this methodology with segments between 10 and 40 years in length allows us to assess sampling errors and identify the key timescales for the variability. A similar mean signal is seen with every segment length, justifying the current use of the MJO as a predictor in the extratropics, although the variability in segments of 30 and 40 years (common time periods used in many historical analyses) casts doubt on the reliability of these predictors for the future.

Recent process based analysis has shown that El Niño Southern Oscillation (ENSO) can act to modulate the Rossby wave source associated with the MJO. We investigate this using our statistical approach to assess the impact of ENSO on the MJO teleconnection patterns. In addition to this, we consider lower-frequency modes, for example Atlantic Multidecadal Variability (AMV) and the Pacific Decadal Oscillation (PDO). By compositing the extratropical response to the MJO over positive and negative phases of each of these modes, we see the individual impact of each low-frequency on the MJO teleconnections. Our work suggests updating the current MJO-extratropical predictors to include consideration of the decadal atmospheric and oceanic basic state.

How to cite: Skinner, D., Matthews, A., and Stevens, D.: Decadal variability of the extratropical response to the Madden-Julian Oscillation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1796, https://doi.org/10.5194/egusphere-egu22-1796, 2022.

17:45–17:50
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EGU22-12010
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Virtual presentation
Francois Engelbrecht and Thando Ndarana

Seasonal prediction is generally skillful over the subtropical landmasses of the Southern Hemisphere during summer seasons with strong ENSO (El Niño Southern Oscillation) forcing. Skill is substantially reduced, however, during summer seasons that are ENSO neutral. Over southern Africa, forecast skill is also comparatively less for the spring and autumn seasons, and only marginally exists for winter. This seasonal cycle in predictive skill and the strong dependence of skill on ENSO forcing raise questions about the limits of predictability in the Southern Hemisphere subtropics. Here we explore these potential limits using Atmospheric Model Intercomparison Project (AMIP) simulations. These simulations are part of the larger Coupled Model Intercomparison Project Phase Six (CMIP6), and are constructed using global atmospheric models forced at their lower boundaries with historical sea-surface temperature and sea-ice reconstructions. Radiative forcing is in the form of historical greenhouse gas and ozone concentrations, as well as aerosol emissions, for the period 1979-2014 (the same historical forcings are used in ScenarioMIP of CMIP6). AMIP simulations may be regarded as providing an upper boundary of seasonal predictive skill, at least to the extent that atmospheric inter-annual variability is a response to inter-annual variations in lower-boundary and radiative forcing. AMIP simulations are initialized only once however, and don’t make use of updated initial conditions as in the case of operational seasonal forecasts. Also, although the lower boundary forcing in AMIP simulations may be regarded as ‘perfect’, important coupled processes that influence inter-annual variability may not be represented. Our focus here is on analyzing the skill of AMIP simulations in representing inter-annual atmospheric variability over the subtropical landmasses of the Southern Hemisphere, focusing on rainfall and low-level circulation. NOAA-CIRES-DOE reanalysis v3 and Climatic Research Unit (CRU) data are used for verification. The first stage of analysis consist of constructing a multi-model ensemble of AMIP simulations, with each model contributing a single ensemble member. Such an ensemble isolates to some extent the predictability that may be derived purely from boundary forcing. In the second stage of the analysis, we evaluate skill for those AMIP models for which initial-condition based ensembles have been derived, thereby incorporating the effects of model internal-variability on predictive skill. The resulting evaluations of skill confirm the results from operational seasonal forecasting, namely that a pronounced seasonal cycle in predictive skill exists over the Southern Hemisphere continents in the subtropics, with peak skill in summer in association with ENSO forcing. However, in spring and autumn and particularly in winter, circulation patterns of lower predictability originating from the Southern Ocean impact on atmospheric variability over the subtropical landmasses. Since these circulation patterns seem to be relatively unconstrained by lower boundary and atmospheric radiative forcing, it implies that predictability in the subtropics may be constrained in winter and the transition seasons by the relatively less predictable higher-latitude circulation regimes of the Southern Hemisphere.

How to cite: Engelbrecht, F. and Ndarana, T.: Predictability of inter-annual variability in the Southern Hemisphere subtropics, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12010, https://doi.org/10.5194/egusphere-egu22-12010, 2022.

17:50–17:55
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EGU22-1381
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ECS
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Virtual presentation
Eilat Elbaum, Chaim I. Garfinkel, Ori Adam, Efrat Morin, Dorita Rostkier-Edelstein, and Uri Dayan

End of century projections from Coupled Model Intercomparison Project (CMIP) models show a decrease in precipitation over subtropical oceans that often extends into surrounding land areas, but with substantial intermodel spread. Changes in precipitation are controlled by both thermodynamical and dynamical processes, though the importance of these processes for regional scales and for intermodel spread is not well understood. The contribution of dynamic and thermodynamic processes to the model spread in regional precipitation minus evaporation (P-E) is computed for 48 CMIP models. The intermodel spread is dominated essentially everywhere by the change of the dynamic term, including in most regions where thermodynamic changes dominate the multi-model mean response. The dominant role of dynamic changes is insensitive to zonal averaging which removes any influence of stationary wave changes, and is also evident in subtropical oceanic regions. Relatedly, intermodel spread in P-E is generally unrelated to climate sensitivity.

How to cite: Elbaum, E., Garfinkel, C. I., Adam, O., Morin, E., Rostkier-Edelstein, D., and Dayan, U.: Uncertainty in projected changes in precipitation minus evaporation: Dominant role of dynamic circulation changes and weak role for thermodynamic changes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1381, https://doi.org/10.5194/egusphere-egu22-1381, 2022.

17:55–18:00
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EGU22-3876
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On-site presentation
Caroline Ummenhofer, Nathaniel Cresswell-Clay, Diana Thatcher, Alan Wanamaker, Rhawn Denniston, Yemane Asmerom, and Victor Polyak

The Azores High is a subtropical high-pressure ridge in the North Atlantic surrounded by anticyclonic winds that steer rain-bearing weather systems. The size and intensity of the Azores High modulate the oceanic moisture transport to Europe thereby affecting hydroclimate across western Europe, especially during wintertime. While changes in the North Atlantic storm track have been linked to the variability of the North Atlantic Oscillation (NAO), we focus on North Atlantic variability with a subtropical perspective by focusing on the Azores High independently of the Icelandic Low. The subtropical perspective provides a direct understanding of regional climate variability in the western Mediterranean and reveals dramatic changes to North Atlantic climate throughout the past century and can provide insight into the impact of future warming on the dynamics of the Azores High and associated hydroclimate. Here we show that winters with an extremely large Azores High are significantly more common in the industrial era (since 1850 CE) than in preindustrial times, resulting in anomalously dry conditions across the western Mediterranean, including the Iberian Peninsula. Climate model simulations of the past millennium indicate that the industrial-era expansion of the Azores High is unprecedented throughout the last millennium (since 850 CE), consistent with proxy evidence from Portugal. Azores High expansion emerges after the end of the Little Ice Age and strengthens into the 20th century consistent with anthropogenically-driven warming.

How to cite: Ummenhofer, C., Cresswell-Clay, N., Thatcher, D., Wanamaker, A., Denniston, R., Asmerom, Y., and Polyak, V.: Unprecedented Expansion of the Azores High due to Anthropogenic Climate Change, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3876, https://doi.org/10.5194/egusphere-egu22-3876, 2022.

18:00–18:05
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EGU22-12333
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ECS
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Virtual presentation
Mingyue Zhang, Eva Hartmann, Elena Xoplaki, Sebastian Wagner, and Muralidhar Adakudlu

How did climatic and environmental variability and stress affect past societies in an area of increasing relevance for contemporary planning and policy concerns? The Eastern Mediterranean (EM) and the Nile river basin (Nile) bear a long history of human social dynamics, making it a suitable area for exploring potential interactions between climate variability, extreme events, environmental changes and society over a variety of time scales. The areas contain abundant natural and human-historical archives that preserve information on the climate conditions and impacts on humans and ecosystems covering the past centuries to millennia. So far, the links between climate and societies are examined mainly from the proxy records or the derived paleoclimatic reconstruction perspectives, without addressing the detail of the processes and underlying dynamics that offer the regional climate model simulations. In order to improve our understanding of past climate in the EM and Nile at the regional scale, we developed a spatially high resolved fully-forced paleoclimate version of the COSMO-CLM running over the past 2500 years. All forcings used for the driving ESM, namely volcanic (stratospheric aerosol optical depth), orbital (eccentricity, obliquity, precession), solar (irradiance), land-use and greenhouse-gas changes are implemented to COSMO 5.0-clm16 (see Hartmann et al. for more details). As a starting point for exploring the relationship between climate and society over the last 2500 years, we compared the mean climate conditions (2m temperature and precipitation) of two periods that are 2400 years apart, namely BCE 400-362 and 1980-2018 CE. Overall, the results show that summer temperatures differ by up to 3 degrees between the two periods. In particular, over the tropics, the temperature differences are largest. Precipitation changes vary within the study area and the climate regimes covered. We will further analyze the dynamics and climate variability of the area over the two periods to explore more details of regional and local climate change.

How to cite: Zhang, M., Hartmann, E., Xoplaki, E., Wagner, S., and Adakudlu, M.: The climate of the Eastern Mediterranean and the Nile river basin 2500 years before present: a fully forced paleo regional climate simulation with COSMO-CLM, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12333, https://doi.org/10.5194/egusphere-egu22-12333, 2022.

18:05–18:30