Articles | Volume 4, issue 2
https://doi.org/10.5194/wcd-4-381-2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/wcd-4-381-2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Research article
| 
09 May 2023
Research article |
| 09 May 2023
| 09 May 2023
The impact of the Agulhas Current system on precipitation in southern Africa in regional climate simulations covering the recent past and future
Helmholtz-Zentrum Hereon, Institute of Coastal Systems – Analysis and Modeling, Max-Planck-Straße 1, 21502 Geesthacht, Germany
Eduardo Zorita
Helmholtz-Zentrum Hereon, Institute of Coastal Systems – Analysis and Modeling, Max-Planck-Straße 1, 21502 Geesthacht, Germany
Birgit Hünicke
Helmholtz-Zentrum Hereon, Institute of Coastal Systems – Analysis and Modeling, Max-Planck-Straße 1, 21502 Geesthacht, Germany
Ioana Ivanciu
GEOMAR Helmholtz Centre for Ocean Research Kiel, 24105 Kiel, Germany
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Our study analyses extreme precipitation over southern Africa in regional high-resolution atmospheric simulations of the past and future. We investigated heavy precipitation over Southern Africa, coastal South Africa, Cape Town, and the KwaZulu-Natal province in eastern South Africa. Coastal precipitation extremes are projected to intensify, double in intensity in KwaZulu-Natal, and weaken in Cape Town. Extremes are not projected to occur more often in the 21st century than in the last decades.
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The impact of external climate forcing on the four eastern boundary upwelling systems is investigated for the recent past and future. Under increased radiative forcing, upwelling-favourable winds should strengthen due to unequal heating of land and oceans. However, coastal upwelling simulated in ensembles of climate simulations do not show any imprint of external forcing neither for the past millennium nor for the future, with the exception of the strongest future scenario.
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In this paper, we use the vertical water mass transport data provided by a high-resolution global ocean simulation to study the western Arabian Sea coastal upwelling system. Our results show that: 1). no significant long-term trend is detected in the upwelling time series. 2). the impact of Indian summer monsoon on the simulated upwelling is weak. 3). the upwelling is strongly affected by the sea level pressure gradient and the air temperature gradient.
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Susann Tegtmeier, James Anstey, Sean Davis, Rossana Dragani, Yayoi Harada, Ioana Ivanciu, Robin Pilch Kedzierski, Kirstin Krüger, Bernard Legras, Craig Long, James S. Wang, Krzysztof Wargan, and Jonathon S. Wright
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Nele Tim, Eduardo Zorita, Kay-Christian Emeis, Franziska U. Schwarzkopf, Arne Biastoch, and Birgit Hünicke
Earth Syst. Dynam., 10, 847–858, https://doi.org/10.5194/esd-10-847-2019, https://doi.org/10.5194/esd-10-847-2019, 2019
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Our study reveals that the latitudinal position and intensity of Southern Hemisphere trades and westerlies are correlated. In the last decades the westerlies have shifted poleward and intensified. Furthermore, the latitudinal shifts and intensity of the trades and westerlies impact the sea surface temperatures around southern Africa and in the South Benguela upwelling region. The future development of wind stress depends on the strength of greenhouse gas forcing.
Maria Pyrina, Eduardo Moreno-Chamarro, Sebastian Wagner, and Eduardo Zorita
Earth Syst. Dynam. Discuss., https://doi.org/10.5194/esd-2019-50, https://doi.org/10.5194/esd-2019-50, 2019
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Oliver Bothe, Sebastian Wagner, and Eduardo Zorita
Earth Syst. Sci. Data, 11, 1129–1152, https://doi.org/10.5194/essd-11-1129-2019, https://doi.org/10.5194/essd-11-1129-2019, 2019
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Francisco José Cuesta-Valero, Almudena García-García, Hugo Beltrami, Eduardo Zorita, and Fernando Jaume-Santero
Clim. Past, 15, 1099–1111, https://doi.org/10.5194/cp-15-1099-2019, https://doi.org/10.5194/cp-15-1099-2019, 2019
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A database of North American long-term ground surface temperatures, from approximately 1300 CE to 1700 CE, was assembled from geothermal data. These temperatures are useful for studying the future stability of permafrost, as well as for evaluating simulations of preindustrial climate that may help to improve estimates of climate models’ equilibrium climate sensitivity. The database will be made available to the climate science community.
Oliver Bothe, Sebastian Wagner, and Eduardo Zorita
Clim. Past, 15, 307–334, https://doi.org/10.5194/cp-15-307-2019, https://doi.org/10.5194/cp-15-307-2019, 2019
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Our understanding of future climate changes increases if different sources of information agree on past climate variations. Changing climates particularly impact local scales for which future changes in precipitation are highly uncertain. Here, we use information from observations, model simulations, and climate reconstructions for regional precipitation over the British Isles. We find these do not agree well on precipitation variations over the past few centuries.
Xing Yi, Birgit Hünicke, and Eduardo Zorita
Clim. Past Discuss., https://doi.org/10.5194/cp-2018-63, https://doi.org/10.5194/cp-2018-63, 2018
Revised manuscript not accepted
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In this study, we analyse the outputs of Earth System Models to investigate the Arabian Sea upwelling for the last 1000 years and in the 21st century. Due to the orbital forcing of the models, the upwelling in the past is found to reveal a negative long-term trend, which matches the observed sediment records. In the future under the RCP8.5 scenario, the warming of the sea water tends to stabilize the surface layer and thus interrupts the upwelling.
Sitar Karabil, Eduardo Zorita, and Birgit Hünicke
Earth Syst. Dynam., 9, 69–90, https://doi.org/10.5194/esd-9-69-2018, https://doi.org/10.5194/esd-9-69-2018, 2018
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We analysed the contribution of atmospheric factors to interannual off-shore sea-level variability in the Baltic Sea region. We identified a different atmospheric circulation pattern that is more closely linked to sea-level variability than the NAO. The inverse barometer effect contributes to that link in the winter and summer seasons. Freshwater flux is connected to the link in summer and net heat flux in winter.The new atmospheric-pattern-related wind forcing plays an important role in summer.
Sitar Karabil, Eduardo Zorita, and Birgit Hünicke
Earth Syst. Dynam., 8, 1031–1046, https://doi.org/10.5194/esd-8-1031-2017, https://doi.org/10.5194/esd-8-1031-2017, 2017
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We statistically analysed the mechanisms of the variability in decadal sea-level trends for the whole Baltic Sea basin over the last century. We used two different sea-level data sets and several climatic data sets. The results of this study showed that precipitation has a lagged effect on decadal sea-level trend variations from which the signature of atmospheric effect is removed. This detected underlying factor is not connected to oceanic forcing driven from the North Atlantic region.
Johann H. Jungclaus, Edouard Bard, Mélanie Baroni, Pascale Braconnot, Jian Cao, Louise P. Chini, Tania Egorova, Michael Evans, J. Fidel González-Rouco, Hugues Goosse, George C. Hurtt, Fortunat Joos, Jed O. Kaplan, Myriam Khodri, Kees Klein Goldewijk, Natalie Krivova, Allegra N. LeGrande, Stephan J. Lorenz, Jürg Luterbacher, Wenmin Man, Amanda C. Maycock, Malte Meinshausen, Anders Moberg, Raimund Muscheler, Christoph Nehrbass-Ahles, Bette I. Otto-Bliesner, Steven J. Phipps, Julia Pongratz, Eugene Rozanov, Gavin A. Schmidt, Hauke Schmidt, Werner Schmutz, Andrew Schurer, Alexander I. Shapiro, Michael Sigl, Jason E. Smerdon, Sami K. Solanki, Claudia Timmreck, Matthew Toohey, Ilya G. Usoskin, Sebastian Wagner, Chi-Ju Wu, Kok Leng Yeo, Davide Zanchettin, Qiong Zhang, and Eduardo Zorita
Geosci. Model Dev., 10, 4005–4033, https://doi.org/10.5194/gmd-10-4005-2017, https://doi.org/10.5194/gmd-10-4005-2017, 2017
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Climate model simulations covering the last millennium provide context for the evolution of the modern climate and for the expected changes during the coming centuries. They can help identify plausible mechanisms underlying palaeoclimatic reconstructions. Here, we describe the forcing boundary conditions and the experimental protocol for simulations covering the pre-industrial millennium. We describe the PMIP4 past1000 simulations as contributions to CMIP6 and additional sensitivity experiments.
Maria Pyrina, Sebastian Wagner, and Eduardo Zorita
Clim. Past, 13, 1339–1354, https://doi.org/10.5194/cp-13-1339-2017, https://doi.org/10.5194/cp-13-1339-2017, 2017
Svenja E. Bierstedt, Birgit Hünicke, Eduardo Zorita, and Juliane Ludwig
Earth Syst. Dynam., 8, 639–652, https://doi.org/10.5194/esd-8-639-2017, https://doi.org/10.5194/esd-8-639-2017, 2017
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We statistically analyse the relationship between the structure of migrating dunes in the southern Baltic and the driving wind conditions over the past 26 years, with the long-term aim of using migrating dunes as a proxy for past wind conditions at an interannual resolution.
Juan José Gómez-Navarro, Eduardo Zorita, Christoph C. Raible, and Raphael Neukom
Clim. Past, 13, 629–648, https://doi.org/10.5194/cp-13-629-2017, https://doi.org/10.5194/cp-13-629-2017, 2017
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This contribution aims at assessing to what extent the analogue method, a classic technique used in other branches of meteorology and climatology, can be used to perform gridded reconstructions of annual temperature based on the limited information from available but un-calibrated proxies spread across different locations of the world. We conclude that it is indeed possible, albeit with certain limitations that render the method comparable to more classic techniques.
Xing Yi and Eduardo Zorita
Clim. Past Discuss., https://doi.org/10.5194/cp-2016-124, https://doi.org/10.5194/cp-2016-124, 2016
Revised manuscript not accepted
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In this paper we study the upwelling in the Arabian Sea simulated in two Earth System Models for the last millennium and for the 21st century. Revealing a negative long-term trend due to the model orbital forcing, the upwelling over the last millennium is strongly correlated with the SST, the Indian summer Monsoon and the G.bulloides abundance observed in the sediment records. In the future scenarios the warming of the sea water tends to stabilize the surface layer and hinder the upwelling.
Nele Tim, Eduardo Zorita, Birgit Hünicke, Xing Yi, and Kay-Christian Emeis
Ocean Sci., 12, 807–823, https://doi.org/10.5194/os-12-807-2016, https://doi.org/10.5194/os-12-807-2016, 2016
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The impact of external climate forcing on the four eastern boundary upwelling systems is investigated for the recent past and future. Under increased radiative forcing, upwelling-favourable winds should strengthen due to unequal heating of land and oceans. However, coastal upwelling simulated in ensembles of climate simulations do not show any imprint of external forcing neither for the past millennium nor for the future, with the exception of the strongest future scenario.
Svenja E. Bierstedt, Birgit Hünicke, Eduardo Zorita, Sebastian Wagner, and Juan José Gómez-Navarro
Clim. Past, 12, 317–338, https://doi.org/10.5194/cp-12-317-2016, https://doi.org/10.5194/cp-12-317-2016, 2016
X. Yi, B. Hünicke, N. Tim, and E. Zorita
Ocean Sci. Discuss., https://doi.org/10.5194/osd-12-2683-2015, https://doi.org/10.5194/osd-12-2683-2015, 2015
Revised manuscript not accepted
Short summary
Short summary
In this paper, we use the vertical water mass transport data provided by a high-resolution global ocean simulation to study the western Arabian Sea coastal upwelling system. Our results show that: 1). no significant long-term trend is detected in the upwelling time series. 2). the impact of Indian summer monsoon on the simulated upwelling is weak. 3). the upwelling is strongly affected by the sea level pressure gradient and the air temperature gradient.
J. J. Gómez-Navarro, O. Bothe, S. Wagner, E. Zorita, J. P. Werner, J. Luterbacher, C. C. Raible, and J. P Montávez
Clim. Past, 11, 1077–1095, https://doi.org/10.5194/cp-11-1077-2015, https://doi.org/10.5194/cp-11-1077-2015, 2015
N. Tim, E. Zorita, and B. Hünicke
Ocean Sci., 11, 483–502, https://doi.org/10.5194/os-11-483-2015, https://doi.org/10.5194/os-11-483-2015, 2015
Short summary
Short summary
The atmospheric drivers of the Benguela upwelling systems and its variability are statistically analysed with an ocean-only simulation over the last decades. Atmospheric upwelling-favourable conditions are southerly wind/wind stress, a strong subtropical anticyclone, and an ocean-land sea level pressure gradient as well as a negative ENSO and a positive AAO phase. No long-term trends of upwelling and of ocean-minus-land air pressure gradients, as supposed by Bakun, can be seen in our analysis.
J. A. Santos, M. F. Carneiro, A. Correia, M. J. Alcoforado, E. Zorita, and J. J. Gómez-Navarro
Clim. Past, 11, 825–834, https://doi.org/10.5194/cp-11-825-2015, https://doi.org/10.5194/cp-11-825-2015, 2015
J. J. Gómez-Navarro, J. P. Montávez, S. Wagner, and E. Zorita
Clim. Past, 9, 1667–1682, https://doi.org/10.5194/cp-9-1667-2013, https://doi.org/10.5194/cp-9-1667-2013, 2013
G. Esnaola, J. Sáenz, E. Zorita, A. Fontán, V. Valencia, and P. Lazure
Ocean Sci., 9, 655–679, https://doi.org/10.5194/os-9-655-2013, https://doi.org/10.5194/os-9-655-2013, 2013
O. Bothe, J. H. Jungclaus, D. Zanchettin, and E. Zorita
Clim. Past, 9, 1089–1110, https://doi.org/10.5194/cp-9-1089-2013, https://doi.org/10.5194/cp-9-1089-2013, 2013
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Abrupt transitions in an atmospheric single-column model with weak temperature gradient approximation
The American monsoon system in HadGEM3 and UKESM1
Gill M. Martin and José M. Rodríguez
Weather Clim. Dynam., 5, 711–731, https://doi.org/10.5194/wcd-5-711-2024, https://doi.org/10.5194/wcd-5-711-2024, 2024
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Using sensitivity experiments, we show that model errors developing in the Maritime Continent region contribute substantially to the Asian summer monsoon (ASM) circulation and rainfall errors through their effects on the western North Pacific subtropical high-pressure region and the winds and sea surface temperatures in the equatorial Indian Ocean, exacerbated by local coupled feedback. Such information will inform future model developments aimed at improving model predictions for the ASM.
Clemens Spensberger
Weather Clim. Dynam., 5, 659–669, https://doi.org/10.5194/wcd-5-659-2024, https://doi.org/10.5194/wcd-5-659-2024, 2024
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It is well-established that variations in convection in the tropical Indo-Pacific can influence weather in far-away regions. In this idea, I argue that the main theory used to explain this influence over large distances is incomplete. I propose hypotheses that could lead the way towards a more fundamental explanation and outline a novel approach that could be used to test the hypotheses I raise. The suggested approach might be useful to address also other long-standing questions.
Richard J. Keane, Ankur Srivastava, and Gill M. Martin
Weather Clim. Dynam., 5, 671–702, https://doi.org/10.5194/wcd-5-671-2024, https://doi.org/10.5194/wcd-5-671-2024, 2024
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We evaluate the performance of two widely used models in forecasting the Indian summer monsoon, which is one of the most challenging meteorological phenomena to simulate. The work links previous studies evaluating the use of the models in weather forecasting and climate simulation, as the focus here is on seasonal forecasting, which involves intermediate timescales. As well as being important in itself, this evaluation provides insights into how errors develop in the two modelling systems.
Matthias Fischer, Peter Knippertz, Roderick van der Linden, Alexander Lemburg, Gregor Pante, Carsten Proppe, and John H. Marsham
Weather Clim. Dynam., 5, 511–536, https://doi.org/10.5194/wcd-5-511-2024, https://doi.org/10.5194/wcd-5-511-2024, 2024
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Our research enhances the understanding of the complex dynamics within the West African monsoon system by analyzing the impact of specific model parameters on its characteristics. Employing surrogate models, we identified critical factors such as the entrainment rate and the fall velocity of ice. Precise definition of these parameters in weather models could improve forecast accuracy, thus enabling better strategies to manage and reduce the impact of weather events.
Kieran M. R. Hunt
Weather Clim. Dynam., 5, 345–356, https://doi.org/10.5194/wcd-5-345-2024, https://doi.org/10.5194/wcd-5-345-2024, 2024
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This study investigates changes in weather systems that bring winter precipitation to south Asia. We find that these systems, known as western disturbances, are occurring more frequently and lasting longer into the summer months. This shift is leading to devastating floods, as happened recently in north India. By analysing 70 years of weather data, we trace this change to shifts in major air currents known as the subtropical jet. Due to climate change, such events are becoming more frequent.
William J. Dow, Christine M. McKenna, Manoj M. Joshi, Adam T. Blaker, Richard Rigby, and Amanda C. Maycock
Weather Clim. Dynam., 5, 357–367, https://doi.org/10.5194/wcd-5-357-2024, https://doi.org/10.5194/wcd-5-357-2024, 2024
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Changes to sea surface temperatures in the extratropical North Pacific are driven partly by patterns of local atmospheric circulation, such as the Aleutian Low. We show that an intensification of the Aleutian Low could contribute to small changes in temperatures across the equatorial Pacific via the initiation of two mechanisms. The effect, although significant, is unlikely to explain fully the recently observed multi-year shift of a pattern of climate variability across the wider Pacific.
Franco Molteni, Fred Kucharski, and Riccardo Farneti
Weather Clim. Dynam., 5, 293–322, https://doi.org/10.5194/wcd-5-293-2024, https://doi.org/10.5194/wcd-5-293-2024, 2024
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We describe some new features of an intermediate-complexity coupled model, including a three-layer thermodynamic ocean model suitable to explore the extratropical response to tropical ocean variability. We present results on the model climatology and show that important features of interdecadal and interannual variability are realistically simulated in a
pacemakercoupled ensemble of 70-year runs, where portions of the tropical Indo-Pacific are constrained to follow the observed variability.
Molly E. Menzel, Darryn W. Waugh, Zheng Wu, and Thomas Reichler
Weather Clim. Dynam., 5, 251–261, https://doi.org/10.5194/wcd-5-251-2024, https://doi.org/10.5194/wcd-5-251-2024, 2024
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Recent work exploring the tropical atmospheric circulation response to climate change has revealed a disconnect in the latitudinal location of two features, the subtropical jet and the Hadley cell edge. Here, we investigate if the surprising result from coupled climate model and meteorological reanalysis output is consistent across model complexity.
Julian F. Quinting, Christian M. Grams, Edmund Kar-Man Chang, Stephan Pfahl, and Heini Wernli
Weather Clim. Dynam., 5, 65–85, https://doi.org/10.5194/wcd-5-65-2024, https://doi.org/10.5194/wcd-5-65-2024, 2024
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Research in the last few decades has revealed that rapidly ascending airstreams in extratropical cyclones have an important effect on the evolution of downstream weather and predictability. In this study, we show that the occurrence of these airstreams over the North Pacific is modulated by tropical convection. Depending on the modulation, known atmospheric circulation patterns evolve quite differently, which may affect extended-range predictions in the Atlantic–European region.
Hyunju Jung, Peter Knippertz, Yvonne Ruckstuhl, Robert Redl, Tijana Janjic, and Corinna Hoose
Weather Clim. Dynam., 4, 1111–1134, https://doi.org/10.5194/wcd-4-1111-2023, https://doi.org/10.5194/wcd-4-1111-2023, 2023
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A narrow rainfall belt in the tropics is an important feature for large-scale circulations and the global water cycle. The accurate simulation of this rainfall feature has been a long-standing problem, with the reasons behind that unclear. We present a novel diagnostic tool that allows us to disentangle processes important for rainfall, which changes due to modifications in model. Using our diagnostic tool, one can potentially identify sources of uncertainty in weather and climate models.
Lina Boljka, Nour-Eddine Omrani, and Noel S. Keenlyside
Weather Clim. Dynam., 4, 1087–1109, https://doi.org/10.5194/wcd-4-1087-2023, https://doi.org/10.5194/wcd-4-1087-2023, 2023
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This study examines quasi-periodic variability in the tropical Pacific on interannual timescales and related physics using a recently developed time series analysis tool. We find that wind stress in the west Pacific and recharge–discharge of ocean heat content are likely related to each other on ~1.5–4.5-year timescales (but not on others) and dominate variability in sea surface temperatures on those timescales. This may have further implications for climate models and long-term prediction.
Sam Hardy, John Methven, Juliane Schwendike, Ben Harvey, and Mike Cullen
Weather Clim. Dynam., 4, 1019–1043, https://doi.org/10.5194/wcd-4-1019-2023, https://doi.org/10.5194/wcd-4-1019-2023, 2023
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We examine a Borneo vortex case using computer simulations and satellite observations. The vortex is identified with high humidity through the atmosphere and has heaviest rainfall on its northern flank. Simulations represent circulation and rainfall accumulation well. The low-level Borneo vortex is coupled with a higher-level wave, which moves westwards along a layer with a sharp vertical gradient in moisture. Vortex growth occurs through mechanisms usually considered outside the tropics.
Abu Bakar Siddiqui Thakur and Jai Sukhatme
EGUsphere, https://doi.org/10.5194/egusphere-2023-2779, https://doi.org/10.5194/egusphere-2023-2779, 2023
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We analyze the present and future states of the tropical upper troposphere. Observations and climate model simulations suggest that interactions between disparate families of waves and the mean flow maintain present-day upper-level winds, and each component undergoes complex changes due to global warming. While the net east-west flow of the atmosphere may remain unaltered, this study indicates robust changes to local circulations that may influence tropical precipitation and regional climate.
Chiem van Straaten, Dim Coumou, Kirien Whan, Bart van den Hurk, and Maurice Schmeits
Weather Clim. Dynam., 4, 887–903, https://doi.org/10.5194/wcd-4-887-2023, https://doi.org/10.5194/wcd-4-887-2023, 2023
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Variability in the tropics can influence weather over Europe. This study evaluates a summertime connection between the two. It shows that strongly opposing west Pacific sea surface temperature anomalies have occurred more frequently since 1980, likely due to a combination of long-term warming in the west Pacific and the El Niño Southern Oscillation. Three to six weeks later, the distribution of hot and cold airmasses over Europe is affected.
Francis Nkrumah, Cornelia Klein, Kwesi Akumenyi Quagraine, Rebecca Berkoh-Oforiwaa, Nana Ama Browne Klutse, Patrick Essien, Gandomè Mayeul Leger Davy Quenum, and Hubert Azoda Koffi
Weather Clim. Dynam., 4, 773–788, https://doi.org/10.5194/wcd-4-773-2023, https://doi.org/10.5194/wcd-4-773-2023, 2023
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It is not yet clear which variations in broader atmospheric conditions of the West African monsoon may lead to mesoscale convective system (MCS) occurrences in southern West Africa (SWA). In this study, we identified nine different weather patterns and categorized them as dry-, transition-, or monsoon-season types using a method called self-organizing maps (SOMs). It was revealed that a warmer Sahel region can create favourable conditions for MCS formation in SWA.
Giorgia Di Capua, Dim Coumou, Bart van den Hurk, Antje Weisheimer, Andrew G. Turner, and Reik V. Donner
Weather Clim. Dynam., 4, 701–723, https://doi.org/10.5194/wcd-4-701-2023, https://doi.org/10.5194/wcd-4-701-2023, 2023
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Heavy rainfall in tropical regions interacts with mid-latitude circulation patterns, and this interaction can explain weather patterns in the Northern Hemisphere during summer. In this analysis we detect these tropical–extratropical interaction pattern both in observational datasets and data obtained by atmospheric models and assess how well atmospheric models can reproduce the observed patterns. We find a good agreement although these relationships are weaker in model data.
Daniel Baldassare, Thomas Reichler, Piret Plink-Björklund, and Jacob Slawson
Weather Clim. Dynam., 4, 531–541, https://doi.org/10.5194/wcd-4-531-2023, https://doi.org/10.5194/wcd-4-531-2023, 2023
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Using ensemble members from the ERA5 reanalysis, the most widely used method for estimating tropical-width trends, the meridional stream function, was found to have large error, particularly in the Northern Hemisphere and in the summer, because of weak gradients at the tropical edge and poor data quality. Another method, using the latitude where the surface wind switches from westerly to easterly, was found to have lower error due to better-observed data.
William Torgerson, Juliane Schwendike, Andrew Ross, and Chris J. Short
Weather Clim. Dynam., 4, 331–359, https://doi.org/10.5194/wcd-4-331-2023, https://doi.org/10.5194/wcd-4-331-2023, 2023
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We investigated intensity fluctuations that occurred during the rapid intensification of Hurricane Irma (2017) to understand their effects on the storm structure. Using high-resolution model simulations, we found that the fluctuations were caused by local regions of strong ascent just outside the eyewall that disrupted the storm, leading to a larger and more symmetrical storm eye. This alters the location and intensity of the strongest winds in the storm and hence the storm's impact.
Anne Martin, Martin Weissmann, and Alexander Cress
Weather Clim. Dynam., 4, 249–264, https://doi.org/10.5194/wcd-4-249-2023, https://doi.org/10.5194/wcd-4-249-2023, 2023
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Global wind profiles from the Aeolus satellite mission are an important recent substitute for the Global Observing System, showing an overall positive impact on numerical weather prediction forecasts. This study highlights atmospheric dynamic phenomena constituting pathways for significant improvement of Aeolus for future studies, including large-scale tropical circulation systems and the interaction of tropical cyclones undergoing an extratropical transition with the midlatitude waveguide.
Elliott Michael Sainsbury, Reinhard K. H. Schiemann, Kevin I. Hodges, Alexander J. Baker, Len C. Shaffrey, Kieran T. Bhatia, and Stella Bourdin
Weather Clim. Dynam., 3, 1359–1379, https://doi.org/10.5194/wcd-3-1359-2022, https://doi.org/10.5194/wcd-3-1359-2022, 2022
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Post-tropical cyclones (PTCs) can bring severe weather to Europe. By tracking and identifying PTCs in five global climate models, we investigate how the frequency and intensity of PTCs may change across Europe by 2100. We find no robust change in the frequency or intensity of Europe-impacting PTCs in the future. This study indicates that large uncertainties surround future Europe-impacting PTCs and provides a framework for evaluating PTCs in future generations of climate models.
Kieran M. R. Hunt and Andrew G. Turner
Weather Clim. Dynam., 3, 1341–1358, https://doi.org/10.5194/wcd-3-1341-2022, https://doi.org/10.5194/wcd-3-1341-2022, 2022
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More than half of India's summer monsoon rainfall arises from low-pressure systems: storms originating over the Bay of Bengal. In observation-based data, we examine how the generation and pathway of these storms are changed by the
boreal summer intraseasonal oscillation– the chief means of large-scale control on the monsoon at timescales of a few weeks. Our study offers new insights for useful prediction of these storms, important for both water resources planning and disaster early warning.
Cornelius Immanuel Weiß, Alexander Gohm, Mathias Walter Rotach, and Thomas Torora Minda
Weather Clim. Dynam., 3, 1003–1019, https://doi.org/10.5194/wcd-3-1003-2022, https://doi.org/10.5194/wcd-3-1003-2022, 2022
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Two gap flow events in the Great Rift Valley in Ethiopia were investigated based on observations, ERA5 reanalysis data, and simulations with the numerical weather prediction model WRF. The main focus was on strong winds in the area around Lake Abaya since the winds may generate waves on the lake which help to sustain the lake's ecology. That is important in terms of food supply for the local population. The gap winds exhibit a diurnal cycle and a seasonal dependence.
Matic Pikovnik, Žiga Zaplotnik, Lina Boljka, and Nedjeljka Žagar
Weather Clim. Dynam., 3, 625–644, https://doi.org/10.5194/wcd-3-625-2022, https://doi.org/10.5194/wcd-3-625-2022, 2022
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Potential future changes in the Hadley cells (HCs), either to their strength or their meridional extent, will profoundly impact the global distribution of precipitation. Therefore, to objectively evaluate and inter-compare past and future changes in the overall HC strength between different studies, a unified metric is required. The study proposes two new metrics, which alleviate the spatial inhomogeneities of the HC strength trend.
Ambrogio Volonté, Andrew G. Turner, Reinhard Schiemann, Pier Luigi Vidale, and Nicholas P. Klingaman
Weather Clim. Dynam., 3, 575–599, https://doi.org/10.5194/wcd-3-575-2022, https://doi.org/10.5194/wcd-3-575-2022, 2022
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In this study we analyse the complex seasonal evolution of the East Asian summer monsoon. Using reanalysis data, we show the importance of the interaction between tropical and extratropical air masses converging at the monsoon front, particularly during its northward progression. The upper-level flow pattern (e.g. the westerly jet) controls the balance between the airstreams and thus the associated rainfall. This framework provides a basis for studies of extreme events and climate variability.
Peter Pfleiderer, Shruti Nath, and Carl-Friedrich Schleussner
Weather Clim. Dynam., 3, 471–482, https://doi.org/10.5194/wcd-3-471-2022, https://doi.org/10.5194/wcd-3-471-2022, 2022
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Tropical cyclones are amongst the most dangerous weather events. Here we develop an empirical model that allows us to estimate the number and strengths of tropical cyclones for given atmospheric conditions and sea surface temperatures. An application of the model shows that atmospheric circulation is the dominant factor for seasonal tropical cyclone activity. However, warming sea surface temperatures have doubled the likelihood of extremely active hurricane seasons in the past decades.
Jean-Philippe Baudouin, Michael Herzog, and Cameron A. Petrie
Weather Clim. Dynam., 2, 1187–1207, https://doi.org/10.5194/wcd-2-1187-2021, https://doi.org/10.5194/wcd-2-1187-2021, 2021
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Western disturbances are mid-latitude, high-altitude, low-pressure areas that bring orographic precipitation into the Upper Indus Basin. Using statistical tools, we show that the interaction between western disturbances and relief explains the near-surface, cross-barrier wind activity. We also reveal the existence of a moisture pathway from the nearby seas. Overall, we offer a conceptual framework for western-disturbance activity, particularly in terms of precipitation.
Anantha Aiyyer and Terrell Wade
Weather Clim. Dynam., 2, 1051–1072, https://doi.org/10.5194/wcd-2-1051-2021, https://doi.org/10.5194/wcd-2-1051-2021, 2021
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We diagnose the mean circulations in the extratropics that are associated with rapid changes in the tropical storm storm speeds in the Atlantic. We show that rapid acceleration and deceleration are associated with distinct phasing between the tropical cyclone and weather waves of the extratropics. Over the past 5 decades, rapid acceleration and deceleration of tropical cyclones have reduced in magnitude. This might be related to the poleward shift and weakening of these extratropical waves.
Julianna Carvalho-Oliveira, Leonard Friedrich Borchert, Aurélie Duchez, Mikhail Dobrynin, and Johanna Baehr
Weather Clim. Dynam., 2, 739–757, https://doi.org/10.5194/wcd-2-739-2021, https://doi.org/10.5194/wcd-2-739-2021, 2021
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This work questions the influence of the Atlantic Meridional Overturning Circulation, an important component of the climate system, on the variability in North Atlantic sea surface temperature (SST) a season ahead, particularly how this influence affects SST prediction credibility 2–4 months into the future. While we find this relationship is relevant for assessing SST predictions, it strongly depends on the time period and season we analyse and is more subtle than what is found in observations.
Andrea M. Jenney, David A. Randall, and Elizabeth A. Barnes
Weather Clim. Dynam., 2, 653–673, https://doi.org/10.5194/wcd-2-653-2021, https://doi.org/10.5194/wcd-2-653-2021, 2021
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Storm activity in the tropics is one of the key phenomena that provide weather predictability on an extended timescale of about 10–40 d. The influence of tropical storminess on places like North America is sensitive to the overall average state of the climate system. In this study, we try to unpack the reasons why climate models do not agree on how the influence of these storms on weather over the North Pacific and North America will change in the future.
Philip Rupp and Peter Haynes
Weather Clim. Dynam., 2, 413–431, https://doi.org/10.5194/wcd-2-413-2021, https://doi.org/10.5194/wcd-2-413-2021, 2021
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We study a range of dynamical aspects of the Asian monsoon anticyclone as the response of a simple numerical model to a steady imposed heating distribution with different background flow configurations. Particular focus is given on interactions between the monsoon anticyclone and active mid-latitude dynamics, which we find to have a zonally localising effect on the time-mean circulation and to be able to qualitatively alter the temporal variability of the bulk anticyclone.
Joshua White and Anantha Aiyyer
Weather Clim. Dynam., 2, 311–329, https://doi.org/10.5194/wcd-2-311-2021, https://doi.org/10.5194/wcd-2-311-2021, 2021
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Using a simple general circulation model, we examine the structure of waves in the mid-tropospheric jet over North Africa. We show that waves occur in near-stationary groups or wave packets. As they are not swept out of the jet, this may provide the opportunity for the packets to amplify via feedback from other energy sources like rain-producing cloud complexes and mineral dust that are known to operate here. Our results address the criticism that the easterly jet is too short to sustain waves.
Franziska Aemisegger, Raphaela Vogel, Pascal Graf, Fabienne Dahinden, Leonie Villiger, Friedhelm Jansen, Sandrine Bony, Bjorn Stevens, and Heini Wernli
Weather Clim. Dynam., 2, 281–309, https://doi.org/10.5194/wcd-2-281-2021, https://doi.org/10.5194/wcd-2-281-2021, 2021
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The interaction of clouds in the trade wind region with the atmospheric flow is complex and at the heart of uncertainties associated with climate projections. In this study, a natural tracer of atmospheric circulation is used to establish a link between air originating from dry regions of the midlatitudes and the occurrence of specific cloud patterns. Two pathways involving transport within midlatitude weather systems are identified, by which air is brought into the trades within 5–10 d.
Jack Giddings, Adrian J. Matthews, Nicholas P. Klingaman, Karen J. Heywood, Manoj Joshi, and Benjamin G. M. Webber
Weather Clim. Dynam., 1, 635–655, https://doi.org/10.5194/wcd-1-635-2020, https://doi.org/10.5194/wcd-1-635-2020, 2020
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The impact of chlorophyll on the southwest monsoon is unknown. Here, seasonally varying chlorophyll in the Bay of Bengal was imposed in a general circulation model coupled to an ocean mixed layer model. The SST increases by 0.5 °C in response to chlorophyll forcing and shallow mixed layer depths in coastal regions during the inter-monsoon. Precipitation increases significantly to 3 mm d-1 across Myanmar during June and over northeast India and Bangladesh during October, decreasing model bias.
Giorgia Di Capua, Jakob Runge, Reik V. Donner, Bart van den Hurk, Andrew G. Turner, Ramesh Vellore, Raghavan Krishnan, and Dim Coumou
Weather Clim. Dynam., 1, 519–539, https://doi.org/10.5194/wcd-1-519-2020, https://doi.org/10.5194/wcd-1-519-2020, 2020
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We study the interactions between the tropical convective activity and the mid-latitude circulation in the Northern Hemisphere during boreal summer. We identify two circumglobal wave patterns with phase shifts corresponding to the South Asian and the western North Pacific monsoon systems at an intra-seasonal timescale. These patterns show two-way interactions in a causal framework at a weekly timescale and assess how El Niño affects these interactions.
Benjamin A. Stephens and Charles S. Jackson
Weather Clim. Dynam., 1, 389–404, https://doi.org/10.5194/wcd-1-389-2020, https://doi.org/10.5194/wcd-1-389-2020, 2020
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We analyze abrupt transitions between tropical rainfall regimes in a single-column model (SCM) of the tropical atmosphere. Multiple equilibria have been observed before in SCMs, but here we analyze actual bifurcations. We attribute the transitions to a sudden loss of evaporative cooling in the lower column due to nonlinearities in microphysics. This study may have implications for atmospheric dynamics more broadly but also for understanding abrupt transitions in paleoclimate.
Jorge L. García-Franco, Lesley J. Gray, and Scott Osprey
Weather Clim. Dynam., 1, 349–371, https://doi.org/10.5194/wcd-1-349-2020, https://doi.org/10.5194/wcd-1-349-2020, 2020
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The American monsoon system is the main source of rainfall for the subtropical Americas and an important element of Latin American agriculture. Here we use state-of-the-art climate models from the UK Met Office in different configurations to analyse the performance of these models in the American monsoon. Resolution is found to be a key factor to improve monsoon representation, whereas integrated chemistry does not improve the simulated monsoon rainfall.
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Short summary
As stated by the IPCC, southern Africa is one of the two land regions that are projected to suffer from the strongest precipitation reductions in the future. Simulated drying in this region is linked to the adjacent oceans, and prevailing winds as warm and moist air masses are transported towards the continent. Precipitation trends in past and future climate can be partly attributed to the strength of the Agulhas Current system, the current along the east and south coasts of southern Africa.
As stated by the IPCC, southern Africa is one of the two land regions that are projected to...
