Articles | Volume 2, issue 2
https://doi.org/10.5194/wcd-2-373-2021
© Author(s) 2021. 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-2-373-2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Research article
| 
28 Apr 2021
Research article |
| 28 Apr 2021
| 28 Apr 2021
A dynamic and thermodynamic analysis of the 11 December 2017 tornadic supercell in the Highveld of South Africa
Lesetja E. Lekoloane
CORRESPONDING AUTHOR
South African Weather Service, Pretoria, 0001, South Africa
Global Change Institute, University of the Witwatersrand, Johannesburg, 2050, South Africa
Mary-Jane M. Bopape
South African Weather Service, Pretoria, 0001, South Africa
Tshifhiwa Gift Rambuwani
South African Weather Service, Pretoria, 0001, South Africa
Thando Ndarana
Department of Geography, Geoinformatics and Meteorology, University of Pretoria, Pretoria, 0001, South Africa
Stephanie Landman
South African Weather Service, Pretoria, 0001, South Africa
Puseletso Mofokeng
South African Weather Service, Pretoria, 0001, South Africa
School of Geography, Archaeology and Environmental Studies, University of the Witwatersrand, Johannesburg, 2050, South Africa
Morne Gijben
South African Weather Service, Pretoria, 0001, South Africa
Ngwako Mohale
South African Weather Service, Pretoria, 0001, South Africa
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Thando Ndarana, Lesetja E. Lekoloane, Tsholanang S. Rammopo, Chris J. C. Reason, Mary-Jane M. Bopape, Hector Chikoore, and Francois A. Engelbrecht
Weather Clim. Dynam. Discuss., https://doi.org/10.5194/wcd-2022-2, https://doi.org/10.5194/wcd-2022-2, 2022
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This study considered the upper dynamics associated with the South Atlantic Ocean high pressure system that extends across the South African domain. This extension of this system occurs in two ways. The dynamics are studied by considering the evolution of energy and it is shown that the upper level processes are different between the two types of the extension. The weather systems that occur in the upper develop very differently and have different implications for rainfall over South Africa.
Michael A. Barnes, Thando Ndarana, Michael Sprenger, and Willem A. Landman
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Stratospheric air can intrude into the troposphere and is associated with cyclonic development throughout the atmosphere. Through a highly idealized systematic approach, the effect that different intrusion characteristics have on surface cyclogenetic forcing is investigated. The proximity of stratospheric intrusions to the surface is shown to be the main factor in surface cyclogenetic forcing, whilst its width is an additional contributing factor.
Thando Ndarana, Lesetja E. Lekoloane, Tsholanang S. Rammopo, Chris J. C. Reason, Mary-Jane M. Bopape, Hector Chikoore, and Francois A. Engelbrecht
Weather Clim. Dynam. Discuss., https://doi.org/10.5194/wcd-2022-2, https://doi.org/10.5194/wcd-2022-2, 2022
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This study considered the upper dynamics associated with the South Atlantic Ocean high pressure system that extends across the South African domain. This extension of this system occurs in two ways. The dynamics are studied by considering the evolution of energy and it is shown that the upper level processes are different between the two types of the extension. The weather systems that occur in the upper develop very differently and have different implications for rainfall over South Africa.
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Flow dependence of wintertime subseasonal prediction skill over Europe
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Emergence of representative signals for sudden stratospheric warmings beyond current predictable lead times
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Seasonal climate influences on the timing of the Australian monsoon onset
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Wolfgang Wicker, Inna Polichtchouk, and Daniela I. V. Domeisen
Weather Clim. Dynam., 4, 81–93, https://doi.org/10.5194/wcd-4-81-2023, https://doi.org/10.5194/wcd-4-81-2023, 2023
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Sudden stratospheric warmings are extreme weather events where the winter polar stratosphere warms by about 25 K. An improved representation of small-scale gravity waves in sub-seasonal prediction models can reduce forecast errors since their impact on the large-scale circulation is predictable multiple weeks ahead. After a sudden stratospheric warming, vertically propagating gravity waves break at a lower altitude than usual, which strengthens the long-lasting positive temperature anomalies.
Takumi Matsunobu, Christian Keil, and Christian Barthlott
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This study quantifies the impact of poorly constrained parameters used to represent aerosol–cloud–precipitation interactions on precipitation and cloud forecasts associated with uncertainties in input atmospheric states. Uncertainties in these parameters have a non-negligible impact on daily precipitation amount and largely change the amount of cloud. The comparison between different weather situations reveals that the impact becomes more important when convection is triggered by local effects.
Melissa L. Breeden, John R. Albers, and Andrew Hoell
Weather Clim. Dynam., 3, 1183–1197, https://doi.org/10.5194/wcd-3-1183-2022, https://doi.org/10.5194/wcd-3-1183-2022, 2022
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We use a statistical dynamical model to generate precipitation forecasts for lead times of 2–6 weeks over southwest Asia, which are needed to support humanitarian food distribution. The model signal-to-noise ratio is used to identify a smaller subset of forecasts with particularly high skill, so-called subseasonal forecasts of opportunity (SFOs). Precipitation SFOs are often related to slowly evolving tropical phenomena, namely the El Niño–Southern Oscillation and Madden–Julian Oscillation.
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Weather Clim. Dynam. Discuss., https://doi.org/10.5194/wcd-2022-55, https://doi.org/10.5194/wcd-2022-55, 2022
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We propose a fully data driven, interpretable, and computationally scalable framework to characterize sudden stratospheric warmings (SSWs), extract statistically significant precursors, and produce machine learning (ML) forecasts. By successfully leveraging the long lasting impact of SSWs, the ML predictions outperform sub-seasonal numerical forecasts for lead times beyond 25 days. Post-processing numerical predictions using their ML counterparts yields an up to 20 % performance increase.
Michael K. Tippett, Chiara Lepore, and Michelle L. L’Heureux
Weather Clim. Dynam., 3, 1063–1075, https://doi.org/10.5194/wcd-3-1063-2022, https://doi.org/10.5194/wcd-3-1063-2022, 2022
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The El Niño–Southern Oscillation (ENSO) and Arctic Oscillation (AO) are phenomena that affect the weather and climate of North America. Although ENSO hails from from the tropical Pacific and the AO high above the North Pole, the spatial patterns of their influence on a North American tornado environment index are remarkably similar in computer models. We find that when ENSO and the AO act in concert, their impact is large, and when they oppose each other, their impact is small.
Rachel Wai-Ying Wu, Zheng Wu, and Daniela I.V. Domeisen
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Martin Wegmann, Yvan Orsolini, Antje Weisheimer, Bart van den Hurk, and Gerrit Lohmann
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Constantin Ardilouze, Damien Specq, Lauriane Batté, and Christophe Cassou
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Cedric G. Ngoungue Langue, Christophe Lavaysse, Mathieu Vrac, Philippe Peyrillé, and Cyrille Flamant
Weather Clim. Dynam., 2, 893–912, https://doi.org/10.5194/wcd-2-893-2021, https://doi.org/10.5194/wcd-2-893-2021, 2021
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This work assesses the forecast of the temperature over the Sahara, a key driver of the West African Monsoon, at a seasonal timescale. The seasonal models are able to reproduce the climatological state and some characteristics of the temperature during the rainy season in the Sahel. But, because of errors in the timing, the forecast skill scores are significant only for the first 4 weeks.
Zheng Wu, Bernat Jiménez-Esteve, Raphaël de Fondeville, Enikő Székely, Guillaume Obozinski, William T. Ball, and Daniela I. V. Domeisen
Weather Clim. Dynam., 2, 841–865, https://doi.org/10.5194/wcd-2-841-2021, https://doi.org/10.5194/wcd-2-841-2021, 2021
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We use an advanced statistical approach to investigate the dynamics of the development of sudden stratospheric warming (SSW) events in the winter Northern Hemisphere. We identify distinct signals that are representative of these events and their event type at lead times beyond currently predictable lead times. The results can be viewed as a promising step towards improving the predictability of SSWs in the future by using more advanced statistical methods in operational forecasting systems.
Alberto Caldas-Alvarez, Samiro Khodayar, and Peter Knippertz
Weather Clim. Dynam., 2, 561–580, https://doi.org/10.5194/wcd-2-561-2021, https://doi.org/10.5194/wcd-2-561-2021, 2021
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The prediction capabilities of GPS, operational (low-resolution) and targeted (high-resolution) radiosondes for data assimilation in a Mediterranean heavy precipitation event at different model resolutions are investigated. The results show that even if GPS provides accurate observations, their lack of vertical information hampers the improvement, demonstrating the need for assimilating radiosondes, where the location and timing of release was more determinant than the vertical resolution.
Joel Lisonbee and Joachim Ribbe
Weather Clim. Dynam., 2, 489–506, https://doi.org/10.5194/wcd-2-489-2021, https://doi.org/10.5194/wcd-2-489-2021, 2021
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Why do some monsoon seasons start early, while others start late? For the Australian monsoon, some previous research suggested the El Niño–Southern Oscillation in the months before the onset influenced the monsoon timing. This research tests if this is still correct and if other large-scale climate patterns also influenced onset timing. We found that a strong La Niña pattern usually coincided with an early onset but weak La Niña and El Niño patterns did not show a consistent pattern.
John R. Albers, Amy H. Butler, Melissa L. Breeden, Andrew O. Langford, and George N. Kiladis
Weather Clim. Dynam., 2, 433–452, https://doi.org/10.5194/wcd-2-433-2021, https://doi.org/10.5194/wcd-2-433-2021, 2021
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Weather variability controls the transport of ozone from the stratosphere to the Earth’s surface and water vapor from oceanic source regions to continental land masses. Forecasting these types of transport has high societal value because of the negative impacts of ozone on human health and the role of water vapor in governing precipitation variability. We use upper-level wind forecasts to assess the potential for predicting ozone and water vapor transport 3–6 weeks ahead of time.
Raphael Portmann, Juan Jesús González-Alemán, Michael Sprenger, and Heini Wernli
Weather Clim. Dynam., 1, 597–615, https://doi.org/10.5194/wcd-1-597-2020, https://doi.org/10.5194/wcd-1-597-2020, 2020
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In September 2018 an intense Mediterranean cyclone with structural similarities to a hurricane, a so-called medicane, caused severe damage in Greece. Its development was uncertain, even just a few days in advance. The reason for this was uncertainties in the jet stream over the North Atlantic 3 d prior to cyclogenesis that propagated into the Mediterranean. They led to an uncertain position of the upper-level disturbance and, as a result, of the position and thermal structure of the cyclone.
Peter Pfleiderer, Carl-Friedrich Schleussner, Tobias Geiger, and Marlene Kretschmer
Weather Clim. Dynam., 1, 313–324, https://doi.org/10.5194/wcd-1-313-2020, https://doi.org/10.5194/wcd-1-313-2020, 2020
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Seasonal outlooks of Atlantic hurricane activity are required to enable risk reduction measures and disaster preparedness. Many seasonal forecasts are based on a selection of climate signals from which a statistical model is constructed. The crucial step in this approach is to select the most relevant predictors without overfitting. Here we show that causal effect networks can be used to identify the most robust predictors. Based on these predictors we construct a competitive forecast model.
Kirsten J. Mayer and Elizabeth A. Barnes
Weather Clim. Dynam., 1, 247–259, https://doi.org/10.5194/wcd-1-247-2020, https://doi.org/10.5194/wcd-1-247-2020, 2020
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Tropical storms are key for harnessing midlatitude weather prediction skill 2–8 weeks into the future. Recently, stratospheric activity was shown to impact tropical storminess and thus may also be important for midlatitude prediction skill on these timescales. This work analyzes two forecast systems to assess whether they capture this additional skill. We find there is enhanced prediction out through week 4 when both the tropical and stratospheric phenomena are active.
Christian Barthlott and Andrew I. Barrett
Weather Clim. Dynam., 1, 207–224, https://doi.org/10.5194/wcd-1-207-2020, https://doi.org/10.5194/wcd-1-207-2020, 2020
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The mesoscale convective system (MCS) that affected Germany at Pentecost 2014 was one of the most severe for decades. However, the predictability of this system was very low. By moving the model domain by just one grid point changed whether the MCS was successfully simulated or not. The decisive factor seems to be small differences in the initial track of the convection: cooler air near the coast inhibited development there, but tracks slightly more inland found more favorable conditions.
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Short summary
We analysed a tornadic supercell that tracked through the northern Highveld region of South Africa for 7 h. We found that atmospheric conditions were conducive for tornado-associated severe storms over the region. A 4.4 km resolution model run by the South African Weather Service was able to predict this supercell, including its timing. However, it underestimated its severity due to underestimations of other important factors necessary for real-world development of these kinds of storms.
We analysed a tornadic supercell that tracked through the northern Highveld region of South...
