Numerical simulation of a mesoscale convective system over the east coast of South Africa

Blamey, Ross C.; Reason, C. J. C.

doi:10.3402/tellusa.v61i1.15529

Cited by 10 publications

(21 citation statements)

References 97 publications

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“…While the Agulhas Current region receives 31% of its lightning in the peak period, but 8% in the weakest period, a similar size region over continental Southern Africa (between 21.25°E to 31.25°E and 38.75°S to 28.75°S) receives 51% of its lightning in the peak period and no lightning in the weakest period. During the summer South Africa experiences a variety of thunderstorms from single cell to mesoscale convective complexes and occasional extratropical cyclones [ Blamey and Reason , ; ; Reason and Keibel , ; Tyson and Preston‐Whyte , ], but in winter there is no source of moisture to support the development of thunderstorms [ Dyson , ; Taljaard , ]. The conditions for oceanic lightning, while certainly seasonal, are therefore not as strongly bound to a specific season as the continental lightning.…”

Section: Resultsmentioning

confidence: 99%

Processes driving thunderstorms over the Agulhas Current

2013

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[1] Lightning occurs predominantly over land and is not common over the open ocean. We study here one oceanic region in which thunderstorms are frequently found, namely the warm Agulhas Current off the southeast coast of South Africa. The seasonal and interannual lightning variability is derived from satellite and terrestrial data sets. Favorable climatic conditions for lightning are investigated using both ERA-Interim and NCEP/ NCAR reanalysis data. We find peak lightning in austral autumn over the Agulhas Current but with low seasonality (i.e., there is considerable lightning throughout the year). While the climatological wind direction varies strongly with latitude and season, the wind direction is predominantly northerly throughout the region during thunderstorms. A composite of sea level pressure during thunderstorm days indicates that thunderstorms are related to eastward-propagating synoptic-scale wave trains passing through the Agulhas Current region. The strong convective activity during thunderstorms occur in the warm sector of a cyclone and is associated with horizontal convergence and lifting of warm, moist surface air originating over the warm Agulhas Current.

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Section: Resultsmentioning

confidence: 99%

Processes driving thunderstorms over the Agulhas Current

2013

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“…Moisture inflow from the northern Agulhas Current/southern Mozambique Channel contributed to heavy rainfall associated with MCCs over KwaZulu-Natal/southern Mozambique (134), and from the northern Mozambique Channel for the intense TTT flooding that occurred in Mozambique in January 2013 (130).…”

Section: Africamentioning

confidence: 99%

Major Mechanisms of Atmospheric Moisture Transport and Their Role in Extreme Precipitation Events

Gimeno

Domínguez

Nieto

et al. 2016

Annu. Rev. Environ. Resour.

235

212

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We review the major conceptual models of atmospheric moisture transport, which describe the link between evaporation from the ocean and precipitation over the continents. We begin by summarizing some of the basic aspects of the structure and geographical distribution of the two major mechanisms of atmospheric moisture transport, namely low-level jets (LLJs) and atmospheric rivers (ARs). We then focus on a regional analysis of the role of these mechanisms in extreme precipitation events with particular attention to the intensification (or reduction) of moisture transport and the outcome, in terms of precipitation anomalies and subsequent flooding (drought), and consider changes in the position and occurrence of LLJs and ARs with respect to any associated flooding or drought. We then conclude with a graphical summary of the impacts of precipitation extremes, highlighting the usefulness of this information to hydrologists and policymakers, and describe some future research challenges including the effects of possible changes to ARs and LLJs within the context of future warmer climates.

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“…These cloud bands are the major synoptic rainfall producing system over subtropical southern Africa during the early to mid-summer (Harrison 1984 ; Diab et al 1991 ; Todd and Washington 1999 ; Hart et al 2010 ; Manhique et al 2011 ). Other important rainfall producing systems for the region are mesoscale convective complexes (Blamey and Reason 2009 , 2013 ), cut-off lows (CoLs) (Singleton and Reason 2006 , 2007a ) and ridging anticyclones (Weldon and Reason 2014 ; Engelbrecht et al 2015 ; Engelbrecht and Landman 2016 ).…”

Section: Introductionmentioning

confidence: 99%

Drought in the Eastern Cape region of South Africa and trends in rainfall characteristics

et al. 2020

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Much of the Eastern Cape province in South Africa has been experiencing a severe drought since 2015. This drought has had major socio-economic effects particularly on the large impoverished rural population as well as on some urban areas where supplied water services have broken down in several cases. The region is influenced by both midlatitude and tropical systems leading to a complex regional meteorology that hitherto has not been much studied compared to other parts of South Africa. Here, the ongoing drought is examined in the context of long-term trends and the interannual rainfall variability of the region. Although the region has experienced drought in all seasons since 2015, focus here is placed on the spring (September–November) which shows the most consistent and robust signal. On average, this season contributes between about 25–35% of the annual rainfall total. Based on CHIRPS data, it is found that this season shows a significant decreasing trend in both rainfall totals as well as the number of rainfall days (but not heavy rainfall days) for spring over most of the province since 1981. On interannual time scales, the results indicate that dry (wet) springs over the Eastern Cape are associated with a cyclonic (anticyclonic) anomaly southeast of South Africa as part of a shift in the zonal wavenumber 3 pattern in the midlatitudes. Over the landmass, a stronger (weaker) Botswana High is also apparent with increased (decreased) subsidence over and near the Eastern Cape which is less (more) favourable for cloud band development and hence reduced (enhanced) rainfall during dry (wet) springs. Analysis of mid-century (2040–2060) CMIP5 rainfall projections suggests that there may be a flattening of the annual cycle over the Eastern Cape with the winter becoming wetter and the summer drier. For the spring season of interest here, the multi-model projections also indicate drying but less pronounced than that projected for the summer.

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Numerical simulation of a mesoscale convective system over the east coast of South Africa

Abstract: identified that the development of the MCS and the heavy nocturnal precipitation was due to a combination of the continuous moisture supply into the region, a conditionally unstable atmosphere, and uplift due to low level convergence and the local topography.11

Cited by 10 publications

References 97 publications

Processes driving thunderstorms over the Agulhas Current

Processes driving thunderstorms over the Agulhas Current

Major Mechanisms of Atmospheric Moisture Transport and Their Role in Extreme Precipitation Events

Drought in the Eastern Cape region of South Africa and trends in rainfall characteristics

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