Long-Lived Mesoscale Convective Systems over Eastern South Africa

A climatology of large, long-lived mesoscale convective systems (MCSs) over eastern South Africa for the extended austral summer (September–April) from 1985 to 2008 is presented. On average, 63 MCSs occur here in summer, but with considerable interannual variability in frequency. The systems mainly...

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Bibliographic Details
Published inJournal of climate Vol. 34; no. 15; pp. 6421 - 6439
Main Authors Morake, D. M., Blamey, R. C., Reason, C. J. C.
Format Journal Article
LanguageEnglish
Published Boston American Meteorological Society 01.08.2021
Subjects
Antarctic Oscillation
Climatology
Escarpments
Inflow
Interannual variability
Life cycle
Life cycles
Lower atmosphere
Mesoscale convective systems
Mesoscale phenomena
Moisture effects
Seasonal variation
Summer
Vertical shear
Water inflow
South Africa
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Summary:A climatology of large, long-lived mesoscale convective systems (MCSs) over eastern South Africa for the extended austral summer (September–April) from 1985 to 2008 is presented. On average, 63 MCSs occur here in summer, but with considerable interannual variability in frequency. The systems mainly occur between November and March, with a December peak. This seasonal cycle in MCS activity is shown to coincide with favorable CAPE and vertical shear profiles across the domain. Most systems tend to occur along the eastern escarpment and adjacent warm waters of the northern Agulhas Current with a nocturnal life cycle. Typically, initiation begins in the early afternoon, MCS status is reached midafternoon, maximum extent early in the night, and termination around midnight or shortly thereafter. It is found that most MCSs initiate over land, but systems that initiate over the ocean tend to last longer than those that develop over land. The results also show that there are differences in the seasonal cycle between continental and oceanic MCSs, with oceanic systems containing two intraseasonal peaks (December and April). There is a relatively strong positive relationship between the southern annular mode (SAM) and early summer MCS frequency. For the late summer, the frequency of MCSs appears related to the strength of the Mascarene high and Mozambique Channel trough, which modulate the inflow of moisture into eastern South Africa and the stability of the lower atmosphere over the region.
ISSN:0894-8755
1520-0442
DOI:10.1175/JCLI-D-20-0851.1