Thunderstorms caused by the dryline over the plateau of Southern Africa.
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Source: Journal of Geophysical Research: Atmospheres
The dryline is a narrow area where there is a sudden change in moisture levels. It is often referred to as the “moisture front” and is similar to the cold and warm fronts that create temperature differences. Drylines typically occur in late spring and summer in various parts of the world, including the Great Plains in the US, India, and northern China (Schaefer, 1986, p. 549-572). They are often linked to the development of storms, including severe ones like tornadoes and squall lines.
In their study published in 2023, van Schalkwyk and colleagues examined the occurrence of drylines on the western Plateau of southern Africa between 2010 and 2021. Their research revealed that during early summer in the southern hemisphere (depicted in the left panel of the figure), moist air from the Indian Ocean merges with dry air from the west in the Zambezi River Valley, leading to the formation of drylines. By late summer, the channel of moist air shifts southward to the Limpopo River Valley (shown in the right panel of the figure). Through analysis of lightning data, the authors determined that seventy-six percent of drylines during austral summer (October-March) were accompanied by thunderstorms, which typically occur on the moist side of the dryline. Additionally, their findings indicate that these dryline-induced thunderstorms are often linked to a trough at 500 hPa.
This study is the first to comprehensively examine the formation of drylines in southern Africa and their impact on thunderstorm initiation. It provides a significant contribution to our knowledge of factors influencing intense weather events in the region.
Citation: van Schalkwyk, L., Blamey, R. C., Gijben, M., & Reason, C. J. C. (2023). A climatology of dryline-related convection on the western plateau of subtropical southern Africa. Journal of Geophysical Research: Atmospheres, 128, e2023JD038966. https://doi.org/10.1029/2023JD038966
—Yongyun Hu, Editor, JGR: Atmospheres
Text © 2023. The authors. CC BY-NC-ND 3.0
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