Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

On the Relationship between Circulation Patterns, the Southern Annular Mode, and Rainfall Variability in Western Cape

Version 1 : Received: 24 May 2021 / Approved: 26 May 2021 / Online: 26 May 2021 (11:04:08 CEST)

A peer-reviewed article of this Preprint also exists.

Ibebuchi, C.C. On the Relationship between Circulation Patterns, the Southern Annular Mode, and Rainfall Variability in Western Cape. Atmosphere 2021, 12, 753. Ibebuchi, C.C. On the Relationship between Circulation Patterns, the Southern Annular Mode, and Rainfall Variability in Western Cape. Atmosphere 2021, 12, 753.

Journal reference: Atmosphere 2021, 12, 753
DOI: 10.3390/atmos12060753

Abstract

This study investigates circulation types (CTs) in Africa, south of the equator, that are related to wet and dry conditions in Western Cape, the statistical relationship between the selected CTs and the Southern Annular Mode (SAM), and changes in the frequency of occurrence of the CTs related to the SAM under the ssp585 scenario. Obliquely rotated principal component analysis applied to sea level pressure was used to classify CTs in Africa, south of the equator. Three CTs were found to have a high probability to be associated with wet days in Western Cape, and four CTs were equally found to have a high probability to be associated with dry days in Western Cape. Generally, the dry/wet CTs feature the southward/northward track of the mid-latitude cyclone, adjacent to South Africa; anti-cyclonic/cyclonic relative vorticity, and poleward/equatorward track of westerlies, south of South Africa. One of the selected wet CTs is significantly related to variations of the SAM. Years with an above-average SAM index correlate with the below-average frequency of occurrence of the wet CT. The results suggest that through the dynamics of the CT, the SAM might control the rainfall variability of Western Cape. Under the ssp585 scenario, the analyzed climate models indicated a possibility in the decrease of the frequency of occurrence of the aforementioned wet CT associated with cyclonic activity at the mid-latitudes, and an increase in the frequency of occurrence of the CT associated with enhanced SLP in the mid-latitudes.

Subject Areas

Western Cape; Southern Annular Mode; Circulation type; Africa south of the equator; mid-latitude cyclone

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