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Comments on “The South Indian Convergence Zone and Interannual Rainfall Variability over Southern Africa” and the Question of ENSO's Influence on Southern Africa

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  • 1 Department of Meteorology, The Florida State University, Tallahassee, Florida
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Abstract

Observational and modeling studies have produced extensive evidence of a link between rainfall variability in southern Africa and the Pacific ENSO phenomenon, as well as a link with sea surface temperatures in the Indian and, to a lesser extent, Atlantic Oceans. The consensus of various studies is that the direct cause of reduced rainfall in southern Africa, late in most ENSO events, is abnormally high SSTs in the oceans near Africa. These, in turn, are a response to ENSO. In contrast, the modeling study of Cook produces evidence that a direct link to ENSO is possible via a purely atmospheric response to the Pacific SST anomalies. In this note, this issue of direct versus indirect forcing is examined and Cook's model and its applicability to southern Africa are evaluated. Model output is shown to compare unfavorably with gauge-based climatologies and rainfall anomalies during ENSO events. This might account for the disagreement noted by Cook between her results and observational studies, as well as the disagreement between her results and those of other modeling experiments.

Corresponding author address: Sharon Nicholson, Dept. of Meteorology, The Florida State University, Tallahassee, FL 32306. Email: sen@huey.met.fsu.edu

Abstract

Observational and modeling studies have produced extensive evidence of a link between rainfall variability in southern Africa and the Pacific ENSO phenomenon, as well as a link with sea surface temperatures in the Indian and, to a lesser extent, Atlantic Oceans. The consensus of various studies is that the direct cause of reduced rainfall in southern Africa, late in most ENSO events, is abnormally high SSTs in the oceans near Africa. These, in turn, are a response to ENSO. In contrast, the modeling study of Cook produces evidence that a direct link to ENSO is possible via a purely atmospheric response to the Pacific SST anomalies. In this note, this issue of direct versus indirect forcing is examined and Cook's model and its applicability to southern Africa are evaluated. Model output is shown to compare unfavorably with gauge-based climatologies and rainfall anomalies during ENSO events. This might account for the disagreement noted by Cook between her results and observational studies, as well as the disagreement between her results and those of other modeling experiments.

Corresponding author address: Sharon Nicholson, Dept. of Meteorology, The Florida State University, Tallahassee, FL 32306. Email: sen@huey.met.fsu.edu

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