Summer Rainfall over the Sahel Modeled by the Atmospheric Centers of Action
Abstract
The Sahel zone has experienced a prolonged drought since the late 1950s, and an important problem in climate change is to explain the trend and the interannual variability of Sahel precipitation in this period. In this paper we show that the atmospheric pressure distribution in the region around North Africa is dominated by two centers of action, the Azores High to the west and the South Asia Low to the east. Statistical analysis shows that Sahel precipitation is influenced significantly by the east-west displacements of the Azores High: when the High drifts eastward towards Africa, Sahel experiences diminished rainfall and vice versa. The impact of the South Asia Low on Sahel precipitation is stronger than that of the Azores High. In the years in which the Low is deeper greater amounts of precipitation occurs over the Sahel and vice versa. We present a regression relationship for July-September Sahel precipitation in which the independent variables are the Azores High Longitude and the South Asia Low pressure. This two- parameter model simulates the decrease in the precipitation that occurred in the mid 1950s and the increase that has been seen since the mid 1980s. Moreover, it explains 50 percent of Sahel rainfall variability over 1950-2000. The distributions of anomalies in vertical velocity, humidity and horizontal winds support the statistical results.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.H33E0946H
- Keywords:
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- 3305 ATMOSPHERIC PROCESSES / Climate change and variability