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Internal variability in the moist African easterly Jet - African easterly wave system

Cornforth, Rosalind J and Hoskins, Brian J and Thorncroft, Chris D (2009) Internal variability in the moist African easterly Jet - African easterly wave system. In: The Royal Meteorological Society's 2009 Conference, 29 June- 2 July 2009, University of Reading.

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Abstract

A crucially important component of the West African Monsoon (WAM) and its associated rainfall variability, is the African easterly jet-African easterly wave (AEJ-AEW) system. Despite this, the system continues to pose a tough challenge for General Circulation Models (GCMs) to simulate realistically given the many physical processes involved, and given the multitude of spatio-temporal scales that they act over. For the West African population, any intra-seasonal rainfall variability impacts severely on the local agricultural and water resources, with equally severe consequences on health. This is especially true for the population living in the semi-arid Sahel region which endures the full impact of the AEJ-AEW system. Improved skilful prediction of the monsoon rains over longer time-scales would be of enormous benefit, aiding in the mitigation of high impact situations events such as the flooding during the summer of 2007, and the drought conditions of the last few decades. Here, the African Easterly jet - Easterly wave (AEJ-AEW) system was explored in an idealised model. Prescribed zonally symmetric surface temperature and moisture profiles determine the AEJ which becomes established through meridional contrasts in dry and moist convection. Importantly, moist AEWs were characterized by intermittent periods of growth and decay, with growth preceded by increased mean rainfall and later, weakening AEJs. These dependencies established an internal 8-10 day variability, consistent with intra-seasonal observations of 9-day rainy sequences. The observed 8-10 day cycle of rainy sequences related to the natural life cycle of the moist AEW and its interaction with the AEJ, the upper levels and the precipitation. This is a significant result from the moist life cycle as it offers a new view of the moist AEW life cycle and provides an alternative explanation for the observed intra-seasonal variability of the precipitation over NW Africa.

Item Type:Conference or Workshop Item (Poster)
Uncontrolled Keywords:moist convection; dynamics; intraseasonal variability; general circulation model; African Easterly waves; African Easterly Jet
Subjects:Atmospheric Sciences
ID Code:356
Deposited By:Dr Rosalind J Cornforth
Deposited On:07 Sep 2009 09:35
Last Modified:07 Sep 2009 09:35

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