Recent changes in precipitation, ITCZ convection and northern tropical circulation over North Africa (1979-2007)

This article focuses on some recent changes observed in the Tropics with special emphasis on the African monsoon region using high-resolution gridded precipitation from the Climatic Research Unit (period 1979-2002), outgoing longwave radiation at the top of the atmosphere from the National Oceanic and Atmospheric Administration and atmospheric reanalyses from the Climate Prediction Center (NCEP-DOE2, period 1979-2007). The results show a rainfall increase in North Africa since the mid-90s with significant northward migrations of rainfall amounts, i.e. +1.5 degrees for the 400 mm July to September isohyets, whereas deep convection has significantly increased and shifted northward. The subsidence branch of the northern meridional overturning has also been reinforced and shifted by 1 latitude northward in winter. At larger scale, an unambiguous reorganisation of the circulation with increasing subsidence in high troposphere over the Mediterranean and increasing ascendance in the African Intertropical Convergence Zone in northern summer has been noticed in the meridional cell overturning. After 1993-1994, the migration of the Saharan heat low towards northwest has been more marked (+1 degrees to +2 degrees in latitude; -1 degrees to -2 degrees in longitude), whereas its centre intensified at the peak of the tropical rainy season (+10 gpm thickness in the 700-925 hPa layer). These changes are associated with significant reinforcements of the southwesterly low-level winds and Tropical Easterly jet and with a northward shift of the African Easterly jet. Analyses of Global Circulation Model outputs issued from Intergovernmental Panel on Climate Change (A1B scenario and from forced experiments on the ARPEGE-climat (Action de Recherche Petite Echelle Grande Echelle) and Atmospheric Global Circulation Model show that at least part of these changes could be due to the recent warming observed in the Mediterranean/Saharan region. Copyright (C) 2010 Royal Meteorological Society