Monday, 15 January 2007
Links between West Africa monsoon variability and summer anomalies in the western Mediterranean
Exhibit Hall C (Henry B. Gonzalez Convention Center)
The West African monsoon has an impact on the North Atlantic anticyclone and on the Libyan high. The North Atlantic anticyclone intensifies during the monsoonal season and the anomaly position is related to the intensity and penetration of the monsoon. To the north-east of the monsoonal region the Libyan high controls the anticyclonic flow over the West Mediterranean sea. In specific condition, the Libyan high can be displaced over the West Mediterranean sea to cover part of France as in summer 2003. During the boreal summer, fluctuations of the West Africa monsoon are known to produce significant changes of the regional atmospheric circulation which affects rainfall, moisture, temperature and wind, as far north as the central Sahara desert. Large shifts of the monsoon are partly connected to the anomalous warming of the sea surface in the Guinea Gulf near the equator, providing a connection between the Guinean coastal region and the Sahel through both the thermodynamics and the dynamics, i.e. through the combination of different mechanisms and processes like: evaporation, atmospheric moisture content and its convergence and thus anomalous latent heat, as well as land/sea temperature gradient, latitudinal shift of the inter-tropical convergence zone, modified flux convergence, anomalous rising/subsidence patterns. Through statistical analysis of global NCEP/NCAR reanalysis we show the relation between the intensity of the West Africa monsoon with the position and the intensity of the Libyan high and the relative impact on the summer temperature anomaly and on the occurrence of extremely hot spells over the Western Mediterranean region, and on the subsequent enhancement of drought condition.