Lavaysse C., Flamant C., Janicot Serge. (2010). Regional-scale convection patterns during strong and weak phases of the Saharan heat low. Atmospheric Science Letters, 11 (4), p. 255-264. ISSN 1530-261X.
Titre du document
Regional-scale convection patterns during strong and weak phases of the Saharan heat low
Atmospheric Science Letters, 2010,
11 (4), p. 255-264 ISSN 1530-261X
The West African heat low, which is defined as a thermal depression generally below 700 hPa over West Africa, is stationary over the Sahara during the summer season and is often referred to as the Saharan heat low (SHL). This SHL displays synoptic and intra-seasonal pulsations of its intensity on time scales under 60 days. In this study, we analyse the regional-scale pattern of low troposphere dynamics and convective activity associated with weak and strong phases of the SHL during the summer, using 18 years (1984-2001) of concomitant European Centre for Medium-range Weather Forecasts re-analysis data and satellite observations of brightness temperature provided by the European Union-funded Cloud Archive User Service. Strong SHL phases, defined by an increase of low-level atmospheric thickness, are accompanied by (1) a positive anomaly of temperature in the low layers, (2) a strengthening of the monsoon flow, (3) both a negative anomaly of the divergence flux and an enhancement of the moisture advection over the central Sahel, (4) an intensification of the African easterly jet and (5) enhanced upward vertical motions located south of the inter-tropical discontinuity (ITD). These conditions appear to be favourable for the occurrence of convection over the central Sahel. The strongest, most widespread convective activity over the central and eastern Sahel occurs on the day when the SHL intensity is the strongest. In contrast, a significant decrease of the convective activity was detected over Senegal and to the West of the Jos Plateau. Opposite patterns are found during weak SHL phases, with a negative anomaly of convection over the central and eastern Sahel connected with anomalous subsidence south of the ITD and a negative moisture advection anomaly. Conversely, convection is seen to be enhanced along the Atlantic coast and particularly over Senegal.
Plan de classement
Sciences du milieu [021]
;
Limnologie physique / Océanographie physique [032]
