INTRA-SEASONAL CONVECTIVE MODULATIONS OF THE WEST-AFRICAN MONSOON SYSTEM: ACTIVE PHASES AND PAUSES

HR: 1340h
AN: A43B-0052 [Abstracts]
TI: INTRA-SEASONAL CONVECTIVE MODULATIONS OF THE WEST-AFRICAN MONSOON SYSTEM: ACTIVE PHASES AND PAUSES
AU: * Samuel, L
EM: louvets@u-bourgogne.fr
AF: Centre de Recherches de Climatologie, 6 boulevard Gabriel, Dijon, 21000 France
AU: Bernard, F
EM: fontaine@u-bourgogne.fr
AF: Centre de Recherches de Climatologie, 6 boulevard Gabriel, Dijon, 21000 France
AU: Pascal, R
EM: crct3cyc@u-bourgogne.fr
AF: Centre de Recherches de Climatologie, 6 boulevard Gabriel, Dijon, 21000 France
AB: This study comes within the research of the characterization of the intra-seasonal modulations of the West Africa monsoon system during its annual cycle. Indeed, these fluctuations are not yet well understood and documented, particularly with regard to the main periods of installation of the various Western African rainy seasons and the phases of transition separating them. Also very few studies were interested in these onsets. Objective diagnostic analyses based on PCA decomposition, Varimax rotation and low-pass filters (若 1 month) are performed on the 5-day CMAP rainfall data over West Africa. The northward excursion of the rainbelt can be divided into 4 basic subperiods each composed of an equilibrium period (pause) followed by a rapid increase (active phase) of the system. We suggest easy criteria to automatically detect these events and propose a calendar for the 23 years. The pauses are centered around the 27th-28th March (pause #1), between the 29th April and 2nd May (pause #2), the 11th June (pause #3) and the 24th July (pause # 4) with standard deviations of 7-11 days. The end of the two main pauses (#1 and #3) are respectively associated with the onset of the first Guinean rainy season and the sahelian rainy season. In addition, it appears that these pluviometric modulations are not specific to the west-african monsoon system. Indeed, these can be detected over a larger scale and be linked to deep convective modulations propagating over the whole tropical region. For example, the deep convective anomalies associated with the pause #1 (pause #3) spread eastward (westward) and come from the Eastern Tropical Atlantic. Finally, regarding the daily Outgoing Longwave Radiation NOAA data, it appears that the amplitude of these convective modulations over West Africa is related to the activity of the Madden-Julian oscillation.
DE: 3309 Climatology (1620)
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting