HR: 1340h
AN: A43B-0053    [Abstracts]
TI: The first Guinean rainy season and role of the Subtropical Jet of the Northern hemisphere
AU: * Samuel, L
EM: louvets@u-bourgogne.fr
AF: Centre de Recherches de Climatologie, 6 Boulevard Gabriel, Dijon, 21000 France
AU: janicot, s
EM: serge.janicot@lodyc.jussieu.fr
AF: LODYC, Place jussieu, Paris, 7505 France
AB: The results presented come from studies relating to the mechanisms associated with the annual cycle of the InterTropical Convergence Zone (ITCZ) over West Africa. We have looked at the determination of the onset of the first rainy season over the Guinean coast and at understanding the mechanisms which are associated to this onset, with an aim of improving its forecast. By analysing the fluctuations of OLR and rainfall indexes, it is shown that the mean date (called T0) of this onset is the April 10 over the period 1979-2000 . A wavelet analysis highlights that OLR indexes have strong periodic fluctuations, between 25 and 70 days, around the date of onset, in connection with the installation of the first rainy season. By using composite analyses of mean atmospheric circulation at 925 hPa and 300 hPa, following and preceding T0, we point out an interaction between the variability of the convection over the Guinean coast and the undulations of the Subtropical Jet over Northern Africa. Thus, it is suggested that this onset would occur from an interaction between the meridian shift of the ITZC and an eastward propagation of the upper tropospheric trough in the Northern Subtropical Jet over the Maghreb region. The study of the year 1979 suggests interesting potentialities for the forecast of the date of the onset.
DE: 3374 Tropical meteorology
DE: 3309 Climatology (1620)
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting