87th AMS Annual Meeting

Tuesday, 16 January 2007: 2:15 PM
40 days periodicity mode of variability in the West and Central African monsoon
214C (Henry B. Gonzalez Convention Center)
Flore Mounier, CNRS, Paris, France; and S. Janicot
Poster PDF (1.4 MB)
One of the significant modes of convection at intra-seasonal timescale in the West and Central African summer monsoon, lately presented in the literature, is of 40 days periodicity (hereafter AM) and depicts over West and Central Africa a global modulation of convection. To go further into the understanding of the mechanism explaining AM, a statistical decomposition on a larger domain was performed and two modes modulating significantly the convection over Africa during the summer monsoon and correlated spatially and temporally with AM were obtained (hereafter M1 and M2). Then, using EOF reconstructed indexes over West Africa and composite analysis technique, contributions of M1 and M2 to AM and their tropical or subtropical teleconnections were detailed. M1 modulates slightly convection over the Guinean coast and is linked with a Kelvin wave type eastward propagating structure whose source is an East Pacific strong Madden-Julian Oscillation (MJO) signal. M2 modulates strongly convection over sahelian latitudes and Central Africa by developing a Rossby wave type structure propagating westward. This second mode is of particular interest as it presents some link with the Indian monsoon. It will be detail how subtropical mechanism in the Mediterranean region could explain this tropical teleconnection. Moreover, the 10 days lag between the development of M1 and M2 will be described, to understand how Kelvin waves, Rossby waves and MJO signals are associated a significant 40 days periodicity mode during West and Central African summer monsoon.

Supplementary URL: http://www.lodyc.jussieu.fr/~fmlod/ams4b4.pdf