4A.6
Intraseasonal Variability in the Equatorial Atlantic-West Africa during March-June
Guojun Gu, NASA/GSFC and Univ. of Maryland Baltimore County, Greenbelt, MD
Intraseasonal (30-70 days) variability in the equatorial Atlantic-West African sector during March-June is investigated using various recently-archived satellite measurements and the NCEP/DOE AMIP-II reanalysis daily data. The global connections of regional intraseasonal signals are first examined for the period of 1979-2006 through lagged-regression analyses of convection (OLR), stream function and vector wind anomalies at 200 and 850 hPa against a regional intraseasonal convective (OLR) index. The eastward-propagating features of convection can readily be seen, accompanied by coherent circulation anomalies, similar to those for the global tropical intraseasonal mode, i.e., the Madden-Julian Oscillation (MJO). The TRMM rainfall (3B42) anomalies regressed against both regional rainfall and OLR indices during the TRMM period (1998-2006) manifest similar propagating features as for the OLR anomalies during 1979-2006. The results hence tend to suggest that these regional intraseasonal signals might be closely associated with, or mostly a regional response to the MJO.
Atmospheric and surface intraseasonal variability during March-June of 1998-2006 are further explored using the high-quality TRMM Microwave Imager (TMI) sea surface temperature (SST), columnar water vapor, and cloud liquid water, and the QuikSCAT winds (2000-2006). Enhanced (suppressed) convection or positive (negative) rainfall anomalies approximately cover the entire basin (0-10N, 30W-10E) and are located within the anomalous westerly (easterly) flow regime. Positive SST anomalies appear about ten days earlier than the enhanced convection, and tend to be in the eastern basin. Coherent intraseasonal variations and features can also be seen in other components, as for the MJO identified in the Indian-equatorial west Pacific Oceans. Regional characteristics of these intraseasonal signals are further examined with a special focus on their spatial distributions and variations in the tropical Atlantic basin.
Recorded presentationSession 4A, African Climate: IV. West Africa
Monday, 21 January 2008, 4:00 PM-5:30 PM, 215-216
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