Intra-seasonal convective structure and evolution over tropical East Africa

Climate Research

Emmanuel J. Mpeta¹  Mark R. Jury¹ 

关键词: Intra-seasonal climate;    East Africa;   

DOI  :  10.3354/cr017083

来源: Inter-Research Science Publishing

【 摘 要 】

ABSTRACT: Intra-seasonal convection oscillations over southwestern Tanzania during the December to February season are examined using 15 yr (1979 to 1994) of pentad Outgoing Longwave Radiation (OLR) data and kinematic/thermodynamic parameters from ECMWFdata. Most significant spectral energy for an area-averaged OLR index is concentrated in periods of 16 to 33 d. Time-longitude diagrams of filtered OLR, and zonal wind anomalies at 850 hPa averaged over the 7.5 to 10°S latitude band for the periodNovember to May reveal eastward (62%), westward (11%) and quasi-stationary convective (27%) features. Phase speeds for transient cases are in the range of 2 to 8 m s^-1. In the eastward propagating case study, 1 to 15 January 1993, map sequencesreveal that deep convection shifts northeastward as a southern mid-latitude trough couples with the ITCZ. Convective events over tropical east Africa are associated with an influx of northeasterly Indian monsoon flow followed by increased westerlies fromthe Guinea/Congo region. Eastward propagating OLR anomalies couple with zonal circulations, suggesting that a transient Walker cell emerges periodically from East Africa.

【 授权许可】

Unknown