Intra-seasonal convective structure and evolution over tropical East Africa

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 17:83-92 (2001) - doi:10.3354/cr017083 Intra-seasonal convective structure and evolution over tropical East Africa Emmanuel J. Mpeta*, Mark R. Jury Environmental Studies Dept. University of Zululand, KwaDlangezwa 3886, South Africa *Permanent affiliation: Tanzanian Directorate of Meteorology, Dar es Salaam, Tanzania. E-mail: mjury@pan.uzulu.ac.za 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 ECMWF data. 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 period November 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 sequences reveal 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 from the Guinea/Congo region. Eastward propagating OLR anomalies couple with zonal circulations, suggesting that a transient Walker cell emerges periodically from East Africa. KEY WORDS: Intra-seasonal climate · East Africa Full text in pdf format PreviousExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 17, No. 1. Online publication date: July 04, 2001 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2001 Inter-Research.