A study of climate and weather variability over the tropical southwest Indian Ocean

摘要: The climatology and variability of summer convection circulation over the tropical southwest Indian Ocean is investigated using satellite imagery, routine synoptic observations, outgoing longwave radiation (OLR) data, sea surface temperatures (SST) areal averaged rainfall departures. OLR has a −0.90 correlation with departures minimum (ITCZ) in January February lies across 10°S latitude, extending further south near Madagascar. intensity ITCZ greatest longitudes 20–35°E northern Zambia considerably reduced SW Ocean. Spatial correlations are analyzed for standardized OLR, SST. change sign coherent fashion, creating climatic dipole between southern Africa Interannual trends examined through analysis January–February zonal meridional wind indices constructed from significantly correlated variables at Zimbabwe, Madagascar Mauritius. Circulation dominated by quasi-decadal cycles trend inereasing westerly winds. Zonal shear alternates easterly (barotropic) to together SST appears regulate frequency cyclogenesis. Areally exhibit 6.25 year NE 12.5 18.75 respectively. Summer winds Zimbabwe out phase negatively most summers. presence weather systems assessed daily Hovmoller-type imagery composites. Convective structure transient waves 10°–20°S latitude band, periods 15–20 days common. more prominent summers increased contribute fluctuations SE Africa.