A study of climate and weather variability over the tropical southwest Indian Ocean
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The climatology and variability of summer convection and circulation over the tropical southwest Indian Ocean is investigated using satellite imagery, routine synoptic observations, outgoing longwave radiation (OLR) data, sea surface temperatures (SST) and areal averaged rainfall departures. OLR has a −0.90 correlation with rainfall departures and the OLR minimum (ITCZ) in January and February lies across the 10°S latitude, extending further south near Madagascar. The intensity of ITCZ convection is greatest in the longitudes 20–35°E over northern Zambia and is considerably reduced over the SW Indian Ocean. Spatial correlations are analyzed for standardized departures of OLR, rainfall and SST. The correlations change sign in a coherent fashion, creating a climatic dipole between southern Africa and the SW Indian Ocean. Interannual trends are examined through analysis of January–February zonal and meridional wind indices constructed from significantly correlated variables at Zimbabwe, Madagascar and Mauritius. Circulation variability is dominated by quasi-decadal cycles and a trend of inereasing westerly winds. Zonal wind shear alternates from easterly (barotropic) to westerly and together with SST appears to regulate the frequency and intensity of tropical cyclogenesis. Areally averaged rainfall departures exhibit 6.25 year cycles in NE Madagascar and 12.5 and 18.75 year cycles in SW Madagascar and Zimbabwe, respectively. Summer rainfall and meridional winds in NE Madagascar and Zimbabwe are out of phase and negatively correlated in most summers. The presence of synoptic weather systems is assessed using daily Hovmoller-type satellite imagery composites. Convective structure is dominated by transient waves in the 10°–20°S latitude band, with periods of 15–20 days common. The waves are more prominent in summers with increased easterly shear and contribute to fluctuations in rainfall over SE Africa.
- Anyamba, E. K., Kiangi, P. M. R., Patnaik, J. K., 1982: The mean horizontal motions over the African atmosphere during the southern summer. Proc. Tech. Conf. Climate of Africa, WMO 596, Tanzania, 158–170.
- Arkin, P. A., Kousky, V. E., Janowiak, J. E., O'Lenic, E. A., 1986: Atlas of the tropical and subtropical circulation derived from NMC operational analyses,NOAA Atlas 7, Climate Analysis Centre, Washington, DC.
- Asnani, G. C., 1982: The climate of Africa, including a climate alert system, Proc. Tech. Conf. Climate of Africa, WMO 596, Tanzania, 107–129.
- Beltrando, G., Cadet, D. L., 1990: Interannual variability of the short rain season in E Africa: relationship with general atmospheric circulation.Veille Climatique,33, 19–37, Paris.
- Cadet, D. L., Diehl, B. C., 1984: Interannual variability of surface fields over the Indian Ocean during recent decades.Mon. Wea. Rev.,112, 1921–1935.
- Chang, C. P., 1970: Westward moving cloud patterns in the tropical Pacific as seen from time-composite satellite photographs.J. Atmos. Sci.,27, 133–138.
- Crutcher, H. L., Quayle, R. G., 1973: Mariners worldwide climatic guide to tropical storms at sea.Naval Weather Service, Washington, 426 pp.
- Daniels, J. M., Vernekar, A. D., 1988: Influence of sea surface temperature on intra- and inter-seasonal variations of the ITCZ.Proc 7th Conf. Ocean-Atmosphere Interaction, Anaheim Calif, J 61–64.
- Dennet, M. D., 1978: Variations of rainfall and seasonal forecasting in Mauritius.Arch. Met. Geophy. Biokl. B,25, 359–370.
- Diab, R. A., 1988: Rainfall-producing systems in Natal. Final Rep to FRD, CSIR, Pretoria, 126 pp.
- Dunn, P., 1985: An investigation into tropical cyclones in the SW Indian Ocean, Flood studies: Tech. note 1, Dept Water Affairs, Pretoria, 33 pp.
- Gordon, A. L., Lutjeharms, J. R. E., Grundlingh, M. L., 1987: Stratification and circulation at the Agulhas retroflection.Deep-Sea Res.,34, 565–599.
- Gruber, A., Varnadore, M., Arkin, P. A., Winston, J. S., 1986: Monthly and seasonal outgoing longwave radiation and anomalies.NOAA Tech. Rep. NESDIS 26, Washington DC.
- Halpert, M. S., Ropelewski, C. F., 1989: Atlas of tropical sea surface temperatures and surface winds.NOAA Atlas 8, Washington, 226 pp.
- Hastenrath, S., 1985:Climate and Circulation of the Tropics. Doordrecht, D. Riedel Pub.: 455 pp.
- Harrison, M. S. J., 1986: A synoptic climatology of South African rainfall variations. PhD Thesis, Univ. of Wits., Johannesburg, 341 pp.
- Krishnamurti, T. N., 1979:Compendium of Meteorology, 2, 4, Tropical Meteorology, Ch 10: Indian Ocean disturbances during the northern winter season, WMO 364, 175–185.
- Janowiak, J. E., 1988: An investigation of interannual rainfall variability in Africa.J. Climate,1,3, 240–255.
- Jury, M. R., Pathack, B., Campbell, G., Wang, B., Landman, W., 1991 a: Transient convective waves in the tropical SW Indian Ocean.Meteorol. Atmos. Phys.,47, 27–36.
- Jury, M. R., Pathack, B., Sohn, B. J., 1991 b: Spatial structure and interannual variability of summer convection over southern Africa and the SW Indian Ocean.S. A. J. Sci., (in press).
- Jury, M. R., Pathack, B., Legler, D. M., 1991 c: The structure and variability of surface circulation anomalies over the tropical SW Indian Ocean in the southern summer.S. A. J. Mar. Sci.,11, 1–12.
- Lee, C.-S., Edson, R., Gray, W. M., 1989: Some large-scale characteristics associated with tropical cyclone development in the N Indian Ocean during FGGE.Mon. Wea. Rev.,117, 407–426.
- Love, G., 1985: Cross-equatorial interactions during tropical cyclone genesis.Mon. Wea. Rev.,113, 1499–1509.
- Lyons, S. W., 1991: Origins of convective variability over equatorial southern Africa during austral summer.J. Climate,4, 23–39.
- Matarira, C. H., 1988: A diagnostic study of atmospheric circulation changes associated with rainfall anomalies over SE central Africa, PhD Thesis, Univ. of Thessaloniki, available at the Meteorological Headquarters, Harare Zimbabwe, 183 pp.
- McBride, J. L., Keenan, T. D., 1982: Climatology of tropical cyclone genesis in the Australia region.J. Climatol.,2, 12–33.
- Nicholson, S. E., Kim, J., Hoopingarner, J., 1988:Atlas of African rainfall and its interannual variability. Florida State Univ., 237 pp.
- Padya, B. M., 1989:Weather and Climate of Mauritius. Mauritius, M. Gandhi Inst.: 283 pp.
- Riehl, H., 1954:Tropical Meteorology. New York: McGraw-Hill, 392 pp.
- Riehl, H., 1979:Climate and Weather of the Tropics. London: Academic Press, 611 pp.
- Shannon, L. V., Agenbach, J. J., Walker, N. D., Lutjeharms, J. R. E., 1990: A major perturbation in the Agulhas Retroflection area in 1986.Deep Sea Res.,37, 493–512.
- Stevens, G. L., 1990: On the relationship between global water vapour and sea surface temperature over the oceans.J. Climate,3,6, 634–645.
- Taljaard, J. J., 1972: Synoptic meteorology of the southern hemisphere, in Meteorology of the Southern Hemisphere.Meteor. Monographs,35, 139–213.
- Taljaard, J. J., 1987: The anomalous climate and weather systems over South Africa during summer 1975–1976, Tech Paper 16, SA Weather Bureau, Pretoria, 80 pp.
- Tyson, P. D., 1986:Climate Change and Variability in Southern Africa, Cape Town: Oxford Univ. Press, 220 pp.
- VanHeerden, J., Terblanche, D. E., Schulze, G. C., 1988: The southern oscillation and South African summer rainfall.J. Climatology,8, 577–597.
- Vowinckel, E., 1956: The weather and climatology of the southern Mozambique Channel, Miscelanea Geofisicia Pub. Serv. Met. Angola, Luanda, 63–86.
- Walker, N. D., 1989: Sea surface temperature-rainfall relationships and associated ocean-atmosphere coupling mechanisms in the southern African region, PhD Thesis, Oceanography Dept., Univ. Cape Town, 173 pp.
- Williams, J. B., 1990: Some temporal and regional variations of climate in Madagascar, Tech. Rep. Overseas Devep. Nat. Res. Inst., Chatham Marine, Kent, pp 144.
- Wright, P. B., Mitchell, T. P., Wallace, J. M., 1988: Relationships between surface observations over the global oceans and the southern oscillation, NOAA Data Rep. ERL PMEL-12, 61 pp.
- A study of climate and weather variability over the tropical southwest Indian Ocean
Meteorology and Atmospheric Physics
Volume 47, Issue 1 , pp 37-48
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