Abstract
—The climatology of cyclone formation and behaviour in the South-West Indian Ocean, including landfall in Mozambique and Madagascar, has been investigated. The records used were obtained by merging track data from the Joint Typhoon Warning Centre with data from La Reunion – Regional Specialised Meteorological Centre. During the period 1980-2007, 12.5 cyclones per year were formed; 85% of which in November-April (the cyclone season). The number of intense tropical cyclones increased from 36 during 1980-1993 to 56 during 1994-2007, parallel to a simultaneous but smaller decrease in the number of tropical storms. This increase in intense tropical cyclones occurred at the same time as an increase in the mean sea surface temperature of 0.12˚C. This temperature increase seems insufficient to explain the increased activity. In addition, investigating a longer record (1952-2007) from the same sources indicates a long-term decrease in cyclone frequency as well as in landfall, although this was simultaneous with a substantial increase (about 0.3˚C) in sea surface temperature. However, it is recognised that records before 1980 suffer from too few wind intensity data. From 1980-2007, the number of land-falling cyclones was 64 (compared to 88 from 1952-1979), 16 of which came ashore in Mozambique and 48 in Madagascar. Seasonal variations in areas of genesis and preferred tracks are presented and discussed in relation to a number of indices. Minimum and mean sea surface temperatures for cyclone genesis are also estimated.Keywords: Tropical cyclones, Indian Ocean, Mozambique Channel, global change, sea surface temperatures, ENSO, landfall
Highlights
The present study examines tropical cyclone climatology of the South-West Indian Ocean (SWIO) based on a merged data set to achieve the maximum coverage
The Oceanic Niño Index (ONI), used for defining El Niño-Southern Oscillation (ENSO) is based on the running 3-m mean of ERSST.v3 SST anomaly for the Niño 3.4 region, i.e. 5°N-5°S, 120°-170°W, with 5 consecutive months warmer than or equal to +0.5° for El Niño and cooler than or equal to -0.5° for La Niña
According to Ho et al (2006) cyclone activity increases in the southern Indian Ocean, west of 75°E and decreases east of 75°E during El Niño compared to La Niña years
Summary
Alberto F.Mavume, Lars Rydberg, Mathieu Rouault and Johann R.E. Lutjeharms4 1Universidade Eduardo Mondlane, Faculdade de Ciências, Departamento de Física, PO Box 257, Maputo, Mozambique; 2University of Gothenburg, Department of Earth Sciences, Oceanography, Box 460, SE-405 30 Gothenburg, Sweden; 3Department of Oceanography, University of Cape Town, 7700 Rondebosch, South. The number of intense tropical cyclones increased from 36 during 1980-1993 to 56 during 1994-2007, parallel to a simultaneous but smaller decrease in the number of tropical storms. This increase in intense tropical cyclones occurred at the same time as an increase in the mean sea surface temperature of 0.12 ̊C. Investigating a longer record (1952-2007) from the same sources indicates a long-term decrease in cyclone frequency as well as in landfall, this was simultaneous with a substantial increase (about 0.3 ̊C) in sea surface temperature. Minimum and mean sea surface temperatures for cyclone genesis are estimated
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