On the decoupling of the IODZM from southern Africa Summer rainfall variability

Abstract

The decoupling of the Indian Ocean Dipole/zonal mode (IODZM) from southern Africa's dominant mode of rainfall variability since 1997 is investigated. An approach of using variability as the major descriptive parameter for the observational time series is adopted. This approach enables the identification of epochs differentiated by the examination of low‐frequency signals in the climate data of the Indian Ocean basin. The period of analysis stretches from 1922 to 2008 and focuses on the October to December season so as to capture the most active component of the IODZM events that coincide with the early summer rainfall. The period around 1997/1998 is noted as an important climate regime transition in the Indian Ocean climate system whereas the well known 1976/1977 climate shift appears to be of lesser significance in the region. The temporal manifestation of statistical parameters of the IODZM matches significantly with those of basic atmospheric variables in the western subtropical South Indian Ocean and consistently identifies 1961 and 1997 as important turning points in the Indian Ocean climate system. However, although the relatively high variability of the atmospheric variables quickly decreases after 1997, a corresponding fall in the rainfall and IODZM time series variability is not found. Instead, an abrupt reduction in the correlation between the two time series to insignificant values occurs after 1997. Coincidentally, notable cooling over the western South Indian Ocean is observed during the pre‐1997 positive IODZM events, followed by a synchronized anomalous warming and cooling over the respective western and eastern subtropical South Indian Ocean during the events after 1997. This change is associated with an eastward displacement of the South Indian Ocean anticyclone after 1997. Thus, 1997 is a significant year in the Indian Ocean climate system when a discontinuity acts to decouple the IODZM from the dominant mode of regional rainfall variability. Copyright © 2011 Royal Meteorological Society

Variability of upper‐ocean characteristics and tropical cyclones in the South West Indian Ocean

“…The analysis performed here suggests that an important change occurred after the 1997/1998 El Niño, consistent with Manatsa et al . [] who provided evidence that a turning point in the climate of the Indian Ocean occurred around this time. An epochal variability of T dy trends pre‐1997/1998 and post‐1997/1998 shows large areas of decreasing trend near Madagascar pre‐1997 and an increasing trend in the Mozambique channel and in the central tropical South Indian Ocean after 1998, consistent with Goni et al .…”

“…An important turning point in the climate of the Indian Ocean region occurred around 1997/1998, which was shown to be associated with significant changes in sea surface temperature, chlorophyll, and atmospheric circulation over the Indian Ocean [ Manatsa et al ., ; Dilmahamod et al ., ] and indeed a jump can be seen about this time in Figure in T dy and BLT, and to a lesser extent, SST. It is therefore of interest to look at the epochal variability, pre‐1997/1998 and post‐1997/1998 in T dy over the Indian Ocean.…”

Pacific sea surface temperature linkages with Tanzania's multi‐season drying trends

“…It is interesting to note that the date of MAMJ decline coincides with a shift (reduction) in the strength of the southern Africa/Indian Ocean Dipole correlation (Manatsa et al ., ). After the 1997/1998 El Niño, we observe an enhanced east to west equatorial Pacific SST gradient, a La Niña‐like circulation response, and a large decline in East Africa boreal spring rainfall (Lyon and DeWitt, ; Sohn et al ., ; Dong and Zhou, ; Lyon et al ., ; Funk and Hoell, ).…”

“…Manatsa et al . () find that the southern Africa response to Indian Ocean Dipole events is substantially weaker in this later era. This study and Funk et al .…”

Tailoring seasonal climate forecasts for climate risk management in rainfed farming systems of southeast Zimbabwe

“…It has long been established that a statistically significant correlation exists between ENSO phase shifts and interannual fluctuations in Zimbabwe summer rainfall (Cane et al, 1994;Manatsa et al, 2011b;Unganai and Mason, 2002). The warm phase of ENSO (El Niño) tends to be generally associated with periods of low rainfall and enhanced risk of drought in Zimbabwe, while ENSO's cold phase (La Niña) has a tendency to bring periods of high rainfall and increased risk of flooding.…”