On the relationships between ENSO and autumn rainfall in Iran

An investigation of the relationships between Iranian autumn rainfall and t he El Nino-Southern Oscillation (ENSO) phenomenon was explored for the peri od 1951-1990. A negative correlation between the Troup Southern Oscillation Index (SOI) and rainfall data was found for almost all of Iran. The relati onships were found to be stronger and more consistent over some regions com prising the southern foothills of the Alborz Mountains, northwestern distri cts and central areas. For the other parts of the country, correlations wer e found to be either less significant or non-stationary. It was determined that the associations between SOI and rainfall over central parts of Iran h ave persistently improved for the recent period studied. The impacts of ENS O on rainfall amounts during low and high phases of the SO index were also studied. It was found that during El Nino episodes, the amount of rainfall over various parts of the country was several times more than during La Nin a periods. The associations between SOI and surface air pressure data were found to be poor and insignificant. The possibility of rainfall forecasting was also explored and the results suggest that autumn rainfall could be pr edicted a season ahead for some parts of the country. A mechanism for the i nfluence of the ENSO cycle on Iranian rainfall is suggested. Copyright (C) 2000 Royal Meteorological Society.