On the relationships between ENSO and autumn rainfall in Iran.

An investigation of the relationships between Iranian autumn rainfall and the El Nino–Southern Oscillation (ENSO) phenomenon was explored for the period 1951–1990. A negative correlation between the Troup Southern Oscillation Index (SOI) and rainfall data was found for almost all of Iran. The relationships were found to be stronger and more consistent over some regions comprising the southern foothills of the Alborz Mountains, northwestern districts and central areas. For the other parts of the country, correlations were found to be either less significant or non-stationary. It was determined that the associations between SOI and rainfall over central parts of Iran have persistently improved for the recent period studied. The impacts of ENSO 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 Nina 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 predicted a season ahead for some parts of the country. A mechanism for the influence of the ENSO cycle on Iranian rainfall is suggested. Copyright © 2000 Royal Meteorological Society

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