Abstract
In this study El Nino effects on rainfall in Iran is evaluated. Annual rainfall data of the selected rain gauging stations for the years when El Nino phenomenon has taken place (1973-2012), have been picked up. Next, annual rainfall of the years with and without El Nino phenomenon were compared and then analyzed (correlation is significant at the 0.01 level). Finally, percentage-frequency of the rainfalls influenced by warm Enso condition was obtained. Regarding that El Nino has different affect on rainfall under different regions of the world, the results approved that El Nino, increases rainfall across Iran plateau as annual rainfall is increased from south to north. While less increasing of rainfall is seen for coastal area. Results showed that El Nino causes increasing of annual rainfall in Iran.
Highlights
The term of El Nino phenomenon is used to some annual warm transoceanic current that flows southward right in prolongation of Peru and Ecuador coasts on Christmas time
Iran’s investigations based on rainfall and drought correlation using SOI parameter shows a negative meaningful correlation during autumn in many parts of it. In this investigation autumnal droughts during La Nina and heavy rainfalls during El Nino has been reported (e.g., Nazemosadat, 1999).The study has notified branching the Jet stream in southern regions of Pacific Ocean and has stated on adverse conditions during cold phases (Smith et al, 1986-1989).Outcomes investigations shows dominant role of sea surface temperature in controlling Atlantic and Indian oceanic rainfalls in comparison to El Nino and La Nina phenomena (Nicholson, 1997, Nickelson and Selato, 2000).Indirect El Nino impacts in changing atmospheric circulation patterns and it’s teleconection to other Paramers has referred (Khoshakhlagh, 1998).ENSO warm phases during autumn happen because Jet stream moving directions changes towards southern latitudes
The comparison data related to warm ENSO years and normal years, data about rainfall frequency percent were provided to be used in this investigation
Summary
The term of El Nino phenomenon is used to some annual warm transoceanic current that flows southward right in prolongation of Peru and Ecuador coasts on Christmas time. Iran’s investigations based on rainfall and drought correlation using SOI parameter shows a negative meaningful correlation during autumn in many parts of it In this investigation autumnal droughts during La Nina and heavy rainfalls during El Nino has been reported (e.g., Nazemosadat, 1999).The study has notified branching the Jet stream in southern regions of Pacific Ocean and has stated on adverse conditions during cold phases (Smith et al, 1986-1989).Outcomes investigations shows dominant role of sea surface temperature in controlling Atlantic and Indian oceanic rainfalls in comparison to El Nino and La Nina phenomena (Nicholson, 1997, Nickelson and Selato, 2000).Indirect El Nino impacts in changing atmospheric circulation patterns and it’s teleconection to other Paramers has referred (Khoshakhlagh, 1998).ENSO warm phases during autumn happen because Jet stream moving directions changes towards southern latitudes. Its meridian circulation movements bring wet and higher average rainfalls condition (Ghayour & Khosravy, 1989)
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