Evaluation of the Simultaneous Interactions of ENSO and MJO on the Occurrence of Dry and Wet Spells in Iran

Document Type : Original Article

Authors

1 Professor, Water Engineering Department, College of Agriculture, Shiraz University, Shiraz, Iran.

2 MSc., Member of the Atmospheric-Oceanic Researches Center, Shiraz University, Shiraz, Iran

3 MSc., Member of the Atmospheric-Oceanic Researches Center, Shiraz University, Shiraz, Iran.

Abstract

This study aimed the analyses of the simultaneous effects of two phenomena MJO and ENSO on the occurrence of dry and wet spells in Iran. The study showed that the concurrence of El Niño with the MJO negative phase (El-N) and La Niña with the positive phase of the MJO (La-P) have the highest frequencies. Precipitation amounts and the incidence of dry and wet spells were, therefore, compared for these two distinct alternatives. The results indicated that, in February, November, and December, a nationwide dry condition is expected when La Niña is coincided with the MJO positive phase. On the other hand, the pervasive wet spell is anticipated if the El Niño events have concurred with the MJO negative phase. Although rainfall amount in dry zones of the southern Iran is less than corresponding values in the northern half of the country, the simultaneous impact of the considered Oscillations on the occurrence of dry or wet episodes are more significant for the southern half. For instance, Iranshahr station, in southeastern part of the country, has experienced 96 percent reduction or 90 percent increase in precipitation compared to the longterm mean values as the (La-P) or (El-N) was prevailed. Furthermore, for some stations located in very dry zone of the country including (Birjand, Torbatheidarieh, Tabas, and Yazd) the occurrence of dry or wet periods in April was significantly associated to the (La-P) or (El-N) episodes. For these stations about 105 percent increase or 51 percent decrease compared to the longterm mean precipitation values is anticipated as (El-N) or (La-P) events was prevailed, respectively.
 

Keywords

References

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History

  • Receive Date: 07 April 2012
  • Accept Date: 29 October 2012

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