Study of the number of rainy days and effect of ENSO phenomenon at the country level

In this study the role of ENSO atmospheric-ocean phenomena in variability of the number of country rainy days was studied. For assessment of ENSO role indexes of SOI, MEI, NINO1+2, NINO3.4, NINO3, NINO4, NOI, SST and PNA were used. Zoning map of the country and the number of rainy days showed, rainy days of country wide level is between 15 to 56 days in year, which indicated that more than half of the country is dry annually, between 309 to 350 days without rainfall. The results of applying the Pierson correlation analysis, expressed the relationship between ENSO climatic indexes and the number of rainfall days annual stations isometropia of country. Among the climatic indexes, the correlation between NINO3 index with rainy days was the maximum number of stations and SST index were in the next rank. However PNA climatic index with rainy days showed only four stations had correlation and that PNA index is a weak one. Comparing the number of rainy days in the warm phases (El-Nino) and cold (La-Nina) showed the number of rainy days in El-Nino was more than La Nina phase that confirmed, the occurrence of El-Nino phase increase the number of rainy days of country. Among the stations studied, the highest correlation with the number of rainy days was in Nino3 index Sabzevar (0.49) and the lowest correlation in Shiraz and Bushehr stations (0.28). Calculated correlation coefficient between the number of rainy days with Nino3 and other indexes, expressed the important role of other factors such as geographical factors. So that in the area of South and South-East to Northeast, the correlation or the effect of the ENSO phenomenon increases.