جغرافیا و پایداری محیط (Nov 2014)
Simultaneous Effects of NAO and SOI Phases on Iran’s Climate
Abstract
The present research attempts to study about effectiveness accessibility of Iran’s climate by created changes during the extreme and normal phases of NAO and SOI events. Thus the temperature and rainfall data of 32 synoptic stations from all part of the country has been gathered during the period of 1960 to 2005. The study of relevance between this information and teleconnection data of NAO and SOI by analytical and perceptive statistics methods suggested that the autumn temperature and rainfall has the most relationship with mentioned indexes. So the rest of study focused on relation between time series of the indexes and autumn temperature and rainfall. Because there was no reasonable relation between each individual index and the climate data, the simultaneous effects of both indexes on Iran’s climate were studied. In this way, nine various states were created in the related with the directions of the indexes trend, and the subsequent research were implementing on then. All simultaneous states of indexes and the temperature and rainfall circumstances of the country were investigated again. It was determined that the behaviors of NAO and SOI have the most influence on Iran’s climate, when they are not at the same direction and also are in the extreme level.Occurring the negative SOI and positive NAO simultaneously, the Siberian High, Azores High, and Iceland Low centers are amplified with respect to a long time average which results in the incidence of SH system to Iran reducing the temperature. Besides, the Siberian High, Azores High, and Iceland Low centers are weakened as the positive SOI and negative NAO are occurred which leads to reducing the entrance of SH system and a decrease in precipitation in Iran.
