Climate variability in Iran in response to the diversity of the El Nino-Southern Oscillation

Through emitting large-scale planetary waves, the El Nino-Southern Oscillation (ENSO) contributes to the inter-annual climate variability in extra-tropical latitudes, although the impact may be intervened by the chaotic extra-tropical atmosphere. Using meteorological records of 45 synoptic stations across Iran during the period 1980-2016, impacts of La Nina and the eastern Pacific (EP) and central Pacific (CP) El Nino events on the inter-annual climate variability of Iran are investigated. The data for four EP El Nino, six CP El Nino and nine La Nina events are averaged to produce a composite view of ENSO. On average, annually Iran is anomalously wet during the EP El Nino and anomalously dry during La Nina, and the anomalies in both phases of ENSO are statistically significant. The impact of ENSO depends not only on the strength of the ENSO event in the tropical Pacific but also on the background climate state of the affected regions such that it is found that the impacts of La Nina and the EP El Nino are generally stronger over the warm and arid regions of Iran. It is also found that the ENSO signal changes with season in many climate zones of Iran, indicating complex interactions between ENSO and other seasonally different features of the climate system. In spite of the seasonal variation of the ENSO signal, most regions of Iran have experienced statistically significant anomalously dry conditions during winter and spring of La Nina events. The most noticeable difference between the two types of El Nino is observed over the Makran coastal plain of Iran where the EP and CP El Nino events have been associated with positive and negative precipitation anomalies, respectively.