Study of Decadal Variations of Warm Days and Nights over Iran

Variations and trends of thermal properties of the living environment have caused too much attention to the public and scientific communities. There is evidence of significant changes in the distribution of maximum and minimum temperatures in many parts of the world especially for minimum temperature during winter. In this paper, we deal with number of warm days and nights over Iran. According to ETCCDMI (Joint World Meteorological Organization Commission for Climatology (CC1) / World Climate Research Programme (WCRP) project on Climate Variability and Predictability (CLIVAR) Expert Team on Climate Change Detection, Monitoring and Indices), number of warm days (nights) are defined as number of days (nights) that maximum (minimum) temperature passes 9om percentile of the variable for period 1961-90. Based on obtained results of the first attempt on global view of changes of warm days and nights in 2002, all continents except parts of Canada, Iceland, China and Black Sea Area showed a positive trend for warm nights. Above results also shows about 15% increase in the number of warm nights with respect to 1961-90 base periods. Such a study conduced due to expecting more frequent extreme temperature. From greenhouse gas forced warming of climate. We worked on daily extreme temperatures of 20 Iranian synoptic stations for 1951-2003. Although, Islamic Republic of Iranian Meteorological Organization (IRIMO) currently has more than 160 synoptic stations, we only selected that number of them due to their reliable continuous extreme temperatures data We found positive trends for warm nights (Tn90) for most of the stations under study. These trends are significant except for Arak, Bandar Abbas, Birjand, Ghazvin, and Shahrekd These are almost consistent with many previous findings including our obtained results. We r also found both negative and positive trends for number of warm days (Tx90), which less j number of them is statistically significant. t

Keywords:

Warm days , Warm nights , Extreme temperature , and Greenhouse gases