Analysis Spatiotemporal Variation of Atmospheric Humidity in Iran during 1979-2013

Water vapor is an essential climate variable. Water vapor through latent heat exchanges is the principal method of energy transport through the global atmosphere and it is a dominant greenhouse gas (Held and Soden 2000). Over the oceans، warmer surface temperatures will likely lead to increased evaporation and therefore greater specific humidity، but an approximately constant relative humidity (RH); the greater concentration of water vapor will in turn warm the surface further، since water vapor is a potent greenhouse gas (GHG) (IPCC، 2007; Dessler and Sherwood، 2009). As temperatures rise، the atmosphere’s capacity to hold water increases. As water vapour can be transported vertically through convection and subsidence، and horizontally by atmospheric circulation، changes in surface absolute moisture can effect changes in moisture aloft (McCarthy & Toumi، 2004). The Clausius-Clapeyron relation yields exponential increases in the atmosphere’s water holding capacity with increasing T at approximately 7 % K-1 (Manabe & Wetherald، 1967; Allen & Ingram، 2002; Trenberth et al.، 2005). Knowledge about changes in water vapor in the upper troposphere and lower stratosphere is important because it can result in strong alterations in radiative forcing، hydrological cycle، precipitation intensity، human and biosphere. The aim of this study is analysis spatiotemporal variation of atmospheric humidity of Iran during 1979-2013.