Seasonal asymmetries in the lag between insolation and surface air temperature over Iran during 1971–2017

Abstract

The seasonal cycle in surface air temperature reflects the systematic variation in incoming solar radiation during a year. The current study focused on spatiotemporal analysis of the seasonal asymmetries in the lag between insolation and surface air temperature over Iran and the long-term trend over Iran. To do this, daily gridded surface air temperature data with spatial resolution of 0.25° × 0.25° over Iran during period 1971–2017 has been used. The results demonstrated that the seasonal cycle of surface air temperature did not coincide on annual harmonic. The time lag of maximum surface air temperature between insolation forcing and maximum surface air temperature response varies from 1 to 48 days across Iran. Maximum surface air temperature shows short lags over southeastern regions and long lags over western and northwestern regions. The time lag of minimum surface air temperature relative to winter solstice is less variable than maximum surface air temperature and differs from 26 to 48 days across Iran. The seasonal asymmetries (ASYM) which defined as the time lag of maximum surface air temperature relative to summer solstice minus the time lag of minimum surface air temperature relative to winter solstice generally showed positive values over the northwestern and western regions, indicating prolonged spring. Negative values over the southeastern, eastern and southwestern coastal regions of the Caspian Sea in the north, showing that the winter minimum surface air temperature is delayed more than the summer maximum surface air temperature. Most areas over the country have encountered negative trends in the time lag of minimum surface air temperature. These results suggest that changes in seasonal surface air temperature lags can be a potential predictor of shifting in climatic parameters at a seasonal time scale.