Document Type : Research Paper
Authors
Department of Water Engineering & Oceanic and Atmospheric Research Center, College of Agriculture, Shiraz University, Shiraz, Iran.
Abstract
Climate change has had a significant impact on atmospheric events, including the formation and distribution of clouds. Clouds play a vital role in the Earth's energy balance, and changes in their properties can produce different feedbacks on global warming. The aim of this study is to investigate the seasonal spatial- temporal significant changes in Total Cloud Cover (TCC) during six decades over Iran. The TCC variations during spring, autumn, and winter were compared in 6 decades based on gridded data and statistical methods, identifying significant changes over Iran.
Monthly reanalysis data of TCC were extracted from ECMWF, ERA5 version, with a spatial resolution of 0.25 degrees. The study period spans 60 years, from 1961 to 2021. Seasonal TCC time series were generated by averaging monthly data (three months per season) over the 60-year period. For each season, decadal TCC values were compared at each grid point. The significance of TCC differences between each decade and the compared decade was determined using the Mann-Whitney test, with random event repetition excluded through the Monte Carlo method with 10,000 iterations at a 95% confidence level.
The results indicated that spring TCC significantly increased in the southern and southwestern regions of Iran, while a notable decrease was observed in the northeastern, eastern, and southeastern regions. In autumn, significant changes were limited to small areas in the north, with most regions showing no considerable variation. However, in winter, a widespread reduction in cloud cover was observed over the country, particularly in the Zagros and southwestern regions. This decrease was more pronounced in the sixth decade (2011-2021) compared to previous decades, encompassing regions with moderate to high cloud cover. The findings of this study are highly significant in the context of climate change, particularly regarding the Earth's energy balance and precipitation patterns, which require further investigation.
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