6/14/2023 0 Comments Software smada![]() ![]() The first and last snowfall days (calendar series) changed into Julian days. Then, after determining cold and warm peak times in summers and winters and basing them, the first and last days occur snowfall after warm and cold peak in each year have been respectively identified first and last snowfalls. After statistical review, snowfall data related to 38 stations which have at least 33 years continuous statistics from 1976 to 2008 is considered proper in order to be used in the research. Firstly, snowfall data of all synoptic stations is collected from Islamic Republic of Iran Meteorological Organization (IRIMO) in 3-hourly basis. The current research aims at identifying the role of polar vortex in creating cooling necessary for Iranian first and last snowfalls and finding a way for estimating its occurrence time. Cooling has several reasons, the most important of which may be approaching and locating of polar vortex trough or isolated cut-off low systems from polar vortex on a region. Starting and finishing points of seasons are affected by sun location, which is fixed yearly whereas snowfalls usually begin with cooling and they may happen in any time. ![]() The first and last days of snowfall may be considered as winters’ real starting and finishing points. ![]() From a climatological point of view, a winter day usually is symbolized with cold weather or a snowfall day.
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