Document Type : Science - Research
Abstract
In order to recognize Semnan weather types, in this research 7 variables were studied in Semnan synoptic station from Farvardin,1st,1358 to Esfand, 29th,1382. Cluster analysis on the standardized matrix of data(stnd9094,18) and linking days on the basis of ward method showed that, Semnan has 5 weather types(WT) including:1. Moderate WT, 2. Hot & windy WT, 3.Very cold, Rainy & foggy WT, 4. Very hot, dry & windy WT 5- Very cold & frosty WT. Based on this research results,very hot , dry and windy WT is the most dominant and durable, and Moderate WT is the least frequent and short-lived weather types of Semnan. For every type one day was selected as the representative day. Monthly and yearly frequency of each type was estimated. It was found that the yearly frequency of types has changed since three decades ago. At the end ،the relationship of these types to circulation patterns of the middle level of atmosphere was investigated and to appear that ، the event of each type is affected by the specific circulation patterns.
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