عنوان مقاله [English]
In this study , for analyzing the spatiotemporal changes of the trend for continuity cooling waves of the North West of Iran, the minimum temperature data from year 1981 for 42 synoptic and Climatology stations, which have had maximum statistical length have been used. The extracted data, by using programming facilities in Surfer environment was interpolated and a matrix of size 5082 × 11323 ( cell* day) for a 31-years statistical period was obtained, which was used as a data base in the next stages. For the calculations, the programming facilities in Matlab software and for graphical operations, Surfer software have been used. The results obtained from the study showed that cooling waves, while having high spatial changes, has had sharp daily drops. While the under study areas at the east and north east regions has had the most spatial changes.
However, in the continuation of six and seven days, the spatial variation of coefficient variation is reduced. The results of the trend analysis indicate that the cold waves have experienced many changes during different periods, so that in the first period (1989-1980) and the third (2010-2000), the cooling waves in most studied area has experienced a decreasing trend( especially in the south and south east parts) , While in the second period (1999-1990) the cold waves of the north and north west has had a noticeable increase. So that , this increase is more sensible in the east and the south east part of the study area. In total, it can be said that while the cooling wave trend has been decreased, to ward the recent periods, has had a low covering, so that in two days continuation, this feature is more visible.