نوع مقاله : مقاله پژوهشی
عنوان مقاله English
نویسندگان English
Clouds, as one of the most complex and influential climate variables of climate system, are effective in temporal and spatial distribution of many climatic variables. On the other hand, since clouds have many spatiotemporal changes, therefore, investigating their behavior is very important. Therefore, the aim of the current research is to investigate and analyze the annual cloudiness cycles in Iran and reveal the obvious and hidden behaviors of its time series. For this purpose, daily cloudiness data obtained from the National Meteorological Organization during a period of 31 years for 30 stations were used. Then, the trend of the data studied by Sen Slope Estimator's nonparametric test at the 95% confidence level. The results of data trend analysis and their significance value indicate significant downward changes in 16 stations and significant upward changes in 3 stations and no significant trend was observed in other stations. In order to analyze the harmonics and extracting significant cycles, Spectral Analysis Method was used and the diagrams of periodogram at the 95% confidence level were drawn. The results show that stations including a significant cycle have the highest frequency and are mostly in the south, center, east and northeast of Iran and multi-cycle stations with less frequency are in the north, northwest and southwest regions of the country. Also, by calculating the variance contribution of each cycle, the largest variance contribution for the 14th harmonic and the highest return periods for cycles of 2-5 years with a probability of occurrence of 32% and cycles of more than 10 years with a probability of occurrence of 6% were obtained.
کلیدواژهها English