ویژگی های توصیفی وردایست بر روی جو ایران در فصول تابستان و زمستان

وردایست لایه انتقال بین وردسپهر و پوشن­‌سپهر است. در این پژوهش برای شناخت وردایست بر روی جو ایران از داده‌های دما و ارتفاع ژئوپتانسیل مربوط به پایگاه ecmwf در بازه‌ی زمانی 1979 تا 2018 با تفکیک افقی 0/25 درجه­ در ترازهای مختلف جو و بر پایه افت آهنگ دما (lrt) استفاده شد. نتایج پژوهش نشان داد که در ماه‌های فصل زمستان تغییرات تراز فشار وردایست بر روی ایران از عرض جغرافیایی تبعیت می‌کند و با افزایش عرض جغرافیایی ارتفاع وردایست کاهش می‌یابد، اما در ماه‌های فصل تابستان ویژگی‌های تراز فشار وردایست متفاوت با ماه‌های فصل زمستان است. در این ماه‌ها تغییرات ترازهای فشار وردایست از عرض جغرافیایی تبعیت نمی‌کنند؛ بر روی ارتفاعات زاگرس و کرمان ارتفاع وردایست در پایین‌‌ترین حد خود قرار دارد، در حالی که بالاترین ارتفاع وردایست در این ماه‌ها در عرض‌های جغرافیایی بالاتری نسبت به دیگر ماه‌­ها واقع می‌شود. بررسی دمای تراز پایین و بالای وردایست نیز نشان داد که دمای تراز پایین وردایست در تمام ماه‌های فصول بررسی شده پایین‌تر از دمای تراز بالای آن است و دمای دو تراز با تغییرات ارتفاع وردایست در ماه‌های مختلف دچار تغییر شده است. بررسی تفاضل دمایی دو تراز اطراف وردایست نشان داد که تفاضل دمایی دو تراز اطراف وردایست در فصل تابستان در مقایسه با فصل زمستان قابل توجه‌تر است. این در حالی بود که در فصل زمستان تفاضل دمایی در اکثر مناطق از عرض جغرافیایی تبعیت می‌کند و با افزایش عرض جغرافیایی تفاضل دمایی کاهش می‌­یابد.

Descriptive characteristics of the Tropopause on Iran’s atmosphere in summer and winter seasons

Extended AbstractIntroductionThe tropopause is a thin layer separating the stratosphere from the troposphere and is often characterized by a large change in the thermal, mass and chemical structure of the atmosphere.Compared to global studies on the tropopause and its various features, studies conducted in Iran are very few and the methods used are often less inclusive or the length of the statistical period is limited. For this reason, and considering the importance of the tropopause and its effect on exchanges between the troposphere and the stratosphere, and also due to the lack of information about it in Iran, accurate knowledge of the height of the tropopause in the country using more reliable data sources is a fundamental necessity. To calculate the tropopause, we used daily temperatures of ECMWF reanalysis datasets from January 1979 until December 2018. Gridded data witha spatial resolution of 0.25*0.25 were used. In vertical levels, we used 10 standard isobaric surfaces from 700 to 50 hPa. MethodsThe location of the tropopause thermally and dynamically was defined. According to the WMO (World Meteorological Organization), the tropopause is defined as the lowest level at which the lapse rate decreases to 2°C/km or less, provided that the average lapse rate between this level and all higher levels within 2 km does not exceed 2°C/km.In this study, this index was used to identify the tropopause.In this study, to identify the factors affecting the tropopause, the relationship between the tropopause and spatial variables (latitude and longitude) and altitude was evaluated by general and partial correlations. Results & DiscussionThe results of this study showed that in the months of cold season, the tropopause pressure level on Iran is followed by latitude, and the tropopause height decreases with increasing latitude, but in the months of the warm season (June, July, and August), the tropopause pressure level is different from the months of the winter season.In these months, the changes in the tropopause pressure levels do not follow the latitude; on the Zagros and Kerman heights, the tropopause height is at its lowest, while the highest tropopause elevation is in these months at higher latitudes than in other months.The temperature of the upper and lower levels of tropopause also showed that the temperature of the lower levels of the tropopause in all seasons was below the temperature of the upper levels of the tropopause and the temperature of the two levels changed with the changes in the levels of tropopause pressure in different months.The study of low and high levels of tropopause showed that during the cold season, the temperature of the two levels around the tropopause, following the tropopause pressure levels, follows the latitude, and with increasing latitude, temperature increases in the two levels around the tropopause.In two studied seasons, the lowest temperature of the two levels of the tropopause is consistent with the highest level of the tropopause, but the highest twolevel temperature is only consistent with the lowest tropopause pressure level during the warm season months, and in other months, this observation coordination failed.Investigating the thermal difference between two levels of tropopause showed that the temperature difference between the two levels of the tropopause in the warm season is more significant than that of the cold season, while in the cold season, the temperature difference in most regions of the latitude is obeyed. Slowly, the difference in temperature decreases with increasing latitude. ConclusionExamination of the characteristics of the tropopause and its related factors for summer and winter showed that in each season due to local conditions and changes in largescale factors, the height of the tropopause changes, and therefore the tropopause in each season has completely different characteristics from the other season.Examination of the characteristics of the tropopause and its related factors for summer and winter showed that in each season due to local conditions and changes in largescale factors, the height of the tropopause changes, and therefore the tropopause in each season has completely different characteristics from the other season.