واکاوی همدید شهرهای رکورددار گرما در ایران

امروزه، رکوردهای گرما «به معنای گرم‌ترین شهر کشور در هر روز و دمای آن»، مرتب رسانه‏ای می‌شود. در این تحقیق با تهیه دماهای روزانه 33 شهر کشور از سازمان هواشناسی طی نیمه گرم سال (1971-2010)؛ شهرهای رکورددار، فراوانی و مقادیر دمای آنها مشخص گردید. نخستین نتایج گویای کاهش تدریجی فراوانی شهرهای رکورددار گرما طی سه دهه از 11 شهر به 6 شهر بود. یعنی از این پس شهرهای رکورددار کمتر ولی فراوانی رکوردداری آنها در سال بیشتر خواهد بود و این مخاطره بیشتر متوجه شهرهای آبادان، اهواز و بندرعباس است. در بخش همدید، طراحی الگوهای همدید پرفشارهای آزور و ساهارا و کم فشار سند طی روزهای بالاترین رکوردها نشان داد: 1) کانون‌های پرفشار جنب حاره‌ای آزور در زمان بالاترین رکوردها، در میانه اقیانوس اتلس گروه گرایی دارند ولی در زمان رخداد پایین‌ترین رکوردها، در این اقیانوس پراکنده‌ترند. 2) همین تفاوت برای کانون‌های پرفشاری ساهارا مشاهده می‌شود. 3) کم فشار سند آرایش مداری‌تری از خود نشان داد. در مجموع بالاترین رکوردهای گرما در ایران با تقویت جو پایدار در گستره‌ای از اقیانوس اتلس میانی تا شبه قاره هند همراهی می‌شود.

Synoptic Analysis of Hottest Cities in Iran

IntroductionNowadays, many specialists testify the reality of global warming. This warming affects many thermal anomalies. Some of these anomalies show themselves in the form of warmth records especially over cold and moderate realms. At a national level, the Iranian city with the highest temperature makes new headlines. For instance, in 2015 the temperature of more than 49 degrees Celsius was recorded for GonbadKavoos City in the province of Golestan as the warmest city of Iran.Materials and methodsIn this investigation, we obtained the data of daily temperatures of 33 cities over Iran for warm half of year (1971 to 2010) based on the method of environment to circulation. The extracting of daily records of weather stations and their frequencies were finalized in MATLAB platform. When daily temperature tables were set, the Hottest City (HC), their Frequencies (FC) and their temperatures (TC) were determined. In these tables, cities were sorted based on their descending latitudes. In this stage, the highest records during every year were defined on based on access to daily weather charts and designed synoptic patterns. For instance, the annual highest record of warmth was 19.5 degrees Celsius. It was related to Lengeh port in Southern Iran at 1971. These daily charts were obtained from ENCEP/ENCAR. Based on them, the centers of all highpressure effective systems including Azores, Sahara and Hijaz were determined on base maps in order to design synoptic patterns and their analysis across Atlantic Ocean to Pacific.Results and discussionResults showed RC frequency has reduced from 11 cities to 6 ones during the three last decades. It means, we will have less HC but more FC in future over Iran. This reduction is not gratifying because results show that records have grown for Abadan, Ahwaz and Bandarabbas Cities over Sothern Iran. Designed synoptic patterns of highpressures included Azores and Sahara and Indus Low during high TCs over based maps showed that:1) The centers of Azores Highs appear like a group in the middle of the Atlantic Ocean but they appeared straggly during low ones. 2) We found similar results for Sahara Highs over Africa. 3) Also, the location of Indus Low centers over Southern Asia appeared more zonal in comparison with low records. Altogether, the high TCs in Iran accompanied with barotropic atmosphere from the center of Atlantic Ocean to India Peninsula.ConclusionOverall, the highest records of warmth are accompanied by barotropic atmosphere over Atlantic Ocean to the Indian Peninsula. Alongside weakening of thermodynamic Siberian Highs, it seems that concentration of Azores Highs over Eastern Atlantic Ocean and Saharan Highs over Africa and Hijaz ones over Southern Iran cause an increase in the frequency of high warmthrecords over Iran.