چکیده:
Variability is one of inherent properties of the climate system. In addition to the dynamic nature, the climate system is extremely intertwined nature also, so that its components interact with each other and eventually they are changing each other. In general, the climate of a geographic location is controlled by various factors, including Atmospheric Action Centers (AAC's). AAC's behaviors have an effective role in short and long term changes in weather and climate conditions and components. AAC's of Mediterranean Sea especially its cyclogensis centers in east side of sea have an effective role in Iran precipitation regime. From this point of , this study looking forwards the effects of temperature and pressure components of east Mediterranean cyclogensis centers in rainfall anomalies of west of Iran. Material and methods & In this study have been used two data sets: first, database of Meteorological Organization of Iran, based on 1961 to 2010 data series and then, database of U.S. Environmental Studies Organization based on 1948 to 2014 data series. From the total of months were concerned in this study, 55 months have been selected because their abnormality. By using Pearson method the correlation between precipitation amounts of Iranian stations and temperature and pressure on atmospheric levels of MSL, 850, 500 and 300 hpa was calculated for east of Mediterranean Sea. Then significant correlations were interpolated for whole of west of Iran using IDW methods in ArcGIS and the patterns of iso-correlation countors were plotted as a series of maps. Discussion and Results & Based on results of research the widespread abnormalities of rainfall in west of Iran have correlated more with temperature and pressure changes of upper level synoptic patterns of east section of Mediterranean Sea. Likely, the changes in behaviors of upper levels patterns in east Mediterranean AAC's in cold season and their effects on deepening of Mediterranean Trough and creation the positive vorticity advection in eastern parts of trough have more importance than the patterns in lower levels of atmosphere. In addition , because upper level patterns are far from reach of local ones in low levels, their impacts is more activeness in long distances from Mideast Mediterranean to west of Iran. Also based on results of this study the changes of pressure and temperature components in eastern part of Mediterranean Sea is increasing and significant especially in case of upper levels ACC's. Vertical profiles of abnormalities in all levels of atmosphere confirms increasing of tropospheric temperature and geopotential height over the past three decades (1981-2010) than the normal period (1949-1980). On this basis the different levels of atmosphere from MSL to 300 Hpa have experienced an increase range from 11 to 15 gpm, that for level of 300 Hpa it reach to 35 gpm. But upper parts of atmosphere in levels of 20 to 10 Hpa the feature of decreasing is dominant. In case of temperature of atmospheric levels it was shown that in lower-to-mid levels exists an increase about 0.3Co whereas in upper levels was seen a decrease approximately 1 Co. Conclusion & Based on results the widespread anomalies of rainfall in west of Iran show strong inverse correlation with temperature and pressure changes in Mid-east AAC's of Mediterranean sea at all atmospheric levels. In Northwest of Iran, above mentioned correlations are weak and insignificant. Also the significant increasing trend of temperature and pressure in Mideast of Mediterranean area in relation with its powerful and inverse correlation with rainfall of west of Iran and with concern to developing trend of Global Warming , confirms the more probability of drought occurrence in west and whole of Iran. Although according to results of other researches, the rainfall of Iran hasn't already showed any significant trend, but the synoptic studies on mentioned factors especially the cyclogensis centers in east part of Mediterranean sea, shows an increase in atmospheric pressure and consequent more occurrence of droughts in Middle East and Iran in some future decades.
خلاصه ماشینی:
در مجموع نتایج این پژوهش ، نشان دهنده ی افزایش دما و فشار جو در منطقه ی شرق دریای مدیترانه در دوره ی ٦٥ ساله ی اخیر و بر اساس نتایج مدل سازی تا سال ٢٠٥٠ تداوم این افزایش پیش بینی میشود و همچنین با توجه به رابطه ی وارون و قوی بین تغییرات فشار و دما جو در این منطقه و اثر آن بر ناهنجاریهای بارشی غرب ایران ، احتمال رخداد خشک سالیهای فراگیر در نیمه ی غربی ایران در دهه های اخیر و احتمالا آتی افزایش یافته است .
ازاین رو این پژوهش از یک سو به بررسی میزان چگونگی تغییرات فشار و دما ترازهای مختلف جو بر فراز منطقه ی شرق دریای مدیترانه پرداخته و از طرف دیگر ارتباط مؤلفه های اشاره شده با ناهنجاریهای بارشی فراگیر غرب کشور را در مقیاس ماهانه مورد مطالعه قرار داده است .
از مجموع تمام ماه های مورد مطالعه در این بررسی تعداد ٥٥ ماه دارای شرایط بالا بوده (جدول ١) که مقادیر بارش ایستگاه ها در این ماه ها با میزان فشار و دمای ترازهای مختلف جو (تراز دریا، ٨٥٠،٥٠٠ و ٣٠٠ هکتوپاسکال ) در مرکز شرق دریای مدیترانه ، با روش همبستگی پیرسون آزمون شدند و مقادیر همبستگی و سطح معناداری برای کل 14- http://www.