@article { author = {Darand, Mohammad}, title = {Detection of Geo-potential Height Changes, Vorticity and Sea Level Pressure of Prevailing Circulation Atmospheric Patterns Impacting Iran Climate}, journal = {Physical Geography Research}, volume = {46}, number = {3}, pages = {349-374}, year = {2014}, publisher = {University of Tehran}, issn = {2008-630X}, eissn = {2423-7760}, doi = {10.22059/jphgr.2014.52136}, abstract = {IntroductionThe changes in behaviour of climate and meteorological parameters are closely related tochanges in atmospheric circulation. The analysis of historical atmospheric tropospherecirculation is critically important to global and regional climate change and extremes withregard to its dynamical features. The circulation changes are manifested by a gradual reductionin high-latitude sea-level pressure, and an increase in mid-latitude sea-level pressure associatedwith one phase of the Arctic Oscillation (a hemisphere-scale version of the North AtlanticOscillation. Recent observations have found that the tropical belt running around the equator hasgrown wider, and has expanded by around 2° to 5° latitude and into the adjacent subtropicalregions since 1979. Global greenhouse gas emissions contribute to expansion of the tropics(about 0.05° per decade)in the northern hemisphere tropics. The effect of black carbon andtroposphere ozone emissions are about twice the size of those due to greenhouse gases alone(about 0.07° to 0.12° per decade). The aim of this study is investigation of variability in theintensity of the monthly geo-potential height, vorticity and sea level pressure over synopticcirculation patterns impacting Iran.MethodologyIn order to accomplish this research, daily grid data with spatial resolution of 2.5􀵈2.5 degreeduring 1/1/1960 to 31/12/2012 have been extracted from NCEP/NCAR database. The monthlyaverage sea level pressure and geo-potential height in level of 1000 hectopascal is calculated todetect the action of spatial kernel of each synoptic system. The for this investigation is includingdaily zonal and meridian wind components (Uwnd and Vwnd) data, geopotential height data foreach levels of 1000, 850, 700 and 500 hectopascal levels, and sea level pressure. Vorticity iscalculated by Uwnd and Vwnd components. Then monthly mean is also calculated for eachlevels separately. Although some circulation patterns can operate in special months and seasonsof year but trend analysis has been evaluated for each circulation patterns in whole months andseasons. To detect time series trend, nonparametric Mann Kendal statistic test has been applied.The trend has been tested in 95% confidence level. Sen Estimator is used to calculate trendslope rate.Results and DiscussionSiberian anticyclone, Sudan cyclone, Mediterranean region cyclones (East Mediterranean,Mediterranean and Black sea) and Monsoon and Persian Gulf cyclones have been selectedaccording to the maps of sea level pressure and geopotential monthly means. In total vorticity,geopotential height in different levels and sea level pressure have significant trend in 95%confidence level. The highest variation is observed for high levels at 700 and 500 hectopascal.In winter season, sea level pressure, vorticity and geopotential in 1000, 850, 700 and 500hectopascal levels don’t show significant trend. While in spring and summer the trend ofvorticity in four selected levels is significant and negative, geopotential height and sea levelpressure have positive significant trend. Over cyclonic systems in Mediterranean region, the sealevel pressure and geopotential height show increasing trend especially in winter season. Theslope positive trend on the Sudan is significant in winter. The trend of geopotential height infour selected levels in winter is positive and significant. In other seasons, the trend is positiveexcept in 1000 hectopascal level. Over Monsoon cyclone system in all seasons, geopotentialheight is increasing from 1000 to 500 hectopascal levels. Vorticity trend in low levels at 1000and 850 hectopascal is positive. The increasing geopotential height over Persian Gulf is smallerthan other atmospheric circulation patterns especially in low levels. Vorticity rate contrary toother systems is increasing.ConclusionIncreasing sea level pressure and geopotential height over cyclonic circulation patterns of Sudanand Mediterranean regions especially in cold seasons of year (winter and autumn) result in adecrease in systems cyclonic action, sea level gradient pressure, instability and precipitation inregion. In warm seasons of year (spring and summer) negative trend of vorticity and positivetrend of sea level pressure and geopotential height result in decrease in warm seasonsprecipitation and increase in stability. The results of this study agree with findings of some otherresearchers about increase in warming of troposphere, changes in synoptic systems intensity,instability increase and negative vorticity increase in north hemisphere.}, keywords = {geopotential height,Iran,sea level pressure,synoptic systems,Vorticity Changes}, title_fa = {شناسایی تغییرات ارتفاع ژئوپتانسیل، تاوایی و فشار تراز دریای الگوهای گردش جوی غالب مؤثر بر اقلیم ایران‎زمین}, abstract_fa = {برای انجام این پژوهش، از داده‎های میانگین روزانۀ فشار تراز دریا (SLP)، مؤلفۀ مداری باد (UWND)، مؤلفۀ نصف‎النهاری باد (VWND) و ارتفاع ژئوپتانسیل (HGT) مربوط به پایگاه دادۀ NCEP / NCAR طی بازۀ زمانی 2013- 1960 استفاده شد. به‎کمک آزمون من‌کندال، وردایی میانگین وزنی ارتفاع ژئوپتانسیل، چرخندگی و فشار تراز دریای کرنل فعالیت سامانه‌ها در سطح اطمینان 95درصد آزمون شد. برای برآورد میزان تغییرات، از تخمین‎گر شیب سن بهره گرفته شده است. یافته‌ها نشان داد که بیشترین وردایی در ترازهای 500 و 700 هکتوپاسکال رخنمود داشته است. افزایش فشار تراز دریا و ارتفاع ژئوپتانسیل روی سامانه‌‌های چرخندی سودان و منطقۀ مدیترانه‌، به‎ویژه در فصول بارشی ایران‎زمین (پاییز و زمستان) کاهش کنش چرخندی سامانه‌ها و کاهش شیو فشار و در نهایت کاهش ناپایداری و بارش در منطقه را درپی‌ خواهد داشت. همچنین در فصل گرم سال (تابستان و بهار) کاهش چرخندگی، افزایش فشار تراز دریا و ارتفاع ژئوپتانسیل، به کاهش بارش‌ها و افزایش پایداری منجر خواهد شد.}, keywords_fa = {ارتفاع ژئوپتانسیل,ایران,تغییرات تاوایی,سامانه های همدید,فشار تراز دریا}, url = {https://jphgr.ut.ac.ir/article_52136.html}, eprint = {https://jphgr.ut.ac.ir/article_52136_1cc4008741fe94f4649963e723b1e7a1.pdf} }