شناسایی الگوهای سینوپتیکیِ بارش‌ های سیل خیزِ غرب ایران

یکی از مهمترین و چالش برانگیزترین رخدادهای حدی ، بارش‌ های سنگین است که هر ساله خسارات فراوانی را به دنبال دارد. از اینرو در پژوهش حاضر این رخداد در غرب ایران بررسی شده است. ابتدا با داده‌ های روزانه بارش در ایستگاه‌های سینوپتیک منتخب برای دوره (2000-2015 ) چندین بارش حدی در منطقه شناسایی شد، در ادامه نقشه‌ های مربوط به فشار های تراز دریا، ارتفاع ژئوپتانسیل تراز 500 و 850 هکتوپاسکالی این الگوها در نرم افزار spss با استفاده از تحلیل مولفه‌ی اصلیpci))، برای شناسایی مولفه‌ های اصلی مورد پردازش قرار گرفت نتایج نشان داد تنها یک مولفه 99.99 درصد واریانس این الگو ها را تببین و توجیه می‌کند. بنابراین الگوی مولد تمامی این رخداد ها شرایط مشابهی را دارا بوده است. سپس از بین این الگو های مشابه دو الگوی بسیار شدید انتخاب و مورد آنالیز سینوپتیکی و ماهواره ای قرار گرفت نتایج نشان داد در روزهای همراه با بارش حدی امگای منفی (از سطح 1000تا 200 هکتوپاسکالی و با هسته بیشینه 0.3 پاسکال بر ثانیه) بر روی غرب ایران قرار داشته است، علاوه بر آن رطوبت بالای 70 درصد، قرارگیری در جلوی تراف هایی که از کم ارتفاع ژئوپتانسیل تراز 850 و بویژه 500 هکتوپاسکالی بر منطقه نفوذ داشته، رودبادهایی با سرعت بالای 30 متر بر ثانیه در تراز 200 هکتوپاسکال، سرعت باد سطحی بالای 10 متر بر ثانیه و هسته های تاوایی مثبت همگی شرایط موجود را به نفع تشکیل سیکلون قوی فراهم کرده اند. در نهایت پردازش تصاویر رادار هواشناسی این نتایج را تآیید نمود.

Analysis of synoptic patterns reated to extereme precipitation over west of Iran

Precipitation is not only a critical process in global hydrologic cycle but also an important indicator of climate change (Fu et al.,2016). Precipitation is a key factor of the global water cycle and affects all aspects of human life. Because of its great importance and its high spatial and temporal variability (Thies and Bendix.,2011). Climate change is caused many extreme climatic occurrences in recent decades. One of most important extreme events is extreme precipitation. The changes of temporalspatial patterns of precipitation may potentially cause severe droughts or flood hazards (Jiang et al., 2008). There are many environmental damages which are related to these events. Precipitation events were examined and studied by many researchers. The purpose of the study is evaluating of the structure and origin of the events in the west of Iran. Studies about extereme precipitation is somewhat strong. Robert, 1993 evaluated many flashflood in United States which is related to short wave at 500 hgt level. Many researchers also studied this type of precipitation such as Kumar, 2008 and etc. Trend analysis is another approach is related to this scope. Globally, precipitation increases in equatorial rain bands; decreases in subtropics as greater tropical convection in the rising branch of the Hadley circulation will lead to enhanced subsidence in the subtropics; and increases in highlatitudes due to increase in moisture transport (Huang et al., 2013). Synoptic analysis of the events is required due to increseing trend of this events and tremendous socioeconomic impacts on many places. First, a 99 percentile for recognition of extereme precipitation is applied for daily precipitation during 20002015 at seven weather stations in the west of Iran. Then principal component analysis carried out in order to reduce correlated data (SLP, hgt at 500and 850level) which is associated to synoptic patterns. Two extereme precipitations are selected for synoptic analyses. In order to better perspective of these patterns analyses are performed using sea level pressure, 500 and 800 hgt level, omega, uwind, Vwind, relative humidity, and TRMM precipitation Radar data. TRMM data is used due to satellite systems provide a unique opportunity to monitor Earthatmosphere system processes and parameters continuously and the correct spatiotemporal detection and quantification of precipitation has been one of the main goals of meteorological satellite missions (Thies and Bendix.,2011).The results of precipitation data showed extereme precipitation dates based on 99 percentile are as fallows during 20002015 time period: 29 Jan 2013, 30 Nov 2008 , 3 and 4 feb 2006, 25 Dec 2004, 13 jan 2004, 1 dec 2001, 24 mar 2000, 2 may 2010, 29 and 30 Oct 2015. After identitying extereme precipitations, PCA (principal component analysis) applied for SLP data, Geopotential hight at 500 and 850 levels data in oredr to recognition the synoptic patterns. The results indicate that there is only one component which explains 99 percent of variances of data. Therefore the one synoptic pattern incorporated in formation of extereme precipitation in the west of Iran. Then for better understanding of this pattern, we are selected two extereme precipitation reanalysis data (29 oct 2015) and (13 Jan 2004) and evaluated sea level pressure, 500 and 800 hgt level, omega, uwind, Vwind, relative humidity, and TRMM precipitation Radar data in these dates. The purpose of this proccess was monitoring different parameter in two dates. The results illustrated interesting conditions which is related only to providing appropraite condition for extereme precipitation formation. Many conditions required to the events as fallows: SLP lower than 1000 hpa over the west of Iran, surface relative humidity larger than 70 percent, negative omega lower than 0.3, positive vortices which indicate cyclogenesis. Another most important factor which caused extereme precipitation is location of trough. In all cases, the western of Iran located in front of trough at 500 and 850 hpa. The Precipitation Radar of TRMM satellite also determined same precipitation patterns which are specific for the west of Iran. This is only one part of the heavy precipitation studies at west of Iran the authours sugesst climate change studies such as trend analysis in a long time period, simulation with regional models as Regcm and WRF, appling ERAinterim data which can provide fine spatial resolution up to 0.25 degree over study area which need to be done in order to completion of the results.