واكاوي اثر عوامل محلي در الگوي جريان باد در منطقه درياچه اروميه

Analysis of Local Factors in Wind Pattern in Urmia Lake basin

وزش باد در هر منطقه­ اي تابع عوامل مختلفي در مقياس­ هاي سياره ­اي، منطقه ­اي و محلي است و عامل اصلي انتقال جرم (رطوبت، ذرات جامد و .. ) و ساير ويژگي­ هاي هوا از منطقه‌اي به منطقه ديگر است. در اين مطالعه، با بهره ­گيري از داده­ هاي سه ساعتي جهت و سرعت باد در ايستگاه­ هاي هم ديد اطراف درياچه اروميه و با استفاده از مدل ميان­ مقياس آلودگي هوا TAPM به واكاوي اثر عوامل محلي در شكل­ گيري بادها در اين منطقه پرداخته شد. به اين منظور، با انتخاب روزهاي با شرايط بادهاي محلي از داده­ هاي سه ساعتي ايستگاه‌هاي هواشناسي (اروميه، تبريز، خوي، مراغه و مهاباد، در 6 روز) با تأكيد بر تغيير جهت وزش در طول شبانه روز، سرعت باد، دما و رطوبت براي بادهاي محلي انتخاب شد. نتايج نشان داد كه در 4 نمونه مورد بررسي ناوه كم عمقي با حاكميت بادهاي غربي در منطقه حاكم بوده كه موجب ورود باد با سرعت ­هاي كم و سرعت تقريبي حدود 4 متربرثانيه به منطقه گرديده است. بادهاي حوضۀ درياچه اروميه تحت ­تأثير عوامل مختلف داراي پيچيدگي زياد و تغييرات مكاني و زماني شديد در جهت و شدت وزش است. خروجي هاي مدل گوياي اين است كه امتداد كوهستان­ ها بيشتر از هر عامل ديگر همچون درياچه اروميه در شكل­ گيري بادهاي محلي مؤثر هستند و چاله درياچه در كاناليزه كردن بادهاي شمالي يا جنوبي منطقه در رابطه با بادهاي محلي نقش دارد. اين شرايط باعث شكل­ گيري هسته­ هاي متعدد واگرايي و همگرايي مطابق با راستاي ارتفاعات در منطقه مطالعاتي مي­ شود. همچنين شيب ارتفاعي به سمت درياچه و اختلاف ارتفاع زياد با كوهستان­ هاي پيرامون مهمترين عامل مؤثر در شكل ­گيري بادها در زمان­ هاي مورد مطالعه است.

Introduction The effective factors in formation of atmospheric elements in local and regional scales usually have been trimming and smoothing roles. The identification of wind formation patterns in Uremia lake basin is an important issue for many management and regional planning affairs. In this context: Steven et al. (1992), Neil et al (2003), Zawarreza (2004), Luhar& Hurley (2004) and Kardane et al (2009) can be referred. Various studies have been done related to Urmia basin in generally, but there isn't almost any research about the formation mechanism of regional winds and the effect of local factor on it. In the study we tend to investigate the mechanism of local wind formation in Urmia basin using mesoscale climatic models. Materials and Methods Urmia Lake is a salt lake in the northwestern of Iran. The lake is between the provinces of and West Azerbaijan in Iran, and the southwest of the portion of Caspian Sea. At its full size, it is the largest lake in the Middle East and the sixth largest saltwater lake on earth with a surface area of approximately 5,200 km² (2,000 mile²), 140 km (87 mi) length, 55 km (34 mi) width, and 16 m (52 ft.) depth it is located in high of 1275 meters above sea level Firstly, the data of daily wind of Stations around Lake Urmia has processed in Excel and then the hourly Wind Rose is designed for them. Then using network reanalysis databases of NCEP/NCAR for recognize and analysis atmospheric pressure systems and air masses interring to the basin of Lake Urmia were done. So have been selected 21 typical samples for warm season and 18 typical samples for cool season. The synoptic analysis for selected typical samples were done and finally using the air pollution model (TAPM) as a mesoscale atmospheric model for analyzing these samples. Results and Discussion The selected samples presented in table 4. Also using climatic model for analyzing of atmospheric situation in the days which the local factors are dominance. Finally using synoptic and statistical methods to analysis the results. 14 February. 2003: In this day the statistical investigation of wind data in particular speed and direction of wind indicated that the local factors are main component which control the winds characteristics. The atmospheric barotropic condition and regular fluctuations in daily temperature is the main signal of this local factors dominance. The slope of isobars in our study region is very small. 28 July 2006: The wind situation of the stations which located around the Urmia Lake is homogeny so that 4 meteorological station namely, Tabriz, Khoy, Urmia and Maraghe have strong Morning wind. The high pressure from the north can be seen in the area in this day which cause increase the slope of isobars in this region. Mountainous chain directions and topographic situation play an important role in the patterns of wind blowing. 1August 2003: The condition of wind blowing in surrounding stations of Urmia Lake are not homogeny in this day. Two stations from three investigated stations with names Tabriz and Urmia, have strong morning wind from north and east while Maraghe station has southeastern weak wind and Mahabad and Khoy stations have calm air conditions. 8 October 2006: In this day according the table 6 the condition of wind blowing in surrounding station of Urmia Lake is not homogeny. Two stations form 5 investigated weather stations namely Tabriz and Urmia, have strong morning wind from north and two stations of them namely Maraghe and Khoy weather stations are calm air in morning and in midday have southeastern direction winds. an‎d in Mahabad weather station calm air condition was recorded. This heterogenic condition indicated the influent of local factors. Conclusion In this paper we intend to detect the effects of local factors in formation of local and regional winds in Urmia Lake basin. For this propose have been investigated four typical days that the local winds were observed. Our funding indicated that in all four typical samples days the weak trough that associated westerly is dominance in our study region due to it the low speed wind entering to our study region. Also using TAPM and its numerical and graphical outputs show the topographical condition in our study region can affect the direction of these entrance winds. Also we observed the north south channeled wind in our study region and formation of divergence core according to direction of topography is very attractive. The lake ward slopes of mountain and the height difference between Lake Surface and mountains is very important in formation of local winds.