بررسي ساختار منطقه اي جو در زمان رخداد توفان تندري همراه با تگرگ از 16 تا 18 جولاي 2016 مورد مطالعه: شمال غرب ايران

The Study of regional structure of atmosphere during the thunderstorm hail event on16 to 18 July 2016 Case study: North West of Iran

به دليل همراهي توفان هاي تندري با رگبارهاي باران و توفان هاي تگرگ و نقش موثر آن در ايجاد سيلاب هاي ناگهاني، هم از جنبه ي كشاورزي و هم ازنظر خسارات مالي و جاني، اين پديده همواره موردتوجه محققان بوده است. براي اين منظور ابتدا به بررسي مقادير فشار، دماي هوا و دماي نقطه شبنم در لايه هاي مختلف جو پرداخته شد. سپس، براي بررسي دقيق تر شرايط جوي پارامترهاي دماي هوا، فشار تراز دريا، ارتفاع ژئوپتانسيل، نم ويژه، سرعت قائم، مولفه باد مداري و مولفه نصف النهاري باد از تارنماي (NCEP/NCAR) اخذ شد. همچنين براي بررسي ناپايداري در سطوح مختلف جو از شاخص هاي صعود، موجودي انرژي پتانسيل فرارفتي، آب قابل بارش، K و هواي توفاني استفاده شد. بررسي ها نشان داد كه صعود سريع بسته هوا در منطقه با انرژي پتانسيل همرفتي در دسترس بالايي همراه بوده و سبب شده تا در اين سه روز هواي صعودكننده تا لايه هاي فوقاني جو پيشروي كرده و جوي مغشوش را براي منطقه به وجود آورده است. با بررسي نقشه هاي ارتفاع ژئوپتانسيل و تاوايي تراز 500 هكتوپاسكال در روز اول بارندگي مشخص شد كه توفان تندري حاصل برهمكنش هاي مختلف جو بوده، بطوريكه در تراز مياني جو پشته بسيار قوي با گستره مكاني بيش از 25 درجه عرض جغرافيايي بر روي درياي خزر ايجاد و تا حوالي مناطق عرض هاي قطبي گسترش يافته است. در روز دوم، توفان تندري در داخل پر ارتفاع تشكيل شده بر روي خزر هسته سرد چالي بر جانب شرق تركيه، شمال عراق و شمال غرب ايران ايجادشده كه ارتفاع مركزي آن 5750 ژئوپتانسيل متر مي باشد. در روز سوم، هسته سردچال به بريده كم فشاري بر روي منطقه تشكيل شده كه بيشينه تاوايي مثبت در داخل اين سيستم جوي است.

Thunderstorms are among the first meteorological phenomena، which have attracted human attention. Thunderstorms with rain showers and storms accompanied by hail and their role in causing sudden floods، both in terms of agriculture and human and financial losses، have been noticed by researchers. Rain hail of bullets or pieces of ice ascends very high in elevation due to the weather conditions along with electrical features occurrence. Hail grains or pieces of ice with diameters of 5 to 50 mm occasionally take longer time to be made up. Strong growth of hail through severe and repeated vertical movements of air in cumulonimbus clouds freezes the absorbed water droplets around hailstones. Few thunderstorm hails arrive on land many of which even contain no hail even in the most suitable parts of the clouds. The creation and hail falling، despite being warm and humid in the lower atmosphere and the ascending of clouds condensed with respect to the altitude and cold weather are coupled with the continuing maximum air instability. Because of the importance of hail event، studies on the formation and growth of hail in different countries are conducted for its prediction. In connection with hail and hail storms extensive research work has been carried out in including: Costa et al. (2001)، Simonov and Gergiev (2003)، Whiteman (2003) and Sterling (2003). To investigate the thunderstorm and hails occurred in the region، we examined weather conditions. Initially the values of pressure، temperature and dew point temperature by the radiosonde measurements in different layers of the atmosphere were studied and the plotted graphs were obtained from NOAA. In the next stage for a closer look at weather conditions parameters like air temperature (Air)، sea level pressure (SLP)، geo-potential height (Hgt)، specific humidity (Shum)، vertical velocity (Omega) orbital wind component (Uwnd) and meridional wind component (Vwnd) were analyzed. The data records were collected from the website of the National Center for Environmental Prediction and National Climate Science (NCEP/NCAR). Instability investigation in the atmosphere for different levels of instability indices was applied. Investigation on instability indices showed that on the first day the ascending index values (LI) were at 2-، which are the values added in the next two days. These conditions prove that the atmospheric turbulence is intensified in the days after the first day. By examining the thickness of the atmosphere it is seen on the Azerbaijan area On 16 July that on 5785 geo-potential meters the next day was associated with reduced 51 meter geo-potential added value at the third day. The results also revealed that the atmospheric precipitation of water values is calculated on a three-day index value of 17، 18 and more than 23 mm per day. To check the status of stormy weather index (SWEA) and K we found that the occurrence of thunderstorms in that area started on 16 July، approaching the end of high value added indicators that show strengthening of storms and their destructive mechanism in the day after the end of the other. Investigation of thermodynamic charts showed that rapid convective ascent of available potential energy depending on the weather in the region has been so high and caused the weather to approach three days in advance to the upper layers of the atmosphere and atmospheric turbulence was created for the region. Examining the rainfall map of geo-potential height and vortices in 500 hPa on the first day exhibited that tthunderstorms were the result of interactions of the atmosphere، so that in middle levels the strong condensation of location with a range of more than 25 degrees of latitude on Caspian Sea was created and polar latitudes spread to nearby areas. On the second day، high-altitude thunderstorm in the core atmospheric cut-off formed on the Caspian Sea on the East of Turkey، northern Iraq and North West of Iran created the geo-potential height of the center of the 5750 geopotential meter. On the third day، atmospheric cut-off core to cut area of low pressure was made on the maximum positive vortices in the climate system. Conditions over the surface in the first day of the storm in the region indicated very strong contour of low pressure formed in the North East to West and North West of Saudi Arabia. In front of the two sides one of on Mediterranean Sea and other northern Russia، the contour of the pressure was imported into the Middle East.