تحلیل مکانی و زمانی توفان‏ های تندری در دشت اردبیل

توفان‏های تندری، به‏دلیل رفتار بسیار نامنظم در ابعاد مکانی و زمانی، در منطقه شمال‏ غرب ایران از پدیده‏های آب و هوایی حائز اهمیت به‏شمار می‏روند، زیرا این نوع بارش‏ها نقش بسیار مهمی در فعالیت‏های اجتماعی و اقتصادی مانند تولید محصولات کشاورزی، استفاده از زمین زراعی، و مدیریت منابع آب دارند. در این پژوهش، به‏منظور شناسایی الگوهای سینوپتیک توفان‏های تندری طی بازه زمانی 19612016، از داده‏های ایستگاهی بارش شدید بیش از 50 میلی‏متر و داده‏های فشار ارتفاع ژئوپتانسیل تراز 500 هکتوپاسکال استفاده شده است. روش نقشه‏های خودسازمان‏دهsom  و آزمون پتیت در نرم‏افزار  rبه‏منظور شناسایی الگوهای بارش به‏کار گرفته شده است. براساس نتایج، نُه الگوی جوی در تراز 500 هکتوپاسکال نشان داده شده و تصاویر مربوط به هر الگو در نرم‏افزار grads ترسیم شده است. این الگوها نشان می‏دهند که در بارش‏های شدید بهاره رخداد بلوکینگ امگایی‏شکل، تشکیل ناوه عمیقی بر روی شمال خزر، و پدیده بلوکینگ رکس؛ در الگوهای تابستان بلاکینگ حلقه آتش و بلاکینگ کم‏فشار بریده؛ در الگوی زمستان بلوکینگ رکس؛ و در الگوی پاییز یک ناوه عمیق در بخش شمالی ایران و بلوکینگ کم‏فشار بریده دیده می‏شود. بیشترین درصد بارش متعلق به الگوی b3 با 45درصد فراوانی و کمترین مقدار بارش متعلق به الگوی a1 با 20درصد است.

Spatial Analysis of Thunderstorm in Ardebil Plain

Extended abstract Thunderstorm is one of the meteorological phenomena seen in most parts of the world and is a major threat to modern societies, which operates in more localscale. This natural occurrence, despite having advantages in most cases, due to the sudden occurrence, is the most severe and destructive natural disasters in each year, and cause severe damage to different parts of economies and human casualties. Convective storms usually affect small areas than tropical cyclones. Moreover, their destructive effect is often less than the actual value. Basically, thunderstorms are in the most frequent in the warm seasons on the land surface and in the cold seasons on the oceans many factors influencing the occurrence of thunder storms, including thermodynamic and kinematic conditions of the atmosphere, topography, and surface cover, coastal configuration and atmospheric flows. Ardabil province due to its location in northwest of Iran And being in the vicinity of the Caspian Sea and Gilan province have a several extreme precipitation days in each year, which causes severe damage to the agricultural and livestock sector. In this study, daily largescale circulation patterns are firstly characterized in the northwest area of Iran, Ardabil province, through the use of SOMs technique. Then, the potential implications of circulation types to explain variability and change of the Ardabil precipitation are also attempted. Therefore studding of this phenomena and identifying of synoptic patterns have Great importance for the region. Materials and method The observed daily extreme precipitation records over 50mm used in this study are provided by the Ardabil Meteorological Data Sharing Service System. There are 4 stations in the data sparse Ardabil but their operations started in different years (most are from January 1 in 1961) and there are missing values at some stations in the early decades during the 1961–2016. Additionally, the daily geopotential heights at 500 hPa isobaric level (GH500) with the spatial resolution 2.5° latitude × 2.5° longitude based on extreme precipitation days used for circulation types are obtained from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR,.http://www.esrl.noaagov/psd/data/grided/data.ncep.reanalysis.html reanalysis dataset to identify circulation types. Some of the circulation patterns in Ardabil area were objectively evaluated with Pettit test. Based on this method, a significant abrupt change point is detected in the series of the sum of qerror and terror, which indicates 9 distinct circulation patterns with a 3 × 36 SOM topology can describe the changes in synoptic positions in the Ardabil area. In addition, the maps created in the Grads software are also presented. Result and discussion The largescale circulation classification provides an ideal tool to understand the circulation dynamics and their association with local climate variability. In this study, daily circulation types are objectively studied through the use of SOM technique and are further linked to the extreme precipitation over 50 mm characteristics in the northern area of Iran, Ardabil , during the period 1961–2016. Results show that the SOM method adopted could reasonably classify the daily geopotential height field at the 500 hPa vertical level over Ardabil province. By using an objective determining method (the Pettit test), 9 circulation types are qualified. Most of the severe precipitation patterns in Ardebil are related to the spring and April months, which is the time of the occurrence of thunderstorm in Ardebil. The 500 hpa HGT patterns during spring rainfall are associated with Omega Block, Rex Block and deep wave on Caspian Sea. This atmospheric pattern at the level of 500 Hpa has a completely baroclinic and unstable atmosphere in Ardabil which produced thunderstorm. In summer patterns, Ring Of Fire Block and Cut off Block are seen. This type of Block occurs during the summer, the conditions of high pressure system centre are very stable. Cut off Block, is a deep craft, occurs when highaltitude winds change to high latitudes and leave a lowspin (low pressure) behind them. In autumn pattern, a deep wave in the northern part of Iran and a cut off block are seen. Deep Wave, supplemented by cold weather in northern latitudes. In winter pattern is a Rex Block, which is a set of systems with a strong high stack in the vicinity of a lowaltitude strong lane. Ardebil is located on the eastern side of the wave, is the location of the western winds ascent that creates barocilinc atmosphere and precipitation. In the A1 group, the highest frequency is in May with 30%, in the A2 group with 34% the highest frequency is in April and the lowest frequency is in October with 5%. In the A3 group, the frequency is 15% in February, March, April and May. Also in group B2, the frequency of April, May and August are 8% .In group B3, the highest frequency with 25% and 15% are for October and November. In the C1 group, the JulySeptember months are over 16%. In the C2 group, JanuaryApril are 16% and 8% and in the C3 group, May, June and September are 8%. In the spring, the highest percentage of precipitation belongs to the B3 model with 45% fluctuation and the lowest amount of precipitation belongs to the A1 pattern with 20%. The patterns of A1 and C1 (45%), B1 (35%) and C3 (20%) are summer season patterns, The C1 pattern with (45%) has only some rainfall in winter. The C3 pattern has a rainfall of only 25% and 15% in spring and summer. In autumn, the patterns of A1 (28%), A2 (10%), B1 (15%) and B3 (45%) are highend models. In winter, only A3 patterns with (35%) and B3 with (20%) are rainfall patterns.