تحلیل همدیدی-ماهواره ای مخاطره برف سنگین در استان کرمان

بارش های برف سنگین و فراگیر در عرض های جغرافیایی پایین به عنوان یک مخاطره آب و هوایی غیرمنتظره به حساب می آید. هدف این پژوهش شناسایی رخداد برف های سنگین و فراگیر استان کرمان و تحلیل چگونگی رخداد آن با استفاده از داده های سنجش از دور و بازتحلیل شده می باشد. آمار روزهای برفی ایستگاه های سینوپتیک بین سال های 2000 تا 2015 نشان می دهد که استان کرمان در ژانویه 2008 و 2014 دو رخداد برف سنگین و فراگیر را تجربه نموده است. ابتدا برای محاسبه مدت ماندگاری و مساحت پوشش برف از داده های پوشش برف سنجنده مادیس استفاده شد. نتایج نشان داد که روزهای 16تا 20 ژانویه 2008 و 7 تا 10 ژانویه 2014 بازه زمانی حداکثر پوشش برف در سطح استان کرمان بوده است. در گام بعد شرایط همدید مرتبط با دو رخداد فوق مورد مقایسه قرار گرفت. نقشه های فشار تراز دریا، ضخامت جو و دمای سطح، الگوی یکسانی را در دو رخداد مذکور داشته اند. نفوذ پرفشار قدرتمند سیبری و به دنبال آن قرار گرفتن خط همفشار 1025 هکتوپاسکال، همدمای صفر درجه و هم ضخامت 5500 ژئوپتانسیل متر بر روی منطقه مورد مطالعه در هر دو رخداد برف ملاحظه می شود. اما همبستگی بالای مقادیر ارتفاع ژئوپتانسیل تراز 500 هکتوپاسکال با ترازهای زیرین، مقادیر مثبت تاوایی و شرایط رطوبت نسبی در ژانویه 2014 نسبت به ژانویه 2008 بهتر بوده و همین عوامل موجب گردیده که ارتفاع و گستره ی فضایی برف در ژانویه 2014 بارزتر باشد. نتایج این تحقیق می تواند الگوی مناسبی برای پیش بینی بارش های برف سنگین در این منطقه باشد.

Synoptic conditions of heavy and widespread snowfall in arid environment (case study: Kerman province)

IntroductionHeavy snowfall impacts the ski resort industry, outdoor activities such as snowmobiling and mountain climbing, homes, transportation networks, and vegetation. In the desert environment, such events as considered an unexpected climate hazard, due to incompatibility of human societies of these areas. The purpose of this study is a comparison of two widespread snowfalls during January 2008 and 2014 in the Kerman province, Using remote sensing and reanalysis data. Our results are presented in two main sections. First the temporal variation of the snow area over the Kerman province was investigated. In the next step, synoptically condition during heavy snowfall presented using NCEP/ NCAR data set. The results of the present study can increase our knowledge about the synoptic condition of heavy and widespread snowfall over arid environments.Data and methodThe area of snow cover was calculated in order to determine the duration of snow cover on land surface. For this, we used from MODIS data. For analysis of synoptic reasons during heavy snowfall used from 2.5 ° ×2.5 ° NCEP/ NCAR data. These data include the sea level pressure (SLP), air at the surface level, Geopotential height, Temperature of the upper levels, specific and relative humidity and uwnd and vwnd: zonal and meridional components. ResultsSnow cover area during January 2008 and 2014During January of 2008 Iran has experienced a severe cold wave and more widespread snowfall, compared to the January of 2014. However, despite the severe cold wave of Iran, snow depth and area as well as the minimum temperatures of Kerman province were higher during January of 2014. The snow cover area was maximum at 16 and 17 January 2008 and 8 and 9 January 2014. Variation of daily changes in snow cover area represent important points. First, the snow precipitation was occurred during of the period, and second, temperature condition was suitable for persistence of snow cover on land. Therefore, our synoptic analysis is basis on the beginning and the end of the snow cover on the land. The maximum snow depth at Kerman station during January 2008 and 2014 were reached in 13 and 23 centimeters, respectively. In addition, the minimum temperature at this station during January 2008 and 2014 dropped to 13.8 and 20.8, respectively. Undoubtedly, differences in the minimum temperature, snow depth and area (during 2008 and 2014), can be justified in patterns of pressure on a synoptic scale. Synoptically condition during heavy snowfallMean of Sea level pressure during the presence of maximum snow cover (16 20 January 2008) indicates the high pressure center over eastern parts of Russia. Following this high pressure, Kerman province is covered 1025 hPa isobaric. On the other hand, there is a similar pattern during 710 January 2014. The correlation coefficient between two SLP maps (R= 0.86) confirms this similarity. In addition to, such similarities can be seen at zero temperature isotherm which surrounds the Kerman province. There is a trough axis over the Kerman province, both on January 2008 and 2014. However, the vorticity and relative humidity values are various during two heavy snowfall events. In the January 2014 the vorticity and relative humidity values were higher in comparison of January 2014.ConclusionThe main objective of this study is an estimation of area under snow cover and synoptic condition during heavy snowfall in Kerman province. During January of 2008 the land surface temperature in throughout the Iran is significantly lower compared to the January of 2014. However, the area and depth of snow, severity of coldtemperature is higher during January of 2014. Results show that, there is a similar pattern in the sea level pressure, the thickness of the atmosphere and surface temperature during maximum snow cover in Kerman province (16 20 January 2008 and 7 10 January 2014). The southerly incursions of Siberian highpressure systems (1015 hPa over study area), 0℃ Isothermal curve and thickness of 5500 geopotentioal height was seen during either two event over the study area. The correlation coefficients between Geopotential heights at different levels is stronger in January of 2014 in comparison to January of 2008. In addition, Positive values of vorticity and relative humidity conditions was better during January 2008. All these factors caused that the snow depth and spatial distribution of snow cover were higher in the January of 2014 compared to January of 2008. This study confirms that the remotely sensed products are valuable in the synoptic climatology study.