بررسي دو مورد سيل شديد در استان آذربايجان شرقي از ديدگاه همديدي و حركت شناختي و انطباق آن با پيش بيني بارش مدل GFS (2000-2010)

The study of two cases of severe flooding over the Eastern Azerbaijan Province from the synoptical and kinematic view and coincident of these events with GFS precipitation forecast (period on 2000-2010)

مطالعه آماري در بازه زماني 2000 تا 2010 نشان داد، استان آذربايجان شرقي در معرض سيل هاي متعددي قرار گرفته است بطوريكه فصل بهار با فراواني 66 درصد، تابستان 28 درصد، پاييز 4 درصد و زمستان 2 درصد مي باشد. دو سيل شديد از نظر شدت ميزان خسارات مالي و جاني، شامل سيل 14 مي سال 2007(24 ارديبهشت خرداد 1386) در شهر تبريز و ديگري 18 جون 2009(28 خرداد1388) در شهر ميانه انتخاب گرديد و براي مطالعه وقوع اين دو سيل نقشه هاي همديدي سطوح استاندارد مورد تحليل قرار گرفته است. در سيل تبريز، ناوه وارون گرمايي با امواج كژفشاري كه بواسطه دوبندال يكي پرفشار شمال سيبري و ديگري كم ارتفاع بريده شمال اروپاي مركزي بوجود آمده اند، برخورد داشته است. دراين ناوه هاي كژفشاري سريع مهاجر در روي استان، بزرگي حركت هاي قائم در700hpa ، بوده و بزرگي تاوايي مطلق داخل آنها رويhpa 500، مي­باشد. در سيل ميانه نيز ناوه وارون گرمايي وجود دارد و با مركز سرد كم ارتفاع بريده شده سطوح مياني كه در روي تركيه است، برخورد داشته و سيل شديدي ايجاد كرده است. در اين سامانه، حركت قائم در700 hpa ، و بزرگي تاوايي مطلق داخل 500hpa حدود مي باشد ولي در زمان حادثه سيل، روي استان بزرگي آن محاسبه گرديده است. مقايسه بارش پيش بيني شده تجمعي ازمدلGFS سيل ميانه با گزارش هاي ثبت شده واقعي ايستگاه ها بطور تجمعي هماهنگي خوبي را نشان داد ولي در سيل تبريز هماهنگي مناسبي ملاحظه نگرديد.

Our statistical study showed that during period 2000-2010, Eastern Azerbaijan Province was threated by numerous severe floods. These occurred during spring with a frequency of 66% and summer with 28% and fall with 4% and winter with only 2% frequency. From damages viewpoint, we selected two of most severe floods of the province to work on. The first one was in Tabriz city, centre of Eastern Azerbaijan Province, on 14th of May 2007. The other one occurred in Mianeh city on 18th of June 2009. For studying the two severe floods, we analyzed synoptic charts at all standard levels for 13-15th of May 2007 and 17-19th of June 2009. We found an inverted thermal trough at the earth’s surface impacting with baroclinic short waves trough that moving fast from west to east over the region. The above features were induced by two blocking patterns. First one was a blocking high, located over north of Siberia, and second one was a Cut-off low, located over north of central Europe. The magnitude of upward mention over 700hpa level troughs, was and magnitude of absolute vorticity over 500hpa, level troughs were in the range of . the main pattern for the second flood, occurred in Mianeh, was also an inverted thermal trough at the earth’s surface, impacting a could cut-off low in middle and upper troposphere, located over Turkey for this case, we found that the magnitude of upward motion in the centre of cut-off low at 700hpa was and magnitude of absolute vorticity in the center of cut-off low at 500hpa was but at the same time absolute vorticity over the province was . The total daily amounts of precipitation forecast from GFS model was in a good harmony with recorded daily precipitation in the stations for the Mianeh flood but for Tabriz’s flood, the result was not appropriate.