بررسي همديد كنش هاي چرخندي بر روي ايران

A Synoptic Survey of Cyclone Activity over Iran in 1992

يكي از مكانيسم هاي مهمي كه باعث ايجاد ناپايداري و تراكم در جو مي شود، سامانه هاي چرخندي است. اين پژوهش به بررسي رقومي مراكز چرخندي مؤثر بر ايران و مناطق چرخندزايي و ارتباط آنها با بارش كشور مي پردازد. براي تحصيل اين هدف از داده هاي بازكافت شده ارتفاع ژئوپتانسيل NCEP/NCAR با تفكيك زماني شش ساعته و تفكيك مكاني 2/5 × 2/5 درجه، در شش تراز اول جو براي سال 1371 ش. استفاده شده است. با توجه به محاسبات انجام شده، مشخص گرديد كه بيشينه درصد فراواني چرخندهاي سه تراز اول جو در فصل زمستان، تراز 700 هكتوپاسكال در فصل پاييز و دو تراز 600 و 500 هكتوپاسكال در فصل بهار رخ مي دهد. مراكز چرخندزايي كه چرخندهاي آنها كشور ايران را تحت تأثير قرار ميدهند، شامل منطقه چرخندزايي جنوا، جنوب ايتاليا، جزاير سيسيل و كم فشار گنگ است. همبستگي بين درصد فراواني فصلي چرخندها با ميانگين بارش فصلي كشور نشان مي دهد كه بين درصد فراواني چرخندها با ميانگين بارش كشور رابطه همبستگي مثبت وجود دارد.

Iran country due to laying in the desert belt on the northern hemisphere، are dry and desert climate of many parts of it Predominate. Due to the same location in the atmospheric loss of human life and animal life and it has an important role. an‎d according to the moisture sources in the country and located outside of the atmospheric loss from year to year fluctuations have other roles pluvial systems are more bold. One of the important mechanisms that cause instability and density will be cyclones. Therefore recognition of cyclonic centers and cyclogenesis can in environmental studies، planning and management of water resources and natural disasters، weather forecasts and the country sociol-economic development is necessary and important. Therefore، for identify and positioning cyclonic action is used from reanalysis data geo-potential height NCEP/NCAR with 6-hour time resolution (00، 06 12 ،18 z)and spatial resolution 2.5× 2.5 degree for the 1371 Solar year (93-1992 ). for Cyclone identification in six levels 1000، 925 850 700 600 500 hecto pascal Two conditions are considered Which include the:1- geo-potential height pixel resurvey than every eight neighboring surrounds is low.2- Large gradient geo-potential height on the Cornell Equal to or greater than 100 meters is 1000 km. In this study، first cyclonic centers according to the provisions are intended Identify and then monthly، seasonal and annual plans، drawn and cases were analyzed. According to the calculations performed were determined The maximum cyclone frequency in the first nine months in The 500 hpa level and three months in winter in level 1000 hpa and low they in the levels both 850 and 700 hpa Occurred. Also cyclogenesis centers of the cyclones they affect the country are include Genoa cyclogenesis area، Italy southern، Sicily and Sardinia Islands، southern Greece، Adriatic Sea، West Spain، Libya and Algeria، Iceland and are Pakistan. Finally، a correlation between frequency percentage cyclone monthly with an average monthly precipitation country established Shows that The highest correlation is in hpa 1000 level and in other levels correlation value decreases.finally، Can be said that there is between frequency percentage cyclones with rainfall average country a positive correlation.