شناسايي الگوي همديدي سامانه هاي بندالي موثر بر دماي ايران

Synoptic analysis of blocking patterns affecting the temperature of Iran

رخداد دماهاي حدي بسيار سرد و مداوم در مقياس ماه، فصل و يا سال مي تواند با رخداد سامانه بندالي مرتبط باشد. به منظور آشكار سازي و تعيين الگوهاي فشار مرتبط با رخداد سامانه هاي بندالي موثر بر دماي ايران، داده هاي روزانه مربوط به ارتفاع ژئوپتانسيلي سطح 500 هكتو پاسكال در محدوده N90-0 و E100-W90-، با تفكيك 5 /2 درجه براي دوره 2013-1948 از سايتNCEP دريافت شد. ابتدا بر اساس شاخص آشكار سازي دو بعدي، شرايط رخداد سامانه بندالي در محيط نرم افزار MAT LAB برنامه نويسي و موقعيت آنها مشخص گرديد. در مرحله بعد به منظور تفكيك رخدادهاي موثر بر ايران، منطقه مورد مطالعه به E100W-40- و N80-20 محدود شد.الگوهاي فشار مربوط به سامانه هاي بندالي موثر بر آب و هواي ايران با استفاده روش تحليل عاملي و خوشه بندي چندهسته اي K-means، در محيط نرم افزار SPSS تعيين شدندو از بين آنها الگوهاي سامانه بندالي موثر بر دما استخراج گرديد. كه شامل الگوي امگا جلو محور ريج، الگوي امگا زير محور ريج و الگوي دو قطبي بود. ارتباط هركدام از الگوها از ديدگاه همديدي در سطح زمين و hPa500 و ارتباط آن با دماي سطح زمين مورد تجزيه و تحليل قرار گرفت. ارتباط الگوهاي سامانه بندالي با دماي سطح زمين نشان داد كه رخداد دماهاي بيش از نرمال و يا كمتر از نرمال ناشي از رخداد سامانه بندالي علاوه بر تداوم، با تاخير زماني يك روزه يا كمتر در سطح زمين همراه است.

1-Introduction: On account of continuation nature and being quasi-stationary of blocking events, alternation in their abundance and duration can have a major effect on climatic conditions such as temperature and monthly and seasonal precipitation. The occurrence of very cold temperatures can be related to the blocking occurrence; a very cold temperature in winter (Europe 2009-2010) is connected to the blocking event and negative phase NAO. In our country many studies have been carried out on surveying the synoptic patterns of cold temperatures. In all these studies apart from two cases, the relationship of the blocking model with cold temperatures have not been considered directly, but so far have not been done a comprehensive and long-term research from the role of blocking models on country’s temperature. In this research, the role of blocking on Iran’s temperature in cold season have been investigated in quantity way in order to use a long statistical period in a climatology scale, All the happenings be cleared and on the other hand, the double effects of the blocking event that lead to a temperature less and more than normal become distinct and analyzed and its prevailing models be used in order to necessary per-knowledge and prediction; because reconnaissance and detection of the blocking happening can help to accuracy and carefulness of short-term prediction models. Iran according to its location has most abundance of the blocking event in this cold season, so in this research also only have been analyzed and detected the effective blocking patterns on temperature in these two seasons (fall and winter). 2-Data and Method: Data related to geo-potential height of 500 hPa level in regard to two dimensions index of visible blocking, daily for cold season in year for a 65-year period from 1948 to 2013 in a 2/5 *2/5 network that is appropriate for studying the large-scale occurrences like the blocking was extracted from site NCEP-NCAR for limit 0 to 90 degrees northern latitude and 90 degrees western to100 degrees eastern longitude. Then the investigated zone was bounded according to the knowledge of the limit and the origin of the effective blocking on Iran’ weather from -40 degrees western to 100 degrees eastern longitude and 20 to 80 degrees northern latitude. To better revealing the effect of the blocking on temperature, was considered the maps of analogous temperature with each model in a smaller limit in longitude 20 to 70 degrees eastern and latitude 20 to 50 degrees northern. The Blocking happening conditions were programmed based on two dimensions in software MAT LAB and all the 5-day events and more were extracted. Then in order to decrease the data and their classification was used an analysis way of main ingredients based on ornament S. Then using sorting in K-means way, the prevailing circulatory models of the blocking were extracted that totally 7 circulatory patterns were attained. Among these 7 models, 2 models were identified as effective blocking patterns on temperature that was including omega and double polar pattern. The synoptic Conditions each of the models on the level of ground and 500 hPa level were analyzed. The Temperature conditions on the level of ground were investigated for all the models, and for each of the patterns, an event has been showed on 500 hPa level daily. In this manner, the synoptic models of effective blocking happenings on Iran’ weather were identified to increasing accuracy and carefulness of the temperature predictions. 3-Results and discussion: Atmospheric blocking with regard to its being quasi-stationary and large-scale nature can effect on the level of ground and with respect to the abundance of its happening can also have effect on monthly and seasonal temperature. In general the blocking event has a double-effect on temperature and can lead to a temperature less than normal (cold season) and more than normal (warm season) in the zone. The Blocking is a large-scale complication that its different parts have various synoptic events. This variation in the blocking models of omega kind is more; the zones that are located under influence of forward part, because of falling cold weather from high latitudes face with temperatures less than normal that according to blocking happening severity and its continuity especially in cold season lead to frigidity waves with different severities. Under influence of the zones of ridge axis benefit from a temperature more than normal which this subject has a special importance in cold season for continental zones of high latitude causes a temperature modification for several days and even several weeks in the zones. Two patterns of effective blocking on temperature consists omega pattern: including two sub-patterns in front of ridge axis and ridge sub-axis and Splite pattern model. 4-Conclusion: The Blocking is a large-scale phenomenon with different models that each of its models also has different synoptic conditions. In cold season of year the blocking patterns that are effective on temperature are divided to two general patterns of omega and double-polar. The omega model has two subordinate patterns; one of them is the omega model in front of ridge axis which its under influence zones are together with cold temperatures and less than normal and a low-pressure system on the level of ground, but in the omega model, under influence zones of the model below ridge axis have a temperature more than normal and low-pressure on the level of ground. In the second pattern, the zones which were in front of above ridge with a high height on account of falling air from high latitudes were put under less than normal temperature happenings. Ineffective blocking systems on falling, the block event and falling changes in terms of chronological have a harmony together, but studying relationship of the blocking models with the temperature on the level of ground showed that the events of the temperatures of more and less than normal resulting from the blocking event is together with a one-day chronological delay or less on the level of ground. In general, studying the effective blocking models on the temperatures of less than normal showed that temperature decrease in the model in front of ridge axis of omega kind is usually more than the above high-height forward ridge in double-polar pattern. On grounds of blocking’s being quasi-stationary and continuation nature, the characteristics of resulting from it, there will not have a noticeable alternation in a zone for several days and sometimes several weeks; as a result, the knowledge of its various synoptic models and the different effects of resulting from them on ground can help to accuracy and carefulness of the short-term prediction models and temperature conditions in a way become predicted with a more confident for next several days.