بررسی طغیان های زمستانه بیش از چهار روز (اکتبر- مارس) طی سال های 2021-1989 در ایران

این پژوهش به منظور تحلیل سامانه‌های همدیدی موثر برطغیان های زمستانه در بارش‌های بیش از چهار روز ایران، ، ابتدا مجموع بارش‌های چهار روزه ایستگاه‌های هواشناسی منطقه مطالعاتی در ماه‌های اکتبر تا مارس، محاسبه شد. سپس بر اساس شاخص آندرسن دارلینگ، بهترین تابع توزیع احتمال بر داده‌های بدست آمده، برازش شد و در ادامه بارش‌های حدی ایستگاه‌های تحت بررسی برآورد شد و تعدادی تاریخ توفان چهار روزه در دوره آماری سی ساله بدست آمد. با استفاده از روش خوشه بندی سلسله مراتبی ارتفاع تراز میانی جو، پنج خوشه مختلف شامل چهار ناوه با عمق‌های متفاوت و موقعیت جغرافیایی مختلف و یک کم فشار بریده آشکار شد که از هر خوشه یک سامانه بارشی برای تحلیل همدیدی انتخاب گردید. از بررسی ناوه‌های آشکار شده، دیده شد که در دو مورد، در بخش شرقی ناوه، پشته قوی ارتفاع قرار گرفته است که مانع حرکت شرق سوی ناوه ارتفاع و سبب ماندگاری آن شده است. در این موردها هر چه عمق ناوه بیشتر شده است، پشته نیز عمیق‌تر شده و حرکت ناوه کندتر شده است. سامانه‌های همدیدی عرض‌های میانی هنگام عبور از روی آب‌های گرم دریای مدیترانه به سبب گردش چرخندی، حرکت صعودی ایجاد کرده و مقدار زیادی از رطوبت روی دریا را به ارتفاعات بالاتر منتقل کرده‌اند. بعلاوه بادهای شرقی بخش جنوبی پرفشار روی دریای عمان، مقدار زیادی نم ویژه به جنوب دریای سرخ انتقال داده است که با بادهای جنوبی بخش شرقی ناوه فشاری دریای سرخ به مناطق جنوب، جنوب‌غرب وغرب ایران منتقل شده است. این مقادیر نیز در اثر حرکت صعودی توانسته‌اند در فرایند بارش شرکت کرده و مقدار بارش و تداوم آن را در نیمه غربی ایران افزایش دهند.

investigation of winter floods lasting more than four days (october march) from 1989 2021 in iran

investigation of winter floods lasting more than four days (october march) from 1989 2021 in iranextended abstractintroductionthe phenomenon of precipitation is the final product of several complex atmospheric processes that are different in terms of time and place, and it can be considered one of the climatic characteristics of each region. the diversity of origin, temporal spatial changes of rainfall systems, ground conditions such as altitude and topography, and distance and proximity to moisture sources cause precipitation behaviors, including continuity, to have temporal spatial changes. heavy and continuous rains are significantly effective in supplying water, feeding the underground water table, and storing it in the soil. it can also cause landslides, destruction of vegetation of forests and pastures, severe soil erosion, destruction of water structures, and waste of high volume of surface water resources in arid and semi arid areas; therefore, it has always interested climate and meteorology researchers. in iran, heavy and moderate rainfalls have been investigated from different perspectives. some researchers have investigated heavy rains leading to floods in different regions of the country, and others have zoned rains lasting several days using the clustering method. despite the various analyses conducted by the researchers, due to the difference in the selection of rainfall amounts and the different behavior of synoptic systems, the factors affecting rainfall lasting several days remain in the veil of ambiguity. this research aims to identify the synoptic patterns of rainfall lasting more than 4 days and to investigate the horizontal flux of specific moisture so that by identifying the behavior of this variable and its related fluctuations, accurate and comprehensive planning can be carried out in the direction of managing the country’s water resources. what distinguishes this research from other studies is the method of estimating the limited rainfall of the study stations and the selection of the statistical period leading to 2022.methodology (materials and methods)this research used two series of data; the first series was the daily rainfall data of 120 synoptic stations of the country from its establishment until 2022, which was taken from the national meteorological organization. first, the total four day rainfall of weather stations from october to march was calculated. then, based on the andersen darling index, the best probability distribution function was fitted to the obtained data, and precipitation values above 99% of the fitted curve were obtained, among which the heaviest precipitation was selected. five distinct clusters were identified using the hierarchical clustering technique based on the height of the middle level of the atmosphere. from each cluster, a precipitation system was chosen for synoptic analysis based on three criteria intensity, continuity, and comprehensiveness of precipitation.the second series of data used in this research, which was used for the case study of synoptic systems, was taken from the ncep/ncar archive. these data in a regular grid are limited to 0 to 80 degrees east longitude and 10 to 60 degrees north latitude with a grid step of two and a half degrees, including an area where synoptic waves can be detected. from this series of data, we can refer to the average sea level pressure, altitude, temperature, and relative humidity of the pressure level of 850 hpa, the wind field and specific humidity of the pressure levels of 925 and 700 hpa, the height and the vertical component of the wind level of 500 hpa and the wind field of the level of 200 hpa.results and discussionfive specific patterns were obtained in the hierarchical clustering of the middle level’s height.