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جستجوی مقالات مرتبط با کلیدواژه "atmospheric circulation patterns" در نشریات گروه "جغرافیا"

تکرار جستجوی کلیدواژه «atmospheric circulation patterns» در نشریات گروه «علوم انسانی»
جستجوی atmospheric circulation patterns در مقالات مجلات علمی
  • زهرا قصابی*، ابراهیم فتاحی

    الگوهای گردش جوی نقش اصلی در رخداد پدیده های محیطی به ویژه در مناطق معتدله دارند. این الگوها سبب ایجاد دوره های مرطوب یا خشک می شوند. طبقه بندی الگوهای گردش جوی روزانه و شناسایی مراکز فعالیت آن ها در نواحی مختلف ایران در برنامه ریزی ها موثر است. در تحقیق حاضر از تحلیل مولفه های اصلی و خوشه بندی به منظور طبقه بندی الگوهای گردش جوی روزانه استفاده شد. میانگین روزانه ارتفاع ژیوپتانسیل تراز 500 هکتوپاسکال و فشار سطح دریا طی دوره 2019-1990 در تفکیک °5/0 از ECMWF استخراج شد. محدوده انتخابی شامل 8281 نقطه از E°65-20 و N°55-10، خاورمیانه و ایران را می پوشاند. در تحلیل مولفه های اصلی نقاط وابسته به هم ادغام و ابعاد ماتریس کاهش داده شد، به طوری که 9 مولفه اصلی باقی ماند. از آرایه S برای شناسایی تیپ های هوا و از خوشه بندیK-Means برای طبقه بندی تیپ های هوای روزانه استفاده گردید. همه روزها (10957 روز) به هیجده گروه تقسیم بندی شدند. نقشه های ترکیبی فشار سطح زمین و ارتفاع ژیوپتانسیل تراز 500 هکتوپاسکال و توزیع ماهانه تغییرپذیری الگوها به دست آمد. واگرایی شار رطوبت در هر الگو محاسبه و تحلیل شد. نتایج نشان داد که فراوانی الگوهای 1، 7، 13 و 18 در دوره گرم سال و بقیه الگوها اغلب در دوره سرد سال است. این وضعیت با شرایط همدیدی هر یک از الگوها در سطح زمین و تراز 500 هکتوپاسکال مطابق است، طوریکه در الگوهای گردشی دوره گرم سال کم فشار حرارتی سطح زمین در پایین تر از مدار °35 با پرارتفاع جنب حاره تراز میانی جو همراه است و بیشینه شار رطوبت تراز 850 هکتوپاسکال در بخش های شرقی ایران است. در الگوهای گردشی دوره سرد سال، جریان های جنوبی و جنوب غربی از کم فشار جنوب دریای سرخ، اغلب با ناوه تراز میانی جو همراه است، همگرایی شار رطوبت در جنوب دریای سرخ، بخش هایی از غرب، جنوب غرب، جنوب و شمال غرب ایران، شمال شرق دریای مدیترانه، جنوب غرب ترکیه و شرق دریای سیاه دیده شد.

    کلید واژگان: الگوهای گردش جوی, تحلیل مولفه های اصلی, شاررطوبت, خاورمیانه, ایران
    Zahra Ghassabi *, Ebrahim Fattahi
    Introduction

    The main idea of ​​atmospheric circulation patterns and their classification is to convert a set of atmospheric parameters into a univariate catalog, with cases of similar characteristics grouped together. Easier interpretation of weather conditions would be the advantage of the classification.Many researchers to classify atmospheric circulation patterns have used the principal component analysis (PCA) method. Esteban (2006) in a study of atmospheric circulation patterns in Western Europe, categorized daily synoptic circulation patterns into 20 groups and showed sea level pressure and 500-hPa geopotential height configurations throughout the year. Smith and Sheridan (2018) clustered geopotential height anomalies at levels of 100 and 10-hPa and sea level pressure to study the patterns of tropospheric and stratospheric potential vorticity. In Iran, Raziei (2007) by PCA classification and clustering identified 18 atmospheric circulation patterns for the Middle East and Iran. He showed that patterns with meridional and northwest flow often cause drought and patterns with southwest flow cause wetting. Hanafi (1399) identified the air types in the northwestern region of the country (Maragheh station), and showed that the high geopotential systems of Saudi Arabia and North Africa governed by hot and dry conditions and the Mediterranean and polar cold air masses are involved in creating cold periods.Atmospheric circulation patterns identified for Iran are based on monthly average atmospheric data and with a resolution of 2.5°. Often due to the importance of winter as the main rainy season in Iran, the identification of atmospheric circulation patterns of other seasons has less studied. On the other hand, most studies have conducted regionally in a province/small part of the country. In this study, we have classified the synoptic patterns affecting Iran and the Middle East in the period of 1990-2019, using the PCA method for all seasons and with a higher accuracy using data with 0.5° resolution on a daily time scale. Then, composite maps of the MSLP (Mean Sea Level Pressure) and 500-hPa geopotential height were prepared and analyzed to obtain the frequency of monthly and seasonal occurrence of each investigated pattern. Previous studies have focused mainly on 500-hPa and MSLP parameters. However, in the present study we have used the 850-hPa moisture flux besides the already applied quantities, which can be considered a main and important quantity for the rain occurrence.

    Materials and methods  :

    Geopotential height data of 500-hPa received from the ECMWF (ERA5) at one hour intervals during the period 1990-2019 in the area of 20E-65°E longitude and 10N-55°N latitude. Due to the data volume and software and hardware limitations, data with 0.5° resolution extracted. By calculating the daily average in each grid, the data matrix consisted of 8281 columns (grids) and 10957 rows (number of days). Then the MSLP, 10m wind speed, and 850-hPa temperature and relative humidity maps/data were provided/extracted.The PCA analysis is a method for extracting important variables from a large set of variables in a data set. The main goal is to reduce number of components by finding the ones that explain correlations between the variables. We selected the first nine components covering a large portion of the described variances and ignored other minor components. In the present study, the R language programming were used to analyze the principal components with S array and select the components. To classify air types, K-means clustering was used, so that it presents the most alternating patterns of atmospheric circulation in the study area during the year. After selecting the main components and determining the scores of the components, all days (10957 days) were classified into 18 groups. Sea level pressure and 500-hPa geopotential height maps were prepared and interpreted. Monthly and seasonal frequency of occurrence of each pattern and relationship of spatial distribution of moisture flux at 850-hPa were investigated.

    Results and discussion

    Based on the results obtained from principal component analysis, the first 9 components were selected, which explained 95.93% of the total variance of the data. According to the monthly and seasonal distribution of each pattern, it was observed that cp1, cp7 and cp18 circulation patterns occur in summer and early autumn and cp13 occur in late spring, summer and early autumn. Cp2, cp4, cp6, cp8, cp11 and cp16 occur in late autumn to early spring of the following year and cp3, cp5, cp9, cp10, cp12, cp14, cp15 and cp17 circulation patterns occur in late autumn to spring of the following year. These situations correspond to the synoptic conditions of each pattern at sea level and the level of 500-hPa.In the circulation patterns of the warm period of the year, thermal low pressure of sea level pressure map below 35° N is associated with subtropical high at mid-level of atmosphere. The maximum moisture flux in 850-hPa located in the eastern parts of Iran and the maritime borders of Yemen and Oman which is compatible with southern and southeastern flow. In cp2, cp4, cp6, cp8, cp11 and cp16 circulation patterns that occur in the cold period of the year; south and southwest flow of low pressure in the south of the Red Sea are associated with mid-level of atmosphere. There is convergence of moisture flux in the south of the Red Sea and in parts of the south and southwest of Iran, east of the Black Sea, northeast of the Mediterranean Sea and south of Turkey. In other patterns that occur in the cold period of the year as well as in spring, low pressure in south and center of the Red Sea is associated with trough in the mid-level of the atmosphere. Convergence of moisture flux was in the west, southwest, south an northwest of Iran, northeast of the Mediterranean Sea, southwest of Turkey and south of the Red Sea.

    Conclusion

    In the present study, principal component analysis with S array and K-means clustering was used to classify circulation patterns in Middle East and Iran. The results show significant differences in the arrangement of patterns, the frequency of air types and their path to Iran.

    Keywords: Atmospheric Circulation patterns, principal components analysis, Moisture flux, Middle East, Iran
  • اسماعیل عباسی*، مهدی خزایی
    یکی از مخرب ترین پدیده های هواشناسی که گستره فضایی و بازه زمانی آن کاملا متغیر است و در مقیاس های مختلف خودنمایی می کند توفان های تندری است. پدید ه ای که مقیاس مکانی آن زمانی که در دل چرخندهای حاره ای و مناطق همرفتی کمربند همگرایی بین حاره ای قرار می گیرد بسیار گسترده بوده و از سویی بسیار حیرت آور، زیبا و در عین زیبایی طی شرایطی خاص فوق العاده مخرب می گردد. هدف از انجام پژوهش حاضر شناسایی و تحلیل چنین توفان های مخرب در یک دوره زمانی 25 ساله (1986-2010) در ایستگاه سینوپتیک کرمانشاه می باشد. داده های مورد استفاده در این تحقیق شامل داده های بارش روزانه و کدهای مربوط به پدیده های هواشناسی، پارامترهای دمای خشک، نقطه شبنم، رطوبت نسبی، جهت و سرعت باد جهت محاسبه شاخص های ناپایداری و پارامترهای ارتفاع ژئوپتانسیل، نم ویژه، سرعت قائم، مولفه های باد مداری و نصف النهاری می باشد. نتایج نشان داد که طی دوره آماری مورد بررسی سه توفان تندری بسیار شدید در منطقه مورد مطالعه رخ داده است. بررسی شاخص های ناپایداری حاکی از قرار گرفتن این شاخص ها در طبقه شدید و مناسب جهت رخداد پدیده توفان تندری می باشد؛ همینطور وضعیت دینامیک جو همزمان با رخداد این پدیده نشان از حضور یک ناوه بسیار عمیق در غرب منطقه مورد مطالعه و قرارگیری خروجی هسته رودباد ترازهای 500 و 850 میلی بار بر روی منطقه مورد مطالعه را دارد که در پی این اتفاق پدیده توفان تندری با شدت زیاد همراه با شکل گیری ابرهای کومولوس و رعد و برق و نهایتا بارش های سنگین منطقه مورد مطالعه را تحت تاثیر اثرات مخرب خود قرار داده است؛ این درحالیست که این وضعیت برای دو مورد شناسایی شده یعنی پدیده روز 04 فوریه 2007 و 12 دسامبر 1991 نسبت به دیگر موارد شناسایی شده یعنی  پدیده روز 17 آوریل 1991 شرایط جوی ناپایدارتری را از نظر الگوهای گردشی متوسط مقیاس تجربه نموده است.
    کلید واژگان: توفان های تندری, شاخص های ناپایداری, نمودار اسکیوتی, الگوهای گردشی جو, ایستگاه سینوپتیک کرمانشاه
    Esmaeil Abbasi *, Mahdi Khazayi
    One of the most devastating phenomena of meteorology which varies extensively in spatial and temporal extent and manifests itself at various scales, is thunderstorms. The purpose of this study was to identify and analyze such destructive storms over a period of 25 years (1986-2010) at the synoptic station of Kermanshah. The data used in this research includes daily rainfall data and codes related to meteorological phenomena, dry temperature, dew point, relative humidity, wind direction and wind speed for calculation of instability indices, geopotential height parameters, specific humidity, vertical velocity, and zonal and meridional components. The results showed that during the statistical period of the study, three extreme thunderstorms occurred in the study area during the statistical period of 25 years. The study of instability indices indicates that these indices are in the strong and suitable category for the occurrence of thunderstorm phenomenon; in addition, the dynamics of the atmosphere at the time of the occurrence of this phenomenon indicates the presence of a very deep trough and negative abnormalities in the west of the studied region and positioning of the left half of the Jetstream of levels of 500 and 850 millimeters on the studied area. Following this phenomenon, the thunderstorm intensely affected the region by its destructive effects with the formation of clouds of cumulus and lightning, and finally, heavy rainfall. However, it should be mentioned that for two cases, that is, the phenomenon of February 4, 2007 and December 12, 1991, they experience a more unstable climate due to the average circulation patterns compared to the other identified case, i.e. the phenomenon of April 17, 1991.
    Keywords: Thunderstorms, instability indices, atmospheric circulation patterns, Kermanshah synoptic station
  • بهروز ساری صراف، علی اکبر رسولی، آذر زرین *، محمد سعید نجفی
    در این مطالعه، بر اساس خروجی های مدل WRF-CHEM، الگوهای توزیع قائم سامانه های گردوغبارزا در غرب ایران به دو دسته تقسیم شد: الگوهایی با توزیع قائم در حدود 5/6 کیلومتر و کمتر از 5/3 کیلومتر. الگوهای همدید رخداد گردوغبار در دوره سرد به دو دسته تقسیم می شود: جبه های و غیرجبه های. در الگوی اول جبه های، بیشینه ارتفاع گردوغبار حدود 5/6 کیلومتر است و وابسته به شدت واگرایی در تراز میانی و سرعت قائم بالاسو و استقرار هسته جت بر فراز مناطق منشا گردوغبار است. در الگوی دوم جبه های، بیشینه ارتفاع توده گردوغبار کمتر از 4 کیلومتر است. در این الگو، ارتفاع محدودتر توده گردوغبار وابسته به شدت محدودتر چرخندگی در تراز میانی و موقعیت جت است که عمدتا بر فراز مناطق منشا گردوغبار قرار ندارد. در الگوی غیر جبه های، پهنه های وسیعی از خاورمیانه تحت تاثیر استقرار یک پشته قرار می‏گیرد و الگوی گردشی در تراز زیرین تروپوسفر در شکل‏گیری گردوغبار موثر است. ارتفاع گردوغبار در این الگو حدود 5/3 کیلومتر است. همچنین، مهم ترین عامل در محدودشدن ارتفاع توده گردوغبار در غرب ایران ماهیت سامانه های جوی است. مانع کوهستانی زاگرس در انتشار قائم و افقی گردوغبار اهمیت کمتری دارد.
    کلید واژگان: الگوهای همدید, توزیع قائم گردوغبار, جبهه زایی, کوهستان زاگرس
    Behruz Sari Sarraf, Ali Akbar Rasouli, Azar Zarrin *, Mohammad Saeed Najafi
    Introduction
    Being in vicinity of vast deserts, the west and southwest of Iran are characterized by high-levels of dust events. Western Iran located in the neighborhood of some important dust sources: the Tigris and Euphrates basin in Iraq as well as Syria to the west and the Arabian Peninsula to the south. These sources are among the most active in the dust belt, especially in recent years.
    Overall, sand and dust storms are the most important atmospheric phenomena in arid and semi-arid regions that have been recognized as having a wide range of environmental and climate impacts including distractive effects upon air quality and human health, agricultural activities, land use and soil formation and they are also recognized as the factor of desertification. Dust particles are important components of the earth’s climate system as they affect the balance of solar radiation by scattering and absorption. These feedbacks have a direct link with the intensity and height of the column of dust in the troposphere. The aim of current study are understanding the vertical distribution patterns of Middle Eastern Dust Storms (MEDS) associate with atmospheric circulation patterns and topography in cold period of the year (November-May) in west of Iran.
    Data and
    Methods
    The horizontal and vertical distribution of dust aerosols simulated with chemistry/aerosol module of Weather Research Forecast system (WRF-CHEM). The WRF–Chem configured with the Goddard global ozone chemistry aerosol radiation and transport (GOCART) dust emission scheme to calculate the influx of dust into the atmosphere. The effect of the Zagros Mountains on vertical and horizontal distribution of dust emission examined by WRF model in an area between 16º–44ºN and 33º–65ºE with a 30 km horizontal grid spacing. The FNL re-analysis data set were used to provide the initial and lateral boundary conditions in a control run and in a simulation run by removing the Zagros Mountains.
    The atmospheric circulation pattern is investigated to explain the mechanisms of dust emission in the Middle East and its vertical emission over this region. The hourly visibility and dust dataset of 34 synoptic stations located in the western part of Iran were obtained from the Iran Meteorological Organization (in 2004-2013 period) to extract dust events in the area of study. The NCEP/NCAR 6-hourly reanalysis dataset with 2.5°×2.5° horizontal resolution is used for mentioned period.
    Results And Discussion
    The atmospheric circulation patterns which lead to generation of dust events in the Arabian region classifying in two categories of frontal and non-frontal patterns.
    In the frontal events of MEDS that occur in the cold period of the year, dust is created under the influence of emigrate systems of westerly winds setting in the Middle East region. So that, formation of a divergence system in mid-level of troposphere (500 hPa) leads to formation of a surface convergence center as well as frontogenesis, air uplift and atmospheric instability condition in the source areas of MEDS. In addition the Polar Jetstream position as one of the enhancing factors of instabilities and air uplift in the region has a key function in vertical distribution of MEDS. Generally, MEDS events which occur due to the frontal pattern are similar to the precipitation systems except the lack of humidity in case of dust generation in arid lands of the Middle East region. Frontal patterns are divided into two patterns including Trough and Blocking. These two patterns are the dominant patterns of dust generation in November to May in this region in cold period. In frontal pattern the vertical distribution of column dust divided to two category: in first pattern the maximum height of dust is above 7 km and in second pattern the maximum height is below 4 km. These patterns to be related to the position and strengthen of Polar Jetstream, the strength of mid-levels vorticity and upward motions of air flow. In first vertical distribution pattern there is upward motion to the 9 km of the troposphere where as in second pattern the upward motion is to the 5 km of the troposphere.
    In non-frontal pattern neither frontogenesis happens nor there is a polar front Jetstream which causes instabilities in the Middle East dust storm sources. So that dust generation is due to the regional circulation system in the lower level of troposphere. In this pattern the concentration of dust load is less than frontal MEDS and the maximum height of column dust is below 3.5 km.
    The results of impact of topography in vertical and horizontal distribution of MEDS reveals that the Zagros Mountains have a limit effect on the vertical and horizontal distribution of MEDS. However in the absence of the Zagros Mountains and the main factor which control the vertical and horizontal distribution pf dust storm is the strength of atmospheric systems.
    Conclusion
    Two main patterns of cold period of MEDS are frontal and non-frontal patterns. The vertical distribution of column dust in mentioned patterns are different. In frontal pattern the height of dust are varied between 4 to 7 km in the troposphere. The position and strengthen of Polar Jetstream, the strength of mid-levels vorticity, upward motions of air flow and divergence of moisture flux in MEDS sources are the most important factors which determine the strength and height of dust storm in the middle east in the cold period. In non-frontal pattern the concentration of dust in the troposphere is below 3.5 km. the result of this study reveals that the important of strength of atmospheric systems is more than topography barrier in vertical and horizontal transport of MEDS in west of Iran.
    Keywords: Atmospheric circulation patterns, Column dust height, Frontogenesis, Zagros Mountains
  • ابراهیم فتاحی*، هنگامه شیراوند
    در دوره ی سرد سال، ریزش برف سنگین باعث بروز مشکلات و خسارات زیادی می شود. وسعت خسارات ناشی از ریزش برف های بسیار سنگین در بخش های مختلف پیامدهای دارد، از جمله تخریب ساختمان ها و تاسیسات، اختلال در بخش هایی نظیر حمل و نقل و توزیع سوخت و انرژی در فعالیت های بخش صنعتی و کشاورزی. همچنین، وقوع پدیده ی یخبندان در چنین شرایطی باعث تشدید خسارات می شود. در دوره ی سرد سال، لزوم شناخت و آگاهی از مکانیسم تشکیل چنین پدیده ای، که ریشه در الگوهای گردش جوی در مقیاس سینوپتیکی دارد، می تواند نقش موثری در مدیریت خطر و بحران داشته باشد. هدف اصلی این مطالعه شناسایی الگوهای گردش جوی مربوط به روزهای همراه با ریزش برف سنگین در حوضه های غرب ایران است. در این مطالعه، روزهایی را که حداقل 15 سانتیمتر برف طی 24 ساعت داشتند و ریزش برف در سطح فراگیری گزارش شده بود به منزله ی روز با ریزش برف سنگین انتخاب شد. سپس، برای شناسایی و طبقه بندی الگوهای گردشی مربوط به روزهای فوق، داده های روزانه مربوط به تراز 500 هکتوپاسکال و فشار تراز دریا ی روزها مذکور از مرکز داده های NCEPتهیه شد. برای طبقه بندی الگوهای روزهای همراه با برف سنگین از روش تحلیل مولفه های اصلی و خوشه بندی استفاده شد. سرانجام، الگو های گردش اصلی ریزش برف سنگین در منطقه ی مطالعه شناسایی شد. الگوهای به دست آمده می تواند در امر پیش بینی روزهای همراه با برف سنگین کارایی داشته باشد.
    کلید واژگان: برف سنگین, الگوهای گردش جوی, طبقه بندی, تحلیل مولفه های اصلی, خوشه بندی, غرب ایران
    Ebrahim Fattahi*, Hengameh Shiravand
    Heavy snowfall in the cold period will cause a lot of damages and troubles for society such as collapse of building installations, and confusions in road network and fuel distributions. Freezing event will also make worse the intensity of damages. Therefore, identifying the mechanisms of Atmospheric Circulation Pattern (ACP) which form the heavy snowfall and freezing events will certainly help to manage the risk and mitigate the impacts of the crisis. The main objective of this research was identification of Circulations Patterns (CP) related to snowy days in the basins located in the west and southwest parts of Iran. In this study, the geographical location of the study area is West of Iran in 30- 37degree North latitude and 45 57 - 51 40 East longitude. The region consists of provinces of Kurdistan, Kermanshah, Hamedan, Lorestan, Ilam, Zanjan, Markazi, Chahar Mahal Bakhtiari, Kohgiloye Boyer and parts of West Azerbaijan. In this study, the days which have at least 15 cm of snow in 24 hours, are known as days with heavy snowfall.To choose widespread snowy days, the days that were reported in three stations at least, 3 adjacent provinces and the amounts of the snow were more than 15 cm, are known as heavy snow days. In this research, to analyze the synoptic patterns of heavy snowfall days, daily data of 500 hp level and sea level pressure in 2/5 degree from reanalysis data of NCEP were extracted. All effective systems covered the studied region. The region consisted of 408 point of (20-60) degree in north and (20-80 ) degree in east altitude .To classify and analysis the synoptic patterns of heavy snowfall days Cluster Methods Analysis and Principal Component Analysis were used. To draw average maps of air circulation patterns, pressure data and daily resulted geopotential height of factor analysis and cluster analysis were used. Then four circulation patterns were obtained. Frequency of days with heavy snow – in fourth patterns - showed patterns of CP1 (13 days), CP2 (17 days), CP3 (39 days), and CP4 (12 days). During the under study period, the most frequency belonged to CP3 pattern – 39 day- and the least is belonged to CP4 pattern -12 days. The results obtained of researching synoptic patterns of heavy snowfall in west and south-west of Iran: On days with heavy snowfall in the South West and West of Iran usually Siberian high pressure system extended widely and one toungue towerd east of Aral lake and other toungue developed to south till Tibetan also some times its toungue extend on the Caspian sea and north part of Iran to Europa. Azores high pressure center is usually reinforced and its tongue extends to the Mediterranean Sea, central europa and africa and other tongue semi- west Iran and Mesopotamia. Extension of Siberian high pressure in north part of Iran with cold high pressure in east Europe created Azore high pressure belt.the system turning clockwise will cause falling the cold air. While it is snowing heaviling,the blocking system create between azore - Siberian high pressure in the east europa and its tongue covers western north and west of Iran. Sudan tongue of low pressure is active.this low pressure with orient east northern or north extened to north of Iran and create a partly strong tongue. Low pressure and high pressure tongues, to other hand warm air and cold air, hit together in west of Iran. Most strong ridge in east Europe was located .this ridge mostly extened tiltly from east north of Moscow to south of Red sea. -subtropical High height center in west Mediterranean and Tibetan Plateau reinforced then moved to upper latitudes and caused strong ridges in Asia and europe with axis northern-southern These ridges and low height centers in west of Iran and region of Mesopotamia reinforce ridge in east of Mediterranean and extend to lower latitudes. The ridge cause cold advection the region. In these situation,Polar wandering with axis of northern- southern or eastern north- western south extended to lower such as nourth of caspean sea and west of Iran and in the rigon caused falling cold weather. Ridges of Mediterranean (western-east) in europe and Tibet (northen-southern) in Asia is leaded to tilt in axis of ridge towerd lower latitudes. In such days, studied stations have intense tempreture lapse rate.
    Keywords: Atmospheric Circulation Patterns, heavy snowfall, west of Iran
  • ابراهیم فتاحی، ام السلمه بابایی فینی*
    پدیده هایی نظیر سیل و خشکسالی بر اثر تغییر در فراوانی و ثاثیر گذاری الگوهای گردشی جو در یک منطقه ایجاد می شوند این الگوها نقش اصلی را در رخداد پدیده های محیطی به خصوص در مناطق معتدله دارند. برخی از الگوهای گردشی جو دوره های مرطوب و برخی دیگر باعث ایجاد خشکسالی و کم آبی می شوند. از اینرو طبقه بندی الگوهای بارش زا و خشکسالی زا و شناسایی کانون و شعاع فعالیت هر یک از الگوها در نواحی مختلف ایران می تواند در برنامه ریزی ها موثر باشد.در تحقیق حاضر به منظور طبقه بندی الگوهای همدیدی بارش زا و خشکسالی زا، ابتدا داده های میانگین روزانه مربوط به ارتفاع ژئوپتانسیل تراز 500 هکتوپاسکال و فشار تراز دریا از پایگاه NCEP/NCAR طی دوره آماری 2006-1950 استخراج شد. سپس با استفاده از روش های تحلیل مولفه های اصلی و تحلیل خوشه ایتمامی روزهای مورد مطالعه به هیجده گروه تقسیم بندی شد. نقشه های میانگین فشار سطح دریا و ارتفاع ژئوپتانسیل تراز 500 هکتوپاسکال برای هر یک از الگوهای های هوا ترسیم گردید. به منظور ارزیابی رابطه الگوهای گردشی جو با بارش، شاخص PI برای 54 ایستگاه محاسبه و تحلیل شد. این شاخص احتمال شرطی وقوع بارش در یک الگوی گردشی را تعیین می کند. نتایج شاخص PI مربوط به الگوهای گردشی جو شرایط بارش زایی و خشکسالی زایی بودن هریک از الگوها را نشان می دهد. نتایج تحقیق حاضر نشان داد که الگوهای گردشی جو CP2، CP3، CP5،CP6، CP7، CP9 و CP10جزء الگوهای خشکسالی زا و الگوهای گردشی جو CP1، CP4وCP12 جزء الگوهای بارش زا در سطح ایران زمین می باشند.
    کلید واژگان: الگوهای گردشی جو, بارش زا, خشکسالی زا, تحلیل مولفه های اصلی, تحلیل خوشه ای, ایران
    Dr Ebrahim Fattahi, Dr Omehsalameh Babaee Feeni *
    Atmospheric circulation patterns are responsible for drought and flood occurrences around the globe; specifically in moderate mid latitude climates. While some circulation patterns are responsible for wet spells and floods as well، the drought events can be attributed to some other circulation patterns. Therefore، identification and distinction of dry/wet producing patterns and the geographical extent of Iran that they may affect is very crucial for many environmental planning. In the present study that aims to identify dry and wet producing atmospheric circulation patterns for Iran، the daily mean sea level pressure and 500 H. pa geopotential height corresponding to 1950-2006 period was retrieved from NCEP/NCAR and used as input variables for Principle Component Analysis coupled with Cluster Analysis. By this procedure all studied days were grouped into 18 clusters and their associated composite maps for both levels were drown and considered as the circulation patterns. To assess the relationship between the identified atmospheric circulation patterns and daily precipitation over Iran the Performance Index (PI) which is a conditional probability index was computed for 54 stations and used in the analysis. This index shows the probability of precipitation occurrence conditioned on the occurrence of a given circulation pattern. The result shows that circulation patterns of CP2، CP3، CP5، CP6، CP7، CP9 and CP10 are dry circulation patterns while CP1، CP4 and CP12 are considered as wet patterns in Iran.
    Keywords: Atmospheric Circulation Patterns, Wet circulation patterns, dry circulation patterns, principal Component Analysis, Cluster Analysis, Iran
  • ام السلمه بابایی فینی*، ابراهیم فتاحی
    با توجه به ارتباط تنگاتنگ الگوهای گردش جوی و عناصر اقلیمی، می توان پدیده های فرین آب وهوایی، مانند سیل و خشکسالی و دوره های خشک و تر را به تغییرات الگوهای گردش جوی نسبت داد. برای طبقه بندی الگوهای سینوپتیکی بارش زا، داده های گردآوری شده میانگین روزانه تراز 500 هکتوپاسکال و فشار سطح دریا طی دوره آماری 2008-1950 مورد استفاده قرار گرفت و برای ارزیابی نقشه الگوهای بارش، داده های مجموع بارش روزانه طی دوره آماری 2008-1960 جمع آوری شدند. با استفاده از روش تحلیل مولفه های اصلی، همه روزهای مورد مطالعه را به هجده گروه تقسیم بندی شدند و پس از آن، نقشه های ترکیبی تراز 500 هکتوپاسکال و فشار سطح دریا برای هر یک از تیپ های هوا تهیه شد. برای ارزیابی رابطه الگوهای گردش جوی بر احتمال وقوع بارش و شدت بارش، شاخص PI مورد استفاده قرار گرفت. نتایج پژوهش حاضر نشان داد، الگوهای گردش جوی 4CP، 5CP، 12CP، 1CP و 15CP، جزء الگوهای بارش زای شدید و فراگیر و الگوهای گردش جوی 7CP، 13CP، 16CP، 17CP و 18CP، جزء الگوهای بارش زای ملایم هستند. از نظر توزیع فراونی سالانه، الگوهای گردش جوی 3 CP، 5 CP، 13CP و 15CP در سرتاسر سال و الگوهای گردش جوی 2CP، 6CP و 10CP در فصل تابستان، فعالیت دارند.
    کلید واژگان: الگوهای گردش جوی, تحلیل مولفه های اصلی, خوشه بندی, سواحل جنوبی دریای خزر, شاخص PI
    Omosalameh Babaee*, Ebrahim Fattahi
    Introduction
    Atmospheric circulation patterns play the main role in the natural phenomenon occurring on the earth, especially in temperate regions. Some atmospheric circulation patterns cause wet periods and others cause low water and dried periods. Thus, because the annual occurrence of drought and wet events result from the general circulation of the atmosphere, recognizing atmospheric circulation patterns are explained, to some extent, for the possibility of evaluating these phenomena before occurance. Studies show that the floods and droughts phenomenan are influenced by atmospheric circulation patterns. Given the close relationship between the patterns and climatic elements, we can also attribute the extreme climatic events, such as floods and droughts, and dried and wet periods, to changes in atmospheric circulation patterns. In this study, from average daily data balance of 500 and the sea level pressure over the period 1960 to 2008 at two degrees intersection of the reconstructed data setshave been used. The selected range covers all systems affecting the area under study during the year. This range consists of 408 cells from 20 to 60 degrees in north latitude and 10 to 70 degrees in east longitude. Total daily rainfall data from selected synoptic stations over the statistical period 1960-2008 were used to assess the role of the patterns in rainfall. Many climate scientists dealing with variables with different scale or large volumes of data employ reduction variable and data strategy by principal component analysis (PCA), (Gadyial, S. and R. N. Lyengar 1980, Kalkstein. S. et al. 1998).
    Methodology
    Factor analysis is a statistical technique that establishs a especial relationship among a large number of variables that are seemingly unrelated. It is under a hypothetical model and gathers all the variables in the similar groups. This method retains significant and main components in the same groups and reduce the variables. One of the results of factor analysis is to reduce data dimension. Computational steps of the main component analysis is as follows: a) The data and variables Selection. b) The second stage of a data matrix p × n formation where n is the number of days and p is the number of variables. In the third stage since the selected meteorological variables of the unit are different (For example, C, hPa, meters per second, and so on), a correlation matrix was used as input for the main component analysis. Data correlation matrix are calculated according to the following formula. The fourth step is used to determine the number of factors by Catel test. Loadings matrix was calculated in the fifth stage. Loadings show the relationship between the factors and the primary variables. The relationship between atmospheric circulation patterns and rainfall To evaluate the relationship between atmospheric circulation patterns and rainfall, the following index is applied. This index defines the conditional probability of rainfall occurnece and rainfall intensity in a circulation pattern. The index defines a measure of the relative share of the pattern rainfall in total. Where ni is the number of days with i patterns and Ri is the total rainfall during that days and n is the number of days in the period of the study. If PI<1. Or even much smaller than the unit, the weather or type pattern i does not greatly affect the area rainfall. Thus, an increase in the frequency of occurrence of such a pattern, reduces rainfall and subsequently, causes drought in a region. If the PI in the statistical method is greater than the unit, then chance of rain (probability of precipitation) also increase and wet periods will be prevailed. For example, precipitation takes place when weather is wet and there is an acsending factor, these conditions are provided by atmospheric circulation patterns.
    Results And Discussion
    In this study, using PCA and clustering, eighteen circulation patterns according to the sea levelpressure and 500 hPa level atmospheric condition have been identified over the study area. The results of this study show that there are significant differences in the arrangement of patterns, the weather type frequency and the way they move towards the study region. The PI index is a appropriate criterion to evaluate the Conditional probability of rainfall and rainfall intensity. If the PI index calculated for a wheather type much smaller than unit, wheather type does not play a role in precipitation of that station or region. Therefore, an increase in the frequency of occurrence of such a pattern in a period reduces rainfall and makes the drought events in that region.
    Conclusion
    Due to the PI index and the annual frequency distribution of atmospheric circulation patterns, the results can be summarized as follows. Atmospheric circulation patterns of CP1, CP4, CP5,CP12, and CP15 are part of the patterns leading to heavy and pervasive precipitation. Atmospheric circulation patterns of CP7, CP13, CP16, CP17, and CP18 are part of the patterns leading to moderate precipitation. Atmospheric circulation patterns of CP2, CP8, CP9, C 10, and CP11 are part of the patterns leading to drought, Atmospheric circulation patterns of CP3, CP6, and CP14 are part of the patterns leading to drought. In terms of the annual frequency distribution, atmospheric circulation patterns of CP3, CP5, CP13, and CP15 are active in all seasons of the year, atmospheric circulation patterns of CP2, CP6, and CP10 are active in summer, atmospheric circulation patterns of CP1, CP8, CP9, CP11, CP12, CP14, CP16, C 17, and CP18 in winter, spring and fall and atmospheric circulation patterns of CP7 is active in the spring and fall.
    Keywords: Atmospheric Circulation Patterns, Clustering, North Caspian Sea, PI Index, Principal Component Analysis
  • محمدحسن نامی*، مهدی خزایی
    در این پژوهش به بررسی اثر تغییر اقلیم و نوسانات الگوی گردش های جوی بر روی رودخانه مرزی ارس پرداخته شده است. پژوهش ها نشان می دهد که دلیل اصلی پدیده تغییر اقلیم، انتشار بیش از حد گازهای گلخانه ای در جو می باشد. علت افزایش گازهای گلخانه ای خصوصا دی اکسیدکربن (به عنوان موثرترین گاز گلخانه ای موجد تغییر اقلیم) در سال های اخیر عمدتا افزایش سوخت های فسیلی، احتراق و جنگل زدایی است. بنابراین افزایش های اخیر به طور عموم نتیجه فعالیت های بشری بوده است. حوضه رودخانه ارس هم از اثرات زیانبار تغییر اقلیم و به تبع آن تغییر در الگوی گردش های جوی در امان نبوده است، به طوری که نوسانات ایجاد شده سبب شده تا الگوهای بارشی حوضه رودخانه ارس تغییر مکان داده و عمدتا به سمت عرض های جغرافیایی بالا متمایل شده اند. همین امر موجب شده تا بارش در حوضه رودخانه ارس نه تنها کاهش یابد بلکه نوع بارش ها هم تغییر پیدا کند. هم چنین حساس بودن جریان پایه این رودخانه نسبت به آب سرشاخه های ورودی از کشورهای ایران، ترکیه، آذربایجان و ارمنستان، هر گونه احداث سد یا بند بر روی این سرشاخه ها که موجب کاهش آب ورودی به رودخانه ارس شود، احتمال وقوع تنش های مرزی و خدشه دار شدن روابط سیاسی به ویژه در ارتباط با مسائل انرژی از جمله آب را افزایش می دهد.
    کلید واژگان: تغییر اقلیم, گازهای گلخانه ای, الگوی گردش های جوی, حوضه رودخانه ارس
    Mohammad Hassan Nami*, Mahdi Khazaei
    In this survey, the effects of climate change and fluctuations in atmospheric circulation patterns on the Aras Border River have been studied. Surveys show that the main reason for climate change phenomenon is the greenhouse gases over emission. The main reason for the rise in the greenhouse gases, particularly the Carbon Dioxide (as the most effective factor causing climate change) in recent years, is mainly the increasing use in Fossil Fuels and fires and deforestation as well. Therefore, the reason for recent rise in the greenhouse gases is generally the main performances. Aras river basin has not been safe from Harmful effects of climate change and consequently from the fluctuations in atmospheric circulation patterns, in a way that fluctuations have made the Aras basin river’s rainfall patterns to dislocate and deviate mainly towards the upper Latitudes. This has not only led in a decrease in the rainfalls in the Aras Border River Basin, but also the rainfall patterns to change. Also The River’s basic flow sensitivity to the water of input branches from Iran, Turkey, Azerbaijan and Armenia, building any dams on these branches which decrease the flow of water into the Aras River, increase the probabilities of border tensions and harm the political relations especially related to the issues of energy and water.
    Keywords: Climate change, Greenhouse gases, Atmospheric circulation patterns, Aras river basin
نکته
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