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پژوهش های اقلیم شناسی - پیاپی 9 (بهار 1391)

نشریه پژوهش های اقلیم شناسی
پیاپی 9 (بهار 1391)

  • تاریخ انتشار: 1391/01/01
  • تعداد عناوین: 7
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  • فرامرز خوش اخلاق، محمود داودی، ایمان روستا، اسماعیل حقیقی صفحه 1
    تغییرات شدید دما از جمله کاهش آن، پدیده ای نامطلوب برای موجودات زنده بوده و اثرات نامطلوبی نیز بر فعالیت های کشاورزی، سازه ها و تاسیسات دارد. پژوهش حاضر در صدد شناسایی الگوهای همدید موثر در ایجاد سرماهای شدید در شمال خراسان است تا با شناسایی و پیش بینی زمان درست ورود این الگوها به منطقه بتوان هشدارهای لازم جهت جلوگیری و کاهش اثرات را انجام داد. به منظور مطالعه سرماهای شدید در شمال خراسان ابتدا براساس داده های دمای هوا و سرعت باد و با استفاده از رابطه دمای سوزباد (WCT) روزهای دارای سرمای شدید در دوره آماری (2005-1984) مشخص شد. در این شاخص مقادیر کمتر از 36 به عنوان سرمای شدید محسوب می شود. در داده های بلند مدت ایستگاه های همدید، میانگین مجموع تعداد روزهای با مقدار شاخص کمتر از 36، در 4 ایستگاه، 530 روز بوده است. بنابراین جهت محدود کردن روزهای مورد مطالعه، روزهای با شاخص کمتر از 20 و با پوشش حداقل 3 ایستگاه، برای مطالعه انتخاب شدند. در ادامه به منظور شناسایی و طبقه بندی الگوهای همدید ایجاد کننده سرماهای شدید منطقه شمال خراسان از داده های مربوط به فشار، دما، مولفه باد نصف النهاری و مداری (U، V) (به منظور ترسیم نقشه خطوط جریان و تاوایی) و ناهنجاری فشار و دما در ترازهای مختلف استفاده شد. نتایج نشان داد در 70 درصد موارد سامانه بندالی و در بقیه موارد استقرار ناوه عمیق روی شمال ایران عامل اصلی فرارفت سرماهای شدید به شمال خراسان بوده است. این فرارفت در پی نفوذ سامانه های گرمایی از مسیر شمالی و شمال شرقی و یا نفوذ سامانه های گرمایی یا گرمایی- پویشی از مسیر شمال غربی به عنوان دو منبع اصلی رخ داده است.
    کلیدواژگان: مطالعه همدید، سرماهای شدید، شاخصWCT، شمال خراسان
  • کیوان نوحی، ابراهیم فتاحی، شاهرخ فاتح صفحه 13
    رشد مرکبات مانند هر محصول دیگر، به میزان زیادی به دما وابسته است. اکثر واریته های مرکبات، دماهای به طور نسبی بالا را تحمل می کنند اما افزایش ناگهانی دما همراه با رطوبت نسبی پایین اکثر مواقع برای میوه های جوان خطرناک است. از نقطه نظر کاهش محصول، افزایش ناگهانی دما به بالاتر از حد نرمال در خلال دوره بستن میوه و یا کمی بعد از آن، بیشترین خسارت را ایجاد می کند. مرکبات محصول نیمه گرمسیری بوده و آب و هوای جنوب کشور برای کشت آن مناسب است. گرمای بالاتر از 40 تا 45 درجه سیلسیوس به همراه کاهش رطوبت هوا به میزان20% و کمتر سبب ریزش برگ ها، کم آبی در اثر افزایش تنفس و کاهش کیفیت میوه می شود. چنانچه عوامل فوق تواما در یک روز رخ بدهد، آن روز بر حسب تعریف به عنوان روز بحرانی یا شدیدا بحرانی نامیده می شود. در این بررسی وضعیت اقلیمی استان های خوزستان، هرمزگان، بوشهر و سیستان و بلوجستان که از نظر کشت مرکبات دارای اهمیت است بررسی شده و با به کارگیری داده های روزانه دما و رطوبت نسبی تعداد روزهای بحرانی و شدیدا بحرانی در مقطع دهه محاسبه شده است. میانگین تعداد روزهای بحرانی در بیشتر نواحی استان خوزستان بیش از 28 روز در سال است. بیشترین تعداد این روزها در استان هرمزگان در ناحیه میناب 10 روز، در بوشهر در ناحیه کنگان جم 14 روز، و در سیستان و بلوجستان در ناحیه ایرانشهر 24 روز محاسبه شده است. تعداد این روزها در محدوده مورد مطالعه به صورت نقشه ارائه شده است که می تواند در تصمیم گیری برای گسترش کشت این محصول مفید باشد.
    کلیدواژگان: استان های جنوبی، تنش گرمایی، دمای بالا، رطوبت نسبی پائین، مرکبات
  • بهلول علیجانی، پیمان محمودی *، عبدالجبار چوگان صفحه 23

    یکی از روش هائی که می توان به کمک آن سیر تحولات بارندگی را در گذشته و حال بررسی نمود، آنالیز روند سری های زمانی در مقیاس های مختلف زمانی است. هدف اصلی در این تحقیق بررسی روند سری های زمانی بارش در مقیاس های فصلی و سالانه ایران زمین با استفاده از روش ناپارامتریک برآورد کننده شیب سنس است. برای بررسی این روند و در جهت دستیابی به یک الگوی مناسب در این زمینه، داده های مربوط به جمع بارش ماهانه 44 ایستگاه هواشناسی سینوپتیک برای یک دوره آماری 33 ساله (2008-1976) از سازمان هواشناسی کشور اخذ گردید. بر اساس این روش مشاهده گردید که هیچ گونه روند معناداری در سطح احتمالاتی 05/0 در جمع بارش های فصل بهار ایران مشاهده نگردیده است و در فصل پائیز نیز تنها ایستگاه سنندج دارای روند کاهشی معنادار بوده است. در فصل تابستان نیز در سه ایستگاه نوژه همدان، سقز و زنجان شاهد روندهای افزایشی معناداری در سطح احتمالاتی 05/0 بوده ایم. اما بارش فصل زمستان نسبت به دیگر فصول شاهد بیشترین تغییرات در روند بوده است به طوری که 5 ایستگاه گرگان، کرمان، خوی، سنندج و زنجان در این فصل روند کاهشی معناداری را در سطح احتمالاتی 05/0 داشته اند. روند بارش سالانه نیز حاکی از روند کاهشی معنادار در سطح احتمالاتی 05/0 درصد در 11 ایستگاه از مجموع 44 ایستگاه مورد مطالعه است. تجمع ایستگاه های دارای روند کاهشی در غرب، شمال غرب و شرق ایران می تواند نشانه هائی از تغییر شرایط بارشی در این قسمت از ایران باشد. لذا توجه خاص به تغییرات رخ داده در غرب و شمال غرب ایران می تواند حائز اهمیت باشد.

    کلیدواژگان: ایران، روند، بارش، روش برآورد کننده شیب سنس، تغییر اقلیم
  • محمد تقی زمانیان، محمد باقر بهیار، آزاده کریمی حسینی، مجید وظیفه دوست صفحه 43
    استفاده از نمایه های هواشناسی کشاورزی ماهواره ای می تواند در پایش و پیش بینی خشک سالی کمک نماید. از این رو در این پژوهش با استفاده از سری داده های هفتگی GVI-x، میانگین ماهانه نمایه های خشک سالی ماهواره ای شرایط دما، شرایط گیاه و سلامت گیاه (TCI، VCI و VHI) در دوره آماری 2007-1993 محاسبه گردیده است. سپس تغییرات بارندگی 4 ایستگاه همدیدی منتخب استان اصفهان که دارای طول عمر بیشتری بودند (ایستگاه های اصفهان، شهرضا، نطنز و داران)، در این دوره آماری مطالعه شده و همبستگی بارندگی ماهانه این 4 ایستگاه با میانگین ماهانه نمایه های TCI، VCI و VHI ماهانه در سه نقطه انتخابی 1) بایر، 2) آبی و 3) دیم، در اطراف ایستگاه های همدیدی منتخب، محاسبه شده است. نتایج، همبستگی مناسبی میان نمایه های VCI و VHI با بارندگی را نشان می دهند. بررسی تغییرات نمایه های VCI و VHI که همبستگی بیشتری با بارندگی داشته اند، در مناطق تحت کشت دیم و آبی ایستگاه های داران، اصفهان، شهرضا و نطنز در سال های 2000، 2004 و 2005 و همچنین بررسی سطح تحت تاثیر خشک سالی در استان اصفهان بر اساس نمایه های ماهواره ای خشکسالی، نشان می دهد که سال های 2000، 2004 و 2005 به ترتیب با خشک سالی، ترسالی و سال های نرمال، همراه بوده اند.
    کلیدواژگان: استان اصفهان، خشک سالی، سنجنده AVHRR، نمایه های خشک سالی ماهواره ای
  • داود پرهیزکار، فرهنگ احمدی گیوی صفحه 55
    واچرخند جنب حاره ای خاورمیانه، به طور میانگین دارای نوسان مکانی سالانه در حدود 20 درجه عرض جغرافیایی در راستای شمال-جنوب است. بروز هر گونه بی-هنجاری در این جا به جایی طبیعی می تواند باعث به وجود آمدن بی هنجاری هایی در رژیم های هواشناختی منطقه گردد. با توجه به بحث ارتباط از دور انسو (النینو- نوسان جنوبی) با پدیده های هواشناختی مناطق مختلف جهان، این پژوهش به دنبال بررسی اثر احتمالی انسو بر نوسان سالانه مکانی این واچرخند است. برای انجام این کار، دوره سی ساله 1971 تا 2000 میلادی به عنوان پایه مطالعه انتخاب شده و داده های مولفه مداری باد در تراز 250 هکتوپاسکال که محل حضور جریان جتی جنب حاره ای است، از بانک داده های تحلیل مجدد پایگاه اینترنتی مرکز نوآی امریکا دریافت گردید. سپس بی هنجاری های بخش گذرا (ناشی از حضور تمام نوسان ها) و خالص (تنها ناشی از حضور انسو) در شش سالی که انسو شدیدا فعال بوده است (سه سال النینو و سه سال لانینا)، محاسبه و تحلیل شدند.
    نتایج نشان می دهد که اثر انسو بر نوسان سالانه واچرخند جنب حاره ای و تقویت و تضعیف آن در بین بی هنجاری های بخش گذرا، قابل آشکارسازی نیست. زیرا در سال های هم فاز، توزیع های متفاوتی از بی هنجاری ها در بخش گذرا دیده می شود که حاکی از آن است که انسو در کل، نقش غالب و تعیین کننده ای ندارد. اما با بررسی بی هنجاری های خالص انسو، مشاهده می شود که النینو (فاز گرم انسو) باعث می شود تا نوسان سالانه واچرخند جنب حاره ای خاورمیانه در عرض های پایین تری نسبت به لانینا (فاز سرد انسو) صورت گیرد. به علاوه، در تابستان لانینا، واچرخند جنب حاره ای به قدری به عرض های بالا منتقل می شود که شارش های شرقی بخش جنوبی آن بر روی جنوب شرق ایران قرار می گیرند. به بیان دیگر، در شرایط النینو وضعیت جوی برای بارش های ایران در فصول سرد بهتر از لانینا است و به عکس در تابستان، شرایط برای بارش جنوب شرق ایران در فاز سرد انسو بهتر از فاز گرم آن است. اثرات جزئی انسو تحت تاثیر سایر نوسان های جوی می تواند تضعیف شده و حتی از بین بروند. به همین علت در بی هنجاری های بخش گذرا که متاثر از حضور همه نوسان های جوی است، دیده نمی شوند
    کلیدواژگان: انسو، النینو، لانینا، نوسان سالانه، واچرخند جنب، حاره ای، خاورمیانه
  • قاسم عزیزی، طاهر سفر راد صفحه 69
    پژوهش حاضر به تحلیل ویژگی های رودباد در ارتباط با فاز های مختلف ENSO در سطوح 200 و 300 هکتوپاسکالی طی ماه های سپتامبر، اکتبر، نوامبر و دسامبر می پردازد. در این راستا، سال های 1997، 2008 و 2010 با استفاده از شاخص ONI، بترتیب به عنوان سال های ال نینو، عادی و لانینا انتخاب شدند. داده های مولفه ی مداری و نصف النهاری باد (NCEP-DOE Reanalysis 2) با قدرت تفکیک مکانی 5/2 درجه طول و عرض جغرافیایی به صورت میانگین روزانه، جهت استخراج رودباد گردآوری شدند. با نوشتن برنامه در نرم افزار GrADS هسته های سرعت (بیش از 30 متر بر ثانیه) استخراج و مسیرهای رودباد طی دوره ی آماری فوق با استفاده از نرم افزارArc GIS ردیابی و ترسیم گردیدند. نتایج تحقیق دو مسیر را برای عبور رودباد مشخص می سازد که مسیر جنوبی تر (رودباد جنب حاره) بر فراز ایران و مسیر شمالی تر (رودباد جنب قطبی) در عرض های 40 تا 75 درجه شمالی جریان دارد. مسیر عبور رودباد جنب حاره در سال ال نینو در هر دو تراز 200 و 300 هکتوپاسکالی به عرض های جنوبی تر منتقل می گردد تعداد هسته های سرعت مشاهده شده در سطح 200 هکتوپاسکالی برای رودباد جنب قطبی در سال های ال نینو و لانینا کاهش می یابد در حالی که رودباد جنب حاره در همان دوره افزایش تعداد هسته های سرعت در سال ال نینو و کاهش آن در سال لانینا را نشان می دهد. تعداد هسته های سرعت در سطح 300 هکتوپاسکال برای رودباد جنب قطبی تغییرات زیادی را طی فازهای مختلف ENSO نشان نمی دهد در صورتی که رودباد جنب حاره در هر دو سال ال نینو و لانینا با کاهش تعداد هسته های سرعت مشخص می گردد. فشردگی مسیر عبور رودباد بر فراز ایران طی فاز ال نینو و بازشدگی آن طی فاز لانینا، همچنین افزایش سرعت متوسط هسته های رودباد طی فاز ال نینو و کاهش آن طی فاز لانینا از نتایج پژوهش حاضر است.
    کلیدواژگان: رودباد، ENSO، ONI، هسته های سرعت، مسیر رودباد، میانگین برداری خطی
  • میترا لاله سیاه پیرانی، مجتبی ذوالجودی، ابراهیم فتاحی، حمید مهسا فر صفحه 83
    انقلاب صنعتی روند استفاده از انرژی را شدت بخشید و این یکی به نوبه خود موجب، انتشار روز افزون گازهای گلخانه ای در جو زمین گردید، این امر موجب بروز پدیده ای گردید که پژوهش گران از آن تحت عنوان گرم شدن کره زمین نام می برند.در این رابطه گزارشات هیئت بین الدول تغییر اقلیم، حاکی از این است که چنا ن چه تا سال 2100 میلادی دمای متوسط زمین کاهش نیابد با افزایش برابر 1/1 تا 6/4 درجه سلسیوس رو به رو خواهد شد، این امر به بروز پدیده ای به نام پدیده گرمایش جهانی و تغییر اقلیم حاصل از آن منجرخواهد شد. و به دنبال آن چرخه آبی و یا سیستم منابع آب دچار تغییرات بنیادی خواهد شد. حوضه آبریز کارون بزرگ با داشتن حدود 12 سد بزرگ احداث شده و در حال احداث و با پتانسیل تولید 20 هزار مگاوات تولید نیرو از اهمیت بسیار بالایی برخوردار است. بنابراین آشکار سازی تغییر اقلیم و بررسی آثار و پیامدهای آن در این منطقه از اهمیت بالایی برخوردار است. در این تحقیق با استفاده از داده های مدل های گردش عمومی جو (GCM) تحت سناریوی گازهای گلخانه ای SRES تغییرات بارش و دما در دوره 2039- 2010 برای ایستگاه های اهواز، دزفول و خرم آباد که به عنوان ایستگاه های منتخب حوضه کارون بزرگ می باشند، شبیه سازی شده است. داده های مورد نیاز شامل میانگین دما و مجموع بارش ماهانه در دوره آتی از دو مدل HadCM3 و CSIRO از سری مدل های گردش عمومی جو تحت سناریوی A2 و B1 و با استفاده از روش تناسبی داده های دوره پایه و دوره های آتی تامین شده است، نتایج حاصل، حاکی از، افزایش دما برای هر دو مدل به ترتیب 8/1 و 2 درجه سانتی گراد و کاهش بارندگی 10 و 6 درصد برای دوره 2039-2010 می باشد.
    کلیدواژگان: گرمایش جهانی، تغییر اقلیم، شبیه سازی، گردش عمومی جو، حوضه کارون بزرگ
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  • Khoshakhlagh, ., Davoudim., Roustai., Haghighi, E Page 1
    IntroductionClimatic elements create the climate of a region Air felt temperature differs in different climates. For example, the temperature may be 20° Celsius in a clear day without clouds in March, in a sense of coolness to the temperature region, while the same temperature in summer and in other regional temperatures is considered a cold and uncomfortable. Severe wind blows at below zero temperatures can quickly withdraw heat from the body, to the extent that it may cause freezing of the skin. Wind Chill Temperature index (WCT) is very important and it can be used as a general guideline for deciding clothing requirements in cold weather conditions. North Khorasan Province, is considered as one of the country's Agriculture and Tourism poles But, this region has consistently experienced severe cold weather over the years. Recent studies show that extremely cold weather has sometimes disrupted the lives of the people living in this region. Due to the region's natural resources, mining, tourism, and increasing population, it seems necessary to implement a project the on better utilization in this. This plan will succeed if the mechanism and the role of the major climate systems affecting the climate of this region are correctly identified. Therefore, this study aims to identify major synoptic patterns which create severe cold weather of North Khorasan Province and its arrival to the area, to identify and predict these patterns, and to be alert enough to prevent and reduce the potential damages.Material and methodsThe study of this region (North Khorasan Province) is primarily based on the equation of WCT (equation 1) days with severe cold weathers extracted. Values of less than 36 in this index indicate an extremly cold weathers. The most extreme case happens when the index value is -98. In this case, freezing occurs in 5 minutes.WCT= 74.35 +0.6215T –35.75 (V*0.16) +0.4275 T (V*0.16) (1)In order to calculate the frigid days, first, average daily temperature and wind speed (in 1984-2005) in sample stations of North Khorasan Province are received from the Meteorological organization. Then the temperature and wind are converted from Celsius to Fahrenheit and Nat to miles per hour respectively using the Wind-chill equation, Less than 36 days.To determine the synoptic patterns of severe cold weather in this study area, data related to the pressure, wind components (U&V) for different levels (surface, 500 and 850 hectopascal) is prepared. This data is sent daily to the National Center for Environmental Prediction United State (NCEP/NCAR). The excursion to the study to identify patterns was investigated. For more precise assessment of flow patterns in severe cold weathers time, using the components of orbital and meridional wind, relative vorticity maps were prepared. Vorticity maps by turning the air to determine the type, severity and determine the amount of spread low pressure system and high pressure was used.Results and discussionAmong the stations studied, the highest frequency is Quchan. In terms of severity of the cold is Quchan, Sarakhs station for months but the rest of December has the lowest intensity, but in the months after Quchan placed in other months, respectively Bojnourd and Mashhad are after Quchan.During the occurrence of extreme cold weather in the region, two synoptic patterns have been predominant. The blocking pattern is the most important model in terms of is the number of days and the second pattern is the deep trough in the event severe cold weathers are very effective in the region. The maps of extremely cold weather days indicate that blocking pattern has caused severe deviation of the west winds up and pulling them down to the low latitude. In depth trough pattern due to extreme cold weather there is a trough with the meridional development to the south which pulling down from high latitudes to low latitude, and this axis is located in East Iran. Trough is much deeper it would be more stable. In this model the study area located in the West of a deep trough, was derived from high latitudes which condition have been the cause of this severe cold weathers.In severe cold weathers has been occurred under this model, the advection of air from two sources that include high-pressure area located in West Lake Baykal, and a deep trough that high latitude air advection over the study area.ConclusionThis study shows that Quchan has experienced the highest occurrence of extreme cold weather. Bojnourd, Mashhad, and Sarakhs are in second place. In terms of severity of extreme cold weather, Quchan station is in the first place. In most cases the occurrence of severe cold weathers region, there was the main reason blocking system and a deep trough pattern of other cases as well as the establishment of a deep trough on the North of the study area and placed in the rear main reason is the occurrence of extreme cold weather. Between days with blocking pattern penetrate trough pattern of 17 to 25 degrees North is the variable that caused the temperature in the balance of 1000 and 500 hectopascal order of 5 to -10 and -25 to -40 on days with extreme cold weather pattern. Vorticity value in all the days of extreme cold weather due to this pattern was positive and on the region there was cyclonic circulation. According to the study area close to the source of exposure to the cold weather of Siberia and currents resulting from the tabs on the one hand and due to the high latitude, exposure to cold weather northern currents on the other hand, the region could be affected dynamical systems, thermodynamics and heat, are undergoing severe cold weathers.
    Keywords: Synoptic analysis, severe cold weathers, WCT index, North of Khorasan
  • Noohik., Fattahie., Fateh, Sh Page 13
    IntroductionMain regions of citrus plantation are between 40 degrees northern and southern geographical latitudes. A considerable part of these regions are located at Mediterranean sub tropic (WMO, 1997). Citrus plantation has grown into a global industry for the last 70 years. Producing oil and citric acid is another reason for citrus plantation besides fresh fruit production. Temperature is the most important climatic element in citrus plantation. On the one hand, frosts to threaten yield and on the other hand, high Temperatures through extreme transpiration, make the fruit formation difficult. Optimum means daily temperature for citrus growth is from 23 to 30 degrees Celsius and growth is considerably reduced if the temperature is organization, 2004). Another effective process in the occurrence of heat waves at the southern strip is the air subsidence at a synoptically scale. Regarding the above mentioned studies, the most significant climatic restrictions that affect the yield quantity and quality in southern provinces are high temperature and air dryness. Method and MaterialThe climate of the southern parts of the country is suitable for Citrus plantation. Air temperature more than 40 degrees Celsius, along with relative humidity equal or bellow 20%, cause leaf drop, increase of water loss from the trees through transpiration, and decrease of fruit quality. Most of the shock from high temperatures occurr at fruit formation and youth periods. A sudden increase in air temperature and decrease in relative humidity during this period may result in serious damages. When the mentioned condition occurs in one day, this day is called "a critical day". These conditions often occur in southern provinces. In this study, the climatological situation of some important citrus plantation regions in the southern parts of the country is investigated. Statistical periods differ in different stations and all are ended in 2005. Critical combination of temperature and humidity is extracted from daily data. As the occurrence of temperatures above 45 degrees Celsius at the investigated time period is probable, thus two cases of the critical day are considered in the following manner. 1. Number of days with maximum temperature above 40 degrees Celsius and minimum relative humidity bellow 20% (critical day)2. Number of days with maximum temperature above 45 degree Celsius and minimum relative humidity bellow 20% (very critical day)The program is implemented from mid-April to mid-July. Critical days are important in citrus fruit drop in the region. For better application, the results are submitted in decade and month. Results and DiscussionsNumber of days with maximum temperature equal or more than 40 and 45 degrees Celsius along with minimum relative humidity equal or less than 20% are calculated. Mean monthly critical and very critical days at the region under study is shown in the figure.ConclusionResults show that all stations in Khozestan Province are affected by critical conditions but Safiabad, Shooshtar, Ramhormoz, and Behbahan stations are more at risk. Ize are less affected than the others. In Hormozgan Province, Minab region is most affected. In Boushehr Province, Kanganjam and Bandardaier are more affected. In Sistan and Baluchistan Province, Iranshahr is the most affected area. These results can be applied in making decisions to promote citrus cultivation and create new orchards.
    Keywords: The Southern Provinces, Heat Stress, High Temperature, Low Relative Humidity, Citrus
  • Alijanib., Mahmoudip., Chogana., J. Page 23

    IntroductionPrecipitation has always been under investigation as the most important climatic element from both temporal and spatial perspectives. One of the methods that contribute to the review of the course of precipitation in the past and present is the 'time series trend analysis'. So far, numerous statistical methods have been provided for the time series trend analysis, which can be categorized into two parametric and nonparametric methods. The nonparametric methods are based on the differences between observation data; these methods are independent from statistical distribution and are more appropriate for the series with more skewness and kurtosis. Therefore, the objective of this study is to investigate the precipitation time series trend over Iran in seasonal and annual scales using the Sen’s slope estimator nonparametric method.Materials and MethodsIn order to examine precipitation changes in Iran and make a proper pattern for this field, the data related to total monthly precipitation of 44 synoptic stations in a 33-year statistical period (1976-2008) were received from Iran Meteorological Organization.In order to investigate precipitation time series trend of Iran on seasonal and annual scales, the Sen’s slope estimator nonparametric method was applied. This method is based on a mean slope for the time series and judgment of the significance of the obtained slope in different confidence levels.Results and Discussion The implementation of the Sen’s nonparametric method on in seasonal and annual precipitation time series of 44 synoptic stations indicated that despite the decreasing (28 stations) and incremental (14 stations) signs which were observed in pring precipitations of Iran, no trend was significant at the probability level of 0.05. Also, in autumn, considering that 33 stations had a decreasing trend and 2 stations experienced an incremental one, only Sanandaj station indicated a significant decreasing trend.In summer, due to subtropical high pressure system in Iran, most parts of this vast country lacked any kind of precipitation. However, significant incremental trends were observed at the probability level of 0.05 in Hamedan’s-Nozhe, Saghez, and Zanjan stations.However, winter precipitation had the highest frequency in this trend compared with other seasons since five stations of Gorgan, Kerman, Khoy, Sanandaj, and Zanjan had significant decreasing trends at the probability level of 0.05 in this season. Therefore, because the largest amount of Iran’s precipitations occurs in the winter, any changes in the precipitation trend of this season could be a warning for water domain planners.The annual precipitation trend also indicated a significant decreasing trend at the probability level of 0.05 in 11 stations out of total 44 studied stations. The accumulation of stations with the decreasing trend in the west, northwest and east of Iran might signify changes in precipitation conditions in these parts of Iran. Although of a significant trend in the precipitation time series cannot guarantee the occurrence of climate change in a region, it might enhance the possibility of its occurrence. Therefore, it is essential to consider the occurred changes in the westest and northwest of Iran, especially in Sanandaj station which experienced autumn, winter and annual trend changes.ConclusionUsing this method, the results indicate that there was no significant trend at the probability level of 0.05 in total spring precipitation and autumn precipitation of Iran and; only Sanandaj station experienced a significant decreasing trend. In summer, Hamedan’s-Nozhe, Saghez and Zanjan stations showed significant incremental trends. However, winter precipitation had the maximum trend changes compared with other seasons because Gorgan, Kerman, Khoy, Sanandaj, and Zanjan stations showed a significant decreasing trend in this season which was at the probability level of 0.05. The annual precipitation trend signified a significant decreasing trend at the probability level of 0.05 in 11 stations out of 44 studied stations. The accumulation of stations with decreasing trend in the west, northwest and east of Iran signified changes in precipitation conditions in these parts of Iran. Therefore, special attention should be paid to changes which occurred in west and northwest of Iran.

    Keywords: Iran, Trend, Precipitation, Sen's Slope Estimator, Climate Change
  • Zamaniyan, M. T., Behyar, M. B., Karimi Hosseinia.*, Vazifedoust, M Page 43
    Introduction
    Drought is one of the most harmful environmental phenomena which has a devastating impact on agriculture, environment, economy and society. Drought happens during a period of water deficit in a region due to low precipitation, high evapotranspiration, high groundwater derivation or a mixture of the mentioned factors. Observations from space, especially from the NOAA polar-orbiting satellites, provide a synoptic view, permanent data archive, extra visual information, cost effectiveness, and a regular, repetitive view of nearly all of the earth’s surfaces (Johnson et al. 1993). Hence, remotely sensed data from NOAA’s AVHRR has been commonly used for national to global-scale drought monitoring activities since the 1980s and application of satellite based drought indices of vegetation health (TCI, VCI, VHI) in drought identifying, analyzing, evaluating and monitoring has been studied world widely (Kogan 1997, Vogt et al. 1998, Seiler et al. 2000, Singh et al. 2003, Kogan et al. 2004, Bhuiyan 2008, Rahimzadeh Bajgiran et al. 2008). Materials and methodsThe research was carried out in Isfahan Province which covers an area of about 105'937 km2 located between to and to. In this research, the precipitation data of 14 synoptic stations of Isfahan Province has been first studied and 4 synoptic stations (Isfahan, Shahreza, Natanz and Daran) have been chosen due to their long-term data record and good distribution across the area.In addition to field data, GVI-x data set is used which is provided by NOAA/NESDIS web site (http://www.star.nesdis.noaa.gov/smcd/emb/vci/VH/vh_browse.php). This data set contains NDVI, BT, TCI, VCI, VHI products that are put weekly as HDF files on the website. The used data have a weekly temporal resolution and a 16km2 spatial resolution and cover an area between to and to. Results and discussionMonthly vegetation health indices (TCI, VCI and VHI) in Isfahan Province have been computed from 1993 to 2007 using GVI-x weekly data set to study the application of these indices in drought monitoring. Then correlation of monthly precipitation and monthly air temperature of the selected synoptic stations with the amount of monthly TCI, VCI and VHI in bare, irrigated and rainfed locations (Derived from Isfahan Province land use map) have been calculated.The results indicate that the correlation between precipitation and TCI, VCI and VHI is significant at 10%, 40% and 40% of studied statistics at 90% confidence level. The same amounts for temperature are 40%, 35% and 35%. These results show that VCI and VHI are more reliable for drought monitoring because of their higher correlation with precipitation comparing to TCI which is more correlated with temperature.Studying the annual precipitation variability of selected stations in Isfahan Province during the period 1993-2007 and comparing monthly precipitation to the 15-year average precipitation indicate that the selected stations have experienced in most months of the years 2000, 2004 and 2005 respectively drought, wet and normal conditions. Then drought intensity in irrigated and rainfed locations have been obtained using the amounts of monthly VCI and VHI and table of classification of drought intensity using vegetation health indices (TCI, VCI and VHI) (Bhuiyan 2008). Areal aspect of TCI, VCI and VHI across the province has also been analyzed and drought intensity has been studied based on the table by Bhuiyan (2008) using vegetation health indices (TCI, VCI and VHI) during 1993-2007. ConclusionIn this research the satellite-based drought indices (TCI, VCI and VHI) have been computed in Isfahan Province using GVI-x data set. The correlation of these indices with precipitation data has been studied to evaluate and analyze the application of these indices in drought evaluating and monitoring. The results indicate rather a good accordance of these indices with precipitation variability during the study period and significant correlation between monthly VCI and VHI and monthly precipitation. VCI and VHI variations during the years 2000, 2004 and 2005 shows that in most months of the year 2000, the amount of the indices is less (means less vegetation) than 2004 and the curve of the year 2005 is mainly located between the 2000 and 2004 curves.
    Keywords: Isfahan Province, Drought, AVHRR, Satellite based drought indices
  • Parhizkard., Ahmadi Givi, F Page 55
    IntroductionThe northern branch of the Hadley cell forms the anticyclone centers over the subtropical regions around the world. One of these centers is the Middle East anticyclone that plays a main role in the weather of the region. This center has an annual spatial oscillation in the north-south direction. In summertime, it goes to the high latitudes and makes the weather of the Middle East very dry and hot and in winter; it comes back to the lower latitudes and lets the mid-latitude cyclones go across the northern Middle East and Iran. The main winter precipitation of Iran is closely related to these cyclones. Occurrence of any anomaly in the natural spatial variability changes the meteorological regimes over the region. Since ENSO is one of the global oscillations that can affect the weather in some parts of the world, this study aims to examine the likely effect of ENSO on the oscillation mentioned above. Materials and methodsFor this reason, a 30-year period from 1971 to 2000 has been selected as the basis of this study. Zonal component data of the wind at 250hPa level, that is the level of subtropical jet stream presence, as well as the Oceanic Nino Index (ONI) data received from the data bank of NOAA, are reanalyzed. ONI is the difference between the 30- year average of the Sea Surface Temperature (SST) over the NINO3/4 region and its three-month running average. According to NOAA, for ONI in the range of ±0.5 °C, ENSO is in natural phase and for more than +0.5 °C, in warm phase (El-Nino) and for less than -0.5 °C, in cold phase (La-Nina). For this study the six strongest ENSO years including three El-Nino years (1972, 1982 and 1997) with an ONI more than +1.5 °C, three La-Nina years (1973, 1975 and 1988) with an ONI less than -1.5 °C and three neutral years (1979, 1980 and 1981) are selected. At first, the zonal wind data were separated into two parts: stationary and transient parts. The stationary part is independent from oscillations, so, ENSO does not have any effect on it. It was expected that the effect of ENSO become obvious in the transient part of the data. For this reason, the annual and seasonal anomalies of the transient part of the zonal wind (arising from the presence of all atmospheric- oceanic oscillations) for the six strongest warm and cold phases of ENSO were computed and analyzed. Then, this study shows the net effect of ENSO. Considering the fact that there are three years (1979, 1980 and 1981) with the absence and six years with the strongest presence of ENSO, it can be supposed that in all nine selected years, all of the oscillations were active. Then, by subtracting the neutral phase anomalies from the warm and cold phase anomalies, the roughly net effect of ENSO will be gotten for any phases. In order to do this, at first, the mean of anomalies for all the phases is computed and then subtraction is done. The most important effect of this averaging is modifying the effect of other oscillations and maintaining the effect of ENSO. Because of the fact that in these six years, ENSO was very active, the averaging has no modifier effect on its impact but it is different for other oscillations. This method brings the effect of ENSO to light.This study is followed in point of the correlation coefficient view between SST of the Nino 3/4 and zonal component of wind at the 250 hPa level over a wide area from west of the Middle East to the east of the Pacific.Results and discussionThe figures of the stationery part of the zonal wind at the 250 hPa level shows that the jet stream of the Middle East subtropical anticyclone has a spatial oscillation about 20 degrees in the north-south direction. According to this study, the core of the subtropical jet stream is roughly located in 25 degrees north in winter and 45 degrees north in summer over the Middle East.In the next section, the results of the transient part show that the effect of ENSO on the annual oscillation of the Middle East subtropical anticyclone is not detectable by the distribution of annual and seasonal anomalies of the transient part, because there are different patterns of the distribution of anomalies in the same phases of ENSO. In other words, ENSO does not have a predominant and significant impact on the distribution of anomalies in the presence of other large-scale oscillations and phenomena. It is more likely that the interaction of other oscillations with ENSO substantially weakens the partial effect of ENSO.But the results in the section of the net effect of ENSO are very interesting. Those results indicate that El-Nino keeps the annual oscillation at lower latitudes compared to La-Nina condition, and also prepares the more suitable condition for passing the mid latitude cyclones and then precipitation over Iran and the north of the Middle East region in wintertime. Moreover, the meridional wind shear is very strong in El-Nino comparing to La-Nina. It means the mid latitude cyclones are more active in El-Nino than those in La-Nina. The other notable result shows that the subtropical anticyclone is located at the maximum latitude during the summertime of La-Nina condition, where the latitude is higher than El Nino. In this condition, the easterly waves pass the southeast and south of Iran and create the summer precipitations. ConclusionAccording to this study, ENSO has no dominant effect on the annual oscillation of the subtropical anticyclone over the Middle East. It seems that its effect in a complicated interaction with other global oscillations like NAO and MJO becomes weaker and even disappear. The weak correlation coefficient of the SST over the tropical Pacific and the 250 hPa zonal wind over the Middle East confirms this weak connection. But as an individual oscillation, its warm phase (El-Nino) holds the subtropical anticyclone annual oscillation at the lower latitudes comparing to La-Nina and lets the mid latitude cyclones pass over Iran and rain. It means, the condition for the cold season's precipitations over Iran in El-Nino is better than it in La-Nina. At last, La-Nina moves the Middle East subtropical anticyclone to the higher latitudes in summertime and prepares condition for passing the easterly waves over south and southeast of Iran which form the summer precipitations. This condition is weaker in the summertime of El-Nino.
    Keywords: ENSO, annual oscillation, subtropical anticyclone, Middle East, teleconnection
  • Azizi, Gh, Safarrad, T Page 69
    IntroductionThe El Nino and La Nina each favor a different location for the dips and bulges of the polar jet stream. They also affect the strength of the subtropical jet stream. In this way, they influence the weather in middle latitudes. The influence is greatest in the winter months when the coupling of the tropical and mid-latitude patterns is the best. In most El Nino winters, the warming of the air due to strong convection over warm water over the eastern and central Tropical Pacific helps energies the polar and subtropical jet streams to the north. A strong low pressure develops over the Aleutians. The polar jet stream curves to the north into northwestern North America, while the subtropical jet stream ripples across northern Mexico or the southern United States. During La Nina winters, on the other hand, the polar jet stream is strong and the subtropical jet stream weaker in the vicinity of North America (D’Aleo & Grube, 2002).The effect of ENSO on precipitation and temperature has been studied in detail by a number of Iranian researchers (Khosh Akhlagh, 1998; Azizi, 2000; Ghayor and Asakereh, 2001; Nazem al-Sadat and Ghassemi, 2003; Masoudian 2005, Khorshid Doost and Ghavidel Rahimi, 2006; Yar Ahmadi and Azizi 2007; Hagh Negahdar et al.; 2007). Most of these researches have attributed the increase and decrease of autumn rainfall to El Nino and La Nina respectively. Although it seems that seasonal distribution of rainfall during different ENSO phases does not follow any particular pattern, different patterns can be seen in each of the two compared phases. Givi et al (2009) indicated the positive and negative anomalies of precipitation in each El Nino and La Nina year. Not enough studies have been done on different phases of ENSO that affect the climate of Iran. This study aims to provide a more comprehensive analysis of changes in the 200Hpa jet stream in relation to various ENSO phases (for September, October, November and December).Materials and MethodsIn this study, the Oceanic Nino Index (ONI) provided by the National Oceanic and Atmospheric Administration, is used for defining the ENSO. Whenever ONI based on a threshold of +/- 0.5oC for the Oceanic Nino Index (ONI) at least in 5 three months period is called El Nino/La Nina. ONI values for the three-month periods of 1950 are available through the NOAA website. According to this definition, the El Nino and La Nina years from 1950 to 2010 were classified according to severity. The threshold is further broken down into Weak (with a 0.5 to 0.9 SST anomaly), Moderate (1.0 to 1.4) and Strong (≥ 1.5) events. This report aims to categorize the events as weak, moderate or strong. It has equaled or exceeded the threshold for at least 3 months (Table 1).Consequently 1997, 2008, and 2010 were selected as El Nino, normal and La Nina respectively (Figure 1). The impact of ENSO on autumn precipitation is showed by the former research (for example: Azizi, 2000; Masoudian, 2005); Then September, October, November, and December of the above-mentioned years were selected for studying subtropical jet streams.Figure 1: The time series of ONI (1990 – 2010). The black areas indicate El Nion conditions and the gray areas indicate La Nina conditions.In order to reveal the daily cores of jet stream for September, October, November, and December in the selected years, we use the daily global circulation data based on the NCEP-DOE Reanalysis 2 at 1997, 2008, and 2010. Grid intervals are 2.5º in both latitude and longitude. We used u and v components of wind in 200 and 300 Hpa in which the wind speed is over 30 meters per second; Jet stream paths are drawn after extracting the cores of jet stream. Results and discussionThe study shows that the transition of jet stream in 200 and 300 Hpa during September, October, November, and December is done through two distinct paths in north and south of 40º latitude; The north one known as subpolar jet is located around 40º - 70º latitude, and the south one known as Subtropical jet is located around 25º - 37º latitude. The path widths of subpolar jet stream in El Nino year for both levels (200 and 300 Hpa) are wider than normal year, whereas they are narrower in La Nina year for both of them. In the case of subtropical jet stream its path widths in El Nino year for both levels (200 and 300 Hpa) are narrower than normal year, whereas in La Nina year at 200 Hpa level it is wider and at 300 Hpa level it is thinner. During the El Nino phases, the frequency of jet stream paths at 200 Hpa is the highest for subtropical jet stream and the lowest for subpolar jet stream. During the La Nino phases, the frequency of jet stream paths at 300 Hpa is the highest for both subtropical and sub polar jet streams.The average speed of jet streams core at 200 Hpa is increased during El Nino year and decreased during La Nina year. At 200 Hpa level over Iran, the paths frequency and speed cores are higher during El Nino phase and lower during La Nina phase than normal condition. Whereas the amount of paths and speed cores during both El Nino and La Nina is lower for subtropical jet streams. The increase of the average speed of jet stream cores during El Nino and its decrease during La Nina phase is a notable result of this research.
    Keywords: Jet stream, ONI, ENSO, Linear Directional Mean, Jet Stream Position
  • Laleh Siah Piranm., Zoljodim., Fatahie., Mahsafar, H Page 83
    IntroductionThe Increase in greenhouse gases in recent decades has caused an increasing in the earth's temperature. As recent scenarios of the state board of climate change have predicted global average temperature increase to 0/76 ° C in the last century x up to 6/4°C until 2100 are expected (IPCC, 2001) This phenomenon is called "climate change". Climate change can be very effective on water resources system. In this sense, climate change is considered as one of the major challenges human beings face in future decades.In this study, using the atmospheric general circulation model (GCM) (General Circulation Model) under the scenario of greenhouse gases (SRES), changes in rainfall and temperature in the period 2010-2039 for stations of Ahvaz, Dezful and Khorramabad as selected stations of great Karun basin are simulated. The required data including average monthly temperature and total rainfall in mentioned time period are obtained from two models of HadCM3 & CSIRO and models of Atmospheric general circulation model scenario of a A2 & B1 and can be used from proportional method of basic and future periods. The results suggest an increase in temperature and a decrease in precipitation in the mentioned time period (2010-2039). Materials and MethodsConsidering different heights and natural variation of Karun basin, it is seems normal to find diverse climates in this basin. To evaluate the accuracy of the data and the period of data suitable for this study, three main stations were selected in this basin, among them, Khorramabad station was considered as the mountain part, Dezful station as the middle, and Ahwaz station as the southern part.Simating climate variables at the post periods by models HadCm3& CSIRO Temperature and precipitation are main and basic elements of each climate and are among the main indicators climate Zoning are method of simulating local climate variations in a specific region is to evaluate time periods in a long time statistical period(lager then a few hundred years. Due to lack of long term observations in most parts of the world, the alternative way is using simulation of)AOGCM). These models are based on laws of physics which are presented by mathematical relations. These relations are solved in a three dimensional network at the Earth's surface. For simulating the climate of the Earth, main climate phenomena (Atmosphere, Kryosphere, Biosphere and Hydrosphere) are simulated in separate sub-models. Till now; many models of atmosphere general circulation have been presented by different research centers. In all of them, eight climate variables including precipitation, mean sea level pressure, solar radiation, mean temperature, dew point temperature, minimum temperature, maximum air temperature and wind speed at 10m altitude from earth surface until years 2100 are simulated under different scenarios. In this study, the outcome of two models Had CM3& CSIRO Under scenarios of A2 & B1 refereed to Fourth assessment report IPCC(AR4) are used.Small-scale data Considering the low acuity of places of atmospheric general circulation, using them in local scale is not possible. So, it is necessary to correct them. These corrections are done by decreasing statistical climate precipitation data by Alkuma and colleagues which is based on correction made by difference between man annual observed and simulated data. , is corrected temp. Is corrected precipitation for a specific month., is not corrected simulated temp., is not corrected precipitation., is mean simulated annual temp., is mean simulated annual precipitation for base 30 years period in model GCM. Also is mean observed annual temp is mean observed annual precipitation for the above mentioned (30 years) period?The studies show that mean monthly temperature in model Hadcm3& CSIRO Under scenario of A2 in Karun basin has increased up to 1/7 & 2/2° C and under scenario B1 2° C & 1/8° C, respectively compared to observatory period. Also, mean monthly rainfall is decreased in Karun Basin in models Hadcm3 & CSIRO and under scenario A2 down to 0.9 & 0.4 percent & under scenario B1 down to 2.7 & 4.6 percent, respectively, compared to the observatory period. ResultsThis study show that mean monthly temperature will increase and mean monthly precipitation will decrease in Karun basin in 30 years from now. Studies show that most increase in mean monthly precipitation in model CSIRO under scenarios A2& B1 in November which is 5.2 & 5.8 percent and in model Hadcm3 under scenarios A2& B1 is 15.5& 12.2 monthly precipitation for model CSIRO under scenarios A2& B1 is in march which is 0.4& 4.6 percent and for model Hadcm3 under scenarios A2& B1 in February is 0.9& 2.7 percent respectively. ConclusionIn this paper have tried to present a method for revealing climate change in past periods in local small scale and its relation to greenhouse gases considering climate processes in a specific region. Generally, the results show an increase in temperature and precipitation. Considering the fact that Karun basin is one of the most important basins in our country, and water shortage and drought crisis have been more frequent in this area and have caused regional and national significant problems, and decreased the quality of water resources.It is worthy to get ready and prepared to defend against probable changes. Also, it seems necessary for the qualified responsible authorities to take proper measures against these changes. The results indicate that the effects of greenhouse gases are more obvious in the final years of the mentioned time period. So, we need to worry more.
    Keywords: global warming, climate change, simulation, Atmosphere general circulation, great Karun Basin