ارتباط نوسان شمالگان(ao) با تغییرپذیری دمای زمستانه شمال غرب ایران

نوسانات شمالگان (ao) یکی از الگوهای موثر تغییرپذیری گردش عمومی جو در منطقه برون حاره نیمکره شمالی و از عوامل اصلی کنترل عناصر اقلیمی مانند دما و بارش است. در این پژوهش به بررسی تاثیر فازهای مثبت و منفی این نوسان بر دمای زمستانه شمال غرب کشور، طی دوره آماری 2010-1965 پرداخته شد. به‌منظور دستیابی به اهداف این پژوهش از دو پایگاه داده: 1 داده دمای متوسط ایستگاه‌های همدید شمال غرب کشور و 2 داده‌های جوی شامل متغیر فشار تراز دریا(هکتوپاسکال) و ارتفاع ژئوپتانسیل(متر) استفاده شد. داده‌های جوی از مرکز ملی پیش‌بینی محیطی امریکا (ncep/ncar) دریافت شد. به‌منظور بررسی این داده‌ها محدوده‌ای‌ بین 40 تا 120 درجه شرقی و 0 تا 80 درجه شمالی در نظر گرفته شد. سپس با استفاده از تحلیل خوشه‌ای‌ و ادغام وارد به تحلیل همدید فازها پرداخته شد. یک تقسیم‌بندی سه گروهه برای فاز منفی و تقسیم‌بندی سه گروهه دیگری برای فاز مثبت حاصل شد. برای هرکدام از گروه‌ها یک ماه نماینده تعیین شد. بعداز تحلیل الگوهای فشار به استخراج الگوهای مربوط به این فازها پرداخته شد درنهایت با استفاده از روش همبستگی به بررسی رابطه‌ی نمایه نوسان شمالگان با دمای زمستانه شمال غرب اقدام گردید. نتایج حاصله بیانگر این مطلب بود که میزان دما برای گروه‌هایی با فاز منفی نسبت به فاز مثبت دارای شرایط دمایی پایین تری بوده است. حال‌آنکه طی فاز مثبت این شرایط دمایی افزایش‌یافته است. با توجه به استقرار الگوهای فشار طی فاز منفی و میانگین دمای ماهیانه می توان چنین استنباط نمود که در این فاز شرایط سردتر و پایدارتری نسبت به فاز مثبت در محدوده مطالعاتی حاکم بوده است و به تبع آن در فاز مثبت شرایط دمایی بالاتری نسبت به فاز منفی رخ داده است. بررسی رابطه این نمایه با دمای زمستانه شمال غرب نشان از ضریب همبستگی معکوس و منفی دما با نوسان شمالگان دارد.

Relationship of Arctic Oscillation (AO) and winter temperatures variability on the north- west Iran

Abstract:IntroductionTeleconnection patterns indicates a large variations that happen in the patterns of atmospheric waves and jet streams. Teleconnections are associated with the anomaly of atmospheric large scale and hemisphere circulation. Teleconnection patterns affecting on the amounts of temperature, precipitation, location and intensity of jet streams in the extensive regions. Arctic Oscillation is the leading mode of extratropical circulation from the surface to the lowerlevel stratosphere in the northern hemisphere(Hojati Masoodian, 2018). Arctic Oscillation as one of the teleconnection patterns of the north hemisphere includes an atmospheric pressure anomaly in sea level in the north polar latitudes and middle latitude (45oN); that is shown in negative and positive phases(khosravi et al, 2007). Fluctuations in the Arctic Oscillation create a seesaw pattern in which atmospheric pressure at polar and middle latitudes fluctuates between negative and positive phases(Hojati Masoodian, 2018). The AO pattern controls pressure, temperature and precipitation changes patterns and geopotential level, wind azimuth, in specific periods of year. Arctic Oscillation(AO) is one of the effective patterns in general circulation of atmosphere variability in extratropic region of northern hemisphere and is the main factors in controlling climate elements such as temperature and precipitation. Meanwhile temperature is one of climatic impressible element of the other climatic affective elements which is under the effect of this pattern (khosravi et al, 2007). Since temperature is a main element in the formation of the climate, and its variations can alter the climate structure of each region, therefore, studying the relationship of teleconnection patterns and temperature variability has a large part to be climatological research. In this regard, numerous researches has been carried out on the relationship of Arctic Oscillation (AO) and temperature changes, and the identification and analysis of the patterns of temperature has been considered by different methods in numerous studies. Here, we can be mention researchers such as Thompson and Wallace(1998), Wallace(2000), Thompson(2000), Cintia(2000), Roger et al(2000), Gong et al(2002), Philip et al(2002), Gong and Wang(2003), Daoyi and Shaou(2003), Wang et al(2005), Bond and Harrison(2006), Turkes and Erlat(2008), Sun and Ahn(2014) and in Iran, Masoodian(2005), Nazemalsadat et al(2006), Khosaravi et al(2007), Nasr isfahani et al(2008), Khoshakhlagh et al(2008), Esfandiari et al(2009), Khorshiddost et al(2010) and Alizadeh et al(2011). Since the identification of temperature patterns and its variations is very important for management and planning, this research seeks to evaluate and analyze the relationship of Arctic Oscillation (AO) and winter temperature variability on the north west Iran.Materials and methodsIn this research we examined the effect of this oscillation positive and negative phases on northwest winter temperature of country during 19652010. To achieve this goals, two databases was used. First, the mean temperature data of northwest synoptic stations of country and second, atmospheric data including sea level peressure variable ( hPa) and geopotential height(m). Atmospheric data were recieved from NCEP/NCAR. To study these data, a framework has been considered between 40120 degree eastern and 0 80 degree northern with resolution of 2.5*2.5 degree that have been borrowed from database of (NCEP/NCAR) dependent to National Atmosphere and Oceanography Institute of USA. Then, agglomerative hierarchical cluster analysis on the basis of ward linkage method have been done on data of negative and positive phases in Matlab software. A three groups classification has been obtained for negative phase and the other 3 groups classification for positive phase. Each group was assigned to an exponent month. After analyzing the patterns, we educed the patterns related to these phases. Finally, we studied the relationship between Arctic Oscillation exponent and north west winter temperature by using correlation method. All of these steps and calculations conducted by using Matlab, GrADS and Surfer. Results and discussionObtained results represented that the temperature value in negative phase groups was lower than positive phases. Whereas this temperature condition was increased during positive phases. According to pressure patterns deployment during negative phase and monthly temperature average, we can deduce that in this phase, the cooler and more stable conditions have prevailed in studied region than positive phase and consequently, the higher temperature condition has been accurred in positive phase than negative phase. ConclusionStudying the relationship of the exponent with winter temperature in northwest indicate the inverse and negative correlation coeficient with Arctic Oscillation.