Journal of Spatial Analysis Environmental Hazards
تحلیل فضایی مخاطرات محیطی
Journal of Spatial Analysis Environmental Hazards
Literature & Humanities
http://jsaeh.khu.ac.ir
1
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2423-7892
2588-5146
10.61186/jsaeh
fa
jalali
1393
10
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gregorian
2015
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سازوکار شکلگیری باد گرمش در البرز
Mechanism of Garmesh wind formation on western half of Alborz Mountains
تخصصي
Special
پژوهشي
Research
<p dir="RTL" style="text-align: justify;"><span style="font-family:nasimyw;"><strong>برای بررسی شرایط جوی در زمان وقوع باد گرمش، روزهای شاخص این پدیده از بانک اطلاعاتی 29 سالهی باد گرمش گیلان (2010-1982) استخراج شد. میدانهای فشار، دما، نم ویژه، ارتفاع ژئوپتانسیلی، سرعت قائم، مؤلفههای مداری و نصفالنهاری باد، فرارفت رطوبت و دما، جریان، تاوایی نسبی و برش قائم کمیتهای دینامیکی در سامانههای منجر به این پدیده در همه ترازهای جوی مطالعه شد. از تصاویر سنجندهی مودیس، ماهوارههای ترا و آکوا برای تأیید وجود ابرناکی و بارش (برف) در دو سوی رشتهکوه البرز استفاده شد. به سبب ابرناکی و وقوع بارش در هنگام باد گرمش سه دسته الگو شناسایی شد: دستهی اول موارد رخداد باد گرمش همراه با آسمان صاف و بدون پدیده در دو سوی رشتهکوه البرز، دسته دوم فقط وجود ابرناکی در هنگام باد گرمش و دسته سوم موارد همراه با وقوع بارش را در دامنهی جنوبی رشتهکوه البرز در زمان باد گرمش شامل میشود. نتایج نشان میدهد که تفاوت این سه دسته، علاوه بر الگوی سطوح میانی و فوقانی وردسپهر، در الگوی همدیدی توده</strong><strong><span dir="LTR"></span></strong><strong> هوای مستقر در سطح زمین است. در دسته اول و دوم، استقرار توده هوای پرفشار در نواحی مرکزی فلات ایران و نفوذ زبانهی کمفشار در شمال رشتهکوه البرز موجب شکلگیری جریانهای جنوبی به سمت سواحل جنوبی دریای کاسپین و افزایش سرعت باد در لایههای زیرین وردسپهر میگردد. اما در دستهی سوم گسترش کمفشار به سمت دامنهی جنوبی البرز و نواحی شمالغربی ایران، شکلگیری مولفهی مثبت باد نصفالنهاری را به سمت دامنههای شمالی و پشت به باد البرز در پی دارد. </strong></span></p>
<p style="text-align: justify;"><span style="font-family:times new roman;">Mountain systems have an important role on meteorological variations. Different components of the mountain affect the atmospheric parameters and have essential role in atmosphereic circulation. Garmesh wind is one of the most well-known phenomena that are related to mountain systems. In this research, mechanism of garmesh wind are identified using database of garmesh wind in the last 29 years and using remote sensing technology from 2005 to 2010.</span></p>
<p style="text-align: justify;"><span style="font-family:times new roman;">To survey the Synoptic and dynamic conditions of atmospheric patterns in the Garmesh wind’s events in the region, SCDATA of several synoptic stations in Gilan province, including Rasht, Bandar Anzali, Astara and Jirandeh are used which had continuous long-term data in 1982-2010period After Identification of days with Garmesh wind, daily images of Modis sensor of terra and aqua satellites in visible band and 7-2-1 band are monitored for checking the cloudiness on the both sides (southern and northern slops) of Alborz mountains and data of Jirande station in southern slop of Alborz mountains are used for detecting atmospheric phenomena like precipitation and snowfall. Also for studying the synoptic and dynamic pattern of this phenomena, reanalysis data from NCEP/NCAR were used.</span></p>
<p style="text-align: justify;"><span style="font-family:times new roman;"> In this research, Based on the presence or absence of the atmospheric phenomenon (like rainfall and snowfall), three categories were identified. In the first category, Garmesh winds were happened in clear sky conditions and without any atmospheric phenomena on both side of mountain’s slope. In the second category, only cloudiness was seen at the time of the Garmesh wind. In the third category, precipitations (in this research, snowfall) were seen in southern slope of Alborz Mountains.</span></p>
<p style="text-align: justify;"><span style="font-family:times new roman;">Statistical analysis of Garmesh wind in central plains of Gilan</span></p>
<p style="text-align: justify;"><span style="font-family:times new roman;">Totally, Occurrence of Garmesh wind was 479 days in Rasht, during 1982-2010. The frequency of occurrence of this phenomena was in January, February, November and December and rarely, in September and June. Clouds that observed in the time of Garmesh wind were: Altocumulus (type 4), Cirrus, CirroCumulus.</span></p>
<p style="text-align: justify;"><span style="font-family:times new roman;">Patterns of Garmesh wind mechanisms on western half of Alborz Mountain:</span></p>
<ul>
<li style="text-align: justify;"><span style="font-family:times new roman;">B1. Garmesh wind without any phenomena</span></li>
</ul>
<p style="text-align: justify;"><span style="font-family:times new roman;"> This category includes11 cases of total 47 studied cases. 29 January 2008 is an example of clear sky condition in the time of Garmesh wind. In this pattern, in the surface zonal extension of Mediterranean dynamical low pressure’s contours from west of Caspian to Gilan plain and at the same time formation of cold high pressure cell on Zagros mountains caused strong pressure gradient on southern coastal zone of Caspian Sea, As it led to the the increase of wind velocity in Rasht airport synoptic station from 11 kilometer per hour in 00 UTC to 36 kilometer per hour in 12 UTC. Dominance of warm core on southern Caspian versus dominance of cold surface air on Iran Plateau indicates adiabatic warming in northern slope of Alborz Mountains.</span></p>
<ul>
<li style="text-align: justify;"><span style="font-family:times new roman;">B2. Garmesh wind with cloudiness</span></li>
</ul>
<p style="text-align: justify;"><span style="font-family:times new roman;"> This category includes 34 cases of total 47 studied cases. Free of air mass’s patterns in the surface and conditions of atmospheric flows in low-troposphere that are similar to previous category, transition of height trough in mid-troposphere and high-troposphere can be name variant component verses previous category.</span></p>
<ul>
<li style="text-align: justify;"><span style="font-family:times new roman;">B3. Garmesh wind and precipitation (snowfall)</span></li>
</ul>
<p style="text-align: justify;"><span style="font-family:times new roman;"> This category includes 2 cases of total 47 studied cases. At the same time, surface high pressure was on Iran Plateau and low pressure system was on Caspian Sea and also Gilan providence that caused the formation of Northerly stream and west-east stream to southern coastal zone of Caspian Sea and backward of Alborz Mountains like other patterns, snowfall occurred on southern slope of Alborz Mountains. Strong southern and south-western stream and strong positive vorticity on southern slope of Alborz Mountains by deep height trough in low-troposphere has an important role on intensification of vertical motions on lee ward of Alborz Mountains.</span></p>
<p style="text-align: justify;"><span style="font-family:times new roman;"> Garmesh wind is an atmospheric phenomenon that occurs as a result of interaction between atmospheric systems in synoptic scale and topography on back ward of mountain. In the other words, existence of Alborz Mountain’s as a great wall has an important role in the interaction between synoptic systems and formation of Garmesh wind.</span></p>
<p style="text-align: justify;"><span style="font-family:times new roman;"> Formation of Garmesh wind phenomena in Gilan province, is affected by extension of Siberian high pressure’s counters and sub-tropical high pressure on central of Iran Plateau and also existence of advection of pressure’s counter like sub-polar low pressure and or the Mediterranean Sea on north of Alborz mountains are required. Without any notification to origin of air masses, three categories has been observed based on existence or absence of Phenomena (in this research, sowfall)</span></p>
<p style="text-align: justify;"><span style="font-family:times new roman;"> In 700 and 500 hPa, Geopotential height patterns and relative vorticity field indicate that in the first category, wide parts of Iran is affected by high height and negative vortisity like low troposphere, during peak hours the wind. But in the second and third category (specially in third category ) existence of upper trough and easterly extension of trough caused to reduction of height and formation of strong positive vorticity in upper level and all over of air column in both south and north slopes of Alborz mountains.</span></p>
مخاطرهی باد گرمش, چرخند سطحی, جریانهای جنوبی, تصاویر سنجندهی مودیس, رشتهکوه البرز.
Garmesh wind, cyclone, Southern Stream, Modis sensor images, Alborz mountains.
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