The Study of Snowfall Hazard Mechanisms in Gilan State (1963-2012)

Document Type : Research Article

Authors

• Forogh Momenpoor ¹
• Samaneh Negah ²
• shabnam Hadinejad Sabori ¹
• Nima Farid Mojtahedi ¹
• Ebrahim Asadi Oskooiee ³

¹ expert of gilan meteorological office

² Azad University of Tehran

³ Ferdowsi University of Mashhad

10.22067/geo.v3i1.25371

Abstract

1. Introduction
Heavy snow hazards, although have less frequency in comparison with extreme weather events such as freezing, but are major hazards in midlatitudes (smith, 2009, 196). Heavy snow damages manmade structures, crops, casualties, even between urban and rural ways of blocking.(Briant. 69, 2005. Ohara et al, 2009, 1611). Various definitions have been offered for heavy snow, those are classified in terms of 'intensity', 'height', 'visibility'. Note that in heavy snow conditions, geographical features and the climate of each region should be considered.
2. Study Area
Central part of Gilan plain has located in the Southwestern of Caspian sea where Alborz Mountain belt are surrounded the area from South of it. According to the available snow data, this plain sometimes has affected by heavy snowfall. In the recent 50 years, it has experienced 12 year with heavy snowfall.
3. Material and Methods
In order to achieve the days with heavy snowfall, we used a combination of data that obtained from reputable newspapers (70 years) and interviews with knowledgeable people because of lack of long-term data. These snowy days were compared with daily synoptic stations data (1963-2012) to ensure that the event was heavy snow. Snow storms were studied through three major methods 1- snow volume classification, 2- synoptic atmospheric conditions, and 3- case studies of major events separately. The second and third approaches are considered in this study. To study of synoptic and dynmical mechanism of heavy snowfall, Zonal and meridional component of wind, geopotential height, omega, temperature, and sea level pressure with netcdf format were used from NCEP/NCAR on Iran ,then other parameters like stream, vertical motion, convergence, relative vorticity and cross section of these parameters were plotted.
4. Results and Discussion
During 50 years (1963-2012), 80 days with heavy snowfall were identified in 30 waves that classified in two patterns. IN The first pattern, High-pressure air mass with different origins, such as oceanic and continental (southeast Scandinavian Arctic high pressure, Siberian high-pressure and Western Europe high-pressure) was attended. In the second pattern, combination of low pressure and high pressure were seen, that 10 cases of 30 cases of heavy snowfalls were in second pattern. In this pattern, the role of Caspian Sea, Mediterranean Sea, Black Sea, Red Sea and Persian Gulf that the air masses originated there or has been strengthened with the establishment, is undeniable. Deep-tropospheric dynamical cyclones from the West, Northwest and Southwest are imported and carrying heat and moisture fluxes to the southern coast of the Caspian Sea. Influence and establishment of dynamical or semi permanent anticyclones from higher latitudes accompany by anticyclonic circulation and cold air advection (negative vorticity ) at lower level of the troposphere in South coast of Caspian sea. This situation considerably increases the pressure gradient in the northwestern part of the Iran and the southwest of Caspian Sea. Eastward moving of trough with strong positive vorticity and considerable circulation counterclockwise in the middle and upper levels of the troposphere cause to strengthening of ascending motion in the middle and lower levels of the troposphere and convergence. Temperature fields in the middle and lower levels of the troposphere show a deep temperature trough and cold advection to the southwest coasts of the Caspian Sea. With The formation of cold front and significant reduction in temperature, all factors appropriate for conversion liquid phases of precipitation to snow. High pressure pattern is the main pattern of heavy snowfall that 20 cases of 30 cases of heavy snowfall in the region are included. However the Caspian Sea is the source of heat and humidity and enhances upward motions, the role of the Alborz Mountains as dynamical factors in high pressure vertical motion cannot be ignored. These dynamical and semi-permanent anticyclones that are imported from the north and northwest, cause to strengthening anticyclonic circulation associated with negative vorticity at lower levels of all regions of the atmosphere in the northern part of the Caspian Sea. Cold air advection from higher latitudes and available humidity conditions, cause a sharp reduction in temperature and snow is formed. In addition to the lower levels of the troposphere, barotropic conditions cause a positive vorticity and convergence which increase vertical movement at mid-troposphere. Surface cyclones in the south of the Alborz Mountain and the mid-tropospheric trough cause omega be positive that represents the upward movement. Despite the establishment of a strong anticyclone in the lower troposphere in Guilan, omega-negative values (upward movement) is observed due to a mechanical climb mountains reveals. Because of the trough in the mid-tropospheric level, omega be positive and matches with the convergence field (positive). The establishment of a surface anticyclone in the lower levels of the troposphere from Guilan plain until north Caspian, a negative relative vorticity and anticyclonic circulation occurs. With height increasing (from the level of 700 hPa), because of the unstable waves and their associated cyclonic circulation, the vorticity is positive and it is maximum in the middle troposphere. Because of the surface cyclone in southern Alborz Mountains, cyclonic circulation is observed and positive vorticity increases with altitude.
5. Conclusion
Surface anticyclones or in pairs with cyclones are the main factor for cooling and northern flux. The intensity of performance due to the location of formation, establishment and spread of air mass, Strengthening and attenuation of cyclone and anticyclone center, changes of dynamical parameters (vorticity, vertical motion,‌convergence) due to mountain forcing, thermodynamic factors due to pass of air mass over water (surface flux forcing) during the system activity, change the speed of westerly current in middle troposphere. In some cases, exist of omega blocking in middle level of troposphere from Eastern Europe to Eastern Caspian Sea, cause to stay deep trough on north of Iran. Cross section of wind shows a convergence zone in low level of troposphere in Sefidrod delta between Shahrod valley until north of Manjil valley and there is an instability between 850 to 700 hPa level too. However negative vorticity, because of surface anticyclone on Caspian Sea, cause the descending motion, but existence of ascending motion indicative dominance of role of Alborz topographic forcing in mechanical rising of air mass.

Keywords

• Heavy Snow Hazard
• Surface Anticyclone
• Westerlies
• blocking
• convergence zone
• Guilan province

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References

استانداری گیلان. 1384. بحران سفید، نگاهی به رخداد برف سنگین در بهمن 1383. چاپ اول. رشت:استانداری گیلان.

سازمان هواشناسی کشور. آمار سه‌ساعته متغیرهای هواشناسی ایستگاه‌های همدیدی رشت، بندرانزلی، کیاشهر، لاهیجان، آستارا.

تالش انسان‌دوست، فرشته. 1374. آتش‌سوزی یا بیماری‌های مهلک، سیل و خشکسالی و... طی سال‌های 1340- 1270 در استان‌های گیلان ‌و ‌مازندران. گیله‌وا. شماره 34. صص 44-46.

خسروی دانش، علیرضا و دیگران. ‌1384. جغرافیای استان گیلان. تهران: شرکت چاپ و نشر کتابهای درسی ایران.

خودزکو، الکساندر. 1385. ‌سرزمین گیلان. چاپ اول. ترجمه سهامی، سیروس. رشت: فرهنگ ایلیا.

رابینو، ه. ل. 1374. ولایت دارالمرز ایران، گیلان. چاپ دوم. ترجمه جعفر خمامی‌زاده. رشت: انتشارات طاعتی.

روزنامه اطلاعات، سال 24. اول دی ماه تا 29 اسفند 1328. شماره 7102-7186 . تهران.

‌روزنامه باختر امروز، اول دی ماه تا 29 اسفند 1328. شماره 119-193. تهران.

‌روزنامه کیهان، سال 8 . اول دی ماه تا 29 اسفند 1328. شماره 2003-2087. تهران.

رضایی، پرویز و دیگران. 1389‌. روند بارش برف در جلگه مرکزی گیلان و پیامدهای ناشی از آن. چشم‌انداز جغرافیایی. سال پنجم. شماره 12. 72-57.

سجادی، سید محمدتقی. ‌1378. تاریخ و جغرافیای تاریخی رامسر. چاپ اول، تهران: انتشارات معین.

عباسی،‌هوشنگ. 1386. گیلان در سفرنامه‌های سیاحان ایرانی، دانشنامه فرهنگ ‌و‌ تمدن ‌گیلان‌.چاپ اول. رشت: فرهنگ ایلیا.

علی‌دوست، احمد. ‌1384. خطی بر دیوار. چاپ اول. رشت: گیلکان.

عظیمی دوبخشری، ناصر. 1388. جغرافیای انسانی و اقتصادی گیلان. دانشنامه فرهنگ و تمدن گیلان. چاپ اول. رشت: نشر فرهنگ ایلیا.

فرید‌مجتهدی و دیگران. 1385. واکاوی همدیدی رخداد بارش برف سنگین فوریه 2005 استان گیلان. علوم جغرافیایی. شماره 4. مشهد.

فخرایی،ابراهیم. 1355. گیلان در گذرگاه زمان. چاپ اول. تهران: انتشارات جاویدان.

فهیمی‌نژاد، الهام و همکاران. 1386. .تحلیل سینوپتیکی و فضائی توفان برف استان گیلان(فوریه 2005).، سومین کنفرانس بین‌المللی مدیریت جامع بحران در حوادث غیرمترقبه. تهران.

گنجی، محمدحسین. 1378. هواشناسی گیلان، کتاب گیلان. چاپ اول. تهران: گروه پژوهشگران ایران.

مشایخی،حبیب ا... .1381. نگاهی همه‌سویه به تنکابن. چاپ اول. تهران: انجمن آثار و مفاخر فرهنگی.

Ahrens, C. D., 2009. Meteorology Today: An Introduction to Weather, Climate, and the environment. Ninth edition, Brooks/Colecengage Learning Academic Press, 1-549.

Alidost, A., 2005: Line on the wall.First Edition. Rasht: Gilakan press.

Azimi dobakhsheri, N,. 2008. The Econiomical and the human geography of Guilan, the encyclopedia of guilan culture and civilization, Nashre-farhangh-e ilia. Rasht.

Bakhtar Emroz newapaper., 1949. No 193-119, 1 Dey-29 Esfand, Tehran.

Brown, Richard., Russell, J. Y., 1970. Some Relationships between 850 Millibar Lows and Heavy Snow Occurrences Over the Central and Eastern United States. monthly weather review, vol 98, NO 5, 399-401.

Bryant, E., 2005. Natural Hazards. Cambridge Press, 1-312.

Changnon, S. A., Changnon, D., 2005. SnowStorm Catastrophes in the United State. Environmental hazard, 9, 158-166.

Changnon, D., Merinsky C., Lawson M,. 2008. Climatology Of Surface Cyclone Tracks Associated With Large Central And Eastern U.S Snowstorms 1950-2000. Monthly Weather Review,136, 3193-3203.

Ettelaat newapaper, 1949. No 7186-7120, 1 Dey-29 Esfand, Tehran.

Evans, M., Michael L. J., 2009. correlation between analyses and forecasts of banded heavy snow ingredients and observed snowfall. Weather and forecasting, 24, 337-350.

Esteban, Pere., Jones, D. P., Martin-Vide, J., Mases, M., 2005. Atmospheric circulation patterns related to heavy snowfall days in andora, Pyrenees. Internatonal Journal of Climatology, 25, 319–329.

Fahiminezhad, E., hejazizadeh, Z.,B., ziaeeyan, P,. 2007. Synoptic and spatial analysis snow storm province. 3rd International Conference on Integrated Natural Disaster Management. Tehran.

Fakhrai, E., 1976. Guilan in the passage of time. Javidan Press, Tehran.

Farid, M. Nima., Khoshakhlagh, F., Naeeri, M., Afsharmanesh, H., 2006. Synoptic analysis of heavy snowfall in 2005 February province. Journal of Geographic Sciences, 4,133-157.

Ganji, M, H., 1999. Guilan book. Groups of Iranian researchers Press, Tehran.

Glossary of Meteorology., 2009. Snow. American Meteorological Society. Retrieved 2009-06-28.

General Governor Office, 2005. White Crisis, A Glance to Heavy Snowfall Event in February 2005.Firat edtion.Rasht: General Governor Office.

Kunkel, K. E., Pielke Jr, R. A., Changnon, Stanley. A., 1999. Temporal Fluctuation in Weather and Climate Extremes That Cause Economic and Human Health Impact: A Review. Bulletin Of The American Meteorological Society, Volume 80, Issue 6, 1077-1098.

Mashayikhi, H., 2001. A comprehensive study on Tonekabon, Society for the appreciation of cultural works and dignitaries, Tehran.

Miyazawa, S., 1968. A Mesoclimatological Study on Heavy Snowfall, Meteorology and Geophysics, vol 19, no 4, 487-550.

Ohara, B., Kaplan, M., Underwood, J., 2009. Synoptic climatological analysis of extreme snowfall in the Sierra Nevada. Weather and forecasting. 24. 1610-1624.

Khosravi Danesh, A., 2005. Guilan geography. Publishing company of books. Tehran

Sajadi, M., 2008. History and historical geography of Ramsar. Moein press, Tehran.

Jianqi, Sun., Huijun, Wang., Wei, Yuan., Huopo, Chen., 2010. Spatial-temporal feature of intense events in china and their possible change. Journal of geophysical research, vol 115, 1-8.

Smith, K., Petley, N. D., 2009. Enviromental Hazards, assessing risk and reducing disaster. Routledge Press, 1-383.

Talesh Ensandost, F., 1995. Fire or fatal diseases, floods and droughts during 1340 – 1270 in Gilan and Mazandaran provinces. Gileva, 34, 44.

Uccellini, L. W., Kocin, P. J., 1987. The Interaction Of Jet Streak Circulations During Heavy Snow Events slong The East Coast Of The United States. Weather and Forecasting, 2, 289-308.