فرارفت

Open Access Article

1 - Determining the Calendar of Frost on the basis of Probability of Occurrence (Case Study: Ardabil Province)
Mehry Akbary Soheila Mozaffari

10.22034/jest.2020.26525.3554

Background and Purpose: Since frost hazard can affect the human life, construction activities, agriculture and energy consumption and its distribution, being aware of the time of occurrence of frost can help in managing this hazard. In the present research, for the firs More

Background and Purpose: Since frost hazard can affect the human life, construction activities, agriculture and energy consumption and its distribution, being aware of the time of occurrence of frost can help in managing this hazard. In the present research, for the first time, effective parameters on frost separating advection or radiation types and return periods with probability of occurrence are calculated. Data and Methodology: In this research, using synoptic stations minimum temperatures in Ardabil province, dates of frost for the first time in the fall and last time in spring extracted and frosts were separated by their types (Radiation or Advection). Principal Component Analysis (PCA) was implemented on all meteorological variables in frosty days for each station. Time series of beginning and end of radiation and advection frosts using statistical distributions were analyzed and best fit distribution were selected and calculated in SMADA website. Findings: The highest and lowest frequency of frost days, respectively have happened in Khalkhal and Parsabad stations. Monthly frost analysis showed that the highest and lowest frequency of frost days respectively happened in January and October. The earliest date for the beginning of radiation frosts and advection frost (Khalkhal), respectively, have happened on September 19 and October 10 and latest date for the beginning (ParsAbad) respectively, happened on November 12 and December 12. Discussion and Conclusion: Generally, in Ardabil province 47% of frosts started with radiation frost and 53% started with advection frost which can increase the danger of frost in late summer crops. Products must be harvested before the cold air advection (5 October, based on the results of this study). 73% of frosts were terminated with radiation frosts and 27% were terminated with advection frosts which can be concluded in the spring time. It is possible to combat the radiation frosts and there is a significant reduction in losses. Based on the analysis of probability of frost occurrence, first radiation and advection frost in Ardabil with 90% probability, respectively, will occur at 18th and 23th of October. Advection frost date average of Ardabil station with a probability of 50% is 9th of November, in Pars-Abad, 1st of December, in Khalkhal, 26th of October and on 18th of November in Meshkin Shahr station. Manuscript profile

Open Access Article

2 - Synoptic analyzing the occurrence of strong wind and dust storm in Shiraz in March 2019
Ashraf Asadi

As transition seasons approach at the end of the winter season, changes in movement patterns and wind speed in mid-latitudes are inevitable. On March 22, 2019, a strong wind accompanied by heavy dust and muddy rain for a large part of the day resulted in the injury of s More

As transition seasons approach at the end of the winter season, changes in movement patterns and wind speed in mid-latitudes are inevitable. On March 22, 2019, a strong wind accompanied by heavy dust and muddy rain for a large part of the day resulted in the injury of several citizens and significant damage in the city of Shiraz. For this reason, this research was conducted with the aim of investigating the synoptic conditions of the formation of this phenomenon. Earth surface data from the Meteorological Organization and variables of air temperature, geopotential height, sea level pressure, zonal wind, meridional wind, specific humidity, and omega were used as upper atmosphere data to investigate the upper level of the atmosphere. Using these variables, geopotential height roughness map patterns, frontal formation process, vorticity advection, humidity, thickness pattern, earth surface pressure patterns, Jetstream, Omega, and Hof-Muller diagrams of the third type of Jetstream and Omega were drawn at different levels. The results showed that the location of the studied area under the positive advection zone in the east of the western wind channel, which leads to high divergence and low convergence, the establishment of temperature trend and front formation, and especially the descent of the polar front wind to the lower atmospheric levels, the conditions Synoptic have provided for the occurrence of strong air ascent and the formation of strong gusts caused by it. Manuscript profile

Open Access Article

3 - تحلیل همدیدی مخاطره امواج گرما در شمال غرب ایران
علی محمد خورشیددوست سعید زنگنه یوسف زارعی سعید محمودی

دما از عناصر اساسی اقلیم است لذا تغییرات ناگهانی یا کوتاه مدت و درازمدت آن می‌تواند ساختار آب و هوای هر محلی را دگرگون سازد. در این پژوهش تحلیل سینوپتیکی امواج گرمایی هجده ساله اخیر(1999-2016) در شمال غرب ایران مورد بررسی قرار گرفت. با استفاده از داده‌های دمای روزانه، م More

دما از عناصر اساسی اقلیم است لذا تغییرات ناگهانی یا کوتاه مدت و درازمدت آن می‌تواند ساختار آب و هوای هر محلی را دگرگون سازد. در این پژوهش تحلیل سینوپتیکی امواج گرمایی هجده ساله اخیر(1999-2016) در شمال غرب ایران مورد بررسی قرار گرفت. با استفاده از داده‌های دمای روزانه، موج‌های گرما را که با افزایش ناگهانی و هماهنگ دما در همه ایستگاه‌های انتخابی منطقه شمال غرب ایران رخ داده بود، بر روی نمودار به صورت ماهانه(72 نمودار) مشخص گردید، که با این روش 14 موج گرما با شدت‌های مختلف شناسایی گردید. سپس با استفاده از داده های NCEP-NCAR و نرم افزار GRADS و چهار سطح تراز دریا، 850، 700 و 500 هکتوپاسکال، انتخاب گردیدند و نقشه‌های سینوپتیکی تهیه گردید و مورد تحلیل همدیدی قرار گرفتند. بر اساس نتایج بدست آمده با قرار گرفتن پشته حاصل از مراکز واچرخندی بر روی نیمه غربی ایران در روز اوج موج گرما، و با همگرا شدن هوا سبب فرونشینی و نشست هوا و در نهایت گرم شدن آن به صورت آدیاباتیک می‌شود. بررسی موج گرما از 48 ساعت قبل از شروع آن تا پایان موج و گذشتن از روی منطقه نشان می‌دهد که مراکز پرفشار جنب حاره ابتدا بر روی عربستان و شمال شرق آفریقا بسته می‌شوند و از روی دریای سرخ و عربستان عبور کرده و تا پایان موج گرما از شرق ایران گذشته و بعد از آن ضعیف شده و به عرض‌های پایین جابجا می‌شوند. Manuscript profile

Open Access Article

4 - The synoptic study of heavy rain fall (200mm or more during 24 hours) over the southern coasts of Caspian Sea due to mean temperature of thickness 1000/500mb, in 2th of October 2001
H. Ardakani M. Poratashi M. Kheirandish

The mean annual precipitation over the southern part of Caspian coastal area is around 1000-1500 mm; therefore, this amount of precipitation is very important and is a considerable point of attention. With reference to statistical data, during 30 years (1972-2001), it More

The mean annual precipitation over the southern part of Caspian coastal area is around 1000-1500 mm; therefore, this amount of precipitation is very important and is a considerable point of attention. With reference to statistical data, during 30 years (1972-2001), it showed that there were only 10 cases of similar events. We found that, best synoptic patterns for this condition is the mobile cold anticyclones which is moving almost rapidly from Europe and Scandinavia to the north of Black Sea and then moving to the Caspian Sea. These anticyclones have strong cold advection in eastern part and warm advection in the western part and their pressure center are about 1040 mb or more. But those anticyclones are very slow moving or almost stagnant over the area and could not cause these events. The upper-air chart showed that, spatial axis of upper ridge over them is a normal baroclinic condition. The value of cold advection in eastern part of anticyclones computed from 700 mb was -12ºc/12hours, but warm advection in western part of them, were not the same values. Consequently, the month of October is the most effective with compassion of the other months, because, during the summer times (July, August, September). The thermal low over the country frequently extending over the Caspian Sea and SST will increase, so, such patterns with strong cold advection, will cause severe instability over Caspian Sea. Manuscript profile

Open Access Article

5 - Synoptic analysis of Caspian torrential rains, Case Study: Winter floods in 2012 Noushahr
A. Mohammadi M. Salighe E. Hamidy A. Hesamy

Torrential rains in the southern Caspian Sea, has been of interest for researchers and different solutions have been offered. The analysis shows that thesuggested mechanisms are all derived from a single model. These theories are different only in appearance. This singl More

Torrential rains in the southern Caspian Sea, has been of interest for researchers and different solutions have been offered. The analysis shows that thesuggested mechanisms are all derived from a single model. These theories are different only in appearance. This single model is the basic mechanism of the Caspian Sea rainfall in autumn and winter. Torrential precipitation more occurs in autumn and less in winter. In this paper, winter floods in Noushahr city in 2012 have been studied. By posing different theories governing the precipitation of the Caspian Sea, next to one another, the pattern was introduced for the torrential rains. Results indicated that the floods were caused by the passage of low pressure systems from the North Caspian Sea. Low pressure cold front has passed over Noushahr on 11 November 2012. The cold front on 12 November 2012, located near the center of Iran, at 35 latitude. With the influx of cold air behind the cold front caused floods in Noushahr city. Cold advection over the sea caused too much moisture absorption by the air. The results also showed that the ridge of high pressure that immigrated from the north Mediterranean had important role in the passage of the cold front is Noushahr city. The ridge is moving cold front to lower latitude finally passes through the north of Iran. The cause of ridge formation was cold air advection on the Caspian Sea. Manuscript profile

Open Access Article

6 - The Case Study of Synoptic Systems that Caused Heavy Snow in Tehran City in February,2003
H. Ardakani S.P. Aghaei Eramsadati F. Arkian

Heavy snowfall and its aftermath is an example of atmospheric phenomenon which can cause serious harm to many parts of the natural and human environment. In order to identify the effective synoptic characteristics and patterns at the events of heavy snow in Tehran in th More

Heavy snowfall and its aftermath is an example of atmospheric phenomenon which can cause serious harm to many parts of the natural and human environment. In order to identify the effective synoptic characteristics and patterns at the events of heavy snow in Tehran in the present study, the snowfall data are collected from the Mehrabad airport weather station archives over the years 2000-2009. From the total number of 150 snowy days that had been recorded, synoptic maps have been created for 19 February, 2003, using data from the GFS, with an accuracy level of 1.0o×1.0o, by GrADS software. Temperature advection maps have also been created using CFSR data. Studying the synoptic maps at different atmospheric levels revealed that during the period of heavy snowfall in February, 2003, the formation of low-pressure over the Mediterranean Sea and on the other hand the formation of high-pressure and its ridge over Caspian Sea are visible and the transition of the two systems causes intensive pressure gradient over the area under the study. Simultaneously at the level above, a low and trough forms that the transition of this trough to the aforementioned area leads to the creation of snowfall. Analyzing the amounts of absolute vorticity and the vertical motion reveals advection of absolute vorticity and the negativity of the vertical motion () which imply the instability and ascending air mass that will eventually result in the occurrence of heavy snowfall. Studying the amounts of temperature advection at 200 hPa also represents warm advection. Manuscript profile

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