جستجوی مقالات مرتبط با کلیدواژه "synoptic analysis" در نشریات گروه "هواشناسی"

There are substantial changes in climate elements, particularly precipitation, over time, and understanding these changes provides the knowledge necessary to maximize the efficiency of nature. As part of this study, dry autumns were determined during the statistical period of 1987-2016 by calculating the standard precipitation index using DIC software based on the environmental approach to circulation. Based on the reconstructed NCAR/NCEP data, combined maps of 500 hPa, 700 hPa, and 1000 hPa specific humidity were obtained from the reconstructed data, and Hof-Müller diagrams of 700 and 1000 hPa specific humidity were analyzed. Based on the results of this research, it is apparent that in dry autumns, there are strong positive anomalies on the earth's surface, indicating the weakening of low pressures and the prevention of low pressures from entering. Due to the high altitude rule, there are positive anomalies compared to the long-term average at 500 hectopascals. As a result, lower latitudes' hot, humid climate has not been transferred to the region. Furthermore, the Hof-Muller diagrams at the levels of 700 hPa and 1000 hPa are examined in the dry autumns of the northwest at latitude 38°N and longitude 48°E, indicating an apparent decrease in specific humidity for this level. In 4 cases out of 5 study samples, Sudanese low-pressure systems and Sudanese-Mediterranean systems had a significant impact on injecting moisture into the study area, especially in the southern latitudes (15 to 30°N).

In this research, the influence of the polar jet streams on the daily rainfall of synoptic stations in Iran in the cold season (autumn and winter) during a period of 30 years (1988-2017) has been studied. Based on the threshold of rainfall exceeding 30 mm as heavy rainfall and based on the 95th percentile, 972 days were identified and clustered as days of heavy rainfall in 31 synoptic stations of Iran, and the representative days of each cluster were selected. In the following, in order to find behavioral patterns and investigate the interaction of the polar jet stream on the intensification of the processes of frontal formation and the occurrence of heavy precipitation, the data of the zonal and meridian wind component, divergence, geopotential height, vertical velocity of the atmosphere (omega), vorticity, relative humidity, specific humidity, temperature and average sea level pressure were studied. The results of these analyzes showed 6 circulation patterns in the region, each of these patterns, due to the dominance and establishment of numerous troughs and ridges in the atmosphere, on the path of the polar front jet stream transfer to the middle latitudes of the earth and also the fluctuations of its seasonal average position have been influential. The results showed that the meridian mode of the jet stream axis has caused the creation and production of cores for the rate of occurrence of more rainfall in the western region of Iran.

In this research, the occurrence of hail analyzed based on instability indices in Northwest of Iran. For this purpose, meteorological codes related to hail (27, 87, 89, 96 and 99) in the years of 1995 to 2018 were extracted and analyzed statistically. Instability indices such as CAPE, LI, KI, TTI, L.C.L, PW and SWEAT were used for hail patterning. For the days of hail occurrence, instability indices were calculated from the skew-t diagram of Tabriz station. Then, hail occurrence days were clustered by using hierarchical cluster analysis method. After that, a representative day from the third cluster was selected and examined synoptically. The cluster results showed that hail occurrences were classified into three pattern. In the first pattern, the instability indices were weak and hail has occurred at the synoptic scale. The second pattern showed the instability conditions in the atmosphere with the occurrence of hail and the ascent of air in the region. In the third model, the instability indices showed the intensity of the thunderstorm and the occurrence of hail. In this model, the Convective Available Potential Energy (CAPE) has increased, which indicates the buoyancy and ascent of the air. In the third pattern representative day, the formation of cut-off low at 500 hectopascal level and the presence of low pressure in the Southeast of Iran has caused hail in Northwest of Iran.

Cyclonic systems are generally unstable conditions messenger that result from the spread of significant disturbances that occur in atmospheric currents. In this study, daily rainfall data of 4 catchments and gridded data (ECMWF) with 6-hour time steps and spatial separation of 0.25 * 0.25 from 1979 to 2004 were used. using with the cluster analysis method 3 atmospheric patterns were extracted. where the center of the trough in 500 and 700 hPa Stacking on top of each other, the geopotential height is the minimum and the geopotential gradient will be the maximum and will lead to the occurrence of the most cyclogenesis, Which occurred in the first pattern these conditions and resulted in average heavy rainfall of 38.6 mm. In the second pattern, none of the conditions of stacking on top of each other and deeping of the trough, and this has led to the lowest average heavy rainfall of 32.7 mm. In the third pattern, the condition of matching of the two centers of the troughs is established, but they do not condition of deeping trough And have led to heavy rainfall of 36/1 mm which is less than the first pattern. Also, the most cyclogeneses location in the eastern Mediterranean to Iraq, heavy rains caused by cyclones are born in this region. The results also showed that most of the moisture comes from the Red Sea. the subtropical jet stream plays a role in strengthening and ascending, in the north of Saudi Arabia and the Persian Gulf.

Identifying and studying freezing level is an important issue in aviation weather science. Due to the global warming climate, the altitude of freezing level, especially in the subtropical, is increasing, which has attracted the attention of many meteorological and climatological researchers, and many studies have been conducted in this field. To quantify these changes, it is necessary to statistically study the changes in freezing level elevation due to climate change and global warming. In this study, in order to identify the freezing level at each point, temperature information was used at different levels of the atmosphere above that point. The oldest and most common method for determining freezing level is the use of radio-sounding data, and this method is performed twice a day at 00 and 12 UTC. Therefore, due to the dispersion of this data in the period under study (if available), this information was collected at three stations of Mehrabad, Mashhad, and Kermanshah airports. Analysis of freezing level changes in selected airports of the country, in different months, seasons, and years using the Mann-Kendall test, does not show an upward or downward trend. In other words, monthly and seasonal changes in the height of this level in different years are not dependent on climate change. Synoptic investigating indicate that changes in the altitude of the freezing level at different years depend on atmospheric systems and the synoptic conditions of the studied month or season.

In synoptic climatology, relying on the principle of changes in the analysis and explanation of environmental conditions of the earth's surface from changes in pressure patterns, the most climatic phenomena of the earth's surface can be explained, analyzed and predicted. One of the most important of these phenomena is the temperature (especially the minimum temperature temperature). Scientists believe that climate change occurs in the form of extreme temperature events, especially extreme temperature. Understanding the interactions between different components of tourism is one of the desirable solutions that are studied to study climate change and public climate. Flavors, especially in mid-latitudes, are among these components. Therefore, the purpose of this study is to analyze the synchronous minimum temperature of Tabriz.

Using daily average data during the period 1988 to 2017 from the synoptic station of Tabriz city, a hybrid synoptic map (500 HP level, surface, omega and vortices) prepared by GRADS software and examined. Data were selected in SPSS software using hierarchical clustering method and representative days to investigate the relevant issue.

The results show the positive effects of vortex (at the level of 500 HP) on the occurrence of extreme temperatures due to the presence of blocking systems, cold air subsidence of high latitudes at the upper level and high pressure systems (anticyclones) at ground level. The amount of omega at the level of 500 HP was positive on all days in the study area.

Finally, a positive vortex at the level of 500 HP has caused a drop in temperature at the ground level. In addition, anticyclone systems at the ground level have subsequently reduced the temperature and the occurrence of extreme temperature in Tabriz city station.

Dust storm is a complex process that is influenced by the interactions of atmospheric systems and is basically caused by conditions such as high wind speeds, bare soil and dry air. In recent years, the occurrence of this phenomenon in the Middle East is increasing. Continuation of more than a decade of drought in Iran and other countries in the West Asian region, along with the impact of other environmental factors, has led to a crisis of natural resources and environment in the region; As the country is currently facing serious problems such as water shortage, drought and dust. The Middle East is part of the dust belt that stretches from Africa to western and central Asia. Favorable weather conditions, along with other factors mentioned above, have caused the southern and southwestern regions of Iran to be affected by dust hotspots outside the country's geographical borders. In general, at certain times of the year, the activity of dust sources located in the areas of central Saudi Arabia, as well as the deserts of Jordan, intensifies dust in the southern regions of Iran. In this study, several severe and pervasive dust storms were investigated in which dust sources in the southern shores of the Persian Gulf were active and affected the southern half of Iran. After selecting some severe and pervasive events for each case separately, the following actions were taken. Investigation of weather code and visibility in the synoptic stations of Iran and neighboring countries; Spatial monitoring of storms with True-color images of MODIS sensor; Investigation of effective atmospheric systems and analysis of atmospheric conditions leading to dust occurrence using ERA-Interim data with horizontal resolution of 0.75 × 0.75 degrees; Implementation of HYSPLIT Lagrangian model by backward method to determine the transmission path of dust storm. The study of these dust events showed that in general, the formation of pressure gradient with changes in mean sea level pressure due to the entry of atmospheric systems or changes in surface temperature, increases wind speed near the surface, which if the ground surface is favorable causes dust emission. The wind direction determines the dust path. In addition, with the presence of weather front in the cold seasons, changes in wind velocity (speed and wind direction) provide suitable conditions for the activation of dust hotspots and ultimately cause the emission and transport of dust particles; Therefore, with the activation of dust sources in the countries located on the southern shores of the Persian Gulf, with each of these synoptic patterns, dust is emitted from these areas.

This article is intended to monitor and identify the cause of the fog occurrence on the roads of the Iran that don’t have access to meteorological observation stations. For this purpose, the case study of Mashhad-Baghcheh Road, April 4, 2017, has been considered, leading to an accident of more than one hundred cars, killing one and injuring 60 people. Due to the lack of observation stations on roads, it is used the MSG satellite images during the meteorological events to monitor the phenomenon and analyzed the most important atmospheric parameters including temperature, wind, pressure, dew point temperature, low clouds and also short wave and long wave radiations on the surface level. Also, geopotential height, temperature, relative humidity and vertical velocity were measured at 850 and 700 mb levels to find the low level atmospheric circulations. The results of this study indicate that a 15 minutes after the occurrence of the phenomenon, the monitoring MSG satellite imagery is available which is a very suitable tool for very short-term forecasts. The geographical location of the area as well as blowing KATA wind has led to the fog occurrence in this region, which despite the pressure decrease, the stability of the air column has been strengthened so that vertical velocities do not exceed the high currents. Dew point deficit is also about 4 ° C at the Earth's surface. It seems that the role of satellite observations in the very short term forecasts of weather conditions, including the May incident, is denied.

Today, dust phenomenon is a new problem that affects on human life. However, the weather conditions in major planning decisions are common. Although dust in North KHorasan is a occasionally phenomenon, but it can lead to more attention. Therefore, it should be considered for the recognition and management. In this study, synoptic data of Bojnord, maps of different levels, climate data and SODAR output directed to investigate the dust phenomenon occurred in Bojnord. Studies demonstrate that pressure patterns play an important role in this area in the formation of dust. The convergence due to pressure gradient and low pressure make a strong wind near the ground. This causes dust spread in different layer and environment that the result is reduced visibility and air quality.