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Volume 1, Issue 2 (7-2014)
Ultra violet radiation has some useful effects and some harmful effects on human health an d create many diseases. Nowadays not only declined but the usefulness of the therapeutic effects of the Sun in the treatment of diseases such as rickets, psoriasis and eczema have been proved. But prolonged exposure to radiation of the Sun is not always beneficial and may cause acute and chronic effects on the health of the skin, eyes and immune system. Ultraviolet radiation of the Sun is one of the most destructive waves for life on Earth. So Ultraviolet radiation index and predict its rate (1 to +11) as well as the analysis of this indicator will help people to protect themselves against the Sun
Ozone station , global ozone measurement stations and only stratosphere in Isfahan, Iran, which is in the South and in the Northern geographical position latitude 32' 31 and 70 ' 51 is located over the East. The altitude of this station from sea is 1550 m. Also atmospheric parameters in this station which are measured daily include temperature, pressure, humidity, wind speed and direction and in the upper levels of the atmosphere at 12 GMT with the help of Joe's high temp radio instrument.
The first step to do this research was gathering of climatic data and the statistical and quantitative analysis in order to study on the subject. Ultraviolet radiation data on the same basis of assessment, ozone station during the period January 2001-December 2010 has been collected. The second batch of data information gathered from meteorological station of Isfahan climatic elements from 2001 to 2010. This data is based on monthly averages for analysis of solar UV radiations from meteorological solidarity with the country.
Adjust the time series at the first step in the study and analysis of the data was done in order to equal intervals in these regular categories and methods of statistical analysis was carried out on them and the overall process of UV changes in the form of daily, monthly, quarterly and annually. Also part of the analysis that was carried out on the data, check how the sequence or they had over time; this way specify whether data periodically changes or trends have been or not. Once the data is based on the time of occurrence, sort and arrange the time series on them.
Annually analysis of UV index showed the general variation is a common feature of studied years but in the spring season have high variation in compared with other season. The main reason of this variation may be related to sunlight angle that can be showed atmosphere effect on received radiation. Descriptive statistic result indicated that the highest mean of UV index is 6.52 and minimum were 4.8 that have very high variations and may be it has different harmful effects. Also seasonal analysis showed highest UV index created in hot summer related to highest temperature in this season. The computational modeling of UV index against years in different season indicates there do not exist a linear relation between two factors. The correlation analysis of UV index and some climatic factors showed there are a significant relation between temperature with 0.8570 coefficient that can be said in relation to increase of temperature, UV rate increased and vice versa and with cloud cover correlation coefficient is -0.393 that have significant negative relation.
Results showed that the peak time period are output in the first half and the second half of the year, landing in the specified time series. As well as through a linear fit to all charts, increase or decrease of the radiation, changes the trend in recent years, showed that based on the ultraviolet radiation changes the average increase in the spring and summer and fall and winter shows a decline. Also according to the ultraviolet radiation in daily statistics review ozone assessment station in the studied period (2001-2011) maximum amounts of ultraviolet radiation index, (11.5) observed in the middle of the summer and the minimum amounts of radiation index (0.5) observed in mid-winter.
Volume 1, Issue 3 (10-2014)
Thunderstorm is one of the most severe atmospheric disturbances in the world and also in Iran, which is characterized by rapid upward movements, abundant moisture, and climatic instability. Since this phenomenon is usually accompanied with hail, lightning, heavy rain, flood and severe winds, it can cause irreparable damage to the environment. Investigation of spring thunderstorms has a great significance regarding the irreparable damages can cause by them and also because of the higher frequency of this phenomenon in the spring and the necessity for preparedness and disaster mitigation actions. To identify the locations of the major thunderstorm risk areas, the entire country with an area of 1648195 square kilometers, which is located between the 25°-40° north latitude and 44°-63° east longitude is considered. Spatial distribution of the occurrence of hazardous spring thunderstorms was analyzed using a series of monthly thunderstorm frequency data obtained from 25 synoptic stations over a 51-year-long period (1960-2010). Ward's hierarchical clustering and Kriging methods were used for statistical analysis. Initially, total number of thunderstorms in April, May and June were considered as the frequency of occurrence of thunderstorm in different stations in the spring. Measure of central tendency and dispersion which consists of the sum, minimum, maximum, range and coefficient of variation, standard deviation, and skewness were used to clarify the changes of thunderstorms and to determine the spatial and temporal climatic distribution of spring thunderstorms. An appropriate probability distribution function was chosen to determine the distributions of the data. Due to the large volume of data and the uneven distribution of stations, cluster analysis and kriging methods were used to classify different regions into homogeneous groups for zoning and spatial analysis of spring thunderstorms, respectively. The statistical characteristics of spring thunderstorms were reviewed and fitted with a 3-parameter Weibull distribution. Regions considered for this study were classified in four separate clusters according to the simultaneity of thunderstorms in the spring. After zoning, it was found that the highest rates of thunderstorm took place in the northwest and west of country. The northeast of Iran has the second highest number of thunderstorm occurrence. The least number of thunderstorm event had happened in the central and southern half of the country. According to the descriptive statistics parameters, maximum number of thunderstorms occurred in May.. Based on the results of the cluster analysis, there is a similar trend in the central and eastern regions, the rest of the country was clustered into five distinct homogeneous regions, including the northwestern, western, southern, northern, central northern and northeastern regions. Zoning results indicate that the highest number of the occurrence of this phenomenon in the country is concentrated in the northwestern and western regions. Higher frequency of occurrence of thunderstorms in the northwestern and western regions may be attributed to local topographic conditions like high mountains, orientation of the terrain, solar radiation on slopes and existence instability conditions, hillside convection, the presence of water resources and specific climatic conditions in these areas. In addition, as a result of a continuous surface obtained by the method of interpolation with the least amount of systematic error and also the use of correlation functions for recognizing the spatial structure of the data and estimating the model error when using the Kriging method, the weights are chosen in order to have a more optimized interpolation function. Also the cluster analysis may significantly reduce the volume of operation without affecting the results and will help in finding a real band due to more appropriate classification of different geographic areas with greater spatial homogeneity and minimal variance within the group. Based on the results of the spatial analysis, it is clear that Kriging and Ward cluster analysis methods are appropriate for thunderstorm zoning and classification of different regions according to occurrence of thunderstorm, respectively.
Volume 2, Issue 3 (10-2015)
Forest fire is one of the important problems in Iran which is caused by different factors such as human and natural factors. One of these factors is climate conditions that can be created by heat wave and special circulation of atmospheric phenomena. Occurrence of forest fire in north of Iran have different impacts on environment such as destruction of natural. According to the position of Iran in the dry climate zone provides required conditions for this hazard. Unfortunately,every year thousands of hectares of precious green cover is burned. Forest fires have harmful effects on human life directly,or in directly and lead to environmental destruction and pollution, global warming, loss of vegetation, and dry soil erosion. As a result, research on forest fires will become necessary. The study region is Mazandaran province forests located in north of Iran with area of 23756.4 square Kilometers.The main object of this study is to detect the forest fires using satellite data and associated analysis with synoptic approach based on weather maps.
To detect fire in the study area different satellite data such as synchronized and geostationary satellite data were used. In this study, MODIS satellite imagery and global algorithm detection of fire to detect fire in the forest and meadows of Mazandaran province were used. The climate data including weather station data and weather map were used. Other data include data of LST and vegetation products of MODIS. In order to downscale the global data an appropriate threshold was defined. In the proposed method, After geometric correction and radiometric the cloud mask was removed, And then fire potential was identified with different thresholds and tests. Three fire episodes of Savadkooh 2006, Noor , 2009 , and Behshahr, 2010 were selected for study.
Results showed a threshold value of 310 ° K for MODIS sensor band 22 is good for a global scale. Cold and small fires are not detected, Therefore Local threshold was used. In addition, surface temperature and vegetation mapping , chlorophyll amount of vegetation were used before and after the fire episode.It became apparent that the amount of chlorophyll was reduced and the temperature was increased after the fire.
The synoptic maps of the fire day showed a low pressure over the region and mid level systems indicated the advection of warm air over the area. Surface stations showed the increase of temperature and reduction of moisture during the fire days over the long period mean values.
According to the results of the study the ground level data accompanied the upper level images and pressure patterns.
Universal high performance of fire detection algorithm was used to identify areas of forest fires Using MODIS satellite images and global algorithm modified to suit the characteristics of the study area fire detection. Then three of the fires were identified with this method. The algorithms with MODIS images and weather data together indicated the validity of the study and performance of this algorithm to identify the location of fire in the study region. Therefore the method of this study can be used in other areas to detect forest fires.
Volume 5, Issue 1 (6-2018)
The occurrence of any climatic fringes, including annual tropical storms, leave irreparable risks in its dominated areas. Understanding these events and knowledge of the time of their occurrence can be helpful in managing the unexpected incidents caused by them. Tropical cyclones are important natural turbulent processes in tropical and middle ecosystems in a number of regions of the world. Among the dynamic conditions of the atmosphere for the formation of tropical storms, there are three basic conditions: 1. The vertical wind shear should be limited between the 850 to 200 mb and the wind speed between these levels should be less than 10 meters per second. Such a situation allows the formation of a straight column, without breaking, to initiate tropical storms. 2- The formation state of tropical storms should be such that at least it is five degrees of latitude distant from the equator. Such conditions provide the minimum of Coriolis force to provide the tropical cyclic rotation along with other fundamental and apparent forces of the atmosphere and they occur following the pressure forces, Coriolis and centrifugal forces, cyclostrophic winds, and cyclic circulation in the center of the low pressure. 3- The presence of turbulence or discordance with vorticity and the convergence in the lower troposphere, or the anticyclone rotation and divergence in the upper levels of the atmosphere before the onset of activity, and the formation of tidal disturbances. Tropical storms are created by the presence of various dynamic and thermodynamic factors such as sea surface temperature and moisture content (thermodynamic properties), and flow and vertical winding functions (dynamic characteristics).
The parameters studied in this study for the dynamic and thermodynamic analysis of the tropical rotation of 1948 generally included the mean sea level pressure, geopotential heights, zonal and meridional components of wind, convection available potential energy, convective stabilization index, vertical velocity, relative vorticity, Sea surface temperature, humidity, and cloud cover levels which are drawn from the European Center for Medium Forecast Scale (ECMWF) with spatial resolution of 0.75 applying GRADS software. The study of combinational maps of 500 milligrams of geopotential heights and vorticity advection on the first day of the cyclone (1948/06/05) indicates the presence of a very strong low-altitude center with seven closed curves on the Arabian Sea. The most inner curve of this low-altitude center has the lowest elevation with 5650 geopotential meters height and the maximum vorticity advection and downright negative velocity of 10 and 0.5 Pascal to seconds, respectively. The above-mentioned Jetstream map with a maximum speed of 16 m / s, which covers the east of the center of the altitude, contributes to the greater divergence of this system. The formation of a very strong negative eddy in the 500-mb equilibrium also indicates intense instability at the site of the tropical cyclone and is actually a factor in the formation and reinforcement of such cyclones .The above-mentioned low altitude continues its cyclonic rotation at the level of 850 mb with two closed curves, and the maximum vorticity advection and downright negative velocity of 16 and 0.6 Pascal to second, respectively, due to the presence of lower level radar with a maximum speed of 20 m / s on the south side and similarly, in the south-east, it continued to circulate more rapidly at a rate higher than 500 mb, which results in the formation of the first pressure packet with a central
pressure of 997.5 mb on the sea surface. The high amount of specific humidity of 850 mb from the start of cyclone activity (12 g / kg), and the increase in this parameter in the next days of activity reaches 14 g / kg and also 4.5 g / kg at 500 millimeter equilibrium point to the high humidity at the location of the low-pressure center and the optimum conditions for the extraction of heavy rainfall in the eye wall of cyclone. Cloud cover maps also indicate a climber air density of up to 500 mb and the formation of a cloud at different levels of the atmosphere at the site of the formation of tropical rotation. The results show that the formation of the lower Jetstream, along with the tropical cyclone event (from 05 to 08 of 1948) affecting the southern coast of Iran, has been able to create severe air mass divergences in the left half of the nucleus and following this mechanism and the relationship between this velocity nucleus and the lower levels of the atmosphere and the sea level in the vertical direction, with the convergence of the mass, has been accompanied with the reduction of density and, finally, the reduction of pressure and the formation of turbulence, as the first ring for the development of tropical cyclones; therefore, the altitude of 850 mb and jet stream located at this elevation affected by the high-rise phenomenon on the western shores of the ocean (sometimes in the east of Madagascar) is considered as one of the most effective dynamic factors for the birth and development of this tropical cyclone on the southern coast of Iran. The tropical cyclone was formed from June 5 to June 8, 1948, at approximately 16 degrees north and 60 degrees east on the Arabian Sea. And, in general, the interaction between high pressure tongues on Saudi Arabia, Tibet and Iran, and the tropical cyclones has prepared the conditions for the activity and displacement of the tropical rotation. Previous studies of tropical storms have considered other synthetic systems, such as cyclones over Europe, and the integration of cyclones on the Mediterranean and Oman, as well as the displacement of the axis of tropical cyclones at middle and upper levels of the atmosphere affective in the escalation and displacement of the storm. It is also believed that the southern coast of Iran is also effective, and in general, less attention is paid to the causes of the development of the storm.
Key words:Tropical Cyclone, dynamic and thermodynamic analysis, low level jet stream, Thermodynamic parameters, Southern coast of Iran
Volume 6, Issue 2 (9-2019)
The application of Extreme value analysis method in heat wave hazard climatology; case study in Mid-Southern Iran
Abstract
Greenhouse warming poses the main cause of atmospheric hazards’ exacerbation and emergence in recent years. Earth planet has been witnessing frequent and severe natural hazards from the distant past; however, global warming has strongly influenced the occurrence of some atmospheric hazards, especially the ones induced by temperature and has increased the frequency and severity of those risks. Such extreme risks arising from temperature element and being affected by global warming could be referred to hot days and their frequency more than one day which undergo heat waves. Of the studies conducted worldwide in conjunction with the phenomenon of heat waves, the following can be pointed out; Schär (2015) has focused his studies on the Persian Gulf and the worst heat waves expected in this area. The recent work revealed an upper limit of stability which enables the adaptability of human body with heat stress and humidity. If people are exposed to a combination of temperature and humidity over long periods higher than this level, they will lead to hyperthermia and death, because heat dissipation from the body is physically impossible. Paul and al-Tahrir (2015) using a high-resolution regional climate model demonstrated that such a situation can occur much earlier. In Iran, in relation to heat waves, Ghavidel (2013) analyzed climatic risk of Khuzestan province in 2000 regarding super heat waves using the clustering approach. The obtained results unveiled the establishment of a low pressure at ground level and high pressure dominance at mid-altitudes up to 500 hp as well as the increase in atmosphere thickness having led to the ground overheating. Added to that, the source of heat entering into Khuzestan is advective and hot and dry air transport through Arabian Peninsula, Iraq and Africa. Ghavidel and Rezai (2014) addressed in a study to determine the temperature-related threshold and analyze the synoptic patterns of super heat temperatures in southeast region of Iran; the results of study approved that the only pattern effective on the occurrence of super heat days in Iran’s southeast is the establishment of the Grange’s heat low-pressure at ground level and subtropical Azores high elevation dominance at 500 hPa level. In this study, absolute statistical indicators, also recognized as above-threshold values approach, were used in order to identify, classify and heat waves synoptic analysis in the warm period of the year in the southern half of Iran. To use above-mentioned indicators, firstly daily maximum temperature statistics of studied stations with the highest periods were averaged every day once in June to September and once for the months of July and September. Using statistical indicators of long-term mean and standard deviation or base period, indicators would be defined for the classification of heat waves and days with peak extreme temperatures. In such classifications, usually long-term average or base period is multiplied by 1 to 3 to 4 times standard deviation and each time is account for the factor of each class.
To select the days for synoptic analysis, averaging was performed of all classified waves into four heat wave categories of low, intermediate, strong and super heat; accordingly based on the maximum blocks in each class of heat waves, days that had the highest temperature values were selected as the class representative for mapping and synoptic analysis.
This study dealt with investigating heat waves synoptic during the year’s warm period in the southern half of Iran. Studies showed that a variety of synoptic systems in the year’s warm period affect the study area. As well as, synoptic analyses concluded that in the southern half of Iran over the year’s warm period when occurring heat waves, low-pressure status dominates the ground level (caused by Gang’s low-pressure and local radiant mode); thus high-pressure status with closed curves is prevailing in atmosphere’s upper levels that gives rise to the divergence, air fall and Earth's surface heating. Studying the status of the atmosphere thickness in the days with the heat wave in the study area indicates its high altitude and thickness that this itself implies the existence of very hot air and susceptibility of the conditions for the occurrence of heat waves. In addition, wind maps at atmosphere’s different levels well illustrate the wind of very warm and hot air masses from the surrounding areas to the southern part of Iran; therefore it can be noted that aforementioned hot air masses mainly wind from places like different regions of the Arabian Peninsula, Iraq, North Africa and the low latitudes to the study area.
Keywords: Synoptic analysis, heat waves, maximum blocks, southern half of Iran.
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