جستجوی مقالات مرتبط با کلیدواژه "تواتر" در نشریات گروه "جغرافیا"

The issue of urban climate has been greatly addressed in the recent years. The migration of human beings to cities, along with the density of the residential units, the noise of urban vehicles and dangers of air pollution and many other things have had bad effects for the human beings like asthma, bronchitis, cardiovascular diseases, and skin cancer. The issue of air pollution is one of the main factors in urban climatology. The knowledge of climatology emphasizes on the effects of atmospheric pollution on the climate and vice versa. The investigation about the effects of air pollution on climate features has greatly been conducted in the east Iran. In the warm seasons of the year, especially in summer, Subtropical High pressure (STHP) covers large areas of lower, middle and upper levels of atmosphere. This extends vertically on top of the high pressure at 200 hp to 700 hp and results in a clear sky with no clouds and rain. Subtropical High Pressure (STHP) all over the country varies from one day to other day. In some areas it is very close to the earth surface, in the south east parts of Iran in some days it is about 2000 or 3000 meters above the earth surface and allows warm, low moist air. This situation sometimes spreads to northern Iran and causes monsoon rain with increase in temperature and decrease in air ascent. This means that when the height and activity of the STHP is high, there is suitable condition for clear sky and direct solar radiation. On top of the inversion water vapor content of the air is so low that it cant be measured. Subtropical system in high altitude is one of the reasons for the formation of deserts in Iran. Subtropical high is getting stronger with increasing height from the ground, while the polar high becomes weaker with increasing altitude.
As a matter of fact, mechanism for summer subtropical high pressure on Iran is a part of the Azores high pressure on the region. Thus, the above factors have caused the greatest events in the summer in Tabriz so that the city has experienced dangerous contaminants. With the beginning of autumn, the maximum and the minimum values of the dangerous contaminants was shifted compared with other seasons. However, in autumn there are dangerous infected cells in northern city of Tabriz in November and October, while in December the infected cells are in the center of Tabriz. The purpose of this study was to evaluate the frequency of Tabriz dangerous contaminants. For this purpose, the data of pm10 pollution index in the 8 years period (2005 to 2012) were evaluated by the Environmental Protection Agency in Tabriz (EPAT) for five stations of Baghshomal, RAhahan, Abrasn, Hakim Nezami, and Rastekhocheh. The index of this research is the day that the pm10 value of 420 is larger. The frequency and continuity of these dangerous days for each station were analyzed and investigated. In this study, we have used MATLAB for statistical analysis and SURFER for the mapping.
The results of the analysis have indicated that there were many dangerous air pollution events in summer in all stations with more dangerous contaminants in August as the highest frequency of the occurrence of dangerous infections.This indicates that formation of subtropical high pressure dominated on Tabriz play a key role in air pollution. However, in winter the occurrence of dangerous pollution has been reduced in most of the stations. Among the stations of this study, the stations of Baghshomal and Abrasan had the most dangerous pollution. The number of the days of infection in both stations has reached to more than 400 days during the study period. Furthermore, the results of the continuation of the dangerous contaminants of pm10 index indicate that more continuity of the pollution was in Baghshomal station and the lowest in Rahahan and Hakimnezami stations.
The spatial distribution of pollutant cells is varied in different months in Tabriz. However, based on PM10 density the dangerous pollution in most of the months has been formed in the city center. In January, February, June, September, October (multi-core) and December there were the core and the density of pollution in the city center. In March and August, the maximum contamination of Tabriz has been observed in the East. Intensity of infestation was observed only in April, July and November in west Tabriz while the maximum condensation has been observed in the northern and the southern parts of the Tabriz. Tabriz had no nuclei condensation of dangerous pollution in July.

Freeze is one of the serious climatic phenomena that influences different aspects of human life including agriculture, transportation and energy. Effects of freeze in agriculture section are more than other sections. Effects of freezes in agriculture section appeare more than its earliness or lateness aspects. In Ardabil Province, in most years, early and late freezes have caused serious damages to agricultural products. For example, in Farvardin 1393, gardens of Ardabil Province recompensed more than 4 billion Rials due to late spring cold. Due to this cold, 21000 Hectares of gardens of this province recompensed.
Of the causes of extensions of recompenses resulted from climatic phenomena like freezes is unknown remaining of dimensions and nature of this phenomenon. In occasions of occurrence of early and late freezes, to decrease recompenses resulting from it, it is needed to have a coherent management program; that to prepare this program, it is needed to know different aspects of this phenomenon. In this research, it is tried to determine beginning and end dates of early and late freezes and to investigate several cases of properties of these freezes along with its possibility.
Data used in this study is minimum temperature as daily in 15-year statistical period (from 1996 to 2010) in stations of Ardabil Province. After collecting and setting data, series of data were planed as Juliuseous date that first day-counting of data was considered October and beginning and end dates of freezes (lack of temperature to zero and under zero Centigrade) were analyzed. In this research, knowledge of possibilities and also an approach called Markov’s Chains were used.
Accordingly, continuity and possibility of occurrence of early and late freezes are considered in different continuities of, various intensities of early and late freezes and possibility of its occurrence and possibility of succession of different states freezes are investigated.
Analyzing beginning and end dates of occurrence of freezes shows that general trend of day-counting of beginning date of freezes in Parsabad Station is decreasing and moves toward hot season. In stations of Ardabil and Khalkhal, this trend is increading. In Khalkhal Station, beginning dates of freeze moves toward cold season with intensity of 1.07 day per year and has started later.
Investigating end dates of freezes according to regression analysis shows that general trend of day-counting of dates was decreasing by 0.517 day per year in Parsabad Station and was increasing by about 0.29 and 0.14 day per year in stations of Ardabil and Khalkhal, respectively.
Early freezes start in November in Parsabad Station and in October in stations of Ardabil and Khalkhal.
Continuity of early freezes in Parsabad Station in less than other stations so that in this station freezes have not lasted more than 2 days. In Khalkhal Station, continuity of freezes is more than other stations so that in Khalkhal Station continuity of freezes has been less.
In Parsabad Station, due to lower height temperature was higher than other stations and intensive freezes are not observed. In Khalkhal Station, number of freezes is more than other stations. In this station, 11 intensive freezes lower than -3 centigrade have occurred that there is 2.37 per cent of possibility of its occurrence in October.
The most important results resulting from above-mentioned topics are as follows: - Day-counting trend of beginning of early freezes is decreasing in Parsabad Station and is increasing in stations of Ardabil and Khalkhal. Day-counting trend of end of late freezes is decreasing.
- Early freezes begin in November in Parsabad Station and in October in stations of Ardabil and Khalkhal. Late freezes are in April in Parsabad Station and in May in stations of Ardabil and Khalkhal.
- Continuity of early freezes in Parsabad Station is less than other stations and in Khalkhal Station, continuity of freezes in more than other stations. In late freezes in Khalkhal Station, continuity of freezes has been less.
- In terms of intensity of freezes, early intensive freeze has not happened in Parsabad Station. In this area, due to low height, temperature is more than other stations and intense freezes are not observed. In Khalkhal Station, number of intensive freezes with possibility of occurrence of 2.37 per cent in October is more than other stations.
- In terms of succession of different states of freeze and without freeze, in early freezes there is the highest possibility of occurrence of freeze after freeze in Khalkhal Station with 63.31 per cent, and in late freezes in Ardabil Station, occurrence of freeze is with 61.54 per cent after the state of without freeze.