Climatology
Atefeh Hoseini Sadr; bromand salahi; Gholam Hasan Mohammadi
Abstract
The aim of this study is to investigate the long-term fluctuations and trend in horizontal visibility in the northwest of Iran. For this purpose, hourly horizontal visibility data from 7 synoptic stations were used for the period of 1951-2020. The Koschmieder approach was used to calculate the extinction ...
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The aim of this study is to investigate the long-term fluctuations and trend in horizontal visibility in the northwest of Iran. For this purpose, hourly horizontal visibility data from 7 synoptic stations were used for the period of 1951-2020. The Koschmieder approach was used to calculate the extinction coefficient. Moreover, the Mann-Kendall and Rdit tests were applied to examine the trend of horizontal visibility. Also, the percentages of very good visibility (>19 km) compared with bad (<10 km) visibilities. Based on the results the annual average of horizontal visibility in northwest of Iran is ~13 km. This study showed three different fluctuation periods in the regional average of horizontal visibility: the first period (1951-1985) showed a sharp decrease in the visibility, the second period (1987-2005) was characterized by a low and stable visibility, and the third period showed a recent relative improvement. The regional average of horizontal visibility (extinction coefficient) exhibited a significant decreasing (increasing) trend of -0.167(0.0017) km per year at a confidence level of 0.01. The significant decreasing trend was confirmed in all stations except for the Ardabil station. The most severe decreasing trend was detected in Sanandaj and Zanjan stations with rates of 0.183 and 0.179 km year-1, respectively. The region-average of Rdit statistic in northwest Iran in the early 1950s was ~0.85, but it decreased to around 0.3 in the 1990s. Despite the recent improvement in horizontal visibility, reaching the reference distribution (i.e. Rdit=~0.5), the decreasing trend of horizontal visibility was still confirmed. The percentage of trend analysis of very good and bad visibility showed an increase in bad visibilities (from 5% to 25%) and a decrease in very good visibilities (from 80% to 5%), which confirms the decreasing trend in horizontal visibility. Hazy condition with 38.7% was the most influential weather phenomenon in visibility degradation.
Climatology
Saeid Jahanbaksh; Gholam Hasan Mohammadi; shahnaz rashedi; Atefeh Hoseini Sadr
Abstract
In this study, non-parametric Mann-Kendall test was used to analyze the trend of monthly mean minimum temperature in the Northwest of Iran. For this purpose, the data from 35 synoptic stations in the cold part of year including November, December and January-to-April have been used in the period of 24 ...
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In this study, non-parametric Mann-Kendall test was used to analyze the trend of monthly mean minimum temperature in the Northwest of Iran. For this purpose, the data from 35 synoptic stations in the cold part of year including November, December and January-to-April have been used in the period of 24 years (1987-2010). Kriging interpolation method was used to obtain spatial distribution of mean minimum temperature over study area. The results showed that the minimum temperature in most parts of study area is rising so that in the months of February, March and December respectively in 22, 19 and 17 stations of the 35 stations were determined an increasing trend. While only in April, at 6 weather stations decreased and this parameter is relatively stable in November and January. Spatial distribution of monthly mean minimum temperature indicated that this element is lower in the mountainous parts of study area (including Northwest and Southeast) and whiles in lowlands (including Northeast and Southwest parts), is higher than its regional average. It was also found that regional minimum temperature and its trend in the Northwest of Iran Does not have the same characteristics in different months, so that this parameter in January and in April increased and decreased in November and December. Finally, in November and December minimum temperature has not substantially changed.
Climatology
Saeed Jahanbakhsh Asl; Shahnaz Rashedi; Mehdi Eslahi
Abstract
Freezing is one of the weather phenomena that almost happen in parts of the east Azerbaijan province such as Maragheh causing significant losses in agriculture, industrial activities, and transportation. The end of this research is studying of distribution and freezing return periods in Maragheh synoptic ...
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Freezing is one of the weather phenomena that almost happen in parts of the east Azerbaijan province such as Maragheh causing significant losses in agriculture, industrial activities, and transportation. The end of this research is studying of distribution and freezing return periods in Maragheh synoptic station during 48 year period (1343-1391) based on the minimum daily temperature. The methods of this study is Gumbel distribution method, three parameter log-logistic method and log-logistic method to analyzing probability of freezing parameters occurrence (starting date, ending date, length of the freezing season, length of the growing season).The Results of the computation of the spring and fall freezing return periods show that the first freezing in the fall starts on 10 Aban and the last freezing end on 17 Farvardin. Also analyzing of the beginning and end freezing trend shows that fall's freezing have an ascending trend , in other words, the dates of the occurring fall freezing goes ahead and spring's freezing have a descending trend. It means that, the dates of spring freezing go back. Therefore, length of the cold season according to the global warming becomes shorter.
Climatology
Bahlol Alijani; Hasan Farajzadeh
Volume 19, Issue 52 , June 2015, , Pages 229-256
Abstract
Natural environment is regulated according to the climatic conditions. Human communities are forced to adjust themselves to these conditions. Identifying the intensity, frequency and timing of climatic events can help solve the environmental problems and ease the coherent planning to mitigate these events ...
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Natural environment is regulated according to the climatic conditions. Human communities are forced to adjust themselves to these conditions. Identifying the intensity, frequency and timing of climatic events can help solve the environmental problems and ease the coherent planning to mitigate these events changing behavior. To achieve this objective in the Northwest of Iran, daily minimum and maximum temperature data from 13 stations were obtained from the Meteorological Organization of Iran in the quality control format for the existing data period. Sixteen Extreme indices were extracted by RClimDex package and their changing behavior was checked by Mann – Kendall method. The results showed that the frequency of cold indices decreased but the frequency of extreme warm indices increased during the study period. According to the results of wavelet analysis all the extreme cold indices showed a significant periodic fluctuations of 2 to 4 years. Among the warm indices only the warmest days index (TXx) showed 2 to 4 years fluctuation and the number of tropical nights (TR20) exhibited 4 to 8 years of significant fluctuation.
Volume 16, Issue 41 , November 2012, , Pages 237-250
Abstract
Ozone is a very small part of earth atmosphere, but its presence is nevertheless vital to human well-being. Most ozone resides in the upper part of the atmosphere. This region called the stratosphere is more than 10 kilometers above earth's surface. About 90 percent atmospheric ozone is contained in ...
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Ozone is a very small part of earth atmosphere, but its presence is nevertheless vital to human well-being. Most ozone resides in the upper part of the atmosphere. This region called the stratosphere is more than 10 kilometers above earth's surface. About 90 percent atmospheric ozone is contained in the ozone layer or ozonosphere which shields every living thing from ultraviolet light from the sun. Total ozone is all the ozone in the atmosphere. Total ozone values often report in Dobson units. Typical values vary between 200 to 500 Dobson over the globe. Total ozone varies strongly with spatial (latitude) and temporal over the planet. This paper with using different statistical as regression analysis, variance analysis and Student-Newman-Keuls (SNK) methods tried to discover the relationship between total ozone and time variation in monthly, seasonal and annual time scale in Isfahan ozone metric station. Analysis of variance shows significant different between time series means p<0.01. The best series agreement with the among of ozone is seasonal series so that average of among of ozone shows a significant in each season with S.N.K test but monthly and yearly mean of ozone don't show significant difference in all of months and years . Spring has the maximum of seasonal mean of ozone and fall has the minimum of it. Results of study on trend indicate a no significant trend in the annual mean in the time series.
