نشریه نیوار
پیاپی 80-81 (بهار و تابستان 1392)

Many countries around the world use many various methods of climatic classification and zoning, but a few standards are being used in Iran therefore it can be said that solid precipitations including snowfall have been paid too little attention in discussing the nation ‘s precipitation. Thus, in the present research, the frequency of days having the snowfall phenomenon was studied for 50 Iranian synoptic stations using graphic, statistical and surfacing methods during the 1970-2000 period. The results of the present research indicate Zanjan station has the most frequent snowy days while such stations as Jask and Chabahar lack snowy days in the study period, total average of snowy days is between 8 and 9 also the trend of snowy days was increasing during the period, which was more visible from 1980 to 1993. After which it was decreasing again. During this period, the year of 1992 with an average of 15-16 snowy days. And year of 1973 with an average of 2-3 snowy days had the most and the fewest snowy days, respectively. Due to the phenomenon of thermal delay, the month of Bahman had the largest number of snowy days for coastal station while this was the case in month of day for off coastal stations. Given multivariate regression calculations, it was found that the relationship between altitude and latitude with the number of snowy days is a significant, direct one while it is significant and inverse between alteration coefficients and latitude. surfacing pattern of observed and calculated snowy days in Iran was displayed by using surfer software, in which variables of longitude, latitude, and number of snowy days were employed, which confirmed compatibility between the calculated and observed surfacing pattern of regression equations. On the basis of surfacing pattern of snowy day’s frequencies, maximum frequency is observed in northwestern part of our country.

Climatic factors, especially rainfall, the most significant periods of time. Recognizing these changes, allowing optimum utilization of nature provides. The present research has been carried out with the purpose of time-based fluctuations of precipitation, the determination of droughts and wet periods, and the possibility of their prediction for Ahvaz. The wet and dry (droughts) periods and their intensity and successiveness have been estimated through the calculation of Z standard score and five-year moving mean. The possibility of their prediction has been accomplished by the use of time series models of Halt-Winters and auto regression. For doing so, we have applied the 45-year data precipitation records of Ahvaz synoptic station (1955 -2009). Results of our study indicate that the predicted values through Auto-regression have more proximity with the observed values.

In this paper we study on trend and variation in climatic parameters in North east of Iran. Calculation and analysis on rainfall and humidity on the average of minimum and maximum temperature parameters have been performed over the period of 1986 to 2005. The selected stations are Mashhad, Bojnourd, Quchan, Sabzevar, Sarakhs and Torbat Heydarie. The Mann-Kendall has been used to illustrate trends of this parameters. Minimum and maximum temperatures at all stations show an increasing trend. This results show that the temperature has remarkable change in winter than other seasons. Therefore, this will effect on rainfall pattern which will lead gradually to change on flow pattern and ultimately impact on water resources management of region. Rainfall and humidity does not show a clear trend. The results show that if this trend persists, Extreme conditions maybe change and increased flooding and droughts in this region.

Inlets play an important role in controlling sediment movement and distribution in coastal areas. Therefore, recognizing effective factors in the hydro-dynamicity of inlets known as transmission process and determining the geometry and formation of inlets is of paramount importance. Short waves are among the major factors shaping an inlet. The breaking of wave in shallow water in the mouth of inlets causes the formation of long shore current and sand transport in this area. The purpose of this study was to find out how period wave could interactively affect the sediment. To this end, a coastal basin that is connected to the open sea through a mouth is simulated in mike 21 software. For this simulation, a 10*50 meter un-structured triangular flexible mesh in a finite difference model at one second intervals was used; short waves were sent to the mouth of the inlet at varying periods. Simulation results show that the flow and sedimentation patterns interactively don’t change the morphology of the inlet. While with increasing wave period, amount of flow velocity and sedimentation rates change low.

Trend analysis of climatic factors, especially precipitation time series can show the climatic situation of a region. Simultaneous comparison of the results of trend and drought indices in a region tends to better regional climatic analysis. To study the precipitation trend in Tehran Province, the historical data 1985-2007) of four main synoptic stations namely, Abali, Dushantpeh, Karaj and Mehrabad were provided in this study. The results of non-parametric Mann-Kendall and Sen Statistics were calculated and compared in monthly, seasonal and annual time scale series in this period. Also, a graphical analysis of the trend was carried out using Kendall statistics. The standardized precipitation index (SPI) in annual time series was used for regional drought analysis. The results of Mann-Kendall and Sen Trend tests showed that there is no particular trend in seasonal time series, but using of the Sen Test was revealed the trend in the annual series data of the Abali and Karaj stations at 99% confidence level. Abali and Karaj stations are located at very high level above sea. This attribute and much precise of Sen Test based on the non-zero data may be the reasons for the trend appearance in these stations. Monthly precipitation analysis obtained by the Kendall test was increasingly trend in the most stations. The graphical analysis was also represented the increasingly monthly precipitation trend in the region. The comparison of the precipitation and drought processes showed for annual scale time series the Sen Test reveals the trend value better than the trend in the Kendall test.

The model of estimating the daily relative humidity from the relative humidity of the local standard time Iran and the parameters of daily precipitation, minimum, maximum and average daily temperature in desert and semidesert is the subject of this article. Clustering the149 stations by 9 available phenomena (temperature, precipitation, evaporation, relative humidity, range of annual temperature, altitude climate stations and three Indices Demartan, Ivanov and Torrent White) were done. 60 stations Clustered in the desert and semi-arid region by partitioning around mediods. Systematic sampling design for selecting a sample was used. Different patterns of linear and nonlinear regression fitted on the sample data and the best models were determined in monthly and annual scales. Calibration models presented in this paper and compared with conventional models of old patterns showed that the accuracy of new patterns is better. Our criterion is Mean square errors.

Dust storm is an atmospheric phenomenon having adverse effects on the environment. These storms can have detrimental effects on economy and health of societies and create climate changes. Understanding the nature, origin, and effects of dust storms is important in determining their appropriate mitigation measures. In this review article, factors causing the occurrence of dust storms and their effects on environment, health, and economy as well as methods for locating and controlling them are discussed. This review article was conducted on various aspects of dust storms through internet and library search. Key words like Dust storm, environmental impacts, health, Air Quality، the Middle Eastern Dust event، were used to search for articles and publications in various databases such as Science Direct, Google Scholar, Springer, Magiran, and Iran Medex between 2014 and 2000. Totally, 200 articles were collected, 69 of which were chosen based on their relevance. Dust particles ascend as high as 6 kilometers and spread to 6000 kilometer across the surface, which reduces the horizontal vision to 103 to 104 meters. Atmospheric dust blocks the sun light and can also cause respiratory diseases, including meningitis and Rift Valley fever and asthma and viral diseases, and damage to the DNA skin and lung cells are. Increased to 10 micrograms per cubic meter in the concentration of particles smaller than 10 microns (PM10) at the time the dust phenomenon, the mortality rate of 0. 5- 1 percent increase.