جستجوی مقالات مرتبط با کلیدواژه « دمای کمینه » در نشریات گروه « جغرافیا »

Today, pre-risk awareness has become an integral part of the national development management and planning system in many countries (Civiacumar et al., 2005). Agriculture is inherently sensitive to climatic conditions. The minimum temperature, which has been identified as the most vital determining factor in the distribution of plant species on the planet, can be both a limiting factor and a factor in the spread and species distribution (Rodrigo, 2000: 155). Therefore, in this study, we examined the changes in minimum temperatures in the statistical period (1980-2010) and predicted these changes in the 2050s (2065-2046) in the Northwest of the country using the LARS-WG microscale method and model output. Atmospheric pairings of HadCM3 and MPEH5 were addressed. The prediction of minimum temperature variations to determine the extent of its future changes and considering the necessary measures to minimize the adverse effects of climate change on agricultural products were of great importance. In this regard, general atmospheric circulation models (GCMs) are designed that can simulate climatic parameters. 

In the present study, the output data of two HadCM3 and MPEH5 general circulation models based on two scenarios A2 and B1 were analyzed by LARS-WG statistical method in 21 synoptic stations located in the Northwest of the country. The results were monthly and periodic on the base period (1980-1999) and the 2050s (2046-2065), thereby the minimum temperature was evaluated and analyzed. In assessing the LARS-WG model, the observational and simulation error data were evaluated using MSE, RMSE, MAE and R2, and the model was evaluated for the appropriate region. The results showed that the minimum temperature in the future period will increase compared to the base period in the study area. This increase in air temperature at the study area is based on the HadCM3 and MPEH5 models, on average, 1.9 and 1.7 degrees Celsius to 2065 horizons compared to the base period. The north-eastern part of the northwestern region of Iran will have higher temperatures than the semi-southern regions. In fact, the cooler regions of the high latitudes will face more incremental changes in the amount of minimum temperatures. The results and achievements of this research are important for long-term plans for adaptive measures in the management of fruit gardens, agricultural products and water resources management. In order to calibrate and ensure the accuracy of the LARS-WG microscale model, the model was first implemented for the basic statistical period (1980-2010); then the minimum temperature output and its standard deviation were compared with the observational data of the studied stations, which indicated a small difference between the observed and simulated values ​​and also deviated from their criteria. 

The results of evaluation of observational and simulated data by LARS-WG microscale model using RMSE, MSE and MAE error measurement indices for the studied stations indicate that there is a significant difference between the simulated values ​​and the values ​​of the observed observations. There is no critical 0.05 significance levels, and Pearson correlation values ​​between simulated and real data are acceptable at the significance level of 0.01. The obtained results show that the accuracy of the model varies in different stations. In general, the results of error measurement indices indicate that the LARS-WG model is of good accuracy for micro-scaling the parameters under study. In order to better represent and ensure the accuracy of the prediction as well as to investigate the uncertainties in the studied models, the simulated values ​​were compared and observations were made on a long-term average during the base period in the studied stations using comparative graphs. As can be seen, the observed and generated values ​​in the base period at all stations are very close to each other and the LARS-WG model has been successful in simulating the studied parameter. After evaluating the LARS-WG model and ensuring its suitability, the data predicted by the model for two scenarios A2 and B1 using HadCM3 and MPEH5 models and were examined on a monthly and long-term basis. The study of the status of minimum temperature changes of the studied stations in the future period (2065-2056) shows that the minimum temperature is based on both scenarios and in all months and stations compared to the period, the base has increased. Due to the large number of study stations, only stations located in provincial centers of this study are listed. 

Cold and frost are one of the most significant climatic hazards on fruit trees. This type of climate risk affects different parts every year, especially the cold regions of the northwest of the country. Studies show that in recent years, the rate of economic damage to fruit trees in this region has increased, so in this study, the outlook for changes in minimum temperatures in this region using the LARS-WG statistical microscale model and output two HadCM3 global model and MPEH5 were introduced in the 2050s (2065-2046). For accuracy and precision of the models, error measurement indices and coefficients of determination and correlation were used. The results showed that the LARS-WG model has a good ability to simulate the studied variables in the study area. The results of long-term prediction of the studied models show that the minimum temperature values ​​will increase in all study stations, which is based on HadCM3 and MPEH5 models on average. In the 2050s, and it will be 1.9 and 1.7 respectively, compared to the base period. The results of the studies of Kayo et al. (2016), Sharma et al. (2017), Khalil Aghdam et al. (2012), Qaderzadeh (2015), Sobhani et al. (2015) and Khalili et al. (2015) were confirmed. In general, based on the studied scenarios and models, the minimum temperatures are expected to increase in the study area in the future. By increasing it, the yield of some crops that need cold during the growing and productive period would decrease. It can also reduce snowfall, followed by frost on crops and lack of water in dry seasons. Therefore, due to the fact that following the climate changes, the conditions of the agricultural climatology are also changing, it is necessary for the relevant officials and planners in the agricultural sectors to adopt the necessary strategies to reduce the consequences and adapt to the new climate.

Frost and freezing are important and risk generating factor in the agricultural sector of the country. Frost is a phenomenon that at low temperatures which could damage or destruct the plant organs. Various studies by researchers show that last spring frost (LSF) and first autumn frost (FAF) along with gradual global warming have significant impacts on agriculture and natural resources. Teleconnection patterns represent large changes which can periodically alter other atmospheric patterns such as temperature, wind, humidity and precipitation in regional and global scales. The purpose of this study was to investigate the effect of different teleconnection indices on variability of FAF and LSF events during the last 31 years at 12 Synoptic stations of Iran.

To detect the relationships between frost events and teleconnection patterns we used two different data sources. As the first source, the screen daily minimum air temperature (Tmin) were used as the frost indicator. We also applied 10 different teleconnection indices in daily and monthly scales. Daily minimum air temperature were obtained from the Iran Meteorological Organization (IRIMO) for the historical period of 1985-2015. The teleconnection indices were also utilized for the same period (http://www.cdo.noaa.gov). After the data quality control, the outlier data were removed from the analysis. Normality of data was evaluated by Kolmogorov-Smirnov test. For time series with normal distribution (P <0.05), the Pearson’s significance test was performed. For other time series, when the normal distribution was not the case, Spearman's nonparametric test was applied.

In case of lag-free correlations in the monthly time scale the strongest correlation between teleconnection indices and minimum temperature was observed for NAO- (-0.76), in February for Isfehan Station, which can cause a delay in occurrence of last spring frost. By applying the time lag to the correlation, the strongest correlation was found for AMO+ with time lag of 11 month. In seasonal time scale, the strongest lag-free correlations were found for AO-during the last spring frost (LSF). By applying time lag-correlation, the strongest correlation was evident between Tmin temperature and AMO+, indicating that this index was the most influencing teleconnections (with 3 seasons lag). In comparison with the normal phase, the occurrence of El Niño causes earlier autumn and spring frost events. In contrast, La Niña event will postpone the dates of autumn and spring frosts. This means that if La Niña occurs in winter, the strongest effect will be appeared in the autumn of the following year. The correlation between the El Niño, La Niña and Normal phases with minimum temperature showed that the La Niña phase has the highest effect on shifting the dates of the minimum temperature event.The strongest correlation between the minimum temperature of autumn and teleconnection patterns (correlation coefficient of 0.382) was observed for AO- , highlighting the fact that the occurrence of the Negative phase of this phenomenon leads to the cause a delay in occurrence of first autumn frost (FAF). For the last spring frost (LSF), the strongest correlation was found for SOI- index (correlation coefficient of 0.665) for Hamedan station, leading to early spring cold in the region. The correlation between the phases of the El Niño, La Niña and Normal with minimum temperatures showed that the La Niña phase has the most effective phase affecting the minimum temperature. The results of this research can be used for wise managing of risk factors and arranging appropriate time of planting agricultural products, as well as insurance for agricultural products.

This study highlighted the impact of teleconnection phenomena on shifting the dates of autumn and spring frost. It was shown, that the occurrence of teleconnection can significantly shift the date of first and last frost in the study region. For some teleconnections cause the advance, but for others may postpone (up to 50 days) the frost event. We found different results for lag-free correlations compared to lag-correlations. For instance, for monthly analysis of lag-free correlations, the strongest correlation between teleconnection indices and minimum temperature was found for NAO- (-0.76), but for lag correlations, the strongest correlation was found for AMO+. In comparison with the normal phase, the occurrence of El Niño causes earlier autumn and spring frost events. The results showed that Shifting the Date of First )Autumn( and Last )Spring( Frost Events at the stations were related to a number of teleconnection patterns such as AMO, SOI, NAO, AO and MEI. In contrast, La Niña event will postpone the dates of autumn and spring frosts. Further works are required to better understanding of the impacts of teleconnection events on other meteorological parameters such as humidity which was not investigated in this research.

Climate change is nowadays a major cause of concern in water related fields because it may cause more severe, shortened or prolonged droughts or floods in the future. In this research was tried to the best model of climate change is determined from the climate change models to determining the minimum temperature, maximum temperature and precipitation for the Birjand synoptic station. For this reason, 35 models of GCM were determined for each of variables of the minimum temperature, maximum temperature and precipitation. Initially, for each of the weather variables, the values ​​of each of the fifth report models for the base period and the synoptic station of Birjand were determined and compared with the results of the synoptic station in Birjand. Results showed that the rainfall data of GISS-ES-R, CNRM-CM5, CSIROMKMK3.6 models are most similar to the data of the Birjand synoptic station. For maximum temperature, GISS-ES-R, CNRM-CM5, CSIROMKMK3.6 models and for the minimum temperature, the GISS-ES-R, GFDLCM3 and MIROC-ESM models have the minimum error values and results of these models had the best similarity with the observed data. From comparison of model data with synoptic station data showed that the highest percentage of relative error of rainfall, minimum temperature and maximum temperature is shown for 1(January), 2(February) and 5(May) months, respectively. In comparing the differences between GCM models and Birjand station data for precipitation, the maximum temperature and minimum temperature are the fifth (May), third (March) and first (January) months, respectively, than the rest of the months.

Cold and frost waves are are among the most important natural phenomena, occuring in the cold period of the year. The reason why the frost phenomenon has been considered is it's feedbacks on the nature and human life, which sometimes has been associated with negative severe tension and sometimes positive feedbacks, particularly in agriculture and gardening. This study has tried to analysis of daily, as monthly and seasonal, frosts of Southern Khorasan province. To do this, the minimum daily temperature of synoptic stations of Southern Khorasan province were used for a 27 years period (1988-2014). And to investigate the probability and frequency of the frost days, Markov chain model was used. Results illustrated that Ghaen city in the north, and Birjand city in center of Southern Khorasan province, had the maximum occurrence and frequency of the frost days, respectively. Among the stations, Nehbandan city has experienced the minimum probability of frost days. Two-days continuities in all stations, revealed the minimum return period, indicating the less continuity of frost days in Southern Khorasan province.. All the analyzed stations in the studied area, except for Nehbandan, which generally hasn't experienced any frost day, are characterized by Markov chain, first class. In other words, any occurrence of frost days, depend on climate conditions of past days. The beginning of autumn frost days of Southern Khorasan province, is in November, known as the first autumn frost; and the beginning of winter frost is concentrated in January. The maximum frosty cycle in October have been occurred in Ghaen station about 0.058, and in November in Ferdos and Boshrooye stations about 0.05 and 0.043, respectively. Results confirmed the obvious role of high and mountain regions in the frequency and continuity of frost days in the province.

Introduction1
The change climate and global warming is a problem in the world. The climate is changing and the global warming is happening. Increasing the green house gases compactness is the reason about this phenomenon (Dettinger et al, 2004, 2). According to IPPC report Average annual temperature of the earth has been raised between 0.3 to 0.6º because spreading the greenhouse gases and this report predicts this amount will increase between 1 to 3.5º till 2100(Masahbavani&Morid, 2005,41).
These are cusses drought, flood sharp, and snowmelt, storms and increasing air temperature in different regions. These phonemes are in the whole world but they have different together. Climate change is an important environmental challenge in recently years.
In the north Karun basin have altitude higher than 2500 m and snowfall. Therefore, it has supply water important role in Karun River. We will analysis the effect of minimum air temperature on snow cover and discharge changes in Karun River. In this basin, snowfall has more than rate of precipitation to whole basin.
According to studied in different regions in the world, rainfall annual has downward but heavy rains have upper ward trend. Average air temperature, maximum air temperature, minimum air temperature and evaporation have upper ward trend. In addition, flooding and flood huge have upper ward. However, these parameters have caused decreasing water resources.
That the temperature increasing, melting of polarized, the world’s seas level rise and change in are result of that. Among the negative affects about climate change are Non-uniformly distributed rainfall, increasing and continuity the droughts and finally on water resources in all over the world. North Karun basin has 2300km2 area. This basin is south west Iran. This basin is one of the basins important at supply water resources in southwest Iran. The volume water is resources almost 10billionm3 in North Karun basin.
We used to record by power ministry and meteorological organization in 1984-2014.These data are included air temperature minimum , ice daily, snow cover and discharge. In this research for changes assessment, simulation and forecast the minimum temperature has been used data as for 4 synoptic stations in the north Karun basin. Research period in stations divided to 2part:30 and 25 years. Therefore, the purpose of this research is evaluation changes of minimum temperature in the past and forecast that in the future and changes compare than observer period.
from CMIP5 were selected for future climate change projections over the HNZ under a very-low forcing scenarios (RCP2.6), a medium stabilization scenarios (RCP4.5) and a very high baseline emission scenarios(RCP8.5). CMIP5 data were interpolated to the spatial scale (0.4˚×0.4˚).there for downscaling by Matlab software (0.2˚ ×0.2˚). In the following we used for correction model in accordance with the equation:(Equ1) Also we used to of indexes Bias, RMSE and R for assessment models that their used in forecasting data in North Karun basin.One models of CMIP5 under, RCP4.5 and RCP8.5were utilized in this study.
The mention that for output CMIP5 and scenarios RCP4.5 and 8.5 is done compare, and finally the CMIP5 and MNA-44_ICHEC-EC, RCP4.5 scenario choice for simulation and forecast.
Eventually temperature changes were evaluated. In addition, we used to change snow cover of MODIS TERRA and Aqua satellite Image monthly for during 2000-2014.
-Mann- Kendall test one of the most important nonparametric tests is Mann- Kendall test. The following equation can be used: (Equ2) (Equ3) (Equ4) (Equ5) (Equ6) (Equ7) The climate change is causing water stress. The increasing air temperature, drought and decreasing water are signs climate change in the whole world. The results indicative to exist changes at minimum air temperature, snow cover and discharge in North Karun Basin. The results shown that minimum air temperature has upper ward at 95% and it is increasing between 0.1Cº to 4.4Cº in particular at cold season (November, December, January, February). In addition, Snow cover, ice daily and discharge have decreasing trend. Also, the results simulator by GCM shown that air temperature trend will perpetuate in this basin at future period. Therefore, the increasing air temperature minimum, decreasing snow cover and discharge are causing water stress in North Karun Basin and Karun River. The results show that air minimum temperature increased cause water resources decreasing and supply hydro-electric in the feature period

Temperature is important in the consumption of water and energy through which influences the activities of humans, especially in urban areas. The high variations of temperature in both diurnal and annual scales increases the consumption of energy in winter and summer seasons to moderate the climate to live with. The higher the temperature range the higher the energy consumption. In hot season the higher consumption of water makes the critical impact of temperature manifolds. These circumstances become crisis as we take into account the warming of the temperature and decreasing the water and energy sources of the country, especially in dry regions such as Qum region where the water is already scarce.
The climate of Qum is getting warmer with more heat waves in summer increasing the demand for more electricity and water consumption. Based on the present conditions and increasing trend of global warming the managers and people should become aware of the higher water and energy demands in the future.
This study aims to identify the effect of temperature on consuming water and electricity and gas to manage the consumption of energy and environmental pollution by using less and healthier energy. It is hopeful that the findings from the study can help to manage the energy and purge the environment ofQom. This study tries to uncover the energy and water crisis of the city to make the managers to take actions before the crisis happens.
Material and In order to study the relation between temperature trend and utility consumptions in the city of Qum, the daily min and max temperatures of Qum weather station during 2007-2013 period were obtained from the Meteorological Organization of Iran. The daily utility consumption data for water, electricity and gas have been obtained from the related organizations for the same period.
To calculate the relation between temperature and energy consumption the daily temperature index was defined:〖TI〗_t=T_ti w_i
〖 TI〗_t = daily temperature index
T_(ti )= daily min or max temperature
w_i = the consumer index of year i and was calculated from: w_i= P_i/P
P_i = totalconsumers of year i
P = total consumers of the base year.
The monthly variations of energy consumption was calculated from: E_(ij )=ij /¯E j
ij = consumption of month i of year j
j=consumption of year j
The relation between temperature and energy components of gas, water and electricity is high and significant. This value is .80 for gas, .79 for water and .71 for electricity. Natural gas is very sensitive for min temperature while the other two are most related to max temperature. The analysis of results showed that the relation increased after a threshold. This threshold was 2000000 cubic meters per day for natural gas, 250000 cubic meters per day for water and 8000 mega wat per day for electricity. This means that all of these components are not sensitive to temperature increase because people use them for their normal life. But only when the temperature increases the extra amounts should be used to keep the living conditions tolerable. These thresholds could be used as an indicator of global warming impact on energy consumption. Which changes the normal life trend and takes it toward the hazardous fates at critical steps.
The thresholds show on the other hand the impact of extreme temperature values such as very low or very high temperatures. For example in winter very low temperatures are very important in increasing the consumption of natural gas to make homes warm enough to live in. Iranians do not use electricity for warming house. This is why that the consumption of electricity is not very critical in winter. But cooling the houses is dependent only on electricity in the warm period of year. Water consumption has also been highlighted in the warm season due to its use in air conditioners and green space maintenance. During the cold season water is used only for living basic needs.
There is a direct relation between temperature increase and energy consumptionespecially in the extreme values of temperature. This means that normal temperature increase or in other words the normal variations of temperature do not change the energy consumption dramatically. Only critical warming or cooling of the weather affects the energy and the users and managers should be aware of this problem. Water and electricity are sensitive for higher temperatures of warm season while natural gas is sensitive for very cold temperatures in winter season.

Introduction Temperature is a factor feels by human body and body sense changes when the outside temperature changes for the reason of the heat transfer between body and the environment.
Wind chill is caused by the wind in lower temperature and the higher the wind speed and the lower the temperature, the wind chill and its effects on the creatures would increase. The WCT is important, since it’s an index which shows people how to dress up or to be optimum on energy consumption. When it feels cold due to the wind chill, it could contribute greatly to decision making in urban design and fair and optimum distribution of fuel. The main purpose of this paper is to study the effect of wind chill on reducing the temperature that body feels, also when this done, it could help decision makers in social, political issues as well as peoples clothing and etc based on the wind chill index.
Material and Methods This research has been done about the determination of the temperature which our body feels based on the wind chill index in Isfahan.Isfahan with an area of about 105937 square kilometers has been placed between 30 degrees and 43 minutes to 34 degrees and 27 minutes of north latitude of equator and 49 degrees and 36 minutes to 55 degrees and 31 minutes of east longitude of Greenwich meridian. In this article we can calculate the wind chill index (WCT) from equation 1.
WCT=13.12.6215T-11.37V0.16.3965TV0.16 (1)
V: wind velocity in terms of km (hr) and T: air temperature in terms of °c
Results and discussion From the studies we have done the table results indicated that the month of October is the beginning of the wind chill and the end of it would be in May. But since the frequency of occurrence of this phenomenon in these two months is much lower than other months, will not be discussed in this article. Therefore April, November, December, January and February and March were considered to study. The occurrence of wind chill at Knur Biabanak station was 228 times during 23 years (8395 days). The highest of the wind chill occurrence was 2257 times in February and its lowest was 39 times in May. The wind chill has occurred in Naein station 432 times in the month of February. And this number is the highest occurrence of wind chill in a month.
Conclusion In this article, we have studied the effect of wind speed on the minimum temperature reduction in Isfahan province. Wind chill reduces the emotional temperature on the human body. The results of this research showed that the wind chill factor has been felt 2196 times at Isfahan airport station and 228 times at Khur station as the highest and the lowest numbers recorded, respectively. In the month of February we had 2257 times of wind chill occurrence in the statistical period that has been the most frequency of wind chill occurrence and the lowest number was 39 times in May. The minimum temperature and wind chill in the month of January respectively was -1.6 and -5.6 degrees Celsius. On average, wind blowing will cause the minimum temperature to reduce 4 degrees in this month. The zoning results of the minimum and the wind chill temperatures in Isfahan province indicate that the vulnerable areas of the wind chill in Isfahan are located in the center and western half (overlooking the mountains) of the province . In these regions some stations due to the topographic conditions are more vulnerable to the wind chill. These stations include Isfahan airport, Daran, Ardestan and Naien that they are the most vulnerable areas of the province against the wind chill. Also the month of February is considered as the most critical month in terms of wind chill effects on human body and the most widespread zone of wind chill happens in this month.

Daily weather information is currently available for about 40000 stations across the world. But, distribution of these stations is relatively uneven in some parts of the world. Moreover, there are often large amounts of missing values (Schuol and Abbaspour, 2007:301). Using generated data can help to fill missing or even to correct erroneously measured data (Fodor et al., 2010: 91). LARS-WG is a stochastic weather generator which can simulate weather data under both current and future climate conditions at a single site (Semenov and Barrow, 2002: 3).
There is another watershed modeling problem, which weather stations are often outside of/or at a long distance from the watersheds. So, recorded data may not meaningfully indicate the weather taking place over a watershed. Therefore, some researchers have developed radar data to supply precipitation inputs in watershed modeling (Fuka et al., 2013: 1). But, these data are only available in small parts of the world. So, considering additional methods to generate weather conditions over watersheds is necessary. Using reanalysis dataset (CFSR) is one option (Fuka et al., 2013: 1).
Dile and Srinivasan (2013) investigated CFSR climate data in the Lake Tana basin in the Nile basin. The results showed simulations with CFSR and conventional weather gave trivial differences in the water balance components in all except one watershed. In the four zones, both weather simulations indicated similar annual crop yields. Nevertheless the conventional weather simulation results were better than the CFSR weather simulation, but they can be applied as important option for regions where no weather stations exist such as remote subbasin of the Upper Nile basin. Soltani and Hoogenboom (2003) evaluated the weather generators WGEN and SIMMETEO for 5 Iranian locations. The results showed that WGEN was successful to generate maximum and minimum temperatures and SIMMETEO was acceptable to reproduce minimum temperature and solar radiation.
The objective of current study was assessment of accuracy of weather generator LARS-WG and CFSR data in simulation of climate parameters of Chaharmahal and Bakhtiari province.
The study was conducted in Chaharmahal and Bakhtiary province. This province, with an area of 16532 km2, is located between to 31° 09' to 32° 48' north latitude and 49° 28' to 51° 25' East longitude and provides more than 10% of the water resources of Iran.
1- LARS-WG model
LARS-WG model applies complex statistical distributions for simulation of meteorological variables. The basis of this model to simulate dry and wet periods is daily precipitation and radiation series semi-empirical distribution. The temperature is estimated by Fourier series. The output of this model includes minimum temperature, maximum temperature, precipitation and solar radiation (Babaeian et al., 2007: 62).
2- Required data for LARS-WG model
Required data for LARS-WG model includes daily maximum temperature, minimum temperature, precipitation and solar radiation (sunshine hours). These data were provided for four selected synoptic weather stations (Shahrekord, Koohrang, Boroojen and Lordegan).
3- CFSR data
Reanalysis is a systematic approach to produce data sets for climate monitoring. Reanalysis data are created through a fixed data assimilation design and models which use all available observations every 6 hours over the period being analyzed. CFSR data has a global horizontal resolution of 38 km. The CFSR adjacent stations were determined for the four mentioned stations.
Daily weather data of each station during 1991-2010 was implemented in the LARS-WG model. For assessment of both data, the comparison of statistical indices such as RMSE, MBE, MAE and R2 was used in daily, monthly, annual and decade scales.
The results showed that there is no correlation between the output of LARS-WG model and observed daily precipitation data in each of the four stations. The values of these coefficients for minimum and maximum temperatures increased in all stations. In general, due to high values of RMSE and MAE, this model was not successful in simulation of daily climate parameters. Performance of the model to simulate monthly and annual scale was better than daily. Ability of LARS-WG model in simulation of long-term period (decade) was satisfactory. Also, results indicated that monthly and annual climate parameters by CFSR data have been predicted by a more effective performance. Because statistical indices of CFSR data are lower than LARS-WG. These data underestimated the precipitation in Shahrekord station. RMSE and MAE values of monthly precipitation are 20.49 and 11.19 respectively In Shahrekord station, for CFSR data. These values for annual precipitation are 92.88 and 72.51. For LARS-WG model in monthly scale, RMSE and MAE values are 41.45and 24/75 and these values in annual scale are 164.75 and 123.43.
In recent years, it is necessary to get accurate and long-term meteorological data due to climate events and scarcity of meteorological stations across the country. So, it is a reasonable solution to use weather generators. The objective of current study was assessment of accuracy of weather generator LARS-WG and CFSR data in simulation of climate parameters of Chaharmahal and Bakhtiari province. In general, the results showed the ability of LARS-WG model in simulation of long-term period (decade) data. So, values of statistical indicators are not satisfying in short-time periods. Statistical indices of CFSR data are lower than LARS-WG in simulation of short-time period (monthly and annual). They are highly correlated with the observations and they can simulate climate parameters in short- time. Therefore, considering the purposes of any specific research, both LARS-WG model and CFSR dataset can be used. Moreover, CFSR data can be applied as valuable option for regions where there are no weather stations.

Today, climate change and its anomalies, one of the important issues raised in the world. Detection of changes on temperature and precipitation as the most important climatic elements, is used as primary evidence of climate change in many parts of the world. This paper investigates the temperature trend of Iran of annual, monthly and seasonal scales. For this purpose minimum, average and maximum temperature data of 38 synoptic stations, over the period of 50 years (1960-2010) with good distribution, were obtained from Iran meteorological organization.  Then the temperature trend parameters were investigated (studied) by Mann Kendall nonparametric test. The results showed that the general temperature trend is increased in most of the stations for different time scales; however this intensity of increase decreases from the minimum to maximum temperature. On monthly, in June and July, and on seasonal, in summer, the increase of temperatures are higher than other time. Although the most frequency positive trend of the maximum and average temperature observed in the winter, but for a few of the stations was significant. While in warm seasons especially in the summer, the frequency of station with positive significantly trend is higher. In terms of spatial, the stations that located in the Alborz Mountains, South West and South East of IRAN have experienced higher temperatures than other areas of the country and in some station such as SHAREKORD, URIMA, KHORRAMABABD AND BANDAR ABASS trend of temperature in different scale is mostly decreasing.

The main purpose of this article is، showing similar fluctuation of temperature series and their consistency with what happened in the global level. In addition، it determines new estimates of regional seasonal and annual temperature trends over Iran، after the detection of artificial and natural non homogenous points of 33 synoptic stations for the period of 1960 2010. The 22 stations with shorter records are used only to confirm variability during overlapping periods as evidence. Due to similarity of the results of homogeneity tests and also to prevent of complexity، assessing of data homogeneity have been surveyed only by using the results of Standard Normal Homogeneity test (SNHT)، expert judgment and Metadata. The results showed، the country may be segmented to 10 such regions in terms of trends and variability of temperature. In addition، it was shown، the country with having different climatic type and with facing similar natural fluctuation، have experienced similar variability and fluctuation of temperatures in all regions at nearly equal rates of 0. 4-0. 5 and 0. 2-0. 3 (°C /decade) for annual minimum and maximum temperature، respectively in Iran. Non homogeneities in the temperature series relate mostly to relocation and changes of environmental conditions at individual stations. In the case of ignoring these non homogeneities، it is appeared errors in the statistical characteristics of temperature، Furthermore، it will be followed uncertainties in spatially averaged trends. The finding in earlier work of a few individual stations with negative trends is found to be due to artificial effects like relocation.

Zayanderoud Basin is one of the important agricultural areas in country level because of climatic variety and resuscitative water of Zayanderoud River. Since frost phenomenon especially late spring frost incurs great damages on fruit trees and agricultural products of this region، it is necfessary to study frost in this basin. In this research، the intensity of frost during cold period and spring season in Zayanderoud Basin in five thresholds: mild (0 to -5 0C)، moderate (-1. 5 to -10 0C)، strong (-1. 10 to -150C)، very strong (-1. 15 to -20 0C) and extraordinarily strong (lower than -200C) was studied using daily minimum temperature statistics of 13 meteorological stations during 16-years statistical period (1992-1993 to 2007-2008). Frequency zoning map of different frost intensities was also drawn in ARC MAP environment. The results of research show that all studied stations of Zayanderoud Basin experience mild to very strong frost during cold period، but the extraordinarily strong frost only is occurred within elevated regions (above 2000 m). In spring season، mild frost is occurred in until late Farvardin month and within elevated stations until third decade of Ordibehesht and moderate frost is only occurred within 2000 m stations and above in Farvardin month. Strong frost is only occurred in the studied north-western region. According to zoning maps، north-western Zayanderoud Basin is hazardous in terms of the frequency of occurrence of different frost intensities.

Siberian high is a large synoptic system in planet scale that considers the most important center of atmosphere action for cold period in Eurasia. This high that depend on the coldest and the most condensed air mass in north hemisphere, concentrate itself as a seasonal and semi – permanent synaptic system between Baykal and Balkhash lakes, and it’s western tongue affect the climate of extensive regions of Iran. Therefore, the goal of this synoptic study is to explain key interactions between the atmosphere and surface environment and in other words exploration of the relationship between the circulation patterns of Siberian high pressure and minimum temperatures in Iran. Up to now, many studies about Siberian high have been done by several individuals that we will refer to some studies which have been done in Iran and world. In the world, Lydolph (1977), Ding and Krishnamurti (1987), Sahsamanoglou et al (1991), Zhang et al (1996), Mokhov and Petukhov (1999), Choen et al (2001), Haghton et al(2001), Gong et al(2001,2002), Takaya and Nakamura (2004), Panagiotopoulos et al (2005) and Lingis and Thompson(2005) are individuals that have carried out investigations about siberian high. In Iran, the investigations have been done too which can point to investigations of Abdolhoseini (1358), Alijani (1369), Balighi (1375), Chokhachizadeh (1376), Jahanbakhsh et al (1378), Azizi and Yousefi (1384) and kaviani et al (2007). This research try to reveal the climatic impacts of pressure systems on Iran climate by using the statistic and synoptic methods study the role of Siberian high system at the Slp in spatial distribution of the minimum temperatures in Iran. In this research, for analyzing the temporal variations of the Siberian system have been applied the daily data of sea level pressure at 12GMT in NCEP NCAR database with spatial resolution of 2.5×2.5 in a 55 years period including 20089 days from Dey, 11th, 1329 to Dey, 10th,1384). To recognize and analyze the temporal patterns of Siberian high system and by considering the mean position of this system and it’s spatial developing relative to Iran and the maximum of it’s action intensity in sea level that often is conformity with surrounding and middle limits of Balkhash and Baykal lakes (Lingis and Thompson,2005, Gong et al 2002, Sahsamanoglou et al, 1991, kaviani et al, 1386 and Chokhachizadeh, 1376) we have selected the suitable framework of 62.5 – 120o east and 40 – 62.5o north for this system. Then, calculation and standardization of mean daily of sea level pressure have been done from 1330 to 1383. Thus, a matrix with size 19724 1 was obtained as standardized Siberian high index (SSHI) that included the anomalies of positive phase (Siberian high presentation) and negative phase (absence of the Siberian high) in each day. To analyze and interpret the effect of Siberian high system on minimum temperatures in Iran, have been applied the information of 663 synoptic and climatology stations in Iran with statistical period of 1961 – 2004 from minimum daily temperature data of stations that at least had statistical period of 10 years. On this basis, the data of minimum daily temperature of 423 stations have selected and analyzed. At first, the value of minimum daily temperatures was standardized for analyzing the effect of Siberian high on minimum temperatures of Iran. After standardization, two calendars have been conformed as standardized value of daily minimum temperature and standardized Siberian high index and selected a temporal period from 1340 to 1382 consist of 15705 days from 16071 days for studying the effect of Siberian high system on daily minimum temperature in Iran. Then, for understanding how effects of the Siberian high system on daily minimum temperature in Iran, the contingency table method and the 2 statistic calculated in math-lab soft ware were appleid. The study of time series of index value for intensity of this high system in studied time period indicate that the lowest anomaly was equal to -2 and the highest anomaly in studied period was equal to +3/5. The lowest anomaly of negative phase has occurred on Tir, 25th, 1335 and the highest anomaly of positive phase was on Azar, 5th, 1366. The results of study the time series of intensity index indicated that the nature of index behavior at mentioned level vary alternately and tendency to change between two positive and negative phase is evident in the half -year time periods. In addition, it indicates the decreasing and increasing behavior in itself internal-year variability continuously. The anomaly of negative phase relate to non Siberian high and predominance the Asia low in hot period of year and the anomaly of positive phase of index indicate predominance the Siberian high in cold period of year. The average of positive phase intensity for Siberian system is 0.88 and the average of negative phase intensity is -0.80. The frequency of occurrence days of positive phase is 9469 days and the frequency of occurrence days of negative phase is 10255 days. Therefore, in mentioned statistical period, the positive phase (Siberian high) was dominant in 48% of period and the negative phase (non Siberian system and Asia low presentation) was dominant in 52% of period. The study of time series of average the Siberian high intensity index in positive phase indicate that the most violent positive anomaly was occurred in 1335 and 1355 and the most weak of it were in 1357 and 1370. In addition, the study of time series for days frequency of existence and absence of the Siberian high in occurrence the negative and positive phase indicate that the average of negative phase dominant was nearly 190 days and the average of positive phase dominant was about 175 days. The least period of dominant for positive phase was 143 days (1338) and the greatest was 210 days (1370). The period of dominant for negative phase wasn’t shorter than 155 days (1370) and longer than 222 days (1338). By study the time variations of the frequency of Siberian high activity days in positive phase occurrence that had ascending behavior during recent 50 years, it seems that in spite of relative decrease of the frequency of days for Siberian high activity in 1930’s, totally, the frequency of days for activity of this system have been increased during recent 50 years. This research indicated that standardized intensity Siberian high index is able to revealing the time variations of Siberian high. The analysis of time series of standardized intensity Siberian high index in positive phase period (predominance and presentation the Siberian high) indicated that intensity of Siberian high activity have the alternate behavior. Comparison between frequency of positive phase occurrence days and negative phase event days in the studied level showed that during recent 50 years the appearance and activity days of SH were definitely less than absence days of this system. At he same time, the frequency of activity days for this system was increasing during recent 50 years. In the other hand, this study indicated that the frequency of presentation days Siberian high have tendency to increase. The study of obtained results by using the contingency table method at time period (1340 – 1382) for revealing the effect of Siberian high system on occurrence of daily minimum temperatures in Iran showed that at the 95% confidence level, daily temperature minimum in about 93% of studied stations (393 out of 423) isn’t independent of influence of Siberian high pressure at the Slp. this subject indicate the strong relationship and connection between daily minimum temperatures in extensive regions of Iran and Siberian high at the Slp.

Human life has been affected by the weather conditions. Since weather conditions may be favorable or adverse, human has tried to defend himself against climatic conditions through understanding the nature of the climate. These efforts led to the identification of the origin and how they were created. Such knowledge is also more accurate and more scientific.In synoptic climatology, by relying on the accepted principle of explanation and analysis of environmental changes of the earth surface through the changes of pressure patterns, it is possible to more explain, analyze, and forecast the climatic phenomena of the earth surface.One of the most important climatic disasters that threaten our country, are cold wave and sever freezing that in some years covers large areas of the country. Freezing usually occurs with the entry of the air masses of below zero degrees. These air masses accompanied with relatively stable and multi-day cold waves that may lead to adverse effects. For example, scarce and extreme cold of January and February 2005 in Iran, which has covered a wide and extensive part of the country. For synoptic explanation and analyze of the sweeping cold wave of Iran, minimum temperature of the stations within the province of Chaharmahal & Bakhtiari was selected and then the data of sea level pressure (SLP) & geo-potential height of middle level of atmosphere was select for explaining this event.

The temperature phases could determine its effects on the environment. One of the important temperature phases that could be a disaster is frost. Frost has important roles on Biological activity as well as on economical. In current paper in order to analyze frost in Iran, we used database of minimum temperature of Iran. This data based is arranged for 43 years (15992 days) and 15 ×15 KM resolution (7187 pixels for all over Iran). So the database has 15992×7187 dimensions. All the operating calculations have performed on this matrix. As in classical documents zero degrees Celsius have been chosen as threshold for frost in the database. The analyses have been taking place on the temperature equal or below of this threshold. It has been done by using softwares such as Surfer and MATLAB. Time series analyses of frost shows those 9224 days out of 15992 days have experienced the frozen day. There are a strong oscillatory behavior and weak, not statistical significant trends in frost temperature time series as well as a jump in its middle. Oman Sea cost as well as Persian Gulf shores never have experienced the frost days. The height lands and high latitudes area has most experiences in freezing days as well as in extensive. The average of maximum days with frost was 145 days.