نشریه پژوهش های اقلیم شناسی
پیاپی 11 (پاییز 1391)

Ozone is one of the atmospheric constituents which is very important in warming and pollution of the atmosphere. Its concentrations (above 120 ppb) in the upper atmosphere increase the earth’s temperature and in the lower atmosphere pollute the air and causes damages for human and plant life. It causes some problems such as respiratory diseases in humans. It is more dangerous in urban environments where the presence of moisture and other pollutants increases its polluting function. That is why studying its concentration and variation in the lower atmosphere is very important. In Iran there is only one surface ozone measuring station which is in Firouzkooh and is a Background Air Pollution Monitoring Station. The station was established in 1993 at the 2986m above sea level. Due to its higher elevation, the measurements reflect general or background of ozone concentration in the country. In this paper we have investigated at first variations of the surface ozone concentration and then studied relations between ozone concentrations and important Meteorological Parameters such as temperature and wind. For the purposes the daily values of Ozone were obtained from the station for the period of 1999-2003; the maximum period of data availability. Weather elements such as temperature, precipitation, wind speed, sunshine duration, sea level and surface pressure, relative humidity, and cloudiness of the station were also extracted for the same period. Mean concentration of surface ozone was 54.1 ppb for the period. 20 ppb was the lowest value measured during the study period in November and the highest value was 125 ppb in May. More than 70 percent of ozone concentrations were observed between 46 and 65 ppb. Survey of the monthly mean of the surface ozone shows that it increases from January and reaches its maximum in June, while in the second half of the year it has a decreasing trend until December. The monthly mean ranged from 50ppb in winter months to 60 ppb in summer months, Moreover based on the analysis made on the monthly and seasonal data, variations of the maximum is more than that of the minimum and so the seasonal variations were much less than the monthly values, which shows that it is strongly affected by the sunshine hours and the temperature. Consideration of surface ozone concentrations and the weather elements showed different positive and negative relations. Sea level pressure (QFF), relative humidity, cloudiness, and precipitation showed negative correlations while wind, temperature, sunshine duration, surface pressure (QFE), and visibility showed positive correlation with ozone concentrations. The Correlations of Ozone concentration with surface pressure, wind velocity, precipitation, and visibility was very low. Sunshine duration and sea level pressure had the highest control on the variations of ozone concentrations. Some weather phenomena such as thunderstorms had remarkable increasing effect on the ozone concentration while fog and haze decreased it effectively. Study results of the monthly and seasonal averages show that except for July, the surface ozone is increasing in the dry periods of the year (which is reconciled on the hot period of the year), and with the exception of March, it decreases in the wet period (the cold period of the year). These exceptions can be interpreted due to higher values of cloudiness, precipitation and relative humidity in July, and higher values of ozone in the upper levels and its transformation from the stratosphere to the troposphere in March. In general, concentrations of surface ozone were higher in warm months and lower in cold period of the year. Warm and sunny days increased the concentration while the cloudy and rainy days showed lower concentrations. Winds blowing from dry and warm regions from the south and southwest increased the concentration and winds from the cold humid northern regions lowered the concentration.

In this paper, the authors have studied the large-scale atmospheric circulation over southwest Asia during a boreal summer. First, substantial characteristics and nature of the large-scale atmospheric circulation are investigated. Then, temporal variability of the circulation was examined during a 61-years period (1948-2008). The findings indicate that the onset of the Asian monsoon is associated with the formation of a permanent westward flow in the upper troposphere. The corresponding maximum convergence and subsidence locations of the flow are the energy sinks over the southwest Asia and east of the Mediterranean Sea, respectively. Maintenance of the large-scale atmospheric subsidence creates a transverse meridional gradient in the temperature field; therefore, the meridional large-scale circulation is changed and this in return creates a transverse Hadley circulation which forms over southwest Asia. Investigating nature of the summertime anticyclones over southwest Asia reveals that the anticyclones are dominant in all tropospheric levels. They are originally formed either as a result of the descending air which is basically originated from the monsoon region, or by accumulated heat of the surface of high plateaus in the mid-troposphere due to intensive vertical advection of heat over southwest Asia, or a combination of both. The result also reveals that among the physical, dynamical, and Jet indices, the physical index more favorably shows characteristics of the summertime circulation. Based on the physical index, it’s found that the averaged summer season timing starts on June 7 and ends on September 28 over southwest Asia. Investigations on the temporal variability of the atmospheric circulation, indicates a considerable decreasing of summer length in the recent decades. On this basis, although the starting time of the summer shows very small changes in its long-term trend, the trend line shows an eight to nine days decreasing in the season’s length during the study period. The result revealed that the decreasing of summer length from 117 days to 109 days over southwest Asia is mainly due to the early ending of summertime in recent decades. It is also found that both the southwest Asia and the Asian monsoon regions have experienced similar decreasing trend in their summer large-scale circulation strength during the study period. Examining the synoptic scale atmospheric components showed a considerable strengthening of the Arabian high and low and the Shomal wind over the Arabian Peninsula. On the other hand, the Turkmenistan anticyclone, the Pakistan low and the Sistan wind in the east and northeast of Iran plateau experienced a slight weakening in their activity. Also, Examination of the horizontal divergence field shows an increasing trend in the intensity of anticyclonic circulation on Iran and on the Zagros convergence zone in recent years. The NCEP/NCAR daily reanalysis dataset (Kalnayet al. 1996) in a 61-years period (1948-2008) were used to study the summer atmospheric circulation. In this research, variables of the Geopotential Height (gpm), Temperature, and Outgoing Long wave Radiation (OLR), zonal and meridonal wind components the dataset were used to calculate horizontal divergence field, divergent wind, relative vorticity and diabatic heating. We first examined the sinks and sources of energy in regional scale. Then, zonal and meridional large-scale circulations as well as their vertical structure were analyzed for April-October months in the period over southwest Asia to derive prevailing circulation patterns. Three regional indices including physical index, Jet Index, and dynamical index were designated to determine the starting/ending time and the length of summer seasons as well as to study the intensity of the atmospheric circulation over southwest Asia. The indices provided the possibility of assessing different aspects of the summer circulation. We also used the gpm, relative vorticity, horizontal divergent fields and diabatic heating charts to investigate structure of anticyclones on Iran and Arab countries in midtroposphere and the Turkmenistan anticyclone, the Pakistan low and the Zagros convergence zone in lower troposphere. Finally, the temporal variations of the summer circulation components were studied using the most suitable variable for each component. The results show that the monsoon circulation is the main factor controlling the large-scale summer circulation over southwest Asia. However, the surface heat forcing has the main role in the formation and maintenance of atmospheric circulation in the lower and middle troposphere. Investigation of the synoptic scale circulations, show that the Zagros chain is effective on formation of anticyclones over Iran. In fact, the vertical advection of heat induced by the elevated heat source in western Iran has a key role on the formation of a thermally-driven anticyclonic circulation in mid-troposphere. On the other hand, formation of the Turkmenistan anticyclone and the Arabian anticyclone has different mechanisms. Formation of the Turkmenistan anticyclone in the lower troposphere is mainly due to the convergence and subsidence of the air with monsoon origin in southwest Asia at the levels below 600 hPa. While the Arabian anticyclone is strengthened by the descending air originated from the monsoon system as well as thermal forcing from surface and vertical advection of heat from the high lands in the western Arabian Peninsula. Application of circulation indices in this research led to recognition of the main characteristics of summertime atmospheric circulations including the starting/ending time, length, and intensity of the boreal summer over the southwest Asia. Examination of the temporal variability of the summertime atmospheric circulation over southwest Asia, show that the summer duration has been reduced considerably in recent years. Early ending of the summer can be physically related to the early ending of the transverse gradient in meridional temperature field during the recent 2-3 decades in the study region. The documents also indicated that shortening of the summer and weakening of the atmospheric circulation over southwest Asia has a relationship with shortening of the monsoon season and also weakening of the monsoon circulation over south and Southeast Asia. However, the correlation between the monsoon circulation and large-scale atmospheric circulation over southwest Asia shows a decreasing trend. The latter can be an indicator of increasing regional-scale factors role on the southwest Asian climate. The overall result of this study indicates that from 1980 onward, the inter-annual variation in the intensity of the activity of atmospheric circulation components has been considerably decreased compared to the time before 1980.

The central Mediterranean Sea is well known as a cyclogenesis area. The Jet streams associated with divergence, are important factors in cyclogenesis in the area. The Subtropical and polar jet streams are flowing normally in the upper layer in 300- 200 hPa. Although the subtropical or polar jet is associated with cyclogenesis, sometimes the cyclones develop in lower latitudes with respect to the interaction region of the jet streams.Method and Material: The meridional and zonal wind, vertical motion, geopotentail height (gpm) and mean sea level pressure (mslp) from the reanalysis data of NCEP/NCAR were derived. The data are being archived from 1948 with a 2.5 degree horizontal resolution at 17 levels. Then, the divergence and positive vorticity advections were calculated by the wind data. Finally, the composite structure of several Mediterranean cyclonic systems was plotted and the figures for the case study (21 and 23 Feb 1974) were obtained. The wind speed of 45 m/s ms with a 0/5 ×10-5 s-1 divergence in the exit region of the subtropical jet in 25 to 27.5 No latitudes is demonstrated in the composite Figures for the formed cyclonic event. In addition there is a north-south polar jet in Western Europe of its left exit with weak divergence. In the cases with the process of cyclone development, normally the wind speed increase to 50m/s ms and more and an intensive horizontal wind shear forms in the left side of the Subtropical jet. Intensified convergence in 850 hPa and upward motion in 500 hPa are favorable factors for cyclogenesis development and changes in the related wind filed cause an increase in divergence up to 1 ×10-5 s-1. In the Central Mediterranean, cyclones are developed normally by presence of the subtropical jet stream near the North of Libya. In the case study, of 21 Feb 1974, the maximum wind speed of 62 m/s ms were observed in the exist region of the jet over North Libya with a north-east to south-west direction in 200 hPa. The inverted pressure trough was formed in lower troposphere under the upper level jet and weak divergence field. The positive vorticity advection coincided with maximum upward motion in east of the upper trough was above the midlevel inverted trough. the upper level wind speed and divergence field extended from north Libya to central Mediterranean and west Turkey were developed and led to increase of convergence in 850 hPa in east of the cyclone. In middle level, the trough amplification is associated with enhancement of upward motion and positive vorticity advection. Thus the cyclone was developed due to forcings from lower and upper levels and mid-level forcings support cyclogensis. Although the subtropical and polar jets can affect central Mediterranean cyclogenesis by a composite structure, so that cyclone can be formed in the polar jet left exit and developed in subtropical jet left exit. Thus, cyclones develop only by subtropical jet and form by both subtropical and polar jet. Review of weather system shows expansion of the inverted pressure trough on 21 Feb 1974 to central Mediterranean from Africa, affected by Subtropical jet associated divergence filed. The polar jet was not observed on the day. Within the next 24 hours ending to 23 Feb, wind speed in 200 hpa reaches to 72 m/s with intensified cyclonic curvature and caused upper level divergence and favorable conditions for cyclogenesis. So, some central Mediterranean cyclones can be formed and developed only by subtropical jet without interaction by polar jet.

Surface solar radiation is an important parameter in hydrological, meteorological, climatological and crop yield models. Some parameters such as precipitation and temperature are widely available. By contrast, direct measurements of surface solar radiation are very sparse in most regions, especially in highland and mountainous regions. Lack of adequate observations on solar radiation has ever been a persistent problem in studies of land-surface processes. Hence, alternative techniques are required to estimate solar radiation. Apart from astronomical and geographical factors, incoming solar radiation is strongly modified by cloud cover, the underlying surface albedo, atmospheric turbidity, absorption and scattering. Empirical models which express global solar radiation as a function of these variables have been proposed by various investigators. Since most proposed empirical models are not flexible but rather restrictive in their application, their suitability for a particular location would largely depend on validation against actual measurements. Mashhad is located at latitude 36º 17ʹ 45ʺ -N, longitude59º 36ʹ 43ʺ -E and at 992 meters altitude. Because of its situation, the city experiences different air masses and has a specific changing climate. Considering the Average temperature and precipitation (14.1 °C and 255.2 mm, respectively), the city has a semi-arid climate based on Demartonne Method. The average sunshine hours and solar radiation intensity in the city are about 2892 hours/ year and 195 W/m2, respectively. In this study, we used temperature data, sunshine hours, relative humidity and precipitation to estimate the solar radiation (Rs). To compare the estimated and measured data, we used the measured solar radiation by Pyranometer that is available for 10 years (1994-2003). Extraterrestrial radiation (Ra) was calculated by the equation obtained by Allen and his colleagues (Allen et al., 1998). In this study we investigated two solar radiation models - Angstrom–Prescott and Garg and Garg models- and determined their coefficients for Mashhad. For this purpose, the least squares error method was applied. To calculate coefficients of both equations, we used the MATLAB programming language. We used the data sets of 1994-2000 for calibration and 2001- 2003 for validation. Some of the radiation models are based on the cloudiness. Therefore in this study we developed 2 new radiation models based on cloudiness data. These two models are generally presented as equation 11 and 12: In these equations N is fraction of cloudiness (octal) and A, B, C, K and M are constant coefficients. Based on available data from 1994-2000, coefficients of Angstrom–Prescott Model were determined as a=0.25 and b=0.42. High determination coefficient (R2of 0.87 and 0.89 for calibration and validation respectively, and low RMSE (2.46 and 5.15) and MBE (-0.14 and -4.63) confirm that the coefficients are acceptable. Also coefficients of Garg and Garg model were determined as X=0.27, Y=0.42 and Z=-0.0028.The amounts of R2 (0.87 and 0.89 for calibration and validation stages), RMSE (2.45 and 5.08) and MBE (-0.11 and -4.56) show that the coefficients of Garg and Garg model are acceptable too. As mentioned before, Cloudiness is one of the most important parameters for determination of solar radiation and many equations were developed based on this parameter. Therefore, in this study, two models were developed based on cloudiness. The first equation obtained using 1994-2000 data sets are as follow: For these equations, determination coefficient is equal to 0.84 and 0.82, respectively. Although water vapor is effective on solar radiation and Angstrum-Prescott model is better than Garg and Garg model, but there isnt much difference between these two models. So, because of requiring less meteorological data than Garg and Garg model, Angstrum-Prescott model is suggested. Of the two developed models in this study, equation 1 has more accuracy and validity than equation 2. Meanwhile, developed models have higher accuracy compared to Angstrom-Prescott and Garg & Garg models. Also, we should consider the fact that, Angstrom-Prescott model for calculating the radiation requires two parameters, which from these two parameters the N value can be obtained. Additionally, this value may not be accurate for the study area. Overall, using developed Model 1 cab is recommended for this research when only cloudiness parameter is known.

In recent years, many researchers have studied the effect of ENSO’s teleconnection on the precipitation over various parts of Iran; however, few studies have been done to investigate the effect of ENSO on meteorological parameters. This paper aims to study the effect of ENSO on the surface pressure over Iran and the Middle East. In order for this to be done, a 30-year era (1971-2000) has been selected as the base of research and the sea surface pressure data, as well as the Oceanic Nino Index (ONI) data, has been obtained from the NOAA website. ONI is the difference of the 30 years average of the Sea Surface Temperature (SST) over the NINO3/4 region from its three months running average. Nine ENSO years including three warm phases (El-Nino), three cold phases (La-Nina) and three neutral phases were collected. El-Nino years are 1972, 1982 and 1997, La-Nina years are 1973, 1975 and 1988 and neutral years are 1979, 1980 and 1981. At first, the stationary part of surface pressure data has been separated from the transient part. Since the stationary part is independent from oscillations like ENSO, then only the transient part of pressure has been studied for three El-Nino and three La-Nina years, which are the strongest in the era. In the next part of the research, the partial (net) effect of ENSO has been separated from the effects of other oscillations (i.e. MJO and NAO). The main theory is based on this fact that there are three years (1979, 1980 and 1981) that ENSO were not active and six years with the strongest presence of ENSO. If it is supposed that in all nine selected years all of the oscillations were active, then by subtracting the neutral phase anomalies from warm and cold phase anomalies, the roughly net effect of ENSO will be gotten. In order to do this, at first the mean of anomalies for any phase is computed and then subtracting is done. The most important effect of this averaging is modification of the effect of other oscillation and maintaining the effect of ENSO. Because in these six years ENSO had been very active (SST anomaly more than 1.5 ºc) and the averaging has no any modifier effect on its impact. In continue, the zonal averaging of the net anomalies over the Middle East (from 30 degree east to 70 degree east) for any latitude has been done and the curves of meridianal distribution of it have been investigated. Finally, the correlation coefficient between sea surface pressure and SST of Nino3/4 area is computed by the Pearson product-moment method. The results show that the distributions of anomalies in the same phase (warm or cold) of ENSO years are different. For example, in winter of 1972 all of the Middle East were beholder of positive anomaly whereas in 1982 and 1997, positive anomalies are only seen in the west part of the region (Figures are not shown). In other words, the distribution of the transient part of surface pressure over the Middle East does not follow the ENSO phases. The existences of weak correlation coefficient amounts between ONI and surface pressure data, which are computed by the Pearson method, emphasize these results, especially over northern Middle East and Iran. In next part of the study which is related to the net effect of ENSO, the results are very interesting. In the warm phase of ENSO, there is a wide and strong positive anomaly of pressure over the Black Sea and Eastern Europe during the cold seasons, which made the condition suitable for forming blocking high in these areas. The formation of blocking over Eastern Europe causes the mid latitude and Mediterranean cyclones to pass over Iran and to rain, frequently; whereas, in the cold phase of ENSO, only in autumn the same condition has been seen but with less intensity. These results are very close to the results of other Iranian researchers that say wet year is accompanied by El-Nino and dry year is accompanied by La-Nina. But it must be attended that this effect is not dominant at the presence of other oscillations (former discussion). It seems that the effect of ENSO is weakened or annihilated by the effect of other oscillation during a complicated non liner interaction. This study indicates also, in comparison to El-Nino, La-Nina keeps the Iranian heat low in higher latitudes in summer time. After this displacement the easterly waves may pass over southeast and south of Iran and forming the summery rainfalls of the mentioned areas. In other words, the probability of summery rainfalls over southeast and south of Iran in La-Nina condition is much more than it in El-Ninos. The curves of the meridional distribution of the zonal mean of net anomalies of sea surface pressure are shown that the net anomalies in the El-Nino condition are more positive than those in the La-Nina condition for all latitudes (Figure 2). In winter season the slope of the El-Nino curve is more than La-Nina's at higher latitudes. It confirms the blocking high forming on the north part of the Middle East in wintertime of El-Nino. The results show similar variations for both El-Nino and La-Nina at lower latitudes. It is also seen that in summer season the anomalies of La-Nina at all latitudes are negative whereas the anomalies of El-Nino are positive for latitudes higher than 40 north degree. It means that Iranian heat low is kept at lower latitudes in El-Nino condition comparing to La-Ninas. Since there are different patterns in transient part of sea surface pressure over the Middle East for the same phases of ENSO, then it is concluded that ENSO has no predominant effect on the pressure distribution over the region. But the net effect of it shows that in the warm phase, the condition is suitable for passing the mid latitude and Mediterranean cyclones over Iran and to rain during the cold seasons, frequently; whereas, in the cold phase of ENSO, only in autumn the same condition has been seen but with less intensity. The slope of meridional distribution of net anomalies of the El- Nino which is more than La-Nina's at higher latitudes, confirms this subject. This study indicates also, in comparison to El-Nino, La-Nina keeps the Iranian heat low in higher latitudes in summer time. After this displacement the easterly waves may pass over southeast and south of Iran and forming the summery rainfalls of the mentioned areas.

A tropical cyclone (TC) is a low-pressure system that forms on the warm waters of the tropical and subtropical oceans. Intensive tropical cyclones are called “Hurricanes” and are hazardous for marine transportation, ports and even to aircrafts and so on. Pressure at the center of these systems reduces to 1005 hPa and lesser. Wind velocities of hurricanes may exceed 33 m/sec. In general, there is a theory that says a tropical cyclone (TC) occurs in two stages:• Stage 1: TC occurs when the mesoscale convective complexes (MCC) produce a mesoscale vortex.• Stage 2: TC occurs when a second blow up of convection at the mesoscale vortex initiates the intensification process of lowering central pressure and increasing swirling winds. The Main regions for TC (and hurricane) generation are the Gulf of Guinea toward the Carrabin Sea, eastern parts of the Pacific Ocean in Philippines and yellow Sea and south of Indian peninsula in Maldives isles toward west. Most of the TCs in Indian Ocean move toward west and northwest. In rare conditions the country of Oman, southeast of Iran and south of Pakistan are affected by a TC (hurricanes) impacts. Return period for this movement of the TCs (and hurricanes) towards the north is very long. The Gonu and Phet TCs were two extraordinary tropical storms that reached to the north coasts of the Indian Ocean. It is suggested that Global Warming might be a main cause for the next unexpected behaviors of TCs In this study, data and climatic information of NOAA/ESRL were used to provide Maps of the Sea surface temperature (SST) changes and its anomalies, pressure changes in the 3 levels of 850,500 and 250Hpa to study horizontal wind speed within the lower, middle and upper troposphere and investigate causes of the PHET TC occurrence. Then, to determine motions of the Phet in its life, two main parameters namely changes of Omega and geo-potential height in lower and middle troposphere were evaluated on the basis of Attraction and Buoyancy rules. To determine changes due to storm movement in affected areas by the Phet, we selected parameters of Temperature and accumulated rainfall and analyzed rainfall from satellite images field measured by the TRMM and temperature anomaly field from synoptic charts of 850 and 500 hPa levels (difference from longtime average). Results of this study show that increase of north Indian ocean SST up to 32Co associated with SST of the Bay of Bengal and Regressive movement of STHP from the Indian peninsula, Pakistan, the Persian Gulf due to onset of the monsoonal southwesterly flows from equator are the basic factors for onset and development of the TCs and hurricanes such as the Gonu or the Phet. Also inspections of storm tracks show that they follow the rule of “Attraction and Buoyancy. According to the rule the Phet from the beginning stage until 4th June moved toward the Oman coasts due to far effects of the Balkan surface low. But northward expansion of the STHP in that region (moving to the south coasts of Iran) by reinforcing closed cells of the monsoon on Pakistan from 4 June onwards, the storm’s path was deviated toward southeastern coasts of Iran and then toward south parts of Pakistan. Geopotential heights variations analysis in 850 and 500 hPa levels on 1 to 6 June, better show the STHP effects on passage tracks and intensity of storm. Polar satellite images show the most severe storm and rainfall (600 mm) in west of the Indian ocean on 2 and 3 of June. Generally, movements of rainfall cells of the mentioned storms have a close relation with the 500 hPa motion field of weather patterns. Forecasting of movement tracks for tropical cyclones is very important in weather forecasting. Predictions of tropical cyclone tracks in north of the Indian Ocean may be based on the rule of “Attraction and Buoyancy”, therefore it can determine movement tracks of storms in this region. The rule is based on relation and reaction among changes of the pressure and omega parameters in low, middle and upper levels of the atmosphere. Timely predictions can reduce damages due to these risks. Damages caused by tropical cyclones because of their heavy rainfall and severe winds, have placed the climate system in the class of horrible natural hazards. For Example PHET cyclone damages in Oman were more than 600m dollars. Also 10 thousand people in Pakistan have been moved and 16 killed. On the southeastern coast of Iran, on the fourth and fifth days of its formation, particularly in the Chabahar Port, the Sea wave height raised to 13m and dust storms with visibility reduced to less than500m. Over the recent decades, frequency of the tropical cyclones in the North Indian Ocean has shown a significant increasing trend. Based on this trend, in future occurrence of such storms in the northern coastlines of the Golf of Oman will be more possible

The relative humidity (RH) is one of the important variables of atmosphere. Average weekly, monthly and annually relative humidity is usually required. These averages calculated based on averaging daily relative humidity (DRH). Thus increasing the accuracy in estimating DRH causes the accuracy of the above averages. Conventional methods for estimating the DRH is mean relative humidity for local standard hours of Iran (6:30, 12:30 and 18:30) by equation (1). This equation is a global standard procedure that using by Iran Meteorological Organization and the Ministry of Energy (e. g., [1], [2]). 6:30 12:30 18:30 RH = 0.33RH + 0.33RH + 0.33RH (1) There are some weakness points in relation (1) which causes large errors. Yao (1974) showed that the beta function has good fitting to the DRH. The behavior of DRH curve is skewed, so it is nonsymmetrical. Therefore, using the eq.1 increases errors. Corvallis (2008) proposed the relationship (2) as a default for eq.1 It has little bias for several months. Eq.2 shows that the DRH is dependent only to 3 and 15 Greenwich hours (morning and afternoon). It is observed that the effect of morning RH is approximately 2-times of afternoon RH. morning afternoon RH = 0.65RH + 0.35RH (2) The DRH curves are dependent on the climatic conditions and the months of years. Court and Waco (1956) Said that DRH which is obtaining by averaging the morning and afternoon DRH is not accurate and it is greater than the actual DRH. They also found that the DRH is greater than the average of daily minimum and maximum RH and they stated that it is depends to the months too. Day (1917) calculated the average monthly RH and concluded that it is dependent tothe month, season and geographical coordinates and has errors. The errors are negative in some places and regions. The previous studies show that the estimation of DRH by the standard three hours is not accurate and dependent to the month and climate. The Purpose of the present paper is to establish a new relationship for estimating DRH with the standard hours and also adding the temperatures and daily precipitation into these relationships. Moreover,the climates and months are also involved in relationships. We presented an equation for every month too. Iran was partitioned by around medoids clustering method (PAM) with 9 variables and it is separated into three clusters. The relationships that presented in this paper are suitable for the Mountainous cluster. The Spss.18 Software (step by step method) fitted patterns. This was done after data screening. Survey tables show the model acceptance and powerful fitting (for annual pattern with adjR 2=0.995). Transformation at several predictors causes the increasing the goodness of fit some monthly patterns. The table (1) shows annual pattern of DRH. The DRH in the months depends on the logarithm of a day before DRH (RHY). The patterns witch presented in this paper were compared and calibrated with the old traditional and Oregon patterns (equation 1 and 2). The mean square error criteria (MSE) were used for these purposed. The results showed that our patterns are more accurate. MSE of our patterns are the lowest. The intercept of our patterns are nonzero and so it has physical meaning. Because the zero-DRH is not possible in the mountain regions. Moreover the RH of 15-hours has the greatest impact on the estimating DRH. This has been inconsistent with traditional and Oregon's patterns. The all Patterns that presented in this paper are purposed for Iran's mountainousregions. These equations decrease the errors of DRH.

Parameters such as strength and depth are characteristics of temperature inversion. Inversion strength is defined as the temperature difference between the surface and the top of the inversion and the depth of inversion is defined as the height of the inversion from the surface. The common approach in determination of these parameters is field measurements by Radiosonde. On the other hand the Radiosonde data are too sparse, so the main objective of this study is modeling the temperature inversion using MODIS thermal infrared data. There are more than 200 days per year in which the temperature inversion conditions are present Tehran. Mehrabad airport weather station was selected as the study area. 120 inversion days was selected from 2007 to 2010 where the sky was clear and the Radiosonde data were available. Brightness temperature in bands 27, 28, 31, 32, 33 and 34 of MODIS was calculated for these days. Then brightness temperature difference between the paired bands BT6.7-BT11, BT7.2-BT11, BT13.3-BT11, and BT13.6-BT11 were calculated and the correlation coefficients between these pairs and the inversion depth and strength calculated from Radiosonde were calculated. The results showed poor linear correlation. This could be due to the change of the atmospheric water vapor content. The polynomial mathematical models were used for modeling the temperature inversion. In order to calculate polynomial coefficients brightness temperature differences and the depth and strength of the temperature inversion obtained from of Radiosonde data, were entered in equations. Due to the large search space for finding the optimal model, Genetic algorithms were deployed. A model with the lowest terms and highest possible accuracy was obtained. The Model was built upon the differences between brightness temperatures in thermal bands. This for inversion strength resulted in as:Comparison with the Radiosonde measured data indicate that the inversion strength can be estimated with RMSE of 0.6o C and R2 of 0.84. Also depth of inversion can be estimated with RMSE of 45.59 m and R2 of 0.82. In this study, the methods of estimation of strength and depth of atmospheric temperature inversion using MODIS images were investigated. The method applied here consists of relationship between strength and depth of inversion with the differences of brightness temperatures extracted from MODIS thermal bands of 27, 28, 31, 32, 33 and 34. A multi parameter linear regression equation was applied to pairs of temperature differences and the strength and depth of inversions measured by Radiosonde at Mehrabad airport, Tehran. Due to the large searching space, an intelligent algorithm such as Genetic algorithm was deployed. Although the results are not as good as those achieved at polar region, still it is promising.