In this study, cloud formation and its seeding efficiency at room temperature have been envestigated by different particles such as ambient aerosols, salt, and smoke induced by burning match. In the first step, the effect of ambient aerosol concentration on the time of clearing cloud was considered. Since the aerosols concentration is almost constant during the day, there for it is accepted as base point for comparison of not-seeded and seeded condition for cloud formation and precipitation. The effect of aerosols concentration variation in different days also was considered. In the second step, the effect of salt and smoke injected as seeding nuclei to the chamber on the cloud clearing time was studied. The salt solution density was used with 20, 30 and 40 g/lit. The time of cloud clearing by the salt nuclei is less than ambient aerosols. The results showed, the more salt solution density, the less cloud clearing time. In most experiments with increasing smoke concentration the precipitation increased too and extraordinary amounts of smoke concentration rarely caused cloud to be overseed. The experimental results on nucleation efficiency showed that hygroscopic and giant salt particles are more efficient than smaller smoke particles but with respect to higher concentrations of smoke it is observed that the cloud has precipitated in shorter time by smoke nuclei. In fact, if it would be possible to make the experiments under the quantity control coditions, the cloud could be cleaned with salt nuclei in the shorter time.

Introduction: Cloud seeding is one of the most known aspects of weather modification in most regions of world, that according to the World Meteorological Organization among all weather modification applications, most of operational projects were focused on the increase in rain. Determination of the area under effect of seeding materials, known as the target area during measuring its efficiency is one of the most challenges in applying the cloud seeding method. In the current method of determining the target area, in measuring the cloud seeding project in Iran, the seeding materials from shooting place is transferred in GIS environment for two hours using wind speed and direction output of WRF mode in wind direction. Considering the complexities and lack of present sureness in determination methods of target area, in this paper it was attempted to provide a new method in order to determine the target area using the martial distribution model.

In this study, a one-dimensional transient cumulonimbus cloud is modeled to be seeded by liquid CO2. The model includes microphysical and dynamical processes associated with glaciogenic seeding by homogenous ice nucleation and two thermal terms associated with seeding by −90 ºC liquid CO2. For this model, the study concentrates on five types of hydrometeors, namely, cloud droplet, cloud ice, snow, hail/graupel, and rain. Point and horizontal seeding methods are implemented to observe their implications for rainfall enhancement, amount of hail/graupel production, vertical cloud extension, and radar’s reflectivity. In addition, the seeding temperature effects on the rainfall and microphysical processes are investigated. The results of the study show that, the rainfall enhancement and rainfall intensity in the point seeding case are more than those in the horizontal seeding. Moreover, the study reveals that, there is a vertical cloud extension enhancement of 0.5 km for clouds with top height of 10.5 km. The most important sources of the rain water production are found to be the accretion of cloud water by rain (P RACW) and by snow (P SACW), and for the graupel production is dry growth of the graupel (P GDRY). The results of this study are confirmed by the results of other investigators and are found to be comparable with the recorded data at rain gauge stations.

One of the main obstacles of sustainable developmenthas been the limitation of water resources and the shortage of precipitation. In orther to challenge this problem, cloud seeding is considered one of the modem methods in this respect. One of the most necessary factors in suitable site selection for cloud seeding is precipitation climatology. The present research has been performed in this region, using of daily precipitation data of regionstaionsin 20 yearstatisticalperiod. Findings of this research show that more than 80 percent of yearly rain in this region has been in winter and early in spring (between December to Aprill) while more than go percent of this rain is in winter. The rain is not the same in all places and isohyet is more than 300mm so that the fuost yearly rain is an the central high mountains such as Hezar, laleh zar and the Barez mountaions. About 35 Percent of rain in the most region stations devotes to rainy periods of heavy (between 10 to 3Omm)and rainy periods of exceptional (more than 30mm). More than 60 percent of wet periods is made up one day rain 30 percent of two day successive rain and less than 10 percent 3 or greater day rain. Rainy periods of heavy and exceptional and 3 or greater - day rains are also in centeral mountains of this region. Therefore from December till Aprill and the southern slops of central mountains of region, have provided suitable conditions for the performance of cloud seeding projects.

Numerous numerical experiments have been performed to cloud model seeding over the last two decades. Silver iodide nucleation has been parameterized using different methods in these studies. The results of these studies indicate that cloud seeding can change the distribution of precipitation in most cases. Moreover, most of these numerical simulations have been used only in the field of convective cloud seeding and are incapable of complete simulation of atmospheric conditions. For this purpose, the governing equations should be parameterized in three dimensions for the general case and be used in the appropriate model. In this study, the effect of cloud seeding, whether increasing or decreasing in rainfall, has been studied. For this purpose, the WRF numerical model has been developed to simulate the cloud seeding. Since, it is virtually impossible to repeat experiments under similar meteorological conditions, a model that can simulate the effect of cloud seeding on microphysical processes and precipitation could avoid many speculations or inaccurate estimates. The basic hypothesis of cloud seeding is based on the physical principle that at sub-freezing temperatures the equilibrium vapor pressure relative to ice is lower than the equilibrium vapor pressure relative to liquid water. Therefore, the saturated environment with 100% relative humidity relative to water (RHW = 100%) will be supersaturated relative to ice at temperatures below zero degrees Celsius (Pruppacher and Klett, 2010). As a result, in a cloud that is saturated with liquid water and composed of supercooled cloud water droplets, ice particles grow rapidly to form larger and heavier drops which could be fall as rain drops. In that environment, tiny, supercooled cloud droplets either grow in upward motion or evaporate to provide vapour for ice to grow. Therefore, in the cloud seeding with silver iodide, ice particles are expected to be produced and grow in the cold part of the cloud, and the liquid water of the cloud will be transformed into ice phase species more quickly. The operational cloud seeding project has been carried out in the northwest area of Iran. At the time of operational project, the seeding target area was under the influence of the eastern Mediterranean low pressure center, this trough has caused the formation of divergence in its downstream in the upper levels of the atmosphere in the target area and has led to the formation of severe upward movements. Stable and thick clouds have formed in the area. Under the above mentioned environmental conditions, 44 pyropatrons of 4% silver iodide were fired at the target area by a seeding aircraft. Silver iodide particles measuring 0. 1 to 1 mm are very effective in freezing nuclei. In this study, the effect of seeding is coded based on the model of Meyers et. al (1995) and Seto et. al (2011) by applying the seeding conditions into the Morrison scheme code within the WRF model and changing the number density and mixing ratio of cloud ice due to the silver iodide injected into the atmosphere. By simulating the effect of cloud seeding, meteorological quantities, including precipitation under seeding conditions, are estimated by changing the Morrison microphysical scheme in the WRF model. The WRF numerical model was also run in control mode (without applying cloud seeding relations). By comparing the output rainfall of the numerical model in seeding mode with the output rainfall of the numerical model in control mode, the amount of cloud seeding effect was determined. The results showed that the changes resulting from seeding in the studied cloud seeding operation were not favorable in all stations, and in some cases, the decrease in precipitation was seen 2 hours after seeding. This decrease in some stations, such as Maragheh, Tabriz, Sahand, and Khoy, starts from seeding time and continues until the end. But in a station like Sarab, although the rainfall decreases slightly at the beginning of cloud seeding, over time, it increases to 7% after two hours. While seeding in Parsabad, and Ahar stations resulted in precipitation enhancement by 3%, 9%, and 27% two hours after seeding, respectively.

Determination of affected area by seeding agents, the so-called target area, is an essential requirement for evaluation of cloud seeding projects. The most conservative and credible estimates of seeding effects were obtained from control matches drawn from outside the operational target within 2 hours of the time that each unit was seeded initially (DeFelice et al., 2014). A coupled modeling system consisting of the mesoscale WRF model and the Hybrid Single-Particle Lagrangian Integrated Trajectory Model (HYSPLIT), provides capability to simulate the transportation and dispersion of seeding materials and to characterize target area on the map. This study is devoted to sensitivity analysis of simulated dispersion patterns to several parameters including different configuration based on physical parameterizations used in WRF model, horizontal and temporal resolution of WRF and spatial resolution of HYSPLIT, to determine the most probable dispersion patterns. Since temperature and wind parameters are the most important parameters in cloud seeding operations, they are measured instantaneously at 1-second intervals at the flight height of the airplane during each flight and therefore, they are very valuable data to assess the performance of the WRF model in simulating these fields. Hence, at first the WRF model outputs such as temperature and wind are validated by data measured by the airplane. Results indicate that there is an acceptable agreement between field data and WRF outputs that are going to be used as input data for dispersion model. In this study, eight configurations of the WRF model based on different physical parameterization schemes are used for 34 flights in cloud seeding project in 2015 and HYSPLIT model is run by these types of input data and resulting target area are compared on the map. Then, HYSPLIT model is run for four selected seeding operations according to three temporal and two horizontal resolutions of input data in addition to three spatial resolutions of HYSPLIT model and the transport of seeding plumes is characterized on the geographical map. The results indicate that dispersion model is sensitive to all mentioned parameters. Also, in most cases, dispersion model results at the flight height of cloud seeding aircraft are significantly influenced by the input data provided by the WRF model. In addition, the dispersion model results are less sensitive to other parameters. Furthermore, when the spatial resolution of the HYSPLIT model is close to the horizontal resolution of the input meteorological data provided by the WRF model, affected area of seeding agents is more integrated and therefore there is a greater degree of certainty in determining the target area.

In world droughty regions, precipitation Enhancement through cloud seeding is one of the modem methods for water sypply in this respect. It is possible to succeed through identifying suitable site selection for cloud seeding and wide studies on climatology of cloud. The present research has been performed in southern mountains of Kerman, using the data of clouds in Barn, Baft. miandeh, Kahnouj, Sirjan and Minab stations and also upper atmosphere statiOn of Kerman. Findings of the research show that the most frequencies of occurrence of low clouds and overcast sky are observed in rainy cold months (from December till April especially March) in the region. The highest percentfrequency (60-94%) of height of clouds base with vertical development occur in the range of 2760 to 3760m above sea-level in Kerman, Baft and Sirjan stations. From December till March freezing level is in the lowest height in the range of 2998 to 3473m (ASL), and is closer to the heIght of low clouds base.Furthermore, more than 90% of the mean height of base,of low clouds occurs in above freezing level. Therefore from December till April, the height in which the highest percent of occurence of freezing level and the maximum height of low cloud base occur, have more suitable conditions for the performance of cloud seeding projects in the region.

Iran is located in an arid and semi-arid region and has experienced a reduction of average rainfall in recent years. This has turned the attention to the use of new methods such as cloud seeding to achieve more water resources. In this regard, cloud seeding operations have been carried out in the country since 1998. The purpose of this study was to evaluate cloud seeding projects in the 2015 water year (January, February, and March 2015) in the central region of Iran, including the provinces of Yazd, Kerman, Fars, Isfahan, and some adjacent provinces. The evaluation was performed statistically using stepwise multiple regression. Two different approaches have been used for evaluation. In the first approach, precipitation at stations located in the target area of cloud seeding operations is estimated based on the precipitation at stations in the control area using stepwise multiple regression and then taking into account a 90% confidence interval for this estimate, the effectiveness or ineffectiveness of the cloud seeding operation at each station is determined. In the second approach, the volume of precipitation in each province in the target area is estimated based on the precipitation in stations outside in the control area using stepwise multiple regression and then by considering a 90% confidence interval for this estimate, the effectiveness of cloud seeding operations on the rainfall volume of each province has been investigated. The target area in different months was selected based on the HYSPLIT model results. Due to the inconsistent spatial distribution of rain gauges in the target areas, parts of the target areas lacking enough rain gauges were excluded from further analysis. To define the boundaries of the exclusion areas, Inverse Distance Weighted (IDW) method was used to find the influence of the radius around each rain gauge. The influence radius values were selected as 93940, 89569, and 149015 m for the months of January, February, and March, respectively. Finally, the minimum value of 89569 m was selected as the influence radius. The results of both methods indicate the impact of cloud seeding operations this year in these areas. In particular, the volume of precipitation in February in all provinces located in the target area of cloud seeding operations has increased from 15 to 80 percent. Surface runoff generated from the increased precipitation due to cloud seeding were estimated by the two methods of Soil Conservation Service (SCS) and Rational method. The estimated surface runoffs generated by SCS and rational methods were 1318. 5 and 1329. 5 million m3, respectively. The groundwater recharge in the three months of January, February, and March is estimated as 105. 3, 425. 6, and 156. 3 million m3, respectively. It is important to note that runoff and groundwater recharge estimations by the method used in this study are subject to high uncertainties, and the estimations can only represent the order of magnitude of impacts of cloud seeding operations, and therefore, exact numbers should not be used for water resources planning and management purposes. Further investigation in areas with more rain gauges can assist in a more accurate assessment of could seeding operations.

Fog is one of the meteorological events that help reducing the horizontal and vertical visibility. Despite usefulness in agriculture and protection of plants against freezing; it has an important role in life and property damages in transportation sector. This natural and destructive event causes major difficulties in aviation and prevents flight operations. Generally, fur fog dispersion and clearing weather, it is necessary to have knowledge about formation and types of fogs and investigate them in detail. New technologies for fog dissipation must then be applied for fog dispersion using cloud seeding technology. In this paper, after reviewing the processes of formation of fog and its physical construction, long term data and diagrams of foggy days in 30 cities of Iran were made and consequently zoning maps were produced. Field research results of fog dissipation in different regions of Iran were then discussed. Results of field tests indicate that cloud seeding method using liquid carbon dioxide by moving vehicle for super - cooled fog is one of the best methods and causes clearing weather and increasing visibility field after 30 minutes. The successful results of tests indicate that cloud seeding method could be applied for fog dissipation and clearing the atmosphere. In last part of the paper, numerical microphysical processes of super - cooled cloud seeding are discussed.

One of the most important factors in suitable site selection for cloud seeding projects is to study the atmospheric flows and the winds conditions of the region. The present research has been perfonned in centeral Iran, using the data of speed and direction of the winds on the upper levels of atmosphere in Kennan, Bandar Abbass, Shiraz and Isfahan stations and surface wind data of the Earth in Kennan ,Bandar Abbass, Baft, Yazd, Shiraz and Isfahan synoptic stations. Windroses of the atmospheric standard levels show that the highest ffequencies of winds and the direction and the speed of air flows are in the west and south- west of these regions in the rainy cold months. In rainy days, more than 80 percent of the winds blow in west at the 700 Hpa level of these stations. In the same rainy days, the direction of prevailing winds is in the middle and upper levelsof atmospherein these stationsis between1800-3300and the highestspeeds at the 700 Hpa, the 500 Hpa and the 300 Hpa are 54 kts, 98 kts and 162 kts, respectively. The direction of prevailing winds at the surface are between 1800- 3600 and the highest speed is 18kts. Is south and south -west and even south-east winds" direction at the 850 Hpa of Bandar Station in, rainy days, in addition to the high mountains of Kennan, are close to the sea in the south. These flows receive. heat and humidity while passing the south waters and strike the southern slops of the mountains. When they enter in to the centerallran, they can play an important the mountains. When they enter in to the centeral Iran, they can play an important role in increasing instability and precipitation. Based on the fmdings of the present research, it is concluded that using the above mentioned positive points is vel)" necessary to carry out the cloud seeding projects and that radar can be installed in the central mountains of south Kerman and Shir-Kuh in a place which can cover 170°-340°