نشریه نیوار
پیاپی 74-75 (پاییز و زمستان 1390)

Land Surface Schemes (LSMs) are among the most important components used in climate predictions, numerical weather prediction and hydrology. Their most important task is the solution of energy and water budget in land surface. MM5 model is the fifth- generation NCAR / Penn State mesoscale model used in studying of air pollution, numerical weather prediction and hydrology. This model contains of land surface parameterization schemes, radiation, convection, boundary layer and rainfall schemes, which are connected directly to each other. The Land surface parameterization scheme in this mesoscale model contains of Bucket, Force-Restore, five- layer soil, OSU and PX schemes. In this paper, according to the importance of the land surface schemes, it has been tried to study the physics details of these land surface schemes used in mesoscale model of MM5 in detail.

The effect of accuracy of weather prediction on all aspects of normal life and special affairs is clear. Today, with optimal utilization of various models and knowledge of their accuracy, the effective steps have been taken in order to achieve this aim. The operational use of one of these models, global model, has not been done yet in our country. In this study, the barotropic model with spectral method was developed to predict the geo-potential field. Due to the high volume of information and capacity limitation of personal computers, model is performed with low resolution. Geo-potential field is predicted with leap frog scheme, and then with using the reverse of these conversions we can return to physical space from spectral space.Implementation of this model shows relatively good results. Some assumptions such as existence of baroclinic atmosphere, releasing latent heat and considering earth topography, can achieve a better prediction from this model.

One of the natural calamities that have influenced Khuzestan Province because of geographical situation and its neighborhood with big areas of desert regions is undesirable phenomenon of dust. So for dust considering, it select 10 synoptic stations in Khuzestan province with recording data from 1996 to 2005 years. Statistical analysis is performed by using spatial distribution maps and trend diagram that are extracted from geographical information system software's (GIS) for the aim of statistical analysis. It is found that the average of dusty days in warm period is more than cold period of the year. In Khuzestan region, the number of dusty days decreases from the west to east. Spring among seasons and July among months have the most average number of dusty days. Annual trend of days associated with this phenomenon is increased during 1996 to 2005.

Oscillations and changes in climatic elements due to global warming make variability in precipitation tempo-spatial distributions. Precipitation fluctuations, as one of the probable results of inter-decade climate changes, can have a significant effect in environmental and humane fields. Following the phenomena of atmosphere getting warmer and fluctuation's occurrences and changes in climate factors, we have used the daily precipitation data of 260 stations located inNorthwest of Iran in the present research and made benefits of Kriging interpolation technique as an optimal interpolation technique and have changed the location data into wide range data. Besides the presentation of a clear and exact image of the general conditions of precipitation, we tried to show the normal climate conditions by using force mapping technique and precipitation deviation maps. The results showed that from the first to the fourth decade, the negative anomaly progress during all the months of the year in average annual precipitation amount is increased and the precipitation in a wide range of the region had a decreasing trend in the whole period. However, the third decade has been a seasonal precipitation phase and the fourth decade is considered to be the dry phase.

Sediment transport is one of the most important parameters in coastal engineering issues. It is very important to define the sediment transport rate in the sea morphology and construction of port installation, ponds and waterfronts. The issue mentioned above is so affective on anticipated design life, safety of which against sedimentation and defining the dredging period. Sediment transport in Shahid Bahonar port was evaluated in the research. First, Sediment transport was calculated using data such as wave, flow and aggregation of the region and semi – empirical methods. Then it was compared with sediment transport resulted from hydrographic maps and it is calibrated. The results demonstrated that Biker method is more accurate in the region.

Khuzestan province which is located in southwest of Iran usually has low rainfall although sometimes heavy rain events records in this area. Recognition of Mechanism of forming, trajectory and humidity content of weather systems, that are associated with rain event, can have role important in distinction early flood, control flood, raceway, and watershed and reduce flood damage. First, the dates of heavy rains exceeded to 70 mm, occurring in Khuzestan province, were extracted during 1960 to 2000. Then using NCEP\NCAR reanalysis data, synoptic structure including mean sea level and geopotential height at 500 hPa levels were examined in all rain events, afterward, the composite structure was obtained by averaging in similar cases and finally synoptic structure composite was analyzed. Over all, the result showed five different synoptic patterns that can produce heavy rains in south western parts of Iran. They are called Sudan, special Sudan that extended to eastern Mediterranean, Sudan- Mediterranean low, northern Africa, Mediterranean low pressure, respectively. The results of this study also showed that in addition to Sudan lows, Mediterranean systems can produce heavy rains in south western part of Iran although their frequencies are less than Sudan lows. Also some weather systems that formed in west northern of Africa, after passing from north eastern Africa and Red sea close to Saudi Arabia and Iran, have important role to produce heavy rains in this region. Because of importance of forming area of weather systems and their trajectories in heavy rain events, it should pay more attention in determining the weather systems types that produce heavy rains in Khuzestan province.

Evapotranspiration is one of the basic parameters for agricultural water planning. Thereare various formulas to estimate this parameter such as FAO Penman-Montith method and Evaporation pan method. In the pan method, the amount of reference evapotranspiration (ETo) estimated by multiplying pan coefficient to amount of water vapor from evaporation pan. One of the limitations of pan method is the need to weather parameters (e.g., relative humidity and wind speed) to estimate Kp. In case we have access to these weather parameters other methods of evapotranspiration estimation are preferred. The aim of this study was to determine monthly and seasonal values of Kp in the Kermanshah province. Kp was estimated by dividing calculated ETo (It is calculated based on daily weather data) over pan evaporation. Spatial and temporal variations of Kp have been investigated based on daily weather data (2000 – 2009) in four synoptic weather stations in Kermanshah province. Results showed that Kp in summer is lower than in autumn and spring. Moreover, results indicated that Kp has inverse relation with altitude. In addition daily and monthly pan coefficients have been calculated for Kermanshah airport station based on the FAO method and compared with the estimated pan coefficients in the current study. However, there was low correlation between daily results, but correlation coefficient between monthly results was high (R2=0.89).