In order to determine the types of rain producing weather in Tehran, the rainy days of the station (days with more than or equal to 1 millimeter) were identified during the 1990-95 period. The 12 GMT pressure and height data of the area 200-47.5° and 35°-67.5°E were -extracted from the NCEP Reanalysis file for the grid points 2.50 apart. The synoptic systems and flow directions were determined according to the objective method of computing VORTICITY. The results first showed 24 pressure patterns for the three groups of light, moderate, and heavy precipitation days. Then these patterns were re-grouped according to their similarities into 10 weather types. These types consist of two cyclonic and anticyclonic, and 8 directional types corresponding to 8 geographical directions. The most frequent type was the Easterly and the most important rain producing type was the cyclonic type. The anticyclonic type was the least rain producing type. Cyclonictypes were more dominant and developed mostly in winter. The anticycloictypes showed lower frequency and concentrated in spring.This study showed that the VORTICITY COMPUTATION method is very effective and accurate and capable of quantifying the power of the weather types. The 500 hpa level had more significant effect on the precipitation than the surface pressure changes. The Syrian trough was the most important upper level system which controls the precipitation of Tehran.

In this paper, variable confinement parameters were successfully developed for compressible VORTICITY confinement. Three variable confinement parameters, that have velocity dimension, were defined, based on three artificial dissipation schemes. The resulting confinement parameters are functions of the spectral radii of the Jacobian matrices and the Jacobian matrices themselves.Therefore, the confinement parameter implicitly contains the grid size and other local fluid properties. Preliminary results for moving vortices showed that the new confinement parameters allow the capture of vortical layers that, effectively, do not decay in time, like Hu et al.'s confinement. Calculations of the supersonic base flow and supersonic shear layer showed good agreement with experimental and analytical data, especially for the variable CUSP confinement parameter. When variable confinement parameters are used, the tuning constant is equal to, or larger than, the equivalent value of the constant confinement (Hu et al.). This means that the tuning constant varies in a range smaller than that of the Hu et al. constant confinement, especially for the CUSP confinement parameter.

In order to investigate the spatial and temporal variations of relative VORTICITY in Iran, we have extracted the mean monthly relative VORTICITY data from the NCEP Reanalysis data site for the window of 45 to 62.5 degrees east and 25 to 40 degrees north for the 1971-2005 period with 2.5 degrees resolution. The mean monthly maps of the extracted data were drawn and described.The results showed that in winter season most of the country is under the positive relative VORTICITY indicating the existence of instability over the country and invasion of westerlies resulting in rain. The spring season was the same as winter, but toward the end of the season the negative VORTICITY was invading the country from the south. So that, in summer most of the country was occupied by the negative voriticity and resulted stability. During this season only the southern coasts of the Caspian was out of the negative VORTICITY occupation. During fall season the winter conditions were dominating the country from the north.

The apparent mass effect is enhanced significantly when the motion of a body changes quickly, such as a flapping wing or an impulsively started plate. Previous method for calculating the apparent mass of a given body needs to adopt the assumption of ideal flow and know the potential of velocity field arising in the fluid due to the motion of the body. However, the assumption of ideal flow is contrary to real fluid field and it is hard to obtain the potential of velocity field in most cases. In this paper, a new method based on the VORTICITY moment theorem for calculating the apparent mass of the body of revolution in the axial direction due to axial acceleration is developed. This method has no assumption of ideal flow and establishes the relationship between the apparent mass and the VORTICITY loops adjacent to the surface of the body. Using this method, the value of the apparent mass can be easily figured out and the physical mechanism of the apparent mass can be revealed from the view of the VORTICITY loop. The comparisons between different bodies have shown the influences of the fineness ratio (the ratio of the length to the maximum diameter) and the trailing edge type on the apparent mass.