A GIS application for weather analysis and forecasting Through combining analyses at various levels with past analyses, the weather forecaster endeavors to visualize in his mind the weather processes at work, like the large-scale vertical motion, convection, radiative or advective cooling, etc. Fig. 4. is an ArcView generated map of the wind flow pattern at 500 hPa with the low pressure trough marked in green. The same trough as manifested at 850 hPa also is marked in the same chart by superimposing the 850 hPa wind flow pattern over the 500 hPa wind flow pattern. The locations of the trough at various levels of the atmosphere helps the forecaster in understanding the tilt, if any of the trough with elevation, which has high bearing on the expected weather of the trough. A forecaster studying the sequence of evolution of a weather system in a current chart requires analyzed chart for the previous hour of observation, and indicate the movement of weather systems like centers of low and high pressure, trough and ridges, etc. This is commonly done by marking positions of the centers of the system at the 6-hourly intervals and joining the successive points by a broken line, resulting tracks give ideas on movement of the system. In the Arc View plotted analyzed maps, the time sequence of maps can be super imposed and locations marked. The distance between successive locations is automatically obtained form the tools available. Conventionally, this work is done by the synoptitian using an illuminated tracing or 'light' table. The successive charts are placed one above the other and successive positions of the systems are marked. In figure 5, the movement of the trough along the 500 hPa level during the period 11th to 19th December 2000 is shown. Superimposing the 500 hPa wind flow pattern successively, for these days in the ArcView GIS created the map. Such maps help the forecaster study the speed and intensity of the trough in the past days for forecasting its behavior in the coming days. In the GIS distance between successive locations of the trough is readily available through the click of the mouse at the locations of interest, for calculation of its speed of progression.  Fig. 5. Locations of a low pressure trough in the westerlies at 500 hPa at 5.30 A. M. IST during 11th to 19th Dec. 2000. Once the forecaster is able to explain the recent weather evolutions taking place, he will be in a position to make prognosis of their future behavior from the knowledge of the physical and dynamical processes taking place in the atmosphere. It is of paramount importance that the forecaster is able to explain the processes realizing the current situation perfectly well before an attempt on forecasting its future behavior. In the processes of generating satisfactory explanation for weather systems, the forecaster need examine the weather charts of different levels of past few days back and forth. There is a necessity of superimposing the analyzed maps of different weather parameters one above the other for studying the physical processes at work in the atmosphere leading to the manifested weather. . In the figure Fig. 6. the specific humidity analysis is superimposed on the wind flow pattern using GIS, to study the moisture distribution and convergence in the atmosphere, in order to identify potential areas for fog, cloud, and rain formation. Conventionally a forecaster does this manually, and connecting between the weather systems available in the charts is done mentally. Success of this - procedure depends on the mental alertness of the forecaster, his experience and knowledge in the subject. In the case of the weather charts generated through GIS, these works can be carried out any number of times with the click of the mouse. The GIS platform provides opportunity for connecting the weather systems physically across the charts of different days and levels.  Fig. 6. Super imposition of the wind flow pattern and specific humidity (gm/kg) at 5.30 A.M. IST on 17th Dec. 2000. The red arrows show the wind flow, and the white contour lines with blue colored numbers across show the specific humidity distribution. The multicolored background is the surface created out of the specific humidity values. |