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Show tain SECTION 3. 0 SPECIAL SUPPORT STUDI ES 3. 1 tJumerical Models The advantages of applying numerical studies to e xperimental cloud seeding projects come from the ability to separate and study the various physical processes, and to isolate their effects on precipitation. Evaluation technique are enhanced by the predictions of a realistic model that can be compared to observed values. Various modification techniques can be simulated and the model used as a tool to optimize the effect of modificatio n procedur es . The Asol basic model used on this project has been d~scribed in previous reports, but Fon a brief description of the model, as we ll as present and projected improve- strea ments, is 1ncluded here. 3. 1. 1 Two Dimensional Mountain Airflow In the flow section of the model the motion is considered to be in an (x, z) plane with the x-axis along the wind and z-axis in the vertical. The total flow in this plane can be separated, using perturbation techniques, into a steady basic current and a small perturbation current. Adiabatic steady state frictionless motion is assumed. After solving the equations for the differential form of the perturbation velocity and neglecting the smaller terms 2 (7) + (f( z) - k ) w = 0 where w is the amplitude factor of the vertical velocity (sinusoidal with wave number k) and f (z) = ~ u 2 + (8) and t The equa modi and · The usec 194! 5ar mot rou u giv, This equation has been used for most of the past work on mesoscale flow over see mountains (Queney 1947, Scorer 1949, Wurtele 195 3, Palm 1958, Sawyer to 1960). Methods of solving it differ in detail but, in general, some simple distribution off (z) has been chosen and Fourier's theorem used. 3,1 1 Usi If the sinusoidal lower boundary condition is of the form ( 0 = f (k) cos kx = ha exp (-ak) cos kx Cal( (9) the equation may be integrated over all wave numbers to give an i dea l moun· 40 tion |
