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<br />4 <br /> <br />2.0 METHOD <br /> <br />The atmospheric water balance study described here is done two <br /> <br />dimensionally with coordinates of pressure and horizontal distance <br /> <br />along the direction of the wind. The air and terrain are assumed to <br /> <br />be uniform in the direction perpendicular to the flow. Along the plane <br /> <br />defined by the wind direction and pressure are one rawinsonde site and <br /> <br />two radiosonde sites located as shown schematically in Figure 1, The <br /> <br />rawinsonde is located upwind of the cloud, one radiosonde is near the <br /> <br />crest of the ridge and cloud and the other is downwind of the cloud. <br /> <br />Precipitation from the cloud is measured as well as possible over the <br /> <br />area using precipitation gauges and snowboard data. These precipitation <br /> <br />~ <br /> <br />data are to be used as a check on the aerological analysis. <br /> <br />e <br /> <br />Balloon ascents are made from each of the three stations at approxi- <br /> <br />mately two hour intervals during the precipitation episode. The data <br /> <br />" <br /> <br />received is then used to compute vertical profiles of temperature, mixing <br /> <br />ratio, and equivalent potential temperature for all three stations. Pro- <br /> <br />files of wind speed and direction are obtained from the upwind station <br /> <br />alone. The profiles are then plotted in time sequence for each station, <br /> <br />resulting in pressure-time cross sections for each of the above para- <br /> <br />meters at each station. A value of any of those parameters may then be <br /> <br />interpolated to any pressure and time desired at the station locations. <br /> <br />Trajectories of individual air parcels are then determined using <br /> <br />the assumption that the equivalent potential temperature, 8e, is con- <br /> <br />served. <br /> <br />.. <br /> <br />8e <br /> <br />8 exp [ <br /> <br />L w <br />CpTs <br /> <br />(1) <br />