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<br />radiometer data collection was tested. The experiments took advantage of the mobility of one radiometer, <br />as well as the measurements of two radiometers, to more completely describe the spatial and temporal <br />evolution of SL W in winter storms over mountainous terrain. The barrier under study was a relatively <br />isolated plateau which had roads open during the winter to allow crossing the barrier by vehicle. <br /> <br />A variety of storm situations were studied, but it was thought beforehand that the orographic stage of a <br />storm, in the absence of mesoscale bands, would be most conducive to study with a mobile platform since <br />the cloud field might be relatively steady-state, and fixed in position. In this situation the mobile <br />radiometer was used to develop a profile of liquid depth as a function of position over the windward slope. <br />Multiple traverses were made to' determine the variability of the cloud field. In the presence of mesoscale <br />cloud bands the intention was to monitor the liquid amounts in the band over the windward slope using the <br />mobile radiometer, while the stationary radiometer measured the liquid remaining in the band at the top of <br />the mountain barrier. The mobile radiometer.was also used to determine if cloud liquid varied, in a <br />persistent manner, across the top ofthe plateau, or along the upwind edge of the plateau. Selective <br />stationary positioning of the mobile radiometer allowed for a variety of upwind/downwind comparisons <br />between the two radiometers. <br /> <br />The mobile radiometer will be shown to have an advantage in following the changing spatial <br />characteristics of a mountain cloud system. In addition the mobile system is shown to offer a better means <br />of describing topographic influences by providing measurements over a scale generally greater than that <br />obtained by.radiometer scans. The two-radiometer system is covered in one example, and this technique <br />suggests an improvement over the evaluation of a cloud system by one unit, in that both upwind and <br />downwind liquid evolution can be simultaneously monitored. <br /> <br />SUMMARY AND DISCUSSION OF RESULTS <br /> <br />A new technique for studying the spatial characteristics of supercooled liquid water in winter storms over <br />mountainous terrain has been described. The examples presented focused on mainly on measuring the <br />location of liquid water relative to the terrain on the windward slope of the Plateau._ Past studies of <br />supercooled liquid water in the mountains of Utah and elsewhere in the western United States have <br />documented the temporal variability of liquid from storm to storm and on a smaller scale within the same <br />storm. In a few cases, radiometer scan data have been used to determine the spatial variability of SLW <br />(Sassen et aI., 1990). Mesoscale phenomena have been shown to sometimes produce a periodic variability <br />in cloud liquid (Sassen et aI.I990). For these reasons the mobile experiments on the windward slope <br />(Route I) during this first year of experimentation, were repeated as often as possible (52 traverses during <br />the 2-month project) to document the spatial variability of SL W more completely. At least one prior study <br />(Heggli et aI.1983) used several seasons of aircraft data to document the spatial characteristics of SL W <br />over the windward slope of the Sierra Nevada. The limitation with aircraft is the inability to detect SL W <br />close to the terrain, where other studies (e.g. Heggli and Rauber, 1988) have shown that the bulk of SL W <br />exists. Unaffected by this limitation, the complete mobile radiometer data set should provide .a much <br />. . <br />more accurate representation of the distribution of SL W relative to terrain. <br /> <br />A description of four mobile radiometer experiments from three different winter storin periods was <br />provided. This represents only a small fraction of the experiments conducted during at least 10 storm <br />periods during the 1991 Utah/NOAA field program, but some interesting results were obtained. The <br />modified D~ mobile platform proved to be capable of measuring liquid and vapor depth. The <br />measurements were made at times under adverse weather and road conditions, but data loss was probably <br />no worse than when a radiometer is operating in a stationary mode. Some extreme situations with very <br />poor visibility were avoided. <br /> <br /> <br />38 <br />