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1 I 8.15. Huggins, A. w., 1995: Mobile microwave radiometer observations: spatial characteristics of supercooled cloud water and cloud seeding implications. J. Applied Meteorology, 34, 432-446. ABSTRACT Previous studies of the spatial distribution of supercooled liquid water in winter storms Qver mountainous terrain were performed primarily with instrumented aircraft and to a . lesser extent with scans from a stationary microwave radiometer. The present work describes a new technique of mobile radiometer operation that was successfully used during numerous winter storms that occurred over the Wasatch Plateau of Central Utah to determine the integrated depth of cloud liquid water relative to horizontal position on the mountain barrier. The technique had the advantage of being able to measure total liquid from the terrain upward, without the usual terrain avoidance problems that research aircraft face in cloudy conditions. The radiometer also collected data during several storms in which a research aircraft could not be operated because of severe turbulence and icing conditions. Repeated radiometer transacts of specific regions of the plateau showed significant variability in liquid water depth over 30-60 min time periods, but also revealed that the profile of orographically generated cloud liquid was consistent, regardless of the absolute quantities. Radiometer liquid depth generally increased across the windward slope of the plateau to a peak near the western edge of the plateau top and then decreased across the relatively flat top of the plateau. These observations were consistent with regions where maximum and minimum vertical velocities were expected, and with depletion of cloud liquid by accretional ice particle growth across the mountain barrier. A comparison of data from the mobile radiometer and a stationary radiometer verified the general decrease in liquid depth from the windward slope to the top of the plateau and also showed that many liquid water regions were transient mesoscale features that moved across the plateau. Implications of the results. relative to the seeding of orographic clouds, were that seeding aerosols released from valley-based generators could at times be inhibited by stable conditions from reaching appropriate s.upercooled I iquid water regions and, as found, by others, the region of cloud most likely to be encountered by an AgI seeding agent released from the ground was also relatively warm compared to the ice-forming capability of the particular agent used in these experiments. Also, one convective case study that exhibited relatively wann temperatures in the cloud layer indicated that even in conditions that permit vertical transport to supercooled liquid zones, sufficient time for ice particle growth and fallout from seeded plumes on this plateau may be lacking. CONCLUSIONS A mobile microwave radiometer system has been developed that has proven to be very useful inthe study of orographic liquid cloud development. The system was operated during numerous winter storms on all weather roads that cross the Wasatch Plateau of central Utah. In addition to the measurement of microwave emission by liquid water and water vapor, the measurement of outside air temperature permitted the detection of temperature inversions in the mountain-valley system. Location measurements were made using geographic landmarks and road markers, but the system has now been equipped with a global positioning system (GPS) so atmospheric data and location data can be merged into the same dataset. Provided an adequate road network is available, the mobile radiometer can collect data in all but the most adverse conditions. Several experiments on the plateau were conducted by the mobile radiometer when 60