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I I I I I I I I I I I I I I I I I I I However~ from the meteorological and hydrological studies there is sufficient encouragement that Phase II should be strongly considered by TVA manag~ment. The purpose of this field effort would be to determine through in-situ and remote measurements the temporal and spatial distribution of supercooled liquid water and ice crystals concentrations in cloud over the eastern TVA region during March~ April and May. In addition the transport and dispersion of ground and aerial released aerosols as well as wind flows over the basin would be determined during various weather conditions. These observations would help to confirm or deny as well as expand on the preliminary conclusions arrived at by the Phase I results. One note of caution is that one 3-month field program will be at the mercy of whatever weather regime occurs during this3-month effort. The representativeness of this weather regime can be compared to the 6 years used in the Phase I study. Hopefully the cloud and precipitation occurrences during this 3-month field effort will fall within the range of cloud and preci- pitation distributions found in Phase I. 3.0 Individual Study Results 3.1 Precipitation Statistics Daily precipitation totals above Chattanooga for both the intensive study years 1982-87 and for the period back through 1970 were compared to long-term records. The period of intensive study was much drier than the previous decade. In fact~ only 3 months of the 18 studied had precipitation exceeding the 97 year means. The results of this fairly simple study showed that months with below normal precipitation generally have as many precipitation days as do the wet months, they just lack the one or two extreme precipitation days which build up the daily average precipitation in a wet month. The fact that the average daily precipitation amounts are relatively light in the drier months suggests an opportunity for the application of cloud seeding to enhance precipitation assuming these weakly precipitating cloud systems provide suitable oppor- tunities. 3.2 Cloud and Precipitation Characteristics Six years of satellite imagery were analyzed to determine cloud characteristics and cloud organization over the eastern TVA region. Half-hourly images were used and summarized in 6 hourly averages. The study showed that large~ organized mesoscale convective systems~ either complexes or convective bands (squall-lines)~ produced almost 43 percent of the basin precipitation in March-May for the 6 years. Deep stratiform clouds asso- ciated with synoptic scale systems contributed 32 percent of the precipitation. Thunderstorms contributed 10 percent, and an additional 10 percent was contri- buted by the combination of cirrus/middle cloud and shallow stratus. Only those cloud types reaching well above the freezing level contributed substantially to the basin precipitation. xvi