GROUND-CLOUD-RELATED WEATHER MODIFICATION EFFECTS J. Lee, Energy and Environmental Systems Division Argonne National Laboratory, Argonne, Illinois 60439 1. INTRODUCTION The proposed heavy lift launch vehicle (HLLV) would emit a large amount of thermal energy to the atmospheric boundary layer. The buoyancy resulting from this thermal energy release will raise the exhaust ground cloud to an altitude from several hundreds to several thousands meters, depending upon the ambient meteorological conditions. Meanwhile, the upward convective motion of the ground cloud and the surrounding air may result in the formation of a water- saturated cloud and associated precipitation. In addition, cloud microphysical processes may be affected by the production in the rocket exhaust of both cloud condensation nuclei (CCN) and ice-forming nuclei (IN). The principal concerns about inadvertent weather modification by SPS rocket effluents are (1) the possibility that the ground cloud might temporarily modify local weather and (2) the cumulative effects of nearly 500 launches per year. We shall discuss these issues of concern through the consideration of (1) the possible alteration of the microphysical processes of clouds in the general area due to rocket effluents and debris and cooling water entrained during the launch and (2) the direct dynamical and thermodynamical responses to the inputs of thermal energy and moisture from the rocket exhaust for given ambient meteorological conditions. 2. MICROPHYSICAL ASPECTS The central issue of these aspects is the possible production of cloud condensation nuclei and ice nuclei in the rocket exhaust ground cloud. Cloud condensation nuclei serve as particles upon which water vapor condenses to form water droplets that in turn form clouds and fogs. They play an important role in determining the colloidal stability of clouds and the formation of precipitation. In general, the addition of CCN may tend to slow down the warm rainformation processes if the total CCN exceeds 103 cm-3. However, if very large hygroscopic particles (giant nuclei with radii >25pm like those expected to come from launch pad debris) are present, the rain-formation process may be accelerated. In the Florida area, some rainfalls are associated with condensation-freezing processes in a deep convection cloud system. In an IN- deficient, supercooled cloud, the addition of IN is expected to stimulate ice nucleation processes and lead to precipitation, although the effectiveness of this process by means of artificial cloud seeding remains controversial. The recent measurements of Atlas/Centaur ground cloud1 indicated that concentrations of CCN were meteorologically significant. The initial emission was approximately 1.2 x 1017 CCN (active at 0.5% supersaturation); later, CCN were produced in the ground cloud at a rate of approximately 1 CCN cm"3s”1. Field and laboratory measurements1*2 of a Tital III ground cloud indicated that both the IN and CCN concentrations were of meteorological significance. The initial emission of CCN from the Tital III was approximately 1018 (active at 0.5% supersaturation) and further CCN were produced at a rate of 0.5 - 1 CCN cm”3s-1 for a period of four hours after launch. The high concentration of cloud condensation nuclei observed in both solid- and liquid-fueled clouds could alter the frequency and persistence of fogs and haziness on the surface and the precipitation processes in warm clouds.
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