HR: 1330h
AN: A53A-07    [Abstracts]
TI: The Influence of the Electric Field on Thunderstorm Microphysical Development Simulated with an Explicit Microphysics Model
AU: * Phillips, V T
EM: vaughan.phillips@noaa.gov
AF: Phillips, V.T.J., Atmospheric and OceanicSciences Program (AOS), Princeton University, Princeton, NJ 08540 United States
AU: Andronache, C
EM: andronac@bc.edu
AF: Andronache, C., Boston College, Chestnut Hill, MA United States
AU: Sherwood, S
EM: steve.sherwood@yale.edu
AF: Sherwood, S., Department of Geology, Yale University, New Haven, NH United States
AB: Electric fields influence the microphysics of aerosol-cloud interactions. Hence, nucleation of ice is sensitive to the charge on nuclei. Furthermore, there is an increase in the collision efficiency when charged aerosol particles collide with droplets ('electroscavenging'), and rates of contact ice nucleation are enhanced by the charge on aerosol particles (Tinsley et al. 2000, Tripathi and Harrison, 2002). In addition, electric fields (EF) affect the collisional growth rate of hydrometeors and their fall velocity. The aim here is to assess how the collection efficiency for the coagulation of hydrometeors may be modified by a typical EF in a thunderstorm. Particular focus is given to effects on the generation of anvil ice particles. This is done by imposing a realistic EF in the control simulation with an Explicit Microphysics Model (EMM) of the storm, observed on 18th July 2002 near Florida during the Cirrus Regional Study of Tropical Anvils and Cirrus Layers - Florida Area Cirrus Experiment (CRYSTAL-FACE), as described by Phillips et al. (2005). An additional aim is to analyze how updraft speed (w) and environmental CCN concentration may affect the charge separation process. The warm rain process is intensified and there is a 30-40% reduction in the anvil ice concentration when an evolving height-dependent EF, typical of continental electrified thunderstorms, is prescribed and applied to the collection efficiencies for coagulation processes in the model. The electric dependence of the collision efficiency for drop-drop collisions is the cause. There is a 150% increase in the broad peak of average mixing ratio of rain near the freezing level (see Figure 1). This boosts the mixing ratio of precipitation-sized ice in the lower half of the mixed phase region, changing the number of charging collisions and depleting the supercooled cloudwater. Primarily because of the high sensitivity of the Hallett-Mossop (H-M) process of ice particle multiplication with respect to changes in the warm rain process, the total charge separated is reduced by about an order of magnitude when these electric fields are applied to coagulation processes. This suggests that an electrical-microphysical feedback may exist between the electrification, warm rain and H-M processes in continental storms that are similar to this particular model cloud. Furthermore, the total charge separated is reduced by an order of magnitude, when w is reduced by 40%, at each EF strength assumed for coagulation. This is because graupel particles are smaller and H-M splinters are fewer. Some aspects of the land-ocean contrast in lightning occurrence are also discussed. Phillips, V.T.J., S. Sherwood, C. Andronache et al. (2005). Q. J. R. Met. Soc. In press. Tinsley, B. A., R. P. Rohrbaugh, M. Hei, and K. V. Beard, (2000). J. Atmos. Sci., 57, 2118-2134. Tripathi S.N. and Harrison R.G., (2002). Atmos. Res., 62, 57-70.
DE: 0320 Cloud physics and chemistry
DE: 3324 Lightning
SC: Atmospheric Sciences [A]
MN: 2005 Joint Assembly