Monday, 23 January 2012: 2:15 PM
Charge Modulation of Aerosol Scavenging
Room 244 (New Orleans Convention Center )
The presence of electric space charge in clouds occurs both at the borders of layer clouds, and in the updrafts of convective clouds (Grenet-Vonnegut process) and in the updraft regions of cyclones. Monte-Carlo processes introduced into a trajectory model of scavenging have produced an extensive set of rate coefficients for the modification of Brownian and phoretic scavenging rates by same-sign electric charges on aerosol particles and droplets. For small particles (less than about 0.1 microns in radius) the long-range repulsion significantly reduces the scavenging rates (electro-anti-scavenging) below the Brownian and phoretic values, and increases the scavenging time constants beyond the tens of minutes for typical clouds. For large particles (of effective radius greater than about 0.1 microns) the short range image force increases scavenging rates (electro-scavenging). The net effect is to increase CCN concentration and narrow and shift the size distribution to smaller sizes. Rosenfeld et al. (2009) have shown that such changes in CCN size distributions can increase updraft vigor and ultimately increase precipitation in barotrophic storms. In baroclinic storms an increase in vorticity is also expected to result.