Abstract
Abstract. The effects of electric charges and fields on droplet collision–coalescence and the evolution of cloud droplet size distribution are studied numerically. Collision efficiencies for droplet pairs with radii from 2 to 1024 µm and charges from −32 r2 to +32 r2 (in units of elementary charge; droplet radius r in units of µm) in different strengths of downward electric fields (0, 200, and 400 V cm−1) are computed by solving the equations of motion for the droplets. It is seen that the collision efficiency is increased by electric charges and fields, especially for pairs of small droplets. These can be considered as being electrostatic effects. The evolution of the cloud droplet size distribution with the electrostatic
effects is simulated using the stochastic collection equation. Results show
that the electrostatic effect is not notable for clouds with the initial
mean droplet radius of r¯=15 µm or larger. For clouds with the initial r¯=9 µm, the electric charge without a field could evidently accelerate raindrop formation compared to the uncharged condition, and the existence of electric fields further accelerates it. For clouds with the initial r¯=6.5 µm, it is difficult for gravitational collision to occur, and the electric field could significantly enhance the collision process. The results of this study indicate that electrostatic effects can accelerate raindrop formation in natural conditions, particularly for polluted clouds. It is seen that the aerosol effect on the suppression of raindrop formation is significant in polluted clouds, when comparing the three cases with r¯=15, 9, and 6.5 µm. However, the electrostatic effects can accelerate raindrop formation in polluted clouds and mitigate the aerosol effect to some extent.
Funder
National Natural Science Foundation of China
National College Students Innovation and Entrepreneurship Training Program
Reference28 articles.
1. Albrecht, B. A.: Aerosols, cloud microphysics, and fractional cloudiness,
Science, 245, 1227–1230, https://doi.org/10.1126/science.245.4923.1227, 1989.
2. Baumgaertner, A. J. G., Lucas, G. M., Thayer, J. P., and Mallios, S. A.: On the role of clouds in the fair weather part of the global electric circuit, Atmos. Chem. Phys., 14, 8599–8610, https://doi.org/10.5194/acp-14-8599-2014, 2014.
3. Beard, K. V.: Terminal velocity and shape of cloud and precipitation drops
aloft, J. Atmos. Sci., 33, 851–864, https://doi.org/10.1175/1520-0469(1976)033<0851:TVASOC>2.0.CO;2, 1976.
4. Beard, K. V. and Ochs III, H. T.: Collection and coalescence efficiencies for
accretion, J. Geophys. Res., 41, 863–867, https://doi.org/10.1029/JD089iD05p07165, 1984.
5. Beard, K. V., Durkee, R. I., and Ochs, H. T.: Coalescence efficiency
measurements for minimally charged cloud drops, J. Atmos. Sci., 59,
233–243, https://doi.org/10.1175/1520-0469(2002)059<0233:CEMFMC>2.0.CO;2, 2002.
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