1Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing, 100871, China
2NOAA Earth System Research Laboratory, Boulder, CO 80305, USA
3Chinese Academy of Meteorological Sciences, Beijing, 100081, China
Received: 30 Mar 2012 – Discussion started: 03 May 2012
Abstract. This study investigates the vertical transport of a passive tracer in a shallow cumulus boundary layer using large eddy simulations. The tracer source is at the surface in one case, and in the inversion layer in the other case. Results show that shallow cumulus clouds can significantly enhance vertical transport of the tracer in both cases. In the case with surface-borne pollutants, cloudy regions are responsible for the upward transport, due to the intense updrafts in cumulus clouds. In the case where pollutants are aloft, cloud-free regions are responsible for the downward transport, but the downward transport mainly occurs in thin regions around cloud edges. This is consistent with previous aircraft measurements of downdrafts around cumulus clouds and indicates that the downward transport is also cloud-induced. Cumulus convection is therefore able to both vent pollutants upward from the surface and fumigate pollutants in the inversion layer downward into the lower boundary layer.
Revised: 19 Oct 2012 – Accepted: 05 Nov 2012 – Published: 03 Dec 2012
Chen, G., Xue, H., Feingold, G., and Zhou, X.: Vertical transport of pollutants by shallow cumuli from large eddy simulations, Atmos. Chem. Phys., 12, 11319-11327, doi:10.5194/acp-12-11319-2012, 2012.