Abstract
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.
Highlights
Apart from affecting the vertical structure of tropospheric radiative heat flux divergence, and modulating hydrologic cycle, convective clouds can enhance the vertical mixing of gaseous matter and aerosol
A passive tracer is used in large eddy simulations for studying the vertical transport of pollutants by shallow cumuli
The tracer source is continuous for 4 h at the surface in one case, and is instant in the inversion layer in the other case to investigate both the upward and downward transport associated with cumulus clouds
Summary
Apart from affecting the vertical structure of tropospheric radiative heat flux divergence, and modulating hydrologic cycle, convective clouds can enhance the vertical mixing of gaseous matter and aerosol. More recent studies proposed a refined view of vertical mass transport by cumulus that downdrafts outside clouds are confined in thin shell regions around cloud edges, and that the subsiding shell is attributed to evaporative cooling (Heus and Jonker, 2008; Heus et al, 2009; Jonker et al, 2008) This result can explain the finding that pollutants in the environment far away from cumulus clouds mix very slowly throughout the cloud layer (Verzijlbergh et al, 2009). Yin et al (2005) found that deep convective clouds can transport aerosols from the boundary layer, detrain and re-entrain the aerosols into the middle levels of clouds This process contributes to a large fraction of the aerosols inside hydrometeors (∼ 40 % by mass).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
