The response of precipitation to aerosol through riming and melting in deep convective clouds Z. Cui1, S. Davies1, K. S. Carslaw1, and A. M. Blyth1,2 1Institute for Climate and Atmospheric Science, School of Earth and Environment, University of Leeds, UK 2National Centre for Atmospheric Science, UK
Abstract. We have used a 2-D axisymmetric, non-hydrostatic, bin-resolved cloud model to
examine the impact of aerosol changes on the development of mixed-phase convective clouds.
We have simulated convective clouds from four different sites (three continental
and one tropical marine) with a wide range of realistic aerosol loadings and initial
thermodynamic conditions (a total of 93 different clouds).
It is found that the accumulated precipitation responds very differently
to changing aerosol in the marine and continental environments.
For the continental clouds, the scaled total precipitation reaches a maximum
for aerosol that produce drop numbers at cloud base between 180–430 cm−3
when other conditions are the same. In contrast, all the tropical marine clouds
show an increase in accumulated precipitation and deeper convection
with increasing aerosol loading.
For continental clouds, drops are rapidly depleted by ice particles
shortly after the onset of precipitation. The precipitation is dominantly
produced by melting ice particles. The riming rate increases with aerosol
when the loading is very low, and decreases when the loading is high.
Peak precipitation intensities tend to increase with aerosol up to drop
concentrations (at cloud base) of ~500 cm−3 then decrease with further
aerosol increases. This behaviour is caused by the initial transition
from warm to mixed-phase rain followed by reduced efficiency of mixed-phase rain
at very high drop concentrations. The response of tropical marine clouds
to increasing aerosol is different to, and larger than, that of continental clouds.
In the more humid tropical marine environment with low cloud bases we find
that accumulated precipitation increases with increasing aerosol.
The increase is driven by the transition from warm to mixed-phase rain.
Our study suggests that the response of deep convective clouds to aerosol
will be an important contribution to the spatial and temporal variability
in cloud microphysics and precipitation.
Citation: Cui, Z., Davies, S., Carslaw, K. S., and Blyth, A. M.: The response of precipitation to aerosol through riming and melting in deep convective clouds, Atmos. Chem. Phys., 11, 3495-3510, doi:10.5194/acp-11-3495-2011, 2011.