Detailed cloud resolving model simulations of the impacts of Saharan air layer dust on tropical deep convection – Part 1: Dust acts as ice nuclei W. Gong1, Q. Min1, R. Li1, A. Teller2, E. Joseph3, and V. Morris3 1Atmospheric Sciences Research Center, State University of New York at Albany, 251 Fuller Rd, Albany, New York 12203, USA 2Energy, Environment and Water Research Center, The Cyprus Institute, Nicosia, Cyprus 3NOAA Center for Atmospheric Sciences, Howard University Washington, DC 20001, USA
Received: 26 Jan 2010 – Accepted: 26 Apr 2010 – Published: 19 May 2010
Abstract. Observational studies suggest that the Saharan Air Layer (SAL), an elevated
layer (850–500 hPa) of Saharan air and mineral dust, has strong impacts on
the microphysical as well as dynamical properties of tropical deep
convective cloud systems along its track. In this case study, numerical
simulations using a two-dimensional Detailed Cloud Resolving Model (DCRM)
were carried out to investigate the dust-cloud interactions in the tropical
deep convection, focusing on the dust role as Ice Nuclei (IN).
The simulations showed that mineral dust considerably enhanced heterogeneous
nucleation and freezing at temperatures warmer than −40 °C, resulting in
more ice hydrometeors number concentration and reduced precipitating size of
ice particles. Because of the lower in the saturation over ice as well as
more droplet freezing, total latent heating increased, and consequently the
updraft velocity was stronger.
On the other hand, the increased ice deposition consumed more water vapor at
middle troposphere, which induces a competition for water vapor between
heterogeneous and homogeneous freezing and nucleation. As a result, dust
suppressed the homogeneous droplet freezing and nucleation due to the
heterogeneous droplet freezing and the weakened transport of water vapor at
lower stratosphere, respectively. These effects led to decreased number concentration
of ice cloud particles in the upper troposphere, and consequently lowered the cloud top height during
the stratus precipitating stage.
Acting as IN, mineral dust also influenced precipitation in deep convection.
It initiated earlier the collection because dust-related heterogeneous
nucleation and freezing at middle troposphere occur earlier than homogeneous
nucleation at higher altitudes. Nevertheless, the convective precipitation
was suppressed by reduced collection of large graupel particles and
insufficient fallout related to decreased sizes of precipitating ice
hydrometeors. On the contrary, dust increased the precipitation in
stratiform precipitation through deposition growth. Overall, the
comprehensive effects of mineral dust suppressed the precipitation by up to
Citation: Gong, W., Min, Q., Li, R., Teller, A., Joseph, E., and Morris, V.: Detailed cloud resolving model simulations of the impacts of Saharan air layer dust on tropical deep convection – Part 1: Dust acts as ice nuclei, Atmos. Chem. Phys. Discuss., 10, 12907-12952, doi:10.5194/acpd-10-12907-2010, 2010.