Interactions of mineral dust particles and clouds: Effects on precipitation and cloud optical properties

Abstract

[1] Numerical simulations were performed to investigate the effect of cloud-processed mineral dust particles on the subsequent development of cloud and precipitation and possible effects on cloud optical properties. A two-dimensional (2-D) nonhydrostatic cloud model with detailed microphysics was used. The initial aerosol spectra used in the 2-D model consisted of both background cloud condensation nuclei and mineral dust particles. These were taken from the results of three successive runs of a parcel model that simulates the interaction of dust and sulfate particles with cloud drops and trace gases and then evaporates the cloud drops. The results show that insoluble mineral dust particles become effective cloud condensation nuclei (CCN) after passing through a convective cloud. Their effectiveness as CCN increases because of a layer of sulfate that is formed on their surface as they are first captured by growing drops or ice crystals and then released as these hydrometeors evaporate. Upon entering subsequent clouds, these particles increase the concentration of the activated drops and widen the drop size distribution. The present work shows that in continental clouds the effect of cloud-processed dust particles is to accelerate the formation of precipitation particles, although the amount of precipitation depends on the concentration of the large and giant CCN. In maritime clouds the addition of cloudprocessed aerosol and mineral dust particles has a minimal effect on precipitation because the cloud starts with many large particles already. The addition of more CCN to either maritime or continental clouds increases their optical depth, even for those cases in which the precipitation amount is increased.

Generation of Internally Mixed Insoluble and Soluble Aerosol Particles to Investigate the Impact of Atmospheric Aging and Heterogeneous Processing on the CCN Activity of Mineral Dust Aerosol

“…In general, as mineral dust is transported and processed in the atmosphere it can develop a soluble coating typically composed of sulfates or nitrates, or organic species, consequently changing the physicochemical properties of the aerosol. Because the presence of soluble species on the dust surface increases the particle CCN activity, there will be an enhancement in the concentration of cloud droplets formed from mineral dust aerosol, consequently decreasing precipitation efficiency and changing the radiative properties of the cloud (Levin et al 2005;Rosenfeld et al 2001;Yin et al 2002). This work shows that CaCO 3 that has undergone chemical processing by nitrogen oxides to form calcium nitrate acts as a much more efficient CCN than freshly emitted CaCO 3 .…”

Direct radiative effects during intense Mediterranean desert dust outbreaks

“…and Chen, 2007), precipitation (Yin et al, 2002) and wind profiles (Choobari et al, 2012). In order to investigate the impacts of desert dust outbreaks on temperature fields in the atmosphere, we have reproduced the altitude-latitude cross sections (up to 8 km above mean sea level, a.m.s.l.)…”

CALIPSO observations of transatlantic dust: vertical stratification and effect of clouds

“…Twomey, 1977;Li-Jones et al, 1998;Kaaden et al, 2009;Schladitz et al, 2011;Ansmann et al, 2011). However, after being lifted in the air and mixed/coated with water-soluble materials such as sea-salt, sulfate, or nitrate by atmospheric processing (Levin et al, 1996;Yin et al, 2002), dust hygroscopicity can increase, which can cause changes in optical properties. In addition to mineral dust particles serving as ice nuclei (IN) (e.g.…”