Most atmospheric motions of different spatial scales and precipitation are closely related to phase transitions in clouds. The continuously increasing resolution of large-scale and mesoscale atmospheric models makes it feasible to treat the evolution of individual clouds. The explicit treatment of clouds requires the simulation of cloud microphysics. Two main approaches describing cloud microphysical properties and processes have been developed in the past four and a half decades: bulk microphysics parameterization and spectral (bin) microphysics (SBM). The development and utilization of both represent an important step forward in cloud modeling. This study presents a detailed survey of the physical basis and the applications of both bulk microphysics parameterization and SBM. The results obtained from simulations of a wide range of atmospheric phenomena, from tropical cyclones through Arctic clouds using these two approaches are compared. Advantages and disadvantages, as well as lines of future development for these methods are discussed.

[1] The size distribution and chemical composition of aerosol particles during a dust storm in the eastern Mediterranean are analyzed. The data were obtained from airborne measurements during the Mediterranean Israeli Dust Experiment (MEIDEX). The dust storm passed over the Mediterranean Sea and extended up to an altitude of about 2.5 km. The uniqueness of this dust storm is that approximately 35% of the coarse particles up to about 1 km in height were internally mixtures of mineral dust and sea salt. Just north of the dust storm, large convective clouds developed, and heavy rain was recorded by the radar on the Tropical Rainfall Measuring Mission satellite. The chemical and physical properties of the particles are used as initial conditions for conducting a sensitivity simulation study with the two-dimensional detailed spectral bin microphysical model of Tel Aviv University. The simulations show that ignoring the ice-nucleating ability of the mineral dust, but allowing the soluble component of the mixed aerosols to act as efficient giant cloud condensation nuclei (CCN), enhances the development of the warm rain process in continental clouds. In our simulations the rain amounts increased by as much as 37% compared to the case without giant CCN. Introducing similar coarse-mode particles into more maritime-type clouds does not have significant effect on the cloud or on the amount of rainfall. On the other hand, allowing the mineral dust particles to also act as efficient ice nuclei (IN) reduces the amount of rain on the ground compared to the case when they are inactive. The simulations also reveal that under the same profiles of meteorological parameters, maritime clouds develop precipitation earlier and reach lower altitudes than continental clouds. When the dust particles are active as both giant CCN and effective IN, the continental clouds become wider, while the effects on the more maritime clouds is very small. Citation: Levin, Z., A. Teller, E. Ganor, and Y. Yin (2005), On the interactions of mineral dust, sea-salt particles, and clouds: A measurement and modeling study from the Mediterranean Israeli Dust Experiment campaign,

We explore the effects of increases in aerosol concentration on cloud lifetime for warm convective clouds using a two‐dimensional single cloud model and three‐dimensional large eddy simulations (LES). The models include size‐resolved treatment of drop size distributions and warm microphysical processes. It is shown using a variety of soundings representing marine trade cumulus, and continental convective clouds that contrary to expectation, an increase in aerosol concentration from very clean to very polluted does not increase cloud lifetime, even though precipitation is suppressed. Cloud lifetimes are statistically similar although individual clouds may experience decreases in lifetime of 10–40%. An evaporation‐entrainment feedback that tends to dilute polluted clouds more than clean clouds is identified. It is proposed that the small changes in cloud lifetime are due to competing effects of precipitation suppression and enhanced evaporation, with the latter tending to dominate in these shallow clouds.

Abstract. Numerical experiments were carried out using the Tel-Aviv University 2-D cloud model to investigate the effects of increased concentrations of Cloud Condensation Nuclei (CCN), giant CCN (GCCN) and Ice Nuclei (IN) on the development of precipitation and cloud structure in mixedphase sub-tropical convective clouds. In order to differentiate between the contribution of the aerosols and the meteorology, all simulations were conducted with the same meteorological conditions.The results show that under the same meteorological conditions, polluted clouds (with high CCN concentrations) produce less precipitation than clean clouds (with low CCN concentrations), the initiation of precipitation is delayed and the lifetimes of the clouds are longer. GCCN enhance the total precipitation on the ground in polluted clouds but they have no noticeable effect on cleaner clouds. The increased rainfall due to GCCN is mainly a result of the increased graupel mass in the cloud, but it only partially offsets the decrease in rainfall due to pollution (increased CCN). The addition of more effective IN, such as mineral dust particles, reduces the total amount of precipitation on the ground. This reduction is more pronounced in clean clouds than in polluted ones.Polluted clouds reach higher altitudes and are wider than clean clouds and both produce wider clouds (anvils) when more IN are introduced. Since under the same vertical sounding the polluted clouds produce less rain, more water vapor is left aloft after the rain stops. In our simulations about 3.5 times more water evaporates after the rain stops from the polluted cloud as compared to the clean cloud. The implication is that much more water vapor is transported from lower levels to the mid troposphere under polluted conditions, something that should be considered in climate models.

This study evaluates the possible impact of aerosol solubility and regeneration on warm-phase orographic clouds and precipitation. The sensitivity evaluation is performed by simulating cloud formation over two identical 2D idealized mountains using a detailed bin microphysical scheme implemented into the Weather Research and Forecasting model (WRF) version 3. The dynamics, thermodynamics, topography, and microphysical pathways were designed to produce precipitating clouds in a linear hydrostatic mountain wave regime. The cloud over the second mountain is affected by regenerated aerosols advected from the cloud over the first mountain. Effects of aerosol solubility and regeneration were investigated with surface relative humidity of 95% and 85% for both clean and polluted background aerosol concentrations. Among the findings are the following: 1) The total number of cloud drops decreases as the aerosol solubility decreases, and the impacts of aerosol solubility on cloud drops and precipitation are more significant in polluted clouds than in clean clouds. 2) Aerosol regeneration increases cloud drops and reduces the precipitation by 2%–80% in clouds over the second mountain. Regenerated aerosol particles replenish one-third to two-thirds of the missing particles when regeneration is not considered. 3) Different size distributions of regenerated aerosol particles have negligible effect on clouds and precipitation except for polluted clouds with high aerosol solubility. 4) When the solubility of initial aerosol particles decreases with an increasing size of aerosol particles, the modified solubility of regenerated aerosol particles increases precipitation over the second mountain.