Abstract A two-dimensional version of the Pennsylvania State University mesoscale model has been applied to Winter Monsoon Experiment data in order to simulate the diurnally occurring convection observed over the South China Sea. The domain includes a representation of part of Borneo as well as the sea so that the model can simulate the initiation of convection. Also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle. This allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck, which typically occupies several hundred kilometers of the domain. Frank and Cohen's cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area. The major conclusions are: Ice phase processes are important in determining the level of maximum large-scale heating and vertical motion because there is a strong anvil componen...

Numerical study of convection observed during the Winter Monsoon Experiment using a mesoscale two-dimensional model [presentation]

Social Network Analysis

The software package OPAC (Optical Properties of Aerosols and Clouds) is described. It easily provides optical properties in the solar and terrestrial spectral range of atmospheric particulate matter. Microphysical and optical properties of six water clouds, three ice clouds, and 10 aerosol components, which are considered as typical cases, are stored as ASCII files. The optical properties are the extinction, scattering, and absorption coefficients, the single scattering albedo, the asymmetry parameter, and the phase function. They are calculated on the basis of the microphysical data (size distribution and spectral refractive index) under the assumption of spherical particles in case of aerosols and cloud droplets and assuming hexagonal columns in case of cirrus clouds. Data are given for up to 61 wavelengths between 0.25 and 40 μm and up to eight values of the relative humidity. The software package also allows calculation of derived optical properties like mass extinction coefficients and Angstrom coefficients. Real aerosol in the atmosphere always is a mixture of different components. Thus, in OPAC it is made possible to get optical properties of any mixtures of the basic components and to calculate optical depths on the base of exponential aerosol height profiles. Typical mixtures of aerosol components as well as typical height profiles are proposed as default values, but mixtures and profiles for the description of individual cases may also be achieved simply.

Optical Properties of Aerosols and Clouds: The Software Package OPAC

A new bulk microphysical parameterization (BMP) has been developed for use with the Weather Research and Forecasting (WRF) Model or other mesoscale models. As compared with earlier single-moment BMPs, the new scheme incorporates a large number of improvements to both physical processes and computer coding, and it employs many techniques found in far more sophisticated spectral/bin schemes using lookup tables. Unlike any other BMP, the assumed snow size distribution depends on both ice water content and temperature and is represented as a sum of exponential and gamma distributions. Furthermore, snow assumes a nonspherical shape with a bulk density that varies inversely with diameter as found in observations and in contrast to nearly all other BMPs that assume spherical snow with constant density. The new scheme’s snow category was readily modified to match previous research in sensitivity experiments designed to test the sphericity and distribution shape characteristics. From analysis of four idea...

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Explicit Forecasts of Winter Precipitation Using an Improved Bulk Microphysics Scheme. Part II: Implementation of a New Snow Parameterization

Aerosols are of central importance for atmospheric chemistry and physics, the biosphere, climate, and public health. The airborne solid and liquid particles in the nanometer to micrometer size range influence the energy balance of the Earth, the hydrological cycle, atmospheric circulation, and the abundance of greenhouse and reactive trace gases. Moreover, they play important roles in the reproduction of biological organisms and can cause or enhance diseases. The primary parameters that determine the environmental and health effects of aerosol particles are their concentration, size, structure, and chemical composition. These parameters, however, are spatially and temporally highly variable. The quantification and identification of biological particles and carbonaceous components of fine particulate matter in the air (organic compounds and black or elemental carbon, respectively) represent demanding analytical challenges. This Review outlines the current state of knowledge, major open questions, and research perspectives on the properties and interactions of atmospheric aerosols and their effects on climate and human health.

Atmospheric aerosols: composition, transformation, climate and health effects.

Microphysics of Clouds and Precipitation

A theoretical model is described which determines the efficiency E with which aerosol particles of radius r are collected by water drops of radius a due to the combined action of Brownian diffusion, thermo- and diffusiophoresis and electric forces, in the absence of inertial impaction effects. The results of this model are combined with the results of our earlier model which determines the collection efficiency of drops for particles due to the combined action of inertial impaction, thermo- and diffusiophoresis and electric forces, in the absence of effects due to Brownian diffusion. Both models combined quantitatively determine the variation of E vs r for 0.001≤r≤10 μm, and 42≤a≤310 μm, for relative humidities up to and including 100%, and for electric charges on drops and aerosol particles ranging in magnitude up to that found under thunder-storm conditions. In particular, a combination of both models allows a quantitative description of the particle size range where the collection efficiency o...

On the Effect of Electric Charges on the Scavenging of Aerosol Particles by Clouds and Small Raindrops

Water vapor in the lower stratosphere may play significant roles in the atmosphericradiative budget and atmospheric chemistry; hence it is important to understand itstransport process. The possibility of water vapor transport from the troposphere to thestratosphere by deep convection is investigated using three-dimensional, nonhydrostatic,quasi-compressible simulations of a Midwest severe thunderstorm. The results show thatthe breaking of gravity waves at the cloud top can cause cloud water vapor to be injectedinto the stratosphere in the form of plumes above a thunderstorm anvil. Meteorologicalsatellites and aircrafts have observed such plumes previously, but the source of watervapor and the injection mechanism were not identified. The present results reveal thatthere are two types of plumes, anvil sheet plumes and overshooting plumes, in thisinjection process and that the process is diabatic. A first-order estimate of this plumetransport of water vapor per day from the upper troposphere to the lower stratosphere wasmade assuming that all thunderstorms behave the same as the one simulated. Other tracechemicals may also be similarly transported by the same mechanism.

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Moisture plumes above thunderstorm anvils and their contributions to cross-tropopause transport of water vapor in midlatitudes

A theoretical method is given which allows computing the acceleration to terminal velocity of cloud and raindrops at various levels in the atmosphere. For drops of equivalent radius 800 μm ≤ a0 ≤ 3500 μm our theoretical predictions were found to agree well with the results of an experimental study carried out in the UCLA Rain-Shaft. For drops of 20 μm ≤ a0 ≤ 80 μm our theoretical predictions were found to agree well with the experimental results of Sartor and Abbott (1975). Experiment and theory indicate that in air of 1000 mb and 20°C, drops of a0 > 1000 μm need distances of at least 12 m to accelerate to terminal velocity.

Acceleration to Terminal Velocity of Cloud and Raindrops.

Experiments have been carried out to determine the efficiency with which aerosol particles of 0.25 μm radius are collected due to Brownian diffusion, and due to hydrodynamic, phoretic and electrical effects by water drops of 150 to 2500.μm equivalent radius falling in subsaturated air. In the absence of electrical effects it was found that with increasing drop size the collection efficiency decreases to a minimum and then rises again as the collection due to phoretic forces is overcompensated by the collection due to hydrodynamic forces. With further increase in drop size the collection efficiency was found to rise to a maximum, This rise was attributed to hydrodynamic effects in the rear of the drop which increase as the stagnant eddy at the downstream end of the falling drop increases in size, but progressively decrease as the drop assumes a size, and thus a Reynolds number, large enough for turbulent eddies to be shed from the rear of the drop. The present results are qualitatively consistent ...

Pao K. Wang

Papers

Microphysics of Clouds and Precipitation

On the Effect of Electric Charges on the Scavenging of Aerosol Particles by Clouds and Small Raindrops

Moisture plumes above thunderstorm anvils and their contributions to cross-tropopause transport of water vapor in midlatitudes

Acceleration to Terminal Velocity of Cloud and Raindrops.

An Experimental Determination of the Efficiency with Which Aerosol Particles are Collected by Water Drops in Subsaturated Air