Contributions to atmospheric physics 

About: Contributions to atmospheric physics is an academic journal. The journal publishes majorly in the area(s): Aerosol & Water vapor. It has an ISSN identifier of 0005-8173. Over the lifetime, 252 publications have been published receiving 4399 citations.

Single-scattering properties of complex ice crystals in terrestrial atmosphere

Abstract: Various ice crystal shapes including fernlike geometry, plates with dendritic extensions and with sector-like and broad branches, fractal geometry, and aggregates, have been numerically defined on the basis of available observations. The surface roughness of ice crystals is also accounted for by specifying the facet-tilt distribution in terms of Gram Charlier series for the small facets of which the rough surface consists. These ice crystal geometries along with those defined in our previous studies may approximately represent the ice crystal shapes frequently observed in cirrus clouds. An improved Monte Carlo/ray-tracing method has been developed to compute the single-scattering parameters for these complex ice crystals. The polarization configurations of the localized waves associated with Fresnelian rays are comprehensively accounted for by the improved method in ray-tracing procedure. Complex ice crystals, in particular, those with fernlike structures, scatter more energy in the angular region 2°-20° and in the lateral and backward directions than hexagonal ice crystals. The former ice crystal geometries normally produce smaller polarization values. In particular, a substantial reduction for the negative polarization associated with the backscattering is found as a result of the complex crystal geometries. The surface roughness of ice crystals incorporated into the single-scattering calculation tends to smooth out the scattering peaks corresponding to halos. The roughness also significantly reduces the backscattering. When a substantial roughness condition is imposed, the computed phase function and the polarization configuration of scattered light are essentially featureless. A database of the single-scattering parameters of ice crystals at solar wavelengths covering 0.2-5 μm has been established for various ice crystal shapes and sizes. This database can be useful in the parameterization of the bulk radiative properties of cirrus clouds to account for the effects of ice crystal size distribution and the percentage of various crystal habits. By applying this database to cold and warm cirrus clouds, it is demonstrated that the scattering and absorption characteristics of these clouds depend on both the size distribution and the shapes of ice crystals.

A qualitative geophysical explanation for hot spot dust emitting source regions

Abstract: A survey of the sources of dust given by Professor J. Prospero in the Alfred Wegener Conference showed that rather than homogeneous large areas of dust emissions, much of the global supply of dust comes from relatively small (compared to the size of deserts) consistently active dust producing areas. These areas were named hot spots. To explain these hot spots, I have reviewed what is known about the production mechanisms of dust. From this review I would offer that the primary geophysical explanation of hot spots is lack of nonerodible roughness elements, low threshold friction velocity, and lack of aggregation or crusting. These conditions often apply in depositional environments.

Measurements and modelling of aerosol single-scattering albedo : Progress, problems and prospects

Abstract: The net effect of atmospheric aerosols in the radiation balance is determined by both their scattering and absorption of solar radiation. The combined optical effect is expressed in the single scatter albedo, {omega}, of the particles. Currently available data on {omega} are insufficient for definitive use in climate models because most of them are not corrected for the method-dependent effect of the scattering portion of the aerosol on the measured absorption, most refer to the dry state of the aerosol, and the coverage of the globe is far from being complete. Standardisation and calibration of the measurements is needed. Modelling exercises using currently available data on {omega} should clearly state that corrections are required. The purpose of this review is not to suggest a particular range of values for single scatter albedo. Rather, it is to illustrate that the uncertainties are currently imbedded in various data sets because of the lack of calibration, the possibility that many of the extant methods systematically overestimate light absorption coefficients, and the necessity of including the influence of humidity in models. (orig.) 95 refs.