Sergey Oshchepkov

In situ measurements of the scattering phase function of stratocumulus, contrails and cirrus

Original measurements were obtained in stratocumulus, contrails and cirrus clouds by using a new optical airborne probe, the ‘Polar Nephelometer’, which is the first airborne instrument to make direct in situ measurements of the scattering phase function of cloud particles over a broad range of sizes (from a few micrometers to about 500 µm diameter). Preliminary measurements show that in stratocumulus water droplet cloud, the measured phase function fits very well with the phase function derived from direct PMS probes measurements. This definitively confirms the reliability of the Polar Nephelometer for airborne measurements. In contrails and natural cirrus, measured scattering phase function indicates major differences with those used in cloud models which assume ice spheres or simple geometric shape of ice particles. These results highlight new potential insights on both modelling of climate processes and methodologies for cloud remote sensing from satellite measurements.

Assessment of cloud optical parameters in the solar region: Retrievals from airborne measurements of scattering phase functions

A data set of approximately 60,000 airborne measurements of angular scattering coefficients was used to reproduce a representative set of both microphysical parameters and single light-scattering characteristics (angular scattering coefficient, asymmetry parameter, single-scattering albedo, and extinction coefficient) for three types of clouds. The measurements were limited to a wavelength of 0.8 mm and to 28 scattering angles near uniformly positioned from 15° to 155°. Microphysical and optical characteristics were computed at wavelengths of 0.8, 1.6, and 3.7 mm, which are needed for the direct and inverse modeling of radiative transfer. The estimation of these characteristics is achieved through cloud microphysical parameter retrievals, taking into account the variation of water droplet and ice crystal size as well as cloud phase composition. We present both average values and possible variability of microphysical and single-scattering characteristics for three types of clouds with respect to their particle phase composition (i.e., water droplets, mixed phase, and ice crystals in cloud). The variations are presented separately due to both random instrumental errors of optical measurements and possible changes in the microphysical parameters within a separated specific cloud category. The microphysical parameter retrievals are validated by comparison with collocated direct particle size distribution measurements. Additionally, the estimated single light-scattering characteristics are in reasonable agreement with those available from the literature.

Statistical analysis of cloud light scattering and microphysical properties obtained from airborne measurements

A new statistical analysis of the in situ scattering phase function measurements performed by the Laboratoire de Meteorologie Physiques airborne polar nephelometer is implemented. A principal component analysis along with neural networks leads to the classification of a large data set into three typical averaged scattering phase functions. The cloud classification in terms of particle phase composition (water droplets, mixed-phase, and ice crystals) is done by a neural network and is validated by direct Particle Measuring Systems, Inc., probe measurements. The results show that the measured scattering phase functions carry enough information to accurately retrieve component composition and particle size distributions. For each classified cloud, we support the statement by application of an inversion method using a physical model of light scattering to the average scattering phase function. Furthermore, the retrievals are compared with size composition obtained by independent direct measurements.

Ground-Based Solar Extinction Measurements to Identify Soot- Like Components of Atmospheric Aerosol

Soot-like components of atmospheric aerosol is known to be one of an important factor of air pollution. This matter is especially high priority near the sources of industrial pollution and the composition of atmospheric aerosol would be the most quantity here. In contrast to usual background atmospheric aerosol, solar radiation is especially absorbed by soot-like components in passing through the atmosphere.

Particle sizing of mixed-phase and cirrus clouds from phase function measurements

A new method of particle sizing for mixed-phase and ice clouds proposed and tested by numerical simulation in authors papers is applied here to experimentally measured scattering phase function. The method enables us to identify each component of a bi-component cloud composed of ice crystals and water droplets and to retrieve separately a size distribution for each cloud component. We use mainly available referenced data to test the inversion method with respect to the retrieval of size composition of mixed-phase and ice cloud under both single- and bi-component assumption and try to explain the known fact of the discrepancy between measured scattering phase functions for an ice cloud and those theoretically predicted by the ray tracing treatment, for instance, for convex ice crystals. Applying the inversion method enables us to show that one of effective ways to describe the scattering phase function behavior of mixed-phase and ice clouds is the bi-component assumption. It is rather natural for a mixed-phase cloud because of the existence of water droplets and ice crystals in the cloud simultaneously. On the other hand, one of an important physical reason for the bi-component assumption in an ice cloud lies in the well known fact that, as the cloud is transformed from water phase to ice one a high proportion of the particles can frequently stay as small supercooled water droplets even at very low temperature.

Inverse scattering problem for mixed-phase and cirrus clouds

A new method of particle size retrieval is proposed of rice crystal and mixed phase clouds. The method enables us to identify each component of a bi-component cloud composed namely of ice crystals and water droplets and to retrieve separately size distributions of each cloud component. Its capability is explored as usually by using synthetic multi-angular data of scattered light intensity. Various cloud microphysical characteristics are modeled by assuming two non-interacting cloud components such as liquid or supercooled droplets and cubic or hexagonal ice crystals with regular simple geometrical shapes as a first approximation. The sensitivity of the method is tested for different relative concentrations of the cloud components varying over a wide range. Firstly, we investigate the applicability limits of the single-component cloud approximation in retrieving particle size distributions of a bi-component cloud. Secondly, we test the method to retrieve simultaneously the size distributions of both the components in mixed-phase clouds, and discuss the conditions of its applicability.