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  • Author or Editor: Belay B. Demoz x
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Belay B. Demoz, Renyi Zhang, and Richard L. Pitter

Abstract

Systematic observations of the sizes, shapes, and degrees of riming of ice particles falling at a downwind station of a major mountain barrier are presented. The observational station was equipped to measure ice-particle masses from 1 µg to a few milligrams, and to measure ice-particle dimensions, habits, degrees of riming, and degrees of aggregation. The results are shown to be useful in learning where ice nucleation and growth take place in the cloud system.

The present study analyzed dissipating and developing winter orographic storm systems, which are representative of more than 60% of the storms observed over the study region. It suggests that most of the needles and columns observed at the ground may be formed by secondary ice production. Heavy riming was associated with light precipitation, while high precipitation rates were correlated with a high number fraction of aggregate crystals. Aggregation was found to be important in the process of precipitation development and the aggregate mass was mostly contained in the dendritic crystal growth region.

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Zhien Wang, Kenneth Sassen, David N. Whiteman, and Belay B. Demoz

Abstract

Mixed-phase clouds are still poorly understood, though studies have indicated that their parameterization in general circulation models is critical for climate studies. Most of the knowledge of mixed-phase clouds has been gained from in situ measurements, but reliable remote sensing algorithms to study mixed-phase clouds extensively are lacking. A combined active and passive remote sensing approach for studying supercooled altocumulus with ice virga, using multiple remote sensor observations, is presented. Precipitating altocumulus clouds are a common type of mixed-phase clouds, and their easily identifiable structure provides a simple scenario to study mixed-phase clouds. First, ice virga is treated as an independent ice cloud, and an existing lidar–radar algorithm to retrieve ice water content and general effective size profiles is applied. Then, a new iterative approach is used to retrieve supercooled water cloud properties by minimizing the difference between atmospheric emitted radiance interferometer (AERI)–observed radiances and radiances, calculated using the discrete-ordinate radiative transfer model at 12 selected wavelengths. Case studies demonstrate the capabilities of this approach in retrieving radiatively important microphysical properties to characterize this type of mixed-phase cloud. The good agreement between visible optical depths derived from lidar measurement and those estimated from retrieved liquid water path and effective radius provides a closure test for the accuracy of mainly AERI-based supercooled water cloud retrieval.

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