32nd Conference on Broadcast Meteorology/31st Conference on Radar Meteorology/Fifth Conference on Coastal Atmospheric and Oceanic Prediction and Processes

Thursday, 7 August 2003: 9:30 AM
MM-Wave Radar Structure and Microphysical Characteristics of Mixed Phase Altocumulus Clouds
Larry R. Belcher, North Carolina State University, Raleigh, NC; and L. D. Carey, J. M. Davis, J. A. Kankiewicz, and T. H. Vonder Haar
Poster PDF (570.0 kB)
The ninth Complex Layered-Cloud Experiment (CLEX-9), conducted over western Nebraska from 8 October to 4 November 2001 provided in-situ microphysical and radar measurements of mid-level clouds from the University of Wyoming King Air research aircraft (UWKA). Microphysical measurements include cloud liquid water (LWC) and ice water contents (IWC) from a suite of microphysical probes (e.g., PMS 2D-C, 2D-P, and DMT-100 Probe). The 95-GHz Wyoming Cloud Radar (WCR) was also deployed on the UWKA, providing radar reflectivity (Z) observations. Integration of the in-situ and radar data provides the opportunity to investigate the structure and bulk microphysical characteristics of the mixed-phase clouds sampled during 8 mission days.

Observations of LWC show peak values up to 1 g m-3 with average values at or slightly below 0.1 g m-3. Values of IWC rarely exceeded 0.3 g m-3 and exhibited average values near 0.03 g m-3. The distribution of LWC and IWC within the clouds is consistent with previous work showing larger values of LWC (IWC) near cloud top (in the middle to lower portions of the cloud). Radar derived cloud depths ranged from 0.5 to 3 km. Radar reflectivity, LWC, and IWC observations of mature altocumulus revealed all water or mixed-phase cellular structure with all ice fallstreaks often cascading beneath the generating cells. These generating cells, which were characterized by elevated LWC, IWC (depending on altitude and temperature) and Z, occurred with regular periodicity (~ 1 km) associated with dynamically active regions within the cloud. When present, the fallstreaks of ice often merged together, forming a fairly homogeneous, enhanced radar reflectivity echo (Z > 8 dBZ) beneath the cells.

A power-law relationship between IWC and Z (i.e., IWC=aZb) from particle size spectra was also investigated. Analysis of in-situ data yielded an average a=0.0103 and b=0.555. The mean values of a (b) are in good agreement with coefficients inferred from individual cases, which range from 0.005 to 0.018 (0.428 to 0.612). WCR reflectivity observations will be utilized in these Z-IWC equations to infer cloud-scale structure of IWC, statistical behavior of IWC as a function of temperature and distance from cloud top, horizontal and vertical homogeneity of IWC and the relationship of these properties to the in-situ identified all liquid or mixed-phase generating cells at cloud top.

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