Jingjing Tian

Date of Award

January 2014

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Atmospheric Sciences

First Advisor

Xiquan Dong

Abstract

This study presents an algorithm for retrieving the Deep Convective Systems (DCSs) ice cloud microphysical properties using the DOE Atmospheric Radiation Measurement (ARM) Ka-band Zenith Radar (KAZR) reflectivity during the Midlatitude Continental Convective Clouds Experiment (MC3E) at the ARM Southern Great Plain (SGP) site ( 36° 36' 18.0" N, 97° 29' 6.0" W) from April-June 2011. It is a challenge to retrieve DCS ice cloud microphysical properties due to the attenuation of cloud radar reflectivity, unknown particle size distributions (PSDs), and the bulk habit of the ice particles within the sample volume. To address the most pronounced of these radar limitations, the original KAZR reflectivity measurements have been adjusted using data collected with both a collocated unattenuated 915-MHz profiling radar system UHF ARM Zenith Radar (UAZR) and a Joss-Waldvogel impact disdrometer (JWD). Additionally, aircraft in-situ measurements provide PSDs and best-estimate ice water content (IWC) for validating radar retrievals. With the aid of the scattering database (SCATDB), the relationships between backscatter cross section (σ) and particle dimension (D) are parameterized for four ice crystal habits (bullet rosettes, snowflakes, columns and plates).

The DCS ice cloud IWC and effective radius (re) on 20 May 2011 during the MC3E have been retrieved from adjusted KAZR reflectivity assuming a modified gamma distribution with size shape α and a bullet rosette σ-D relationship. The averaged IWC and re from

radar retrievals over the stratiform rain (SR) region of the DCS are 0.34 g m-3 and 338 µm, in excellent agreement with aircraft in-situ measured IWC (0.34 g m-3) and re (337 µm). Over the anvil cloud (AC) region, the retrieved and measured IWCs are 0.18 g m-3 and 0.23 g m-3 and their respective re values are 250 µm and 305 µm. The radar retrieved re and IWC can increase to 283 µm and 0.23 g m-3 if a 2 dB uncertainty is added to the adjusted KAZR reflectivity over the AC region, following the sensitivities of 13%/2 dB in re and 26%/2 dB in IWC.

These retrieval results are also compared with Geostationary Operational Environmental Satellite (GOES) retrieved cloud effective diameter (De) during MC3E. In addition to the spatially averaged GOES retrievals within a 1°×1° grid box centered over the ARM SGP site and the temporally averaged ARM retrievals within 1 hr (±0.5 hr GOES image), the ARM-retrieved De values were also averaged from cloud top down to where the reflectivity is around 0 dBZ to best match the GOES retrievals. During daytime, GOES retrieved De, on average, agrees with the ARM retrievals within ~25 µm despite the vastly different temporal and spatial resolutions of vertically pointing ground-based radar and cloud-top-viewing satellite instruments. GOES retrieved cloud top heights (CTHs) are also compared with ARM KAZR reflectivity profiles, having an excellent agreement with differences of ~0.2 km.

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