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- Title
The Vertical Structure of Liquid Water Content in Shallow Clouds as Retrieved From Dual‐Wavelength Radar Observations.
- Authors
Zhu, Zeen; Lamer, Katia; Kollias, Pavlos; Clothiaux, Eugene E.
- Abstract
Observations collected over 3 months by the beam‐matched second‐generation Ka/W band Scanning Cloud Radar located at the Atmospheric Radiation Measurement Program Eastern North Atlantic observatory are used to advance existing liquid water content (LWC) retrieval techniques, quantify retrieval uncertainty, and subsequently characterize the impact of cloud dynamics and rain rates on the vertical distribution of LWC in boundary layer clouds both precipitating and broken. A threefold technique is proposed that involves (1) temporally averaging measured radar reflectivities collected at two wavelengths to 30‐s resolution, (2) smoothing via fitting a second‐degree polynomial to their dual‐wavelength ratios within 187.5‐m vertical overlapping sliding windows, and (3) averaging the multiple LWC estimates produced at each height. It is estimated that this technique reduced LWC retrieval uncertainty to 0.10–0.65 g/m3, depending on cloud thickness. Although individual retrievals remained noisy, statistics on subgroups of height‐normalized LWC profiles show that, on average, the vertical distributions of LWC in most of the observed clouds followed a linear relationship with a degree of adiabaticity ranging from 0.6 to 0.2 for 200‐ to 600‐m thick clouds. However, nonlinear LWC profiles were present in subgroups of cloud segments presenting intense (0.1–0.5 mm/hr) drizzle rates where LWC was observed to pool near cloud base and in subgroups of cloud segments within strong (0.6 m/s) downdrafts near cloud top where LWC was coincidently reduced. This nonlinearity is inconsistent with the use of adiabatic cloud assumptions for process studies and supports further development of retrievals like the one proposed. Key Points: Shallow and broken cloud liquid water content is retrieved using SACR2 dual‐wavelength observations with uncertainty ~0.10–0.65 g/m3Nonlinear liquid water content distributions were observed within clouds in regions of high rain rate and strong cloud top downdraftBecause of compensating effects, on average, the LWC profiles observed were linear with degree of adiabaticity ranging from 0.6 to 0.2
- Subjects
CLOUDS &; the environment; WATER depth; METEOROLOGICAL observations; WAVELENGTHS; ATMOSPHERIC Radiation Measurement Program (U.S.)
- Publication
Journal of Geophysical Research. Atmospheres, 2019, Vol 124, Issue 24, p14184
- ISSN
2169-897X
- Publication type
Article
- DOI
10.1029/2019JD031188