Abstract
Abstract. The partition of cloud and drizzle water path in precipitating clouds plays a key role in determining the cloud lifetime and its evolution. A technique to quantify cloud and drizzle water path by combining measurements from a three-channel microwave radiometer (23.8, 30, and 90 GHz) with those from a vertically pointing Doppler cloud radar and a ceilometer is presented. The technique is showcased using 1 d of observations to derive precipitable water vapor, liquid water path, cloud water path, drizzle water path below the cloud base, and drizzle water path above the cloud base in precipitating stratocumulus clouds. The resulting cloud and drizzle water path within the cloud are in good qualitative agreement with the information extracted from the radar Doppler spectra. The technique is then applied to 10 d each of precipitating closed and open cellular marine stratocumuli. In the closed-cell systems only ∼20 % of the available drizzle in the cloud falls below the cloud base, compared to ∼40 % in the open-cell systems. In closed-cell systems precipitation is associated with radiative cooling at the cloud top <-100Wm-2 and a liquid water path >200 g m−2. However, drizzle in the cloud begins to exist at weak radiative cooling and liquid water path >∼150 g m−2. Our results collectively demonstrate that neglecting scattering effects for frequencies at and above 90 GHz leads to overestimation of the total liquid water path of about 10 %–15 %, while their inclusion paves the path for retrieving drizzle properties within the cloud.
Highlights
Marine stratocumulus clouds have a significant impact on the Earth’s radiation balance as they reflect a greater amount of solar radiation back to space compared to the ocean surface and emit a similar amount of longwave radiation as the surface
The visible imagery and cloud-top temperature reported by the Spinning Enhanced Visible and Infrared Imager (SEVIRI) on board the geostationary Meteosat satellite were used to confirm the presence of similar cloud conditions around the site as those observed at the site
Brightness temperature observations from a microwave radiometer, profiles of lidar attenuated backscatter, and profiles of the first three moments of the radar Doppler spectra serve as input to the retrieval algorithm
Summary
Marine stratocumulus clouds have a significant impact on the Earth’s radiation balance as they reflect a greater amount of solar radiation back to space compared to the ocean surface and emit a similar amount of longwave radiation as the surface The processes affecting their highly organized spatial structure and their spatial and temporal variability are a topic of active research (Wood et al, 2015). The radar reflectivity is proportional to the sixth moment of the DSD and was used to retrieve liquid water content that is the third moment of DSD by Frisch et al (2002) For this purpose, new algorithms are developed that can extract key cloud and drizzle properties such as liquid water content and drop effective radius from a combination of active (e.g., radar, lidar), and passive (broadband or narrowband radiometers) sensors (e.g., Frisch et al, 1995; Fielding et al, 2014).
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