Vertical velocity retrievals in marine stratocumulus clouds

Poster PDF

Description

The motion-stabilized NOAA W-band cloud radar was deployed as part of the VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REX) field campaign, observing southeastern Pacific stratocumulus in 2008; the ARM Mobile Facility (AMF) W-band ARM cloud radar (WACR) cloud radar was deployed at Graciosa, Azores, in summer 2009–2010. We retrieve vertical air velocity from stratocumulus clouds in these locations using radar reflectivity and mean Doppler vertical velocity moments, employing the constraint that gravitational settling of hydrometeors is independent and uncorrelated to air vertical motion (Pinsky et al. 2010).

This method constructs a lookup table of mean fall speeds as a function of reflectivity and properties of the cloud, e.g., height. We find that the mean fall speed dependence on height and reflectivity is variable in time, but that the time average lookup table is robust. We test the dependence of the lookup table on fundamental properties of the cloud, e.g., distance from cloud top and cloud thickness, with the goal of explaining variations in the fall speed-reflectivity relation with these variables.

Retrieved vertical velocities are relatively robust to the choice of the lookup table. We compare this simple moment-based vertical velocity retrieval with vertical velocities from other AMF-Graciosa optimal retrievals.