Mark A. Miller — Rutgers University
Virendra Prakash Ghate — Argonne National Laboratory
Category
Cloud Properties
Description
(a) Mean vertical velocity and the associated standard deviation, (b) mean reflectivity, (c) updraft fraction, (d) downdraft fraction, (e) updraft fraction conditionally sampled at 0.5 ms-1, and (f) downdraft fraction conditionally sampled at -0.5 ms-1 as a function of height for active, passive, and forced clouds.
Non-precipitating marine fair-weather cumulus clouds, or cumulus humilis, have a large impact on the boundary layer structure and on the earth’s radiation budget. Due to their marine location, short lifetime, and small spatial scales, their observations still remain sparse. These clouds are further classified as forced, active, and passive clouds, based on their role of venting mixed-layer air into free troposphere, with each type having a distinct morphological and dynamical structure. The current deployment of Atmospheric Radiation Measurement (ARM)’s Mobile Facility (AMF) on the island of Graciosa in the Azores gives an opportunity to sample this important component of the climate system. Data from the vertically pointing W-band ARM Cloud radar (WACR) collected during a 10-hour period on 26 June 2009 are analyzed to understand the morphology and dynamics of these clouds. The WACR- observed cumuli are classified to identify 85 forced, 3 active, and 4 passive clouds. The mean in-cloud vertical velocities are found to be 0.22 ms-1, 0.38 ms-1, and -0.48 ms-1 within forced, active, and passive clouds, with an updraft fraction near cloud base of 80%, 60%, and 20%, respectively. Although the preliminary results are based on few samples, they are remarkably consistent with the expectations based on theory and highlight the need to distinguish between different fair-weather cumulus cloud types. The data available at the end of the two-year deployment offer the opportunity to characterize the morphology and dynamics of these clouds under variety of aerosol concentrations.
