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Title: Untangling Dynamical and Microphysical Controls for the Structure of Stratocumulus

Stratocumulus clouds that are an important component of the Earth climate system can exhibit diverse structures, from solid decks to broken cloud fields with strikingly different abilities to reflect solar radiation. Amazingly, these different cloud formations can occur within the same or nearly the same environment, as evident by a common presence of pockets of open cells surrounded by overcast areas. These intriguing features not only provide for spectacular satellite images, but also present a challenge for climate models striving to predict the correct cloud amount. While open cells have been linked to the presence of precipitation and low droplet concentrations, complete understanding of the many complex and interacting processes leading to their formation is lacking. Here we show that the structure of stratocumulus can be linked to two timescales: an updraft timescale, t_up, and a precipitation initiation timescale, t_r. When drizzle is initiated within updrafts (t_r ≤ t_up), cloud water in the outflow is depleted enough that an overcast cloud cannot be sustained. Using a simple parcel model, we relate these timescales to three observable parameters (droplet number concentration, Nc, cloud depth, H, and updraft speed, w) and derive a functional representation for this relationship. Well-documented observed and simulatedmore » cases of open and closed cell stratocumulus fit well into the classification based on our model.« less
Authors:
; ;
Publication Date:
OSTI Identifier:
1094932
Report Number(s):
PNNL-SA-96521
400402000
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Geophysical Research Letters, 40(16):4432–4436
Research Org:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
dynamical; microphysical; stratocumulus; climate; cloud; satellite