Title: Estimates of entrainment in closed cellular marine stratocumulus clouds from the MAGIC field campaign

Abstract

Entrainment of warm, dry air from above the boundary layer into the cloud layer has a significant impact on stratocumulus clouds in the marine boundary layer. During the MAGIC field campaign, the Atmospheric Radiation Measurement (ARM) mobile facility was deployed aboard a container ship that made regular transects between Los Angeles, California and Honolulu, Hawaii. Observations made during MAGIC transects were collocated with observations from the Geostationary Operational Environmental Satellite (GOES-15) and European Centre for Medium-range Weather Forecasting (ECMWF) reanalysis model. From these data, hourly estimates of entrainment velocities in closed cellular stratocumulus cloud conditions were calculated from the mixed-layer mass budget equation, modified to accommodate observations sampled from a moving platform. The technique is demonstrated using observations collected during Leg 15A (46 h) and then extended to 178 h of data. The average entrainment velocity was 7.83 ± 5.23 mm/s, and the average large-scale vertical air motion at cloud top (obtained from reanalysis) was -2.56 ± 3.31 mm/s. The vertical air motion at cloud top was positive (upward) during 36 h (~20%) with a mean of 2.68 mm/s. Entrainment velocity is highly variable and on average the MAGIC observations show no dependence of entrainment velocity on longitude or anymore » pronounced diurnal cycle. When binned by inversion strength, the mean entrainment velocity and mean large-scale vertical air motion mirrored each other, with both exhibiting substantial variability. Collectively, our results suggest a mean entrainment-velocity behaviour associated with the background state, with large changes in entrainment velocity forced by strong variability in internal boundary-layer properties like turbulence, radiation, and inversion strength. This cautions against using climatological mean estimates of entrainment velocities or neglecting instances with upward large-scale vertical air motion.« less

Authors:

Ghate, Virendra P.  ^[1];

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Mechem, David B. ^[2]; Cadeddu, Maria P. ^[1]; Eloranta, Edwin W. ^[3]; Jensen, Michael P. ^[4]; Nordeen, Michele L. ^[5]; Smith, Jr, William L. ^[5]

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+ Show Author Affiliations

1. Environmental Science Division, Argonne National Laboratory Lemont Illinois
2. Department of Geography and atmospheric science, University of Kansas Lawrence Kansas
3. University of Wisconsin Madison Wisconsin
4. Brookhaven National Laboratory Upton New York
5. NASA Langley Research Center Hampton Virginia, USA

Publication Date:

Thu Mar 28 00:00:00 EDT 2019

Research Org.:

Brookhaven National Laboratory (BNL), Upton, NY (United States); Argonne National Laboratory (ANL), Argonne, IL (United States); Univ. of Kansas, Lawrence, KS (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Biological and Environmental Research (BER); National Science Foundation (NSF)

OSTI Identifier:

1503731

Alternate Identifier(s):

OSTI ID: 1503733; OSTI ID: 1504387

Report Number(s):

BNL-211484-2019-JAAM
Journal ID: ISSN 0035-9009

Grant/Contract Number:  

SC0012704; AC02-06CH11357; SC0006736; SC0016522; AGS-1445831

Resource Type:

Published Article

Journal Name:

Quarterly Journal of the Royal Meteorological Society

Additional Journal Information:

Journal Name: Quarterly Journal of the Royal Meteorological Society; Journal ID: ISSN 0035-9009

Publisher:

Royal Meteorological Society

Country of Publication:

United Kingdom

Language:

English

Subject:

54 ENVIRONMENTAL SCIENCES; boundary layer; entrainment; stratocumulus