Estimates of entrainment in closed cellular marine stratocumulus clouds from the MAGIC field campaign
[1];
- Environmental Science Division, Argonne National Laboratory Lemont Illinois
- Department of Geography and atmospheric science, University of Kansas Lawrence Kansas
- University of Wisconsin Madison Wisconsin
- Brookhaven National Laboratory Upton New York
- NASA Langley Research Center Hampton Virginia, USA
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 any 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.
- Research Organization:
- Brookhaven National Laboratory (BNL), Upton, NY (United States); Argonne National Laboratory (ANL), Argonne, IL (United States); Univ. of Kansas, Lawrence, KS (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Biological and Environmental Research (BER); National Science Foundation (NSF)
- Grant/Contract Number:
- SC0012704; AC02-06CH11357; SC0006736; SC0016522; AGS-1445831
- OSTI ID:
- 1503731
- Alternate ID(s):
- OSTI ID: 1503733; OSTI ID: 1504387
- Report Number(s):
- BNL-211484-2019-JAAM
- Journal Information:
- Quarterly Journal of the Royal Meteorological Society, Journal Name: Quarterly Journal of the Royal Meteorological Society; ISSN 0035-9009
- Publisher:
- Royal Meteorological SocietyCopyright Statement
- Country of Publication:
- United Kingdom
- Language:
- English
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