Title: Summertime Marine Boundary Layer Cloud, Thermodynamic, and Drizzle Morphology over the Eastern North Atlantic: A Four-Year Study

Journal Article · · Journal of Climate
 [1];  [1]
  1. a Department of Environmental Sciences, Rutgers, The State University of New Jersey, New Brunswick, New Jersey
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Abstract Summertime remote sensor and in situ data from 2016 to 2019 collected at the ARM Eastern North Atlantic (ENA) Observatory are combined with aircraft measurements from the Aerosol and Cloud Experiments in the Eastern North Atlantic (ACE-ENA) campaign to quantify marine boundary layer (MBL) cloud, thermodynamic, and drizzle morphology in the region. A radar reflectivity–rainfall rate relationship ( Z – R ) is developed from aircraft data and 6-h cloud morphological regimes are identified from ENA data using a k -means algorithm driven by three independent inputs quantifying cloud thickness, drizzle intensity, and cloud field geometric complexity. Four separate MBL structural regimes representing non- or weakly drizzling single-layer stratocumulus, drizzling stratocumulus and cumulus-coupled stratocumulus, deep convection, and broken clouds embedded in northerly flow are identified. Single-layer stratocumulus is indicated when weak subtropical anticyclones are significantly west of the ENA site, and the MBL is cooler and drier than when drizzling and cumulus-coupled stratocumulus and broken clouds are observed. Drizzling and cumulus-coupled stratocumulus clouds are observed on the eastern flank of strong subtropical anticyclones in deep warm moist air masses with wind speeds exceeding 7 m s −1 and strong near-surface wind shear. Broken clouds exhibit strong wind shear near the inversion, while single-layer stratocumulus clouds have lower wind speeds and minimal shear. Net latent heat fluxes in the subcloud layer resulting from a combination of the ocean surface heat flux and evaporating drizzle average near zero over long periods in drizzling and cumulus-coupled stratocumulus. The ECMWF reanalysis version 5 (ERA5) is found to accurately represent single-layer stratocumulus properties, while producing significant discrepancies when drizzling stratocumulus and cumulus-coupled stratocumulus are observed.

Research Organization:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). Atmospheric Radiation Measurement (ARM) Data Center
Sponsoring Organization:
USDOE; USDOE Office of Science (SC), Biological and Environmental Research (BER)
Grant/Contract Number:
SC0013489; SC0022246
OSTI ID:
1873202
Journal Information:
Journal of Climate, Journal Name: Journal of Climate Journal Issue: 14 Vol. 35; ISSN 0894-8755
Publisher:
American Meteorological SocietyCopyright Statement
Country of Publication:
United States
Language:
English

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54 ENVIRONMENTAL SCIENCES
Aircraft observations
Cloud microphysics
Drizzle
Marine boundary layer
Radars/Radar observations
Reanalysis data