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Cloudiness and Marine Boundary Layer Dynamics in the ASTEX Lagrangian Experiments. Part II: Cloudiness, Drizzle, Surface Fluxes, and Entrainment

American Meteorological Society

The Analysis of the Atlantic Stratocumulus Transition Experiment (ASTEX) Lagrangians started in Part I is continued, presenting measurements of sea surface temperature, surface latent and sensible heat fluxes from bulk aerodynamic formulas, cloud fraction, and drizzle rate for the two Lagrangians, mainly using data from horizontal legs flown by the Electra and C130. Substantial drizzle, averaging 1 mm day−1 at the surface, was measured during the first Lagrangian. The surface fluxes increased rapidly as the air mass advected over rapidly increasing SST. Cloud fraction remained high throughout. During the second Lagrangian, drizzle formed in the stratocumulus layer but mainly evaporated in the deep, dry cumulus layer and the subcloud layer before reaching the surface. Stratocumulus cloud cover was thickest when moist air lay above the inversion and then it dissipated to leave only cumuli once dry air advected over the inversion. Three methods are compared for determining entrainment rate (European Centre for Medium-Range Weather Forecasts analyses of mean vertical motion, calculation of a water budget, and the ozone flux–jump method). While all three methods have significant uncertainties, their predictions are all consistent with an entrainment rate of 0.7 ± 0.3 cm s−1 for the first Lagrangian and 0.6 ± 0.3 cm s−1 for the second Lagrangian. Corresponding estimates of the time-dependent horizontal divergence are also presented. Estimates of the cumulus mass flux, internal mixing time, and entrainment dilution time for the boundary layers observed during the two Lagrangians are also presented. Copyright 1995 American Meteorological Society (AMS). Permission to use figures, tables, and brief excerpts from this work in scientific and educational works is hereby granted provided that the source is acknowledged. Any use of material in this work that is determined to be “fair use” under Section 107 of the U.S. Copyright Act or that satisfies the conditions specified in Section 108 of the U.S. Copyright Act (17 USC §108, as revised by P.L. 94-553) does not require the AMS’s permission. Republication, systematic reproduction, posting in electronic form, such as on a web site or in a searchable database, or other uses of this material, except as exempted by the above statement, requires written permission or a license from the AMS. Additional details are provided in the AMS Copyright Policy, available on the AMS Web site located at (http://www.ametsoc.org/) or from the AMS at 617-227-2425 or copyright@ametsoc.org.

Text

2016-11-07

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/32958

Bretherton, Christopher S.,Austin, Philip H., Siems, Steven T. 1995. Cloudiness and Marine Boundary Layer Dynamics in the ASTEX Lagrangian Experiments. Part II: Cloudiness, Drizzle, Surface Fluxes, and Entrainment. Journal of the Atmospheric Sciences 52(16) 2724–2735.

Reviewed

Austin Philip H.

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