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Arctic Low-level Boundary Layer Clouds: In-situ Measurements and Simulations of Mono- and Bimodal Supercooled Droplet Size Distributions at the Cloud Top Layer : Volume 14, Issue 10 (05/06/2014)

By Klingebiel, M.

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Book Id: WPLBN0003996913
Format Type: PDF Article :
File Size: Pages 37
Reproduction Date: 2015

Title: Arctic Low-level Boundary Layer Clouds: In-situ Measurements and Simulations of Mono- and Bimodal Supercooled Droplet Size Distributions at the Cloud Top Layer : Volume 14, Issue 10 (05/06/2014)  
Author: Klingebiel, M.
Volume: Vol. 14, Issue 10
Language: English
Subject: Science, Atmospheric, Chemistry
Collections: Periodicals: Journal and Magazine Collection, Copernicus GmbH
Historic
Publication Date:
2014
Publisher: Copernicus Gmbh, Göttingen, Germany
Member Page: Copernicus Publications

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Molleker, S., Weigel, R., Borrmann, S., Wendisch, M., Neuber, R., Meyer, J.,...Lozar, A. D. (2014). Arctic Low-level Boundary Layer Clouds: In-situ Measurements and Simulations of Mono- and Bimodal Supercooled Droplet Size Distributions at the Cloud Top Layer : Volume 14, Issue 10 (05/06/2014). Retrieved from http://ebooklibrary.org/


Description
Description: Institute for Physics of the Atmosphere, University of Mainz, Mainz, Germany. Aircraft borne optical in-situ size distribution measurements were performed within Arctic boundary layer clouds, with a special emphasis on the cloud top layer, during the VERtical Distribution of Ice in Arctic Clouds (VERDI) campaign. The observations were carried out within a joint research activity of seven German institutes to investigate Arctic boundary layer-, mixed-phase clouds in April and May 2012. An instrumented Basler BT-67 research aircraft operated out of Inuvik over the Mackenzie River delta and the Beaufort Sea in the Northwest Territories of Canada. Besides the cloud particle and hydrometeor size spectrometers the aircraft was equipped with instrumentation for aerosol, radiation and other parameters. Inside the cloud, droplet size distributions with monomodal shapes were observed for predominantly liquid-phase Arctic stratocumulus. With increasing altitude inside the cloud the droplet mean diameters grew from 10 Μm to 20 Μm. In the upper transition zone (i.e. adjacent to the cloud-free air aloft) changes from monomodal to bimodal droplet size distributions were observed. It is shown that droplets of both modes co-exist in the same (small) air volume and the bimodal shape of the measured size distributions cannot be explained as an observational artifact caused by accumulating two droplet populations from different air volumes. The formation of a second size mode can be explained by (a) entrainment and activation/condensation of fresh aerosol particles, or (b) by differential evaporation processes occurring with cloud droplets engulfed in different eddies. Activation of entrained particles seemed a viable possibility as a layer of dry Arctic enhanced background aerosol was detected directly above the stratus cloud might form a second mode of small cloud droplets. However, theoretical considerations and a model simulation revealed that, instead, turbulent mixing and evaporation of larger droplets most likely are the main reasons for the formation of the second droplet size mode in the uppermost region of the clouds.

Summary
Arctic low-level boundary layer clouds: in-situ measurements and simulations of mono- and bimodal supercooled droplet size distributions at the cloud top layer

Excerpt
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