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An overview of the microphysical structure of cirrus clouds observed during EMERALD-1

Gallagher, M.W. and Conolly, P.J. and Whiteway, J. and Figueras-Nieto, D. and Flynn, M. and Choularton, T.W. and Bower, K.N. and Cook, C. and Busen, Reinhold and Hacker, J. (2005) An overview of the microphysical structure of cirrus clouds observed during EMERALD-1. Quarterly Journal of the Royal Meteorological Society, 131, pp. 1143-1169. DOI: 10.1256/qj.03.138.

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Abstract

High-resolution ice microphysical, turbulence, heat and water vapour flux data in cirrus clouds were collected by the Airborne Research Australia’s (ARA) Egret Grob 520T research aircraft during the first EgretMicrophysics with Extended Radiation and Lidar experiment (EMERALD-1). The in situ cirrus measurements were guided by simultaneous airborne lidar measurements collected by the ARA Super King Air research aircraft which flew below the cirrus and whose horizontal position was synchronized with the Egret. This allowed the microphysics and turbulence measurements to be interpreted and evaluated within the context of large-scale cirrus structure and its evolution. A significant feature of the clouds observed was the presence on occasion of active convective columns. Large variations in the cirrus dynamics were observed, with significant variations in the ice crystal habit from cloud top to cloud base and within the evaporating fall-streaks of precipitation. However, on average the picture presented is consistent with that shown by Heymsfield andMiloshevich, and by Kajikawa and Heymsfield, with the upper supersaturated region of the cloud acting as an active particle-generation zone where homogeneous nucleation proceeds apace; ice crystals there are initially dominated by small irregular or spheroidally shaped particles, some of which can be identified as proto or ‘germ’ rosettes. These are then observed to grow into more open bullet rosette and columnar types as they fall into the less supersaturated middle and lower layers of the cloud. The mean recognisable ice particle size fell within a very narrow size band, 70–90 μm, but the actual size distribution is thought to increase in a continuous manner to smaller sizes. However, there are currently instrument limitations that make it difficult to confirm this unambiguously. Unlike most previous studies, however, the cirrus clouds observed here were mostly devoid of pristine plate-like crystals, as nucleation and growth within the planar growth regime was rarely encountered. During some cases bullet rosettes, once formed, did undergo transition to the plate growth regime with complex crystal shapes resulting. The mean size of pristine bullet rosettes was again confined to a relatively narrow range. The likely nucleation processes dominating in cirrus clouds are discussed in the light of the observations. Very high concentrations of small ice crystals were sometimes detected, concentrations reaching a maximum of 10 000 Lcm<sup>-1</sup>. There is strong evidence supporting these high concentrations which are probably produced by the homogeneous freezing of aerosol.

Document Type:Article
Title:An overview of the microphysical structure of cirrus clouds observed during EMERALD-1
Authors:
AuthorsInstitution or Email of Authors
Gallagher, M.W.Univ. of Manchester, Manchester, UK
Conolly, P.J.Univ. of Manchester, Manchester, UK
Whiteway, J.University of Wales, Aberystwyth, UK
Figueras-Nieto, D.Univ. of Manchester, Manchester, UK
Flynn, M.Univ. of Manchester, Manchester, UK
Choularton, T.W.Univ. of Manchester, Manchester, UK
Bower, K.N.Univ. of Manchester, Manchester, UK
Cook, C.University of Wales, Aberystwyth, UK
Busen, ReinholdUNSPECIFIED
Hacker, J.Airborne Research Australia, Adelaide, AU
Date:2005
Journal or Publication Title:Quarterly Journal of the Royal Meteorological Society
Refereed publication:Yes
In Open Access:No
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:131
DOI:10.1256/qj.03.138
Page Range:pp. 1143-1169
Status:Published
Keywords:Aircraft, Climate, Concentration, Habit, Ice-size distribution, Microphysics
HGF - Research field:Aeronautics, Space and Transport (old)
HGF - Program:Space (old)
HGF - Program Themes:W EO - Erdbeobachtung
DLR - Research area:Space
DLR - Program:W EO - Erdbeobachtung
DLR - Research theme (Project):W - Projekt Partikel und Zirren II (old)
Location: Oberpfaffenhofen
Institutes and Institutions:Institute of Atmospheric Physics > Atmospheric Trace Species
Deposited By: Dr.phil.nat. Reinhold Busen
Deposited On:21 Jun 2007
Last Modified:11 Nov 2014 21:56

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