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  • Author or Editor: J. Ström x
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K. B. Noone
,
K. J. Noone
,
J. Heintzenberg
,
J. Ström
, and
J. A. Ogren

Abstract

This study presents a new technique for making in situ measurements of cirrus cloud microphysical properties. Sampling of cirrus clouds was performed using a counterflow virtual impactor (CVI). The CVI was used to sample cloud elements larger than 4 µm in aerodynamic diameter. In conjunction with a Lyman-α hygrometer, this gave a direct measurement of the condensed water content. Sampling the cloud elements with the CVI also allowed the authors to examine the size distribution of the residual particles produced by evaporation of the cloud elements. This study discusses and evaluates the CVI technique for use in sampling cirrus clouds, especially for sampling small cloud elements. Measurements of condensed water content and cloud-element (crystal and droplet) concentrations for cirrus uncinus, floccus, and cirrostratus clouds made using the CVI during the International Cirrus Experiment experiment are presented. Examples of size distributions of the residual aerosol particles from cirrus cloud elements are also presented.

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J. Ström
,
R. Busen
,
M. Quante
,
B. Guillemet
,
P. R. A. Brown
, and
J. Heintzenberg

Abstract

During the pre-EUCREX (European Cloud and Radiation Experiment) intercomparison of airborne instrumentation in January 1992, nine hygrometers mounted on three different aircraft were compared. Although the different instruments are based on completely different principles and the three aircraft have very different flying characteristics, humidity data from both vertical profiles as well as horizontal flight legs showed good agreement. Despite the different aircraft limitations the intercomparison was done with the aircraft in close formation. In terms of relative difference in mixing ratio, most instruments agreed to within ±5% for values down to about 0.1 g kg−1. For mixing ratios between 0.03 and 0.1 g kg−1 most instruments agreed to within ±15%. Systematic differences between the instruments suggest that in joint experiments where data will be shared, the same algorithms for evaluating and converting humidity parameters should be used whenever possible.

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