Arctic ice clouds over northern Sweden : microphysical properties studied with the Balloon-borne Ice Cloud particle Imager B-ICI
2018
Abstract. Ice particle and cloud properties such as particle size, particle shape and
number concentration influence the net radiation effect of cirrus clouds.
Measurements of these features are of great interest for the improvement of
weather and climate models, especially for the Arctic region. In this study,
balloon-borne in situ measurements of Arctic cirrus clouds have been analysed
for the first time with respect to their origin. Eight cirrus cloud
measurements have been carried out in Kiruna (68 ∘ N), Sweden, using
the Balloon-borne Ice Cloud particle Imager (B-ICI). Ice particle diameters
between 10 and 1200 µm have been found and the shape could be
recognized from 20 µm upwards. Great variability in particle size
and shape is observed. This cannot simply be explained by local environmental
conditions. However, if sorted by cirrus origin, wind and weather conditions,
the observed differences can be assessed. Number concentrations between 3 and
400 L −1 have been measured, but the number concentration has reached
values above 100 L −1 only for two cases. These two cirrus clouds are of
in situ origin and have been associated with waves. For all other
measurements, the maximum ice particle concentration is below 50 L −1
and for one in situ origin cirrus case only 3 L −1 . In the case of
in situ origin clouds, the particles are all smaller than 350 µm
diameter. The PSDs for liquid origin clouds are much broader with particle
sizes between 10 and 1200 µm . Furthermore, it is striking that in
the case of in situ origin clouds almost all particles are compact (61 %)
or irregular (25 %) when examining the particle shape. In liquid origin
clouds, on the other hand, most particles are irregular (48 %), rosettes
(25 %) or columnar (14 %). There are hardly any plates in cirrus
regardless of their origin. It is also noticeable that in the case of
liquid origin clouds the rosettes and columnar particles are almost all
hollow.
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