Ice particle properties of Arctic cirrus

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 were carried out in Kiruna (68° N), Sweden. Ice particle diameters between 10 μm and 1200 μm were found and the shape could be recognised from 20 μm upwards. Great variability in particle size and shape was 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/L and 400/L were measured, but only for two cases the number concentration reached values above 100/L. These two cirrus clouds were of in-situ origin and were caused by gravity and mountain lee-waves. For all other measurements, the maximum ice particle concentration was below 50/L and for one in-situ origin cirrus case only 3/L. In the case of in-situ origin clouds, the particles were all smaller than 350 μm diameter. The number size distribution for liquid origin clouds was much broader with particle sizes between 10 μm and 1200 μm. Furthermore, it is striking that in the case of in-situ origin clouds almost all particles were compact (61 %) or irregular (25 %) when examining the particle shape. In liquid origin clouds, on the other hand, most particles were irregular (48 %), rosettes (25 %) or columnar (14 %). There were 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 were almost all hollow.