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. Ice particle and cloud properties such as particle size, particle shape andnumber concentration influence the net radiation effect of cirrus clouds.Measurements of these features are of great interest for the improvement ofweather and climate models, especially for the Arctic region. In this study,balloon-borne in situ measurements of Arctic cirrus clouds have been analysedfor the first time with respect to their origin. Eight cirrus cloudmeasurements have been carried out in Kiruna (68 ∘  N), Sweden, usingthe Balloon-borne Ice Cloud particle Imager (B-ICI). Ice particle diametersbetween 10 and 1200  µm have been found and the shape could berecognized from 20  µm upwards. Great variability in particle sizeand shape is observed. This cannot simply be explained by local environmentalconditions. However, if sorted by cirrus origin, wind and weather conditions,the observed differences can be assessed. Number concentrations between 3 and400 L −1 have been measured, but the number concentration has reachedvalues above 100 L −1 only for two cases. These two cirrus clouds are ofin situ origin and have been associated with waves. For all othermeasurements, 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 ofin situ origin clouds, the particles are all smaller than 350  µm diameter. The PSDs for liquid origin clouds are much broader with particlesizes between 10 and 1200  µm . Furthermore, it is striking that inthe case of in situ origin clouds almost all particles are compact (61 %)or irregular (25 %) when examining the particle shape. In liquid originclouds, on the other hand, most particles are irregular (48 %), rosettes(25 %) or columnar (14 %). There are hardly any plates in cirrusregardless of their origin. It is also noticeable that in the case ofliquid origin clouds the rosettes and columnar particles are almost allhollow.

Arctic ice clouds over northern Sweden: microphysical properties studied with the Balloon-borne Ice Cloud particle Imager B-ICI