Summertime Arctic Aircraft Measurements during ACCACIA

Abstract. Arctic Climate is not represented with a high degree of certainty in current climate; part of this is due to Arctic clouds not being well modelled. There have been very few in-situ measurements in the region until recent years, where coverage still remains sparse. Whilst a lot is known regarding lower latitude cloud microphysics, the same cannot be said for Arctic cloud microphysics where cloud interactions and feedback mechanisms are known to vary from those at lower latitudes. This paper reports data from the 2013 ACCACIA project where aerosol and cloud data were collected over eight flights sampling in the region around Svalbard during July.

Clouds from six out of the eight flights were found to be mixed phase to some extent, with in-cloud flight-mean droplet number concentrations ranging from 21.7–132 cm⁻³ across all flights where clouds were sampled between 262 and 283 K. Cloud droplet diameter was found to increase from cloud base to cloud top within sampled stratocumulus layers which were noted to lift and deepen when moving out from over the sea-ice to over the open ocean. Cloud ice particles concentrations, when present, ranged from 0.42–0.88 L⁻¹, with irregular, stellar and columnar habits noted. Results suggest a small number of ice nucleating particles were active in the region, with conditions intermittently present such that secondary ice processes were able to glaciate small portions of the cloud.

The purpose of this paper is to provide a more extensive range of data for the development of improved parameterisations for use in models applied to Polar regions.