Balloon-borne measurements of ice particle shape and ice water content in the upper troposphere over Northern Sweden

Ice clouds play an important role in the energy budget of the atmosphere. They are at high altitudes, absorb longwave radiation from below and, as they are cold, emit little infrared radiation. This greenhouse effect warms the Earth-atmosphere system. On the other hand, ice clouds have a cooling effect by reflecting incoming solar short wave radiation. The net effect is crucial for the atmosphere, but will depend highly on the cloud's horizontal extent, vertical position, ice water content (IWC), and ice particle microphysical properties such as size and shape. Targeting these upper-tropospheric, cold ice clouds, a series of in-situ balloon-borne experiments has been started at Kiruna, Sweden, which is located at 68°N. Fewer measurements exist at these high latitudes compared to mid-or tropical latitudes. Also temperatures in the upper troposphere can be around -60 °C, a temperature range under-represented in available in-situ data. Experiments are launched from Esrange Space Center. Ice particles are collected with a balloon-borne replicator and also imaged in-situ, and measurements are complemented by a radiosonde added to the instrument. Particle shape and size as well as IWC are determined from the replicas and images. The data are analysed to reveal relationships between IWC and other measurements such as temperature and volume extinction coefficient. Such relationships can be used for validation and improvement of satellite retrievals of IWC from, for example, thin cirrus measurements with satellite-borne lidar, such as on the future EarthCARE mission.