Measurement of cloud condensation nuclei
Together with the Institute for tropospheric research, TROPOS, in Leipzig, Germany, measurements of the concentration of cloud condensation nuclei were started in December 2013. For this purpose, a cloud condensation nuclei counter (CCNc, Droplet Measurement Technologies, US) of TROPOS has been installed at Princess Elisabeth station - during December 2013 to mid-February 2014, from December 2014 to mid-February 2015, and again from December 2015 to mid-February 2016. A CCNc measures how many particles are activated to droplets at a specific supersaturation (with respect to water; usually between 0.1 to 0.7%). Simultaneously, the other instruments in the aerosol shelter measure the total particle number concentration and their size distribution. The information from the particle size distribution helps to derive the critical particle diameter necessary for droplet activation. There are empirical relations to derive from this information constraints on the ambient aerosol type. The relation between total particle number and how many of them could be activated to droplets gives further information on the overall ambient aerosol type. First analyses indicate that the aerosol consisted mainly of material with a hygroscopicity close to that of sulfate. For example, on 6 December 2014, a sudden increase in particle total number happened (from about 300 to 6000/cm3), but the concentration of cloud condensation nuclei increased only slightly (to a maximum around 300 /cm3, even at a high supersaturation of 1.0%. This indicates that the strong increase in particle number was caused by mainly small, rather freshly formed particles. Such particles are too small to be easily activated to cloud droplets. The size information also tells us that these particles must have been produced recently (<1day), otherwise they would have grown in size. Information on the concentration of cloud condensation nuclei and their critical activation diameter is very useful to improve the parameterisation of the aerosol influence on cloud formation within weather forecasting or climate models.
Evolution of total particle number concentration and of the concentration of cloud condensation nuclei (at 5 different supersaturations with respect to water); courtesy of Paul Herenz, Heike Wex, TROPOS, Leipzig, Germany
Radio soundings at Princess Elisabeth Antarctica
The Royal Meteorological Institute of Belgium (RMI) supports via an in-kind contribution the AEROCLOUD research by supplying the necessary equipment for radio soundings at the Princess Elisabeth station. With the radio soundings, vertical profiles up to 20 to 30 km height of temperature, humidity, pressure, wind speed and wind direction are measured. These data are important for interpretation of the larger scale meteorological and atmospheric dynamic conditions. They are also needed to locate temperature inversions and heights of low and high wind speed (low level jets, jet stream,...), and to characterise the conditions around cloud levels. For the radio soundings, a GRAW GS-E ground station and DFM-09 radiosondes have been used during the BELARE 2015-2016 expedition, organised by the Belgian Polar Secretariat.
The image below shows the vertical profile of the data from a balloon launch on 6 January 2015. To be seen is a strong temperature inversion at around 2500 m altitude and the temperature inversion at the tropopause at around 9500 m. The freezing point temperature was always below the absolute temperature, i.e., no saturation for ice formation was reached. The wind data did not show special features, except that around the tropopause and in the lower stratosphere (9-15 km) the wind direction differed.
Data of the radio sounding on 6 January 2015