The Heidelberg Aeolotron - a new facility for laboratory investigations of small scale air-sea interaction

The study of small-scale air sea interaction still lacks suitable facilities. No facilities are available with large fetches and correspondingly high wave ages. Furthermore almost no large facility is suitable for measurements with sea water, is clean enough for controllable experiments with surface films or sufficiently gas tight for gas exchange measurements. Currently a new large annular wind/wave facility with quasi unlimited fetch is under construction at the Institute for Environmental Physics of Heidelberg University. An annular facility is not a new idea. A 40 m diameter facility (``storm basin'') was already built shortly after World War II in Sevastopol for wind/wave interaction studies. Various small circular facilities for air-sea gas exchange studies have been used since the late seventies at Heidelberg University and later at Woods Hole Oceanographic Institution for air-sea gas exchange studies. The new facility builds on the experience with these facilities but now reaches a critical size. It has an outer diameter of 10 m, the channel is 0.65 m wide and 2.4 m high and can be filled with water up to a height of 1.2 m. It is thus a rather deep facility. Only the wind/wave flume of the Hydraulic facility at Scripps Institution of Oceanography is deeper with a depth of 1.5 m. Since the maximum phase speed of the waves is 3.4 m/s, high wave age conditions can be reached at least for low and medium wind speeds. The facility is designed for a maximum wind speed of 15 m/s. Water currents can be generated separately by a set of thrusters. The air space is gas tight and the materials that come into contact with the water and air make experiments possible with de-ionized water, artificial seawater, surfactants, and reactive gases. Water temperatures and heat fluxes across the interface range from 5o to 35oC and from -0.5 to 1 kW/m2, respectively. We plan to focus in the next decade on measurements revealing the mechanism of air-sea gas transfer including the effects of surfactants and waves. The new facility will be open for guest scientists. The experimental possibilities of the facility are detailed to show the opportunities for international cooperation.