During the winter season 2001/2002 a field experiment takes/took place in a limestone area with sinkholes of different sizes in the Eastern Alps. The largest sinkhole, some 50 m deep and approxiamately one km in diameter is called Grünloch and became famous long ago, when temperature measurements at the bottom showed minimum values below –50 deg C (-57 deg C being the absolute minimum). This location at an elevation of roughly 1300 m msl represents the spot with the coldest surface temperature ever recorded in Central Europe.

Sinkholes represent an excellent natural laboratory to study the formation, the maintainance, fluctuations and the dissipation of temperature inversions during fair weather episods with undisturbed radiative conditions. A snow cover minimizes the effect of surface heat fluxes, therefore the winter season, i. e. the season of snow cover, is the best time for such investigations. The air temperature under optimal conditions may decrease more than 30 deg below the value in the free atmosphere at the same level. In a typical year the snowcover starts to build up in November and ends in May.

In a joint effort of scientists from different institutions dense arrays of recording surface temperature sensors (a total of 58 stations), a few fully instrumented (temperature, humidity, wind, global radiation) automatic surface weather stations and a mast for profile measurements was installed in the autumn of 2001. During special campaigns tethersonde measurements and profile measurements with mobile equipment were conducted to study the vertical temperature profile and the wind field during the formation, fluctuations and dissipation of inversions. An overview will be given about the experimental design and the key initial results will be of the collected data will be presented.