On the influence of the altitude of sinkholes on their minimum temperature and a new device for their accurate measurement

Sinkholes represent an excellent natural laboratory to study formation, the maintenance, fluctuations and dissipation of temperature inversions during fair weather episodes with undisturbed radiative conditions. One of the first sinkhole meteorological observations in history were made at a place in the Northeastern Austrian limestone Alps, called Gstettner Alm or Gruenloch. It was known from that early observations, that the air temperature at the bottom of the sinkhole may decrease to values some 30 degrees (Centigrade) or more below the ambient temperature at the same level, leading to the lowest temperatures in Central Europe known so far (around –52 deg C). Such extreme events can only occur when a snow cover is existing, which minimizes the surface heat flux. During the recent few years, comparable experiments have been carried out in the USA.

The strength of temperature inversions and formation of cold pools in sinkholes is determined by topographical and meteorological parameters as well as surface conditions. Whiteman et al., 2004 studied the effects of different sinkhole geometry of three additional sinkholes in the vicinity of the Grünloch basin for snow-free and snow covered situations. They found that the drainage area and depth of the sinkhole are not the primary topographic factors but that the sky view factor is the main controlling parameter for the cooling of the basins.

Dorninger et al., 2008 studied the meteorological events affecting the evolution of temperature inversions or cold-air pools in the 1-km diameter, high-altitude (1300 m MSL) Gruenloch basin using data from a line of temperature data loggers running up a basin sidewall, nearby weather stations and weather charts. Nighttime cold-air pool events observed from October 2001 to June 2002 are categorized into undisturbed inversion evolution, late buildups, early breakups, turbulent erosion at the inversion top, and temperature disturbances occurring above or within the cold air pool.

In the recent campaign 2007/2008 5 sinkholes at the Dachstein plateau and nearby surrounding have been equipped with temperature loggers to investigate the influence of different altitudes on the minimum temperature. The altitudes of the sinkhole floors differ roughly by 1000m. The depths of the sinkholes vary between 30 and 170m. We can assume that the same meteorological conditions are affecting the sinkholes due to their vicinity. First results of this campaign will be presented in the talk.

A great measurement problem arises from the varying snow-pack during the winter season. The accurate position of the measurement sensor related to the snow surface is normally not known since a daily inspection is not possible. Even worse, the sensor might be completely snow covered. A recent developed sensor lift will be described in the talk which allows for accurate measurements even in areas with a snow depth of up to 4m.