An observational study on the surface boundary layer with a hot air balloon

Abstract

For many years the tower observation has played main role on the study of the surface boundary layer and has shown many important results. However, the tower observation method cannot observe higher atmosphere than the tower's height and it is difficult and expensive to construct a sufficiently high tower to observe a top of a little thick surface boundary layer. Therefore, we planed to investigate the surface boundary layer with a hot air balloon and carried out an observational study on the lower planetary boundary layer as a pre-experiment. In this observational system, it is noticeable that some compensations for movement of an anemometer and attentions to distance between sensors and the hot air balloon must be taken when one intends to suspend an anemometer and a thermometer from a hot air balloon. Then influence of the distance to the thermometer was investigated and the hot air balloon was shown to scarcely influence the thermometer when the distance between the hot air balloon and the thermometer was longer than 40 m. The compensations for movement of the suspended supersonic anemometer were designed with a DGPS, a compass, and a clinometer. Estimated errors in wind direction and speed caused from the above compensation methods were 0.6 deg of azimuth, 0.027 deg of inclination, and 0.0061 ms(exp -1) of wind speed. These errors were much smaller than accuracy of the suspended supersonic anemometer, which were 3 deg of azimuth and 0.05 ms(exp -1) of wind speed. Observational results from 07:44 to 08:34 JST on 19December 2004 showed some gravitational waves clearly, whose period changed with the atmospheric stability in a temperature inversion layer at about 730 m level from the ground surface. Cold moist air moved downward and intruded under ascending warm dry air like a convectional movement.