| Popis: |
It is well known that the gas in an ascending helium or hydrogen filled balloon cools faster than the surrounding atmosphere for night ascents. The cooler balloon then removes heat from the surrounding air, resulting in regions of cooler air in the trailing wake. This can affect data from air temperature sensors, including temperature variance sensors from which optical turbulence level is determined. This paper reviews the thermodynamics and heat transfer of the cooling. On seven Thermosondes, an instrument that measures temperature variance across a 1m distance, the normal "rod thermistor" mean temperature sensor was augmented with a very fast, micro-bead temperature sensor. The micro-beads did detect cooler regions that were not evident in the rod thermistor data. These cooler regions were often associated with the detection of increased temperature variance. Unfortunately, all micro-beads flew under benign atmospheric conditions. This resulted in rather low uncorrected optical turbulence levels. In addition, wind shear was generally low, which favors wake interactions, and, indeed, many regions of possible wake interaction were identified. Removal of the interaction regions reduced the optical turbulence performance factors from a maximum of 62%, for the least turbulent flight, to less than 7%, for the highest turbulent flight. More experiments should be performed for a wider range of shear and turbulence conditions. |
