Influence of Meteorological Balloons on Temperature Measurements with Radiosondes: Nighttime Cooling and Daylight Heating

Abstract

Temperatures measured by radiosondes ascending on free-flying balloons within middle latitudes above the troposphere differ significantly from measurements made with the same radiosondes descending on parachutes after the balloons have burst. During ascending flights, values measured below the balloons are too low for night ascents, and ton high for daylight ascents. The divergences grow with decreasing air pressure. During night ascents, the adiabatic gas temperature decreases within the balloon, lowering the balloon skin temperature. During daylight ascents, in contrast, solar radiation heats the balloon skin, superimposing a heating effect upon the adiabatic cooling effect on the balloon skin. In each case the resulting surface temperature of the balloon affects via heat exchange the airstream passing the balloon. Both effects grow with increasing height. Temperature diffusion velocity calculations show a very long stability of the wake. Since the radiosonde sensor will measure mainly the temperature within the balloon wake, the aforementioned influences cannot be neglected, if true temperature measurements are the aim.