Radiosonde temperature, humidity, and pressure response at low temperatures

The response of radiosondes to an instantaneous change of environment was studied by taking the instruments from a warm building into the cold environment at South Pole Station. After being initialized inside, the radiosondes were carried outside and placed on the snow surface, where they were left until they reported stable values of temperature, pressure and relative humidity. Three models of radiosondes were tested: Vaisala RS80, Atmospheric Instrumentation Research (AIR) 4A, and AIR 5A.

The reported temperature equilibrated to the outside conditions within 30 seconds. However, it frequently took 30 minutes before the relative humidity outside was accurately reported. Surprisingly, the reported pressure rose by several millibars over a five-minute period when the sonde was taken outside. In the RS80s this bias was as large as 10 mb, and disappeared in about 30 minutes. In the AIR sondes, the maximum pressure bias was never much over two millibars, but seemed not to disappear over time.

The RS80s were also tested to see if, once equilibrated to the outside conditions, they could respond to smaller changes that could be encountered in flight. The results in this case indicate that, with some corrections for time lag, the RS80 can provide accurate data at low temperatures if allowed to equilibrate initially.

The results of these tests together indicate that the quality of upper-air data in cold regions could be improved if radiosondes are stored and prepared at ambient temperature, or are given at least 30 minutes to equilibrate after being prepared inside.