Solar and Thermal Radiation Errors on Upper-Air Radiosonde Temperature Measurements

Abstract

tmospheric temperature and humidity profiles are important for weather prediction, but climate change has increased the interest in upper-air observations asking for very high-quality reference measurements. This paper discusses an experimental approach to determine the radiation-induced error on radiosonde air temperature measurements. On the one hand, solar shortwave and thermal longwave radiation profiles were accurately measured during radiosonde ascents from the surface to 35-km altitude. On the other hand, air temperature was measured with several thermocouples on the same flight, simultaneously under sun-shaded and unshaded conditions. The radiation experiments reveal that thermal radiation errors on the very thin thermocouple of the Meteolabor SRS-C34 radiosonde are similar during night- and daytime. They produce a radiative cooling in the lower troposphere and the upper stratosphere, but a radiative heating in the upper troposphere and lower stratosphere. Air temperature experiments with several thermocouples, however, show that solar radiation produces a radiative heating of about +0.2°C near the surface, which linearly increases to about +1°C at 32 km (~10 hPa). The new solar radiation error profile was then applied to SRS-C34 measurements made during the Eighth WMO Intercomparison of High Quality Radiosonde Systems, held in Yangjiang, China, in July 2010. The effects of thermal and solar radiation errors are finally shown in contrast to the 10 other internationally used radiosonde systems, which were flown during this international campaign.