Assessment of Biases of Radiosonde Temperature Measurements in the Upper Troposphere and Lower Stratosphere using COSMIC and CHAMP Radio Occultation Data

Radiosondes are the only operational instruments that have provided continuous atmospheric pressure, temperature, and humidity measurements in the troposphere and lower stratosphere (~25 km) for more than three decades. Although their horizontal distribution is inhomogeneous, and their density is relatively low (particularly over the oceans and polar regions), radiosonde measurements are widely used for air temperature trend analysis. However, because the quality of radiosonde measurements varies with height and instrument type, air temperature trends constructed from radiosonde measurements are subject to significant uncertainty. In this study, we compare temperature profiles derived from Global Positioning System (GPS) Radio Occultation (RO) data from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) from 2006 to 2008 and CHAllenging Minisatellite Payload (CHAMP) from 2002 to 2008 with those from different types of radiosonde systems from 12 to 25 km to assess the performance of these radiosonde systems in the upper troposphere and lower stratosphere. Because the measurements obtained from the GPS RO limb-sounding technique are free of satellite-dependent and geographical-dependent biases, the radiosonde temperature biases for different instrument types at different geographical locations are identified. In addition, because GPS RO data are not affected by the temperature variation of the satellite component, we are also able to identify the radiosonde temperature biases due to possible radiative errors resulting from instrument characteristics for different types of radiosonde systems.