Evaluation of radio occultation measurements for long-term tropopause monitoring

Research suggests that changes in tropopause structure can both indicate and impact changes in the global climate system. The Global Positioning System radio occultation (RO) technique shows tremendous potential for monitoring the global tropopause due to its precision, temporal consistency, and global measurement density. This study examines the capability of RO to monitor the global tropopause by addressing three specific objectives: (1) quantify sources of uncertainty in individual RO tropopause measurements, (2) examine mean biases and long-term stability of RO tropopause parameters with respect to those obtained from radiosondes, and (3) distinguish between errors due to processing and RO instrument differences by comparing tropopause parameters from different RO products. Measured tropopause uncertainty is shown to be due largely to the nonlinear nature of the tropopause. Global mean temperature and height biases between RO instruments and radiosondes are small. One long-term RO dataset examined in this study showed spurious temperature trends, but these have since been corrected. Tropopause measurements from different RO instruments are generally very small as long as datasets are processed similarly. These results confirm the precision of RO data, but also demonstrate the importance of careful, consistent processing for long-term tropopause temperature studies. Unlike tropopause temperatures, tropopause heights do not appear to be significantly affected by the differences in processing examined in this study.