Assessing Radiometric Calibration, Retrieved Atmospheric Temperature Profiles Quality and Radiative Transfer Model Accuracy Using GPS-RO temperature Profiles in the Summer Stratospheric Hemisphere

The summer stratospheric hemisphere is a uniquely simply environment in which to study the performance of satellite-based atmospheric sounders. The stratosphere is primarily in radiative balance with high pressure over the pole and weak axisymmetric easterly flow persisting for months. Temperature is highly correlated zonally and intercomparisons between observations have precision better than 1 K over zonal distances greater than 1,000 km. Therefore good sampling statistics are possible with infrequent observations because mismatch error grows slowly with increasing coincidence time and distance. In this presentation we compare ATMS and CrIS radiances in stratospheric temperature sounding channels against calculated radiances from GPS radio occultation (GPS-RO) profiles and numerical weather forecast (NWF) models. The GPS-RO comparisons are generally good in the mid-stratosphere, while the NWF intercomparisons are generally poorer, limited by radiation modeling of the stratosphere in the NWF. We have analyzed dependence of the radiance residuals on cloud contamination in tropospheric channels, because clouds are not expected to influence stratosphere-sensing IR radiances and this is a simple test on the CrIS instrument performance. ATMS brightness temperatures are sorted by latitude and scan angle and compared with near coincident GPS-RO temperature profiles to separate errors in radiative transfer modeling from antenna pattern and spectroscopy. We demonstrate the value of stratospheric observations for characterizing instrument performance, which can than be applied to climatically more interesting regimes.