Temperature Trends and Anomalies in Modern Satellite Data: Infrared Sounding and GPS Radio Occultation
Trends in monthly average, zonal average temperature in the stratosphere as retrieved from highly accurate modern satellite data are intercompared and compared with climate reanalyses from 2003 through 2014. The data sets used are those of Atmospheric Infrared Sounder and Global Positioning System (GPS) radio occultation, and the reanalyses are those of MERRA and ERA-Interim. Trends produced by all data sets agree to within 0.02 K/year in the lower stratosphere and 0.05 K/year in the middle stratosphere. A number of retrieval errors are found that introduce incorrect trends and seasonal anomalies. Adding microwave data to the infrared retrieval changes trends by approximately 0.01 K/year, thus improving agreement with the other data sets. The signature of the quasi-biennial oscillation in temperature and the annual cycle of temperature over Antarctica as retrieved from infrared data contain null-space errors of more than 3 K due to erroneous priors used in retrieval. Nonuniformity in GPS radio occultation gives rise to errors because changes in received GPS signal strength alter the upper boundary initialization in radio occultation retrieval. Finally, an incorrect specification of atmospheric water vapor introduces an erroneous seasonal cycle of temperature as retrieved from GPS radio occultation data in the upper troposphere. All of these time-dependent retrieval errors can be corrected with future research and improvements to spectral infrared and GPS radio occultation retrieval systems.