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Abstract. Temperature and ozone changes in the upper troposphere and lowerstratosphere (UTLS) are important components of climate change. In thispaper, variability and trends of temperature and ozone in the UTLS areinvestigated for the period 2002–2017 using high-quality, high verticalresolution Global Navigation SatelliteSystem radio occultation (GNSS RO) data and improved merged satellite data sets. As part ofthe Stratosphere-troposphere Processes And their Role in Climate (SPARC)Reanalysis Intercomparison Project (S-RIP), three reanalysis data sets,including the ERA-I, MERRA2 and the recently released ERA5, are evaluated fortheir representation of temperature and ozone in the UTLS. The recenttemperature and ozone trends are updated with a multiple linear regression(MLR) method and related to sea surface temperature (SST) changes based onmodel simulations made with NCAR's Whole Atmosphere Community Climate Model(WACCM). All reanalysis temperatures show good agreement with the GNSS RO measurementsin both absolute value and annual cycle. Interannual variations intemperature related to Quasi-Biennial Oscillation (QBO) and the El Nino–SouthernOscillation (ENSO) processes are well represented by allreanalyses. However, evident biases can be seen in reanalyses for the lineartrends of temperature since they are affected by discontinuities inassimilated observations and methods. Such biases can be corrected and theestimated trends can be significantly improved. ERA5 is significantlyimproved compared to ERA-I and shows the best agreement with the GNSS ROtemperature. The MLR results indicate a significant warming of0.2–0.3  K per decade in most areas of the troposphere, with astronger increase of 0.4–0.5  K per decade at midlatitudes of bothhemispheres. In contrast, the stratospheric temperature decreases at a rateof 0.1–0.3  K per decade , which is most significant in the SouthernHemisphere (SH). Positive temperature trends of 0.1–0.3  K per decade are seen in the tropical lower stratosphere (100–50  hPa ). Negativetrends of ozone are found in the Northern Hemisphere (NH) at150–50  hPa , while positive trends are evident in the tropical lowerstratosphere. Asymmetric trends of ozone can be found in the midlatitudes oftwo hemispheres in the middle stratosphere, with significant ozone decreasein the NH and increase in ozone in the SH. Large biases exist in reanalyses,and it is still challenging to do trend analysis based on reanalysis ozonedata. According to single-factor-controlled model simulations with WACCM, thetemperature increase in the troposphere and the ozone decrease in the NHstratosphere are mainly connected to the increase in SST and subsequentchanges of atmospheric circulations. Both the increase in SSTs and thedecrease in ozone in the NH contribute to the temperature decrease in the NHstratosphere. The increase in temperature in the lower stratospheric tropicsmay be related to an increase in ozone in that region, while warming SSTscontribute to a cooling in that area.

Variability of temperature and ozone in the upper troposphere and lower stratosphere from multi-satellite observations and reanalysis data