Variability of temperature and ozone in the upper troposphere and lower stratosphere from multi-satellite observations and reanalysis data
Authors: Shangguan Ming , Wang Wuke , Jin Shuanggen 
Published: May 2019

Abstract. Temperature and ozone changes in the upper troposphere and lower
stratosphere (UTLS) are important components of climate change. In this
paper, variability and trends of temperature and ozone in the UTLS are
investigated for the period 2002–2017 using high-quality, high vertical
resolution Global Navigation Satellite
System radio occultation (GNSS RO) data and improved merged satellite data sets. As part of
the 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 for
their representation of temperature and ozone in the UTLS. The recent
temperature and ozone trends are updated with a multiple linear regression
(MLR) method and related to sea surface temperature (SST) changes based on
model simulations made with NCAR's Whole Atmosphere Community Climate Model
(WACCM). All reanalysis temperatures show good agreement with the GNSS RO measurements
in both absolute value and annual cycle. Interannual variations in
temperature related to Quasi-Biennial Oscillation (QBO) and the El Niño–Southern
Oscillation (ENSO) processes are well represented by all
reanalyses. However, evident biases can be seen in reanalyses for the linear
trends of temperature since they are affected by discontinuities in
assimilated observations and methods. Such biases can be corrected and the
estimated trends can be significantly improved. ERA5 is significantly
improved compared to ERA-I and shows the best agreement with the GNSS RO
temperature. The MLR results indicate a significant warming of
0.2–0.3 K per decade in most areas of the troposphere, with a
stronger increase of 0.4–0.5 K per decade at midlatitudes of both
hemispheres. In contrast, the stratospheric temperature decreases at a rate
of 0.1–0.3 K per decade, which is most significant in the Southern
Hemisphere (SH). Positive temperature trends of 0.1–0.3 K per decade
are seen in the tropical lower stratosphere (100–50 hPa). Negative
trends of ozone are found in the Northern Hemisphere (NH) at
150–50 hPa, while positive trends are evident in the tropical lower
stratosphere. Asymmetric trends of ozone can be found in the midlatitudes of
two hemispheres in the middle stratosphere, with significant ozone decrease
in 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 ozone
data. According to single-factor-controlled model simulations with WACCM, the
temperature increase in the troposphere and the ozone decrease in the NH
stratosphere are mainly connected to the increase in SST and subsequent
changes of atmospheric circulations. Both the increase in SSTs and the
decrease in ozone in the NH contribute to the temperature decrease in the NH
stratosphere. The increase in temperature in the lower stratospheric tropics
may be related to an increase in ozone in that region, while warming SSTs
contribute to a cooling in that area.