1.6 Evaluating stratospheric temperature trends in WACCM

The temperature of the stratosphere has decreased over the last several decades because of the combined effects of increases in well-mixed greenhouse gases (GHGs) and changes in stratospheric ozone. How well is this behavior simulated in current generation chemistry-climate models?  Recent work in ACOM has aimed at deriving updated estimates of stratospheric temperature changes from satellite measurements (beginning in 1979), and making detailed comparisons with simulations from WACCM.

The observational record of satellite temperature changes in the middle and upper stratosphere has recently been updated (1979-2015) based on combining measurements from SSU, MLS and SABER satellite instruments (Randel et al., 2016), and these data are available to the wider community (https://acomstaff.acom.ucar.edu/randel/SSU%20data.html). Time series of global average temperature anomalies from these data are shown in Fig. 1, compared to WACCM results (this version of WACCM includes specified SSTs, observed changes in greenhouse gases and ozone depleting substances, along with volcanic and QBO effects). Overall the model shows excellent agreement to satellite observations for the global averages, including long-term stratospheric cooling, solar cycle and volcanic effects. Current work is aimed at understanding detailed behavior of the long-term temperature changes and difference among separate WACCM realizations.

Sample template image

Figure 1. Time series of global average temperature anomalies for 1979-2015 derived from satellite measurements (black lines) for different satellite channels (with weighting functions shown at left, covering altitudes from the lower troposphere to the upper stratosphere). Red lines show the corresponding results from three separate WACCM realizations.

Randel, W.J., A.K. Smith, F. Wu, C.-Z. Zou and H. Qian, 2016: Stratospheric temperature trends over 1979-2015 derived from combined SSU, MLS and SABER satellite observations. J. Climate, 29, 4843-4859, doi:10.1175/JCLI-D-15-0629.1