Atmospheric Temperature Changes and their Drivers (ATC) SPARC Activity

1. Atmospheric Temperature Changes and their Drivers (ATC) SPARC Activity Amanda Maycock (University of Leeds, UK), Andrea Steiner (WEGC, University of Graz, Austria) SPARC DA workshop, Reading, UK, 26th October 2017

2. ATC Activity – Establishment Atmospheric Temperature Changes and their Drivers(ATC) Activity – Launch • The ATC Activity was launched in 2016. • It evolved from the long-standing SPARC Stratospheric Temperature Trends activity. • We held out first science workshop in Graz in April 2016.

3. ATC Activity – Establishment Atmospheric Temperature Changes and their Drivers(ATC) Activity – Members

4. ATC Activity – Scientific priorities Two Main Foci Atmospheric temperature variability and trends,and their uncertainty in climate data records (CDRs): (i) fromthetropospheretothemesosphere (ii) inclusionofemergingnovelobservationalrecords, e.g., limb-viewinginstrumentswithhigh verticalresolution (iii) improvinguncertaintyinformation Attribution of atmospheric temperature changes: (i) Comparison between GCMs/CCMs and CDRs (ii) Attribution of temperature trends to radiative and dynamical drivers

5. Recent progress – lower troposphere temperature TLT • A new lower-tropospheric temperature product, RSS v4.0 TLT, has been constructed from measurements of MSU channel 2 and AMSU channel 5 using an optimized adjustment for diurnal effects (local time drift)by Mears and Wentz (2017) • Resulting global- scale trend (70S–80N) 1979–2016 are 0.174°C/decade Mearsand Wentz, 2017

6. Recent progress – Troposphere temperature trends in satellite observations and models • Tropospheric warming rates (TMT) in climate models and observations have been compared by Santer et al. (2017a,b). • Models overestimate warming rates in early 21st century, partly due to systematic deficiencies in some model forcings (Santeret al., 2017c). • Tropospheric warming trends larger than from natural variability only. • Trends 1979–2016: 0.199/0.202/0.142°C/decade for RSS/STAR/UAH Santer et al., 2017b

7. Progress – Troposphere-stratosphere temperature trends in satellite observations and models • Stratosphere and troposphere temperature trends from the WACCM model were compared with satellite observations (Randel et al., 2017). • Good agreement in trends at tropical latitudes is found, but larger differences in polar regions where internal variability may contribute to observed and modeled trends. • Trend period 1979 –1997 (ozone depletion): Antarctic lower stratosphere cooling Randelet al., 2017

8. Progress – Troposphere-stratosphere temperature trends in satellite observations and models • Trend period 1998–2014 (recovery): 2-3 times less cooling in global upperstratosphereandwarmingobservedin Antarcticlowerstrat. Randelet al., 2017

9. Progress – Stratosphere temperature trends in satellite observations and CCMI models • Updated comparison of stratospheric temperature trends in CCMI model simulations with reprocessed satellite records • Reprocessed SSU datashowbetter agreement of NOAA & UKMO global temperatures (Nash and Saunders, 2015;Zou et al., 2014) • Models now in good agreement in SSU2/3 cf. CCMVal2 and CMIP5 models (Thompson et al, 2012) • Long-term cooling in SSU1/MSU4 still slightlyweaker in models WMO 2018 Ozone Assessment, first order draft Source: Maycock, 2017

10. Progress – Reanalyses and observations • Long et al. (in review) compare temperature trends in reanalysis with AMSU/SSU observations in the SPARC S-RIP activity. Some reanalyses reveal substantial differences (CFSR, others within ±0.5 K difference). Caution is advised for using reanalysis temperatures for trend detection. Long et al., in review

11. Progress – Comparisons and use of RO observations • Atmospheric variability including Kelvin waves, the QBO and ENSO (Scherllin-Pirscher et al., 2017; Wilhelmsen et al. 2017, in revision). • Comparisons with models, tropopause region & convection regions (Schmidt et al., 2017; Steiner et al., 2017, in review). • Temperature biases in the UTLS for different radiosonde types characterized (Ho et al., 2017). • Stratospheric temperature changes 2002–2016 from AMSU on the AQUA satellite and GPS RO are found consistent (Khaykin et al., 2017). • Stratospheric temperature changes 2002–2016 from GPS RO and different radiosonde records are found consistent, MSU/AMSU records still some differences (Ladstädteret al., COSMIC-IROWG 2017). [Wilhelmsenet al. 2017]

12. Progress – model/data comparison – RO record • Assessment of the consistency of 15-yr multi-satellite RO records • Temperature deviation to all-satellite mean for 20°S to 20°N • Consistency at 25–35 km within ~0.2 K • UTLS at 8–25 km within ~0.1 K Deviation from satellite mean 25–35 km WEGC OPSv5.6 RO record 05/2001–02/2017 Deviation from satellite mean 8–25 km Steiner et al., OPAC-IROWG 2016; COSMIC-IROWG 2017

13. Recent progress – Attribution of temperature changes 70hPa monthly temperature anomalies 20N-20S mean annual cycle amplitude Ming et al., ACP, 2017 • Green shows full annual cycle from reanalysis data • Black shows total contribution to annual cycle from ozone and water vapour • Light blue shows contribution to annual cycle from dynamical forcing • Take home message: together the annual cycles in ozone and water vapour contribute ~30% of the peak annual cycle in temperature in the tropical lower stratosphere.

14. ATC Activity – EGU 2017 session

15. Plans for 2018 • Joint paper 1 • Peer-previewed paper on climate data records for temperature: updated radiosondes, reprocessed GPS RO data, SSU/AMSU merged products, lidar data. • Not only a review of recent literature but also to contain new science. • Aim for complete first draft by early next year. • Joint paper 2 • Peer-reviewed publication on the analysis of CCMI model temperature trends and comparison to updated satellite measurements. • Paper in support of WMO 2018 Ozone Assessment. • Aim for submission early next year.

16. Plans for 2018 • ATC activity has teamed up with the SPARC LOTUS Activity to propose a joint session for the EGU 2018 for which the ATC co-chairs are co-conveners. • Call for abstracts now open. Closes 11 January 2017 • We plan to have a next dedicated two-day ATC activity workshop in mid-2018. One day will be dedicated to discussion of the towards paper finalization. One day will be dedicated to open science contributions.

17. References – ATC contributions 2017 References: Ding, Q., and Q. Fu (2017), A warming tropical central Pacific dries the lower stratosphere. Clim. Dyn., https://doi.org/10.1007/s00382-017-3774-y. Garfinkel, C. I., S.-W. Son, K. Song, V. Aquila, and L. D. Oman (2017), Stratospheric variability contributed to and sustained the recent hiatus in Eurasian winter warming, Geophys. Res. Lett., https://doi.org/10.1002/2016GL072035. Ho, S.-P., L. Peng, and H. Vömel (2017), Characterization of the long-term radiosonde temperature biases in the upper troposphere and lower stratosphere using COSMIC and Metop-A/GRAS data from 2006 to 2014, Atmos. Chem. Phys., https://doi.org/10.5194/acp-17-4493-2017. Ivy, D. J., S. Solomon, N. Calvo, and D. W. J. Thompson (2017), Observed connections of Arctic stratospheric ozone extremes to Northern Hemisphere surface climate, Environ. Res. Lett., doi:10.1088/1748-9326/aa57a4. Khaykin, S. M., B. M. Funatsu, A. Hauchecorne, S. Godin-Beekmann, C. Claud, P. Keckhut, et al. (2017), Postmillennium changes in stratospheric temperature consistently resolved by GPS radio occultation and AMSU observations, Geophys. Res. Lett., https://doi.org/doi:10.1002/2017GL074353. Li, J., D. W. Thompson, E. A. Barnes, and S. Solomon (2017), Quantifying the lead time required for a linear trend to emerge from natural climate variability, J. Climate, https://doi.org/10.1175/JCLI-D-16-0280.1. Long, C. S., M. Fujiwara, S. Davis, D. M. Mitchell, and C. J. Wright (2017), Climatology and Interannual Variability of Dynamic Variables in Multiple Reanalyses Evaluated by the SPARC Reanalysis Intercomparison Project (S-RIP), Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2017-289, submitted. Mears, C. A., and F. J. Wentz (2017), A satellite-derived lower-tropospheric atmospheric temperature dataset using an optimized adjustment for diurnal effects, J. Climate, https://doi.org/10.1175/JCLI-D-16-0768.1. Ming A., A. C. Maycock, P. Hitchcock, and P. Haynes (2017), The radiative role of ozone and water vapour in the annual temperature cycle in the tropical tropopause layer, Atmos. Chem. Phys., doi: 10.5194/acp-17-5677-2017.

18. References – ATC contributions 2017 References: Randel, W. J., L. Polvani, F. Wu, D. E. Kinnison, C.-Z. Zou, and C. Mears (2017), Troposphere-stratosphere temperature trends derived from satellite data compared with ensemble simulations from WACCM, J. Geophys. Res.-Atmos., https://doi.org/10.1002/2017JD027158. Santer, B. D., S. Solomon, G. Pallotta, C. Mears, S. Po-Chedley, Q. Fu, F. Wentz, C.-Z. Zou, J. Painter, I. Cvijaovic, and C. Bonfils (2017a), Comparing tropospheric warming in climate models and satellite data, J. Climate, https://doi.org/10.1175/JCLI-D-16-0333.1. Santer, B. D., S. Solomon, F. J. Wentz, Q. Fu, S. Po-Chedley, C. Mears, J. F. Painter, and C. Bonfils (2017b), Tropospheric warming over the past two decades, Scientific Reports, https://doi.org/10.1038/s41598-017-02520-7. Santer, B. D., et al. (2017c), Causes of differences in model and satellite tropospheric warming rates, Nature Geosci., doi:10.1038/ngeo2973 Scherllin-Pirscher, B., W. J. Randel, and J. Kim (2017), Tropical temperature variability and Kelvin-wave activity in the UTLS from GPS RO measurements, Atmos. Chem. Phys., 17(2), 793–806, https://doi.org/10.5194/acp-17-793-2017. Schmidt, T., L. Schoon, H. Dobslaw, K. Matthes, M. Thomas, and J. Wickert (2016), UTLS temperature validation of MPI-ESM decadal hindcast experiments with GPS radio occultations, Meteorol. Z., https://doi.org/10.1127/metz/2015/0601. Steiner, A. K., B. C. Lackner, and M. A. Ringer (2017). Tropical convection regimes in climate models: evaluation with satellite observations. Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2017-669, in review. Wilhelmsen, H., F. Ladstädter, B. Scherllin-Pirscher, andA. K. Steiner (2017). Atmospheric QBO and ENSO indices with high vertical resolution from GNSS radio occultation temperature measurements. Atmos. Meas. Tech. Discuss., 2017, https://doi.org/10.5194/amt-2017-226, in review. ATC webpage: http://www.sparc-climate.org/activities/temperature-changes/

19. Thank you for your attention.andi.steiner@uni-graz.ata.c.maycock@leeds.ac.uk