ECVS IN THE STRATOSPHERE

Transcription

1 METEOROLOGY ECVS IN THE STRATOSPHERE O 3, H 2 O, AEROSOL, N 2 O, CH 4, CFCS, HCFCS, HFCS, SF 6, PFCS, AND TEMPERATURE Michaela I. Hegglin, University of Reading UK

2 GCOS COMPOSITION ECVs EXTEND INTO THE STRATOSPHERE ESA Climate Change Initiative Collocation meeting ESRIN October

3 GCOS COMPOSITION ECVs EXTEND INTO THE STRATOSPHERE New definition of stratospheric ECVs: High-vertical resolution ozone, water vapour, aerosol, transport tracers and temperature from the upper troposphere to the stratopause. ESA Climate Change Initiative Collocation meeting ESRIN October

4 OBSERVATIONS Golden age of past limb satellite observations that is ready for exploitation. SPARC Data Initiative provided first comprehensive intercomparison of US and European instruments. solar occultation TES Aura stellar occultation SMILES ISS limb emission HIRDLS Aura limb scattering nadir MLS ACE MAESTRO Aura SCISAT 1 ACE FTS SCISAT 1 SCIAMACHY Envisat GOMOS Envisat MIPAS Envisat SAGE III Meteor 3M SMR Odin OSIRIS Odin POAM III SPOT 4 POAM II SPOT 3 MLS UARS HALOE UARS SAGE II ERBS SAGE I AEM B LIMS Nimbus No future satellite limb sounders with the capability to measure long-lived GHGs are foreseen for the future. Ground-based (e.g. NDACC) observations have limited spatial and temporal coverage, and coarse vertical resolution. SPARC Data Initiative Report (Eds. Hegglin & Tegtmeier), in print ESA Climate Change Initiative Collocation meeting ESRIN October

5 STRATOSPHERIC ECVs AND CLIMATE Long-lived GHGs in the stratosphere affect both local temperatures and surface climate! IPCC ~Altitude (km) Water vapour increase Ozone increase Methane increase tropopause Latitude (degrees) Latitude (degrees) Latitude (degrees) Relative Radiative Forcing GHGs contribute to warming of surface climate (and aerosols to cooling). In the stratosphere, most GHGs lead to a local cooling. ESA PREMIER: Report for mission selection, 2013 Dynamical feedbacks from chemistry-climate coupling extend to the surface (e.g., Antarctic ozone hole impact on Southern hemisphere surface climate during summer). ESA Climate Change Initiative Collocation meeting ESRIN October

6 STRATOSPHERIC ECVs AND OZONE GHGs from tropospheric sources are destroyed in the stratosphere, affect chemistry, and impact the natural balance of the ozone layer.! WMO/UNEP ozone assessment Future mix of GHG emissions will determine the future state of the ozone layer (with CH 4 and N 2 O having opposing effects on stratospheric ozone chemistry). Transport of GHGs through the stratosphere determines their lifetimes. Lifetimes of GHGs can be derived from vertical gradients (SPARC Lifetimes Report, 2014) Hegglin et al., WMO 2015; after Fleming et al., 2013 ESA Climate Change Initiative Collocation meeting ESRIN October

7 STRATOSPHERIC AEROSOL Hegglin et al., in preparation SAGE II HALOE POAM II POAM III OSIRIS SAGE III GOMOS SCIAMACHY ESA Climate Change Initiative Collocation meeting ESRIN October

8 IMPORTANCE OF STRATOSPHERIC AEROSOL Stratospheric aerosol is considered in total radiative forcing calculations and is important to understand interannual variability. It is currently understood to have contributed up to ¼ to the hiatus in global warming after 1998 (Solomon et al., Science 2010). NB, just increase from rising methane is considered in these models. NB, lifetime of longlived GHGs is important factor in determining radiative forcing IPCC AR5 (Figure 8-18), 2014 ESA Climate Change Initiative Collocation meeting ESRIN October

9 SPARC DATA INITIATIVE AEROSOL Quality-control and merging of stratospheric aerosol products is not straightforward due to the wavelength dependency of retrievals. A new scaling approach introduced in the SPARC Data Initiative allows for an easier comparison and may also be used for merging. Raw timeseries Scaled timeseries Hegglin et al., in preparation; SPARC Data Initiative Report (Eds. Hegglin & Tegtmeier), in print ESA Climate Change Initiative Collocation meeting ESRIN October

10 STRATOSPHERIC OZONE Tegtmeier et al, JGR 2013 ESA Climate Change Initiative Collocation meeting ESRIN October

11 IMPORTANCE OF STRATOSPHERIC OZONE Total column ozone showed no decline in the tropics. WMO 2014, after Shepherd et al., Nature Geoscience 2014 However, decomposition into tropospheric and stratospheric column ozone reveals that stratospheric ozone decline was masked by an increase in tropospheric ozone. Provides independent constraint on tropospheric ozone, a major GHG but hard to constrain from tropospheric measurements Comparison to limb sounder measurements from the SPARC Data Initiative was crucial to prove model result. ESA Climate Change Initiative Collocation meeting ESRIN October

12 STRATOSPHERIC WATER VAPOUR Hegglin et al, JGR LIMS SAGE II UARS-MLS HALOE POAM III SMR(1) SMR(2) SAGE III MIPAS SCIAMACHY ACE-FTS Aura-MLS ESA Climate Change Initiative Collocation meeting ESRIN October

13 IMPORTANCE OF STRATOSPHERIC H 2 O Water vapour is the most important natural greenhouse gas in the atmosphere and provides a positive feedback to the climate forcing from CO 2. A stratospheric water vapour trend of 0.4 ppmv/decade (as was apparently observed over Boulder) over would have led to global surface warming that was 44% of that from CO 2 alone. The assumed constant water vapour increase induces a strong latitudinal structure in the cooling of the stratosphere! important for dynamical feedbacks Changes are largest in the UTLS Forster & Shine, GRL 1999 ESA Climate Change Initiative Collocation meeting ESRIN October

14 THE STRATOSPHERIC H 2 O PUZZLE Hurst et al., JGR 2011 At most one-third of the observed trend over Boulder can be explained by CH 4 oxidation. Wang, Seidel & Free, JGR 2012 Also, tropical tropopause temperatures, understood to be the main other driver of stratospheric water vapour changes, show rather a negative or zero trend. ESA Climate Change Initiative Collocation meeting ESRIN October

15 NEW MERGING APPROACH LEADS TO NEW ANSWERS Large discrepancies are seen between instruments. CMAM30 (gray) compares very well with SAGE II and HALOE between Determine the offsets with respect to CMAM30. Bias-correct the data records relative to MLS, using CMAM30 as transfer function. Result: homogenized time series of stratospheric water vapour, which can be merged. Allows extension of the water vapour record back into the late 1980s, based on SAGE II. H 2 O [ppmv] Diff H 2 O (obs-cmam20) [ppmv] bias-corrected with bias H 2 O-corrected [ppmv] a b c d Hegglin et al., Nature Geoscience 2014 Tropical H hpa HALOE SCIAMACHY ACE-FTS SAGE II MIPAS Aura-MLS SMR Jan 90 Jan 95 Jan 00 Jan 05 ESA Climate Change Initiative Collocation meeting ESRIN October

16 SANITY CHECK Tropical water vapour and temperature anomalies (scaled with respect to their interannual variability) show a strong correlation. Residuals (differences between the scaled variables) mostly fluctuate around zero. Hegglin et al., Nature Geoscience 2014 CMAM ESA Climate Change Initiative Collocation meeting ESRIN October

17 STRATOSPHERIC H 2 O CHANGES (late 1980s to 2010) Trends in the lower to mid stratosphere are seen to be negative, not positive as would be inferred from the Boulder record! In the upper stratosphere, the trends are positive. The vertical structure in the changes indicates structural changes in the Brewer-Dobson circulation. Hegglin et al., Nature Geoscience 2014 ESA Climate Change Initiative Collocation meeting ESRIN October

18 STRATOSPHERIC SF 6 Tegtmeier et al, ESSD submitted ESA Climate Change Initiative Collocation meeting ESRIN October

19 IMPORTANCE OF HALOCARBONS AND FLUORINATED SPECIES Long-lived tracers can be used as age-of-air indicators. Stiller et al., ACP 2012 Trends derived from MIPAS SF 6 measurements between for example indicate a slowing of the stratospheric circulation. Difference from Hegglin et al. (2014) is explained by a difference in the time periods considered.! Note, need for long-term observational records! ESA Climate Change Initiative Collocation meeting ESRIN October

20 MERGING TEMPERATURE DATA RECORDS Stratospheric temperatures are a key indicator of stratospheric changes. Using a new merging method (based on MIPAS limb measurements as a transfer function between SSU and AMSU), the extended SSU record shows excellent agreement with the CMIP5 model mean and trends over There still remain issues on the latitudinal structure in temperature changes. McLandress et al., ACP 2015 Thompson et al., Nature 2012 ESA Climate Change Initiative Collocation meeting ESRIN October

21 FUTURE NEEDS! CCI+ Improve and understand climate data records (CDRs) of stratospheric ECVs in order to understand climate variability and trends and the mechanisms that drive them! support international assessments and contribute to GCOS goals Should extend to stratospheric ECVs other than ozone. Should improve data products that will be merged into CDRs (SPARC Data Initiative) Perform inter-comparison of ECVs derived using different data sources and merging approaches to gain confidence in the products and assess uncertainty. Assess consistency of variability and trends in water vapour, ozone, aerosol and temperature, including link to circulation changes (other ECVs). Yields information on consistency between ECVs in terms of geophysical structure. Yields info in terms of cross-talk in retrievals (e.g. strat. aerosol in SST retrievals) Also important consideration for joint analysis of nadir and limb observations (CH 4 ). Need for limb satellite sounders to be able to extend ECVs into the future. In absence of future limb measurements, can use ground-based measurements to determine long-term changes, but need to test their representativeness using the golden age of satellite limb sounders. ESA Climate Change Initiative Collocation meeting ESRIN October

22 CHEMISTRY-CLIMATE COUPLING Climate change is expected to lead to a strengthening of the stratospheric circulation, which affects ozone and other trace gases. The decrease in water vapour is expected to lead to a decrease in the surface temperature response. It is important to understand the magnitude of these radiative-chemical couplings. Hegglin and Shepherd, Nature Geoscience 2009 Nowack et al., Nature Climate Change 2014 ESA Climate Change Initiative Collocation meeting ESRIN October

23 COUPLING BETWEEN OZONE AND TEMPERATURE Ozone is strongly coupled to temperature in the mid to upper stratosphere, and also in the polar vortex. A free-running version of the CMAM chemistry-climate model is compared to a version in data assimilation mode and indicates that a better representation of temperature improves the ozone field. Shows the use of a model to quantify the coupling. Hegglin, unpublished work for CSA ESA Climate Change Initiative Collocation meeting ESRIN October

24 Wavelength bands GCOS stratospheric ECVs of long-lived trace gases can be detected in (based on SPARC Data Initiative instruments). SPARC Data Initiative Report (Eds. Hegglin&Tegtmeier), in print ESA Climate Change Initiative Collocation meeting ESRIN October

25 SATELLITE INSTRUMENT EVALUATION Hegglin et al, JGR 2013 First study to show that SAGE II has a decent H 2 O product. Key point: opportunity to extend the satellite water vapour record backward in time! ESA Climate Change Initiative Collocation meeting ESRIN October

26 COMPARISON WITH BOULDER RECORD CMAM30 and satellite mean have been shown to yield consistent results, with a strong correlation between temperatures and water vapour. H 2 O anomaly [ppmv] H 2 O diff [ppmv] a Satellites merged Boulder in-situ CMAM30 CMAM30-subsampled b Jan 80 Jan 85 Jan 90 Jan 95 Jan 00 Jan 05 Jan 10 Although short-term fluctuations agree better, the long-term trend cannot be reconciled with either the model or the satellite record. ESA Climate Change Initiative Collocation meeting ESRIN October

27 PREDICTION OF FUTURE TRENDS Stratospheric water vapour is predicted to increase by about 1 ppmv by the end of the 21 st century. However stratospheric chemistry-climate models (CCMVal) do not agree on the trend over the past 50 years. Gettelman, Hegglin et al., JGR 2010 ESA Climate Change Initiative Collocation meeting ESRIN October

28 The ozone hole thereby affects tropospheric surface climate during austral summer outside SH high latitudes, e.g. in the tropics. Jet latitude ozone ozone depletion recovery Hadley cell width Son et al., JGR 2010 (also McLandress et al., JClim 2011 The ozone-hole induced surface wind changes have potential implications for ocean circulation and carbon uptake (Cai & Cowan, J Clim 2007; Lenton et al., GRL 2009) ESA Climate Change Initiative Collocation meeting ESRIN October