1 / 20

Tropospheric response to Solar and Volcanic forcing

Tropospheric response to Solar and Volcanic forcing. Joanna Haigh, Mike Blackburn and Rebecca Day. Outline. Climate change context Observed solar variability Amplification of the solar signal – stratospheric O 3 Regressed variations in tropospheric climate

stacey
Télécharger la présentation

Tropospheric response to Solar and Volcanic forcing

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Tropospheric response to Solar and Volcanic forcing Joanna Haigh, Mike Blackburn and Rebecca Day

  2. Outline • Climate change context • Observed solar variability • Amplification of the solar signal – stratospheric O3 • Regressed variations in tropospheric climate • Modelled response to stratospheric heating (IGCM)

  3. IPCC radiative forcing

  4. Natural causes of climate change Explosive volcanoes Solar activity

  5. Observations of total solar irradiance >2 solar cycles Absolute values uncertain ~0.08% (1.1Wm-2) variation C. Frölich, PWDOC http://www.pmodwrc.ch/

  6. Reconstruction using solar indices Extrapolate an index which correlates with TSI over the observed period Several indices! IPCC: change in radiative forcing since 1750: 0.3  0.2Wm-2 Conversion TSI to RF: 4 disc-area 0.7 albedo Sunspot number (grey); Amplitude of sunspot cycle (red); Length of sunspot cycle (black); aa geomagnetic index (green) IPCC TAR http://www.grida.no/

  7. Amplification of Solar Forcing • Solar UV and impact on stratospheric O3 (Haigh 1994) • - solar cycle variation ~7% at 200nm (cf 0.08% in TSI) •  absorption by O3 stratospheric heating •  downward IR flux into troposphere •  dynamical impacts on troposphere •  changes in O3 • Modulation of low-level cloud • cover (Svensmark & Friis- • Christensen 1997) • - assumed mechanism involving • galactic cosmic rays

  8. Dynamical Correlations • 30hPa geopotential height (Labitzke & van Loon, 1997) • - 4 solar cycles, 10.7cm solar radio-flux • 200hPa subtropical temperature (Haigh, 2003) • - 1979-2000 multiple regression

  9. 35°N T (200hPa) regressions • Multiple regression of zonal mean T (200hPa) • NCEP-NCAR reanalysis • - solar variability (red) • volcanic aerosol (green) • QBO (cyan) • NAO (blue) • ENSO (black) • trend (straight black line) • amplitude/phase of annual & semi-annual cycles 35°S 35°S T at 35°S Haigh (2003)

  10. NCEP-NCAR reanalysis 1979-2000 shading: <95% significance Temperature regressions trend ENSO Volc solar NAO QBO Haigh (2003)

  11. QBO [u] volcanic trend ENSO solar NAO NCEP-NCAR reanalysis, 1979-2002 Zonal wind regressions 95% significance: u ~ 0.5 ms-1

  12. Regressed extremes of zonal wind solar min solar max Jets weaken, shift poleward low aerosol PinaTubo Jets weaken, shift eq’ward

  13. GCM response to stratospheric UV, O3 [T] regression: NCEP-NCAR reanalyses GCM response: HadAM3 L58 smaller amplitude Larkin et al (2000)

  14. Idealised GCM experiments IGCM, Held-Suarez forcing: Newtonian heating; Rayleigh friction (PBL)  Modify reference state in lower stratosphere Reference state [ T ] Climate average [ T ]

  15. Zonal wind [ u ] MMC [ Ψ ] Heat flux [ v’T’ ] Momentum flux [ u’v’ ] Control climate

  16. Stratospheric heating experiments U5 Experiments: Increase stratospheric reference [ T ] E5 : 5K * cos2φ U5 : 5K P10 : 10K * sin2φ Effect is to lower and tilt reference tropopause E5 P10

  17. Response to stratospheric heating [T] [u] U5 E5 P10

  18. “volcanic” eddy flux response : U5–C [u] [T] [u’v’] [v’T’]

  19. “solar” eddy flux response : E5 – C [u] [T] [u’v’] [v’T’]

  20. Conclusions • Modelled responses agree with analysis regressions • Suggests that dynamical eddy feedbacks dominate over moist feedbacks in troposphere • Future work • Causality chain from ensemble spin-up experiments • Zonally symmetric model to separate eddy feedbacks from zonally symmetric processes

More Related