Tropospheric response to Solar and Volcanic forcing Joanna Haigh, Mike Blackburn and Rebecca Day.
-
Upload
brandon-mchugh -
Category
Documents
-
view
213 -
download
0
Transcript of Tropospheric response to Solar and Volcanic forcing Joanna Haigh, Mike Blackburn and Rebecca Day.
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 O3
• Regressed variations in tropospheric climate
• Modelled response to stratospheric heating (IGCM)
IPCC radiative forcing
Natural causes of climate change
Explosive volcanoes
Solar activity
Observations of total solar
irradiance
>2 solar cycles
Absolute values uncertain
~0.08% (1.1Wm-2) variation
C. Frölich, PWDOC
http://www.pmodwrc.ch/
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/
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
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
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°N
35°S
T at 35°S
T (200hPa) regressions
Haigh (2003)
Temperature regressions
NCEP-NCAR reanalysis
1979-2000shading: <95% significance
Haigh (2003)
trend
solar
QBO
ENSO
Volc
NAO
Zonal wind regressions
NCEP-NCAR reanalysis,1979-2002
[u]
trend
solar
volcanic
ENSO
NAO
QBO
95% significance: u ~ 0.5 ms-1
solar min
solar max
Jets weaken,shift poleward
low aerosol
PinaTubo
Jets weaken,shift eq’ward
Regressed extremes of zonal wind
GCM response to stratospheric UV, O3
[T] regression:NCEP-NCAR reanalyses
Larkin et al (2000)
GCM response:HadAM3 L58
smaller amplitude
Idealised GCM experiments
IGCM, Held-Suarez forcing:
Newtonian heating; Rayleigh friction (PBL)
Modify reference state in lower stratosphere
Reference state [ T ]
Climate average [ T ]
Control climate
Zonal wind [ u ] MMC [ Ψ ]
Momentum flux [ u’v’ ] Heat flux [ v’T’ ]
Stratospheric heating experiments
Experiments:
Increase stratospheric reference [ T ]
E5 : 5K * cos2φ
U5 : 5K
P10 : 10K * sin2φ
Effect is to lower and tilt reference tropopause
U5
E5
P10
Response to stratospheric heating
U5
E5
P10
[T] [u]
“volcanic” eddy flux response : U5–C
[T][u]
[u’v’] [v’T’]
“solar” eddy flux response : E5 – C
[T][u]
[u’v’] [v’T’]
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