SORCE Science Meeting, 18-19th September, 2012
‘Top-down’ solar modulation of the
North Atlantic or Arctic Oscillation
Sarah Ineson
with thanks to Adam Scaife, Martin Andrews, Jeff Knight (Met Office)
Lesley Gray (Oxford), Amanda Maycock (Cambridge)
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Content
• Motivation – a review of recent literature
• Solar minimum / solar maximum experiment with UV
changes based on SIM data
• Seasonal to decadal prediction
• Could a future descent into a ‘grand solar minimum’
have an impact on regional surface climate?
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The North Atlantic or Arctic
Oscillation and winter temperature
pressure anomalies
Winter 1962/63
temperature anomalies
Weakened pressure
gradient  -ve North
Atlantic Oscillation
Winter 2009/10
Cold advection
into Europe and
eastern U.S.
Cold, calm
and dry
Winter 1999/00
Strengthened pressure
gradient  +ve North
Atlantic Oscillation
Warm Europe and
eastern U.S.
Mild, stormy and wet
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Observed Solar Variability and
winter surface climate
11 year solar cycle
–ve NAO and more blocking
at solar minimum for reanalysis period
Earlier historical record?
Woollings
et al.,
2010, GRL
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Met Office
2m temperature
Observed solar variability
Solar maximum minus solar minimum from the 11 year
cycle. Descending wind anomalies - winter only strongest in NH
N. Hemisphere winter
S. Hemisphere winter
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Kuroda and Kodera, 2002, JMSJ
Some experiments have shown
encouraging signs:
Low geopotential heights over Arctic in some months
Variable temperature signal
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Met2006
Office
Matthes
etcopyright
al., JGR,
New satellite UV data (SIM)
SIM measured a decline in ultraviolet from 2004-2007 that is a
factor of 4 to 6 times larger than typical previous estimates
Harder et al., 2009, GRL
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Solar minimum / solar maximum
experiment with UV based on SIM
data
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Experiment – solar minimum /
solar maximum with UV based on
SIM data
• Hadley Centre ocean-atmosphere climate model.
85 levels – well resolved middle atmosphere upper boundary at 85km
mesosphere
• Solar minimum (80 yrs): control run
• Solar maximum (20 x 4 yrs): perturbation of
+1.2Wm-2 to 200-320nm UV band. Only the UV is
altered.
stratosphere
• Climatological ozone
Solar forcing of winter climate variability in the Northern
Hemisphere. S. Ineson, A.A. Scaife, J.R. Knight, J.C. Manners, N.J.
Dunstone, L.J. Gray and J.D. Haigh. Nature Geoscience, 2011
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troposphere
Cooling of the equatorial
stratopause at solar minimum
Weaker meridional temperature gradient
Weakened westerly flow
Annual zonal mean temperature
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Climatological winter zonal mean
winds are westerly
- Vertically propagating planetary waves in winter
only
Dissipating
waves exert a
zonal force
Zonal winds in
turn affects the
propagation and
dissipation of
waves….
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zonal mean u-velocity
Poleward and downward
propagation of wind anomaly –
winter only
Oct
Nov
Dec
Jan
Feb
Mar
Similar to wave mean flow interactions seen in other contexts…
e.g. QBO, internal variability, sudden stratospheric warmings
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Mechanism: descent through the
stratosphere
increase in
planetary wave
driving F
deceleration just
below easterly wind
anomaly
descent of the
anomaly
zonal mean zonal wind (contours) and EP flux
divergence (colours)
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Winter surface climate response
model (solar min – max)
sea level pressure
surface temperature
NB – little direct
effect on global
mean temperature
Reanalysis (1957-2010)
x
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model
N. European
temperature
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Lesley
Gray Met Office
Seasonal to decadal prediction
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Is the solar signal large enough to
be useful?
Sea level pressure signal
Signal to noise ratio
purple (green) contour
indicates 50 (25)% of
interannual standard
deviation
• Potentially important for seasonal to decadal forecasting.
• Historically skill in prediction of the NAO is very low
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Recent UK winters
Heathrow Dec 2010
Winter visitor
Eurostar 2009/10
Christmas Eve 2010
Newton Poppleford 21.12.2010
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Met Office
Source:
www.bbc.co.uk/news
Source: NERC Satellite Receiving Station, Dundee
University, Scotland
http://www.sat.dundee.ac.uk
Experiments with the decadal
forecast model
• ‘Enhanced UV’ – based on regression between OSF and SIM data
• Forecast system – GloSea4 (HadGEM3)
• 4-member ensembles, initialised 1st November, run for 5 years, annual
start dates from 1960 - 2008
• Outer tercile solar composites formed from 2nd, 3rd, and 4th winters of
the ensembles
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Jeff Knight, Martin Andrews
Decadal forecast model
– initial results
Solar max – min
enhanced uv - control
+ve T, max
near
stratopause
+ve NAO
• Larger solar signal with enhanced UV (experiment working correctly!)
• Signal not as large as expected?
possible reasons: transient solar forcing, ocean feedback may be too
weak …
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Jeff Knight, Martin Andrews
Regional impact of future descent
into a grand solar minimum?
Met Office + Lesley Gray (Oxford) and Amanda Maycock
(Cambridge)
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Possible decline in future solar
activity
• Any reduction in global mean temperature due to decline is likely to be a
very small fraction of projected anthropogenic warming (e.g. Feulner and
Rahmstorf 2010, Jones et al. 2012)
• Could there be a regional effect? (e.g. Rozanov et al. 2012)
Sensitivity experiments using HadGEM2-CC L60 RCP8.5 climate
model
Explore uncertainty in spectral
irradiance with two experiments.
Lockwood (2010)
scenario
difference in solar forcing relative to
control at end of 21st century (Wm-2)
obs
scenario
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‘a’ (Lean)
‘b’ (SIM)
TSI -1.7
UV -0.2
TSI -1.7
UV -1.7
Winter (DJF) response to
declining solar forcing (20502069) relative to RCP8.5
Zonal mean temperature (contours) and
u-wind (colours)
cooling of winter stratosphere and
weakening of northern hemisphere
westerly jet
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Mean sea level pressure
negative AO/NAO - like
pattern
Winter (DJF) surface
temperature response (20502069) relative to RCP8.5
Reduction of ~10% relative
to RCP8.5 warming for N.
European box
Regional near-surface
winter temperature
differences
Change in number of
winter frost days
(Tmin < 0)
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Summary
• Increasing modelling evidence to support the observed modulation
of the AO/NAO by UV solar variability
- uncertainties in magnitude of forcing, ozone
• We have a mechanism for how this works which fits with previous
understanding and involves amplification of what is a small energetic
perturbation
• The signal may be large enough to play a useful role in seasonal to
decadal climate prediction for Europe
• If the sun’s future output declines to Maunder Minimum levels and
the UV forcing is stronger, as SIM suggests, then the resulting UV
changes could be an important additional regional forcing on top of
future climate change
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Thank you!
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Mechanism: Impact on the troposphere
Decreased vertical wind shear
Reduced baroclinic eddy growth:
Growth Rate =
= 0.3Uzf
NH
Expect negative NAO/AO
c.f. Scaife et al., Clim. Dyn., 2011
Arctic Oscillation / North
Atlantic Oscillation response
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C
W
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