Overview of solar irradiance effects on the Earth

HEPPA-SOLARIS Workshop, 9-12 October 2012, Boulder, USA
Overview of
solar irradiance effects on the
Earth‘s
atmosphere and climate
Katja Matthes1 and Lesley Gray2
1GEOMAR
Helmholtz-Zentrum für Ozeanforschung Kiel, Germany
2Centre for Atmospheric Sciences, Dep. of Atmospheric, Oceanic and Planetary Physics,
University of Oxford, UK
Motivation:
natural vs. anthropogenic factors
IPCC (2007)
Questions
•  How does the Sun influence natural climate variability (in
particular with respect to decadal predictability)?
•  What is the role of the stratosphere and how does the exchange
with the troposphere work?
•  Which mechanisms (top-down, bottom-up) are important for
solar influences on climate?
•  What is needed in climate models to investigate the solar
influence?
3
Solar Variability
(1975-2010)
Sunspot number
F10.7 cm flux
Magnesium ii
Open solar flux
Galactic cosmic ray
counts
Total solar irradiance
Geomagnetic Ap index
Gray et al. (2010)
Solar Variability
(1600-2010)
Total solar irradiance
Galactic cosmic ray counts
Geomagnetic aa index
Aurora sightings
Sunspot number
Beryllium10 concentrations
Gray et al. (2010)
Climate Observations: Stratosphere
Correlations F10.7cm flux vs.
30hPa temperatures in July
....beginning with the pioneering work of Karin
Labitzke and Harry van Loon
30hPa Heights North Pole vs. F10.7 cm
flux - February
Labitzke,
Labitzke and van Loon ....
Tropospheric Winds
Schematic of Jetstream
NCEP Zonal Mean Wind (m/s)
(1979-2002)
11-year Solar Signal (Max-Min)
blocking events => cold winds from the
east over Europe
blocking events longer lived for solar
minima (Barriepedro et al., 2008)
Haigh, Blackburn, Simpson
Surface Temperatures/Precipitation
11-year Solar Signal (Max-Min)
Composites
Dec/Jan/Feb
Sea surface temperature:
11 Max peak years
Precipitation:
3 Max peak years
van Loon, Meehl, White
Climate Observations: Carbon-14 (Solar Proxy)
ice-rafted debris N.
Atlantic: solar min
(larger C14 production)
greater sea ice extent
sedimentary
deposition in Alaska:
wetter, colder
conditions
stalagmite properties
in Oman: reduced
monsoon precipitation
Gray et al. (2010)
Climate Observations
Whole host of other observational studies that have shown solar
cycle variations in the troposphere and at the surface e.g.
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  Temperatures (pioneering work of Labitzke and van Loon)
Sea surface temperatures
Mean sea level pressures
Zonal winds
Vertical winds
Tropical circulations: Hadley circulation, Walker circulation
Mid / high latitude ‘annular modes’
Clouds / precipitation
BUT...... signals are predominantly regional ......
Surface Temperatures: IPCC
anthropogenic + natural forcings
Solar variations cannot
explain observed 20th
century global
temperature changes
long-term trend in solar
activity appears to be
decreasing, as we
come out of the current
‘Grand Maximum’
natural forcings only
Climate Observations: Summary
" Lots of examples of 11-yr solar influence at surface, but
scattered in different regions and sporadic in time.
" No evidence that solar variations are a major factor in
driving recent climate change; if anything, radiative forcing
looks as though it is reducing as we possibly come out of the
current grand maximum.
" BUT, as we start to predict climate on a regional basis, it
will be important to include solar variations in our models.
Climate Models
" Majority of coupled ocean-atmosphere climate models
include only total solar irradiance (TSI) variations i.e. the socalled ‘bottom-up’ mechanism.
" More recent climate models now include the ‘top-down’
mechanism via the stratosphere with spectrally resolving
solar irradiance changes
" Some specialist models also now include charged particle
effects, e.g. energetic particle fluxes, solar proton events etc.
=> talk by Dan Marsh on Thursday afternoon
How does stratosphere-troposphere coupling work?
How is it represented in current climate models?
Mechanisms: Sun - Climate
C. Jackmann
J.-E.
Kristjansson
L. Goncharenko
K. Kodera
A. Seppälä
G. Meehl
Gray et al. (2010)
Mechanisms
Percentage variability
Smax minus Smin
~6% near 200nm
(ozone formation)
~4% 240-320nm
(absorption by ozone)
~0.07% in TSI
‘Bottom-up’ mechanism:
wavelengths reaching the
Earth’s surface (TSI)
‘Top-down’ mechanism: UV
wavelengths influence the
stratosphere (SSI)
Gray et al. (2010)
‚Bottom-up‘
Mechanisms (TSI)
Increased solar absorption during
Smax in cloud-free subtropical oceans,
increases evaporation;
increased moisture converges into
precipitation zones, intensifies
precipitation and upward vertical
motions, which strengthens Hadley
and Walker circulations;
stronger subsidence in subtropics
gives positive feedback that reduces
clouds and allows increased solar
forcing.
van Loon, Meehl, White, Cubasch
Some examples and open questions
Observed Annual Mean Solar Signal
Ozone (%/100 f10.7) and Temperature (K/100 f10.7)
SAGE I/II Data (1979-2005)
SSU/MSU4 (1979-2005)
+2%
+2%
+1K
+2%
95% significant
Randel and Wu (2007)
Randel et al. (2009)
Solar Maximum:
More UV radiation => higher temperatures
More ozone => higher temperatures
Discrepancy in Observed Solar Signal
ERA40 (1979-2008)
+2K
?
SSU/MSU4 (1979-2005)
+1K
+1.5K
Frame and Gray (2010)
95% significant
Randel et al. (2009)
What is the observed solar signal?
Dynamical Interactions and Transfer
to the Troposphere
10-day mean wave-mean flow interactions (Max-Min)
u
EPF
Stratospheric waves
(direct solar effect)
Tropospheric waves
(response to stratospheric changes)
How does stratosphere-troposphere
work?
Matthes et al.coupling
(2006)
How is it represented in current climate models?
Solar Cycle & NAO
Solar Max: NAO positive
(high index)
Colder stratosphere => stronger NAO,
i.e. stronger Iceland low, higher
pressure over Azores
⇒  amplified storm track
⇒  mild conditions over northern Europe
and eastern US
=> dry conditions in the mediterranean
Why do the models differ in the strength of the solar response?
What is the role of the sun for decadal climate predictability?
Solar Signal in Tropical Stratosphere:
Models vs. Observations
Temperature (K)
Ozone (%)
•  direct signal in upper stratosphere acceptably represented in models
•  large differences in vertical structure below 10hPa between CCMs as well
as observations; aliasing or non-linear interactions with ENSO, QBO and
volcanoes?
Manzini and Matthes et al., Chapter 8 „Natural Variability
of Stratospheric Ozone“, SPARC CCMVal report (2010)
Coupled Atmosphere-Ocean Effect
WACCM without ocean
Observed precipitation between
Solar Max and Min
WACCM with ocean
Meehl, Arblaster,
Arblaster, Matthes,
Matthes, Sassi,
Meehl,
and van
Loon,
(2009)
Sassi,
and
van Science
Loon, 2009,
Science
Uncertainty in solar spectral irradiance
and its impact on climate modeling
Shortwave Heating Rate Response
TSI [in percent]
150
SSI /
200
0
WR-2002
SUSIM
NRLSSI
SATIRE
COSI
OAR
SCIAMACHY
SORCE
SORCE reanalysis
100
50
SORCE reanalysis
SORCE
SCIAMACHY
OAR
COSI
SATIRE
NRLSSI
-100
SUSIM
WR-2002
-50
200-400
400-700
700-1000
Pressure (hPa)
0.1
1
GEOSCCM NRLSSI
GEOSCCM SORCE
IC2D NRLSSI
IC2D SORCE
EMAC−FUB NRLSSI
EMAC−FUB SORCE
WACCM NRLSSI
WACCM SORCE
WACCM* NRLSSI
ECHAM6 NRLSSI
HadGEM3 SORCE
MMM NRLSSI
MMM SORCE
60
55
50
45
40
35
10
Height (km)
Relative Contribution to TSI
30
25
1000-2430
20
100
−0.6 −0.4 −0.2
0
0.2
0.4
0.6
Which SSI data set is most reliable and should be used for climate modeling?
Ermolli, Matthes, Dudok de Witt et al., ACPD (2012)
Mechanism Sun-climate
„Top-Down“
„Bottom-Up“
Gray et al. (2010)
What is the role of atmospheric vertical coupling Meehl
processes
and ocean
et al. (2008)
coupling for the solar signal?
Open issues/uncertainties
• observed solar signal
• non-linear relations between solar signal and other
external factors in stratosphere/troposphere
• role of the stratosphere and the ocean
(top-down vs. bottom-up)
• spectral solar irradiance forcing data
• role of the sun for decadal climate predictability
• other contributions (particles) to solar influence on
climate
Thank you very much!