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.

" " " " " " " "

  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!