Solar Forcings of the Climate System

Does solar variability influence climate?

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Earth, Venus, and Mars

Planet S a Te Ts

(W m-2) (K) (K)

Earth 1361 0.3 255 288Venus 2600 0.77 230 753Mars 600 0.17 216 216

Greenhouse Effect

• What is the Greenhouse Effect?• First, what it is not:

– A greenhouse effect.– The atmosphere does not trap heat, nor does it trap radiation.– The atmosphere does not “re-radiate” radiation that it has (not) trapped.– The atmosphere does not act like a blanket.

• The Greenhouse Effect: the Earth’s surface receives radiation from two sources:– Sun (60%)– Atmosphere (40%)

Where Does the Atmosphere Get Its Energy?

Heat Source

Heat Flux*

[W/m 2] Relative InputSolar Irradiance 340.25 1.000Heat Flux from Earth's Interior 0.0612 1.8E-04 Radioactive Decay 0.0480 1.4E-04 Geothermal 0.0132 3.9E-05Infrared Radiation from the Full Moon 0.0102 3.0E-05Sun's Radiation Reflected from Moon 0.0034 1.0E-05Energy Generated by Solar Tidal Forces in the Atmosphere 0.0034 1.0E-05Combustion of Coal, Oil, and Gas in US (1965) 0.0024 7.0E-06Energy Dissipated in Lightning Discharges 0.0002 6.0E-07Dissipation of Magnetic Storm Energy 6.8E-05 2.0E-07Radiation from Bright Aurora 4.8E-05 1.4E-07Energy of Cosmic Radiation 3.1E-05 9.0E-08Dissipation of Mechanical Energy of Micrometeorites 2.0E-05 6.0E-08Total Radiation from Stars 1.4E-05 4.0E-08Energy Generated by Lunar Tidal Forces in the Atmosphere 1.0E-05 3.0E-08Radiation from Zodiacal Light 3.4E-06 1.0E-08Total of All Non-Solar Energy Sources 0.0810 2.4E-04* global average

Physical Climatology, W.D. Sellers, Univ. of Chicago Press, 1965Table 2 on p. 12 is from unpublished notes from H.H. Lettau, Dept. of Meteorology, Univ. of Wisconsin.

Large-scale energy sources that act continuously or quasicontinuously in the atmosphere and at its boundaries.

Solar ForcingThe U.S. Climate Change Science Program (USCCP)Vision for the Program and Highlights of the Scientific Strategic Plan, 2003

Key Gaps in the Science of Climate Change

The nature and causes of the natural variability of climate and its interactions with forced changes are uncertain:

• Because of the large and still uncertain level of natural variability inherent in the climate record and the uncertainties in the time histories of the various forcing agents (and particularly aerosols), a causal linkage between the buildup of greenhouse gases in the atmosphere and the observed climate changes during the 20th century cannot be unequivocally established.

• The value of indirect effect of ozone changes induced by solar ultraviolet irradiance variations remains highly uncertain.

Perturbation at TOA: FNETref – FNET+50%

Calculated using the on-line code at http://snowdog.larc.nasa.gov/cgi-bin/rose/flp0404/fup.cgi

SORCE Measures TSI and SSI

Solar Radiation and Climate Experiment (SORCE)

http://lasp.colorado.edu/sorce/

Instrument λ Range (nm) ∆λ (nm)

TIM: Total Irradiance Monitor TSI (all) -

SIM: Spectral Irradiance Monitor 200-2700 1-30

SOLSTICE: Solar Stellar Irradiance Comparison Experiment

115-320 0.1

XPS: XUV Photometer System 0.1-27, 121.6 7-10

TIMEDSEE

SORCE spacecraft was launched on 25 January 2003, and its mission is through 2008.

27-Year TSI Data Record

Greg Kopp, SORCE Science Meeting, 20-22 Sept. 2006

Composite Relies on Continuity

Current climate record plan relies on continuity and mission overlap.

But why the offsets?

Greg Kopp, SORCE Science Meeting, 20-22 Sept. 2006

The SORCE/TIM and TSI Variations

NIST calculates diffraction

should lower these reported

results.

Correction not yet applied by ACRIM or ERBE Teams

• 2005 TSI Accuracy Workshop indicated missing corrections to some TSI instruments and possible causes of instrument offsets

• NASA’s Glory program is creating the TSI Radiometer Facility to compare TSI instruments on an absolute scale

• LASP will be taking a SORCE/TIM ground instrument to NIST later this year to perform power comparisons

– Other TSI instruments to follow for NIST comparisons

• DeToma & White “Empirical Modeling of TSI” Solar Physics paper:

– “The model for the TIM TSI time series gives the best fit... TIM TSI measurements are the most precise because of its new instrumental design.”

Greg Kopp, SORCE Science Meeting, 20-22 Sept. 2006

Energy budget within the atmosphere after Kiehl and Trenberth [1997]. The numbers give the globally and annually averaged solar (left side of the figure) and longwave (right side) irradiances [W m-2].

340.25 W m-2

340.25

Composites Rely on Continuity and Stability

Two primary TSI composites differ by 40 ppm/yr caused by 2 years of marginal quality data – not even a gap!

?

Greg Kopp, SORCE Science Meeting, 20-22 Sept. 2006

SSI Critical for Atmospheric and Climate Studies

• Atomic and molecular species dominate absorption in the ultraviolet

[Figure from P. Pilewskie, Solar Physics, 2005]

• Water (clouds) and aerosols dominate the absorption and scattering in the visible and near infrared

Chemistry Climate Models Need SSIGISS GCM [Rind et al., 2004; Shindell et al., 2006]

NCAR WACCM [Marsh et al., 2007]

HAMMONIA [Schmidt and Brasseur, 2006]

CMAM [Beagley et al., 1997]

A problem discovered at DOE ARM

Harrison et al., Geophys. Res. Lett. 26, pp. 1715-1718, 1999

SSI and Climate

atmospheric extinction

irradiance at surface

Spectral Irradiance Contributions to Climate:• Mechanisms of climate response are highly wavelength dependent

– Direct surface heating for wavelengths > 300 nm– UV absorption in the stratosphere and radiative and

dynamical coupling with the troposphere.– Interaction with interact with internal modes of climate

variability (ENSO, NAO, and the QBO)

• Greatest relative variability occurs in the ultraviolet; greatest absolute variability occurs in mid visible (direct)

• Uncertainty in solar forcing must be reduced to separate natural from anthropogenic radiative forcing.

• TOA spectral distribution of solar radiation needed to interpret spectrally dependent radiative processes in the atmosphere at the surface.

300

Short Time Scale Solar Variability

• Solar time variability is a function of wavelength.– TSI constrains the magnitude of the variability, but not its spectral

distribution.– The Earth’s response to solar variability is wavelength dependent.

Jerry Harder, SORCE Science Meeting, 20-22 Sept. 2006

SIM Observed Solar Variability

Wavelength (µm)

Solar spectral variability produces variability in atmospheric heating

• Measured difference in spectral irradiance from “Quiet Sun” on 11 Feb. 2006 and two active states:

- Plage dominated: 27 Oct. 2004- Sunspot dominated: 15 Jan. 2005

• Instantaneous spectral heating rate calculated for the observed irradiance differences.• Integrated heating differential over the visible and near-infrared spectrum is on the order of 0.1 K day-1.

Pilewskie and Harder, SORCE Science Meeting, 20-22 Sept. 2006

TSIS Science OverviewUnderstanding Solar Forcing for Policy Decisions

Radiative Forcing of Climate Change: Expanding the Concept and Addressing Uncertainties (2005), Committee on Radiative Forcing Effects on Climate, THE NATIONAL ACADEMIES PRESS, 2005