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Solar Forcings of the Climate System Does solar variability influence climate? S o (1 − albedo)πRE2 = FIR 4π RE2 So (1 − albedo) = FIR = σTe4 4 ⎧ So ⎫ Te = ⎨ (1 − albedo)⎬ ⎩ 4σ ⎭ 1 4 by Peter Pilewskie, April 20, 2007 Earth, Venus, and Mars Planet S (W m-2) a Te (K) Ts (K) Earth Venus Mars 1361 2600 600 0.3 0.77 0.17 255 230 216 288 753 216 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? Large-scale energy sources that act continuously or quasicontinuously in the atmosphere and at its boundaries. Heat Flux* Heat Source Solar Irradiance Heat Flux from Earth's Interior Radioactive Decay Geothermal Infrared Radiation from the Full Moon Sun's Radiation Reflected from Moon Energy Generated by Solar Tidal Forces in the Atmosphere Combustion of Coal, Oil, and Gas in US (1965) Energy Dissipated in Lightning Discharges Dissipation of Magnetic Storm Energy Radiation from Bright Aurora Energy of Cosmic Radiation Dissipation of Mechanical Energy of Micrometeorites Total Radiation from Stars Energy Generated by Lunar Tidal Forces in the Atmosphere Radiation from Zodiacal Light Total of All Non-Solar Energy Sources * global average Physical Climatology, W.D. Sellers, Univ. of Chicago Press, 1965 Table 2 on p. 12 is from unpublished notes from H.H. Lettau, Dept. of Meteorology, Univ. of Wisconsin. 2 [W/m ] 340.25 0.0612 0.0480 0.0132 0.0102 0.0034 0.0034 0.0024 0.0002 6.8E-05 4.8E-05 3.1E-05 2.0E-05 1.4E-05 1.0E-05 3.4E-06 0.0810 Relative Input 1.000 1.8E-04 1.4E-04 3.9E-05 3.0E-05 1.0E-05 1.0E-05 7.0E-06 6.0E-07 2.0E-07 1.4E-07 9.0E-08 6.0E-08 4.0E-08 3.0E-08 1.0E-08 2.4E-04 Solar Forcing The 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 TIMED SEE Solar Radiation and Climate Experiment (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 SORCE spacecraft was launched on 25 January 2003, and its mission is through 2008. http://lasp.colorado.edu/sorce/ 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 • 2005 TSI Accuracy Workshop indicated missing corrections to some NIST TSI instruments and possible causes calculates of instrument offsets diffraction should lower • NASA’s Glory program is creating the TSI Radiometer Facility to compare these reported TSI instruments on an absolute scale results. • 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 Correction not yet applied by ACRIM or ERBE Teams precise because of its new instrumental design.” Greg Kopp, SORCE Science Meeting, 20-22 Sept. 2006 340.25 W m-2 340.25 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]. 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 Chemistry Climate Models Need SSI GISS 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] • • Water (clouds) and aerosols dominate the absorption and scattering in the visible and near infrared Atomic and molecular species dominate absorption in the ultraviolet [Figure from P. Pilewskie, Solar Physics, 2005] A problem discovered at DOE ARM Harrison et al., Geophys. Res. Lett. 26, pp. 1715-1718, 1999 SSI and Climate 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) atmospheric extinction irradiance at surface 300 • • 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. 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 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 Wavelength (µm) TSIS Science Overview Understanding 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