Relationships Between the Sun and Climate: Time Scales of Decades to Centuries
advertisement
Relationships Between the Sun and Climate: Time Scales of Decades to Centuries Judith Lean Naval Research Laboratory, Washington DC Observed Sun-Climate Relationships .. Holocene, past millennium, past century How Much Does Solar Energy Output Vary? What are the Mechanisms for Sun-Climate Relationships? .. direct, indirect, resonnances Summary Earth and Sun Variations in the Holocene EARTH ~5oC )F=0.6 Wm-2 ? SUN solar-related surface temperature changes of order #0.5oC are evident in the past 1,000 years Stuiver et al., 1997 North Atlantic Climate Bond et al., Science, 2001 drift ice and cooler surface water in the Nordic and Labrador seas repeatedly advected southward and eastward to warmer sub-polar regions • surface winds and surface ocean hydrography are apparently influenced by solar variability • 1500-year cycle may involve solar variability • North Atlantic Deep Water may amplify solar signals InterTropical Convergence Zone Neff et al., Nature, 2001 ITCZ: - surface level circulation of Northern and Southern Hadley cells converge - controls tropical rainfall, Indian Ocean monsoon δ18O in stalagmites in Oman track ? 14 C for 3,000 years in mid-Holocene (when summer monsoon was stronger than present) high solar activity low ? 14C low δ18O high rainfall Earth and Sun Variations in the Past Millennium EARTH Little Ice Age ∆T~0.8 oC Glacial Ice Age ∆T~5oC SUN • C20th warming exceeds variations in prior centuries. • Significant variability exists prior to the industrial epoch. Long-Term Solar Variability and Climate Change: 1600-2000 dominant solar forcing dominant volcanic forcing Tamboora Coseguina anthropogenic plus solar forcing Krakatoa Lean, Beer & Bradley, GRL, 22, 3195, 1995 Lean, Annu. Rev. Astron. Astrophys., 35, 33, 1997 Solar Centennial Cycles, Drought and Culture • semi-arid regions are particularly vulnerable to hydrological changes • severity of past droughts exceeds contemporary events Equatorial East Africa Verschuren et al., Nature, 2000 Maya Lowlands Hodell et al., Science, 2001 high solar activity → low ∆ 14C → high δ18O → increased drought → cultural collapse 206-208 yr components of ∆ 14C and δ18O vary in phase Earth and Sun Variations in the Past Century - instrumental record Surface temperature changes are nonuniform.. globally and temporally 0.6 1900-1950 Global annual mean surface temperature anomalies 1960-2000 0.4 Sunspot numbers http://giss/nasa/gov Solar Variability Detected in MSU Data Michaels and Knappenberger, 2000 El Chichon Pinatubo MSU global temperature residuals – with effects of ENSO and volcanoes removed -- track the solar cycle El Nino La Nina Amplitude ~ 0.1oC Data: Sato et al., 1993, Jap. Met. Agency, Christy et al., 1998 North and Wu (2001) detected solar cycles in C20th instrumental surface temperatures … 2X larger than expected from EBM simulation with sensitivity 2oC for 2CO2 Solar Cycles and Global Sea Surface Temperatures SEA SURFACE SOLAR TEMPS IRRADIANCE White et al., 1997, 1998 30hP Pressure Surface near 24 km varies ~ 0.1 km during Solar Cycle Changes in a constant pressure level reflect changes in integrated temperature below. K. Labitzke & H. van Loon Solar Decadal “Cycles” in Climate 3-5 Global surface temperature 10 27 Mann and Park 1994 Central England temperature 3.1 5.2 7.5 14.5 23 76 Mason 1976 4.5 US east coast temperature 9 20 22 Global marine air temperature Newell et al. 1989 22 US drought SOURCE Mitchell et al. 1979 9.9 Beijing rainfall 18.7 56 84 126 Hamseed et al. 1983 11 US rainfall 18.6 Curie and O'Brien 1988 18.4 Nile floods 22 77 Hameed 1984 South American rainfall African rainfall 3.8 3.5 7 20 10-12 18 Seleshi et al. 1994 North Atlantic pressure 3.4 5 11 PERIOD (years) Karl and Riebsame 1984 Kelly 1977 Southern oscillation 3 3.8 North American forest fires 6 10-12 11 22 34 Auclaire 1992 8 9.3 11.3 14.8 Atlantic tropical cyclones 22 51.3 133 Cohen and Sweester 1975 Tropical corals 3.3 4.6 6 8 11 17 Dunbar et al. 1994 some periods other than the 2.2 year QBO present in climate records Burroughs 1992; Lean & Rind, 1998 Solar Variability and Recent US Drought DROUGHT AREA INDEX POWER SPECTRUM Cook et al., 1997 • Drought Area Index reconstructed from tree-rings since 1700 DROUGHT AREA INDEX BANDPASS FILTERING •Solar and lunar effects interact to modulate DIA • Ocean-atmosphere interactions in the North Pacific may be responsible How Much Does Solar Energy Output Vary? Source Energy (Wm-2) Solar Cycle Change (Wm-2) Deposition Altitude Solar Radiation • total • UV 200-300 nm • VUV 0-200 nm 1366 15.4 0.15 1.2 0.17 0.15 Particles • electron aurora III • solar protons • galactic cosmic rays 0.06 0.002 0.0000007 Joule Heating of Thermosphere • E=100 mVm-1 0.14 Solar Wind 0.0003 surface 10-80 km 50-500 km 90-120 km 30-90 km 0-90 km 100-500 km above 500 km Long-Term Solar Irradiance Variations are Speculated Are Long-Term Solar Irradiance Variations Occurring? NO: Sunspot Numbers reconstructed total irradiance cycles track sunspot numbers YES: Geomagnetic Activity reconstructed total irradiance cycles plus varying background track aa index YES: Cosmogenic Isotopes reconstructed total irradiance cycles plus varying background track ? 10Be Are Long-Term Solar Irradiance Variations Occurring? YES: Ca HK Flux in Sun-like Stars • observed Ca HK brightness in 13 Sunlike stars exhibits a greater range of variation than is seen in the present-day Sun (Baliunas & Jastrow, 1990) • reconstructed solar irradiance with varying background matches the stellar distribution better than with activity cycles, alone (Lean et al., 2001) Terrestrial Solar Activity Proxies Vary with Sun’s Open Flux * closed flux modulates irradiance Open Flux Radial Interplanetary Magnetic Field Geomagnetic Activity Cosmic Ray Fluxes at Earth Wang et al., 2000 How do Open and Closed Flux Vary with Solar Activity over Many Cycles? 24 June 2002 open flux in coronal holes • Magnetic sources are deposited as bipolar regions, with monotonically increasing strength EIT284 closed flux in active regions • Flux transport model simulates evolution of the surface magnetic field – transport by meridional flow, diffusion, rotation • Current-free extrapolation of simulated surface magnetic fields estimates the magnetic configuration of the corona EIT304 NSO Simulations with NRL’s Photospheric Flux Transport and Potential Field Extrapolation Models surface magnetic fields of opposite polarity • Open flux is estimated from fields that are radial at 2.5RSun Sheeley et al., Solar Phys., 1986; Wang and Sheeley Sheeley,, ApJ ApJ,, 1991, 1992 Secular Changes in Open Flux Occur Without Corresponding Changes in Closed Flux Lean & Wang, SPD, 2002 Sun-Climate Mechanisms? solar energy output near UV VIS IR radiation Xrays EUV radiation galactic cosmic rays solar wind energetic particles heliosphere & IMF UV radiation thermosphere ionosphere mesosphere & lower thermosphere stratosphere & ozone climate magnetosphere energetic particles Climate Response to Direct Solar Forcing )T = κ ) F = κ (S-S0)×0.7÷4 )T = surface temperature change (oC) )F = climate forcing (Wm-2) κ = climate sensitivity (oC per Wm-2) GISS GCM SIMULATION OF TIME-DEPENDENT CLIMATE RESPONSE TO SOLAR FORCING SINCE 1600 • • • • • 8oH10o horizontal resolution with 9 vertical layers variable mixed layer depth with 250 meter max depth specified "Q" flux for ocean heat transport heat diffusion through bottom of mixed layer 0.8-1oC per Wm-2 sensitivity Rind, Lean and Healy, JGR, 104, 1973, 1998 GISS GCM Simulation of Solar-Induced Surface Temperature Changes since 1600 model ocean heat flow dampens decadal response C20th temperature changes of ~0.2 o in response to adopted total solar irradiance variations: 0.45 oC since 1700 Climate Feedbacks Account for 65% of Response to Solar Forcing in GISS GCM Simulation water vapor: 35% sea-ice/ snow cover: 10% cloud cover: 20% Latitude Rind and Overpeck, 1994 Regional Climate Impacts of Solar Total Irradiance Variability Longitude Solar UV Radiation Influences Ozone Stratosphere O3 has 2% solar cycle variation Troposphere Surface 6% Solar UV-Induced Ozone Changes may Influence Climate Dynamical Coupling via Wind-Wave Interactions Lower Middle Atmosphere Atmosphere Radiative Forcing Sensitivity Radioactive Coupling via Absorption and Emission Change Ozone & Temperature Change Winds & Planetary Waves Change Temperature Advection & Temperature Change Winds & Planetary Waves Change Climate SOURCE: NASA Solar Influences on Climate Workshop, Tucson 2000 Regional Impacts of Solar Cycle UV-Induced Ozone Changes GISS stratospheric GCM simulation reproduces solar cycle variation in geopotential height near 24 km (30-mbar) Shindell, Rind et al, Science, 1999; JGR, 2000 GISS GCM simulated solar cycle ozone changes influence NH high latitude winter climate Solar Variability is one of Many Causes of Climate Change Anthropogenic Forcings • atmospheric GH gases - CO2, CH4, CFCs, O3, N2O • tropospheric aerosols - direct and indirect effects of sulfate, soot, carbon, biomass burning, soil dust, clouds Natural Forcings • solar variability - direct and indirect effects • volcanic eruptions - stratospheric aerosols Land Cover Changes Internal Oscillations • Climate Change Science, An Analysis of Some Key Questions, NRC, 2001 • IPCC, 1992, 1995, 2001 • atmosphere-ocean couplings - ENSO (2-7 yrs), Arctic Oscillation (decadal)... Pacific Decadal Oscillation (PDO), North Atlantic Oscillation (NAO) Climate Forcings 2.4 2 1 CO2 0.35 halocarbons N2O CH4 tropospheric ozone 0.25 fossil fuel burning 0 -1 -2 -3 stratospheric ozone 0.2 sulphate 0.4 0.05 0.3 mineral aviation dust contrails & cirrus biomass burning 0.1 0.25 solar landuse (albedo) indirect aerosol 0.23 warming 3 2.4 Wm -2 in next 50 years cooling Radiative Forcing (Wm-2) IPCC 2001: 1750-2000 Future Anthropogenic Forcing Scenario IS92a Global Warming in the Twenty-first Century: An Alternative Scenario (Hansen et al., PNAS, 2000) • • • • rapid warming in recent decades driven by non-CO2 GHGs future forcing by non-CO2 GHGs reduced to zero future aerosol forcings cancel net forcing in next 50 years reduced to 1 Wm-2 EBM Simulations of Past Climate Change with Multiple Forcings forcings Crowley, 2000 simulation: κ ~ 2oC for 2CO2 • simulated temperatures match Mann et al. reconstruction • solar & volcanic forcings account for pre-industrial variations ~0.2oC • 20th century mismatch GISS GCM Simulations of Past Climate Change with Multiple Forcings forcings Robinson et al., 2001 simulation: κ ~ 4oC for 2CO2 • simulated temps track borehole record • omitting solar forcing → .. higher sensitivity to GHGs .. poorer tracking of centennial variations Solar and Anthropogenic Atmospheric Influences Differ with Height O3 production Mesosphere Stratosphere Hartley bands SR bands Ly α window O3destruction Troposphere 315 Stratosphere & Ozone solar increase → warming CO2 increase → cooling volcanoes → warming Surface & Climate solar increase → warming CO2 increase → warming volcanoes → cooling Climate System Oscillations EL-NINO SOUTHERN OSCILLATION http://www.pmel.noaa.gov, http://topex-www.jpl.nasa.gov El Nino La Nina • warm equatorial Pacific temps •Easterly trade winds subside • increased rain in South US & Peru • West Pacific droughts • cold equatorial Pacific temps • large E-W pressure difference • strong trade winds • winters are warmer in SE USA, colder in NW NORTH ATLANTIC OSCILLATION Positive NAO • strong subtropical high, deep Icelandic low • stronger, northerly Atlantic storm tracks • warm, wet European winters • mild, wet, US winters http://www.ldeo.columbia.edu/NAO Negative NAO • weak subtropical high & Icelandic low • weaker, east-west storm paths bring cold air to N.Europe • US east coast snowy winters Solar Variability May Influence Climate Oscillation Modes Dettinger and White, JGR, submitted, 2001 ENSO: solar total irradiance cycle http://coaac.ucsd.edu/PERSONNEL/WHITE/ excites delayedaction oscillator of the tropical Pacific air-sea climate NAO/AO: solar activity (decadalcentennial) volcanoes GHGs O3 depletion polar stratosphere cooling/heating simulated tropical SST and zonal-wind variations larger than expected from simple direct forcing (by 2 to 3 X) decadal ENSOlike variations with comparable climatic impacts Science, 294, 7 Dec 2001: Haigh, Bond et al., Shindell et al. stratospheric polar vortex strong/weak tropospheric circulation NAO/AO pos/neg SUMMARY: Long-Term Sun-Climate Relationships There are numerous empirical Earth-Sun connections on time scales of decades to millennia - the result of solar forcing, internal oscillations or ...? Climate models simulate paleo-temperature trends in response to plausible solar forcing - are long-term solar irradiance trends occurring? - GCM’s don’t simulate 11-year temperature cycles because feedback time responses are too long ..realistic? - do decadal solar variations amplify climate oscillations? Climate response to solar forcing is regionally specific and concurrent with responses to other forcings - fingerprint of climate change is complex - different responses in pre- and post industrial epochs? Determining climate response to solar variability has been attempted for over a century .. problem is difficult, unsolved…. and a unique opportunity. Solar Forcing of Ice Ages? Ice volume has a pronounced 100,000 cycle associated with the eccentricity of Earth’s orbit (Hayes, Imbrie & Shackleton, 1976) 100,000 Variations in 10Be production by solar magnetic activity may also occur on 100,000-year time scales (Sharma, 2002) Future Solar Forcing of Climate Lean, GRL, 2001 •11-year cycles based on Schatten et al., 1996 Hathaway et al., 1999 Thompson, 1993 • background is ±0.04Wm -2/year Anthropogenic Scenarios • IS92a IPCC, 1995 • Alternative Hansen et al, 2000 Sun’s role in future climate change depends on irradiance cycles and trends relative to anthropogenic scenarios
0
advertisement
Download
advertisement
Add this document to collection(s)
You can add this document to your study collection(s)
Sign in Available only to authorized usersAdd this document to saved
You can add this document to your saved list
Sign in Available only to authorized users