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Solar Variability and Climate:From Mechanisms to Models

Terry NathanAtmospheric Science ProgramUniversity of California, Davis

OUTLINESUN-CLIMATE CONNECTIONS

CHALLENGES

11-YEAR SOLAR FORCING

KEY CIRCULATION COMPONENTS OF CLIMATE SYSTEM

SOLAR VARIABILITY, OZONE AND WAVES

PATHWAYS AND INTERFACES

FUTURE

ILWS 2009, Brazil

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SUN-CLIMATE CONNECTIONS

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Global Average Radiative Forcing (RF) Estimates

LOSULevel of Scientific

UnderstandingIPCC 4th Assessment Report 2007

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warming Beijing

Tan et al., 2004

Paleo Sun–Climate Synopsis…when solar activity is high….

warmingTasmania

Hill et al., 2007

weakened upwelling and trade winds (warmer SSTs)Cariaco BasinBlack et al., 1999

tree-rings Chile

Roig et al., 2001Nordemann et al.

Mayan drought Cariaco Basin

Hodell et al., 2001Haug et al., 2003

increasedtemperature &

moistureSW Alaska

Sheng et al., 2003high rainfall

OmanNeff et al., 2001

warmingNorth AtlanticBond et al., 2000

droughtEquatorial East Africa

Verschuren et al., 2000

drought Western USCookl et al., 2001

stronger monsoonWangxiang caveZhang et al., 2008

significant local changes do not imply global changes of equal magnitude

streamflowParana River

Mauas et al., 2008.

Courtesy J. Lean

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Natural and Anthropogenic Change in Earth’s Atmosphere

2km LOWER TROPOSPHERE 5km MID TROPOSPHERE 19km LOWER STRAT

Courtesy of Judith Lean

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11-YEAR SOLAR FORCING

- Total solar irradiance (TSI) changes

- Solar spectral irradiance (SSI) changes

- 11-year solar cycle modulation in high energy particles (e.g., solar protons, galactic cosmic rays)

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CHALLENGES

- TSI Variations <0.1%

- Identification of pathways that communicate and amplify solar variability throughout the atmosphere and oceans

- Address discrepancies between models and observations

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1600 1700 1800 1900 2000 YEAR

From Lean, Ann. Rev of Astron. & Astrophys., 1997

<0.1%

Total Solar Irradiance (TSI) changes

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Solar Spectral Irradiance (SSI) changes

4%0.5%

Adapted from Strobel (1978) JGR

Variations in SSI over the Solar Cycle

Stratospheric Ozone

Heating Rates

8%

20%

From Lean, Ann. Rev of Astron. & Astrophys., 1997

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KEY CIRCULATION COMPONENTS OF CLIMATE SYSTEM

- Quasi-biennial oscillation (QBO)

- Hadley circulation, subtropical jets…

- Stratospheric polar vortex

- Brewer-Dobson circulation

- Planetary waves

……..

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Quasi-biennial Oscillation (QBO)

Time–height plot of equatorial zonal wind (u) in m/s between about 20 and 35 km altitude above sea level over a ten-year period. Positive values denote westerly winds and the contour line is at 0 m/s.

After Holton et al

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Hadley Circulation, Subtropical Jets …

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Stratospheric Polar Vortex

660

Pole

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Brewer-Dobson Circulation

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Planetary Waves

Brewer-Dobson

Vertically Propagating

Planetary Waves

WAVE DRAG

Stratospheric Polar Vortex

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SOLAR VARIABILITY, OZONE AND WAVES

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Connection betweenSSI and PWD

Variations in Solar Spectral

Irradiance

Zonal-MeanVariations in

Ozone Heating

“TRADITIONAL”

PWD

Longitudinal Variations in

Ozone Heating

“NEW”

Vertically Propagating

Wave

Zonal-Mean Flow

Residual Mean Meridional Circulation,

Planetary Wave Drag(propagation / attenuation)

PWD

EP-Flux Divergence

Why is PWD so important?

F

F = Fyj + Fzkmomentum flux

heat

flux

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WKB Solution for EP-Flux Divergence (1-D)

cclyikxdZzmizBzAzz

Z

sin)exp(')'(exp)](),([)](ˆ),(ˆ[

0

z

iri dmAmm0

2 '2exp|| F

nAttenuatio

i

nPropagatio

r zmizmzm )()()( SSI-Modified Vertical Wavenumber (Refractive Index)

SSI-Modified Planetary Wave Drag

(SSI)10

*0 F

Fvf

t

u

Nonlinear function of

SSI

Zonal-Mean Flow Equation

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Ozone-Modified Downward Control

Adapted from Holton 2004

z

dzXfy

w ')(* 01

010 F

Residual Vertical Velocity“Downward Control”

To what extent is the divergence of Eliassen-Palm flux (i.e., PWD) affected by the solar-modulated, planetary wave induced ozone heating?

F

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PATHWAYS AND INTERFACES

21Surface

Impacts on Upper Atmospheric Chemistry and DynamicsDirect RF of the Lower Atmosphere

Tropical Upwelling

Vertically PropagatingPlanetary Waves

PWD

EQUATOR POLE

Polar Vortex

Vertically PropagatingTropical Waves WD

Quasi-biennial Oscillation

QBO

OZONE

Variations in SSI and TSI - Solar Proton Events – Cosmic Rays

OZONE

450 latitude

Downwelling

Mid

dle

Atm

osp

her

eT

rop

osp

her

e

HADLEY clouds clouds cloudsclouds

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FUTURE