Total Solar Irradiance and SolarLuminosity

2nd SOLAR-C Science Definition Meeting, ISAS/JAXA, 9. March 2010
Wolfgang Finsterle

Physikalisch-Meteorologisches Observatorium Davos
1 World Radiation Centre

TSI on SOLAR-C(A) —Science Goals●Solar luminosity– Variability over the solar cycle?
– Standard Solar Model boundary condition– Stellar evolution theory●Meridional circulation and north-south
asymmetries of the solar activity (dynamo)– Meridional temperature gradient– Discriminate between different models forlatitudinal dependency of TSI variability2

Luminosity ↔ Stellar StructuredL2=4r
− ●
Steady-state assumption: dr●

242L=4r
T=4rSolar Luminosity: ꙩsurfaceꙩꙩ∫ − ●Tsurface is linked to Tcore via energy production
process (p-p chain efficiency scales with Tcore4)➔

Accurate measurement of Lꙩ thus allows us todetermine the solar surface and coretemperatures and to validate the Standard
Solar Model and stellar evolution theory

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Observational Requirements
for Solar Luminosity✔Integrated disk measurements✔High heliographic latitude✔ At 40° the effect of the polar areas appears
with 64% of its amplitude✔Low noise level✔ thermal stability✔ temporal stability

4Additional Benefits —Meridional Temperature●●●

5Meridional temperature measured withHINODE suffers from uncertainty inphotometric calibration of the images
Integrated-disk measurements of TSI atdifferent latitudes eliminate this problem
1K ~ 1 Wm-2 (~700 ppm)

Latitudinal Heat Flow●

Conical (rather than cylindrical) rotation
profile is indicative of latitudinal heat transfer
and/or thermal forcing from the tachocline[Miesch et al., 2006]●6Variability of order of 1 – 10 K have been
predicted by simulations and measured byhelioseismic inversions [Brun et al., 2010]

Simulations vs. Observations
hot at highlatitudes

cool at low and high latitudes
warm at mid latitudes
T≈10 K near the surface

warm at midlatitudes

cool at lowlatitudes

GONG

MDI

Brun et al., 20107

PMO6/PREMOS ThermalStability
K

0.7 %

W

0.07 %

8W

New TSI Radiometer

Highly symmetrical design for improved thermal
stability and control of heat flows
9Thermal Stability (-10 – 30 °C)

0.007 %Reproducibility of measurements better than 10 ppm
10What do we expect to see?
VIRGO Irradiance with Krivova Model subtracted (Krivova et al., 2003)-10.8 ppm per degree(4 σ)-7.2 ppm per degree(7 σ)heliographic latitude of SoHO
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N-S Asymmetry in Variability
Irradiance Variability

heliographic latitude of SoHO
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Results from VIRGO/SOHOWm-2

Full Width at Half Maximum (Irradiance Variability)

VIRGO~1.2 Wm-2~0.9 Wm-2
VIRGO – Krivova Model

heliographic latitude of SoHO
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SOHOSOLAR-C(A)“The influence of an inclined rotation axis on solar irradiance variations”

KnaackKnaack et al. 2001

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Summary of VIRGO Results●Ascending phase of solar cycle 23 appeared
to be asymmetric– Larger variability on the southern hemisphere– Fully explained by Krivova TSI reconstruction– High-latitude observations allow todiscrimination between conflicting model
predictions– Accurate measurement of N-S asymmetry

may help to better understand the solar
dynamo15

Summary of Scientific Returnfrom TSI on SOLAR-C(A)●Solar Luminosity– Temperature of solar core and surface●Energy production rate●

Differential rotation, meridional circulation●●Re-calibrate standard solar model and stellar
evolution theories

Asymmetries in activity pattern– Discriminate between conflicting models– Confine dynamo governing parameters

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