Solar-C Science Definition Meeting
ISAS/JAXA, November 18-21, 2008
Sagamihara

Solar Irradiance Observations
 for Solar-C Plan-A for Solar-C Plan B
Werner Schmutz
PMOD/WRC, Switzerland

Overview

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Observed TSI

combine to composite

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Observed TSI

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TSI composite-0.4 W/m2

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Long term trend

10Be  open magnetic

flux  proxy for thelong term trend of TSI= 1.6 W/m2 ?

19.11.2008= 0.4 W/m2 ?

Conclusion: Plan B If we want to know how the irradianceinfluences the terrestrial climate thenwe have to continue measuring theTotal Solar Irradiance until the next minimum

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Solar-C Plan A
Plan A: Solar-C out of the ecliptic
 What do we know about the latitude dependence of
the irradiance?
– Very little and very uncertain. Most recent paper:
Rast et al. 2008 (based on PSPT) : “We have found a weakenhancement of the mean continuum intensity at polar
latitudes (continuum intensity enhancement 0.1%-0.2%,
corresponding to a brightness temperature enhancement of2.5 K)”– Intensity at different view angle is NOT latitudional radiancevariation!
Rast et al. investigated the equator to pole difference of thelimb darkening function, which reflects essentially the solar
structure in height.

– We have one more piece of evidence ….

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Model of TSI

Solar TSI activity is modeled
quite accurately with the modelof Krivova et al. 2003
We use this model to remove
the activity contributions fromthe observed TSI
 this yields a quite Sun TSI

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Krivova et al. 2003, A&A 399 L1

TSI: Time dependence

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TSI: Time dependence

TSI(observed) – TSI(modelled)= “quite Sun”

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TSI: Time-latitude dependence

Compare to latitudedependence of SOHO

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TSI: Latitude dependence

TSI as a function ofheliospheric latitude

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TSI: Latitude dependence

TSI with activity removed

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Empirical TSI accuracy

Difference between active absolute radiometers 2003 – 2006
Possible - but unlikely because two2
<VIRGO-TIM> = 4.54
W/mradiometers,
VERY±0.03
different
TIM/SORCE
andVIRGO/SOHO, corresponds
to only±30ppm !
behave are almost identical
Trend: 20 ppm in 4 years ⎝ < 5 ppm/year !!
Is the latitudinal dependence aninstrument effect?
(see above Acrim III)19.11.2008

What do we expect?

?
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Hardware option 1
As:

PREMOS/PICARD
launch June 2009

TSI radiometer+ 6 (x 2) (UV) filter channels(replaces a full Sun spectrograph)
Advantage:high speed sampling
TSI: 0.1 Hz
filter channels 30 Hz•

MASS: 11 kg•

Overall Dimensions:
270 x 327 x 160 mm•

Power Requirement
13 W nominal

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Hardware option 2As:DARA/PROBA3(phase A study)

TSI 3-channel radiometer
Advantage:– long-term stability– high speed sampling: 0.1 Hz•

MASS: 4 kg•

Overall Dimensions:
156 mm x 182 mm x 228 mm•

Power Requirement
3.5 W nominal

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Conclusions
Solar-C Plan A:
Total Irradiance Radiometer (4 kg):– Latitude dependence of irradiance (Now unknown!) boundary condition to meridional circulation
 true luminosity of the Sun

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Conclusions
Solar-C Plan A:
Total Irradiance Radiometer (4 kg):– Latitude dependence of irradiance (Now unknown!) boundary condition to meridional circulation
 true luminosity of the Sun

Solar C Pan B:
Total Irradiance Radiometer (4 kg)– High temporal resolution (full Sun)
option (+7 kg): 6-channel filter radiometer allows FUV + UV spectral reconstruction(10 to 300 nm)
19.11.2008