Photometric Observations of Solar Irradiance Variability from SFO

Photometric Observationsof Solar Irradiance Variability

from SFO

Gary Chapman, Angie Cookson and Dora Preminger

San Fernando Observatory (SFO)California State University, Northridge

(CSUN)

About CSUN

According to the “Master Plan” for the California State University (the CSU)

there is no direct allocation of time for faculty research (unless one has a research grant)

it does not allow the grantingof Ph. D. degrees at any State University

Data Description

CFDT=Cartesian Full-Disk TelescopeDaily observations (digital images) continue using

CFDT1 (since 1986) and CFDT2 (since 1992).Observations obtained on about 60% of days.Fully processed images available on the Web ().Photometric indices available on request.

Data Description, Cont'd.

Basic Observing TechniqueLinear photodiode array is oriented N-SImage is scanned using Earth's rotationSky transparency is recorded every lineOriginal idea from Gordon Hurford passed on by

Hugh Hudson at WARTS workshop(SP-310)

Image Size & Scale

CFDT1

Size: 512 x 512 pixelsScale: 5.12 arc-sec/pix

CFDT2

Size: 1024 x 1024 pixelsScale: 2.5 arc-sec/pix

Wavelengths & (BPs)

CFDT1672.3 (10) nm472.3 (10) nm393.4 (1.0) nm

CFDT2672.3 (10) nm472.3 (10) nm393.4 (1.0) nm393.4 (0.3) nm780.0 (10) nm997.0 (10) nm

Scientific Justification

Need to understand and remove solar changes from other forms of climate forcing.

Spacecraft measurements of TSI and SSI not imaged.

Our program measures relative changes due to solar activity.

Our photometric indices correlate with TSI with R2 as high as 0.95.

Photometric Indices

Red ImagesPhotometric Sum [uses ALL pixels]

Σr = ∑i (ΔI/I) Φr(μ) [no feature identification]Photometric Sunspot Index (model)

PSI = CS ∑AS (3 μ + 2) [≤ -8.5%, only]K-line Images

Σk = ∑i (∆I/I) Φk(μ) [no feature identification]

PFI = Cp ∑Af (3μ + 2)(1/μ – a) [≥ 4.8%, only]

REGRESSION RESULTS

S = S0 + A * Σr + B * ΣK

S0 = 1360.81 ± 0.004 W/m2

A = 1.025 ± 0.008B = 0.1257 ± 0.001R2 = 0.9495N = 1253

Scientific Just. (cont'd)

Our data can be used to correct S/C upsets.Our data can be used to connect different S/C TSI

(having different scale factors).Imaged data necessary to understand the sources

of TSI and SSI variations.

Bolometric Contrast

The Bolometric Contrast, α, is the bolometric irradiance deficit of a sunspot as seen from the

surface of the Sun, not from the Earth.

A similar term for faculae/ network is not so easy; the facular contrast is a sensitive function of disk

position.

Bolometric Contrast, con't.

The bolometric contrast, αeff, of a sunspot is the irradiance deficit as seen at the surface of the sun; not from the earth. It is given by

DEF/(2 * PSI)

The bolometric contrast, when integrated over the solar sky of a sunspot, gives its luminosity deficit.

PSPT & SFO Deficits, μhems

DEF[PSPT(red)] = A + B * DEF[SFO(red)] + C * DEF[SFO(blue)]

A = 23 ± 28 μhemB = 0.791 ± 0.168 C = 0.214 ± 0.112R2 = 0.99 N = 53

16301212 590

64K

45K

27K

Annual Means

Student Involvement

Students carry out research with the help of faculty and staff.

Students are often co-authors of refereed papers.The most recent example is Mike Wesolowski

(Wesolowski et al. Solar Phys. 2008) who is in the Ph. D. program at Waterloo University.

Known or Potential Users

C. Fröhlich (VIRGO)S. Dewitte (DIARAD)J. Morrill (NRL)J. Pap and H. JonesT. Woods & SORCE teamJ. Fontenla (LASP, Boulder)G. DeToma (LASP)G. Thiullier (PICARD)R. Willson (ACRIMSAT)

Acknowledgements

The observations and analyses have been carried out by staff and many CSUN students, both undergraduate and graduate.

Work has been partially supported by grants over the years from both NASA and NSF.