solar-stellar variability workshop, hao, march 19, 2014 - j. harder page 1 solar-stellar variability...

Solar-Stellar Variability Workshop, HAO, March 19, 2014 - J. Harder

Solar-Stellar Variability WorkshopSORCE Photometry

Jerald [email protected], 1-303-492-1891

With thanks to Mark Rast

Juan FontenlaStéphane Béland


Topic Outline

Introduction to the SORCE SIM• Instrument capabilities and limitations

Comparisons with PSTP & SRPM SIM observations via Strömgren filter equivalents Moving forward – the Radiometric Solar Imager

& TSIS


• Instrument Type: Féry Prism Spectrometer• Wavelength Range: 200-2400 nm• Wavelength Resolution: 0.24-34 nm• Detector: ESR, n-p silicon, InGaAs• Absolute Accuracy: 2-8%• Relative Accuracy : ~0.5-0.02% (240-2400 nm)• Long-term Accuracy: 0.3-0.025%/yr (240-2400 nm)

Instrument overview

• Field of View: 1.5x2.5˚ total• Pointing Accuracy/Knowledge: 0.016˚/0.008˚• Mass: 21.9kg• Dimensions: 88 x 40 x 19 cm• Orbit Average Power : 17.5 W• Orbit Average Data Rate: 1.5 kbits/s• Redundancy: 2 Redundant Channels

Harder J. W., G. Thuillier, E.C. Richard, S.W. Brown, K.R. Lykke, M. Snow, W.E. McClintock, J.M. Fontenla,

T.N. Woods, P. Pilewskie, 'The SORCE SIM Solar Spectrum: Comparison with Recent Observations' ,

Solar Physics, 263, Issue 1 (2010), pp 3, doi:10.1007/s11207-010-9555-y

Pagaran, J., J. W. Harder, M. Weber, L. E. Floyd, and J. P. Burrows, ‘Intercomparison of SCIAMACHY and SIM vis-

IR irradiance over several solar rotational timescales’, A&A, 528, A67 (2011), doi: 10.1051/0004-

6361/201015632, 2011.


A word about resolution…

SIM measures the irradiance weighted by the bandpass. Low resolution instruments respond to the density of lines,

not to individual lines.


SORCE spacecraft & thermal events

Thermal events change instrument performance most typically through wavelength shift & light path through prism. Degradation corrections must account for these changes.

Time period of Version 17 remains the most stable and reliable time period of SIM operations.


SIM degradation correction and long-term accuracy

Long-term degradation corrections in SIM are based solely on measured instrument quantities.• Correction is based on the comparison of two identical (mirror image)

spectrometers that have been exposed at different rates.

• Corrections for photodiode detectors in the same channel are made by comparison with the spectrally flat ESR detector after correcting for the different optical paths through the prism.


Spectral variability nomogram

• SIM observations consistent with an overall decrease in the temperature gradient in the active (magnetic) solar photosphere.

• The change in T-gradient occurs in solar atmospheric layers close to the Teff value.

Harder et al., GRL,, 2009


Independent observations with anti-solar cycle trends

Features contrast varies with wavelength and heliocentric angle and corresponds to the

slope of T vs. P.(5 ’s between 525 to 677 nm)

Sanchez Cuberes et al., ApJ,2002 Topka et al., ApJ 1997

Preminger et al.., ApJ,2011

The photometric sums exhibit similar temporal patterns: they are negatively correlated with solar activity, with strong short-term variability and weak solar-cycle variability.

Moran et al., Sol. Phys., 1992


PSPT feature identification & time series

Feature area determined from intensity analysis of PSPT images Analysis done as a function of disk position and time Full disk irradiance determined from disk position and emitted intensity from each atmospheric model

Ca IIK393.45 nm, 0.273 FWHMIdentify Active Regions

Red Continuum607.095 nm, 0.458 FWHM

Identify Umbra & Penumbra

SRPM Mask ImageIdentify 7 solar Features


SIM & PSPT Facula + Plage

SIM 280 nm irradiance is proportional to the measured facular area in PSPT


SIM & PSPT sunspot umbra & penumbra #1

Further corrections needed to account for wavelength stability later in mission.

• 2 arc-sec error in prism rotation angle ≈ 0.145nm ≈ 8% of a prism step


SIM & PSPT sunspot umbra and penumbra #2

Decreased irradiance is observed even when sunspot blocking is not indicated by PSPT 607 nm images.


Solar spectral irradiance variability in SRPM

Fontenla, J. M., et al. , JGR, 2011

SRPM analysis is able to capture offsetting trends observed by SIM, but the magnitude of the effect are different.


Solar spectral irradiance variability in NRL SSI

Sunspot Case:

04/30/2005

Facula-Plage:

08/29/2005

Solar Min Ref:

11/09/2007J. Lean,

GRL., vol. 27, pp 2425, 2000.


Strömgren Filters wrt Brightness Temperature


SIM integrated over Strömgren bands


PSPT observations of facula

• Some facula and plage have negative contrast at red continuum wavelengths

• Position of dark faculae on the disk is not a simple function of heliocentric angle

• The fraction of dark Facula decreases into SC23 minimum and increases into rising phase of SC24


A compelling need for the Radiometric Solar Imager (RSI)

Is the time dependence because the faculae (or unresolved underlying flux distributions) are changing, or because the CLV against which their contrast is measured is changing?Ground based instrumentation can only measure photometric contrast compared to some definition of the background “quiet-sun.”

• we do not know the center-to-limb variation of the “quiet-sun,” against which these contrasts are measured

• we do not know whether the structures, or the background against which they are measured, or both, are changing with solar cycle

• these differences are important in our interpretation of the solar spectral irradiance


• Full disk photometric images with relative pixel-to-pixel precision of 1:103

• Separate radiometer which shares imager filter wheel and precision aperture determines throughput of filter

• A filter transmission measurement prevents ambiguities in filter bandpassAdvantage:

Spectrometer does not require absolute calibration Can have high resolution, but limited bandpass

RSI Concept


• 100 mm diameter entrance pupil and a 12.5mm aperture stop where the filters are positioned

• Placing the filters at the aperture stop significantly reduces the spatial uniformity requirements for the filters compared to placing them just before the focal plane array, and make them much smaller than placing them at the entrance

• Light path (ray angles) through filters is however slightly different in telescope than into radiometer

RSI Design


TSIS SIM designed for long-term spectral irradiance measurements (climate research)

Incorporate lessons learned from SORCE SIM (& other LASP programs) into TSIS SIM to meet measurement requirements for

long-term JPSS SSI record

Specific required capabilities over SORCE SIM

Reduce uncertainties in prism degradation correction to meet long-term stability requirement

• Ultra-clean optical environment to mitigate contamination

• Addition of 3rd channel to reduce calibration uncertainties

Improve noise characteristics of ESR and photodiode detectors to meet measurement precision requirement

• Improved ESR thermal & electrical design

• Larger photodiode dynamic range integrating ADC’s (21 bits)

Improve absolute accuracy pre-launch calibration

• NIST SI-traceable Unit and Instrument level pre-launch spectral calibrations (SIMRF-SIRCUS)

SORCE SIM

TSIS SIM

TSIS SIM derives heritage from SORCE SIM


ConclusionsThe SIM observations indicate solar cycle trends both in- and out of phase with the TSI.

• Interpretable in terms of the solar brightness temperature and temperature gradients with the solar atmosphere

• SIM integrated over Strömgren v, b, & y filters reflect anti-solar cycle behavior with the u-filter in phase.

• The v, b, & y filters may not be adequate proxies of the TSI for sun-like stars

SIM ultraviolet observations show a high degree of consistency with:

• Facula and plage areas measured by PSPT

• Calculated spectral irradiance estimated form SRPM

• SIM irradiance at 607 nm tends to under-estimate the reported PSPT sunspot areas and decreased irradiance is observed even when sunspot blocking is not indicated by PSPT 607 nm images.

PlansContinued analysis of SIM data to determine behavior in SC24 is essential2017 deployment of TSIS SIM is mandatory to further this research – but gaps are inevitable and difficult to resolve for SSI measurementsThe development of radiometric imagery is the next logical step for understanding solar variability and understanding the stellar connection


EXTRAS


Estimated trend uncertainties in the Visible

Best observation for degradation corrections for SIM is 04/2004 to 05/2007, but magnitude of uncertainties similar in the 2007-2011 period

Uncertainty in the visible comparable to 2σ noise levels but reaches a minimum level at ≈2×10-4. Errors in the 2003-2004 and after 2011 time period require further refinements

• Improved wavelength registration will reduce uncertainties in the visible


Improvements to be implemented in Version 20 (release planned for late spring 2014)

Implement dynamical wavelength shifter based on instrument dispersion equations to account for thermal/mechanical stresses induced by spacecraft power cycling – Must be applied to every spectrum Particularly important for visible and infrared wavelengths from Sept 2011 to present

time

Reanalysis of photodiode and prism glass refractive index temperature coefficients due to decreased temperature stability

Correct for non-exposure related photodiode degradation Not well represented in Version 19

Perform AB comparisons and determine ray path through the prism Particularly important for first year of the mission and after full-time power cycling of

the instrument

Version 20 analysis for UV and IR spectral regions has not started


The RSI will:

• Elucidate the underlying causes of solar spectral variability by making first radiometric measurements of the resolved solar disk

• First radiometric determination of center-to limb profiles of the quiet-sun and solar magnetic elements as a function of solar cycle

• First determine of the photospheric temperature gradient both within and outside of magnetic flux structures using opacity conjugate wavelengths

• Determine the veracity and cause of spectral irradiance trends for terrestrial climate modeling

solar-stellar variability workshop, hao, march 19, 2014 - j. harder page 1 solar-stellar variability...

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