Solar Irradiance Reference Spectra (SIRS): for IHY2007 Whole Heliosphere Interval (WHI)

Transcription

1 Solar Irradiance Reference Spectra (SIRS): for IHY2007 Whole Heliosphere Interval (WHI) Tom Woods, Phil Chamberlin, Rachel Hock, Jerry Harder, Marty Snow, Frank Eparvier LASP / CU tom.woods@lasp.colorado.edu 29-Feb-08 K D Wood Colloquium, Tom Woods 1

2 Recent Press on Solar Minimum

3 IHY WHI Whole Heliosphere Interval (WHI) is an international coordinated observing and modeling effort to characterize the 3-dimensional interconnected solarheliospheric-planetary system. Period is March 20, 2008 to April 16, 2008 Solar Carrington Rotation 2068

4 Solar Cycle Minimum Yet? Standard definition of solar cycle minimum is the minimum in SSN smoothed over 1-year <SSN> minimum level ~ 0-5 Not seen minimum yet! however minimum will not be obvious until 6 months after the event But do have minimum conditions now.

5 PSPT Images Used to Identify Solar Features April were very quiet days Day Features areas (relative to solar disk area) A B D F H P S R 2008/04/ e e e /04/ e e-005 [figure from Juan Fontenla]

6 Solar Activity During WHI April 10-16, 2008 QS Interval PSPT images are used to generate feature areas Sunspot Area 14-Apr-08 Moderate solar activity in late March Faculae/Plage Area Very low solar activity during April Active Network Area Quiet Network Area [figure from Mark Rast]

7 Is the Solar Modern Maximum over? The two VIRGO-based and ACRIM-based composite time series of TSI indicate similar downward trend for current solar minimum A 0.02% decrease is observed for both sets Is this real solar long-term change or just instrumental degradation effect? ACRIM Composite VIRGO Composite -0.02% -0.02% [figures from Greg Kopp]

8 Other evidence for lower minimum? SORCE SOLSTICE minimum result suggests lower FUV irradiance (~0.3 SC variation) -0.3 X SC Variability SOLSTICE 2008/1996 SOLSTICE long-term precision estimate [figure from Marty Snow, COSPAR 2008]

9 Lower Solar Polar Magnetic Fields Polar fields (Wilcox Solar Obs.) are ~40% less than previous 3 cycles Similar to reconstructed polar fields during Dalton Minimum (1800s) 1/2 Dalton Min. [figure from Wang et al., Ap. J., 2005]

10 Three Spectra for WHI Interval Quiet Sun (solar cycle minimum) Reference Spectrum WHI Quiet Sun dates of Apr (Rocket 14-Apr-2008) SORCE SIM dates of 9-Nov days Active Reference Spectra Sunspot Darkening (TSI) : Mar Faculae Brightening (TSI): Mar 30 Apr 4

11 Spectral Distributions for WHI Irradiance Sets How to combine? consider accuracy, spectral resolution, degradation, etc. select wavelength boundaries or averages? SOHO SEM SORCE XPS (0-40) NOAA SBUV ( ) SORCE SOLSTICE ( ) SORCE SIM ( ) TIMED XPS (0-40) TIMED SEE EGS (26-195) Rocket EVE (6-106)

12 Solution for Reference Spectra Spectral Intervals / Resolution 0.1- intervals on centers Note that SIM instrument resolution (above 310 ) is much less than 0.1- Selected Wavelength Intervals Did have to fill (no measurements) EGS ( ) XPS Rocket EVE (6-105) SORCE SOLSTICE ( ) SORCE SIM ( ) DATA: and htt //l l d d /li i d/

13 WHI Solar Irradiance Full Range First time to have Solar Spectra Irradiance (SSI) measurements covered from at same time during solar minimum conditions.

14 WHI Solar Irradiance: Rocket EVE & SEE

15 WHI Solar Irradiance: SORCE SOLSTICE

16 WHI Solar Irradiance: SORCE SIM

17 WHI Solar Irradiance: Solar Variability UV variability 1% at 200 and > 10% for λ < 110 Lower chromosphere (200, Mg II 280 ) similar to Planck function change in temperature by +5 K (green line) NUV-Visible-NIR variability Sunspot / Faculae ratio shown in panel (6) Photosphere variability (sunspot darkening) similar to Planck function change in temperature by -0.2 K (green line)

18 Comparison To ATLAS-3 Reference Spectrum Thuillier et al. (2004) included ATLAS 3 reference spectrum near minimum May 1997 rocket measurement for < 119 March 1995 UARS and ATLAS-3 observations for > 119 Expect SIRS Minimum / ATLAS-3 ratio to be less than 1 (ATLAS-3 not at minimum) Differences are mostly within instrument uncertainties (red)

19 Comparison to XPS Level 4 (CHIANTI) Differences by factors of 10 at high resolution Much better agreement at 5- resolution (green)

20 Summary Three new reference spectra for the WHI SIRS Minimum (quiet Sun) Sunspot Active Faculae Active Variability is representative of solar rotation (but much smaller than solar cycle) UV active variability is all positive at λ < 260 Indicates lower chromosphere global-average temperature change of about +5 K NUV-Vis-NIR sunspot variability is mostly negative Indicates photospheric global-average temperature change of about -0.2 K SIRS Minimum spectrum compares well with the ATLAS-3 reference spectrum (Thuillier et al., 2004) Differences are mostly within instrument uncertainties (accuracy) ATLAS-3 was not at solar minimum though