1. Recent Solar Irradiance Data From SBUV/2 and OMI Matthew DeLand and Sergey Marchenko Science Systems and Applications, Inc. (SSAI) SOLID WP-2 Workshop LPC2E, Orleans, FRANCE 14-15 October 2013

2. Solar Measurements from Ozone Instruments Determine stratospheric, total column ozone abundance by measuring backscattered UV radiation. Solar measurements used to determine top-of-atmosphere irradiance (for calculation of I/F), long-term calibration changes. Typically use same optical path as radiance measurements, with addition of solar diffuser. Usually get only one measurement sequence per orbit. Balance science opportunity with instrument degradation effects. No provision for on-orbit end-to-end characterization (although light sources are often carried and used).

3. SBUV/2 Design Double monochromator, bandpass = 1.1 nm FWHM, wavelength range = 160-405 nm. Field of view = 11.3° x 11.3°. Nadir view only. Solar measurements: Only possible when satellite reaches NH terminator (p.m. orbit). Deploy diffuser with high incidence angle (53°, 62°), view Sun until θ > 90°. Absolute diffuser reflectivity is < 2%. Discrete mode: Measure 12 discrete wavelengths (e.g. 252- 340 nm, 277-283 nm) during 32 second scan, 1.25 second sample integration time. 8-12 solar scans per orbit. Used for ozone calibration, Mg II index. Sweep mode (continuous scan): Measure 1680 wavelengths over 160-405 nm (~0.15 nm sampling) during 192 second scan, 0.1 second integration time. 2 solar scans per orbit.

4. SBUV Solar Timeline Aura OMI

5. SBUV/2 Status Current operations for NOAA-16 (daily sweep mode, daily discrete Mg II) are continuing. NOAA-17 satellite shut down April 2013. NOAA-18 SBUV/2 chopper wheel stalled in December 2012, still not working. NOAA-19 SBUV/2 Hg lamp door jammed in closed position in April 2010, recovered in 2 days. Solar measurements restricted since then (weekly sweep, discrete ozone; no Mg II) to minimize diffuser degradation. OMPS (Ozone Mapping Profiler Suite) on Suomi NPP satellite (launched October 2011) includes SBUV/2 follow-on (nadir profiler). Solar calibration measurements only made weekly to limit degradation over nominal 7-year lifetime.

6. NOAA-16 Mg II Index

7. OMI Solar Measurements Launched on EOS Aura satellite 15 July 2004. Single monochromator covers 264-504 nm with three detectors, 0.4-0.6 nm resolution. 2-D CCD collects up to 60 simultaneous spectra for every image (2-second integration time). Up to 77 images available in single orbit measurement sequence. Solar measurements use special viewing port, aluminum and quartz volume diffusers. Current data are well-suited for creating solar activity indexes (DeLand and Marchenko, JGR-Atmospheres [2013]).

8. Sample OMI Spectrum DeLand and Marchenko [2013, JGR in press]

9. OMI Mg II Index

10. Mg II: OMI vs. SBUV/2

11. Mg II and Mg I Index from OMI

12. Ca II K Index: OMI and NSO

13. OMI Irradiance Data Solar measurements use reflecting diffusers with different duty cycles (quartz volume = daily; aluminum = weekly, monthly). Use different duty cycles to characterize diffuser changes. Remaining throughput changes are fairly small, but do show different behavior during 2005-2006 compared to later period. Assume change in measured irradiance during solar minimum (mid-2007  mid-2009) is only caused by instrument degradation. Derive degradation rates and estimate solar variations for Cycle 24. Small seasonal variations (~0.3%) due to goniometry must be addressed. CCD design allows hundreds of spectra to be averaged over small time interval to reduce statistical noise. Sampling is also improved due to “spectral smile” between different rows.

14. UV2: Low-refl. terrain UV2: IceVIS: Ice UV1 Radiometric Stability Marchenko and Jaross [Aura Science Team, 2012]

15. OMI Degradation Rates Rows 11(UV1)+22(UV2)+22(VIS) Rows 27(UV1)+54(UV2)+54(VIS)

16. Cycle 24 Spectral Variability Blue = OMI data (2 nm bins) Red = NRLSSI model

17. Spectral Features in Averaged Data Red line = solar spectrum over wavelength interval (arbitrary units) Mg II Mg I Si II Black line = Difference in OMI monthly average data (7/2012-9/2013 vs. 7/2007-8/2009) Ca II K, H H-beta CH, Fe IH-gamma H-delta

18. Cycle 24 Time Series LinesContinuum

19. OMI Summary and Status Instrument health is good. Continued satellite operations through 2015 recently approved by NASA Senior Review. Solar activity index data sets are posted on-line. Evaluating and validating irradiance results. Plan to write up for publication in near future. Expect continuation of similar solar data with TROPOMI instrument, scheduled to launch on ESA Sentinel 5 Precursor mission in December 2014.

20. Spectral Features in Raw Data Red line = solar spectrum over wavelength interval (arbitrary units) Mg II Mg I Si II Black dots = Difference in OMI monthly average data (May 2013 vs. May 2008) Ca II H Ca II K H-gamma CH, Fe I