Comparison of SORCE/TIM with SFO* Ground based Photometry

Transcription

1 Comparison of SORCE/TIM with SFO* Ground based Photometry Gary Chapman, Angela Cookson, and Dora Preminger *San Fernando Observatory Department of Physics & Astronomy California State University, Northridge

2 San Fernando Observatory (SFO), Cal State Northridge Nordhoff St, Northridge, CA This work is supported in part by NSF grant ATM

3 Why Ground Based Photometric Images can identify sources of TSI variation. Ground based data can identify and help correct short term upsets in spacecraft data. Ground based data can help bridge the different native scales of spacecraft data.

4 SORCE/TIM TSI Data TIM information, specifications, and data products available at Measures TSI with 50 second cadence 6 hr and 24 hr averaged values available

5 SFO Photometric Data CFDT1 & 2 (Walton et al (1998,Sol.Phys. 179, 31; x 512 CFDT1 images, 5 square pixels 1024 x 1024 CFDT2 images, 2.5 square pixels Images produced by 512 or 1024 scans of a 512 or 1024 linear diode array nm red, 10 nm bandpass nm Ca II K, 1 nm bandpass Single red image, Ca II K image from two co added scans

6 CFDT2

7 Sample Images The next 6 images correspond to the following wavelengths: 997 nm, BP = 10 nm (IR) 780 nm, BP = 10 nm (NIR) 672 nm, BP = 10 nm (red) 472 nm, BP = 10 nm (blue) 393 nm, BP = 1 nm (wide K) 393 nm, BP = 0.3 nm (narrow K)

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14 SFO Image Processing Photometric images produced in several wavelengths: CFDT1 since 1988; CFDT2 since Robust algorithms developed for producing photometric contrast images and determining relative irradiance contributions of solar surface features (sunspots, faculae, and plage) from these images. (Walton et al (1998 Sol.Phys )) Solar indices computed, including photometric sums ( ), sunspot areas and deficits, and facular areas and excesses, for the purpose of TSI modeling. (Preminger, Walton, & Chapman 2001, Sol.Phys )

15 SFO Photometric Sum ( ) Index Photometric Sum ( ) has been one of the most successful photometric indices produced. (Preminger, Walton, & Chapman 2002, JGR, 107 6) r and K, used in multi variable linear regressions against space based TSI, produce the best results. r and K are disk integrated sums determined from red and Ca II K line contrast image pixels, respectively; each pixel is weighted by the appropriate limb darkening. r and K do not require feature identification, i.e., determining whether a pixel belongs to a sunspot, facula, or network.

16 SFO Photometric Sum ( ), continued measures the relative change in spectral irradiance in filter passband due to all features assumes image noise is symmetric around zero, causing bright and dark_ noise_ pixels to cancel, leaving only contributions from real features r measures irradiance contributions from photospheric structures seen in red continuum images K measures variability of the upper photosphere/lower chromosphere seen in Ca II K images

17 Figure 1: TIM TSI and SFO model with 2 residuals (R = )

18 Results and Discussion 1253 days of data from 2003 March 02 to 2010 May 05. A two parameter fit of SFO r and K to TIM TSI gives R2= with the following equation TIM TSI = S0 + a1 r + a2 K where S0 = / Wm 2 These results provide further support for the hypothesis that the quiet Sun is constant over time (at least over the solar cycle).

19 Figure 2: A linear regression of K from CFDT1 against K from CFDT2 for a quiet period in summer 2007.

20 Figure 3: A linear regression of r from CFDT1 against r from CFDT2 for a period in June (r2 = 0.979)

21 Previous two regressions The K line regression had an r2 = The red regression had an r2 =

22 Interesting Historical Note Abbot (1958) determined the solar constant was cal./cm2 min. This converts to 1360 W/m2 at low sunspot number (SN). He also found the solar constant varied with sunspot number as W/m2 per unit SN. A modern value might be 0.01 W/m2 per unit SN.

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24 More results (same time period) Using sunspot deficits (DEF) and a facular model (PFIFA) we find: TIM TSI = So + a1 x DEF + a2 x PFIFA 2 With R = , So = / and a1 = / and a2 = /

25 Summary 7 years of SORCE and SFO data R2 = 0.95 TIM fit well with two SFO photometric indices

26 Acknowledgements This work was partially supported by grants from NASA and the NSF most recently NSF ATM and NASA NNX11AB51G. Many of the observations were obtained by students, both graduate and undergraduate, at CSU, Northridge.

27 Abstract Total Solar Irradiance (TSI) measurements have been available from the TIM instrument on the SORCE spacecraft since We compare SORCE/TIM TSI data, both 24 hour and 6 hour averages, with photometric indices from red and Ca II K line images obtained on a daily basis at the San Fernando Observatory (SFO). For 1375 days, from 2003 March 02 to 2010 May 05, we compare the data in linear multiple regression analyses. The best results come from using two photometric indices, the red and K line photometric sums ( ), and SORCE TSI 6 hour averages interpolated to the SFO time of observation. For this case, we obtain a coefficient of multiple correlation, R2, of and a quiet Sun irradiance of S0 = ~ / Wm 2. These results provide further support for the hypothesis that the quiet Sun is constant over solar cycle time intervals.