Intercalibration of Solar Soft X-Ray Broad Band Measurements from SOLRAD 9 through GOES-12 |
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| Authors: | Werner M Neupert |
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| Institution: | (1) Department of Physics, Montana State University, Bozeman, MT, 59717-3840;(2) STE Laboratory, Nagoya University, 3-13 Honohara, Toyokawa, 442-8507, Aichi;(3) Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, 113-0033 Tokyo;(4) Present address: MELCO Inc., 325 Kami-Machiya, Kamakura, 247-8250 Kanagawa, Japan;(5) Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Sagamihara, 229-8510, Kanagawa;(6) Kwasan Observatory, Omine-cho, Kitakazan, Yamashina-ku, 607-8471, Kyoto;(7) National Astronomical Observatory, 2-21-1 Osawa, Mitaka, 181-8588 Tokyo;(8) Department of Physics, Saint Paul's University, 3-34-1 Nishi-Ikebukuro, Toshima-ku, 171-8501 Tokyo; |
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| Abstract: | The two-band soft X-ray observations of solar flares made by the Naval Research Laboratory’s (NRL) SOLar RADiation (SOLRAD)
satellites and by the Geostationary Orbiting Environmental Satellites (GOES) operated by the National Oceanic and Atmospheric Administration’s (NOAA) Space Weather Prediction Center have produced
a nearly continuous record of solar flare observations over a period of more than forty years (1969 – 2011). However, early
GOES observations (i.e., GOES-2) and later (GOES-8 and subsequent missions) are not directly comparable due to changes in the conversion of measured
currents to integrated fluxes in the two spectral bands that were adopted: 0.05 – 0.3 (or 0.4) nm, which we refer to as XS
and 0.1 – 0.8 nm (XL). Furthermore, additional flux adjustments, using overlapping data sets, were imposed to provide consistency
of flare-flux levels from mission to mission. This article evaluates the results of these changes and compares experimental
GOES-8/GOES-2 results with changes predicted from modeled flare spectra. The factors by which recent GOES observations can
be matched to GOES-2 are then optimized by adapting a technique first used to extrapolate GOES X-ray fluxes above saturation
using ionospheric VLF radio phase enhancements. A nearly 20% increase in published GOES-8 XL data would be required to match
to GOES-2 XL fluxes, which were based on observed flare spectra. On the other hand, a factor of 1.07 would match GOES-8 and
later flat-spectrum 0.1 – 0.8 nm fluxes to GOES-2 XL if the latter data were converted to a flat-spectrum basis. Finally,
GOES-8 observations are compared to solar soft X-ray estimates made concurrently with other techniques. Published GOES-8 0.1 – 0.8 nm
fluxes are found to be 0.59 of the mean of these other determinations. Rescaling GOES to a realistic flare spectrum and removing
a 30% downward adjustment applied to the GOES-8 measurements during initial data processing would place GOES-8 and later GOES
XL fluxes at 0.94 of this XL mean. GOES-2 on the same scale would lie at about 0.70 of this mean. Significant uncertainties
in the absolute levels of broad band soft X-ray fluxes still remain, however. |
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