[1] Near peak activity of two X-class solar flares, on 28 October and 4 November 2003, the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED)/Solar EUV Experiment (SEE) instrument recorded order of magnitude increases in solar EUV irradiance, the TIMED/Global Ultraviolet Imager (GUVI) observed simultaneous increases in upper atmosphere far ultraviolet (FUV) dayglow, and the European Incoherent Scatter Scientific Association (EISCAT) radar and the Ionospheric Occultation Experiment onboard the PICOSat spacecraft recorded corresponding changes in E-region electron densities. Calculations of the FUV dayglow and electron density profiles using Version 8 SEE flare spectra overestimate the actual observed increases by more than a factor of 2.0. This prompted the development of an alternative approach that uses the FUV dayglow and associated E-layer electron density profiles to derive and validate, respectively, the increases in the solar EUV irradiance spectrum. The solar EUV spectrum required to produce the FUV dayglow is specified between 45 and 27 nm by SEE's EGS measurements, between 27 and 5 nm by GUVI dayglow measurements, and between 5 and 1 nm using a combination of the GOES X-ray data and the NRLEUV model. The energy fluxes in the 5-to 27-nm bands (at 5-10, 10-15, 15-20, and 20-27 nm) are randomly varied in search of combinations such that the full spectrum (l < 45 nm) replicates the GUVI dayglow observations. In contrast to the Version 8 SEE XPS observations, solar EUV spectra derived using the multiband yield approach produce electron densities that are consistent with those observed independently. The new multiband yield algorithm thus provides a unique tool for independent validation of solar EUV spectral irradiance measurements using FUV dayglow observations.
NOAA's GOES-13 satellite, launched in May 2006, includes a new solar sensor, called EUVS (Extreme UltraViolet Sensor), that measures energy fluxes in five broad-band spectral channels that span the region from 1 to 130 nm. Here, we report on measurements made during the mission's six-month post-launch test (PLT) period which provided nearly continuous observations from August through November 2006 and the recording of an X9 flare that occurred on 5 December 2006. In this paper, we present a calibration model for the GOES EUVS that incorporates the effects of pointing offsets, cross-disk radiance variability (radiance refers to partial-disk emission), and changes to assumed spectral shapes. Appendices are included that report on the sensitivity to these effects. The main body of the paper gives a description of the model and data recorded during the PLT period. Comparisons are made with time-coincident measurements from TIMED/SEE (Version 10.02), SOHO/SEM, and SORCE/ SOLSTICE for the time period August-November. Comparisons are made with SORCE/XPS for the 5 December flare. In general, there is agreement among the data sets within expected measurement uncertainties. There will be a series of EUVSs extending into the next generation of GOES (starting with GOES-13). The initial performance of GOES-13 EUVS, including 5-channel measurements approximately every 11 s on a nearly continuous basis, suggests that the EUVS series will play a key role over the next many years in monitoring solar EUV variability.
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