Abstract

Accurate measurements of the solar EUV irradiance at the absolute lowest minimum irradiance levels, or an EUV minimum ‘reference spectrum’ are essential for many aspects of the Heliophysics system. Some applications include quantifying the solar EUV variability as well as estimating the energy in... Show moreAccurate measurements of the solar EUV irradiance at the absolute lowest minimum irradiance levels, or an EUV minimum ‘reference spectrum’ are essential for many aspects of the Heliophysics system. Some applications include quantifying the solar EUV variability as well as estimating the energy input into the Earth and Mars’ Ionosphere and Thermosphere during these solar conditions. Prior to the recent solar minimum, there were no direct observations of the a complete EUV reference spectrum due to limited spectral or spatial coverage, lack of an absolute calibration for the instrument, or timing issues from rockets or satellites not observing during these times in the solar cycle. Measurements from the Solar EUV Experiment (SEE) onboard the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite have for the first time measured a solar EUV minimum reference spectrum at an accuracy of <20% and 1 nm bins throughout the solar cycle minimum. The SEE team recently released a Version 10 data product improving the long-term degradation correction, which improves the accuracy of SEE’s most recent observations of the solar minimum. This degradation correction was characterized using measurements from a sounding rocket (P.I. Tom Woods, CU/LASP) containing the rocket version of the Solar Dynamics Observatory (SDO) EUV Variability Experiment (EVE) that was launched very near solar minimum on April 14, 2008. The EVE instrument has a better spectral resolution of 0.1 nm as well as a better accuracy of <10% when compared to the SEE measurements. The SEE and EVE spectra will be presented and compared to other EUV measurements from SOHO SEM and reference spectra such as the ‘Hinterregger’ (SC21refw), the Warren 2001, and the ATLAS spectra. Reference spectra produced by empirical models such as the Flare Irradiance Spectral Model (FISM), Solar Irradiance Platform (SIP), and HEUVAC will also be discussed. New more accurate results of Earth’s neutral atmospheric and electron density and temperature profiles that use the latest measured EUV minimum reference spectra as input into the TIMEGCM model will be presented. Show less