Q_EUV vs. Other EUV Proxies: A Re-Evaluation of Solar EUV Proxies for Thermospheric and Space Weather Investigations

F_10.7, Mg II, and F₃₀ are widely used proxies for variability in solar Extreme UltraViolet (EUV, 5–120 nm) irradiance. An alternative proxy for solar EUV variability is Q_EUV, an indirect measure of total solar EUV irradiance, retrieved from observations of Earth's Far UltraViolet (FUV, 120–300 nm) airglow and from empirically modeled solar EUV spectra. Daily Q_EUV derived from FUV airglow is available from the Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics (TIMED) Global Ultraviolet Imager (GUVI) and Global-scale Observations of the Limb and Disk (GOLD) missions, as is Q_EUV from empirical solar EUV spectrum. Spectral measurements from GOLD are also used to retrieve lower-middle thermospheric temperature, termed as T_disk. The availability of GOLD T_disk and Q_EUV provides a new opportunity to reassess the effectiveness of various solar EUV proxies for thermospheric use. This investigation showed that Q_EUV has the best correlation with GOLD T_disk compared to all the other EUV proxies. Therefore, it can be used as an alternate proxy for total solar EUV variability, on day-to-day to solar cycle time scales.