Correlations between thermospheric density and temperature, solar EUV flux, and 10.7‐cm flux variations

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Abstract
Simultaneously measured thermospheric N2 densities and solar EUV fluxes obtained by the AE‐E satellite are compared with ground‐based solar 10.7‐cm fluxes and calcium plage measurements. Short‐wavelength (coronal) EUV emissions correlate better with thermospheric density than the 10.7‐cm flux, although the reduction in density residuals is small. Correlation of density with a calcium plage index was somewhat worse than with 10.7. Although the overall correlation of 10.7‐cm flux with EUV fluxes is high, the best fit slopes are different for short‐ and long‐term variations, and there are instances where the short‐term behavior of various EUV emissions and that of the 10.7‐cm flux are distinctly different. For both density and EUV, a two‐factor formula based on daily 10.7‐cm flux and a running mean of the 10.7‐cm flux provides a better fit than using the daily 10.7‐cm flux alone.