Fig. 4

PTRIP simulation results of red and blue auroras. a, The red line (630.0 nm) and blue lines (391.4 nm and 427.8 nm) auroral emission profiles with the background atmosphere calculated by the DTM for the condition on May 11^th and with electron and H-ENA fluxes obtained by the TED and MEPED instruments, respectively. The solid blue lines show the intensities calculated for electron precipitation only. Paths 1–6 correspond to the passage of MetOp-1 at 10:37 UT, NOAA-18 at 11:22 UT, MetOp-3 at 11:31 UT, MetOp-1 at 12:19 UT, NOAA-18 at 13:05 UT, and MetOp-3 at 13:12 UT. The sky blue denotes the resonance scattering intensity of N₂⁺ first negative bands. The sky blue curve is the N₂⁺ resonant scattering intensity as calculated from the GITM’s active-time simulation result, while the dotted lines are the N₂⁺ resonant scattering intensities for the fixed N₂⁺ ion densities of 10, 30, and 100 cm^-3. b, Comparison of auroral emission profiles between the two background atmospheres on May 9th and 11^th with the same incident electron and H-ENA fluxes during Path 3.