Precipitating electron energy of pulsating aurora estimated from multi-wavelength optical observations

Pulsating aurora (PsA) is characterized by quasi-periodic intensity modulations with a period of a few to tens of seconds which is known as the main modulation. Electrostatic Cyclotron Harmonic waves and whistler-mode waves are known to cause the pitch angle scattering of energetic electrons in the magnetosphere. In particular, whistler-mode chorus waves play a crucial role in the pitch angle scattering of electrons. The lower-band chorus causes precipitation of electrons whose energy is greater than several keV [Miyoshi et al., 2015]. The energy of precipitating electrons causing PsA may be estimated from ground-based optical observations. Ono [1993] observed the emission intensities of PsAs at wavelengths of 427.8 and 844.6 nm using a photometer in Antarctica, and estimated the energy of precipitating electrons by combining the ratio of the emission intensities at the two wavelengths and the model calculation. However, Ono [1993] conducted observations using the instrument with a narrow field-of-view, and the energy estimation using all-sky imagers has not yet been performed. In Tromsoe, Norway, several highly-sensitive EMCCD cameras have been operated, which have simultaneously observed all-sky images of the emission intensity at the two wavelengths (427.8 and 844.6 nm) with a sampling frequency of 10 Hz. In this study, we investigate the spatio-temporal variations of precipitating electron energy using these EMCCD camera data. We estimated the precipitating electron energy of PsA by comparing the emission intensity ratio of the two emission lines using the all-sky image and the emission intensity calculation results obtained by the GLobal airglOW (GLOW) model [Solomon, 2017]. We have also developed a code coupling simulation using both the test particle simulation GEMSIS-RBW that calculates wave-particle interactions and the GLOW model, and we compared the ratios at different wavelength between the model and the observations. The analysis showed that the spatial distribution of precipitating electron energies are not uniform, and a few keV differences are found inside the patch.