Spatio-temporal characteristics of the precipitating electron energy of pulsating aurora derived from multi-wavelength optical measurements

Abstract:

Pulsating aurora (PsA) is characterized by quasi-periodic intensity modulations with a period of 2-20 s 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, and PsA is considered to be generated by the precipitating electrons with energies of several to 100 keV. In particular, whistler-mode chorus waves play a crucial role in the pitch angle scattering of the electrons. The lower-band chorus causes precipitation of electrons more than several keV, and the upper-band chorus causes steady precipitation of less than 1 keV [Miyoshi et al., 2015]. The precipitating electron energy of pulsating aurora may be estimated from the ground-based optical observations. Ono et al. [1993] observed the emission intensities of pulsating auroras at wavelengths of 427.8 and 844.6 nm using photometers, and estimated the energy of the precipitating electrons by combining the ratio of the two emission intensities and the model calculation. However, Ono et al. [1993] conducted observations using the instrument with a narrow field-of-view, and the energy estimation using all-sky imagers has not been performed. In Tromsoe, Norway, several highly-sensitive EMCCD cameras have been operated, which have simultaneously observed the 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 addition, a five-wavelength photometer has also been operative in Tromsoe. In this study, we investigate the spatio-temporal variations of precipitating electron energy using these EMCCD cameras. The optical data taken from EMCCD cameras have been calibrated by simultaneous measurements with the collocated photometer fixed to look along the magnetic field line. We estimated the precipitating electron energy of the pulsating aurora 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 GLOW model [Solomon, 2017]. In the presentation, we show the spatio-temporal characteristics of the precipitating electron energy of the pulsating aurora and discuss how the wave-particle interaction process characterizes the properties of pulsating aurora.