Multiple time-scale beats in aurora: precise orchestration via magnetospheric chorus waves

Abstract

the brightness of aurorae in earth's polar region often beats with periods ranging from sub-second to a few tens of a second. past observations showed that the beat of the aurora is composed of a superposition of two independent periodicities that co-exist hierarchically. However, the origin of such multiple time-scale beats in aurora remains poorly understood due to a lack of measurements with sufficiently high temporal resolution. By coordinating experiments using ultrafast auroral imagers deployed in the Arctic with the newly-launched magnetospheric satellite Arase, we succeeded in identifying an excellent agreement between the beats in aurorae and intensity modulations of natural electromagnetic waves in space called "chorus". In particular, sub-second scintillations of aurorae are precisely controlled by fine-scale chirping rhythms in chorus. The observation of this striking correlation demonstrates that resonant interaction between energetic electrons and chorus waves in magnetospheres orchestrates the complex behavior of aurora on earth and other magnetized planets.

Over‐Darkening of Pulsating Aurora

“…This comparison again demonstrates an exact one‐to‐one correspondence between these two periodic phenomena, which has already been reported by Hosokawa, Miyoshi, et al. (2020).…”

“…Later, Hosokawa, Miyoshi, et al. (2020) employed the wave data from Arase to show the complete one‐to‐one correspondence between the temporal variations of PsA and LBC. In particular, they identified two sets of good correspondence: (1) Between the main pulsation and chorus bursts, and (2) between the internal modulation and chorus elements, as predicted by Miyoshi, Saito, et al.…”

First Direct Observations of Propagation of Discrete Chorus Elements From the Equatorial Source to Higher Latitudes, Using the Van Allen Probes and Arase Satellites

“…These waves can be both a source and a loss mechanism for radiation belt particles (Horne & Thorne, 1998; Meredith et al, 2003; Miyoshi et al, 2003; Reeves et al, 2013; Thorne et al, 2013; Turner et al, 2012). They are also believed to be responsible for diffuse and pulsating aurora (Agapitov et al, 2018; Hosokawa et al, 2020; Kasahara, Miyoshi, et al, 2018; Miyoshi, Saito, et al, 2015; Nishimura et al, 2010; Ozaki et al, 2019; Thorne et al, 2010), and possibly for plasmaspheric hiss as well (Bortnik et al, 2008, 2009; Meredith et al, 2013; Santolik et al, 2006), although there are alternative theories (e.g., Falkowski et al, 2017). Additional studies and current open research questions related to chorus waves can be found in Ripoll et al (2020) and references therein.…”

Estimation of the emission altitude of pulsating aurora using the five-wavelength photometer

“…These observational results imply that PsA is the two-dimensional projection of the characteristics of chorus waves in the magnetosphere. Although recent literatures, which analyzed the simultaneous groundsatellite observations, have revealed the correspondence between PsA and chorus waves (e.g., Kasahara et al 2018;Hosokawa et al 2020), it is still unclear what factors control these periodic variations.…”