Abstract
Using a ground-based five-wavelength photometer, which has been operative in Tromsø, Norway since February 2017, we have statistically analyzed the lifetime of O(1S) to reveal the emission altitude of pulsating aurora (PsA). For the statistics, we have extracted intervals of PsA using an EMCCD all-sky imager on 37 nights during 3 months from January to March, 2018. By performing a cross-correlation analysis between the time-series of 427.8 nm (N2+ first negative band) and 557.7 nm oxygen emissions, we derived the distribution of the lifetime of O(1S). The mean of the lifetime is 0.67 s and the mode is around 0.7 s. We estimated the emission altitude of PsA using the lifetime of O(1S) and then carried out a case study, in which we compared the temporal variations of the emission altitude with the peak height of E region ionization obtained from the simultaneous observation of the EISCAT UHF radar. We confirmed an overall agreement between the two parameters, indicating the feasibility of using the current method for estimating the energy of precipitating electrons causing PsA. In addition, we have derived the statistical characteristics of the emission altitude of PsA. The result shows that the emission altitude becomes lower in the morning side than in the midnight sector, which indicates that the energy of PsA electrons is higher in the later MLT sector. Especially, there is a decrease of the emission altitude at around 06 MLT. However, the model calculation infers that the energy of cyclotron resonance between magnetospheric electrons and whistler-mode chorus waves does not change so much depending on MLT. This implies that the observed change of the emission altitude cannot be explained only by the MLT dependence of resonance energy.
Highlights
Pulsating aurora (PsA) is a category of diffuse aurora, which is characterized by luminosity blinking with a periodicity ranging from a few to a few tens of seconds (Yamamoto 1988)
Hosokawa and Ogawa (2015) investigated the variation of ionospheric electron density profile during PsA using the European Incoherent SCATter (EISCAT) radars and indicated that the energy of PsA electrons tends to be higher in the morning side
In this study, we estimated the emission altitude of PsA using the lifetime of O(1S) derived from the five-wavelength photometer in Tromsø, Norway
Summary
Pulsating aurora (PsA) is a category of diffuse aurora, which is characterized by luminosity blinking with a periodicity ranging from a few to a few tens of seconds (Yamamoto 1988). Such a quasi-periodic luminosity variation is called the main pulsation [(Hosokawa et al 2015) and reference therein]. PsAs are generally observed in the morning side during the recovery phase of auroral substorms (Kvifte and Pettersen 1969). It has been reported that there is a one-to-one correspondence between the amplitude variation of chorus waves and the luminosity modulation of PsA (Nishimura et al 2010, 2011). 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
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