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

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(1 S) 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 (N 2 + first negative band) and 557.7 nm oxygen emissions, we derived the distribution of the lifetime of O(1 S). 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(1 S) 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.

Periodicities and Colors of Pulsating Auroras: DSLR Camera Observations From the International Space Station

“…Kawamura et al. (2020) measured a lifetime of oxygen atoms that produce the 557.7‐nm emission by a photometer at Tromsø, Norway. They calculated an altitude of PsAs by using the measured lifetime.…”

“…Another possible cause is the difference in latitude. Hosokawa and Ogawa (2015) and Kawamura et al (2020), who suggested the increase in the energy of PsA electrons, performed their observations in Tromsø, Norway (MLAT: 66.  7 E…”

“…They found no overall MLT dependence in the flux, but they also noted a slight increase in the flux after 6.5 MLT at higher energy band (  E 30 keV) at the same time. Kawamura et al (2020) measured a lifetime of oxygen atoms that produce the 557.7-nm emission by a photometer at Tromsø, Norway. They calculated an altitude of PsAs by using the measured lifetime.…”

An Automated Auroral Detection System Using Deep Learning: Real-time Operation in Tromsø, Norway

“…Since 2011, Nikon digital cameras (D5000, D5100 and D7200) have been capturing all-sky images almost every night from September to March with a temporal resolution of less than one minute at Ramfjordmoen Research Station in Tromsø, Norway (69.6 • N, 19.2 • E); the station is operated by the UiT -the Arctic University of Norway. These images were not originally planned to be used for a statistical analysis of the auroras, as they were obtained to evaluate weather conditions during the acquisition of atmospheric temperature/wind observations using a sodium LIDAR [37][38][39][40] and multi-wavelength observations of auroras using a photometer [41][42][43] . The digital cameras used were D5000 during 2010-2014, D5100 during 2015, and D7200 during 2016-2021.…”

OI 630.0‐nm and N2 1PG Emissions in Pulsating Aurora Events Observed by an Optical Spectrograph at Tromsø, Norway

“…There might be the quenching effect on OI 557.7 nm, which could make its emission lifetime shorter (cf. Brekke & Henriksen, 1972; Kawamura et al, 2020; Scourfield et al, 1971). However, their results indicate that the time delay can survive in the case of 557.7 nm.…”