Estimation of the emission altitude of pulsating aurora using the five-wavelength photometer
Estimation of the emission altitude of pulsating aurora using the five-wavelength photometer
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DOI：
10.1186/s40623-020-01229-8
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发表时间：
2020-07-10
影响因子：
3
通讯作者：
Fujii, Ryoichi
中科院分区：
文献类型：
--
作者：
Kawamura, Yuki;Hosokawa, Keisuke;Fujii, Ryoichi
利用自2017年2月起在挪威TromsO运行的地面五波长光度计，统计分析了O（S-1）的寿命，揭示了脉动极光（PsA）的发射高度。为了统计，我们利用EMCCD全天成像仪提取了2018年1 - 3月3个月的37个夜晚的PsA间隔。通过对427.8 nm （N-2（+）第一负波段）和557.7 nm氧发射的时间序列进行互相关分析，得出了O（S-1）的寿命分布。寿命的平均值为0.67 s，模态约为0.7 s。我们利用O（S-1）的寿命估算了PsA的发射高度，并进行了实例研究，将发射高度的时间变化与EISCAT超高频雷达同步观测得到的E区电离峰高度进行了比较。我们证实了这两个参数之间的总体一致，表明使用当前方法估计引起PsA的沉淀电子能量的可行性。此外，我们还导出了PsA的发射高度的统计特征。结果表明：清晨扇区的发射高度比午夜扇区的发射高度要低，说明后期扇区的PsA电子能量较高；特别是在06 MLT附近，发射高度有所下降。然而，模型计算推断，磁层电子与哨子模合唱波之间的回旋共振能量随MLT的变化不大。这意味着观测到的发射高度的变化不能仅仅用共振能量的MLT依赖性来解释。
Using a ground-based five-wavelength photometer, which has been operative in TromsO, Norway since February 2017, we have statistically analyzed the lifetime of O(S-1) 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(S-1). 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(S-1) 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.