第3回極域科学シンポジウム/第36回極域宙空圏シンポジウム 11月27日（火） 国立極地研究所 2階大会議

Kitamura Kentarou

Kodokura Akira

Saita Satoko

Tanaka Yoshimasa

Yamagishi Hisao

National Institute of Polar Research Repository

   Characteristics of Pc5 pulsations deduced from antarctic geomagnetic observations during the Relativistic Electron Enhancement (REE) events at the Outer Radiation Belt  Kentarou Kitamura1, Satoko Saita2, Yoshimasa Tanaka3, Akira Kadokura3, and Hisao Yamagishi3 1Tokuyama College of technology 2Research Organization of Information and System, The institute of statistical mathmatics 3National Institute of Polar Research   In order to understand how ULF pulsations accelerate relativistic (MeV) electrons in the outer radiation belt, magnetic variation data observed at Antarctic stations are analyzed. In the present study, the magnetic data observed at H057 and Skallen (the location of the stations are shown in Table1) in Antarctica are used to analysze the characteristics of the Pc5 pulsations during the stormtime Relativistic Electron Enhancement (REE) events. These two stations are located at the same latitude and spread in longitudes of 1.7 degrees. In general, the estimation of the azimuthal wave number of the PC5 pulsations is difficult due to a strong latitudinal dependence of the field line resonance. The pair of the stations used in this analysis is quite suitable to estimate the azimuthal wave number. We selected 24 CIR (Corotating Interaction Region) events with the condition that the relativistic electron flux observed by GOES satellites exceed 103. For these 24 events, the superposed epoch analysis is conducted for the horizontal component of the magnetic field data. As shown in Figure1, several important features are cleared in the relationships between the PC5 observed on the ground and relativistic electron flux variations at geosynchronous orbit. First, although the power spectrum density (PSD) of the Pc5 pulsations increases corresponding to the increase of the solarwind velocity, the H/D ratio of the PC5 power shows obvious change after 0.5 days from enhancement of the PSD, which corresponds to the apparent start time of relativistic electron flux enhancement (REE). This indicates that the toroidal oscillation of PC5 becomes predominant in the inner magnetosphere at the start time of the REE. Second, although the phase difference between two stations largely fluctuates before the start of REE, it shows certain values with small variances during the REE events. The estimated azimuthal wave numbers (m) of the H and D components are 1.62 ± 0.99 and -2.25 ± 2.86, respectively. The eastward propagation of the toroidal Pc5 with the low m number of 1.62 suggests that the relativistic electrons at the inner magnetosphere are accelerated by the drift resonance with the toroidal Pc5 pulsations (Elikington et al, 2003).              Table 1.  Location of the stations.  Gra. Lat. Gra.Lon. Mag.Lat Mag.Lon L H057 -69.16 40.98 -66.42 72.29 6.2 Skallen -69.67 39.40 -66.42 70.53 6.2   References Elkington, S. R., M. K. Hudson, and A. A. Chan, Acceleration of relativistic electrons via drift‐resonant interaction with toroidal‐mode Pc‐5 ULF oscillations, Geophys. Res. Lett., 26(21), 3273–3276, doi:10.1029/1999GL003659, 2003.   [nT2/Hz] [degrees] [nT2/Hz] [06-15MLT] Figure1. Superposed epoch analysis for 24 Pc5 events. 

Characteristics of Pc5 pulsations deduced from antarctic geomagnetic observations during the Relativistic Electron Enhancement (REE) events at the Outer Radiation Belt

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Characteristics of Pc5 pulsations deduced from antarctic geomagnetic observations during the Relativistic Electron Enhancement (REE) events at the Outer Radiation Belt

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