High Frequency Analyzer (HFA) of Plasma Wave Experiment (PWE) onboard the Arase spacecraft

Abstract

The High Frequency Analyzer (HFA) is a subsystem of the Plasma Wave Experiment onboard the Arase (ERG) spacecraft. The main purposes of the HFA include (1) determining the electron number density around the spacecraft from observations of upper hybrid resonance (UHR) waves, (2) measuring the electromagnetic field component of whistler-mode chorus in a frequency range above 20 kHz, and (3) observing radio and plasma waves excited in the storm-time magnetosphere. Two components of AC electric fields detected by Wire Probe Antenna and one component of AC magnetic fields detected by Magnetic Search Coils are fed to the HFA. By applying analog and digital signal processing in the HFA, the spectrograms of two electric fields (EE mode) or one electric field and one magnetic field (EB mode) in a frequency range from 10 kHz to 10 MHz are obtained at an interval of 8 s. For the observation of plasmapause, the HFA can also be operated in PP (plasmapause) mode, in which spectrograms of one electric field component below 1 MHz are obtained at an interval of 1 s. In the initial HFA operations from January to July, 2017, the following results are obtained: (1) UHR waves, auroral kilometric radiation (AKR), whistler-mode chorus, electrostatic electron cyclotron harmonic waves, and nonthermal terrestrial continuum radiation were observed by the HFA in geomagnetically quiet and disturbed conditions. (2) In the test operations of the polarization observations on June 10, 2017, the fundamental R-X and L-O mode AKR and the second-harmonic R-X mode AKR from different sources in the northern polar region were observed. (3) The semiautomatic UHR frequency identification by the computer and a human operator was applied to the HFA spectrograms. In the identification by the computer, we used an algorithm for narrowing down the candidates of UHR frequency by checking intensity and bandwidth. Then, the identified UHR frequency by the computer was checked and corrected if needed by the human operator. Electron number density derived from the determined UHR frequency will be useful for the investigation of the storm-time evolution of the plasmasphere and topside ionosphere.

A Systematic Study in Characteristics of Lower Band Rising‐Tone Chorus Elements

“…The relationships suggested in the present study should be examined by comparing with other in situ observations, such as those from the Arase satellite in the Exploration of energization and Radiation in Geospace (ERG) project (Miyoshi et al, ), which has orbits in a relatively inner portion of the magnetosphere than the THEMIS probes. The Arase satellite is capable to observe chorus elements (Kasaba et al, ; Kasahara et al, ; Matsuda et al, ), the number density of cold plasma derived from both the upper hybrid resonance frequency (Kumamoto et al, ) and the local magnetic field intensity (Matsuoka et al, ), energetic electrons that provide free energy to chorus generating (Kasahara et al, ; Kazama et al, ), and energy exchanges between waves and particles (Hikishima et al, ; Katoh et al, ). A comprehensive study in Arase's data in the future will help us find important clues in understanding the characteristics of chorus elements revealed by the present study.…”

Coincident Observations by the Kharkiv IS Radar and Ionosonde, DMSP and Arase (ERG) Satellites, and FLIP Model Simulations: Implications for the NRLMSISE‐00 Hydrogen Density, Plasmasphere, and Ionosphere

“…The Arase satellite was launched in December 2016 and started regular observations in its full operation mode in March 2017 (Miyoshi et al, ). The Plasma Wave Experiment (PWE)/Onboard Frequency Analyzer (OFA) and High Frequency Analyzer (HFA) instruments onboard the Arase satellite routinely measure the frequency spectrum below 20 kHz and that from 10 kHz to 10 MHz, respectively (Kasahara et al, ; Kumamoto et al, ). The ambient plasma density can be derived along the satellite orbit from the frequency of the upper hybrid resonance emissions observed by OFA and HFA and the local cyclotron frequency measured by the magnetometer (Matsuoka et al, ).…”

The ERG Science Center

“…A typical example is pitch angle distributions of particle fluxes, which merges particle flux data from a particle instrument and magnetic field data from the magnetic field experiment (MGF) ). Another example is electron density data that are deduced using frequency traces of upper hybrid resonance observed by the PWE instrument (Kasahara et al 2018b;Kumamoto et al 2018) and MGF data. Level-3 particle data also go through inter-instrument calibrations to produce particle flux and phase space density data of electrons over a combined energy range of ~ 20 eV to more than 10 MeV.…”