• Title, Summary, Keyword: ULF waves

Search Result 18, Processing Time 0.025 seconds

Magnetopause Waves Controlling the Dynamics of Earth's Magnetosphere

  • Hwang, Kyoung-Joo
    • Journal of Astronomy and Space Sciences
    • /
    • v.32 no.1
    • /
    • pp.1-11
    • /
    • 2015
  • Earth's magnetopause separating the fast and often turbulent magnetosheath and the relatively stagnant magnetosphere provides various forms of free energy that generate low-frequency surface waves. The source mechanism of this energy includes current-driven kinetic physical processes such as magnetic reconnection on the dayside magnetopause and flux transfer events drifting along the magnetopause, and velocity shear-driven (Kelvin-Helmholtz instability) or density/pressure gradient-driven (Rayleigh-Taylor instability) magnetohydro-dynamics (MHD) instabilities. The solar wind external perturbations (impulsive transient pressure pulses or quasi-periodic dynamic pressure variations) act as seed fluctuations for the magnetopause waves and trigger ULF pulsations inside the magnetosphere via global modes or mode conversion at the magnetopause. The magnetopause waves thus play an important role in the solar wind-magnetosphere coupling, which is the key to space weather. This paper presents recent findings regarding the generation of surface waves (e.g., Kelvin-Helmholtz waves) at the Earth's magnetopause and analytic and observational studies accountable for the linking of the magnetopause waves and inner magnetospheric ULF pulsations, and the impacts of magnetopause waves on the dynamics of the magnetopause and on the inner magnetosphere.

Development of Ground-Based Search-Coil Magnetometer for Near-Earth Space Research

  • Shin, Jehyuck;Kim, Khan-Hyuk;Jin, Ho;Kim, Hyomin;Kwon, Jong-Woo;Lee, Seungah;Lee, Jung-Kyu;Lee, Seongwhan;Jee, Geonhwa;Lessard, Marc R.
    • Journal of Magnetics
    • /
    • v.21 no.4
    • /
    • pp.509-515
    • /
    • 2016
  • We report on development of a ground-based bi-axial Search-Coil Magnetometer (SCM) designed to measure time-varying magnetic fields associated with magnetosphere-ionosphere coupling processes. The instrument provides two-axis magnetic field wave vector data in the Ultra Low Frequency or ULF (1 mHz to 5 Hz) range. ULF waves are well known to play an important role in energy transport and loss in geospace. The SCM will primarily be used to observe generation and propagation of the subclass of ULF waves. The analog signals produced by the search-coil magnetic sensors are amplified and filtered over a specified frequency range via electronics. Data acquisition system digitizes data at 10 samples/s rate with 16-bit resolution. Test results show that the resolution of the magnetometer reaches $0.1pT/{\sqrt{Hz}}$ at 1 Hz, and demonstrate its satisfactory performance, detecting geomagnetic pulsations. This instrument is scheduled to be installed at the Korean Antarctic station, Jang Bogo, in the austral summer 2016-2017.

Effects of plasmaspheric density structure on the characteristics of geomagnetic ULF pulsations

  • Choi, Jiwon;Lee, Dong-Hun;Kim, Khan-Hyuk;Lee, Ensang
    • The Bulletin of The Korean Astronomical Society
    • /
    • v.37 no.2
    • /
    • pp.116.2-116.2
    • /
    • 2012
  • The structure of plasmasphere plays an important role in determining properties of geomagnetic ULF pulsations such as Pi 2 pulsations and field line resonances (FLRs) in the Earth's magnetosphere. We have performed a 3-D MHD wave simulation to investigate the generation and propagation of ULF waves in dipole geometry. Various 3-D density structures are assumed, which include a relatively sharp density gradient and gradually less slopes at the plasmapause. The former condition can refer to the plasmasphere from local midnight to dawn, whereas the latter represents the region near noon to dusk where it bulges out. We show how Pi 2 pulsations and FLRs differentially appear at both multi-point satellite locations and ground stations for different local times. Our results suggest that 1) the local radial density structure significantly affects the peak frequencies for Pi 2 oscillations, while the polarization changes remain similar in the radial direction, and 2) the radial location of strong FLRs varies for different density profiles. It is also suggested how multi satellite measurements and ground-based observations can confirm this differential feature in space.

  • PDF