skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Field Line Resonances and Cavity Modes at Earth and Jupiter
Ultra-Low-Frequency (ULF) waves provide a means for the rapid propagation of energy and field-aligned current in planetary magnetospheres. At Earth, the ULF frequency range is usually defined as including waves with periods of 0.2–600 s; however, at Jupiter these waves can extend to periods of tens of minutes. In both magnetospheres, shear mode Alfvén waves can form field line resonances that exist between the ionospheres, with periods of a few minutes at Earth and a few tens of minutes at Jupiter. A major distinction between these two magnetospheres is in the density distribution. Earth has a dense ionosphere full of heavy ions, an extended, cold plasmasphere and a relatively low-density plasma sheet. In contrast, at Jupiter, the ionosphere is largely hydrogen (both in atomic form and in the H 3 + molecular ion), there is no appreciable plasmasphere and the plasma disk is dense and populated with heavy ions (largely sulfur and oxygen) originating at the moon Io and to some extent from other moons. As at Earth, the sharp Alfvén speed gradient above the ionosphere forms an ionospheric Alfvén resonator at Jupiter with periods of seconds. Furthermore, the high-latitude lobes at Jupiter have very low density and a resonant structure can be formed by waves bouncing between the ionosphere and the dense plasma disk. This structure leads to periods of tens of seconds. Finally, the dense Io plasma torus and plasma sheet provide conditions for compressional cavity modes to form in this region. Thus, the structure of the field line resonance modes is quite different at the two planets. Implications of these resonances on auroral particle acceleration will be discussed.  more » « less
Award ID(s):
1840970
PAR ID:
10427352
Author(s) / Creator(s):
Date Published:
Journal Name:
Frontiers in Astronomy and Space Sciences
Volume:
9
ISSN:
2296-987X
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; (, Geophysical Research Letters)
    Abstract The arrival of the Juno satellite at Jupiter has led to an increased interest in the dynamics of the Jovian magnetosphere. Jupiter's auroral emissions often exhibit quasiperiodic oscillations with periods of tens of minutes. Magnetic observations indicate that ultralow‐frequency (ULF) waves with similar periods are often seen in data from Galileo and other satellites traversing the Jovian magnetosphere. Such waves can be associated with field line resonances, which are standing shear Alfvén waves on the field lines. Using model magnetic fields and plasma distributions, the frequencies of field line resonances and their harmonics on field lines connecting to the main auroral oval have been determined. Time domain simulations of Alfvén wave propagation have illustrated the evolution of such resonances. These studies indicate that harmonics of the field line resonances are common in the 10–40 min band. 
    more » « less
  2. ; (, Journal of Geophysical Research: Space Physics)
    Abstract Observations show that magnetic pulsations with frequencies around 1 mHz are frequently detected simultaneously at different latitudes on the ground, in the inner magnetosphere, and in the solar wind. The coupling between oscillations in the dynamic pressure or magnetic field carried by the solar wind and the ultra‐low frequency (ULF) waves detected on the ground at high latitudes has been suggested in several studies. We present results from a numerical study of ultra‐low‐frequency waves detected by the ground magnetometers at middle latitudes during substorm. We investigate the hypothesis that these waves are generated by the ionospheric feedback instability driven by the large‐scale electric field in the ionosphere. This field is associated with the surface waves propagating along the ambient magnetic field on a strong perpendicular gradient in the plasma density occurring in the equatorial magnetosphere. The gradient in the plasma density is associated with the plasmapause. The plasmapause moves to the middle latitude when the plasmasphere erodes during substorm. The energy from the external driver can be coupled to the large‐scale surface Alfvén waves traveling along the field lines into the ionosphere and generating small‐scale intense ULF waves and field‐aligned currents at middle latitudes. The simulations of the two‐fluid magnetohydrodynamics model confirm this scenario, and the numerical results show a good quantitative agreement with the observations. 
    more » « less
  3. ; ; ; ; ; (, Journal of Geophysical Research: Space Physics)
    Abstract The ionospheric Alfvén resonator (IAR) is a structure formed by the rapid decrease in the plasma density above a planetary ionosphere. This results in a corresponding increase in the Alfvén speed that can provide partial reflection of Alfvén waves. At Earth, the IAR on auroral field lines is associated with the broadband acceleration of auroral particles, sometimes termed the Alfvénic aurora. This arises since phase mixing in the IAR reduces the perpendicular wavelength of the Alfvén waves, which enhances the parallel electric field due to electron inertia. This parallel electric field fluctuates at frequencies of 0.1–20.0 Hz, comparable to the electron transit time through the acceleration region, leading to the broadband acceleration. The prevalence of such broadband acceleration at Jupiter suggests that a similar process can occur in the Jovian IAR. A numerical model of Alfvén wave propagation in the Jovian IAR has been developed to investigate these interactions, indicating that the IAR resonant frequencies are in the same range as those at Earth. This model describes the evolution of the electric and magnetic fields in the low‐altitude region close to Jupiter that is sampled during Juno's perijove passes. In particular, the model relates measurement of magnetic fields below the ion cyclotron frequency from the MAG and Waves instruments on Juno and electric fields from Waves to the associated parallel electric fields that can accelerate auroral particles. 
    more » « less
  4. ; ; ; ; ; (, Journal of Geophysical Research: Space Physics)
    Abstract Current sheets are quasi‐1D layers of strong current density, which play a crucial role in storing magnetic field energy and subsequently releasing it through charged particle acceleration and plasma heating. They are observed in planetary magnetospheres and solar wind flows, where they are also known as solar wind discontinuities. Despite significant variations in plasma parameters across different magnetospheres and the solar wind, current sheet configurations can remain fundamentally similar. In this study, we analyze current sheets observed in various regions, including the near‐Earth (within 30 Earth radii) and distant (50–200 Earth radii) magnetotail, Earth's dayside and nightside magnetosheath, the near‐Earth solar wind, and Martian and Jovian magnetotails. We examine three key plasma parameters: the plasma beta (ratio of plasma to magnetic pressure), the Alfvénic Mach number (ratio of plasma bulk flow speed to Alfvén speed in the current sheet reference frame), and the ion to electron temperature ratio. Additionally, we investigate the kinetic, thermal, and magnetic field energy densities. Our cross‐system analysis demonstrates that the same current sheet configuration can exist across a very wide parametric space spanning multiple orders of magnitude. We also highlight the distinct plasma environments of the Martian and Jovian magnetotails, characterized by large populations of heavy ions, emphasizing their significance in comparative magnetospheric studies. 
    more » « less
  5. ; ; ; ; ; ; (, AIP Publishing)
    We present applications of the full-wave solver, Petra-M code for Earth magnetospheric plasma wave physics by leveraging the current effort of the radio frequency wave project. Because the Petra-M code uses the modular finite element method (MFEM) library, the boundary shapes, plasma density profiles, and realistic planetary magnetic fields can be easily adapted. In order to incorporate realistic Earth’s magnetic field into the Petra-M, we utilize the self-consistent magnetospheric flux models for compressed and stretched magnetic fields and realistic magnetospheric magnetic field geometries extracted from global MHD simulations. Using Petra-M code, we then examine ultra-low frequency (ULF) wave propagations in various magnetic field shapes. For example, left-handed polarized electromagnetic ion cyclotron waves in Earth’s dipole and compressed magnetic field are examined to consider waves in the inner and dayside outer magnetospheres, respectively. Mode-converted Alfvén wave propagation is also demonstrated in the compressed (dayside), stretched(nightside), and realistically stretched magnetic field (magnetotail). Therefore, the Petra-M code successfully demonstrates magnetospheric plasma wave propagation despite the spatial scale differences between the fusion devices (~m) and Earth’s magnetosphere (103 − 104km). 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email