Skip to main content
eScholarship
Open Access Publications from the University of California

Scholarly Works (3 results)

  • Thesis
  • Peer Reviewed
UCLA Electronic Theses and Dissertations (2012)

Ultra Low Frequency (ULF) waves are an important mechanism for energy transfer in the Earth's magnetosphere, interacting with a variety of different plasma populations and other plasma wave modes. The solar wind is an important energy source for ULF waves, and there are many pathways through which solar wind energy can drive wave activity. In this thesis, two case studies and two statistical studies are presented to demonstrate the manner in which energy is transferred from the solar wind to magnetospheric ULF waves. These studies demonstrate the viability of both the field line resonance paradigm and global fast (cavity/waveguide) modes as pathways for energy transfer from the solar wind to various sinks of wave energy in the magnetosphere. They also show that the plasmasphere plays an important role in suppressing electromagnetic energy transfer via ULF waves from the solar wind to the inner magnetosphere in the Pc5 frequency band.

The first case study demonstrates the conversion from isotropic to perpendicular energy flux at the field line resonance (FLR) location, providing further validation for the FLR paradigm. The second case study demonstrates that solar wind dynamic pressure fluctuations with a broadband frequency spectrum provide energy to drive a monochromatic global (cavity/waveguide) mode, which in turn provides energy to drive shear Alfv en waves through FLR; this is the first direct observation of energy transfer via a global mode in the Pc5 (2-7 mHz) frequency band outside of the plasmasphere. The first statistical study demonstrates that Pc5 electric and magnetic field perturbations have significantly lower amplitude in the plasmasphere compared to the low density region outside the plasmasphere; this suggests that ULF wave electromagnetic energy incident from the outer magnetosphere is not easily transferred across the plasmapause boundary in the Pc5 frequency range. The second statistical study characterizes global mode waves and provides a lower bound for the occurrence rate, or total time that global modes are observed divided by total observation time, of 1.0%.

    Cover page: Energy Transfer via Solar Wind Driven Ultra Low Frequency Waves in the Earth's Magnetosphere
    • Article
    • Peer Reviewed
    UC Berkeley Previously Published Works (2024)
    The weakly ionized plasma in the Earths ionosphere is controlled by a complex interplay between solar and magnetospheric inputs from above, atmospheric processes from below, and plasma electrodynamics from within. This interaction results in ionosphere structuring and variability that pose major challenges for accurate ionosphere prediction for global navigation satellite system (GNSS) related applications and space weather research. The ionospheric structuring and variability are often probed using the total electron content (TEC) and its relative perturbations (dTEC). Among dTEC variations observed at high latitudes, a unique modulation pattern has been linked to magnetospheric ultra-low-frequency (ULF) waves, yet its underlying mechanisms remain unclear. Here using magnetically conjugate observations from the THEMIS spacecraft and a ground-based GPS receiver at Fairbanks, Alaska, we provide direct evidence that these dTEC modulations are driven by magnetospheric electron precipitation induced by ULF-modulated whistler-mode waves. We observed peak-to-peak dTEC amplitudes reaching ∼ 0.5 TECU (1 TECU is equal to 10 6 electrons/ m 2 ) with modulations spanning scales of ∼ 5-100 km. The cross-correlation between our modeled and observed dTEC reached ∼ 0.8 during the conjugacy period but decreased outside of it. The spectra of whistler-mode waves and dTEC also matched closely at ULF frequencies during the conjugacy period but diverged outside of it. Our findings elucidate the high-latitude dTEC generation from magnetospheric wave-induced precipitation, addressing a significant gap in current physics-based dTEC modeling. Theses results thus improve ionospheric dTEC prediction and enhance our understanding of magnetosphere-ionosphere coupling via ULF waves.
      Cover page: Magnetospheric Control of Ionospheric TEC Perturbations via Whistler-Mode and ULF Waves.
      • Article
      • Peer Reviewed
      UC Berkeley Previously Published Works (2022)
      An interplanetary shock can abruptly compress the magnetosphere, excite magnetospheric waves and field-aligned currents, and cause a ground magnetic response known as a sudden commencement (SC). However, the transient (<∼1 min) response of the ionosphere-thermosphere system during an SC has been little studied due to limited temporal resolution in previous investigations. Here, we report observations of a global reversal of ionospheric vertical plasma motion during an SC on 24 October 2011 using ∼6 s resolution Super Dual Auroral Radar Network ground scatter data. The dayside ionosphere suddenly moved downward during the magnetospheric compression due to the SC, lasting for only ∼1 min before moving upward. By contrast, the post-midnight ionosphere briefly moved upward then moved downward during the SC. Simulations with a coupled geospace model suggest that the reversed E⃗×B⃗ vertical drift is caused by a global reversal of ionospheric zonal electric field induced by magnetospheric compression during the SC.
        Cover page: Geospace Concussion: Global Reversal of Ionospheric Vertical Plasma Drift in Response to a Sudden Commencement
        Top