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The Kelvin-Helmholtz instability (KHI) and its effects relating to the transfer of energy and mass from the solar wind into the magnetosphere remain an important focus of magnetospheric physics. One such effect is the generation of Pc4-Pc5 ultra low frequency (ULF) waves (periods of 45–600 s). On July 3, 2007 at ∼ 0500 magnetic local time the Cluster space mission encountered Pc4 frequency Kelvin-Helmholtz waves (KHWs) at the high latitude magnetopause with signatures of persistent vortices. Such signatures included bipolar fluctuations of the magnetic field normal component associated with a total pressure increase and rapid change in density at vortex edges; oscillations of magnetosheath and magnetospheric plasma populations; existence of fast-moving, low-density, mixed plasma; quasi-periodic oscillations of the boundary normal and an anti-phase relation between the normal and parallel components of the boundary velocity. The event occurred during a period of southward polarity of the interplanetary magnetic field according to the OMNI data and THEMIS observations at the subsolar point. Several of the KHI vortices were associated with reconnection indicated by the Walén relation, the presence of deHoffman-Teller frames, field-aligned ion beams observed together with bipolar fluctuations in the normal magnetic field component, and crescent ion distributions. Global magnetohydrodynamic simulation of the event also resulted in KHWs at the magnetopause. The observed KHWs associated with reconnection coincided with recorded ULF waves at the ground whose properties suggest that they were driven by those waves. Such properties were the location of Cluster’s magnetic foot point, the Pc4 frequency, and the solar wind conditions.
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This content will become publicly available on April 1, 2026
Generation of FTE Signatures by the Kelvin–Helmholtz Instability
Abstract Magnetic reconnection and the Kelvin–Helmholtz instability (KHI) are the two fundamental processes in planetary magnetospheres that can lead to plasma, momentum, and energy transport across the magnetospheric boundary. Flux Transfer Events (FTEs), being characterized by the bipolar variation of the magnetic normal component, are often considered to be generated by magnetic reconnection. However, several possible mechanisms can also give rise to FTE‐like features in the boundary layer and potentially mislead observational analysis; the KHI is one such candidate. Using two‐dimensional magnetohydrodynamics (MHD) simulations, we examine and categorize the signatures observed by several virtual satellites as they pass through the Kelvin–Helmholtz waves along different trajectories. We have shown that the bipolar signatures were identified during the satellite's passage across the spine region and the leading/trailing edge of the KH vortex. The duration of bipolar signatures was also shown to vary depending not only on where the satellite trajectory intersects with the vortices, but also on the density asymmetry on both sides of boundary which in turn affects the relative motion between the vortices and satellite. Further, slight adjustments to the projection angle of the magnetic field are also applied in the simulations, as the signatures of the KHI are very sensitive to the in‐plane magnetic field component. These results can be used as diagnostics when analyzing spacecraft data to help distinguish KHI‐created signatures from FTE.
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- Award ID(s):
- 2308853
- PAR ID:
- 10592647
- Publisher / Repository:
- John Wiley & Sons, Inc.
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Space Physics
- Volume:
- 130
- Issue:
- 4
- ISSN:
- 2169-9380
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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