View in EDS

Kelvin–Helmholtz instability at the fast-slow solar wind interface: a parametric study and implications for ENA observations.

Saved in:
Bibliographic Details
Title: Kelvin–Helmholtz instability at the fast-slow solar wind interface: a parametric study and implications for ENA observations.
Authors: Korolkov, Sergey D.1 (AUTHOR) sergey.korolkov@cosmos.ru
Source: Advances in Space Research. Sep2026, Vol. 78 Issue 6, p6644-6662. 19p.
Subjects: Kelvin-Helmholtz instability, Solar wind, Computer simulation, Shear (Mechanics), Plasma stability, Solar cycle, Heliosphere
Abstract: The velocity shear between the fast polar and slow equatorial solar wind streams in the inner heliosheath provides favourable conditions for the development of the Kelvin–Helmholtz instability (KHI), which may produce observable signatures in energetic neutral atom (ENA) fluxes. A parametric numerical study of this instability is presented, using a 2D axisymmetric gas-dynamic model, isolating it from the heliopause KHI. For a sharp velocity discontinuity, the instability is dominated by short-wavelength modes and remains resolution-dependent. In the nonlinear stage, vortices are larger at higher boundary latitudes. The onset of the nonlinear stage shifts closer to the termination shock as the boundary latitude decreases. Introducing a finite-width transition layer of angular width Δ θ regularises the instability, leading to a converged growth rate and a well-defined spatial scale. For Δ θ = 10 ° , a growth rate γ ≈ 0.46 yr−1 is obtained. The growth rate decreases with increasing Δ θ , and the instability is effectively suppressed for Δ θ ⩾ 15 °. Synthetic ENA flux maps show that the KHI produces detectable signatures only for narrow transition layers (Δ θ ≲ 5 °). The observable signal is best characterised by relative flux variations with respect to a KHI-free background, which reach ∼ 20% at low energies (at 0.055 keV) and up to a factor of five at higher energies (at 0.872 keV) for Δ θ = 2 ° , while no significant imprint is present for broader layers. Solar wind variability does not suppress the internal KHI, in contrast to the heliopause case. Instead, periodic forcing with timescales comparable to the intrinsic growth time (∼ 2–3 yr) enhances the instability, consistent with a resonant response. In addition, solar-cycle latitudinal migration of the fast–slow wind boundary acts as a strong time-dependent driver, substantially amplifying the instability and producing large-scale vortical structures (∼ 25–30 AU) in the heliosheath. [ABSTRACT FROM AUTHOR]
Copyright of Advances in Space Research is the property of Pergamon Press - An Imprint of Elsevier Science and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
Database: Engineering Source
Description
Abstract:The velocity shear between the fast polar and slow equatorial solar wind streams in the inner heliosheath provides favourable conditions for the development of the Kelvin–Helmholtz instability (KHI), which may produce observable signatures in energetic neutral atom (ENA) fluxes. A parametric numerical study of this instability is presented, using a 2D axisymmetric gas-dynamic model, isolating it from the heliopause KHI. For a sharp velocity discontinuity, the instability is dominated by short-wavelength modes and remains resolution-dependent. In the nonlinear stage, vortices are larger at higher boundary latitudes. The onset of the nonlinear stage shifts closer to the termination shock as the boundary latitude decreases. Introducing a finite-width transition layer of angular width Δ θ regularises the instability, leading to a converged growth rate and a well-defined spatial scale. For Δ θ = 10 ° , a growth rate γ ≈ 0.46 yr−1 is obtained. The growth rate decreases with increasing Δ θ , and the instability is effectively suppressed for Δ θ ⩾ 15 °. Synthetic ENA flux maps show that the KHI produces detectable signatures only for narrow transition layers (Δ θ ≲ 5 °). The observable signal is best characterised by relative flux variations with respect to a KHI-free background, which reach ∼ 20% at low energies (at 0.055 keV) and up to a factor of five at higher energies (at 0.872 keV) for Δ θ = 2 ° , while no significant imprint is present for broader layers. Solar wind variability does not suppress the internal KHI, in contrast to the heliopause case. Instead, periodic forcing with timescales comparable to the intrinsic growth time (∼ 2–3 yr) enhances the instability, consistent with a resonant response. In addition, solar-cycle latitudinal migration of the fast–slow wind boundary acts as a strong time-dependent driver, substantially amplifying the instability and producing large-scale vortical structures (∼ 25–30 AU) in the heliosheath. [ABSTRACT FROM AUTHOR]
ISSN:02731177
DOI:10.1016/j.asr.2026.07.039