Browsing by Author "Ma, Xuanye"

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Influence of velocity fluctuations on the Kelvin-Helmholtz instability and its associated mass transport
(2017-09-23) Nykyri, Katariina; Ma, Xuanye; Dimmock, Andrew; Foullon, Claire; Otto, Antonius; Osmane, Adnane
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Kelvin-Helmholtz instability (KHI) and associated magnetic reconnection and diffusion processes provide plasma transport from solar wind into the magnetosphere. The efficiency of this transport depends on the magnetosheath and magnetospheric plasma and field properties at the vicinity of the magnetopause. Our recent statistical study using data from the Time History of Events and Macroscale Interactions during Substorms spacecraft indicates that the amplitude of the magnetosheath velocity fluctuations perpendicular to the magnetopause can be substantial. We have performed a series of local macroscale 2.5-dimensional magnetohydrodynamic simulations of the KHI during strongly northward interplanetary magnetic field and with the initial plasma parameters typical to the dayside magnetopause by perturbing the initial equilibrium with time-dependent perpendicular velocity field fluctuations. The effect of the single-mode and multimode seed spectrums at different frequencies and amplitudes is studied. The plasma transport in Kelvin-Helmholtz vortices is quantified. The results show that when large-amplitude, low-frequency seed velocity fluctuations exist in the magnetosheath, the resulting KH waves grow faster, get larger in size, and can transport more plasma through magnetic boundary, resulting in diffusion coefficient of the order 109 m2/s. The relevance of these findings to the solar wind-magnetosphere coupling is discussed.
On the Dawn-Dusk Asymmetry of the Kelvin-Helmholtz Instability Between 2007 and 2013
(2017) Henry, Zachary; Nykyri, Katariina; Moore, Thomas; Dimmock, Andrew; Ma, Xuanye
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Using data from Time History of Events and Macroscale Interactions during Substorms (THEMIS), a statistical study was performed to determine whether a dawn-dusk asymmetry exists in the occurrence rates of the Kelvin-Helmholtz instability during Parker-Spiral (PS) and Ortho-Parker-Spiral (OPS) orientations of the interplanetary magnetic field (IMF). It is determined from the data that there is a strong preference toward the dawnside during PS orientation, and although a preference to the duskside during OPS is suggested, this requires further study for an unambiguous confirmation. The uncertainty in the OPS result is due to a low number of events, which satisfied our selection criteria. Because IMF is statistically in PS orientation, the Kelvin-Helmholtz instability (KHI) preference for the dawn flank during this orientation may help explain the origin of the plasma sheet asymmetry of cold component ions because it has been shown that KHI can drive kinetic-scale wave activity capable of ion heating.