期刊
JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS
卷 122, 期 11, 页码 11003-11017出版社
AMER GEOPHYSICAL UNION
DOI: 10.1002/2017JA024538
关键词
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资金
- UK Science and Technology Facilities Council (STFC) [ST/N000692/1, ST/P000622/1]
- STFC [ST/N000692/1, ST/P000622/1, ST/M001202/1, ST/M006948/1] Funding Source: UKRI
- Science and Technology Facilities Council [ST/P000622/1, ST/M001202/1, ST/M006948/1, ST/N000692/1] Funding Source: researchfish
Simulations and observations of collisionless shocks have shown that deviations of the nominal local shock normal orientation, that is, surface waves or ripples, are expected to propagate in the ramp and overshoot of quasi-perpendicular shocks. Here we identify signatures of a surface ripple propagating during a crossing of Earth's marginally quasi-parallel (theta(Bn) similar to 45 degrees) or quasi-parallel bow shock on 27 November 2015 06: 01: 44 UTC by the Magnetospheric Multiscale (MMS) mission and determine the ripple's properties using multispacecraft methods. Using two-dimensional hybrid simulations, we confirm that surface ripples are a feature of marginally quasi-parallel and quasi-parallel shocks under the observed solar wind conditions. In addition, since these marginally quasi-parallel and quasi-parallel shocks are expected to undergo a cyclic reformation of the shock front, we discuss the impact of multiple sources of nonstationarity on shock structure. Importantly, ripples are shown to be transient phenomena, developing faster than an ion gyroperiod and only during the period of the reformation cycle when a newly developed shock ramp is unaffected by turbulence in the foot. We conclude that the change in properties of the ripple observed by MMS is consistent with the reformation of the shock front over a time scale of an ion gyroperiod.
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