Ripples going against the flow: How energy propagation determines the global structure of surface waves
Friday
Abstract details
id
Space weather and plasma processes: From the Sun to the Earth
Date Submitted
2021-04-30 11:13:00
Martin
Archer
Imperial College London
Contributed
Ripples going against the flow: How energy propagation determines the global structure of surface waves
M. Archer (Imperial College London), M. Hartinger (Space Science Institute), F. Plaschke (Austrian Academy of Sciences), D. Southwood (Imperial College London), Lutz Rastaetter (NASA Goddard Space Flight Center)
Throughout the heliosphere many different plasma regions with sharp discontinuities at their interfaces are present. The dynamics of these boundaries, surface waves, are one of the main mechanisms of filtering, accumulating, and guiding the energy and momentum of the turbulent disturbances omnipresent in space plasmas throughout their respective systems. Earth’s magnetopause provides an opportunity to study surface waves using in situ (rather than remote) observations. These surface waves typically propagate towards the magnetospheric tail due to their excitation by travelling pressure fronts or shear flows in the same direction. Impulsively excited surface eigenmodes, consisting of surface waves reflecting at the northern and southern ionospheres (thus sharing many conceptual similarities to sausage and kink modes in the solar corona), may prove an exception to this paradigm. Through multispacecraft observations, global MHD simulations, and analytic MHD theory we show that, following impulsive excitation, azimuthally standing magnetopause surface waves result over a wide range of local times across the dayside (9-15h MLT). In this region, surface waves with Poynting vectors directed towards the subsolar point can exactly balance the advective effect of the adjacent magnetosheath flow, leading to no overall energy flow and thus the trapping of surface waves locally. Further downtail, however, the wave’s propagation cannot overcome advection and the usual tailward energy flow occurs, seeding fluctuations that may grow due to the Kelvin-Helmholtz instability and couple to MHD body waves inside the magnetosphere. We therefore explain how the surface eigenmode mechanism originating at the subsolar point can lead to a truly global response of the magnetosphere and how this may also apply at other environments.
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