Negative Potential Solitary Structures in the Magnetosheath With Large Parallel Width

Abstract

AbstractWe report multispacecraft observations by the Magnetospheric MultiScale (MMS) mission of large (80–155 λDe parallel to B) electrostatic solitary waves (ESWs). Observations of the same ESWs at different positions and times enable unprecedented accuracy in determining the size, velocity, and evolution of these nonlinear structures. This particular event is a short series of negative potential solitary waves in the magnetosheath. The observed structures differ in amplitude and speed, merging or colliding with one another. A Vlasov simulation supports initial wave growth by a cold feature in the electron distribution function. Such cold electrons are likely the result of mixing between the cold magnetospheric and warm magnetosheath plasma along a reconnection separatrix. ESW speed and perpendicular size are inconsistent with ion phase space holes. Solving Poisson's equation for the measured potential, we find a reduction in electron density rather than an enhancement expected from an electron soliton. These ESWs have an unusual combination of properties on both ion and electron scales, likely supported by a complex electron distribution in the nonlinear state.