title: Density-transition scale at quasiperpendicular collisionless shocks.
abstract: Measurements of a spacecraft floating potential, on the four Cluster spacecraft, are used as a proxy for electron plasma density to study, for the first time, the macroscopic density transition scale at 98 crossings of the quasiperpendicular terrestrial bow shock. A timing analysis gives shock speeds and normals; the shock speed is used to convert the temporal measurement to a spatial one. A hyperbolic tangent function is fitted to each density transition, which captures the main shock transition, but not overshoot or undershoot nor foot features. We find that, at a low Mach number M, the density transition is consistent with both ion inertial scales c/omega(pi) and convected gyroradii v(sh,n)/Omega(ci,2), while at M>/=4-5 only the convected gyroradius is the preferred scale for the shock density transition and takes the value L approximately 0.4v(sh,n)/Omega(ci,2).
authors.affiliation: Space Sciences Laboratory and Department of Physics, University of California, Berkeley, California 94720, USA. bale@ssl.berkeley.edu
authors.forename: S D
authors.initials: SD
authors.lastname: Bale
authors.forename: F S
authors.initials: FS
authors.lastname: Mozer
authors.forename: T S
authors.initials: TS
authors.lastname: Horbury