Dg. Sibeck et al., A survey of MHD waves in the magnetosheath: International Solar TerrestialProgram observations, J GEO R-S P, 105(A1), 2000, pp. 129-137
We present case and statistical studies of magnetohydrodynamic (MHD) fluctu
ations observed by the Wind and Geotail spacecraft in the Earth's dawn and
dusk magnetosheath. A case study with simultaneous IMP 8 interplanetary mag
netic field observations confirms theoretical predictions that most of the
fluctuations originate in the solar wind rather than at the magnetopause an
d that the fluctuations can be almost absent from the outer magnetosheath.
A second case study indicates that northward plasma velocity perturbations
observed in the prenoon magnetosheath correspond to southward velocity pert
urbations in the postnoon magnetosheath, implying that the MHD perturbation
s apply a torque to the magnetosphere. A statistical survey reveals that th
e fluctuations almost invariably propagate antisunward in the magnetosheath
, independent of their propagation direction relative to the interplanetary
magnetic field.