Low-frequency magnetic field fluctuations in comet P/Halley's magnetosheath - Giotto observations

Abstract

The interaction region between comets and the solar wind is characterized by large amplitude, low frequency magnetic field fluctuations, both within the upstream region as well as in the magnetosheath. Magnetosheath observations of the magnetic field experiment onboard Giotto indicate values of δB/B ≅ O(1). Power spectral peaks appear at frequencies of ≅10 mHz with the spectrum exhibiting a power law dependence with an exponent of the order 2. Radial variation of the fluctuation level does not clearly increase with decreasing distance from the cometary nucleus as observed by the magnetometer onboard Vega-1 and as expected from quasilinear theory. The entrance into the cometary bow shock is furthermore characterized by an order of magnitude increase of the fluctuation level, both of the in- and outbound pass of Giotto.