Spectral Features of Magnetic Fluctuations at Proton Scales from Fast to Slow Solar Wind
R Bruno ; D Telloni ; - ASI Sponsor
Sep - 2015
DOI: 10.1088/2041-8205/811/2/L17

journal : The Astrophysical Journal Letters

Volume : 811 ; Issue : 2
type: Article Journal

Abstract
This Letter investigates the spectral characteristics of interplanetary magnetic field fluctuations at proton scales during several time intervals chosen along the speed profile of a fast stream. The character of the fluctuations within the first frequency decade, beyond the high-frequency break located between the fluid and kinetic regimes, strongly depends on the type of wind. While the fast wind shows a clear signature of both right-handed and left-handed polarized fluctuations, possibly associated with Kinetic $\mathrm{Alfv}\acute{{\rm{e}}}{\rm{n}}$ Wave (KAW) and ion-cyclotron waves, respectively, the rarefaction region, where the wind speed and the Alfvénicity of low-frequency fluctuations decrease, shows a rapid disappearance of the ion-cyclotron signature followed by a more gradual disappearance of KAWs. Moreover, the power associated with perpendicular and parallel fluctuations also experiences rapid depletion, however, retaining the power anisotropy in favor of the perpendicular spectrum.

keywords : interplanetary medium—magnetic fields—plasmas—solar wind—turbulence—waves

Notes : This research was partially supported by theItalian Space Agency (ASI) under contractsI/013/12/0 and I/022/10/2