January 20, 2012, 12:00 pm - 1:00 pm

Director's Seminar, featuring Heliophyscs EPO

George Khazanov (NASA/GSFC), Consequences of the Ion Cyclotron Instability in the Inner Magnetospheric Plasma

Abstract: The inner magnetospheric plasma is a very unique composition of different plasma particles and waves. Among these plasma particles and waves are Ring Current (RC) particles and Electromagnetic Ion Cyclotron (EMIC) waves. The RC is the source of free energy for the EMIC wave excitation provided by a temperature anisotropy of RC ions, which develops naturally during inward convection from the plasmasheet. The cold plasmasphere, which is under the strong influence of the magnetospheric electric field, strongly mediates the RC-EMIC waves-coupling process, and ultimately becomes part of the particle and energy interplay, generated by the ion cyclotron instability of the inner magnetosphere. On the other hand, there is a strong influence of the RC on the inner magnetospheric electric and magnetic field configurations and these configurations, in turn, are important to RC dynamics. Therefore, one of the biggest needs for inner magnetospheric plasma physics research is the continued progression toward a coupled, interconnected system, with the inclusion of nonlinear feedback mechanisms between the plasma populations, the electric and magnetic fields, and plasma waves.

Adolfo F.-Vinas (NASA/GSFC), The Kinetic Physics of the Solar Wind Electron Strahl

Abstract: The solar wind strahl is a field-aligned beam of non-thermal electrons that generally lies in the range of 0.05-1 kev. It has been suggested that the solar wind electron halo forms as a consequence of pitch-angle scattering the strahl. On frequent occasions we have observed in the angular skymaps of the electron 3D velocity distribution functions a bursty-filament of particles connecting the strahl to the solar wind core-halo. When the magnetic field is well off the nominal solar wind flow direction such filaments are inconsistent with any local forces and are probably the result of strong scattering. Observations indicate that the strahl component is frequently and significantly anisotropic with T⊥/T|| ~ 2). The origin of this anisotropy is not clear as no source for the pitch-angle scattering has been observed. There is empirical evidence that the strahl may be, at least in part, a source for the solar wind non-thermal halo component.

Melvyn L. Goldstein (NASA/GSFC), The Curious Relationship Between the Electron Strahl and the Dissipation of Electromagnetic Turbulence in the Solar Wind

Abstract: Recently, the magnetic field data returned from the four Cluster spacecraft have been used to investigate how magnetofluid turbulence in the solar wind is dissipated. Although data from the flux gate magnetometer is limited to frequencies (in the spacecraft frame of reference) to about 10 Hz, the search coil data can be used up to several hundred Hz. The resulting power spectrum shows that a second inertial range is present between the proton and electron inertial length scales. (I will argue that in the frame of the solar wind, the observed fluctuations actually have very low frequencies (< 1 Hz), but very small spatial scales.) There have been approximately 1000 intervals when the four spacecraft can be used together to determine directly the wavenumber spectrum of the fluctuations. Our interpretation is that these fluctuations are propagating nearly orthogonal to the local magnetic field. A preliminary analysis of the properties of these fluctuations suggests that their dissipation is controlled directly by the electron strahl in a manner that creates the observed temperature anisotropy T⊥/T|| ~ 2.