Energy deposition by Alfvén waves into the dayside auroral oval: Cluster and FAST observations

Abstract

[1] We report in situ observations from the Cluster and FAST spacecraft showing the deposition of energy into the auroral ionosphere from broadband ULF waves in the cusp and low-latitude boundary layer. A comparison of the wave Poynting flux with particle energy and flux at both satellites indicates that energy transfer from the broadband waves to the plasma occurs through field-aligned electron acceleration, transverse ion acceleration, and Joule heating. These processes are shown to result in precipitating electron fluxes sufficient to drive bright aurora and cause outflows of energized electrons and O + ions from the ionosphere into the low-latitude boundary layer. By solving an eigenmode equation for Alfvén waves in the observed plasma environment, it is shown that the broadband waves observed at Cluster and FAST are dispersive Alfvén waves. It is demonstrated that these waves have wavelengths perpendicular to the geomagnetic field extending from significant fractions of an L shell down to ion gyroradii and electron inertial lengths and wave frequencies in the plasma frame from 1 mHz up to 50 mHz. These waves are shown to have wavelengths along the geomagnetic field of the order of the field line length between the ionosphere and the equatorial plane and become field line resonances (FLRs) when on closed field lines. It is shown that the inclusion of nonlinear and/or nonlocal kinetic effects is required in the description of these waves to account for accelerated particles observed. On the basis of the wave polarization and spectral properties observed from Cluster and FAST it is speculated that these waves are generated through the mode conversion of surface Alfvén waves driven by tailward flows in the low-latitude boundary layer.Citation: Chaston, C. C., et al. (2005), Energy deposition by Alfvén waves into the dayside auroral oval: Cluster and FAST observations,

Statistical study of the location and size of the electron edge of the Low-Latitude Boundary Layer as observed by Cluster at mid-altitudes

“…The most likely source of the upgoing short duration electron beams inside the electron edge is a wave-particle interaction process. For example, it has been suggested that electrons could be trapped in the parallel electric fields associated with kinetic Alfvén waves and propagate with these waves (Chaston et al, 2005). A parallel electric field existing below the spacecraft and accelerating electrons is also a possible explanation (e.g., Paschmann et al, 2003).…”

Investigation of energy transport and thermospheric upwelling during quiet magnetospheric and ionospheric conditions from the studies of low- and middle-altitude cusp

“…The conclusion from that paper was that particle fluxes seen by Cluster in the exterior cusp were enough to heat the F layer, while the Poynting flux was more than enough to account for the Joule heating in the E ionospheric layer. Also, Chaston et al (2005) studied a conjunction between Cluster and FAST satellite, and a conclusion was, after a comparison of the Poynting and particle fluxes, that the energy deposition to the dayside auroral oval was due to field-aligned electron acceleration, transverse ion-acceleration, and Joule heating.…”

Comparison of Fourier and wavelet techniques in the determination of geomagnetic field line resonances

“…The utility of WT in space physics problems has been demonstrated by a growing number of authors [e.g., Muret and Omidi, 1995;Lui and Najmi, 1997;Gedalin et al, 1998;Lundstedt et al, 2005]. Recently, WT have been applied to the study of ULF waves either from space [Chaston et al, 2005] or from the ground [Waters, 2000]. However, there has not been so far a systematic study of the advantages and/or disadvantages of the WT over the usual FT in the determination of FLRs.…”