Weak Kinetic Alfvén Waves Turbulence during the November 14th 2012 geomagnetic storm: Van Allen Probes observations

TitleWeak Kinetic Alfvén Waves Turbulence during the November 14th 2012 geomagnetic storm: Van Allen Probes observations
Publication TypeJournal Article
Year of Publication2015
AuthorsMoya, PS, Pinto, VA, Viñas, AF, Sibeck, DG, Kurth, WS, Hospodarsky, GB, Wygant, JR
JournalJournal of Geophysical Research: Space Physics
Date Published06/2015
KeywordsKinetic Alfven Waves; Magnetic Storms; Radiation belts; Van Allen Probes
Abstractn the dawn sector, L~ 5.5 and MLT~4-7, from 01:30 to 06:00 UT during the November 14th 2012 geomagnetic storm, both Van Allen Probes observed an alternating sequence of locally quiet and disturbed intervals with two strikingly different power fluctuation levels and magnetic field orientations: either small (~10−2 nT2) total power with strong GSM Bx and weak By, or large (~10 nT2) total power with weak Bx, and strong By and Bz components. During both kinds of intervals the fluctuations occur in the vicinity of the local ion gyro-frequencies (0.01-10 Hz) in the spacecraft frame, propagate oblique to the magnetic field, (θ ~ 60°) and have magnetic compressibility C = |δB|||/|δB⊥| ∼ 1, where δB|| (δB⊥) are the average amplitudes of the fluctuations parallel (perpendicular) to the mean field. Electric field fluctuations are present whenever the magnetic field is disturbed, and large electric field fluctuations follow the same pattern for quiet and disturbed intervals. Magnetic frequency power spectra at both spacecraft correspond to steep power-laws ∼ f –α with 4 < α < 5 for f ≲ 2 Hz, and 1.1 < α < 1.7 for f ≲ 2 Hz, spectral profiles that are consistent with weak Kinetic Alfvén Waves (KAW) turbulence. Electric power is larger than magnetic power for all frequencies above 0.1 Hz, and the ratio increases with increasing frequency. Vlasov linear analysis is consistent with the presence of compressive KAW with k⊥ρi ≲ 1, right-handed polarization and positive magnetic helicity, in the plasma frame, considering a multi-ion plasma. All these results suggest the presence of weak KAW turbulence which dissipates the energy associated with the intermittent sudden changes in the magnetic field during the main phase of the storm.
URLhttp://doi.wiley.com/10.1002/2014JA020281
DOI10.1002/2014JA020281
Short TitleJ. Geophys. Res. Space Physics


Page Last Modified: August 6, 2015