Transcript The recent observation of plasma waves and particles Qianli Ma
The recent observation of plasma waves and particles in the inner magnetosphere Qianli Ma University of California, Los Angeles 2014 GEM Outline • A sketch of waves and particles in the inner magnetosphere. • Recent satellites in the inner magnetosphere. • Wave and particle data measurements and their relations. • Other interesting findings by Van Allen probes. • Summary. What we see in the inner magnetosphere – plasma waves and particle populations In the inner magnetosphere, the particles perform energy and charge dependent drift motion. The anisotropy and positive gradients in the particle distribution can provide the free energy for wave excitation. The waves can cause the lose or acceleration of the particles. The diffusion processes become important in the inner magnetosphere, and the wave and particle measurement is an important focus in the recent spacecraft missions. [Thorne GRL 2010] Time series of frequency spectrum Satellite orbits in the inner magnetosphere Van Allen Probes: Highly elliptical equatorial orbits 1.1 RE to 5.8 RE 9 hours period THEMIS inner satellite (A, D, E): Highly elliptical equatorial orbits 1.1 RE to 10 or 12 RE 22 hours period Cluster: Elliptical polar orbits 3 RE to 19 RE 57 hours period GOES: Geosynchronous orbit 6.6 RE 24 hours period Satellite instruments and data THEMIS Van Allen Probes • EFI: electric field variations. • ECT: particle measurements. HOPE: low energy particle flux up to 45 keV. MagEIS: 30 keV to 4 MeV electrons and 20 keV to 1 MeV ions. REPT: energetic electrons (up to 10 MeV) and protons ( up to 75 MeV). • EMFISIS: wave measurements. WFR: 10 Hz to 12 kHz electric and magnetic fluctuation matrix. HFR: 10 kHz to 400 kHz electric fluctuation. • EFI: DC to 12 Hz electric field. • FGM: background B0 and low frequency (< 64 Hz) magnetic field fluctuations. • SCM: magnetic fluctuations up to 4 kHz. • DFB: spectral processing. • ESA: particle flux from a few eV to 25 keV (ion) or 30 keV (electron). • SST: particle flux from 25 keV to 6 MeV. E-flux Ellipticity Normal WFR WFR E B Angle (90°) HFR Observation of waves and particles – whistler-mode Chorus [Li et al. GRL 2013] • Intense chorus waves outside the plasmapause are observed between 0.1 fce and 0.8 fce. • Ellipticity ~ 1: right-hand nearly circularly polarized. • Increase in electron energy flux indicates stronger convection or injection. • Chorus waves excitation may be associated with the electron convection. E-flux Ellipticity Normal WFR WFR E B Angle (90°) HFR Observation of waves and particles – Plasmaspheric Hiss • Broadband structureless hiss emissions are observed inside the plasmapause. • Wave normal angle is low > nearly field-aligned propagation. • Wave ellipticity is ~1. • Increase in electron energy flux is observed inside the plasmapause. Ne P-flux PA P-flux Ek Normal Angle B Observation of waves and particles – EMIC waves [Zhang et al. GRL 2014] • EMIC waves are observed in H+ band only (#1), and in both H+ and He+ band (#2). • The “nose-like” structure in proton distribution is also observed. • The an-isotropic in the proton pitch angle distribution may be the source of the waves. Ellipticity Normal WFR WFR E B Angle P-flux (90°) HFR AE Observation of waves and particles – magnetosonic waves • Magnetosonic waves are observed between fcp and fLHR. • Wave normal angle is close to 90° => nearly perpendicular propagation. • Wave ellipticity is ~0 => nearly linear polarization. • Proton ring distribution is also observed. • ∂f/∂vper > 0 in proton ring distribution may provide the source of wave excitation. Statistical study of waves example – Global distribution of whistler-mode Chorus • 2 years survey of chorus waves using THEMIS wave magnetic field data. • Chorus waves are strongest near prenoon sectors, near magnetic equator, at disturbed conditions. • RMS averaged wave amplitude peaks at ~60 pT. [Li et al. GRL 2009] Several messages from Van Allen Probes – The local acceleration of energetic electrons • Electron phase space density increased by nearly 3 orders in less than 12 hours. • Electron phase space density peaks around L* = 4.2 during the acceleration. • The local acceleration around L* = 4.2 is robust. [Reeves et al. Science 2013] Several messages from Van Allen Probes – The relativistic storage ring • In the first 4 days, the storage ring at L ~ 3.2 resulted from the loss of more distant electrons in the outer zone L > 4. • The outer zone electrons recovered and were variable. • The storage ring was stable until the abrupt demise by the storm. [Baker et al. Nature 2013] EMFISIS B wave MagEIS E-flux Several messages from Van Allen Probes – Direct observation of wave particle interactions • One to one correlation between electron bursts and chorus wave intensification was observed. • The pitch angle distribution of electrons (with maxima at 75-80°) indicates wave-particle interactions. [Fennell et al. GRL 2014] Summary • The recent spacecraft provide high resolution data about the space environment, plasma waves and particle populations in the inner magnetosphere. -- A great opportunity to better understand the space. • More interesting phenomena are right behind the spacecraft data. -- Check the data out!