Study of Wave-Particle Interaction Using Wind/ACE Data

Transcription

1 Study of Wave-Particle Interaction Using Wind/ACE Data Lan Jian University of Maryland, College Park NASA Goddard Space Flight Center Collaborators: M. Stevens, S. P. Gary, A. F. Viñas, P. S. Moya, C. T. Russell, T. Broiles, J. Kasper, R. Alexander Solar Probe Plus SWG Washington D.C. September 15, 2016

2 Jian et al. (2014) Introduction Electromagnetic waves near the proton cyclotron frequency (fpc) and higher than Alfvén wave frequency Ion cyclotron waves (ICWs): left-hand (LH) polarized in plasma frame Magnetosonic waves: right-hand (RH) polarized in plasma frame Intermittent observations of such waves in quiet solar wind have been reported in Behannon (1976), Tsurutani et al. (1994), Jian et al. (2009, 2010), etc. Are these waves generated at the Sun and then transported outward by the solar 2 wind? Or are they generated locally in the interplanetary medium?

3 Ion Velocity Distribution from Wind/SWE fpc Gary et al. (2016) n: the projection axis on which the distribution was measured

4 Proton Condition for Extensive Wave Periods: T /T// vs. β// Instability thresholds for protons are from Maruca et al. (2012) using the case j = p and ζ = 0.5. Color indicates the occurrence rate normalized by the total count in each category The extensive waves are distributed slightly closer to the instability thresholds than in general solar wind, especially the LH ones

5 Proton Beam Condition for Wave Periods average higher higher faster Solar wind thermal proton spectra are fit to model velocity distribution functions consisting of a bi-maxwellian core and a secondary Maxwellian population using techniques developed by the SWE team In 2005, beam protons are observed ~46% of the time in wave events, more often than 25% for all solar wind In comparison with non-wave solar wind, the proton beam density is slightly higher in wave events. In RH waves, the proton beam drifts away from protons faster than nonwave solar wind

6 Example of Plasma Condition for Extensive Wave Periods Jian et al. (2016)

7 Wave Dispersion Analysis Because the waves propagate close to B and the wave amplitude is small, it is appropriate to use the linear dispersion relation D(k,,, s, Ns, U s,t s,t s) Ek( )=0 D for the dispersion tensor, Ek( ) for the electric field eigenmodes subscript s for core protons, beam protons, α-particles, and electrons IC1, 2, 3: ICWs associated with α particles, core protons, beam protons RHF (RHB): magnetosonic waves parallel (antiparallel) to B Jian et al. (2016)

8 Statistics from Wave Dispersion Analysis Gary et al. (2016, for slow wind) and Jian et al. (2016, for fast wind) have found some waves are consistent with the ICWs, and some are consistent with magnetosonic wave At 1 AU, B 6 nt, fpc Hz, TPC 11s, Twave TPC/0.01 = 1100s At 10 Rs, B 2000 nt, fpc 31 Hz, TPC 0.032s, Twave? SPP plasma data cadence: 8 s-1 is expected to resolve the simultaneous ion velocity distribution for waves

9 Do the Waves Heat or Accelerate Heavy Ions? ACE Events #1 and 7 last longer than 1 hour. Within them, the drift speed of O6+ relative to protons increases by km/s However, there are changes of relative drift and temperature at other times too, possibly due to turbulence, small current sheets in the solar wind Similar results are obtained from the observations of wave periods and heavy ions in other days It is hard to definitely determine if there is direct local effect using ACE data

10 What About Using SPP Observations? fsc/fpc Left-handed in s/c frame 5-8 ±1 Approximate fsw/fpc The waves are widely observed from 0.3 to 1 AU At 10 Rs VA ~ 21 VA, 1AU, the Doppler shift term does not dominate any more Flux gate magnetometer of SPP: 293 s-1, Nyquist frequency 5fpc, can observe the waves well Can the thermal proton and α-particle distribution be fit by bi-maxwellian functions? Is the drift speed of proton core and beam ~ VA? Are the drift speeds of heavier ions with respect to protons ~ VA? How well can we observe the instability growth and its interaction with particles? Boardsen et al. (2015)