Magnetospheric Ion Cyclotron Waves characterized by two cold

Magnetospheric Ion Cyclotron Waves characterized by two cold plasma ion beams Scott A. Boardsen • Phase bunched cold ion beams are observed frequently in the afternoon sector of the outer magnetosphere. • Some ICW events are associated with 2 cold ion beams. • VPHASE >> VBEAM so the modification of ICW is minimal. • The ion beam occurrence wrt ICW is not 1 to 1. • Why are 2 beams as opposed to 1 sometimes observed? • At 10 RE, L_DIPOLE ~25 RE, so propagation time ~ 40 minutes for 25 e. V ion beam. • If one of the beams is the mirror of the other why does phase bunching persist? • Are two beams more likely when the MP is not highly disturbed? MMS SWG FALL 2020, Thursday Oct. 8 th 1 pm Splinter: Magnetosphere Ionosphere Coupling including Cold Plasma Contributions

Single Beam Event : ICW at a WNA of 22° MMS in magnetosphere near model MP. PGSE = [8. 7, 4. 16, 3. 85] RE ICW are observed at WNA~22° with cold ion’s modulated at the ICW frequency. f=0. 1 Hz, f/ f. CP =0. 27, (δB||/δB)2=0. 12, δB/B = 0. 2 (peak to peak)

Cold Ion Beam Centroids Cross Section of Cold Ion Beam

2 Beam Event : ICW at a WNA of 108° MMS in magnetosphere near model MP. PGSE = [8. 7, 4. 16, 3. 85] RE Oblique ICW are observed with cold ion’s modulated at the ICW frequency. Ne = 2. 5 cm-3 (from UHR), Np = 2. 26 cm-3 , NHe++ = 0. 12 cm-3 Debye length = 15 m (cold electrons) f. CP = 0. 75 Hz, f/ f. CP = 0. 33, (δB||/δB)2=0. 0, δB/B = 0. 04 (peak to peak)

K vector estimate using Bellan’s and Phase Analysis. Bell Ph ωSC 1. 64 k. X 0. 90 0. 88 k. Y 0. 41 0. 47 k. Z 0. 10 0. 08 k 9 E-03 9. E-03 f. SC 0. 26 f 0. 25 λ 656 697 ψ(°) 105 106 λ = 622 km (cold plasma wavelength) VP~ 160 km/s (flow frame) VF = [37. 7, -60. 4, 15. 8 ] (spacecraft) VB = ~ 10 km/s (flow frame) Blackobservations Blue-FFT of observations at peak B psd Red- Linear Theory scaled by d. B

Cold Ion Beam Centroids Cross Section of Cold Ion Beam