Variaons in Plasmaspheric Hiss Power with Density

David Malaspina1, Jean-Francois Ripoll2, Xiangning Chu1, George Hospodarsky3, John Wygant4

Van Allen Probes Science Working Group New Jersey, Aug, 2018

1 Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder 2 CEA, DAM, DIF, Arpajon, France 3 Department of Physics and Astronomy, University of Iowa 4 School of Physics and Astronomy, University of Minnesota Hiss Background

! -mode waves

! Usually inside - some exohiss - some in plumes

! -generated, chorus generated, in-situ cyclotron growth /Hz)

[Bortnik+ 2008, Li et al., 2013; Chen et al., 2014] 2 ((mV/m) ! Incoherent superposition of waves 10 (exceptions: Summers+ 2014; Tsurutani+ 2015) Log /Hz) 2 (nT 10

Hiss spectral Log signatures

Thorne+ 2010 Hiss Sorng Background

Magnetic Local Time (MLT) Magnetic Latitude (λ)

L-shell (L or L*) Geomagnetic Activity (Kp or AE)

Kim+ 2015 Common parameterization: (L, L*), Activity (Kp, AE)

BUT: hiss is tightly confined by the plasmapause

/Hz) ! whistler-mode growth / propagation 2 sensitive to density ((mV/m) 10 Log AND: plasmapause location is not tightly correlated with L-shell or geomagnetic activity

/Hz) (only trends, with significant spread) 2 (nT

10 [Moldwin+ 2002 or Verbanac+ 2015] Log Are there better parameterizations? Hiss Sorng by Plasmapause (~3 yrs of Van Allen Probes Stascs (SCM data))

Hiss Power Counts Plasmapause Hiss power slice MLT vs. ΔL Distribution Density 8 – 10 MLT

PP steep Hiss peak narrow, Hiss peak power High amplitude location (ΔL) is uniform with MLT (!) (Plasmapause L = 3 to 4) Located very near PP Strongest on day side Standoff ~1 L

Hiss power is radially organized by plasmapause locaon (at all L) [Malaspina+ 2016] New Results I

May years aer Carpenter: We have re-learned that the plasmapause determines the radial distribuon of hiss

Next queson: Is hiss organizaon controlled by the gradient (plasmapause) or by the density itself?

New Results II

SCM hiss power (2012-11-01 to 2018-01-01), Probe B

MLT 12 – 14 MLT 12 – 14

Hiss power vs. L Hiss power vs. density For 4 ranges of density For 4 ranges of L (simple L)

Density from Vsc, calibrated by fuh Hiss = 40 Hz to 2 kHz inside plasmapause only Magnetosonic waves, charging, eclipse, thrusters all removed New Results II

SCM hiss power (2012-11-01 to 2018-01-01), Probe B

Nearly flat with L ! Strongly varying with density ! For any given density range Regardless of L !

L-shell plays lile to no role (L > 2.5) in determining hiss radial power distribuon New Results III

Flat power variaon w/ L-shell

Persists in all MLT New Results III

Strong power variaon w/ density

Persists in all MLT Conclusions

[1] Hiss power varies weakly with L-value for specific ranges of plasma density

[2] Hiss power increases consistently with plasma density for L > 2.5

[3] Density-parameterizaon for hiss may be a more physically accurate than L-shell parameterizaon for incorporang hiss into diffusive wave models

[4] Hiss vs. Chorus

Hiss power distribuon determined by wave and medium properes (propagaon + refracon) - Plasmaspheric density profile crical to include explicitly

Chorus power distribuon determined by parcle properes (locaon of maximum anisotropy) - Plasmaspheric density profile not crical to include explicitly - PP-sort makes small differences for rare, high-amplitude waves, and locaons close to P’pause

These results submied to GRL (in review): “Variaons in Plasmaspheric Hiss Power with Density” David Malaspina1, Jean-Francois Ripoll2, Xiangning Chu1, George Hospodarsky3, and John Wygant4 Thanks

Thank you to George for presenng !