Varia ons 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
! Whistler-mode waves
! Usually inside plasmasphere - some exohiss - some in plumes
! Lightning-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 Sor ng 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 Sor ng by Plasmapause (~3 yrs of Van Allen Probes Sta s cs (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 loca on (at all L) [Malaspina+ 2016] New Results I
May years a er Carpenter: We have re-learned that the plasmapause determines the radial distribu on of hiss
Next ques on: Is hiss organiza on 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 plasma 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 li le to no role (L > 2.5) in determining hiss radial power distribu on New Results III
Flat power varia on w/ L-shell
Persists in all MLT New Results III
Strong power varia on 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-parameteriza on for hiss may be a more physically accurate than L-shell parameteriza on for incorpora ng hiss into diffusive wave models
[4] Hiss vs. Chorus
Hiss power distribu on determined by wave and medium proper es (propaga on + refrac on) - Plasmaspheric density profile cri cal to include explicitly
Chorus power distribu on determined by par cle proper es (loca on of maximum anisotropy) - Plasmaspheric density profile not cri cal to include explicitly - PP-sort makes small differences for rare, high-amplitude waves, and loca ons close to P’pause
These results submi ed to GRL (in review): “Varia ons in Plasmaspheric Hiss Power with Density” David Malaspina1, Jean-Francois Ripoll2, Xiangning Chu1, George Hospodarsky3, and John Wygant4 Thanks
Thank you to George for presen ng !