Aaron Breneman, Alexa Halford, First Direct Experimental Measurement of loss cone scattering of energetic electrons by whistler mode hiss in the plasmasphere Van Allen Probes/BARREL 2014 cooperative campaign. Aaron Breneman, Alexa Halford, Robyn Millan, Leslie Woodger, George Hospodarsky, Joe Fennell, John Wygant, Cindy Cattell, Lei Dai, Scott Thaller, Bill Kurth, Craig Kletzing, Scott Bounds, Kris Kersten, John Sample, David Malaspina and others

Background Plasmaspheric hiss theorized to scatter 10s to 100s of keV e- into loss cone. Leads to slot region [Lyons and Thorne, 1973] No direct observations linking plasmaspheric hiss and e- precip Particle detectors on satellites can’t typically resolve loss cone at magnetic eq (few deg) RBSP/BARREL simultaneous observations provide this link

Jan 6th conjunction Outer Plasmasphere hiss For two hours the hiss and x-ray signatures closely match! Suggests that hiss is causing the precipitation hiss amplitude X-ray counts Density MagEIS E- flux |B|

Region of coherent hiss/x-rays very large Up to 4 hrs MLT and 2.5 L shells BARREL field of view ~ 0.5 RE at magnetic equator Large-scale correlation of hiss source – possibly due to ULF waves Singular instances of hiss propagating to distant regions Single-event correspondences Coherence of 3.3 min Period fluctuations

Proving that hiss is causing precipitation - 1 All values detrended

Proving that hiss is causing precipitation - 2 X-ray power spec best-matched by hiss High coherence b/t hiss and x-rays from 1-20 min period fluctuations

Explaining x-ray counts via 1st order cyclotron resonance No precip seen on 2X b/c few >200 keV electrons at this location MagEIS flux 10000 1st order cyclotron res energy 1000 100 keV 10 1 3 4 5 6 L shell

Reasons why hiss is causing precipitation X-ray counts mimic hiss amp Higher coherence (1-20 min fluctuations) b/t hiss/x-rays than density/x-rays or |B|/x-rays Normalized power spectra of hiss and x-rays nearly identical. Spectra of density, |B| are different Diffusion rate depends more strongly on hiss amplitude than density or |B| Inferred precipitation energies consistent w/ 1st order cyclotron resonance (10-200 keV). No precip on 2X due to lack of >200 keV e-

Summary First experimental verification that hiss causes precipitation of 30-200 keV e- in outer plasmasphere Correlations observed on widely-varying timescales from 10s of sec to few hrs Event signatures indicate remarkable source coherence up to ∆L shell=2.5 and ∆MLT=4 hrs Evidence shows that the hiss is causing the precipitation via QL diffusion SIMULTANEOUS OBSERVATIONS WITH DISTANT BALLOON PAYLOADS ARE EXTREMELY USEFUL!!!

EXTRA/OLD SLIDES

Outer Plasmasphere hiss Jan 3rd, 2014 X-ray counts on 2I strongly mimic hiss modulation on Van Allen Probe A 9

Jan 6th possible ULF waves asdf

Jan 3rd Slow Mode waves

Jan 6th – short delays A majority of events show no delay (within few 10s of sec uncertainty) Many show delays of up to 1 min Westward- and eastward-trending equally likely Radial inwards- and outwards-trending equally likely

Future plans ….depends on funding Analyze all Van Allen Probes / BARREL conjunctions and build statistical database of correlations Find out if observed precipitation is consistent with cyclotron resonance energies (1st order only?), and pitch angle diffusion timescales Determine how much precipitation can be linked to hiss (slow drizzle or episodic?) Does the modulation correlation extend to higher energy e-? Can we find the same relations b/t chorus and precipitation? Can answer this question with BARREL campaign 1 data!

Jan 6th, MLT and L shell extent Correlated events start to drop off outside of ∆L=1-2 ∆MLT extent up to 4 hrs 13

Jan 3rd, 2014 1st order cycl res energies consistent with precipitating e- energies and MagEIS fluxes Little change in MagEIS fluxes – suggesting that the hiss does indeed cause the precip EMFISIS 1st order cycl res will be dominant. Little Efield – no energization 17

Jan 3rd resonance energies asdf

Flux from pitch angle diffusion Diffusion results close causal loop…waiting for final energy calibrations on BARREL 18

Jan 3rd, 2014 Event timescales range from few hours to 10s of min to 10s of sec 9d3 to 10d3 xray from 30 to 40 pT hiss  10% xray change from 10 pT hiss enhancement.

South Atlantic Anomaly asdf

CRRES observations of simultaneous chorus and precipitation [Imhof, 1992] Very difficult measurement to make b/c detector able to resolve loss cone only for short amount of time This shows why cooperative missions like EFW/BARREL are so important!

EFW/BARREL Goal is to understand mechanisms for energization/de-energization of radiation belts

BARREL campaign: Space weather Few nice flares, couple of CME glancing blows resulting in some auroral activity, otherwise quiet However, very nice RBSP/balloon conjunctions and very interesting observations! High speed stream on Jan 2nd lasted for a while and pumped up radiation belts. Remained elevated for next few days. Bz mostly northward

Jan 6th 2014 conjunction

Jan 3rd conjunction High speed stream, but Bz remained northward

Why precip on 2I but not 2W? Bounce-averaged Daa Diffusion results close causal loop…waiting for final energy calibrations on BARREL Local Daa FSPCa precip 2I

Hiss/precipitation - current narrative Hiss (200<f<2000 Hz) thought (partially?) to come from chorus Needs “embryonic source” (chorus suggested) [Thorne, 1973] Ray tracing studies [Chum et al., 2005, Bortnik et al., 2008] Observations of similar hiss/chorus modulation [Bortnik et al., 2009] Observed amplitudes explained as [Chen, L.J. et al., 2012] Ducting of chorus Some local growth (few dB) However, we see hiss at < 100 Hz Local cyclic growth [Thorne, Li, et al., JHU SWG, 2014] Other waves? DOZ Chorus? L>9, probably Interacts w/ up to few hundred keV e- (1st order cycl res) Theorized to precipitate e- leading to slot region [Lyons and Thorne, 1973]