1. 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

2. 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

3. 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|

4. 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

5. Proving that hiss is causing precipitation - 1
All values detrended

6. 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

7. 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

8. 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 ( keV).
No precip on 2X due to lack of >200 keV e-

9. Summary
First experimental verification that hiss causes precipitation of 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!!!

10. EXTRA/OLD SLIDES

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

12. Jan 6th possible ULF waves
asdf

13. Jan 3rd Slow Mode waves

14. 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

15. 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!

16. 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

17. 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

18. Jan 3rd resonance energies
asdf

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

20. 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.

21. South Atlantic Anomaly
asdf

22. 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!

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

24. 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

25. Jan 6th 2014 conjunction

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

27. 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

28. 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]