First Direct Experimental Measurement of loss cone scattering of energetic electrons by whistler

mode hiss in the plasmasphereVan 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

For two hours the hiss and x-ray signatures closely match!

Suggests that hiss is causing the precipitation

Density

MagEIS E- flux

|B|

X-ray countshiss amplitude

Outer Plasmasphere hiss

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

Coherence of 3.3 minPeriod fluctuations

Single-eventcorrespondences

Proving that hiss is causing precipitation - 1All values detrended

• X-ray power spec best-matched by hiss

• High coherence b/t hiss and x-rays from 1-20 min period fluctuations

Proving that hiss is causing precipitation - 2

Explaining x-ray counts via 1st order cyclotron resonance

• No precip seen on 2X b/c few >200 keV electrons at this location

Mag

EIS

flux

L shell3 4 5 61

10

100

1000

10000

keV

1st order cyclotron res energy

X-ra

y co

unts

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

Jan 3rd, 2014• X-ray counts on 2I

strongly mimic hiss modulation on Van Allen Probe A

9

Outer Plasmasphere hiss

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

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

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?

• Diffusion results close causal loop…waiting for final energy calibrations on BARREL

Bounce-averaged Daa

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]