M.E. Usanova

Un ive rs i t y o f A lber ta Canada

Understanding the role of EMIC waves in radiation belt and ring current dynamics:

Recent Advances

Acknowledgement The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7–SPACE–2010–1) under grant agreement n. 284520 for the MAARBLE (Monitoring, Analyzing and Assessing Radiation Belt Energization and Loss) collaborative research project.

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Radiation Belts and Ring Current

IRB: 100 MeV protons ORB: 0.1 - 10 MeV (“killer”) electrons RC: 10 - 200 keV H+, He+, O+

Inner radiation belt

Outer radiation belt

Ring current Courtesy: NASA

Plasmasphere Region of cold (eV) and dense* (103 particles/cm3) plasma of ionospheric origin mainly corotating with the Earth

3 - 6 Re

Courtesy: NASA

Losses of Energetic Particles

slow

Z+

Z+

Z+

Z+

3. Wave-particles interactions

2. Coulomb collisions

1. Charge exchange with neutral atoms

Losses to the atmosphere Magnetopause losses

1. Magnetopause shadowing

2. Outward radial diffusion

Why Wave-particle Interactions?

… and relativistic electron flux variability during different storms

Wave-particle interaction required to explain short storm recovery phase (loss of energetic ions)…

Reeves et al., 2003

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Background: Electromagnetic Ion Cyclotron (EMIC) Waves

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  Transverse plasma waves generated by wave-particle interaction (ion cyclotron instability)

  Energy source: 10 - 100 keV protons with Tperp > Tpara

  Typical amplitudes in space: ~1 - 10 nT in B, ~1 mV/m in E

  Typical frequencies: 0.1 - 5 Hz (Pc 1 range)   He+ and O+ may introduce additional stop bands and split

the wave spectrum into three branches

EMIC Cyclotron Resonance 7

EMIC waves can interact resonantly with energetic ions and relativistic MeV electrons if Doppler-shifted wave frequency (in the frame of reference of the particle) matches the particle cyclotron frequency:

k|| is the the wave number and v|| is the particle velocity parallel to the

background magnetic field. Resonant particles may exchange energy and momentum with the waves and be accelerated along the background magnetic field and precipitate into the atmosphere while non-resonant particles sustain the wave oscillatory motion.

!

" # k||v|| =$%,

% =1

1# v 2 c 2

EMIC Wave Dispersion Relation 8

EMIC wave dispersion relation for parallel propagation in a plasma composed of 70% H+, 20% He+, and 10% O+ species. The solid curves show the three left-hand polarized modes below the H+, He+, and O+ cyclotron frequencies, respectively. The dashed curve denotes the right-hand polarized mode which becomes important for oblique propagation.

Adapted from Thorne et al., 2006

Stop bands produced by wave energy absorption by He+ and and O+

Localization in the magnetosphere Kennel & Petschek, 1966: high plasma density lowers the instability threshold

Er = B2/8πN/(A2c (1+Ac)).

Summers et al., 1998: EMIC waves along the duskside plasmapause due to continuous convective injection of anisotropic ions

Olsen & Lee, 1983: generation of EMIC waves during sudden solar wind impulses due to adiabatic heating

Anderson & Hamilton 1993: EMIC waves close to the magnetopause during modest magnetospheric compressions

Figure by G. Reeves adapted from Summers et al., 1998

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Q: Do observations support this theory?

EMIC Pc1 automated detection algorithm (Bortnik et al., JGR, 2007) 11

EMIC wave identification on THEMIS CDE from July 4, 2007

The automated detection algorithm identifies spectral peaks that stand out (at least one magnitude greater in spectral power) above the noise based on the sliding window FFT One point = 180 s At least 4 consecutive points (12 minutes)

Spectral peak selection criteria

Freq

uenc

y (Hz

)

0.10.20.30.40.50.60.70.80.9

1

13:30 14:00 14:30 15:00 15:30 16:00

13:30 14:00 14:30 15:00 15:30 16:00

!100

!50

0

50

100

150

200

250

300

14:00 14:30 15:00 15:30 16:00 14:29 14:38 14:49 15:01 15:16 15:33 14:28 14:38 14:48 15:01 15:15 15:33 14:35 14:45 14:56 15:10 15:259.7 9.2 8.6 7.9 7.2 6.5 9.7 9.2 8.6 7.9 7.2 6.4 9.5 8.9 8.3 7.6 6.9

UTMLTL

THEMIS C THEMIS D THEMIS E

!He!He !He

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EMIC Occurrence Distribution from THEMIS (Usanova et al., JGR, 2012)

~ 26,000 peaks and a total of 1100 days with EMIC activity

  Data set: THEMIS FGM (2 Hz Nyquist)

  Years: 2007 – 2011 (mostly quiet times: 23 moderate and 3 intense storms)

Low EMIC wave occurrence in the inner magnetosphere

GEO

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EMIC Occurrence vs. Solar Wind Pdyn

More waves on the dayside than on the nightside Probability increases with L-shell EMIC wave probability in the inner magnetosphere is very low, <2%

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EMIC Occurrence vs. AE

  Probability increases with AE   Probability increases with L-shell

EMIC Waves in Plasmaspheric Plumes

Courtesy: Jerry Goldstein

Energetic protons drifting westward from dusk may become unstable when they encounter the enhanced cold plasma densities within the plasmaspheric plume.

Plasmaspheric plume is a portion of the outer plasmasphere on the dayside transported sunward during disturbed geomagnetic conditions.

Case studies: Spasojevic et al., GRL 2004; Fuselier et al., JGR 2004; Morley et al., JGR 2009.

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Expected location of EMIC wave activity

Plume

Cluster Plume Crossings from Whisper

•  Darrouzet et al., Ann Geophys. (2008) routinely identified plume crossing by Cluster. •  Electron plasma density derived from the Cluster WHISPER electron plasma frequency measurements. •  Statistics includes 993 plume crossings between 2001-2006.

Electron density along Cluster trajectories

Schematic showing the plume

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EMIC Waves in Plumes from Cluster FGM (Usanova et al., JGR, 2013)

Magnetic field spectrograms from Cluster FGM with EMIC waves identified by an automated algorithm (Bortnik et al., JGR, 2007).

Freq

uenc

y (H

z)

By

04:25 04:43 05:02 05:21 05:39

2

4

6

8

10Fr

eque

ncy

(Hz)

04:25 04:43 05:02 05:21 05:390

0.2

0.4

0.6

0.8

1

Bz

04:25 04:43 05:02 05:21 05:39

2

4

6

8

10

04:25 04:43 05:02 05:21 05:390

0.2

0.4

0.6

0.8

1

Freq

uenc

y (H

z)

By

08:36 08:55 09:15 09:34 09:53

2

4

6

8

10

Freq

uenc

y (H

z)

08:36 08:55 09:15 09:34 09:530

0.2

0.4

0.6

0.8

1

Bz

08:36 08:55 09:15 09:34 09:53

2

4

6

8

10

08:36 08:55 09:15 09:34 09:530

0.2

0.4

0.6

0.8

1

Freq

uenc

y (H

z)

By

07:20 07:37 07:54 08:12 08:29

2

4

6

8

10

Freq

uenc

y (H

z)

07:20 07:37 07:54 08:12 08:290

0.2

0.4

0.6

0.8

1

Bz

07:20 07:37 07:54 08:12 08:29

2

4

6

8

10

07:20 07:37 07:54 08:12 08:290

0.2

0.4

0.6

0.8

1

Freq

uenc

y (H

z)

By

05:00 05:17 05:34 05:52 06:09

2

4

6

8

10

Freq

uenc

y (H

z)

05:00 05:17 05:34 05:52 06:090

0.2

0.4

0.6

0.8

1

Bz

05:00 05:17 05:34 05:52 06:09

2

4

6

8

10

05:00 05:17 05:34 05:52 06:090

0.2

0.4

0.6

0.8

1Plume boundaries

a) b)

c) d)

Examples of EMIC wave location with respect to the plume: a)  Inside and outside. b)  Inside. c)  Outside. d)  None.

All events observed in the helium branch.

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Event Statistics

38 68 29

858

1

10

100

1000

inside and outside

inside outside none

4% 7%

3%

86%

EMIC waves were observed during 106 (11%) out of 993 plume crossings: 4% inside and outside; 7% inside; 3% outside. Normalized by a satellite dwell time probability in the plume vicinity is ~20 times lower than inside the plume.

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Event Statistics: L-dependence

4 5 6 7 8 9 10 110

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

L shell

Occurrence

•  Low occurrence at low L-shells (below the GEO-orbit). •  Probability increases towards the magnetopause. •  Probability significantly increases with solar wind dynamic

pressure.

Occurrence vs. L

0 2 4 6 80

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

Pdyn (nPa)

Occ

urre

nce

Occurrence vs. Pdyn

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Event Statistics: MLT/L-dependence

0 2 4 6 8 10 12 14 16 18 20 22 244

5

6

7

8

9

10

11

MLT

Lsh

ell

0

10

20

30

40

50

60

70

0 2 4 6 8 10 12 14 16 18 20 22 244

5

6

7

8

9

10

11

MLT

Lsh

ell

0.1

0.2

0.3

0.4

0.5

0.6Number of plumes EMIC occurrence

Most plumes are observed in the duskside sector between L=5-7/MLT=16-22. Increased EMIC occurrence is not seen in this sector.

Enhanced EMIC probability is observed in the noon sector beyond the GEO orbit at: L=6-7 14-16 MLT L=8-9 12-14 MLT L=7-8 14-16 MLT

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Event Statistics: Density and Pdyn vs. L

4 5 6 7 8 9 10 110

10

20

30

40

50

60

70

80

L shell

Elec

tron

Den

sity

(cm

3 )

•  The density difference between the events and non-events is insignificant (left panel).

•  EMIC events occurred during higher solar wind dynamic pressure than non-events (right panel).

4 5 6 7 8 9 10 110

2

4

6

8

10

12

14

L shell

Pdyn

(nPa

)

Events Non-events

Events Non-events

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EMIC waves can propagate to the ground. Q: What can we learn from ground-based and

conjugate ground-satellite measurements?

Ground Opportunities for EMIC Wave Observations

  CARISMA array www.carisma.ca – mostly Canada and US   STEP array http://step-p.dyndns.org/~khay – mostly Canada and US   STEL array http://stdb2.stelab.nagoya-u.ac.jp/magne/induction -

Japan, Russia, Canada   Sodankyla chain http://www.sgo.fi/Data/Pulsation – Finland   Kiruna station http://www.irf.se/maggraphs/puls.php – Sweden   British Antarctic Survey http://space.augsburg.edu/maccs –

Antarctica

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CARISMA Magnetometer Array: Excellent opportunity for ERG magnetic conjunctions!

28 FGMs up to 8 samples/s and 8 ICMs (yellow) up to 100 samples/s spanning several hrs MLT and dL>10

L=2.79

L=11.64

Online data and plots @ www.carisma.ca

Long-lasting EMIC Event from October 11, 2012 (submitted to GRL RBSP special issue)

Magnetic field spectrogram from the CARISMA Pinawa station (L~4) and Dawson (L~6) on October 11, 2012. This event resulted in two companion papers recently submitted to the GRL RBSP special issue.

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Ground and RBSP EMICs and Proton Precipitation at LEO

Conjugate EMIC wave observations from the CARISMA magnetometers and the Van Allen Probes together with proton loss on the LEO-orbit NOAA POES satellite on October 11, 2012.

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Radiation Belt Electron Flux from the Van Allen Probes

Electron flux vs. L between 10-20 October, 2012 from RBSP REPT. A decrease in the flux occurred on October 13 during the minimum Dst (-101 nT).

Intense and long-lasting activity before (19 hours continuously in Canada and Europe) and after but no EMICs during the flux decrease.

EMIC waves

2.3 MeV

2.9 MeV

5.6 MeV

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storm

Summary

•  For comprehensive analysis of EMIC wave role in the radiation belt and ring current dynamics simultaneous satellite and ground observations are warranted.

•  Satellites provide information about the radial extend of EMIC wave activity and in-situ wave and plasma parameters.

•  Ground magnetometers are excellent for identifying MLT extent of EMIC waves. •  Both in-situ and ground observations provide input for radiation belt/ring current

modeling. •  From our satellite observations, probability of EMIC wave in the inner

magnetosphere – region, critical for the radiation belt, for example, is low. •  When present in the “right” place, EMIC waves do not necessarily deplete

radiation belts - future modeling and observational efforts are required to address relativistic electron response to EMIC waves.

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