Transcript RBSP_EFW_meeting_UMN_Jun_2014_DMM

Nonlinear Electric Field Structures
and Magnetic Dipolarizations
in the Inner Magnetosphere
David Malaspina1, Laila Andersson1, Robert Ergun1, John Wygant2,
John Bonnell3, Craig Kletzing4, Geoff Reeves5, Ruth Skoug5,
and Brian Larsen5
[1] CU/LASP
[2] U. Minnesota
[3] U.C. Berkeley
[4] U. Iowa
[5] Los Alamos
Van Allen Probes EFW Team Meeting
2014-06-11
Results
1) Nonlinear electric field structures are observed in the
inner magnetosphere (< 6 Re) over a range of local times
and radial distances [and MLaT]
2) Nonlinear electric field structures are coincident with
magnetic dipolarizations
3) Magnetic dipolarizations occur inside of 6 Re much more
often than previously reported
4) Some dipolarizations with nonlinear electric field power
can be identified as propagating ‘dipolarization fronts’
5) If nonlinear structures are observed, dipolarizations
are almost always observed. The reverse is not true.
Malaspina et al. 2014 GRL (in review)
New as of this talk
Broadband Electrostatic Waves
Broadband Electrostatic Noise (BEN)
Observed on s/c as early as Explorer 45 (1971)
(Anderson and Gurnett 1973)
Matsumoto et al. 1994 (Geotail), ID’d BEN as
Electrotastic Solitary Waves (ESW) in the
magnetotail, using waveform captures
ESW ID’d later in:
plasma sheet boundary layer, lobe boundaries,
polar cusp, magnetopause, bow shock
(Geotail, Polar, Cluster, THEMIS)
Generally: at any boundary layer or strong FAC
Nonlinear Electric Fields (NLE)
Strong Nonlinear E fields!
Sharp E fields FFT’d into
LF broad-band noise
Magnetic analogs often
exist (much lower signal to
noise)
SC-A
Broadband Electrostatic Waves
Electron-acoustic DL
(potential-carrying e- phase
space holes)
(Mozer et al. 2013 PRL)
Show magnetic field spikes (!)
Lorentz transformations of Eprp
Least-squares fits to
Lortenz transform
ΔB2 = -ΔE1 (v|| / c2)
ΔB1 = ΔE2 (v|| / c2)
Speeds of: 0.098c, 0.085c,
0.052c, 0.053c, 0.063c, 0.026c
Voltage drops of: 78V, 153V, 53V,
135V, 210V, and 35V
Structure width sets peak f
Broadband nature of pulse enhances power < 100 Hz
Broadband Electrostatic Waves
Ion-acoustic DL + e- phase space holes
Gap between DL and holes
indicates laminar (stable) DL
[Newman and Andersson 2009]
~200 V potential drop
(673 eV e-, 5.8 keV H+)
Vsound ≈ 1.3x106 m/s
Active two-stream instability
200 V drop w/ ~673 eV electrons
Implies cold population interacting
w/ DL-accelerated e- to form holes
Well formed holes
far from DL
Turbulent E near DL
Poorly formed holes
closer to DL
Nonlinear Electric Fields (NLE)
Modulated waves
Strong E_parallel
(NLE + waves)
Weak E_perp
(mostly waves)
Electrostatic waves w/
rising / falling tones
fce / 2
Harmonics visible
In chorus band
f lh
No magnetic analog
Nonlinear Electric Fields (NLE)
Rising tones when
E is parallel to B
Falling tones when
E is anti-parallel to B
SC-A
Several examples of this
behavior found (different days / sc)
Nonlinear Chorus
Some NLE are:
nonlinear chorus
(strong harmonics)
Harmonics in E and B
Burst data Vb
4) Nonlinear Chorus
Nonlinearities
Strongest in E||
Suggests: chorus and
e- phase space holes mixing
(e.g. Goldman et al. 2013 PRL)
-holes mode-converting into
whistlers during reconnection
simulations
Is E || B, instead of E || k
(e.g. Kellogg 2010)
- chorus phase-trapping eOther E directions and
SCM data is nonlinear,
but much less so.
MLT – L
Integrated E power
< 100 Hz [excludes chorus]
E2 > B2c2 [excludes hiss]
B|| / B < 0.65 [excludes M’sonic]
Also exclude:
- bias sweeps
- L < 2.5
- Maneuvers
Nonlinear structures in the inner
magnetosphere over a wide
MLT and L range (!)
Strongest pre-midnight
- like bursty bulk flows
Extend into dawn
- electron drift?
MLaT – L
Integrated E power
< 100 Hz [excludes chorus]
E2 > B2c2 [excludes hiss]
B|| / B < 0.65 [excludes M’sonic]
Also exclude:
- bias sweeps
- L < 2.5
- Maneuvers
Nonlinear structures strongest
at high MLaT
-related to orbit during
pre-midnight encounter?
-Related to plasma Beta?
Dipolarizations
Runov et al. 2011
Increases in:
Bz, Ey, Ion energy flux, Ion temperature
e- energy flux, e- temperature,
plasma flow velocity
Ion density drops behind front
Dipolarization front timescale:
10’s of seconds (Fast flows in the tail)
Manifestation of substorm current wedge
(wedgelets) suggested:
Liu et al. 2013
Dipolarizations
July 14, 2013 scB
Nonlinear E field activity with:
1) Dipolarizations
2) 1-30 keV electron flux increase
E field activity strongest at sharp
dipolarizations
Dipolarizations
June 1, 2013 scB
Nonlinear E field activity with:
1) Dipolarizations
2) 1-30 keV electron flux increase
24 distinct dipolarizations in < 9 hrs
prior studies: 10 over 6 months (!)
Distinguish dipolarizations using
nonlinear E field activity
(once correlation proven)
Dipolarizations
Nosé et al. 2010:
Mission Demonstration Satellite 1 (MDS‐1)
Geotransfer orbit (500 km – 6.6 Re)
10 dipolarization fronts Earthward of geosynch.
(Most pre-midnight) L = 3.5 – 6.5
All prior works:
10 dipolarization fronts Earthward of geosynch.
Van Allen Probes data for June 1, 2010:
Dozens of dipoliarization fronts inside geosynch.
Difference in selection criteria (!)
(ΔBz or large Vflow required,
Nosé selected for IMAGE conjunctions etc.)
Dipolarizations
Dipolarizations slow as
they approach Earth
6 – 12 Re => Bursty bulk flow
braking region
Strong nonlinear E-fields
in BBF braking region
(8 – 12 Re)
- Double layers, e- holes
- Earthward Poynting flux
- Strong parallel E-fields
[Ergun et al. 2009]
Kinetic Alfven waves
w/ parallel E fields
[Chaston et al. 2012]
McPherron et al. 2011
Speed decreases to zero by 6 Re?
Dipolarization Fronts
Two-spacecraft observations
Mag-field lag: B leads A
Consistent w/ structure
traveling +X / +Y [GSM]
Cross-correlation of Mag data
to get ΔT
ΔT indicated by white lines
E-field ‘fronts’ visible, have same
ΔT as Mag fields
Dipolarization Fronts
Two-spacecraft observations
Mag-field lag: B leads A
Consistent w/ structure
traveling +X / +Y [GSM]
Cross-correlation of Mag data
to get ΔT
ΔT indicated by white lines
E-field ‘fronts’ visible, have same
ΔT as Mag fields
Dipolarization Fronts
Two-spacecraft observations
Mag-field lag: A leads B
Consistent w/ structure
traveling +X or -Y [GSM]
Mag structured at A
Mag smoothed by B
E fields stronger at A
E fields weaker at B
Evidence of ‘dipolarization front’
deceleration?
Context / More slides
Supra-Arcade Down Flows
in Solar Flares
Savage et al. 2011
Similar physics at work for
retracting magnetic field lines
behind reconnection regions at
the Sun and Earth?
Backup / Even More Slides
Statistical Correlation
Pts / min where:
dθBz / dt > 1.5 σ
NL E-field amplitude
Statistical Correlation
Pts / min where:
dθBz / dt > 1.5 σ
NL E-field amplitude
Statistical Correlation
Pts / min where:
dθBz / dt > 1.5 σ
NL E-field amplitude
Statistical Correlation
Pts / min where:
dθBz / dt > 1.5 σ
NL E-field amplitude
October 16, 2012 – April 1, 2014
# orbits
NL E-fields Yes
Dipolarizations Yes
123
(~94%)
Dipolarizations No
8
(~6%)
Total
131
NL E-field measure
When NLE (mV/m)^2 exceeds 1 mV/m (1-sec averaged spectral data)
Dipolarization measure
When density of points satisfying dθBz / dt > 1.5 σ exceeds 6 / min
October 16, 2012 – April 1, 2014
# orbits
NL E-fields Yes
Dipolarizations Yes
123
(~94%)
Dipolarizations No
8
(~6%)
Total
131
NL E-field measure
When NLE (mV/m)^2 exceeds 1 mV/m (1-sec averaged spectral data)
Dipolarization measure
When density of points satisfying dθBz / dt > 1.5 σ exceeds 6 / min
# orbits
NL E-fields No
Dipolarizations Yes
430
(~34%)
Dipolarizations No
830
(~66%)
Dipolarization measure is poor
Picks up ULF waves, Magnetometer response to thrusters, etc.
Need a better one! Or a way to remove ULF times...
Total
1260
Backups for the backups
Flux dropouts likely
from passage into lobes
(rather than plasma sheet)
Strong NLE at lobe boundary,
as on Geotail
Dipolarizations
Dipolarization speed to 0
by 6 Re? (McPherron et al. 2011)
Use:
V = (E x B) / B2
Assuming EB=0 to get axial E
Speeds of 10 -> 100 km/s
(L = 4 – 6)
Speed spikes match NLE
observations
Vaxial (≈ Sunward)
with no assumption on EB
Done