Nonlinear Electric Field Structures and Magnetic Dipolarizations in the Inner Magnetosphere David Malaspina 1, Laila Andersson 1, Robert Ergun 1, John Wygant 2, John Bonnell 3, Craig Kletzing 4, Geoff Reeves 5, Ruth Skoug 5, and Brian Larsen 5 [1] CU/LASP [2] U. Minnesota [3] U.C. Berkeley [4] U. Iowa [5] Los Alamos Van Allen Probes EFW Team Meeting

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. Results Malaspina et al 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 (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

Sharp E fields FFT’d into LF broad-band noise Magnetic analogs often exist (much lower signal to noise) Strong Nonlinear E fields! SC-A Nonlinear Electric Fields (NLE)

Broadband Electrostatic Waves Structure width sets peak f Broadband nature of pulse enhances power < 100 Hz Electron-acoustic DL (potential-carrying e- phase space holes) (Mozer et al PRL) Show magnetic field spikes (!) Lorentz transformations of Eprp Least-squares fits to Lortenz transform ΔB 2 = -ΔE 1 (v || / c 2 ) ΔB 1 = ΔE 2 (v || / c 2 ) Speeds of: 0.098c, 0.085c, 0.052c, 0.053c, 0.063c, 0.026c Voltage drops of: 78V, 153V, 53V, 135V, 210V, and 35V

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 ≈ 1.3x10 6 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 Poorly formed holes closer to DL Turbulent E near DL

Nonlinear Electric Fields (NLE) Modulated waves Strong E_parallel (NLE + waves) Weak E_perp (mostly waves) Electrostatic waves w/ rising / falling tones Harmonics visible In chorus band No magnetic analog fce / 2 f lh

Rising tones when E is parallel to B Falling tones when E is anti-parallel to B Several examples of this behavior found (different days / sc) SC-A Nonlinear Electric Fields (NLE)

Nonlinear Chorus Some NLE are: nonlinear chorus (strong harmonics) Harmonics in E and B

Burst data Vb Nonlinearities Strongest in E || Suggests: chorus and e- phase space holes mixing (e.g. Goldman et al PRL) -holes mode-converting into whistlers during reconnection simulations Is E || B, instead of E || k (e.g. Kellogg 2010) - chorus phase-trapping e- Other E directions and SCM data is nonlinear, but much less so. 4) Nonlinear Chorus

MLT – L Integrated E power < 100 Hz [excludes chorus] E 2 > B 2 c 2 [excludes hiss] B || / B < 0.65 [excludes M’sonic] Also exclude: - bias sweeps - L < 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] E 2 > B 2 c 2 [excludes hiss] B || / B < 0.65 [excludes M’sonic] Also exclude: - bias sweeps - L < Maneuvers Nonlinear structures strongest at high MLaT -related to orbit during pre-midnight encounter? -Related to plasma Beta?

Dipolarizations 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: Runov et al Liu et al. 2013

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 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 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: dθ Bz / dt > 1.5 σ NL E-field amplitude

Statistical Correlation Pts / min where: dθ Bz / dt > 1.5 σ NL E-field amplitude

Statistical Correlation Pts / min where: dθ Bz / dt > 1.5 σ NL E-field amplitude

Statistical Correlation Pts / min where: dθ Bz / dt > 1.5 σ NL E-field amplitude

October 16, 2012 – April 1, 2014 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 dθ Bz / dt > 1.5 σ exceeds 6 / min # orbits Dipolarizations Yes Dipolarizations No Total NL E-fields Yes (~94%) (~6%)

# orbits Dipolarizations Yes Dipolarizations No Total NL E-fields Yes (~94%) (~6%) October 16, 2012 – April 1, 2014 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 dθ Bz / dt > 1.5 σ exceeds 6 / min # orbits Dipolarizations Yes Dipolarizations No Total NL E-fields No (~34%) (~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...

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 ) Use: V = (E x B) / B 2 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