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Introduction on bursty flows Particle distributions and ion acceleration

Bursty Flows and non-linear plasma structures in Earth’s magnetotail as revealed from THEMIS. Introduction on bursty flows Particle distributions and ion acceleration Electron acceleration and effects Linear and non-linear waves: origin? Propagation with flows/dipolarization

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Introduction on bursty flows Particle distributions and ion acceleration

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  1. Bursty Flows and non-linear plasmastructures in Earth’s magnetotailas revealed from THEMIS • Introduction on bursty flows • Particle distributions and ion acceleration • Electron acceleration and effects • Linear and non-linear waves: origin? • Propagation with flows/dipolarization • Relationship to ionospheric effects • Poleward boundary intensifications • N-S arcs within expanding aurora • Flow energy dissipation • Turbulence, dipolarization fronts, ionosphere • Flows as substorm precursors

  2. Early Observations Baumjohann et al., 1990 Fast Vperp flow samples are rare and bursty Angelopoulos et al., 1992 Coherence time ~ few min Dipolarization, Low density, High Temperature, P~const. Angelopoulos et al., 1994 Flow burst occurrence rate increases with distance.

  3. Early Observations: duration, scale properties • Angelopoulos et al., JGR 1995 • BBFs are 10min intervals of flow thatencompass flow bursts • BBFs are important part of substorms • Can account for transport rate if only2RE in width • Need several to account for integratedsubstorm flux circulation • Spatially limited due to gradients • Temporally limited due to dissipation • Cross-scale coupling? • Ionospheric coupling?

  4. 3D nature and relationship to substorm onset 0204UT JGR [Angelopoulos et al, 1995] Substorm Onset: ~0202UT In line with BBF onset BBF lasts 10min becauseflow region is a shell envelopingdipolarization. Both flow shell and dipolarizationexpand latterally and radially Ygsm Xgsm 0215UT Ygsm

  5. Importance for Transport

  6. Near-Earth tail reconnectionLocalization: the case for “point” reconnection Angelopoulos et al., 1998 (Case study on localization) Nakamura et al., 2004 (Cluster statistics on localization) Scales: Vertical: 1.5-2 RE, Azimuthal: 2-3 RESharper gradient on duskside flank

  7. The 3D nature of the Rx process 0204UT JGR [Angelopoulos et al, 1995] Substorm Onset: ~0202UT Ygsm Xgsm 0215UT Ygsm

  8. Sergeev et al., GRL, 1996 Some flow bursts consistent with localized, under-populated bubbles proposed by Pontius & Wolf, 1990 theoretical model (except generation mechanism). Scale size ~ 2RE

  9. Near-Earth BBFs resemble currentdisruption, but move Earthward Angelopoulos et al., GRL 1999 Earthward flows at 10REduring a small substorm agree with (dawnward) gradientanisotropy. Dipolarizationis moving Earthward. (Awaits full resolution/confirmationby multiple spacecraft – THEMIS)

  10. Nakamura et al., GRL, 2004 Average(median) scales are 0.17 (0.13) per 1000km => scale size = 2-3REDusk edge is sharper than dawn edge

  11. Nakamura et al., 2005

  12. Nakamura et al 2004

  13. Thomson et al, 2005; Asano et al., 2004; Runov et al., 2003 • Nakamura et al., 2002 • Can be c/wpi thick • Can filament/bifurcate

  14. Dissipation through Alfvenwave coupling? POLAR Poynting Flux: Keiling et al., 2000 Wygant et al., 2000 Important for ionospheric particle acceleration. Kinetic at POLAR altitudes (6RE), active-time (mostlysubstorm recovery), map topoleward auroral boundary.

  15. Alfven waves: importantenergetically Angelopoulos et al, 2002

  16. Alfven waves: kinetic to the source Angelopoulos et al, 2002

  17. x Substorm study on Feb 26, 2008 (Angelopoulos et al., Science 2008) Probe locations 2008-02-26 04:50UT P3 P1 P2 P4 P5 y

  18. First Event Second Event

  19. Other substorm signatures: Currents, Pulsations

  20. Reconnection onset associatedwith onset of large flux transport(inflow towards the Rx site at P1, P2) Angelopoulos et al., 2008b (reply)

  21. Tail substorm signatures: Fields, Flows, Distributions V┴ V║ P1 P2 V┴ P1 P2 V║ Similar toHoshino et al., 1998 Similar to Nagai et al., 2001

  22. Timing on the ground and in space: TRx 2nd 2nd 1st 1st 3rd 3rd TAI TCD PSBL NS P1 P2 electrons ions

  23. 2008-Feb-22 event Liu et al., 2008

  24. 2008-Feb-16 event Gabrielse et al., 2008

  25. 2008-Mar-01 event Runov et al., 2008

  26. 2nd 2nd 2nd 1st 1st 1st 3rd 3rd 3rd Summary of timing results Note: this is not the classical time sequence: Aurora brightens before near Earth dipolarization Moreover the time delay seems short for Alfven wave propagation Outside-In model Inside out model Reconnection Aurora Current Disruption THEMIS finds:

  27. Open Questions from 2008: • How does Rx communicate with and power aurora so fast (96s)? • What preconditions the tail to reconnect? • Spontaneous tearing? • Driven by ballooning or KH instabilities and cross-scale coupling? • How can mapping be so distorted? • Need to model stretching using THEMIS data for validation (MHD, Tsyganenko) • Consequences of tail stretching for tail stability, particledynamics and wave growth?

  28. Beyond the driver:fate of the fast flows? • Earthward flows contain a significant part of the energy from the reconnection process. Yet their dissipation process is unclear. • Recent studies of the interface between the fast flows and the surrounding medium confirms earlier results, leads to new appreciation of a non-linear (steepened, self-similar, kinetic) interaction of the flows with the ambient medium, resembling a shock wave. Tangential discontinuity is host to interesting Hall physics. • Recent multipoint studies by THEMIS reveal that the injection of plasma to the near-Earth environment is composed of localized (1-2RE) dipolarization fronts that set up vortical structures [Keiling et al., 2008] but may also result in turbulent mixing and current filamentation/heating.

  29. Sergeev et al, 2009

  30. Inward dipolarization: results • Sharp dipolarization fronts: • Have scale size L~500km, i.e., sub-gyroradius, yet they: • Retain their structure/coherence as they travel through stationary plasma • Host a variety of waves, in low hybrid range resembling low hybrid cavitiesin the ionosphere and plasma sheet observed by Cattell et al • Electron heating is observed: • in conjunction with those waves • in conjunction with density depletions at the interface of cold/hot plasma • Ion heating is observed: • In conjunction with the approaching structure, but is more gradual • Flow acceleration can be understood as: • imbalance between pressure/tension [Shanshan Li, 2009, in preparation] • Ion heating can be traced to: • dissipation at the interfaces [Xiaojia Zhang, 2009, in preparation]

  31. Non-linear phenomena within the BBFs/dipolarization Ergun et al, PHP, 2009

  32. Electrostatic Hole Properties (Anderson et al., PHP 2009)

  33. Electrostatic Hole Properties Speed ~ 0.3c LII ~ 50lDeF ~ kTe~3kV

  34. THEMIS configuration and Bz time series during 0745-0805 UT ~3 min 300 km/s

  35. P1 @ [-20.1, -0.6 -1.5] GSM 1.25 s Assuming 300 km/s propagation velocity, the DF thickness is ~400 km < ion thermal gyroradius in the upstream field; comparable to the ion skin depth.

  36. P3 @ [-11.1, -2.8, -2.1] Bz decrease 1.3 s ~400 km A short decrease (~1 s -> 300 km) in Bz (and occasionally other components as well as Bt) prior to the dipolarization front: due to the approaching current layer. Diamagnetic effect(30sec ->2RE)

  37. P5 @ [-11.0, -1.9, -3.3] Increase of Pm Earlier than P3/P4 Interpretation scheme

  38. P1 P2 P3 P4 Angelopoulos et al., 2009 P5

  39. P1 P2 P4

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