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High Latitude Electrodynamics

High Latitude Electrodynamics. Ying Zou (UCLA). Convection & Current system in the magnetosphere. http://stream2.cma.gov.cn/pub/comet/SpaceWeather/comet/hao/aurora/txt/x_r_2_0.htm. Magnetopause current Tail current Ring current Field aligned current: Region 1 & Region 2. [Hughes, 1995].

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High Latitude Electrodynamics

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  1. High Latitude Electrodynamics Ying Zou (UCLA)

  2. Convection & Current system in the magnetosphere http://stream2.cma.gov.cn/pub/comet/SpaceWeather/comet/hao/aurora/txt/x_r_2_0.htm Magnetopause current Tail current Ring current Field aligned current: Region 1 & Region 2 [Hughes, 1995] Anti-sunward flow across polar cap Return flow at lower latitude

  3. Convection & Current system in the ionosphere noon E Upward Downward midnight Region 1: higher latitude Region 2: lower latitude Both dependent on IMF, more pronounced during southward IMF : relatively symmetric two cell : rounded + crescent shapes : structured, confined, slow [Ruohoniemi and Greenwald., 2005] [Papitashvili et al., 2002]

  4. Horizontal current Conductivity Electric field Motion due to collisions: Electrons: ExB Ions: reduced ExB + addition component //E Current: ⊥E: Hall current ∥E: Pedersen current Hall current Pedersen current [Baumjohann and Treumann, 2000] Hall: opposite to the convection, because ions drift slower than the electrons Pedersen: meridional, dusk to dawn forming closed loop between region 1&2

  5. Meso-scale convection and field aligned currents SAPS Fast flow channels Sub-Auroral Polarization Stream (SAPS) Fast flow channels/Bursty bulk flows Session: a. Substorm Expansion Onset b. Tail-inner Magnetosphere Interactions c. Reconnection in the magnetosphere Session: Storm-Time Inner Magnetosphere-Ionosphere Convection

  6. Sub-Auroral Polarization Stream (SAPS) Azimuthal gradient of ring current  Region 2 [Goldstein, 2005a] Weak or no electron precipitation: Low conductivity J=σ · E Low σ Large E  high EXB drift stream (SAPS) Region 1 Region 2 Pedersen [Clausen et al, 2012] Top: Low electron density Bottom: Fast westward stream at low density region (SAPS) poleward [Anderson et al, 1993]

  7. Sub-Auroral Polarization Stream (SAPS) Ring current Ionospheric poleward E field <-> Radially outward E field from inner edge of R2 to that of electron plasma sheet <-> Strong westward flow ripping away portion of plasmasphere Region 2 Dusk Dawn Plasmasphere Electron plasma sheet [Goldstein et al, 2005b] SAPS modifies the duskside plasmapause location, and this has been confirmed by the comparison of simulation and observation [Goldstein et al, 2003]

  8. Bursty Bulk flows (BBFs) • Bursty bulk flows (BBFs), High speed flows, Dipolarizations, Bubbles , Ionospheric fast flows, Auroral streamers… • Meso-scale flux tube in the plasma sheet • Duration: 1-2 min • Longitudinal width: a few Re ∆Bz Ey Bubble: Low entropy: PV P: plasma pressure V: volume of flux tube ∆Ji/Ji0 ∆Je/Je0 Uniform PS Stratified PS with bubbles ∆N/N0 ∆Ti/Ti0 Moving fast ∆Te/Te0 Vx [Chen and Wolf, 1993] [Runov et al., 2009]

  9. Bursty Bulk flows (BBFs) Low plasma pressure  small cross tail current  field-aligned current Upward FAC: auroral streamer Cross-bubble E field: fast, equatorward-orientated ionospheric flow E streamer V=EXB [Sergeev, 1999] Ionosphere footprint of BBFs: Auroral streamers + ionospheric fast flows This has also been well confirmed by observation.

  10. Summary Auroral streamers, coming from the auroral poleward boundary, extend equatorward which may result in substorm disturbances. • Large scale: Two cell convection Region 1 and 2 field aligned currents, horizontal currents • Meso scale: SAPS Bursty bulk flow (BBF) and associated ionosphere footprints (streamers and ionospheric fast flows) [Nishimura et al, 2010]

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