High Latitude Electrodynamics Ying Zou UCLA Convection Current

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High Latitude Electrodynamics Ying Zou (UCLA)

High Latitude Electrodynamics Ying Zou (UCLA)

Convection & Current system in the magnetosphere http: //stream 2. cma. gov. cn/p ub/comet/Space.

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

Convection & Current system in the ionosphere noon E midnight Upward : relatively symmetric

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

Horizontal current Motion due to collisions: Electrons: Ex. B Ions: reduced Ex. B +

Horizontal current Motion due to collisions: Electrons: Ex. B Ions: reduced Ex. B + addition component //E Current: ⊥E: Hall current ∥E: Pedersen current Conductivity Hall current Electric field 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

Meso-scale convection and field aligned currents SAPS Fast flow channels Sub-Auroral Polarization Stream (SAPS)

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

Sub-Auroral Polarization Stream (SAPS) Azimuthal gradient of ring current Region 2 [Goldstein, 2005 a]

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

Sub-Auroral Polarization Stream (SAPS) Ring current Ionospheric poleward E field <-> Radially outward E

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

Bursty Bulk flows (BBFs) • Bursty bulk flows (BBFs), High speed flows, Dipolarizations, Bubbles

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 ∆Bz Longitudinal width: a few Re Ey Bubble: Low entropy: PV P: plasma pressure V: volume of flux tube Uniform PS ∆Ji/Ji 0 ∆Je/Je 0 Stratified PS with bubbles Moving fast ∆N/N 0 ∆Ti/Ti 0 ∆Te/Te 0 Vx [Chen and Wolf, 1993] [Runov et al. , 2009]

Bursty Bulk flows (BBFs) Low plasma pressure small cross tail current field-aligned current Upward

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

Auroral streamers, coming from the auroral poleward boundary, extend equatorward which may result in

Auroral streamers, coming from the auroral poleward boundary, extend equatorward which may result in substorm disturbances. [Nishimura et al, 2010] Summary • 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)