The Magnetospheric Cusp: Solar Wind – Magnetosphere – Ionosphere – Thermosphere Coupling
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Transcript of The Magnetospheric Cusp: Solar Wind – Magnetosphere – Ionosphere – Thermosphere Coupling
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June 19, 2012 GEM - Cusp Tutorial - R. J. Strangeway 1
The Magnetospheric Cusp: Solar Wind – Magnetosphere –
Ionosphere – Thermosphere Coupling
R. J. StrangewayIGPP & ESS /UCLA
Special Acknowledgement to J. Raeder, UNH, and the Community Coordinated Modeling Center.
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Outline
• Introduction – why talk about the cusp?
• Reconnection topology and the cusp – where is the cusp?
• Cusp ion dispersion at middle altitudes – where is the reconnection?
• Cusp ion dispersion at low altitudes – multiple cusps?
• Field-aligned currents – Force balance and cusp dynamics
• Ion outflows – Joule dissipation and electron precipitation
• Neutral upwelling – Important for satellite drag
• Summary
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What is so Special About the Cusp?
• The cusp is the region that provides the most direct path from the solar wind to the ionosphere and thermosphere
• The cusp requires an understanding of several processes: Reconnection topology and Interplanetary Magnetic Field direction
effects (IMF By)
Steady-state, multi-point, and time-varying reconnection
Particle kinematics (time-of-flight, velocity dispersion)
Field-aligned current generation
Joule Dissipation – ion and neutral upwelling and outflows
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Outline
• Introduction – why talk about the cusp?
• Reconnection topology and the cusp – where is the cusp?
• Cusp ion dispersion at middle altitudes – where is the reconnection?
• Cusp ion dispersion at low altitudes – multiple cusps?
• Field-aligned currents – Force balance and cusp dynamics
• Ion outflows – Joule dissipation and electron precipitation
• Neutral upwelling – Important for satellite drag
• Summary
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Anti-parallel merging [Luhmann, 1984]
Luhmann et al. [1984] used Spreiter gas dynamic model to map IMF to the magnetopause
Contours show regions of anti-parallel merging (up to 90˚)
Crooker [1985] used superposition of IMF and Chapman-Ferraro field at magnetopause, considered component merging
Cooling [2001] extended Luhmann et al. [1984] to allow for component merging
B = (0,0,1)(northward)
B = (0,1,0)(By only)
B = (0,0,-1)(southward)
B = (0,-1,-1)
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Cooling Model – Component Merging
Luhmann et al. [1984] Cooling et al. [2001]
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Outline
• Introduction – why talk about the cusp?
• Reconnection topology and the cusp – where is the cusp?
• Cusp ion dispersion at middle altitudes – where is the reconnection?
• Cusp ion dispersion at low altitudes – multiple cusps?
• Field-aligned currents – Force balance and cusp dynamics
• Ion outflows – Joule dissipation and electron precipitation
• Neutral upwelling – Important for satellite drag
• Summary
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Trattner et al. [2012] component and anti-parallel merging
Characteristic signature of cusp is energy dispersed ions
Plot shows Polar data at ~ 5.5 Re
Mapping to magnetopause (source region) uses time-of-flight energy dispersion comparing downgoing to reflected [Onsager et al., 1990]
Multiple dispersion events could be because of:•Multiple reconnection sites•Time-varying reconnection•High latitude and low-latitude reconnection (different history)
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Trattner et al. [2012], different topology
By-dominated – nearly anti-parallel, multiple X-lines?
Southward Bz – anti-parallel, multiple injections from same point
Northward Bz – component merging, extended region
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IMF By – Hemispherical Asymmetry
Østgaard et al. [2005] investigate cusp proton precipitation asymmetry using IMAGE (viewing north) and Polar (viewing south)
Cusp precipitation consistent with locus of anti-parallel merging
Bx contributes to hemi-spherical differences
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Outline
• Introduction – why talk about the cusp?
• Reconnection topology and the cusp – where is the cusp?
• Cusp ion dispersion at middle altitudes – where is the reconnection?
• Cusp ion dispersion at low altitudes – multiple cusps?
• Field-aligned currents – Force balance and cusp dynamics
• Ion outflows – Joule dissipation and electron precipitation
• Neutral upwelling – Important for satellite drag
• Summary
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Newell et al. [2007] – Forward Dispersion
DMSP “FAST”
Note: At low altitudes the spacecraft moves through structures
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Newell et al. [2007] – Reverse Dispersion
DMSP “FAST”
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Newell et al. [2007] – Double Cusp
DMSP “FAST”
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Double Cusp – Wing et al. [2001]
Wing et al. [2001] argue that double cusps are because the dispersing ions come from two different reconnection sites
DMSP data from Newell et al. [2007] (not the same event)
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Outline
• Introduction – why talk about the cusp?
• Reconnection topology and the cusp – where is the cusp?
• Cusp ion dispersion at middle altitudes – where is the reconnection?
• Cusp ion dispersion at low altitudes – multiple cusps?
• Field-aligned currents – Force balance and cusp dynamics
• Ion outflows – Joule dissipation and electron precipitation
• Neutral upwelling – Important for satellite drag
• Summary
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Force Balance
For simplicity assume neutrals at rest (frame of reference)
Ionospheric flow:
Frozen-in electrons:
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IMF By-Dependent Convection
Burch et al. [1985]
By > 0 By < 0
Currents Convection
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Weimer [2001] FAC morphology
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FAST Orbit 8276 – Strong IMF By
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MHD FAC Predictions
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Field Topology – Shock Passage
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FAST Orbit 8284 – Double Cusp?
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Outline
• Introduction – why talk about the cusp?
• Reconnection topology and the cusp – where is the cusp?
• Cusp ion dispersion at middle altitudes – where is the reconnection?
• Cusp ion dispersion at low altitudes – multiple cusps?
• Field-aligned currents – Force balance and cusp dynamics
• Ion outflows – Joule dissipation and electron precipitation
• Neutral upwelling – Important for satellite drag
• Summary
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Ion Outflows
Type 1 Type 2
Type 1 and Type 2 defined by Wahlund et al. [1992]
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Ion Outflows – Including Alfvén Waves
Type 1 Type 2
Type 1 and Type 2 defined by Wahlund et al. [1992]
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Joule Dissipation and Heating RatesPlasma frame:
Neutral frame:
Rate of temperature increase:
Minority species temperature increases more rapidly
See [Strangeway, JGR, 2012]
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Outline
• Introduction – why talk about the cusp?
• Reconnection topology and the cusp – where is the cusp?
• Cusp ion dispersion at middle altitudes – where is the reconnection?
• Cusp ion dispersion at low altitudes – multiple cusps?
• Field-aligned currents – Force balance and cusp dynamics
• Ion outflows – Joule dissipation and electron precipitation
• Neutral upwelling – Important for satellite drag
• Summary
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Cusp Statistics – Knipp et al. [2011]
Poynting flux statistics from DMSP
Southern hemisphere is mirror-reflected about noon as a function of IMF By
Events required |By| > 10 nT
(a) N:By < 0, Bz < 0; (b) N:By > 0, Bz < 0(c) N:By < 0, Bz > 0; (d) N:By > 0, Bz > 0
Red is 100 µW/m2
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Thermospheric Response – Crowley et al. [2011]
CHAMP sees strongly neutral density modulation near the cusp
Modified TIME-GCM using real-time AMIE data shows enhanced densities too
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Poynting Flux Versus Neutral Density – Crowley et al. [2011]
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Small scale FACs – Lühr et al. [2004]
CHAMP also sees large-amplitude small-scale FACs in the Cusp
Lühr et al [2004] argue that these can significantly enhance the heating
Heating rate depends on E2,
But there is an issue with time scales, neutrals heat much more slowly than ions
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Summary
• Reconnection topology controls the location of the cusp
• There is both a high latitude (anti-parallel merging) and low latitude (component merging) source of dispersing ions – depends on IMF orientation
• Field-aligned currents and Joule dissipation in the ionosphere strongly affected by IMF By – I suggest this is high latitude merging
• Ion outflows and neutral upwelling both appear to be associated with Joule dissipation – question of timescales for the neutrals