The Magnetospheric Cusp: Solar Wind – Magnetosphere – Ionosphere – Thermosphere Coupling
Inner magnetospheric dynamics: How the solar wind and outer magnetosphere drive the radiation belts...
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Transcript of Inner magnetospheric dynamics: How the solar wind and outer magnetosphere drive the radiation belts...
![Page 1: Inner magnetospheric dynamics: How the solar wind and outer magnetosphere drive the radiation belts and ring current - Recent advances - Challenges Tuija.](https://reader034.fdocuments.net/reader034/viewer/2022042822/56649e0c5503460f94af4a63/html5/thumbnails/1.jpg)
Inner magnetospheric dynamics: How the solar wind and outer magnetosphere drive theradiation belts and ring current
- Recent advances - Challenges
Tuija I. PulkkinenFinnish Meteorological Institute Helsinki, Finland
![Page 2: Inner magnetospheric dynamics: How the solar wind and outer magnetosphere drive the radiation belts and ring current - Recent advances - Challenges Tuija.](https://reader034.fdocuments.net/reader034/viewer/2022042822/56649e0c5503460f94af4a63/html5/thumbnails/2.jpg)
Space weather chain
1. Solar activity drives solar wind structures and dynamics
2. Solar windinteraction drives magnetosphericdynamics
3. Inner magnetosphereresponds to solar wind and magnetospheric driving
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Inner magnetosphereplasmas• Plasmasphere
• 1-10 eV ions
• ionospheric origin
• Ring current
• 50-500 keV ions
• both ionospheric and solar wind origin
• Outer radiation belt
• 0.1-10 MeV electrons
• magnetospheric origin
(Goldstein et al.)
(Goldstein et al.)
(Reeves et al.)
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Inner magnetospheremodels• Plasmasphere
• cold ion drifts
• electric field
• Ring current
• particle tracing
• drift approximation not always valid!
• Outer radiation belt
• diffusion models
• Mostly: no couplings!
(Goldstein et al.)
(Goldstein et al.)
(Reeves et al.)
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Large-scale models for inner magnetosphere
Fluid description
• MHD simulations solve self-consistent (single-) fluid equations
Kinetic description
• RAM-codes solve the bounce-averaged Vlasov equation in given electromagnetic fields
Empirical models
• magnetic field evolution from fitting empirical models to observations
• particle tracing in drift approximation
Difficulties in modeling the inner magnetosphere
• coupling to ionosphere and solar wind driver important
• coupling of large-scale and microscale processes
• multiple plasma populations (cold plasmasphere, plasma sheet, ring current, radiation belts)
• highly varying E and B in multiple scales
• poor observational coverage (especially electric field)
![Page 6: Inner magnetospheric dynamics: How the solar wind and outer magnetosphere drive the radiation belts and ring current - Recent advances - Challenges Tuija.](https://reader034.fdocuments.net/reader034/viewer/2022042822/56649e0c5503460f94af4a63/html5/thumbnails/6.jpg)
Space weather chain
1. Solar activity: what is the solar wind ?
2. What are thekey processes ?-reconnection-energy transport
3. What are the couplingsto the ionosphere and inner magnetosphere ?
MHD simulations:
Outer boundary: solar driving
Inner boundary:inner magnetosphere
boundary condition
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GUMICS-4 global MHD simulation
Inputs
Solar windand IMF
Solar EUVproxy F10.7
Earth’s dipole field
Models
Ideal MHD Ideal MHD in solar windin solar windand magneto-and magneto-spheresphere
ElectrostaticElectrostaticequations inequations inionosphereionosphere
Couplings
Mapping to ionosphere- precipitation - FAC
Mapping tomagnetosphere- potential
Ma
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ag
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sp
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Ion
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ere
Ion
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ere
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X-line controls energy conversion and inputX-line Energy conversion Energy input
Change of field topology
(Laitinen et al., 2006, 2007)
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X-line controls energy conversion and inputX-line Energy conversion Energy input
Conversion fromplasma to magneticenergy
(Laitinen et al., 2006, 2007)
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X-line controls energy conversion and inputX-line Energy conversion Energy input
Energy flux fromsolar wind intomagnetosphere
(Laitinen et al., 2006, 2007)
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high P
low P
Both Bz and Psw control energy entry
Energy entry:
• driven by reconnection, (IMF Bz), modulated by pressure Psw
Energy conversion:
• strong B-annihilation at the nose, flux generation behind cusps
Ionospheric dissipation:
• driven by frontside reconnection (IMF Bz), rate controlled by Psw
(Pulkkinen et al, JASTP, 2007)
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Both Bz and Psw control energy entry
Energy entry:
• driven by reconnection, (IMF Bz), modulated by pressure Psw
Energy conversion:
• strong B-annihilation at the nose, flux generation behind cusps
Ionospheric dissipation:
• driven by frontside reconnection (IMF Bz), rate controlled by Psw
(Pulkkinen et al, JASTP, 2007)
![Page 13: Inner magnetospheric dynamics: How the solar wind and outer magnetosphere drive the radiation belts and ring current - Recent advances - Challenges Tuija.](https://reader034.fdocuments.net/reader034/viewer/2022042822/56649e0c5503460f94af4a63/html5/thumbnails/13.jpg)
high P
low P
Both Bz and Psw control energy entry
Energy entry:
• driven by reconnection, (IMF Bz), modulated by pressure Psw
Energy conversion:
• strong B-annihilation at the nose, flux generation behind cusps
Ionospheric dissipation:
• driven by frontside reconnection (IMF Bz), rate controlled by Psw
(Pulkkinen et al, JASTP, 2007)
![Page 14: Inner magnetospheric dynamics: How the solar wind and outer magnetosphere drive the radiation belts and ring current - Recent advances - Challenges Tuija.](https://reader034.fdocuments.net/reader034/viewer/2022042822/56649e0c5503460f94af4a63/html5/thumbnails/14.jpg)
Tail dynamics determined by driver • Increasing EY = V.Bz changes magnetospheric response
• increasing Bz stabilizes tail• increasing V increases fluctuations and variability
original run increased Bz increased V
(Pulkkinen et al, GRL, 2007)
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Conclusions from MHD simulations• Energy entry controlled by reconnection
• energy input through magnetopause determines ionospheric dissipation and tail reconnection efficiency
• Solar wind speed is a key controlling factor
• for the same Ey:
• higher V and lower IMF Bz higher activity
• lower V and higher IMF Bz lower activity
• for the same pressure Psw:
• higher V and lower N higher activity
• lower V and higher N lower activity
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Empirical magnetic field modeling
Event-oriented magnetic field models
• empirical formulation of magnetospheric current systems based on Tsyganenko models
• give evolution of current systems for specific events
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magneto-pause
ringcurrent
tailcurrent
What creates Dst?
Early main phase:
• tail current intensifies, causes Dst drop
Later main phase:
• ring current develops, causes Dst minimum
Moderate storms:
• tail current dominates
Intense storms:
• ring current dominates (Ganushkina et al, 2004)
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Drift modeling of particle motion
Particle motion in drift approximation
• conservation of 1st and 2nd adiabatic invariants
• prescribed electric and magnetic fields (test particle approach)
• gives ion energy distributions in the inner magnetosphere
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What drives inner magnetosphere fluxes?
20 - 80 keV 80 - 200 keVStandard case:
• constant dipole B-field, Volland-Stern convection
• low fluxes, low energy
Empirical model case:
• time-dependent B-field, convection from ionosphere (Boyle)
• larger fluxes, more high-energy particles
Dipole
Empirical fields
(Ganushkina et al., 2006)
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Conclusions from empirical models• Inner magnetosphere energy density controlled by
(small-scale) electric and magnetic field variations
• rapid, small-scale variations lead to higher fluxes and more energization of the ring current
• Accurate representation of the large-scale fields is critical for ring current evolution
• B-field variations change particle orbits which leads to losses to magnetopause
• B-field and E-field variations energize particles much more than adiabatic inward convection
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Inner magnetosphereinteractions• Plasmasphere
• supports low-frequency waves
• Ring current
• modifies magnetic field
• participates in wave generation
• Outer radiation belt
• electrons accelerated and scattered by waves
(from Reeves, after Summers et al.)
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Inner magnetospherechallenges• Generation of waves
• interactions between plasmas and fields
• Net balance between sources and losses
• identification of all processes
• External driving
• solar wind, magnetosphere, and ionosphere
WARP Waves andAcceleration of RelativisticParticles
Pulkkinen et al.Cosmic vision call 2007
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Inner magnetospherechallenges• Wave properties
• chorus, hiss, EMIC wave amplitudes, growth rates, location
• Wave-particle interactions
• energy, pitch-angle diffusion
• External driving
• plasma sheet sources, E & B fields, diffusion rates, ionospheric outflow
• solar wind coupling
WARP Waves andAcceleration of RelativisticParticles
Pulkkinen et al.Cosmic vision call 2007