Transcript How the Solar Wind and Outer Magnetosphere Drive the Radiation

Inner magnetospheric dynamics:
How the solar wind and outer
magnetosphere drive the
radiation belts and ring current
- Recent advances
- Challenges
Tuija I. Pulkkinen
Finnish Meteorological Institute
Helsinki, Finland
Space weather chain
1. Solar activity drives solar wind structures and dynamics
2. Solar wind
interaction drives
magnetospheric
dynamics
3. Inner magnetosphere
responds to solar wind and
magnetospheric driving
Inner magnetosphere
plasmas
• Plasmasphere
• 1-10 eV ions
(Goldstein et al.)
• ionospheric origin
• Ring current
• 50-500 keV ions
• both ionospheric and
solar wind origin
(Goldstein et al.)
• Outer radiation belt
• 0.1-10 MeV electrons
• magnetospheric origin
(Reeves et al.)
Inner magnetosphere
models
• Plasmasphere
• cold ion drifts
(Goldstein et al.)
• electric field
• Ring current
• particle tracing
• drift approximation
not always valid!
(Goldstein et al.)
• Outer radiation belt
• diffusion models
• Mostly: no couplings!
(Reeves et al.)
Large-scale models for inner magnetosphere
Fluid description
• MHD simulations solve selfconsistent (single-) fluid
equations
Kinetic description
• RAM-codes solve the bounceaveraged 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)
Space weather chain
1. Solar activity: what is the solar wind ?
MHD simulations:
2. What are the
key processes ?
-reconnection
-energy transport
Outer boundary:
solar driving
Inner boundary:
inner magnetosphere
boundary condition
3. What are the couplings
to the ionosphere and
inner magnetosphere ?
GUMICS-4 global MHD simulation
Couplings
Solar wind
and IMF
Ideal MHD
in solar wind
and magnetosphere
Mapping
to ionosphere
- precipitation
- FAC
Electrostatic
equations in
ionosphere
Mapping to
magnetosphere
- potential
Solar EUV
proxy F10.7
Earth’s
dipole field
Ionosphere
Models
Magnetosphere
Inputs
X-line controls energy conversion and input
X-line
Energy conversion
Energy input
Change of
field topology
(Laitinen et al., 2006, 2007)
X-line controls energy conversion and input
X-line
Energy conversion
Energy input
Conversion from
plasma to magnetic
energy
(Laitinen et al., 2006, 2007)
X-line controls energy conversion and input
X-line
Energy conversion
Energy input
Energy flux from
solar wind into
magnetosphere
(Laitinen et al., 2006, 2007)
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
high P
low P
Ionospheric dissipation:
• driven by frontside
reconnection (IMF Bz),
rate controlled by Psw
(Pulkkinen et al, JASTP, 2007)
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)
Both Bz and Psw control energy entry
Energy entry:
• driven by reconnection,
(IMF Bz), modulated by
pressure Psw
high P
Energy conversion:
• strong B-annihilation at
the nose, flux generation
behind cusps
low P
Ionospheric dissipation:
• driven by frontside
reconnection (IMF Bz),
rate controlled by Psw
(Pulkkinen et al, JASTP, 2007)
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)
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
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
What creates Dst?
Early main phase:
• tail current intensifies,
causes Dst drop
magnetopause
ring
current
tail
current
Later main phase:
• ring current develops,
causes Dst minimum
Moderate storms:
• tail current dominates
Intense storms:
• ring current dominates
(Ganushkina et al, 2004)
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
What drives inner magnetosphere fluxes?
Standard case:
• constant dipole B-field,
Volland-Stern convection
20 - 80 keV
80 - 200 keV
Dipole
• low fluxes, low energy
Empirical model case:
• time-dependent B-field,
convection from
ionosphere (Boyle)
Empirical fields
• larger fluxes, more highenergy particles
(Ganushkina et al., 2006)
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
Inner magnetosphere
interactions
• 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.)
Inner magnetosphere
challenges
• Generation of waves
Pulkkinen et al.
Cosmic vision call 2007
• interactions between
plasmas and fields
• Net balance between
sources and losses
• identification of all
processes
• External driving
• solar wind,
magnetosphere,
and ionosphere
WARP
Waves and
Acceleration
of Relativistic
Particles
Inner magnetosphere
challenges
• Wave properties
Pulkkinen et al.
Cosmic vision call 2007
• 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 and
Acceleration
of Relativistic
Particles