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

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

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.)

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.)

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)

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

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

gn

etos

ph

ereM

ag

neto

sp

here

Ion

os

ph

ere

Ion

os

ph

ere

X-line controls energy conversion and inputX-line Energy conversion Energy input

Change of field topology

(Laitinen et al., 2006, 2007)

X-line controls energy conversion and inputX-line Energy conversion Energy input

Conversion fromplasma to magneticenergy

(Laitinen et al., 2006, 2007)

X-line controls energy conversion and inputX-line Energy conversion Energy input

Energy flux fromsolar wind intomagnetosphere

(Laitinen et al., 2006, 2007)

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)

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)

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)

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

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)

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?

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)

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 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.)

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

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