1. PARTICLES IN THE MAGNETOSPHERE
The main particle populations are:
-- plasmasphere -- ring current
-- radiation belts -- plasma sheet
-- boundary layers (magnetosheath, mantle)
-- polar wind
We have discussed the radiation belts extensively, and the plasma sheet to some extent. We will return to the plasma sheet when discussing magnetic storms.
The plasmasphere represents the relatively cold ionospheric plasma (~ .3 eV or T ~ 2000 K) which is co-rotating with the earth (frictional coupling).
ASEN 5335 Aerospace Environments -- Magnetospheres

2. ASEN 5335 Aerospace Environments -- Magnetospheres
Principal Plasma Populations in Earth’s Magnetosphere
ASEN 5335 Aerospace Environments -- Magnetospheres

3. ASEN 5335 Aerospace Environments -- Magnetospheres
The Plasmapause
The outer boundary of the plasmasphere, at about 4 RE, is where the plasma density undergoes a sudden drop. This is the plasmapause.
Ring Current
However, the plasmapause boundary is very dynamic, and varies between about 3 to 6 RE, sometimes getting as low as 2 RE.
Note that the plasmasphere overlaps a considerable part of the radiation belt region as well as the ring current. However, these represent different particle energy populations.
Radiation Belts
ASEN 5335 Aerospace Environments -- Magnetospheres

4. ASEN 5335 Aerospace Environments -- Magnetospheres
Plasmapause Boundary
Now, the co-rotating plasmasphere sets up a "co-rotation" electric field (to a stationary observer):
Outside the plasmapause the plasma is not co-rotating, and the circulation there is determined by the cross-tail potential.
Essentially, the plasmapause represents the boundary where these two electric fields are of the same order:
Co-rotation
E-field
Dawn-
Dusk
E-field
where BE = equatorial magnetic flux density at the surface, L = distance in RE, and RE = radius of earth.
ASEN 5335 Aerospace Environments -- Magnetospheres

5. ASEN 5335 Aerospace Environments -- Magnetospheres
Putting in numbers,
mVm-1
~ 1 mVm-1 at 4 RE
Put another way, the plasmapause represents the boundary between the "inner magnetosphere" and "outer magnetosphere" plasma circulation patterns. The former is co-rotating, and the latter is strongly influenced by the solar wind interaction (see following figure):
Viewed this way, one expects intensification of the outer magnetospheric circulation to lead to a contraction of the plasmasphere (inward movement of the plasmapause). This indeed happens (see subsequent figures).
In fact, it is thought that the intensified outer circulation leads to a peeling off of outer layers of the plasmasphere, which are then lost as detached plasma chunks in the magnetotail and solar wind.
ASEN 5335 Aerospace Environments -- Magnetospheres

6. Plasmasphere = corotating ionospheric plasma
Plasmapause = boundary between corotating plasma and convecting plasma

7. ASEN 5335 Aerospace Environments -- Magnetospheres
Daily variation of the plasmapause in relation to plasma convection in the magnetospheric equatorial plane
ASEN 5335 Aerospace Environments -- Magnetospheres

8. Solar Wind Driven Convection
EARTH
Solar Wind Driven Convection
Side View
Solar
Wind
Equatorial Plane
Polar View
Connected to solar wind
Closed magnetic field

9. Dissecting the Magnetosphere
Open field region Closed field region

10. ASEN 5335 Aerospace Environments -- Magnetospheres
The EUV Imager on the IMAGE satellite is able to provide information on the
plasmasphere distribution, boundary, aurora and other geospace properties.
Earth's plasmasphere at 30.4 nm (He+ resonant emission). This image from the Extreme Ultraviolet Imager was taken at 07:34 UTC on 24 May 2000, at a range of 6.0 Earth radii from the center of Earth and a magnetic latitude of 73 N. The Sun is to the lower right, and Earth's shadow extends through the plasmasphere toward the upper left. The bright ring near the center is an aurora, and includes emissions at wavelengths other than 30.4 nm. (From Sandel, B. R., et al., Space Sci. Rev., 109, 25, 2003.)
ASEN 5335 Aerospace Environments -- Magnetospheres

11. ASEN 5335 Aerospace Environments -- Magnetospheres
Satellite observations of ion density, showing the plasmapause at several Kp levels
L 
ASEN 5335 Aerospace Environments -- Magnetospheres

12. Flow patterns for cross-tail fields of 0.2 and 0.6 mV/m
For 0.6 mVm-1, the
outer magnetosphere
circulation “intrudes”
upon the plasmasphere.
ASEN 5335 Aerospace Environments -- Magnetospheres

13. ASEN 5335 Aerospace Environments -- Magnetospheres
Detaching of plasma due to changing flow patterns during a magnetic storm
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14. ASEN 5335 Aerospace Environments -- Magnetospheres
“Filling In” of Plasmasphere
With the decay of magnetic activity, the magnetospheric circulation and electric fields return to their previous state but now the outer tubes of magnetic flux are devoid of plasma.
These gradually refill from the ionosphere over a period of days.
The rate of filling is determined by the diffusion speed of protons (formed in the upper ionosphere by charge exchange between hydrogen atoms and oxygen ions) coming up along the field, and by the volume of the flux tube which varies as L4. It therefore takes much longer to refill tubes originating at higher latitude.
Observations of the filling are shown in the following figure. Since active periods may recurr every few days there will be times when the outer tubes are never full and the plasmasphere has some degree of depletion.
ASEN 5335 Aerospace Environments -- Magnetospheres

15. ASEN 5335 Aerospace Environments -- Magnetospheres
“Filling In” of Plasmasphere
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16. ASEN 5335 Aerospace Environments -- Magnetospheres

17. BOUNDARY LAYERS AND PARTICLE TRANSFER TO THE PLASMA SHEET
Solar wind particles find their way from the magnetosheath into the cusp region. There is experimental evidence for this entry, in that particles with characteristic "magnetosheath energy" (i.e., less than 1 keV) have been observed over a limited region centered around 77° magnetic latitude and noon (see following figures).
Such particles on newly-merged field lines flow down towards the earth, mirror there, and then return to find themselves on a field line sweeping back towards the tail. These particles form a particle population known as the "plasma mantle" (see following figures).
At many (~100) RE, these particles are swept into the plasma sheet. Another closer (~ 50 RE) source of plasma sheet particles is the polar wind emanating from the ionosphere at high latitudes (see following figures).
ASEN 5335 Aerospace Environments -- Magnetospheres

18. ASEN 5335 Aerospace Environments -- Magnetospheres
Details of the
Cusp Region
Plasma Mantle
Magnetosheath
Entry
Layer
Low-Latitude Boundary Layer
ASEN 5335 Aerospace Environments -- Magnetospheres

19. Cusp signatures from the IMAGE satellite
Proton precipitation patterns:
Cusp & plasma tail footprint
24 June 2000
~0200 UT
ASEN 5335 Aerospace Environments -- Magnetospheres

20. ASEN 5335 Aerospace Environments -- Magnetospheres
Note: since ~ particles/s impact the dayside magnetopause, and ~ 1026 particles/s are estimated to enter the plasma sheet, only 1% efficiency of this process is required.
ASEN 5335 Aerospace Environments -- Magnetospheres

21. ASEN 5335 Aerospace Environments -- Magnetospheres
Particle Flow in the Merging - Reconnection - Convection Process
dB/dt ≠ 0, induces
E-field, energize particles
“Dipolarization” of the B-field
During the return flow, the particles are also energized in their attempt to satisfy the first adiabatic invariant,
= const
As particles convect towards the earth, B increases, therefore
the particle energies increase. The energy comes from the E-field.
ASEN 5335 Aerospace Environments -- Magnetospheres

22. ASEN 5335 Aerospace Environments -- Magnetospheres
Some of the sunward-convecting particles precipitate into the upper atmosphere and produce the aurora.
video
ASEN 5335 Aerospace Environments -- Magnetospheres

23. ASEN 5335 Aerospace Environments -- Magnetospheres
Numerical Simulation of the Solar Wind - Magnetosphere Interaction
video
ASEN 5335 Aerospace Environments -- Magnetospheres