1
GEM (Student) Tutorial
June 23, 2002
Inner Magnetospheric Shielding,
Penetration Electric Field, and the
Plasmasphere
Jerry Goldstein, Rice University
The Plasmasphere
2
Ionospheric
outflow:
Populates
p’sphere
D. L. Carpenter (Stanford)
“Whistler” wave studies
(ground-based)
Plasmapause:
boundary where dense,
cold plasma ends
M-I Coupling: WG-1+2:
Ionospheric outflow
Wednesday 10:30-noon
Chairs: Lotko, Moore, Peterson
Chappell et al., OGO data
Magnetospheric Convection
1. Generally sunward in the inner magnetosphere
2. Southward IMF
3
Magnetospheric Convection
Explain sharp ppause:
Boundary between
corotation (refilling) and
convection
4
Magnetospheric Convection
5
Plasmapause:
Density gradient marking outer
boundary of plasmasphere-does not need to coincide with the
instantaneous boundary between
convection and co-rotation, because time
scale for p’sphere response is slower than
time scale of convection variations.
WARNING: This is a highly
oversimplified picture!
In reality, convection is
usually very nonuniform
and time-dependent
M-I Coupling: WG-2:
M’spheric convection
Tuesday 3:30-5:30pm
Chair: Ray Greenwald
Conv/corot
boundary
Plasmapause
IMAGE Extreme Ultraviolet Imager (EUV)
6
MOVIE
QuickTime™ and a
decompressor
are needed to see this picture.
EUV data 6:43-10:04, 5/24
REMOTE MEASUREMENT
The Extreme Ultraviolet (EUV) imager
looks at the plasmasphere via
7
Measuring the
Plasmasphere
IMAGE EUV
in situ
Cross-Phase
(ground magnetometer)
IM/S: WG-1:
Plasmaspheric structure
Monday 3:30-5:30pm (observations)
Chair: Dennis Gallagher
Tuesday 10:30-noon (techniques)
Chairs: Moldwin, Chi
Plasma Tails (“Plumes”)
MI Coupling: WG-1:
plasmaspheric tails (“plumes”)
Monday 10:40-noon
Chair: Tom Moore
8
Plasma Tails
“Detached”
plasma
9
The Duskside
Bulge?
Plasma Tails
As Seen in the
Ionosphere
Space Weather Implications...
10
Shielding:
the plasmasheet,
Westward currents
11
Shielding:
Convection increase
due to dawn-dusk E-->
creates partial RC
12
Shielding:
Partial RC closes in
ionosphere via fieldaligned currents
13
Shielding:
Field-aligned currents
create zonal charging.
14
Shielding:
Zonal charging creates
potential drop across IM,
creating dusk-dawn E that
opposes/cancels dawndusk convection E
15
IM Shielding
Instead of this...
E-shielding exactly
cancels Econvection
You get this...
16
IM Shielding
17
Shielding: 15 min - 1 hr
Thus, changes in Solar-wind/IMF
conditions that occur more rapidly than
the shielding time-scale allow convection
field to penetrate past the shielding layer.
E-shielding exactly
cancels Econvection
Perfect shielding might not occur even if
conditions are steady, however. (See Dick
Wolf’s tutorial.)
Penetration E-Fields
18
E-conv UP:
Sunward IM
plasma flow
E-conv
DOWN
E-shielding exactly
cancels Econvection
Tailward IM
plasma flow
Penetration E-Fields
19
E-conv UP:
Sunward IM
plasma flow
E-conv
DOWN
E-shielding exactly
cancels Econvection
Tailward IM
plasma flow
Penetration E-Fields
20
E-conv UP:
Sunward IM
plasma flow
E-conv
DOWN
E-shielding exactly
cancels Econvection
Tailward IM
plasma flow
Geomagnetic Variation of Plasmapause
Size/Shape of Plasmasphere
Depends on strength of convection
Swd IMF
Well-Shielded
Example: Plasmaspheric Erosion
following sudden turn to southward IMF.
21
Geomagnetic (Kp) Variation of Plasmapause 22
ISEE 1 (in situ)
OGO 5 (in situ)
Geomagnetic Variation of Plasmapause 23
IMAGE EUV data
QuickTime™ and a
decompressor
are needed to see this picture.
July 9, 2000:
Quiet
QuickTime™ and a
decompressor
are needed to see this picture.
Aug 11, 2000:
During/After Strong
Convection
IM E-Fields
IM/S: Tutorial:
I.M. E-fields
Monday 9:15-10am
Dick Wolf
IM/S: WG-1:
Near-Earth E-fields
Monday 1:30-3pm
Chairs: Goldstein, Liemohn
24
Simulated Penetration E-Fields
Overshielding: Shoulder
PDC
25
Simulated Penetration E-Fields
Overshielding: Shoulder
Penetration E needed to
explain shoulder (and
other meso-scale
plasmaspheric structure).
26
Ring-Current and the IM E-field
27
Penetration E
needed to
explain
observed ringcurrent (RC)
distribution.
IMAGE HENA
27-39 keV
CRCM Model, 32 keV
IM/S: WG-1:
RC/PS coupling (observations)
Tuesday 1:30-3pm
Chairs: C:son Brandt, Gallagher
RC/PS coupling (modeling)
Tuesday 3:30-5:30pm
Chairs: Liemohn, Reynolds
Conclusions
The plasmasphere is the torus of cold, dense, co-rotating plasma surrounding the Earth
out to 3-5 RE, and is populated by ionospheric outflow.
The plasmapause is the outer boundary of the plasmasphere, but does not need to
coincide with the instantaneous boundary between convection and co-rotation (the “last
closed equipotential” or LCE), because the time scale for plasmaspheric response is
slower than the time scale of convection variations.
Plasmaspheric tails form during periods of high activity (Kp high, or Dst low), and
extend all the way down to the ionosphere. (They can therefore affect Earth
communications.)
The inner magnetosphere tries to shield itself from the convection E-fields, but the
buildup of an effective shielding layer takes time. If the convection strength varies
faster than the shielding time scale (somewhere between 15 minutes and an hour), Efields can penetrate past the shielding layer, and into the inner magnetosphere.
Penetration E-fields can affect both plasmaspheric populations (forming meso-scale
structure such as tails, shoulders and/or bite-outs), and ring current distributions.
28