Inner Magnetospheric Shielding, Penetration Electric Field, and the

Plasmasphere

GEM (Student) Tutorial June 23, 2002

Jerry Goldstein, Rice University

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The Plasmasphere

D. L. Carpenter (Stanford)“Whistler” wave studies

(ground-based)

Chappell et al., OGO data

Plasmapause: boundary where dense,

cold plasma ends M-I Coupling: WG-1+2:Ionospheric outflow

Wednesday 10:30-noonChairs: Lotko, Moore, Peterson

Ionospheric outflow: Populates p’sphere

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Magnetospheric Convection1. Generally sunward in the inner magnetosphere2. Southward IMF

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Magnetospheric ConvectionExplain sharp ppause:

Boundary between corotation (refilling) and

convection

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Magnetospheric ConvectionPlasmapause:

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.

M-I Coupling: WG-2:M’spheric convectionTuesday 3:30-5:30pmChair: Ray Greenwald

WARNING: This is a highly oversimplified picture!In reality, convection is

usually very nonuniform and time-dependent

Plasmapause

Conv/corot boundary

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IMAGE Extreme Ultraviolet Imager (EUV)

REMOTE MEASUREMENTThe Extreme Ultraviolet (EUV) imager

looks at the plasmasphere via

EUV data 6:43-10:04, 5/24

QuickTime™ and a decompressor

are needed to see this picture.

MOVIE

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Measuring the Plasmasphere

IMAGE EUV

in situCross-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

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Plasma Tails (“Plumes”)

MI Coupling: WG-1:plasmaspheric tails (“plumes”)

Monday 10:40-noon Chair: Tom Moore

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The Duskside Bulge?

Plasma Tails

“Detached” plasma

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Plasma Tails

Space Weather Implications...

As Seen in the Ionosphere

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Shielding:the plasmasheet,

Westward currents

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Shielding:Convection increase

due to dawn-dusk E--> creates partial RC

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Shielding:Partial RC closes in ionosphere via field-

aligned currents

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Shielding:Field-aligned currents create zonal charging.

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Shielding:Zonal charging creates

potential drop across IM, creating dusk-dawn E that

opposes/cancels dawn-dusk convection E

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E-shielding exactly cancels E-convection

IM ShieldingInstead of this...

You get this...

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E-shielding exactly cancels E-convection

IM Shielding

Shielding: 15 min - 1 hrThus, changes in Solar-wind/IMF conditions that occur more rapidly than the shielding time-scale allow convection field to penetrate past the shielding layer.

Perfect shielding might not occur even if conditions are steady, however. (See Dick Wolf’s tutorial.)

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E-shielding exactly cancels E-convection

E-conv UP:

Sunward IM

plasma flow

E-conv DOWN

Tailward IM

plasma flow

Penetration E-Fields 18

E-shielding exactly cancels E-convection

E-conv UP:

Sunward IM

plasma flow

E-conv DOWN

Tailward IM

plasma flow

Penetration E-Fields 19

E-shielding exactly cancels E-convection

E-conv UP:

Sunward IM

plasma flow

E-conv DOWN

Tailward IM

plasma flow

Penetration E-Fields 20

Geomagnetic Variation of PlasmapauseSize/Shape of Plasmasphere

Depends on strength of convection

Well-Shielded

Swd IMF

Example: Plasmaspheric Erosion following sudden turn to southward IMF.

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Geomagnetic (Kp) Variation of Plasmapause

OGO 5 (in situ)

ISEE 1 (in situ)

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Geomagnetic Variation of Plasmapause

Aug 11, 2000: During/After Strong

Convection

July 9, 2000: Quiet

IMAGE EUV data

QuickTime™ and a decompressor

are needed to see this picture.QuickTime™ and a

decompressorare needed to see this picture.

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IM E-Fields

IM/S: Tutorial:I.M. E-fields

Monday 9:15-10amDick Wolf

IM/S: WG-1:Near-Earth E-fields

Monday 1:30-3pmChairs: Goldstein, Liemohn

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Simulated Penetration E-FieldsOvershielding: Shoulder

PDC

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Simulated Penetration E-FieldsOvershielding: Shoulder

Penetration E needed to explain shoulder

(and other meso-scale plasmaspheric

structure).

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IMAGE HENA27-39 keV

CRCM Model, 32 keV

Ring-Current and the IM E-field

IM/S: WG-1:RC/PS coupling (observations)

Tuesday 1:30-3pmChairs: C:son Brandt, Gallagher

RC/PS coupling (modeling)

Tuesday 3:30-5:30pmChairs: Liemohn, Reynolds

Penetration E needed to

explain observed

ring-current (RC)

distribution.

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ConclusionsThe 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), E-fields 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.

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