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Simultaneous observations of the dayside magnetosphere by Auroral Imaging and by the

THEMIS satellites.

S. B. Mende

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THEMIS cluster incoming

Observational Scenario. Mag. midday = 15:30 UT

• Pressure pulses do not move the foot of the field line but flux erosion will.

• Field models are expected to be accurate on the dayside.

2 cases: Aug 12, 2007, May 23, 2007

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Mag. Pole

Mag. Pole

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C reaches the magnetosphere at 14:25

These pulsed inflation of the magnetosphere do not result in shifting of the aurora. they are

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Mag. Pole

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Summary of August 12, 2007 event.

1. Tsyganenko field model generally maps the magnetopause boundary either on or often equatorward of the dayside aurora. Inconsistent with aurora on closed field lines.

2. Pulsation seen when the satellites enter the magnetopshere at the magnetopause signifying radial motions of the magnetopause boundary. The latitudinal motion of the aurora does not follow these pulsation. as seen by the satellites are not recognizable in the aurora as a latitude position change the foot point, This suggests that these are pressure pulses which do not move the foot point.

3. There is some correlation of these pulses with auroral intensity.

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May 23, 2007 incoming

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May 23 2007 THEMIS Satellites - in coming close to or within field of view.

Both ACE (as shown) and WIND show the same Bz profile. After Bz positive some time delay before aurora goes poleward. When Bz turns negative very quick response. Aurora shows infation or erosion of magnetosphere.

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May 23, 2007 acde 16:56 incoming

Solar wind density about 5 and speed is about 500 km sec. Pretty active day

THB - 15:11

THC -15:45

THD - 15:53

THE - 17:03

THA - 17:26

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Mag. Pole

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THEMIS B May 23, 2007 incoming. THB is leading the pack

THB enters the magnetosphere at ~15:20 (Ts 15:11)

Geomag. North

THB

PMAF - satellite almost pushed into magnetosphere (field inflation)

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THEMIS D May 23, 2007

THD enters the magnetosphere at ~16:00 (15:53)

PMAF - satellite almost pushed into magnetosphere (field inflation)

Inflation of magnetosphere re-appearance of Solar wind plasma

THD

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THA enters the magnetosphere at ~17:00 (Ts 17:26)

THEMIS A May 23, 2007

THA

12/16/2009 15PMAF - satellite apparently pushed into magnetosphere (field inflation)

Change in Bz causes erosion of flux putting THA into the magnetosheath.

THEMIS A May 23, 2007

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1st PMAF at ~1400 - 1415

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Mag. Pole

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Mag. Pole

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Mag. Pole

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Mag. Pole

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Mag. Pole

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Mag. Pole

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Mag. Pole

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Mag. Pole

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Mag. Pole

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Mag. Pole

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Mag. Pole

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Conclusions/Discussions.

1. Tsyganenko models map the magnetopause boundary either on or often equatorward of the dayside aurora.

(a) The field model may need an adjustment.

(b) What is the quiescent dayside aurora? Precipitation on closed field lines or “leaking” cusp particles.

2. Most radial pulsations in the position of the magnetopause (seen by the satellites) are not reproduced in the aurora as motions of the foot point.

This suggests that they are pressure pulses rather than FTE-s.

3. Some pulsations show up as increases in auroral intensity (mild shock aurora)

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Conclusions/Discussions.

4. Poleward moving auroral forms are associated with sudden inflations rather than the erosions of the magnetosphere.

PMAF-s are unlikely to be associated with FTE-s.