Multi-spacecraft analysis of the geomagnetic tail:

The source of intense and explosive aurora

Miho SaitoSolar-terrestrial environmental laboratory, Nagoya University

8 March, 2013 GCOE conference

CREDIT:NASA/STEREO

Geomagnetic tail

Aurora from space At the initiation of substorm

Saito, M. , 11th ICS, Sep 2012

Is a substorm a manifestation of energy storage and release in the tail ?: 1. Aurora

Model of auroral development [Akasofu, 1964]

From auroral observations, the answer is not obvious.

Is a substorm a manifestation of energy storage and release in the tail ?: 2. Magnetic energy

YES.

When we know HOW the energy is loaded, we may know how it is released, Yan Song ICS11

[Saito et al., 2010 JGR]

In-situ observation of tail and drawback of single spacecraft measurements

7

Five-spacecraft view of tail

THEMIS orbits during 6-7 UT

To Sun

8

Thinning at 11 Re in the pre-midnight (THEMIS)M

agne

tic fi

eld

(SM

)

~20min

9

Textbook view of energy storage in the tail

[McPherron et al., 1973; McPherron, Introduction to Space Physics]

This process results in compression of plasma.

10

Five spacecraft obtain both

spatial structure and its temporal

changes.PT=Pi+Pe+Pb

Pi

Ni

Thinning (~20 min)

The defect of in-situ measurements

removed!

Multi-spacecraft obs. show new types of energy storage process in the geomagnetic tail

New Finding Incompressible change

• Multi-spacecraft obs. improved in-situ diagnosis of the geomagnetic tail– The findings are also useful for forecasting the space

weather• We showed, for the first time, the incompressible

nature before the intense and explosive aurora

Conclusions

Tail

Energy flow

AuroraSolar Wind

Compressibility mattersIs it also the case for space? (Future study)

A paint-cans-and-rifle experiment in “For the love of physics” by Walter Lewin

rifle

paint can

liquid + air -> can deformed liquid filled -> explosion

Result of the shock