Aurora, Substorms, and THEMIS

D. G. Sibeck

NASA/GSFC

THEMIS Project Scientist

Outline

• What do aurora look like?

• Where do aurora occur?

• When do aurora occur?

• Why do aurora occur?

• How will THEMIS help us understand aurora?

• Where can I find out more information?

Quartz Lake State Park, AlaskaSeptember 6, 1996

January 6, 1998

Aurora in Alaska

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March 11, 1998

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Aurora in Lapland

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Loomis Auroral Chart, 1860

You arehere

NorthPole

Elias Loomis

Professor,

Yale

% Nights With Aurora

You can also seeaurora in

Antarctica!

You are stillhere- you havea small butfinite chanceof seeing aurora

Aurora over the Eastern U.S.

You are here

Sometimes theauroral ovalbrightens andexpands overthe continguousUnited States

Good news: Auroras come furthest equatorward here on the East Coast

Bad news: only during severe geomagnetic storms

X

Ground MagnetogramsExample

Summary:One Year ofKp index

Sudden CommencementCompression

StormDisturbance

27 Day Solar Rotation

When Should One Look?

Spring

Fall

At or just before

midnight,

Spring or

Fall

SOHO: Solar Flares and Ejecta

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Our storybegins atthe Sun

Solar Wind Model: Streams and Blast Waves

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Earth’s Magnetic Field

Our Magnetic Shield

Solar Wind Buffetting: Model

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Aurora

Reconnection

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Cause of Aurora

120 km

60 km

Reconnection Model

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Current Disruption

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THEMIS• Science:

– Identify when and where substorms (building blocks of storms) begin

– Distinguish between competing models– Understand substorm physics

• Impact on Society– Predict when and where substorms occur– Understand and guard against substorm-related increases in

radiation belt particle flux, communication disruptions, and current surges in power/pipelines

THEMIS Launch

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Orbital Information

• Launched at Sunset, February 17, 2007

• Presently: all 5 s/c on almost identical orbits:– 1.1 x 14.7 RE with inclination 14.4°, period 31 hours, separated by

100’s to 1000’s km– Apogees between the Sun and the Earth, studying radiation belts

and the outer boundary of the Earth’s magnetic field

• Future…each has its own special orbit to help pinpoint when and where substorm onset occurs

Flows

THEMIS(Time History of Events and Macroscale Interactions during Substorms)

distinguishes amongst competing substorm models

?Rarefaction wave

?

P2P3

P4P5

GBOP1

Careful positioning of5 well-instrumentedprobes and dedicated arrayof ground observatories

Allows us to impartiallytest two competing modelsand determine the cause ofsubstorms

SPACECRAFT AND INSTRUMENTS

SST

ESAEF

IaEFIs

FGM

SCM

Tspin=3s

FIVE IDENTICALLY-INSTRUMENTEDSPACECRAFT (128 kg), EACH CARRYING:

ESA: Electrostatic analyzer measures0.003-30 keV ions/electrons (UCB)

SST: Solid state telescopes measures0.03-6 MeV ions and electrons (UCB)

FGM: Fluxgate magnetometer measures magnetic field to 128 Hz (Germany)

SCM: Search coil magnetometer measures 0.001 - 4 kHz magnetic field (France)

EFI: Electric field instrument on wires andaxial booms 0.0003 - 400 kHz (UCB)

5 THEMISS/C Line Up in Tail Once/4 Days

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Sun

TH-GBOs: High resolution & sensitivityOnset: 11:12:51UT, Intensification: 11:18:30UT

First on THD

Last on THE

2nd on THB

3rd on THA

Mag

neti

c F

ield

Timing a Substorm

THE

THATHBTHD

THC

Sun

March 23, 2007

Dedicated Array ofUS/Canadian Ground Observatories

Provide Daily Auroral Movies

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First Auroral Mosaic MovieFebruary 14, 2007

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Dedicated Array of US and Canadian Ground Stations

FOR MORE INFORMATION

• Principle Investigator: Vassilis Angelopoulos (NASA/JPL)

• Project Scientist: David Sibeck (NASA/GSFC)

• NASA SITE WWW.NASA.GOV/THEMIS

• SCIENCE SITE: themis.ssl.berkeley.edu

• EPO SITE: http://ds9.ssl.berkeley.edu/themis/no_flash.html