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