Transcript BRIEFING TITLE - ALL CAPS 30 Jan 01

Space Weather: Magnetic Storms
31 October 2011
William J. Burke
Air Force Research Laboratory/Space Vehicles Directorate
Boston College Institute for Scientific Research
CRESS
C/NOFS
DMSP
Space Weather
Course Overview
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Lecture 1:
Overview and Beginnings
Lecture 2:
The Aurorae
Lecture 3:
Basic Physics (painlessly administered)
Lecture 4:
The Main Players
Lecture 5:
Solar Wind Interactions with the Earth’s Magnetic Field
Lecture 6:
Magnetic Storms
Lecture 7:
Magnetic Substorms
Lecture 8:
Magnetosphere – Ionosphere Coupling
Lecture 9
The Satellite Drag Problem
Lecture 10:
Verbindung (to help make up for your rash decision not to take
Wollen Sie Deutch Sprechen?)
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Space Weather
Magnetic Storms
Overview
Last week we looked at the Sun as the source of Earth’s space weather.
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• Pressure gradients in the corona drive a H+/e- supersonic solar wind
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Typical densities: ~ 5 cm-3
Typical speeds: ~ 400 km/s
Earth’s magnetic field acts like a cavity in solar wind
Bow shock stands in front of the Earth
• The solar wind carries a weak magnetic field away from the Sun into
interplanetary space called the interplanetary magnetic field (IMF)
– Dungey (1961) argued that when the IMF has a
southward component it should interact strongly
with the Earth’s field to drive magnetic disturbances.
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Experimental studies over intervening 50 years
overwhelmingly confirm Dungey’s hypothesis:
magnetic activity is always preceded by southward
turning of the IMF.
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Space Weather
Magnetic Storms
• In preparing this this presentation it seemed useful to concentrate
on a very simple, but very intense magnetic storm that occurred in
November 2003.
• ACE was at the first Lagrange point L1 where measured the solar wind
density and speed as well as the interplanetary magnetic field (IMF).
• The GRACE satellite was in circular polar orbit near 490 km.
- An onboard accelerometer measured the atmospheric drag on the spacecraft.
- From the accelerometer measurements we inferred globally-averaged mass
densities in the thermosphere and its total energy content
• We compare interplanetary forcing and thermospheric responses with
variations of the stormtime disturbance Dst index
- Dst measured as N-S magnetic variations observed at 4 widely spaced
stations around globe
- Reported at 1-hour cadence as spatial and temporal average BNS
- Linearly proportional to energy in the ring current (Dessler-Parker –Sckopke)
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Space Weather
Magnetic Storms
Three Magnetic Topologies
Magnetic merging
at dayside magnetopause
- IMF: two feet in solar wind
- Closed: two feet on Earth
- Open: one foot on Earth and
one in the solar wind
Closed Field lines
Interplanetary Field lines
Earth
Open Field lines
Solar
Wind
Sun
Open Field lines
Magnetopause
current sheet
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Space Weather
Magnetic Storms
Magnetic Reconnection
in the magnetotail
Northern Lobe
Plasma
Injection
Plasma
Ejection
Earth
Dayside
merging
site
Near Earth
X-line
(activated
during
substorms)
Distant
X-line
Southern Lobe
Dungey’s picture provide a rational
for the existence and dynamics of the
plasma sheet, the then undiscovered
storage region from which auroral
particles are drawn.
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Space Weather
Magnetic Storms
Coronal Mass Ejections
Artistic
rendition
of a flare
and CME
SOHO observations
of a CME ejection
Computer
simulation
of a CME
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Space Weather
Magnetic Storms
- Solar wind density (blue) and
dynamic pressure (red)
- IMF BZ component (bottom)
Solar Wind Density (cm-3)
• The plots to the right show
measurements from ACE at L1:
- Solar wind speed (top)
600
500
400
30
30
25
25
20
20
15
15
10
10
5
5
0
0
Solar Wind Pressure (nPa)
• Largest magnetic storm of last
solar cycle
700
300
48
24
Z
- X-28 class X-ray flare
- Coronal mass ejection
- No solar energetic particles
IMF B (nT)
• Concrete example: consider
November 19 - 23, 2003 Storm
Solar Wind Speed (km/s)
800
0
-24
-48
JD 2003 323
324
325
326
327
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Space Weather
Z
• The symbol VS represents the magnetospheric electric field in the equatorial plane
30
25
25
20
20
15
15
10
10
5
5
0
0
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IMF B (nT)
• The bottom plot shows the magnetospheric
response in the form of the Dst index which
indicates the growth and decay of the
stormtime ring current
30
24
0
-24
-48
3
100
0
-100
 (mV/m)
2
VS
-200
• The storm’s recovery phase (positive Dst slope)
began when VS turned off.
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Dst (nT)
• The storm’s main phase (negative Dst slope)
began when VS turned on.
Solar Wind Pressure (nPa)
• The two top plots repeat ACE measurements
of the solar wind density and pressure
as well as IMF BZ.
Solar Wind Density (cm-3)
Magnetic Storms
-300
-400
0
JD 2003 323:00
324:00
325:00
326:00
-500
327:00
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Space Weather
Magnetic Storms
• The trace in the top panel shows that the
globally-averaged thermospheric density
at 490 km increased by a factor of 6 from
5 ∙10-16 to 3 ∙10-15 grams/cc .
GRACE Altitude 490 km
Mass Density (grams/cc)
• Slide shows thermosphere’s response to magnetic
storm driving
10
-15
10
-16
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• The trace in the middle panel indicates that
the total energy of the thermosphere rose
from 6.2 ∙1017 to 6.8 ∙1017 (Eth ~ 6 ∙ 1016 ) Joules.
• Since the rise occurred in ~12 hour the
average power into the thermosphere was
~ 1.4 ∙1012 Watts.
Thermospheric Energy (Joules)
7 10
17
6.5 10
17
6 10
3
100
0
• Minimum Dst  -475 nT
ERC  1.9 ∙ 1016 Joules
VS
-200
1
Dst (nT)
• The energy of the ring current estimated via D-P-S
relation ERC (Joules)  3.87 ∙ 1013 ∙ |Dst (nT)|
-100
 (mV/m)
2
-300
-400
0
JD 2003 323:00
324:00
325:00
326:00
-500
327:00
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Space Weather
Magnetic Storms
• This slide shows southern auroral ionospheric
response to storm driving on November 20, 2003
• False color EUV image of ionosphere acquired
by NASA’s Polar satellite at an altitude of ~ 9 RE.
Red indicates most intense auroral emissions.
• During large storms auroral particle fluxes into
the ionosphere are their most intense.
• Based on particle and optical measurements from AF, NOAA and NASA satellites,
electron and ion energy precipitation rates and can reach ~ 100 GW.
• This is about a factor of 10 less than the electromagnetic power needed to heat the
global thermosphere.
• Electric and magnetic field measurements from AF and NASA satellites agree with
thermospheric power estimates.
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Space Weather
Magnetic Storms
Summary and Conclusions
• In looking at the magnetic superstorm November 20, 2003 we have been exposed to
a wide sampling of what the Sun can throw at us.
• Be warned however, it does not represent the full spectrum of consequences:
- Halloween storm 2003: severe MeV particle fluxes generated in the solar flare
destroyed ability of ACE to measure solar wind characteristics
- March 1989 storm: brought down Hydro Quebec electric grid.
AFSPC lost ~3500 space objects that it was tracking.
- March 1991 storm: created a new radiation belt in about two minutes.
• In next weeks lecture we will turn our attention to substorms the other geomagnetic
disturbance that occurs after southward turnings of the IMF.
• This type of event involves activations of the near-Earth X line and have much
shorter lifetimes than storms, but they can have deadly consequences for satellites
in geostationary orbit.
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