Solar Drivers of Space Weather
Steven Hill NOAA/SEC
June 14, 2007
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Research Experience for Undergraduates
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Energy and Power in Context
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Outline
• Overview of the Sun
– Interior
– Surface
– Corona
• Solar Drivers of Space Weather
– Coronal Holes
– Flares
– Coronal Mass Ejections (CMEs)
• Summary
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Interior
Courtesy UC Berkeley
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Sunspots and Subsurface Structure
Courtesy S. Kosovichev, Stanford University
(http://soi.stanford.edu/press/ssu11-01/#movies)
Convection and magnetic fields below the solar surface drive the
appearance and physical conditions in sunspots
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Surface and Corona
• The ‘average’ surface
and corona are shown
• Heating of the corona
is a major unsolved
problem in solar
physics
• Note comparisons of
temperature and
density to terrestrial
standards
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Sun at Different Wavelengths
Because of the temperature differences at different heights in the
corona, different wavelengths highlight features and phenomena
occurring at different heights
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Magnetic Fields
Magnetic fields dominate the corona and are responsible for
much of its structure, from coronal holes to active regions
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Solar Wind I
• The mass that the Sun
continuously loses
through the corona is
called the solar wind
• It is highly variable
spatially and temporally
• Major eruptions of
mass are called Coronal
Mass Ejections (CMEs)
SOHO coronagraph movie showing solar
wind, CMEs, and radiation storm
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Solar Wind II
Courtesy C. Russell
Ulysses near polar passes show the
latitudinal structure of the solar wind
speed. Open field at high latitudes
leads to predominantly high speed
winds
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A depiction of the process leading to
the Parker spiral (Parker, 1958).
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11- year Variability
Courtesy Yohkoh SXT
While the total solar irradiance – the solar constant – is nearly constant over
an 11-year cycle, the X-ray irradiance changes by a factor of 100. If flares are
included, then this factor is 10000.
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Outline
• Overview of the Sun
– Interior
– Surface
– Corona
• Solar Drivers of Space Weather
– Coronal Holes
– Flares
– Coronal Mass Ejections (CMEs)
• Summary
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Coronal Holes
• Regions of open magnetic
field related to high speed
solar wind.
• Changes in solar wind
speed at the boundaries of
coronal holes compresses
Earth’s magnetic field.
• Since coronal holes ‘live’
for more than a solar
rotation, these storms
recur.
One solar rotation shows the persistance
of active regions and coronal holes.
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CIRs and Recurring Geomagnetic Storms
• Co-rotating Interacting Regions (CIRs) are regions of compressed,
even shocked, solar wind caused by high speed streams from coronal
holes
• CIRs lead to the majority of recurring geomagnetic storms as they
sweep past Earth
Coronal
Hole
Courtesy C. Russell
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Solar Wind Effects
• Stars, comet Encke,
and the solar wind
• STEREO spacecraft
provides a visual
look at solar wind
effects near 0.5AU
• Tail disconnections
occur at
discontinuities in the
solar wind
Courtesy D. Biesecker & STEREO
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Flares
• Sudden conversions of magnetic energy into thermal
and kinetic energy.
• Closely associated with coronal mass ejections CMEs.
• Rapid changes in solar EUV and X-ray emissions affect
thermosphere and ionosphere.
• Large flares can have an extreme effect.
• In addition, flares are related to energetic particle events
that result in Solar Radiation Storms.
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Stressed Magnetic Fields
• Active region complexity
– Active region magnetic fields become stressed
by convective motions in the photosphere
– As energy builds up it can be released
catastrophically
– Particular morphologies, illuminated by
emitting plasmas, are more susceptible to
eruption
– Region below resulted in flare and CME
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Simple
+
-
Non-Potential: Shear
-
+
Non-Potential: Twist
Non-potential region (twist / sigmoid) prior to flaring as seen by
several instruments (Nitta et al., 2004 – unpublished)
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Solar Eruption Process
• One concept of the
relationship between
flares and CMEs
• Process of magnetic
reconnection is key
• Conceptual models
abound
• Computational
modeling is more
experimental than
predictive
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Lin & Forbes, 2002
Forecasting Flare Effects
9220 0532 //// 0533 LEA C RSP 035-084 III/1
9230+0537
9230 0540
9230 0540
9230 0541
0546
0542
0542
0541
0558
0545
0546
0546
GO8
LEA
LEA
LEA
5
G
G
G
XRA
RBR
RBR
RBR
1-8A
2695
4995
8800
M1.3 1.2E-02
16
30
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9240 B0618 U0619 0624 LEA 2 FLA S05W04 SF 9718
Flares are a source of ‘directly
connected’ energetic particles
(Reames, 1999)
2001-12-04 05:36:57.383 -6.500 1.401
SEC ground system, using both XRS and SXI data, provides flare
locations within two minutes of initial XRS flare detection (‘XFL’ product)
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Radiation storm arrival time
correlates with flare longitude
(Balch, 2000) 25
Record X28 Flare in False Color
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Combined EIT and SXI data.
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Coronal Mass Ejections
• Coronal Mass Ejections (CMEs) are massive
expulsions of matter from the Sun’s outer
atmosphere.
–
–
–
–
400-2000 km/sec speed
1014 to 1016 g
1-4 days to reach Earth
Shock generated radiation storms can reach
Earth much sooner
– Location of the source region on the solar
disk is key to estimating the trajectory of the
CME and its likelihood of hitting Earth
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CME generated shock creates
energetic particle radiation storm
(Reames, 1999)
Ejected material associated with a CME seen by GOES 12 SXI in 2001
(Hill et al., 2001)
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Coronal Mass Ejection
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SOHO Cornograph Observations of a CME.
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IPS Tomography
• Tomographic reconstruction of CMEs in interplanetary space
• Radio sources distant from the solar system are monitored
• Signal scintillation occurs when the CME crosses the line-of-sight
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http://cassfos02.ucsd.edu/solar/tomography/fast_stel_1965.html
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Interplanetary Medium
• Not quite ‘empty’
• Contains ions, elections, currents and magnetic fields
• Solar disturbances propagating toward Earth can be
strongly affected by the state of the IPM and the passage
of previous disturbances
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Interplanetary Medium
• Contains ions, elections, currents and magnetic fields
• Solar disturbances propagating toward Earth can be strongly affected
by the state of the IPM and the passage of previous disturbances
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Summary
• Important, Recurring Themes
– Solar activity evolves from the interior, through many layers
and phases until we see it manifested on the surface and in the
corona
– Magnetic fields thread through every phenomena and
dominate many
– Truly predictive physics-based numerical models of solar
phenomena are not yet available
– Forecasting relies heavily on observations and empirical
models
• Resources:
– MSFC - http://solarscience.msfc.nasa.gov/
– UCB - http://cse.ssl.berkeley.edu/segwayed/lessons/sunspots/
– Flare cartoons http://solarmuri.ssl.berkeley.edu/~hhudson/cartoons/thepages/Shibata.html
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