Sun-Earth System
Overview
Frank Eparvier
eparvier@colorado.edu
303-492-4546
Who am I?
Dr. Frank Eparvier
Research Scientist @ LASP
Training in Aeronomy
Aeronomy = study of how energy inputs drive the physics
and chemistry a planetary atmosphere
Experimentalist: I like to measure things
“Experiment is the test of all knowledge.”
Currently work with instruments that measure the
solar photonic output of aeronomical importance:
Co-I on TIMED-SEE
Co-I on SDO-EVE
PI on GOES-R EXIS
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Why do We on Earth Care about the Sun?
The Sun directly or indirectly provides nearly all
of the energy to the Earth system.
Photons (light of all wavelengths)
Plasmas (charged particles and magnetic fields)
Variability in the solar output drives variability in
the Earth system.
How the Earth system reacts to solar variability
depends on the complicated, interconnected
mechanisms involved in the Sun-Earth system.
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The Sun Side of the Sun-Earth System
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The Earth Side of the Sun-Earth System
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Statistics of the Sun
Radius = 696,000 km  109 REarth
Volume  1,300,000 VEarth
Mass = 1.99x1030 kg  333,000 MEarth
Composition:
Element
Hydrogen
Helium
Heavier
Elements
by Number
92.1%
7.8%
<0.1%
by Mass
75%
25%
<0.1%
All of this is in the form of ionized atoms = plasma
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Solar Energy Source
Pressure at center ~ 250 billion atmospheres
Temperature at center ~ 15 million Kelvin
 Conditions suitable for Nuclear Fusion
Protons squish together produce:
Helium nucleus
Subatomic particles
Light (energy!)
Release of nuclear binding energy during
fusion is the Sun’s internal energy source.
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Energy Output of the Sun
Measure all photonic energy coming from the
Sun at all wavelengths
Total Solar Irradiance = 1361 Watt/m2 at 1 AU
Integrate over entire sphere around Sun:
Power = 3.8x1026 Watts
(That’s a bright light bulb!)
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Energy Flow and Layers of the Sun
Interior of Sun:
Core: Where fusion occurs,
~15 million K
Radiative Zone: Energy
carried outward slowly
(~200,000 yrs) by photons
through a very thick region
of H & He, T~5 million K
Convective Zone: Energy
carried outward via
convection (hot plasma
rises, reaches surface,
radiatively cools, then
sinks again), T~1 million K
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Energy Flow and Layers of the Sun (2)
Atmosphere of Sun:
Photosphere: visible “surface” of Sun,
point where gases go from being
optically thick (opaque) to optically
thin (transparent), T~5700 K
Chromosphere: “bottom” layer of
atmosphere, visible as pink layer of
hydrogen during total solar eclipses,
T~10,000 K
Transition Region: narrow (~100-1000
km) layer between chromosphere and
corona where temperatures rise
rapidly T~10,000 K - 1 million K
Corona: “top” of solar atmosphere
heated to extremes by complex (and
not fully understood) magnetic means,
T~ 2 million K
Solar Wind: extension of corona into
interplanetary space, mostly protons
and electrons streaming out on Sun’s
magnetic field at speeds of ~400-1000
km/s, T~200,000 K at 1 AU
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Differential Rotation of Sun
Core and Radiative Zone rotate rigidly.
Outer layers of Sun rotate differentially.
pole
25 days/rot.
equator
35 days/rot.
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Looking at the Sun
Different wavelengths show us a different Sun.
Features that are dark at one wavelength are bright at other wavelengths.
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Granules
Granules: Convection cells on photosphere, size ~
1000 km (~ size of Texas)
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Sunspots
Sunspots: Magnetically disturbed regions cooler than
surrounding areas (~4000 - 5000 K) of photosphere
(darker), usually come in pairs (N and S magnetic
polarity), size ~ 1500-50,000 km, can last for months
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Magnetic Origin of Sunspots
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Prominences
Prominences & Filaments: Long-lasting (hours or
days) condensations of gases held above the
surface by erupting sections of magnetic field
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Flares
Flares: short duration (minutes to hours) bursts of hot
material out of surface, very bright at all
wavelengths
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Coronal Holes
Coronal Holes: areas of “open” magnetic field
allowing plasma to stream out into solar wind
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Coronal Mass Ejections
CMEs: large “blobs” of plasma (hot ionized gases
enclosed in bubbles of magnetic field) that blow off
the Sun and travel out through the solar system
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Solar Wind and IMF
Solar Wind: Charged particles streaming out from Sun
Interplanetary Magnetic Field (IMF): Solar magnetic field at
distances of the planets
Solar wind flows out along
“open” magnetic field lines.
IMF is twisted into “ballerina
skirt” shape by solar rotation.
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Photon Output of the Sun
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Timescales of Solar Variability
Solar Cycle - months to years
Evolution of solar dynamo with 22-year magnetic
cycle, 11-year intensity (sunspot) cycle
XUV 0-7 nm
Solar Cycle (11-years)
H I 121.5 nm
Solar Rotation - days to months
Solar Rotation (27-days)
Beacon effect of active regions
rotating with the Sun (27-days)
Flares
Flares - seconds to hours
Related to solar solar eruptive
events due to the interaction of
magnetic fields on Sun
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The Solar Cycle
11-year “Sunspot” or Solar Activity Cycle
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Solar Cycle
Sunspots
Magnetogram
Soft X-Rays
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Source of Solar Cycle
11-year sunspot cycle is really a 22-year
magnetic cycle (magnetic field reverses every
11 years).
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Differential rotation of Sun
causes “knotting” of
originally dipole-like
magnetic field.
Solar Maximum: Knotting
peaks ~5.5 years after
“clean” start. Solar activity
and output peaks.
Solar Minimum: Sun
cleans itself up over next
5.5 years into a quite, but
“reversed” dipole field.
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The Solar “Constant”
Solar Cycle
0.1% = 1.4 W/m2
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TSI Variability
Overall, TSI increases during solar max, but sunspots can
“block” sunlight, making TSI drop.
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The Earth System
Earth intrinsically has an atmosphere and a
magnetic field.
Place this into the constantly changing space
environment created by the Sun and you get
complex responses.
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Earth’s Atmosphere Composition & Density
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Solar Photons and the Atmosphere
The Solar Spectrum at top of
atmosphere (similar to 5800 K
blackbody spectrum)
The Solar Spectrum at the
surface of the Earth
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Absorption in Atmosphere
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The Atmosphere and TSI
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Typical Atmospheric Temperature Profile
EUV, FUV, Soft X-rays absorption
and ionization heating
Primarily IR radiating to space cooling,
Some FUV absorption heating
MUV Sunlight absorption by O3 heating
Visible, NIR, NUV absoprtion of sunlight
by air and surface, surface heats from below
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EUV Ionizes the Upper Atmosphere
Solar Minimum
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EUV Ionizes the Upper Atmosphere
Solar Maximum
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Ionosphere Reaction to Solar Variability
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Ionosphere in Itself is Complex System
Ionospheric Electrodynamics
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Earth Has a Magnetic Field
Credit: Tsurutani, 2005
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Earth Reacting to a CME
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The Aurora
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Space Weather Effects on Humanity
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Summary
The Sun-Earth System is Complex
But understandable
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Start with Just Solar Photons
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Add the Earth’s Magnetic Field
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Add the Solar Wind and IMF
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Add CMEs
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