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 R
Earth
Volume  1,300,000 V
Earth
Mass = 1.99x10
30 kg  333,000 M
Earth
Composition:
Element by Number by Mass
Hydrogen 92.1% 75%
Helium
Heavier
Elements
7.8%
<0.1%
25%
<0.1%
Much 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/m 2 at 1 AU
Integrate over entire sphere around Sun:
Power = 3.8x10
26 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 (11-years)
Solar Cycle - months to years
Evolution of solar dynamo with 22-year magnetic cycle, 11-year intensity (sunspot) cycle
XUV 0-7 nm
H I 121.5 nm
Solar Rotation - days to months
Beacon effect of active regions rotating with the Sun (27-days)
Solar Rotation (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
11year “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).
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 quiet, but
“reversed” dipole field.
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The Solar “Constant”
Solar Cycle
0.1% = 1.4 W/m 2
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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 O
3 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
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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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Now you understand the Sun-Earth System!
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