The Solar Cycle
and
Climate
Dr. Martin Snow
Laboratory for Atmospheric and
Space Physics
University of Colorado, Boulder
The Solar Cycle and Climate
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Outline
The Sun
• what makes the sun shine
• observations of sunspots (visible light)
• counting them – 11 year cycle
• magnetic field – 22 year cycle
• solar dynamo
• solar spectrum
The Atmosphere
• what is it
The Solar Cycle and Climate
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Herzsprung-Russel Diagram
The Solar Cycle and Climate
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Size of the Sun
The Solar Cycle and Climate
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Hydrogen Fusion in the Sun
“The Proton-Proton Chain”
The Solar Cycle and Climate
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2
E=mc
Every second in the Sun’s core
600 x 109 kg H
596 x 109 kg He
The Solar Cycle and Climate
4 x 109 kg to Energy
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The Sun in Visible Light
The Solar Cycle and Climate
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Sunspot record
Galileo 1613
~400 years since 1610
Galileo
Schwab
SOHO 2003
Hale
Modern
Maximum
11-year Intensity Cycle
Telescope Observations
22-year Magnetic Cycle
The Solar Cycle and Climate
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Sunspot Latitudes
The Solar Cycle and Climate
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Monthly Averaged Sunspot Numbers
The Solar Cycle and Climate
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Comparison with earlier cycles
SSN Minimum Level
Lowest since 1920s
(3 of 24 are lower)
SC Period Length
Longest since 1900
(4 of 24 are longer)
Minimum Duration
Widest since 1920s
(7 of 24 are wider)
The Solar Cycle and Climate
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So what are these
spots anyway?
A brief detour into atomic physics…
The Solar Cycle and Climate
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Simple Model of Atom
The Solar Cycle and Climate
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Magnetic Fields and Sunspots
P. Zeeman
G. E. Hale

The Solar Cycle and Climate
G.E. Hale, June 1908
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The Sun in 2003
The Solar Cycle and Climate
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Magnetogram (2003)
The Solar Cycle and Climate
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The magnetic nature of sunspots
Hale provided the first proof that sunspots
are the seats of strong magnetic fields
TRACE image
The Solar Cycle and Climate
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Large scale magnetic field
The Solar Cycle and Climate
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“Open” Magnetic Field
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Solar Any
Cycle and
Climatein the Past 40 Years
45% Less Open FluxThe
than
Cycle
Record Low
Interplanetary
What are Magnetic
GCRs? Field
Why do Record
they care
about solar
HIGH
activity?
Galactic
Cosmic Rays
 Highest level of
cosmic rays in the 54
year record.
The Solar Cycle and Climate
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Do we care about
Cosmic Rays?
GCRs may influence rate of
cloud formation.
Cloud cover changes planetary
albedo.
The Solar Cycle and Climate
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Magnetogram (2008)
The Solar Cycle and Climate
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Magnetogram (2011)
The Solar Cycle and Climate
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Magnetic Changes
The Solar Cycle and Climate
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Sunspots are a
symptom
of the Sun’s
magnetic field.
Not the cause.
The Solar Cycle and Climate
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The Sun’s Magnetic Cycle
Hale’s polarity Law (1919)
Well-organized large scale magnetic field
Changes polarity approximately every 11 years
(22 year magnetic cycle)
t = 9 yrs
N
t = 3 yrs
S
N
S
t=0
t = 11 yrs
The Solar Cycle and Climate
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Surface magnetic fields
over the solar cycle
The Solar Cycle and Climate
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Courtesy D. Hathaway
So why does the Sun do
this?
Or rather, what’s going on physically
that produces these magnetic
effects?
The Solar Cycle and Climate
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The Sun’s Differential Rotation
1858: Carrington and Sporer independently observed sunspots
located at higher latitudes are carried around the Sun slower
than sunspots at lower latitudes
Why doesn’t dipole field just get wrapped up tightly by differential
rotation?
The Solar Cycle and Climate
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Alpha and Omega
Differential Rotation
turns poloidal field into toroidal
Shear forces on sunspot pairs
turns toroidal field into poloidal
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Magnetic Butterfly Diagram
The Solar Cycle and Climate
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Differential Solar Rotation
& Solar Dynamo
~3 yr
Slower at Poles
(30-33 days)
???
10-30 yr
Faster at Equator
(25-27 days)
Only in Convection Zone
The Solar Cycle and Climate
From Manfred Küker
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Strength of Polar Magnetic Field
1996 MIN
2008 MIN
1986 MIN
40% weaker than in previous minima. 33
The Solar Cycle and Climate
Solar Spectrum
Remember all that energy generated by nuclear
reactions in the core? Most of it emerges from
the surface as radiation.
The basic shape of the
spectrum is a blackbody
about 6000 K
The Solar Cycle and Climate
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The observed spectrum
Why doesn’t this just look
like a blackbody?
The Solar Cycle and Climate
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Sun also has an
atmosphere!
The Solar Cycle and Climate
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2-slide course on
Radiative Transfer
Cool, less
dense
Hot
Dense
Planck curve for cooler material is not as
bright.
At core of line, only see into atmosphere as far
as the cool gas.
Absorption Line Spectrum
The Solar Cycle and Climate
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2-slide course on
Radiative Transfer
Hotter less
dense
Hot
Dense
Planck curve for hotter material is brighter.
At core of line, only see in as far as hotter
gas. Emission Line Spectrum
The Solar Cycle and Climate
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Different wavelengths
formed at different
heights in atmosphere
Photosphere
(continuum)
Upper photosphere
(cooler gas, absorption lines)
Chromosphere
(hotter gas,
emission lines)
The Solar Cycle and Climate
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MUV variability
The Solar Cycle and Climate
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Variability at a single
wavelength
The ultraviolet
radiation varies
by a factor of ~2
over the solar
cycle
The Solar Cycle and Climate
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Variability at many
wavelengths
The Solar Cycle and Climate
Rottman (2001)
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How much does the
energy output of the Sun
change?
•Most of the power is at visible wavelengths or
longer (shape of the blackbody)
•Most of the variability is at ultraviolet
wavelengths or shorter (structures in the solar
atmosphere)
•So does the tail wag the dog?
Skeptical Cat is Skeptical
The Solar Cycle and Climate
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The observed spectrum
from the SORCE mission
Integrate over all wavelengths
to get total radiative output,
aka Total Solar Irradiance (TSI) or
the “solar constant”
The Solar Cycle and Climate
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Just a word on the words
accuracy and precision
Accurate, but poor precision
Precise, but poor accuracy
Ideally, scientific measurements are
both accurate and precise.
The Solar Cycle and Climate
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Total Solar Irradiance Observations
The Solar Cycle and Climate
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One way to link them is to assume the
most recent is the best.
Solar Cycle
0.1% = 1.4 W/m2
The Solar Cycle and Climate
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4 TSI Composites: Conflicting Results
 SOHO VIRGO PMOD
(Fröhlich) and ACRIM
(Willson) composites
indicate 2008 TSI is
lower than 1996 level
 SOHO VIRGO
DIARAD (DeWitte)
and SORCE TIM /
Model (Lean)
composites indicate
2008 TSI is higher
 Uncertainty for
2008-1996 trend is
about 100 ppm
The Solar Cycle and Climate
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TSI variability can be
bright vs
vs dark
described as good
evil
The Solar Cycle and Climate
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What was TSI doing before 1978?
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Does this matter?
The Solar Cycle and Climate
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Sources of Heating
2500
X
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History – Europe’s Little
Ice Age
1645-1715 – Maunder Minimum
Solar output decreased 0.1-0.3% for 70 years
Earth temperatures were ~0.2-0.4 C colder than the
early 1900s
The Solar Cycle and Climate
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Was this causation, or
just coincidence?
• …or were there many volcanoes about the same time?
• …or does it matter that it was only cold in Europe?
• etc.
Climate research is not
yet at the stage where
we can definitively
answer this question.
The Solar Cycle and Climate
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Climate Change Has Many Sources
Natural Forcings
• solar variability - direct and indirect effects
• volcanic eruptions - stratospheric aerosols
Internal Oscillations
El Nino
• atmosphere-ocean couplings
- El Niño Southern Oscillation (ENSO)
- North Atlantic Oscillation (NAO)
Land Cover Changes
La Niňa
Anthropogenic Forcings
• atmospheric GH gases - CO2, CH4, CFCs, O3,
N2O
• tropospheric aerosols - direct and indirect effects
of soot, sulfate, carbon,
biomass burning, soil dust
courtesy of Judith Lean, NRL The Solar Cycle and Climate
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Climate Influences
El Nino
La Nina
optical thickness at 550 nm compiled by Sato et al. (1993) since
1850, updated to 1999 from
giss.nasa.gov and extended to the
present with zero values
bright faculae
El Chichon
Pinatubo
multivariate ENSO index
- weighted average of the main ENSO
features contained in sea-level pressure,
surface wind, surface sea and air
temperature, and cloudiness in the tropical
Pacific (Walter and Timlin, 1998)
net effect of eight different components
Hansen et al. (2007)
dark sunspots
Net effect of sunspot darkening and facular brightening
- model developed from observations of total solar irradiance
(Lean et al. 2005)
56
courtesy of Judith Lean, NRL The Solar Cycle and Climate
Global Surface Temperature Responses
CRU temperature data, Univ. East Anglia, UK
Combined ENSO + volcanic
aerosols + solar activity +
anthropogenic effects explain
85% of observed temperature
variance
+0.2oC 1997-98 “super” ENSO
-0.3oC Pinatubo volcano
+0.1oC Solar cycle
+0.4oC Anthropogenic effects
from Kopp & Lean 2011
The Solar Cycle and Climate
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Global Surface Temperature Since 1890
CRU temperature data, Univ. East Anglia, UK
0.9K
+0.0015K /decade
-0.0009K /decade
Decompositions of
historical and recent
global surface
temperatures give
consistent individual
natural and
anthropogenic
components:
Natural components
account for <15% of
warming since 1890
+0.005K /decade
+0.054K /decade
0.75K
courtesy of Judith Lean, NRL The Solar Cycle and Climate
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Summary
•The Sun varies due to changes in its magnetic field (the
“dynamo”)
•Sunspot Cycle is 11 years (approximately)
•Magnetic Cycle is 22 years (approximately)
•Solar irradiance is largest source of energy input to the
climate system (BY FAR)
•Natural and Anthropogenic effects both play a role
in determining the temperature of the atmosphere,
but the much larger effect is anthropogenic.
The Solar Cycle and Climate
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Backup Slides
The Solar Cycle and Climate
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Summary of Recent
Solar Minimum
•Fewer Spots
•Lower Magnetic Field
•Weaker Solar Wind
•Lower Irradiance
•Since 1920’s
•Since 1950’s
•Since measurements started
•Than 1996, but no concensus
on earlier results.
“This is not your father’s solar minimum…
…it’s your grandfather’s.”
--- Neil Sheely
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The Solar Cycle and Climate
Where is sunlight
absorbed?
The Solar Cycle and Climate
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Overlapping Cycles
From David Hathaway
If the new cycle’s activity starts appearing
before the old cycle’s activity fades,
do we see the true minimum?
The Solar Cycle and Climate
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