The Sunspot Cycle: Long-Range Predictions for Long-Range Propagation

1
The Sunspot CycleLong-Range Predictions
forLong-Range Propagation

• Dr. David H. Hathaway
• NASA MSFC Space Science Office
• 2014 January 11
• GARS TechFest 2014

2
Outline

• The Sun and Solar Activity
• The Sun and the Ionosphere
• The Sunspot Cycle
• The Suns Magnetic Dynamo
• Sunspot Cycle Predictions

3
The Sun and Solar Activity
4
The Sun
Radius 109 REarth Mass 333,000 MEarth
Surface Temp 9,930 F Surface Density
Air/5000 Core Temp 28 million F Core
Density Gold 8 Composition 70 H 28
He 2 (C, N, O)
5
Sunspots
Sunspots are dark (and cooler) regions on the
surface of the Sun. They have a darker inner
region (the Umbra) surrounded by a lighter ring
(the Penumbra). Sunspots usually appear in
groups that form over hours or days and last for
days or weeks. The earliest sunspot observations
indicated that the Sun rotates once in about 27
days.
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Sunspot Structure
Sunspots are regions where intense magnetic
fields break through the surface of the Sun. The
magnetic field strengths are typically about 6000
times stronger than the Earths magnetic field.
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Solar Magnetism The Key
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Explosive Events

• Solar flares 10-1000X excess in X-rays and
  Extreme Ultraviolet (EUV)
• Coronal Mass Ejections (CMEs) magnetic clouds
  blasted off the Sun
• Solar Energetic Particles relativistic
  particles from flares and CMEs

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CME Impact on Earth
Magnetized clouds of plasma blasted off of the
Sun as CMEs can impact the Earths environment
distorting the magnetic field surrounding the
Earth and producing energetic particles that
stream into the Earths atmosphere to create
aurorae.
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Space Weather
Space weather refers to conditions on the Sun and
in the space environment that can influence the
performance and reliability of space-borne and
ground-based technological systems, and can
endanger human life or health.
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The Sun and the Ionosphere
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The Basics
Extreme Ultraviolet (EUV) and X-rays from the Sun
ionize the gases in the Earths upper atmosphere.
At night the ions and electrons recombine at the
denser lower altitudes (the D and E layer) where
collisions are more frequent. The D layer
disappears at night. The E layer (or patches of
the E layer) can survive the night if the solar
EUV is strong. Solar EUV varies with the sunspot
cycle strong at max.
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The Solar Spectrum
Solar ultraviolet light (UV) is energetic enough
to dissociate O2 molecules and form O3 (ozone) in
the stratosphere. It takes Extreme Ultraviolet
(EUV and XUV) to ionize atoms and molecules in
the ionosphere.
N2 -gt N2 e- for ? lt 80 nm O -gt O e-
for ? lt 91 nm O2 -gt O2 e- for ? lt 103
nm NO -gt NO e- for ? lt 134 nm EUV
produces the F-region XUV ( Ly ß) produces the
E-region X-rays ( Ly a) produce the D-Region
Ly ß 102.6 nm, Ly a 121.6 nm
The solar spectrum from X-rays to Microwaves
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Solar Cycle EUV Variability
Measurements of the flux of radio waves at 10.7
cm (2.8 GHz) have been made three times daily
since 1947 from sites in Canada. This is often
used as a proxy for solar EUV to characterize the
ionospheric forcing. However, measurements of the
actual EUV emissions indicate some deviations
in particular at the last cycle minimum.
30.4 nm
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TIMED SEE
The Solar EUV Experiment (SEE) on the NASA
Thermosphere Ionosphere Mesosphere Energetics and
Dynamics (TIMED) mission was designed to fill in
this EUV Hole. TIMED was launched in 2002 and
is still operating.
Wavelength coverage (2004)
XUV Variability 2002-2013
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SORCE SSI
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MUF and TEC
The Maximum Usable Frequency (MUF) for radio
waves reflected off of the ionosphere is directly
related to the Total Electron Content (TEC) of
the ionosphere. The TEC depends upon both the
solar EUV and X-ray irradiance and geomagnetic
activity. We now have direct observations of
solar EUV/XUV/X-ray emissions no need for
proxies!
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The Sunspot Cycle
19
Sunspot Cycle Discovery
Astronomers had been observing sunspots for over
230 years before Heinrich Schwabe, an amateur
astronomer in Dessau, Germany, discovered in 1844
that the number of sunspot groups and the number
of days without sunspots increased and decreased
in cycles of about 10-years.
Schwabes data for 1826 to 1843
Number of Sunspot Groups per Year
Number of Spotless Days
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23 Full Cycles
Shortly after Schawbe discovery Rudolf Wolf
proposed using a Relative Sunspot Number count.
While there were many days without observations
prior to 1849, sunspots have been counted on
every day since. To this day we continue to use
Wolfs Relative Sunspot Number and his cycle
numbering. The average cycle lasts about 11
years, but with a range from 9 to 14. The
average amplitude is about 100, but with a range
from 50 to 200.
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Sunspot Latitudes
Sunspots appear in two bands on either side of
the equator. These bands drift toward the equator
as the cycle progresses. Big cycles have wider
bands that extend to higher latitudes. Cycles
typically overlap by 2-3 years.
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Sunspot Group Tilt- Joys Law
Sunspot groups are tilted with the leading spots
(the spots seen first as the Sun rotates) closer
to the equator than the following spots. In 1919
Alfred Joy noted that this tilt increases with
latitude on the Sun.
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Hales Magnetic Polarity Law
In 1919 George Ellery Hale found that the
magnetic field in sunspots followed a definite
law, Hales Law such that the preceding and
following spots are of opposite polarity, and
that the corresponding spots of such groups in
the Northern and Southern hemispheres are also
opposite in sign. Furthermore, the spots of the
present cycle are opposite in polarity to those
of the last cycle.
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Three Solar Cycles in Action
In addition to these magnetic polarity changes
and the equatorward drift of the sunspot
latitudes, there are important flows on the
surface and within the Sun Differential Rotation
faster at the equator, slower near the poles
and Meridional Flow flow from the equator
toward the poles along the surface.
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Polar Field Reversals
In 1958 Horace Babcock and Bill Livingston noted
that the magnetic polarities of the Suns weak
polar fields also reverse from one cycle to the
next, and that this reversal happens at about the
time of sunspot cycle maximum (the South reversed
in 1957 the North in 1958).
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The Suns Magnetic Dynamo
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Babcocks Dynamo (1961)
Dynamo models have been developed to explain the
sunspot cycle.
a) Dipolar field at cycle minimum threads through
a shallow layer below the surface. b)
Differential rotation shears out this poloidal
field to produce a strong toroidal field (first
at the mid-latitudes then progressively lower
latitudes). c) Buoyant fields erupt through the
photosphere giving Hales polarity law and Joys
Law. d) Meridional transport cancels preceding
polarities across the equator and carries
following polarity to the poles.
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Polar Fields Seeds for Cycles
The Suns polar fields are the seeds of the next
solar cycle in these dynamo models. We have
direct observations for the last three cycles and
a proxy (polar faculae) for the last 10 cycles.
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Polar Fields as Predictors
There is a strong correlation between polar
fields and the amplitude of the next solar cycle
(hemisphere by hemisphere in terms of peak
sunspot area).
North Blue squares South Red circles Cycles
21-23 are from direct magnetic measurements. Earl
ier cycles are from counting polar faculae.
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Polar Field Prediction forCycle 24
Small Cycle 24 predicted by Polar Fields
(Svalgaard, Cliver, Kamide, 2005)
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Four Years Ago - Minimum
Small Cycle 24 predicted.
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This Year - Maximum
This is the Maximum of Cycle 24! The polar fields
built up during Cycle 23 were a good predictor.
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How are Polar Fields Made?
Back to Babcock (1961)
a) Dipolar field at cycle minimum threads through
a shallow layer below the surface. b)
Differential rotation shears out this poloidal
field to produce a strong toroidal field (first
at the mid-latitudes then progressively lower
latitudes). c) Buoyant fields erupt through the
photosphere giving Hales polarity law and Joys
Law. d) Meridional transport cancels preceding
polarities across the equator and carries
following polarity to the poles.
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Polar Field Production

1. Variations in sources more sunspots more polar
   field
2. Variations in source details more tilt more
   polar field
3. Variations in poleward flow faster flow more
   polar field

Option 1 is the most important cycles will get
bigger (or smaller) in series until something
(Option 2 or 3) breaks the trend.
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Polar Field Production I
Cycles with more sunspots should produce stronger
polar fields which leads to another strong cycle
some other variation is needed to
modulate/regulate this process. Otherwise the
cycles would either grow without limit or decay
to nothing.
We do see long term trends in cycle size they
tend to get bigger and then smaller over 100-year
intervals. Something stops their growth and
something starts them growing again.
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Polar Field Production II
Dasi-Espuig et al. (2010) found that the average
tilt, ltagt, of sunspot groups changed with cycle
amplitude. The small tilt seen in big Cycle 19
may have stopped the further growth of the
sunspot cycles to produce a much smaller cycle
20.
15 16 17 18 19
20 21
Solid line - ltagt from Mt. Wilson Observatory
Dash-Dot line - ltagt from Kodaikanal
Observatory Dashed line sunspot area from
Greenwich Observatory
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Polar Field Production III
We have made measurements of the Meridional Flow
of magnetic elements since 1996 and find
significant variations. The Meridional flow is
fast at cycle minima and slow at cycle
maxima. The slow-down at cycle maxima depends on
cycle strength much slower in Cycle 23 than in
Cycle 24. The faster flow in Cycle 24 should
help to make stronger polar fields and a bigger
Cycle 25.
21 22 23
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The Prognosis for Cycle 25
Cycle 24 has far fewer (and smaller) sunspots
than Cycles 22 and 23. Although the faster
Meridional flow should help overcome this
deficit, the slow rate of change in the polar
fields strongly suggests that polar fields that
will build up over the rest of Cycle 24 will
still be very weak.
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The Incredible Shrinking Sunspot Cycle
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Conclusions

• Solar activity impacts modern technology
• Solar EUV/XUV emissions and magnetic disturbances
  control the ionosphere
• We are making progress in understanding the Solar
  Cycle
• Cycle 24 is at its peak the smallest in 100
  years.
• Cycle 25 may be even smaller yet!