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We
all find comfort with the cyclical and predictable events in nature like
sunrise, the seasons and for radio hams the solar cycles. The solar cycle
is one of those natural rhythmic cycles that has reliably peaked every
eleven year or so. The cycles may vary in intensity and have been as short
as nine years to as long sixteen, but they always eventually arrive and
that is the truth for anyone giving them attention.
What
are the affects beyond radio propagation and how reliable are these
cycles, what if they stopped or dramatically changed in their intensity or
duration, what would it mean?
The
solar cycle
The
solar cycles are generally thought of as the cyclical rise and fall in the
calculated sunspot number over time. The
sunspot number is calculated by multiplying the number of groups of
sunspots by ten and then adding this product to the total count of
individual spots.
The
sunspot number is a way of gauging the level of solar activity or solar
radiation which has a direct effect on the degree of ionization in the
upper atmosphere and ultimately determines the degree of path refraction
of high frequency radio waves. Solar radiation, acting on the different compositions of
gasses at various heights of the atmosphere, generates layers of
ionization and therefore it follows that the number of sunspots can help
predict conditions on radio HF bands.
The point of highest sunspot activity during this cycle is
known as Solar Maximum, and the point of lowest activity is Solar Minimum.
The sunspots will appear in pairs in a more or less
east-west alignment, the eastern sunspot of the pair will be of one
magnetic pole say north and the other western sunspot of the pair will be
magnetic south. In the other hemisphere of the Sun the opposite will be
true. This situation will reverse from one solar cycle to the next. Also
sunspots will be near the solar equator towards the end of a given cycle
and towards the poles at the beginning of the next.
The
detection of the first opposite magnetic polarity sunspots compared to
proceeding cycle's sunspot polarity and the observation of high solar
latitude sunspots will indicate the beginning of the new cycle, cycle 23
ends cycle 24 begins.
A key indicator that the solar maximum has arrived is
that
the sun's magnetic poles flip from north to south that is the Pole that
is magnetic north becomes magnetic south and the Pole that is magnetic
south becomes magnetic north. What this means is that a complete solar
cycle, when the Sun's poles are back to their original magnetic pole is
in fact about 22 years in length.
11,400
years of sunspot history
A
really neat piece of research gives a view of what the sun has been doing
over more than 11,000 years or as far back as the last major ice age
event.
The
Earth is constantly being irradiated by cosmic rays from deep space and
these rays produce in the atmosphere a material known as carbon 14 which
is absorbed by trees among other things. Trees even dead trees retain a
record of the levels of carbon 14 being produced over a very long period
of time. Charged particles from the Sun which are greater during periods
of high sunspot activity repel the cosmic rays and therefore the more
sunspot activity there is the less carbon 14 is recorded in the tree
rings.
Using
the carbon 14 level records the sunspot number estimates have been pushed
back as far as 11,400 years into the past and reveal that the current high
level of solar activity has not occurred for well over 8,000 years. See
figure 1.
The
solar activity during the last 80 to 100 years is by far the exception. A
2003 study found that there had been more sunspots since the 1940s than in the previous
1150 years. The
fact that this period of high activity coincided with the invention and
development of radio is not lost on me! Who knows how a world craving
communication may have develop if the twentieth century was one of the
dead periods of solar activity.
Figure
1: The data for the 11,400 Year Sunspot Number has been graphed using an
Excel spread sheet. 11,000 Year Sunspot Number data can be found courtesy
of the NOAA Paleoclimatology Program and
World
Data
Center
for Paleoclimatology,
Boulder
.
ftp://ftp.ncdc.noaa.gov/pub/data/paleo/climate_forcing/solar_variability/solanki2004-ssn.txt
More
Sunspot Number data:
ROYAL
OBSERVATORY OF
BELGIUM
http://www.sidc.be/index.php
Subtle
changed in their intensity
A
period known as the Maunder Minimum from about 1650 to 1715 suddenly saw very few reports of
sunspots. The Maunder Minimum
coincided with the coldest part of the period known as the Little Ice Age.
While there appears to be a connection there is generally no agreed
mechanism that would have low sunspot numbers connected with the Earth's
climate in such a dramatic way. It may have at least been contributing
factor, but how much of factor is not clear.
The
effect of sunspot activity in relation to climate change is a very
controversial issued at the moment with a complete spectrum of views being
voiced. Generally from what I have read and heard it's for the most part
regarded as minor factor.
Nobody
can deny climate change, as the only constant when it comes to the
Earth's climate is change. The relationship between sunspots and the
Earth's climate is far from understood, which means to me that we can
not be certain if sunspot activity has a minor or more significant role on
our climate. See figure 2 & 3.
The Dalton Minimum was also period of low solar
activity, lasting from about 1790 to 1820. Like the Maunder Minimum it coincided with a
period of lower than average global temperatures.
The
cooler temperatures were exasperated by the eruption in 1815 of
Mount
Tambora
on the
island
of
Sumbawa
, in what is now
Indonesia
. This made the winter of 1816
one of the most miserable and deadly on recorded. The volcanic eruption clearly made things worse, but the cold spell was
well underway from about 1810.
The
year 1816 was referred to in American New England as "eighteen hundred
and froze to death".
See:
A year without a summer http://www.mitosyfraudes.org/Calen/Year1816.html
Much earlier the Sporer minimum
of 1400-1510 was also known as a "little ice age" and saw very
few Sunspots. The world experienced an increase in famines, the Baltic Sea
froze solid in the winter of 1422-1423 and colonies in
Greenland
were starved into oblivion.
Figure
2: Yearly average sunspot numbers from 1610 to 2000
An
interesting comparison is between the above Yearly Average Sunspot Numbers
and the below Yearly Average Mean Temperature for central
England
of a similar period of time. Apart from the two obvious correlations it is
difficult to see many other links due to the general background
temperature noise of other influences, but it is there or is it my
imagination!
Figure
3: The above chart of the annual mean average temperature of central
England
has been graphed using an Excel spread sheet with data accessed from
Met Office Hadley. http://hadobs.metoffice.com/hadcet/
These
monthly temperatures are representative of a roughly triangular area of
the
United Kingdom
enclosed by Lancashire,
London
and
Bristol
. The monthly series, which begins in 1659, is the longest available
instrumental record of temperature in the world.
On a cheery note, I was born in July 1957 during possibly the largest
solar-maximum for 11,000 years. I was trying to work up an angle on this
one, but the best I can do is this. I'm a baby boomer and according to
an entry in Wikipedia the baby boom also peaked around 1957.
Solar
Flares
Solar flares and the related Coronal Mass Ejections (CME)
are the violent explosions on the Sun's surface as a result of a release
of stored magnetic energy in areas near sunspots.
These solar flares often affect the Earth's ionosphere
and disrupt HF radio communications and produce higher noise levels on the
VHF bands.
Solar flare effects vary greatly in magnitude primarily
due to the intensity of the explosion and if it is aimed at or away from
the Earth. Solar flares are far more common during the Sun's solar
maximum, but can occur at any time and often with out warning.
Variations in the solar wind and shockwaves caused by
solar flares buffet the Earths natural magnetic field or magnetosphere
causing the shifting magnetic lines of force to induce electric currents
into long conductors like power transmission lines and even pipelines.
In 1998 a large
flare induced magnetic storm totally shut down the electricity grid
supplying
Canada
's
Quebec
province. The magnetic storm tripped five 735kV lines causing a loss of
some 9450MW of power to the 21350MW load at the time. The system was not
able adapt to the sudden loss of so much power and collapsed in very short
order.
Currents
induced in the long transmission lines and transformer core saturation
which distorted voltages caused system protection to operate and
disconnect the affected vital equipment.
The
strongest flare recorded was in 1859 and witnessed by British astronomer Richard Carrington whom reported two
patches of intensely bright white light coming from the sun. The telegraph which was the high technology of the day
crashed, with reports in the
United States
and
Europe
, of the voltages induced into the long telegraph wires knocking operators
unconscious
and igniting fires due to the magnetic disturbance.
To
gain a perspective on these events a moderate magnetic storm can be about
-100nT (nano-Teslas), an extreme storm would be about -300nT, the storm
that blacked out Quebec measured -589nT and the 1859 storm has been
estimated to have been -1760nT. The implication of an 1859 type storm on
today modern wired world would probably be dramatic.
An
obvious question is how big could a solar flare be? On this I have not
found any real material, however some other stars and stars similar in
size and age to our Sun produce extremely violent flares very frequently,
sometimes as often as every hundred years.
A
particularly violent flare seen on a star slightly less massive than the
Sun in twin star system known as II Pegasi was about one hundred million
times more intense than a typical local solar flare. Had this flare
occurred on the Sun we would not be here to tell the tale, along with most
other life on Earth.
We
are lucky that the Sun seems for the moment at least to be a much gentler
star.
The
Future
Solar
cycle 24 which we are all looking forward too is likely to be a
significant solar maximum and perhaps if we are lucky it may be the second
larges in modern times.
The Sun has
circulating currents of hot plasma much like the ocean currents on Earth
and according David Hathaway of the Solar Physics Group, NASA, the speed
of the circulating current known as the Conveyor Belt determines the
intensity of future solar maximum. The speed of the conveyor belt will
determine the intensity of not the next solar maximum, but the one after.
The speed of the
conveyor belt is measured by observing the speed at which sunspots move on
the surface of the Sun. The conveyor belt moves across the surface of the
Sun sweeping sunspots along with it and then plunges deep in to the
interior to pick up more energy and returns to the surface, a process that
takes from about 30 years to 50 years. See figure 4.
Figure 4: Diagram of the Sun's circulating currents of hot plasma.
The conveyor belt was
moving fast from about 1986 to 1996 meaning lots of magnetic fields will
be swept up for the 2010-2012 solar maximum. This is the basis of
Hathaway's prediction for solar cycle 24.
In recent years
however the conveyor belt has slowed to a speed not seen before. The
conveyor belt normally moves at about 1 metre per second and that's how
it has been since the late 19th century, but the conveyor belt
has decelerated to 0.75 metre per second in the north hemisphere of the
Sun and to only 0.35 metre per second in the south. The slow down
currently being observed mean that Solar Cycle 25 due to peak around 2022
to 2025 is likely be one the weakest in centuries. It is interesting to
note Solar Cycle 25 could be similar to maximums recorded during the Dalton Minimum of 1790 to 1820. There is also
speculation that the slow start to Solar
Cycle 24 is an indicator of it also turning out to be very weak.
Is the Sun about
to go quiet again! Better not get rid of those woolly jumpers.
See http://science.nasa.gov/
for solar prediction stories among many other topics. Many stories are
available as audio files.
Life
under the Sun
The
sun sustains all life on Earth and provides all our power even fossil
fueled power. It is not static, like us it has a beginning and an end and
during its life it will change and evolve. On Earth we have no choice, but
to enjoy what we get from the Sun and learn to adapt to its changes which
are for the most part very gradual, but as research has discovered not
always. Happy DXing!
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