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The
some what orderly solar cycles that have been observed for a little over
three hundred years or so have ebbed and flowed producing some very
intense solar maximum (Peak sunspot and solar activity) and sometimes
almost not shown at all. The low intensity solar cycles, particularly when
there has been a succession of them appear to have a connection with
general climatic conditions on Earth.
Periods such as the Maunder Minimum
from about 1650 to 1715 saw very few reports of sunspots and coincided
with the coldest part of the period known as the Little Ice Age.
The
absence of sunspots or a very active Sun in terms of sunspot activity
seems to have very little observable change in total solar output;
therefore a connection between sunspot activity and the Earth's climate
has struggled to gain credibility. The mechanism may not be entirely
understood, but historic records of climate and sunspot activity seems to
indicate a connection.
The
sunspot connection may at the very lest be a contributing factor as it may
have been during the relatively recent Dalton Minimum. The Dalton
Minimum was a period of low solar activity, lasting from about 1790
to 1820 that also 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.
A
determination of solar activity for the last 11,000 years has been made
using the carbon 14 proxy record.
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.
This
determined record of solar activity sees a striking correlation between
low solar activity and a series of well document cool climate periods
during this time.
Seeing
order in the chaos
These
seemingly random periods of low sunspot activity may have more order and
predictability than appears at first glance.
An interesting paper written by
I. Charvatova in
1999 regarding Celestial
Barycentrics (The orbital mechanics of the solar system) speculates
about much longer duration cycles that impact on the behaviour of the sun
and by extension the earth's climatic conditions.
Not
generally appreciated is the fact the planets of the solar system do not
actually orbit around the sun, they including the sun orbit around the
centre of the solar system's total mass. The Sun representing 99.8% of
the total solar system's mass orbits around a point very close to the
centre, however it can be more than a Sun diameters from the central
point.
The
mechanics of objects orbiting around the central point of the mass in a
celestial system can be more clearly seen when the orbits of binary stars
are observed. Take a two star system where both stars are identical in
mass, both stars will orbit around a point half way between each other.
Fig.
1: Orbital
dynamics of a celestial
object and it's satellite.
Our
sun is influenced by the distribution of the total solar system's mass,
but primarily by the positions of the four largest planets in order of
mass, Jupiter, Saturn, Uranus and Neptune. The below plot the Sun's
position in relation to solar system's centre point over a fifty year
period from 1945 to 1995 clearly shows the dynamics of this tug of war
between the system heavy weights. See Fig. 2.
It is in fact by observing the wobble of distant stars
that astronomer are able to determine if a star has planets, the size
of the planets and the orbit of the planets about the star. This technique
is the method that has resulted in the discovery of all the so called exoplanets
(Planets outside of our solar system) to date.
Fig.
2: The sun's diameter is marked by a thick circle. The position
of the centre of mass relative to the sun's centre marked by a cross and
the respective years is indicated by small circles.
The
orbit of our Sun around the central and moving centre mass of the solar
system generally forms a well ordered pattern referred to as a Trefoil. See below the
pattern that is referred to as a Trefoil pattern.
Fig. 3: Trefoil pattern
sometimes referred to as the trefoil knot.
The
Trefoil pattern or something resembling it is the norm and appears
associated with long periods of relatively consistent solar cycles,
however every now and then this pattern is disrupted and a period of disordered
motion grips the Sun. This abnormal disordered period appears to be
associated with less sunspot activity and generally lower temperatures
here on Earth.
The study by the author proposes that the 4 most influential
planets orbiting around the our Sun produce a number of repeating cycles,
a 2402 year cycle, a number of 178 year periods within the 2402 years, and
a 370 year period also within the 2402 year cycle. They also reveal
the order and chaos within the motions of the Sun around the centre of
mass within these periods.
The below diagram show the Sun's path around the centre of mass
of the solar system for defined periods of time starting in the year 1192
to the year 2134. The six upper plots show the Sun's path in the orderly
Trefoil
type pattern. The lower five plots show the disordered path and the
related grand minima that also saw temperature plunge on Earth.
Fig. 3: Diagram
of the Sun's path around the centre of mass of the solar system for
defined periods of time starting in the year 1192 to the year 2134.
Of interest to us right now is that we are entering (since 1985 and
on going too until 2040) one of these periods of "disordered"
motion. What is most interesting is that the last four
"disordered" periods coincided with the "Wolf", "Sporer",
"Maunder", and "
Dalton" climate minimums.
The table below clearly shows that while the grand minimums are not
all that common they can however last some time.
|
Duration centre year
|
Duration in years
|
Name
|
|
1810
|
40
|
Dalton
|
|
1680
|
80
|
Maunder
|
|
1470
|
160
|
Spörer
|
|
1305
|
70
|
Wolf
|
What's
this have to do with radio?
The solar cycles clearly have everything to do with radio
propagation as it is typically experienced on the HF and low VHF bands.
However such long duration cycles that are at a minimum several
generations in length are difficult to apply practically to ham radio
operations. It is more a point of interest in the ongoing speculation of
what the next cycle will bring and how this marvellous natural feature may
in fact work! It is of particular interest with respect of the new cycle
24 and how it might develop with the view that we are well into a period
of disordered motion as proposed in the author's paper. We may have
front row seats into a greater understanding of not only the solar cycles,
but also to the effects on the Earth's climatic conditions by the subtle affects of these solar cycles.
A grand minimum would make the depressed HF conditions that we have
been experiencing for 2008 the norm for the next generation or three.
All this may be a bit depressing if you like me were looking
forward to nice big solar max, but maybe we have more to worry about other
than not seeing that fantastic F2 opening to Hawaii on six metre! If the
past is any guide a grand minimum would likely disrupt food production,
promote famines and for those living in the extreme northern and southern
latitudes could be directly life threatening.
The
arguments proposed in Charvatova's paper are far from holding centre
stage, however the test of time and observation will determine its place
in our understanding of the relationship that the Earth and her occupants
have with the greater universe.
For more information on long term solar cycles.
See:
http://www.ann-geophys.net/18/399/2000/angeo-18-399-2000.pdf
Author:
I.
Charvatova
Geophysical
Institute
AS
CR, Bočnĭ II, 141 31 Praha 4,
Czech
Republic
Received: 30 September 1999 / Revised: 14
January 2000 / Accepted: 17 January 2000
For more information on centre of mass dynamics.
See:
http://astro.unl.edu/naap/esp/centerofmass.html
For more information on Extrasolar planets. See:
http://en.wikipedia.org/wiki/Extrasolar_planet
For more information on the effects of grand minimums on climate. See:
http://en.wikipedia.org/wiki/Little_Ice_Age
Also
see earlier article 'The Restless Sun - Past and Future of the Solar
Cycle'
(Published in the WANSAC magazine Vol 38 Issue September and
October 200)
http://members.optushome.com.au/vk6ysf/vk6ysf/solarcycles.htm
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