|
Space Weather
Once you've
seen it you'll never forget; it's amazing and fabulous when the sun and
the earth start playing with light. No earthly, human laser-show can
compete with this show which has its source at a very much higher level.
It's known as polar light or the Aurora borealis and is all but impossible
to predict . It suddenly appears and can last for several minutes or
several hours; sometimes days.
What happens? The sun plays the leading part in this masterpiece.
Sometimes it throws out huge amounts of hot gas
and very fast electrically charged particles. These particles dash against
oxygen- and nitrogen atoms in the upper layers of the earth's atmosphere.
The energy that's been liberated forms the Polar Light.
Its the most spectacular proof that there's more between Sun and Earth.
This Solar Wind controls everything there; and controls
Space weather which impacts upon our daily life and
technology.
A real star in the
title role
The Sun is overwhelming important to our life; but how does it affect Space Weather?
To answer that we need to take a detailed look at the sun..
It is the largest object of our solar system and contains approximately 98% of the
total mass. One hundred and nine Earths would be required to
fit across the Sun's disk, and its interior could hold over 1.3 million
Earths. The Sun's outer visible layer is called the photosphere and has a
temperature of 6,000°C (11,000°F). This layer has a mottled appearance
due to the turbulent eruptions of energy at the surface.
Three layers are very important: 
- this photosphere: that's where the sunspots
can occur
- the chromosphere above the photosphere. Solar energy passes through
this region on its way out from the centre of the Sun. Flares
arise in the chromosphere., coupled with coronal
mass ejection.
- the corona; that's the outer part of the sun's atmosphere. In this
region the prominences appear. these are
immense clouds of glowing gas that erupt from the upper chromosphere.
The outer region of the corona stretches far into space and consists
of particles travelling slowly away from the Sun. The corona can only
be seen during total solar eclipses.
Lets have a closer look to these three mentioned phenomenon.
Sun spots
Sunspots are
darker irregular spots at the sun's surface. Sometimes, when the sun goes
down you can see them with the bare eye. The old Chinese astronomers
first described these spots about 800 BC; but it took till Galileo
Galilei, to study them properly, using his telescope.
Sunspots develop as very tiny stains in the photosphere of the sun,
growing out to a group of huge dark area's that will disappear again. These
area's have a lower temperature (about 5000 K) than the surrounding solar
surface (6000 K).  That's
why they have a dark colour. Their amount isn't constant; over
the last 300 years, the average number of sunspots has regularly waxed and
waned in an 11-year sunspot cycle. The Sun, like Earth, has its seasons
but its year equals 11 of ours. The last solar minimum was in 1996, and
the last maximum was in 2001. The next expected minimum is 2007.
During these maxims the sun has an enormous magnetic-activity;
with eruptions spitting huge amounts of hot gas into space: solar flares.
Solar flares
The
solar flares; develop in the chromosphere, above the sunspots. They are intense,
temporary releases of energy. From earth's ground-based observatories the
flares are seen  as bright areas on the sun and can last from minutes to
hours. Flares are our solar system's largest explosive events which can be
equivalent to approximately 40 billion Hiroshima-size atomic bombs. The
primary energy source for flares appears to be the tearing and
reconnection of strong magnetic fields. They radiate throughout the
electromagnetic spectrum, from gamma rays to x-rays, through visible light
out to kilometre-long radio waves. Flares sometimes
are associated with magnetic solar activity; an eruption of
quick electric charged particles: the coronal mass ejection (CME's).
Lethal
Solar Wind: Coronal
Mass Ejections
The
outer solar atmosphere, the corona, is structured by strong
magnetic fields. Where these fields are closed, often above sunspot
groups, the confined solar atmosphere can suddenly and violently release
bubbles or tongues of gas and magnetic fields called coronal mass
ejections. A large CME can contain 10.0E16 grams (a billion tons) of
matter that can be accelerated to several million miles per hour in a
spectacular explosion. Solar material is spit out into space consisting
hot, magnetized, supersonic sort of plasma; carrying
 large
amounts of kinetic and electrical energy. These CME's have an impact on
everything in its way: all the planets, our earth included, unto far
beyond Pluto. This material as you would expect is very hazerdous to
health without proper protection its fatal.
And
it
is this "solar wind" that dictates the Space Weather.
Between Sun and
Earth: interplanetary medium
The
region between the Sun and the planets has been termed the interplanetary
medium. Although once considered a perfect vacuum, this is actually a
turbulent region dominated by the solar wind, which flows at velocities of
approximately 250-1000 km/s (about 600,000 to 2,000,000 miles per hour).
Other characteristics of the solar wind (density, composition, and
magnetic field strength, among others) vary with changing conditions on
the Sun. The effect of the solar wind can be seen in the tails of comets
which always point away from the Sun.
How
can we survive that violence?
The Earth - and all
the other planets - has her own way to protect life against this fatal radiation of the sun. She is also surrounded by a magnetic
field (called the "magnetosphere"); leading the solar wind away
from the planet. Earth's magnetic field can sense the solar wind with its speed,
density and magnetic field. Because the solar wind varies over time
scales as short as seconds, the interface that separates interplanetary
space from the magnetosphere is very dynamic.
Earth's magnetic field is very
similar to the pattern formed when iron filings align around a bar magnet.
Under the influence of the solar wind, these magnetic field lines are
compressed in the Sunward direction and stretched out in the downwind
direction. This creates the magnetosphere, a complex, teardrop-shaped
cavity around Earth. The most of the solar material can only reach the
so-called ionosphere, a layer of Earth's upper atmosphere where photo
ionization by solar x-rays and extreme ultraviolet rays creates free
electrons. Normally the magnetosphere can keep the Suns violence far away,
about 60.000 km in the direction of the Sun. However, during episodes of elevated
solar wind density or velocity, the influence of the sun reaches further inward to
within 36.000 km (and that's the altitude of the highest satellites).
Solar Effects at
Earth
In
the introduction we started with the most spectacular and visible effects
of Solar Wind: the Polar Lights.
But there are a lot more impacts of Solar activity perceived at Earth, and
while our satellite- technology grows, the Solar influence evolves. The
Solar Wind disrupts the earth's magnetic field. And, as the
magnetosphere extracts energy from the solar wind, internal processes
produce geomagnetic storms.
These storms are the trouble-makers in our technology, biology and
climate. But sometimes we get something in return: the magnificent free
laser-show called Aurora, polar lights.
Aurora
The aurora is a dynamic
and visually delicate manifestation of solar-induced geomagnetic storms.
The solar wind energizes electrons and ions in the magnetosphere. These
particles usually enter Earth's upper atmosphere near the polar regions.
 When
the particles strike the molecules and atoms of the thin, high atmosphere,
some of them start to glow in different colours.
Auroras begin
between 60 and 80 degrees latitude. As a storm intensifies, the auroras
spread toward the equator. During an unusually large storm in 1909, an
aurora was visible at Singapore, on the geomagnetic equator. The auroras
provide pretty displays, but they are just a visible sign of atmospheric
changes that may wreak havoc on technological systems.
Our
technology: disrupted Systems
Communications
Many communication systems utilize the ionosphere to reflect radio
signals over long distances. Ionospheric storms can affect radio
communication at all latitudes. Some radio frequencies are absorbed and
others are reflected, leading to rapidly fluctuating signals and
unexpected propagation paths. TV and commercial radio stations are little
affected by solar activity, but for example ground-to-air, ship-to-shore,
and amateur radio are frequently disrupted. Radio operators using high
frequencies rely upon solar and geomagnetic alerts to keep their
communication circuits up and running.
And also some military detection or early-warning systems are also
affected by solar activity.
Every Aviation
Administration routinely receives alerts of solar radio bursts so that
they can recognize communication problems and forego unnecessary
maintenance. When an aircraft and a ground station are aligned with the
Sun, jamming of air-control radio frequencies can occur. This can also
happen when an Earth station, a satellite, and the Sun are in
alignment.
Navigation Systems
Some
navigation-systems, used on ships and by aircrafts, such as Decca and Omega,
are adversely affected when solar activity disrupts their signal
propagation. These navigation systems consists of transmitters located
through out the world. Airplanes and ships use the very low frequency
signals from these transmitters to determine their positions. During solar
events and geomagnetic storms, the system can give navigators information
that is inaccurate by as much as several miles. If navigators are alerted
that a proton event or geomagnetic storm is in progress, they can switch
to a backup system.
GPS signals; are less sensitive, but can be affected when solar activity
causes sudden variations in the density of the ionosphere.
Satellites
Geomagnetic
storms and increased solar ultraviolet emission heat Earth's upper
atmosphere, causing it to expand. The heated air rises, and the density at
the orbit of satellites up to about 1000 km increases significantly. This
results in increased drag on satellites in space, causing them to slow and
change orbit slightly. Unless low-Earth-orbit satellites are routinely
boosted to higher orbits, they slowly fall, and eventually burn up in
Earth's atmosphere.
Skylab is an example of a spacecraft re-entering Earth's atmosphere
prematurely as a result of higher-than-expected solar activity. During the
great geomagnetic storm of March 1989, four of the Navy's navigational
satellites had to be taken out of service for up to a week.
As
technology has allowed spacecraft components to become smaller, their
miniaturized systems have become increasingly vulnerable to the more
energetic solar particles. These particles can cause physical damage to
microchips and can change software commands in satellite- borne computers.
Differential
Charging
Another problem for satellite operators is differential charging.
During geomagnetic storms, the number and energy of electrons and ions
increase. When a satellite travels through this energized environment, the
charged particles striking the spacecraft cause different portions of the
spacecraft to be differentially charged. Eventually, electrical discharges
can arc across spacecraft components, harming and possibly disabling them.
Bulk Charging. Bulk charging (also called deep charging) occurs when
energetic particles, primarily electrons, penetrate the outer covering of
a satellite and deposit their charge in its internal parts. If sufficient
charge accumulates in any one component, it may attempt to neutralize by
discharging to other components. This discharge is potentially hazardous
to the satellite's electronic systems.
Climate
So the sun has surely influence at the earth's atmosphere. But does the
variable solar activity also affect the climate?
The eleven-years cycle should be recognized in the
weather-registrations and other effects. For more than a century
researchers are trying to find possible relations.
Its known that there were only a few solar spots during the little Ice
Age, from 645-1715. You can also think of the amount of solar spots and
the crop-yields during the years.
Since 1979, there are accurate satellite data, showing that you can
hardly find a connection with the eleven-years cycle in solar activity and
the average earth temperature. The variation in temperature is less than
0,01 C.
But there are more and more indications that slower variations of solar
activity surely has its impact on the earth's climate.
Recent research has made clear that part of the global warming, in the
first half of the 20the century, can be explained as a combination of less
volcano-activity (volcanic eruptions cools the atmosphere) and an increase
of solar activity. So merely natural causes for global warming.
During the second half of the 20the century however, global warming can be
explained by human activity, as both the solar -and volcano-activity
didn't change.
Other
effects: biology, electricity, astronauts and pipelines
But
there are more effects: researchers have found that animals with
navigational abilities, like pigeons, whales and dolphins, are very
confused during a geomagnetic storms: they seem to loose their natural
ability of navigation.
A
geomagnetic storm can be harmful for electric transmission systems. As a
result of a huge geomagnetic storm, 6 million people in Montreal, Quebec
were without electric power. Some other area's in the US and Sweden also
lost power.
Rapidly fluctuating fields can induce currents into pipelines.
And last but not least: astronauts can be injured by intense solar flares.
Humans on earth are protected by the earth magnetically field, but in
space humans are subject to the lethal and violent solar wind.
Space weather
Only during the past few decades it has been
realized that solar activity can harm and affect life on earth. Of course
with the growth of our technology, the influence of the Solar Wind
increases.
The
research to solar activity and the impact on human life has become a very
important issue in all kinds of disciplines.
Want
to know more? Visit:
www.spaceweather.com
With thanks to NOAA for provided
information.
Mail
to:
wijke@scribeweekly.com
You can discuss any of the issues raised in
Scribeweekly by joining our forum. Registration is quick and easy
click
here to visit.
|
