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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 6,000C (11,000F). 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.  


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

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.

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.


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:

With thanks to NOAA for provided information.

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