Geomagnetic storm

As a magnetic storm is called a disturbance of the magnetosphere of a planet and especially of the earth ( geomagnetic storm ).

Definition and origin

A Erdmagnetsturm is defined by the damage it has changes of the geomagnetic field, measured in units of Tesla ( [T ] ). For classification is used, inter alia, the Dst index ( disturbance storm time index ) that indicates the global mean attenuation of the horizontal geomagnetic field based on the measurements of certain globally distributed stations. This value is calculated every hour and is available in almost real time. There are many influences on the magnetic field, so fluctuations of ± 20 nt are normal. For comparison: In Central Europe, the horizontal component of the earth's magnetic field is about 20 μT normal, ie 20,000 nT.

A geomagnetic storm is typically divided into three phases. The initial phase is characterized by a weakening of the magnetic field by about 20-50 nT within a few dozen minutes. Not every storm event is preceded by such an initial phase, and vice versa does not follow any such disturbance of the magnetic field, a magnetic storm. The actual storm phase begins when the disturbance is greater than 50 nT, where it is an artificially drawn border. In the course of a typical magnetic storm disturbance continues to grow. The strength of a Erdmagnetsturms is called moderate if the maximum disturbance is less than 100 nT, intense, if the fault does not exceed 250 nT, and otherwise as a super storm. Only rarely a maximum attenuation of about 650 nT is exceeded, which is about three percent of the normal value. The phase lasts a few hours and ends when the strength of the perturbation decreases, so the Earth's magnetic field begins again to grow to its typical strength. This recovery phase ends with the attainment of normal value and can last from 8 hours a week.

The disorder is triggered by shock wave fronts of the solar wind caused by solar flares or coronal mass ejections ( KMA) and require about 24 to 36 hours to reach Earth. It lasts about 24 to 48 hours, in some cases several days - depending on the cause of the fault on the sun. The impact of the shock front, composed of electrically charged particles in the magnetosphere leads to a weakening of the earth's magnetic field, which reaches its minimum after about twelve hours.

Effects

Magnetic storms can have multiple effects, notably from the occurrence of polar lights (aurora borealis or aurora australis) in temperate zones such as Central Europe.

First, magnetic storms affect the Earth's magnetic field, and this, in turn, the formation of the Van Allen Belt. This means that all living things are exposed, especially in the polar regions of increased cosmic radiation because there protects the earth's magnetic field generally less for particularly strong magnetic storms. As the growth of trees in increased solar activity apparently runs faster, they have a 11-year period to include in their annual rings. The reasons for this are not yet clear.

Partly due to temporary changes in the ionosphere radio transmissions can be ( such as radio or mobile) disrupted temporarily. In elongate electrical conductors such as power lines and pipelines currents can be induced by some considerable strength, which can lead to permanent damage.

Before the shock wave front strikes the earth, so before you actually can speak of a magnetic storm, they can already cause damage to satellites. This is in addition to the direct damage caused by induction as on the surface of the earth even to another, more indirect way possible: The shock wave can cause local heating and thus a deformation of the Earth's upper atmosphere, resulting in increased drag on satellites in low orbits (Low Earth Orbit LEO) can result. Track changes or increased fuel consumption are then the result. Overall, according to estimated the European Space Agency, was created in the last few years alone because of failure of satellite damage of more than $ 500 million.

The effects of a solar storm as the solar storm of 1859 (see " History " ) would now be devastating. Because at that time there was no Internet, nor the world was so globally networked as it is today, and depending on the power supply.

History

• Magnetic storms were observed in the early 19th century. Alexander von Humboldt investigated from May 1806 to June 1807, the variation of the direction in which a magnetic compass pointed in Berlin. He registered on December 21, 1806 strong interference and could see the following night auroras; the next morning the disturbances were over.

• On 14 July 2000 a class X5 flare was observed on the Sun, whose coronal mass ejection was pointed directly at the Earth. After the arrival of the shock front on the earth a super storm was measured with a maximum error of -301 nT between the 15th and 17th of July. Technical failures were not known.

• Seventeen major flares were observed between 19 October and 5 November 2003. Among them was the strongest flare detected so far: a class X28 flare, which led to very strong interference to radio communications on November 4. Subsequently, several coronal mass ejections (KMA ) met the earth, which led to temporally overlapping magnetic storms with Dst maximum values ​​of -383 nT, -353 nT and -151 nT. During this period fell in Malmö, Sweden from the entire regional grid. Because the technical equipment had failed for aerial surveillance for 30 hours, air corridors in northern Canada were closed for passenger aircraft. At times, put signals from the satellite and navigation systems. According to Japanese data, the particle cloud is 13 times as large as the earth, and with 1.6 million km / h on the road. Up in tropical regions auroras were seen.

• In June 2011, a magnetic storm caused a temporary malfunction of the probe Venus Express; before a failure of the navigation satellite system GPS was warned. The eruption on June 7 was observed among others by the Solar Dynamics Observatory ( SDO), one designed for solar observation satellite.