photo& Atanas Stepanov

An aurora borealis, which is a rare phenomenon for our geographical latitudes, is the reason for the red colored sky over Bulgaria on November 5. This is what Pencho Markishki, IA with NAO at BAS and Department of Astronomy at SU „St. Kliment Ohridski“.

From Bulgaria, such a phenomenon can only be seen in rare cases – after a powerful coronal mass ejection from the Sun, and if the eruption was in the direction in which the Earth is currently located.

After the stream of charged particles travels the distance between the Sun and the Earth, it bombards the Earth’s magnetosphere and even bends it on its dayside. A geomagnetic storm is brewing, which can disrupt radio communications. These solar plasma particles that enter the upper layers of our atmosphere give rise to the auroras.

In rare cases – when the process is very intense, the aurora borealis can also be observed from lower latitudes.

The intensity of the flow of charged particles is evaluated by the geomagnetic effect it causes, through the so-called planetary Kp index.

It is a balometric (logarithmic) quantity that can have values from 0 to 9 and is determined by numerous ground-based geomagnetic stations located in the northern and southern hemispheres of the Earth. Between 16:45 and 18:45 last night, the Kp index reached and slightly exceeded 8, then began to decline.

These phenomena are monitored with caution, as they are not harmless. In addition to problems with radio communications, after powerful solar flares and the resulting geomagnetic storms, failures can occur in the power systems and cable telecommunications networks of major countries. The reason is that additional voltage is induced in the wires of the power transmission networks, which can disable important equipment. This harmful effect is stronger the greater the total length of power lines in a country’s energy ring.

There is no lack of examples of such problems in history: In 1859, during a magnetic storm, the telegraph lines in the USA and in Europe went out of order. In 1972, also during a magnetic storm, telephone connections were cut in the state of Illinois. In 1989, 6 million Canadians in the province of Quebec were left without heating and lighting after a power outage, again during a powerful magnetic storm.

For geomagnetic storms, forecasts up to 2-3 days ahead are more certain. Longer-term forecasts are based on periods of almost 2 weeks during which an active region on the solar surface, which is the source of the solar wind, is visible from Earth. It is also important how long the given area will remain active on the Sun.

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