Lexicon A-Z

Aurora

The common international and technical term for aurora borealis. A distinction between northern lights (aurora borealis) and southern lights (aurora australis) is rather unusual and is only rarely made in scientific publications, as the aurorae always occur synchronously – albeit with varying intensity in winter and summer. The aurora zone lies slightly polewards from the Arctic Circle – in Europe at around 70°N – and forms a more or less circular structure around the globe – the aurora oval. Even with low geomagnetic activity, it glows green, only very faintly and very far north or polewards. During a geomagnetic storm, it shines bright and colourful (green, red, etc.) and moves towards the equator. In mid-latitudes, it is mainly subvisual, i.e. can only be observed photographically with the sensitive sensors of a digital camera on the poleward horizon, especially in populated areas with light pollution, but sometimes also with the naked eye – even in the centre of Berlin.

CME, ICME

Coronal mass ejection, also known as a “solar storm”

☞ See Lexicon: CME

High-speed stream (HSS)

Fast solar wind from coronal holes

☞ See Lexicon: HSS, CIR

NOAA/SWPC

NOAA(National Oceanic and Atmospheric Administration) is the US government weather service that operates the venerable SWPC(Space Weather Prediction Centre – pronounced “Swippsie”) in Boulder, Colorado. SWPC issues daily space weather summaries and forecasts. They use the WSA-Enlil model, which calculates the solar wind and ICME propagation. In addition, SWPC issues official warnings for radiation storms (“SEP events”), radio blackouts and geomagnetic storms, as well as a forecast of the Kp index for the next three days (the individual values should not be taken too precisely and should only be used as an approximate guide). SWPC continues to operate the DSCOVR satellite, some GOES satellites and, more recently, the SOLAR-1 and is the global central collection point for the data available under “Real Time Solar Wind“.

The G1-G5 scale for geomagnetic storms comes from SWPC and is also often used here on the site:

G1 MINOR STORM (Kp 5) Minor storm
Average frequency: 900 days per 11-year cycle
G2 MODERATE STORM (Kp 6) Moderate storm
Average frequency: 360 days per 11-year cycle
G3 STRONG STORM (Kp 7) Strong storm
Average frequency: 130 days per 11-year cycle
G4 SEVERE STORM (Kp 8, Kp 9-) Severe storm
Average frequency: 60 days per 11-year cycle
G5 EXTREME STORM (>= Kp 9.0) Extreme storm
Average frequency: 4 days per 11-year cycle

SWPC introduces itself in this youtube video: https://www.youtube.com/watch?v=SAVjKx69dIY

UTC

Universal Time Coordinated – the generally used time for the synchronisation of machines (e.g. computers), in aviation, the military, space travel, radio communications and also for space weather. All forecasts are issued in UTC, the times on satellite images or graphical model calculations are always UTC. The daily information from NOAA/SWPC is also always UTC, i.e. Thursday G1 Minor Storm refers to Thursday 0000 UTC to Thursday 2359 UTC. The notation without a separator between hour and minute is common, sometimes the unofficial abbreviation UT is used (strictly speaking, this is a different time), sometimes “Z” (pronounced “Zulu”), sometimes GMT (Greenwich Mean Time) is also used, especially in Great Britain. If there is no unit after the time on this website, it may have been forgotten to include it and it may be either UTC or CE(S)T – Central European (Summer) Time.

UTC = CET -1 h
UTC = CEST -2h
CET = UTC +1h
CEST = UTC +2h

The use of UTC is not somehow screwed up, but the best method of transferring data quickly and without errors. As the difference to Central European Time is not very big, you can usually omit the conversion for announced events, as such calculated times are almost never accurate to the hour.

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