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Space Weather Alert Categorization

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Educational Resources

Space Weather Alert Categorization

Solar storms pose hazards to the near-Earth space environment. After studying these storms, scientists categorize their effects into three main types. These are listed in decreasing severity, as follows:

  1. Geomagnetic storms - the Earth's geomagnetic field is distorted due to the strong solar wind. Through electromagnetic induction, transient electric surges can damage transformers, electronic instruments and navigation equipment. 
  2. Solar radiation storms - streams of energetic particles and plasma pose threats to astronauts in space and to passengers and crews on polar flights.
  3. Radio blackouts - intense X-rays with ionizing power upset the Earth's ionosphere, producing signal scintillations (which mean noise, distortion and attenuation) and disrupting radio communication. 

In general, geomagnetic storms affect the people on Earth most.  Solar radiation storms pose threats mainly to those flying in space and high altitudes, while radio blackouts mainly affect those operations involving navigation or radio communications.

Space weather type Effects Intensity scale Intensity descriptor
Geomagnetic storms Solar wind bursts cause disturbances in the geomagnetic field. G5 Extreme
G4 Severe
G3 Strong
G2 Moderate
G1 Minor
Solar radiation storms Increasing number of energetic particles elevates the radiation level. S5 Extreme
S4 Severe
S3 Strong
S2 Moderate
S1 Minor
Radio blackouts X-ray emissions from the Sun cause disturbances of the ionosphere. R5 Extreme
R4 Severe
R3 Strong
R2 Moderate
R1 Minor

Table 1 - The warning levels of NOAA Space Weather Scales(Source: NOAA Space Weather Prediction Center web site)

The Space Weather Prediction Center (SWPC) of the U.S. National Oceanic and Atmospheric Administration (NOAA) uses the above categorization when issuing alerts and warnings of space weather. This webpage aims at conveying these alerts and warnings to the general public in Hong Kong.


1. "The Potential Role of WMO in Space Weather" - WMO Space Programme, World Meteorological Organization, April 2008.

2. "NOAA Space Weather Scales", NOAA Space Weather Prediction Center