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   Written by: CHIU Hung-yu      December 2009

  1. 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:

    (a) 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.

    (b) Solar radiation storms - streams of energetic particles and plasma pose threats to astronauts in space and to passengers and crews on polar flights.

    (c) 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.

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  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

Last revision date: <13 Feb 2019>