page_title: Space weather
section_title: Long-distance radio signals
hierarchical_section_title: Space weather / Effects / Long-distance radio signals
caption_attribution_description: English: This is a graphic showing the cosmic ray and solar energetic particle environment for aviation radiation.
context_page_description: Space weather is a branch of space physics and aeronomy, or heliophysics, concerned with the time varying conditions within the Solar System, including the solar wind, emphasizing the space surrounding the Earth, including conditions in the magnetosphere, ionosphere, thermosphere, and exosphere. Space weather is distinct from but conceptually related to the terrestrial weather of the atmosphere of Earth. The term space weather was first used in the 1950s and came into common usage in the 1990s.
context_section_description: Radio wave in the HF band (3 to 30 MHz) (also known as the shortwave band) are reflected by the ionosphere. Since the ground also reflects HF waves, a signal can be transmitted around the curvature of the Earth beyond the line of sight. During the 20th century, HF communications was the only method for a ship or aircraft far from land or a base station to communicate. The advent of systems such as Iridium brought other methods of communications, but HF remains critical for vessels that do not carry the newer equipment and as a critical backup system for others. Space weather events can create irregularities in the ionosphere that scatter HF signals instead of reflecting them, preventing HF communications. At auroral and polar latitudes, small space weather events that occur frequently disrupt HF communications. At mid-latitudes, HF communications are disrupted by solar radio bursts, by X-rays from solar flares (which enhance and disturb the ionospheric D-layer) and by TEC enhancements and irregularities during major geomagnetic storms.
  Transpolar airline routes are particularly sensitive to space weather, in part because Federal Aviation Regulations require reliable communication over the entire flight. Diverting such a flight is estimated to cost about $100,000.
caption: All passengers in commercial aircraft flying above 26,000 feet (7,900 m) will typically experience some exposure in this aviation radiation environment.
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