23-6
23.12 Effects of Space Weather on Aircraft Operations.
23.12.1 Communications. HF communications at low- to mid-latitudes are used by aircraft during transoceanic flights and routes where line-of-sight VHF communication is not an option. HF enables a skip mode to send a signal around the curvature of Earth.
HF communications on the dayside can be adversely affected when a solar flare occurs and its photons rapidly alter the electron density of the lower altitudes of the ionosphere, causing fading, noise, or a total blackout. Usually these disruptions are short-lived (tens of minutes to a few hours), so the outage ends fairly quickly.
HF communications at high latitudes and polar regions are adversely affected for longer periods, sometimes days, due to some space weather events. The high latitude and polar ionosphere is a sink for charged particles, which alter the local ionization and provide steep local ionization gradients to deflect HF radio waves, as well as increase local absorption.
Satellite communication signals pass through the bulk of the ionosphere and are a popular means of communicating over a wide area. The frequencies normally used for satellite communications are high enough for the ionosphere to appear transparent.
However, when the ionosphere is turbulent and nonhomogeneous, an effect called scintillation, a twinkling in both amplitude and phase, is imposed upon the transmitted signal. Scintillations can result in loss-of-lock and inability for the receiver to track a Doppler-shifted radio wave.
23.12.2 Navigation and Global Positioning System (GPS). Space weather adversely affects GPS in three ways: it increases the error of the computed position, it causes a loss-of-lock for receivers, and it overwhelms the transmitted signal with solar radio noise.
23.12.3 Radiation Exposure to Flightcrews and Passengers. Solar radiation storms occurring under particular circumstances cause an increase in radiation dose to flightcrews and passengers. As high polar latitudes and high altitudes have the least shielding from the particles, the threat is the greatest for higher altitude polar flights. The increased dose is much less of an issue for low- and mid-latitude flights.
23.12.4 Radiation Effects on Avionics. The electronic components of aircraft avionic systems are susceptible to damage from the highly ionizing interactions of cosmic rays, solar particles, and the secondary particles generated in the atmosphere. As these components become increasingly smaller, and therefore more susceptible, the risk of damage also increases.
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