What phenomenon is caused by ionospheric irregularities and leads to rapid variation of received signal amplitude and phase?

• A. Elevation
• B. Range
• C. Azimuth
• D. Scintillation

Answer: (D)

Scintillation is the phenomenon described here. It happens when small-scale irregularities in the ionosphere’s electron density distort the wavefront of a radio signal as it passes through, causing rapid, random fluctuations in both the received signal’s amplitude and its phase. These fluctuations occur on short timescales—typically seconds to minutes—and depend on frequency, being more noticeable at lower to mid radio frequencies. In practical terms, you may see the signal strength rise and fall quickly while the carrier phase hops around as the scattered waves interfere constructively and destructively. This is driven by ionospheric turbulence in regions with strong density irregularities, such as near sunset or in equatorial and polar areas, and it differs from geometric factors like elevation, range, or azimuth, which describe where the signal is coming from rather than how the medium is altering it.