Which statement best describes Night Effect?

Which statement best describes Night Effect?

• A. Interference lasting several hours during daytime
• B. For about one hour around sunrise and sunset, the ionosphere height changes interfere with ground waves
• C. It does not affect ground wave reception
• D. It only affects satellite signals

Answer: (B)

Twilight ionospheric changes cause interference between ground waves and sky waves. As sunrise or sunset approaches, the ionosphere rapidly shifts in height and density, altering how radio waves propagate. Ground waves travel along the Earth's surface, while sky waves depend on reflection from the ionosphere. When the ionosphere’s height changes during these transition periods, the two propagation paths can arrive with different phases and amplitudes, producing interference that can degrade or modulate reception. This effect typically lasts about an hour around sunrise and sunset, which is why this timing is the best description. It concerns ground-wave reception and the twilight propagation changes; satellite signals follow different paths and aren’t described by this effect.

Twilight ionospheric changes cause interference between ground waves and sky waves. As sunrise or sunset approaches, the ionosphere rapidly shifts in height and density, altering how radio waves propagate. Ground waves travel along the Earth's surface, while sky waves depend on reflection from the ionosphere. When the ionosphere’s height changes during these transition periods, the two propagation paths can arrive with different phases and amplitudes, producing interference that can degrade or modulate reception. This effect typically lasts about an hour around sunrise and sunset, which is why this timing is the best description. It concerns ground-wave reception and the twilight propagation changes; satellite signals follow different paths and aren’t described by this effect.