Question
Which ionospheric region is closest to the surface of Earth?
Answer Options
- A) The D region
- B) The E region
- C) The F1 region
- D) The F2 region
Correct Answer: A
Explanation
The ionosphere is composed of several distinct layers of ionized gas, designated D, E, and F (which often splits into F1 and F2). The D region is the lowest of these ionized layers, located approximately 50 km to 90 km above the Earth’s surface.
Because the D region is the lowest, it is only present during the daytime when sunlight ionizes the air. It is not generally useful for refracting HF radio waves; instead, it acts as a significant absorber of signals, especially at lower frequencies, which is why the 80-meter band is nearly unusable during the day.
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