Question
Which of the following is indicated by a sudden rise in radio background noise across a large portion of the HF spectrum?
Answer Options
- A) A temperature inversion has occurred
- B) A coronal mass ejection impact or a solar flare has occurred
- C) Transequatorial propagation on 6 meters is likely
- D) Long-path propagation on the higher HF bands is likely
Correct Answer: B
Explanation
A sudden and significant increase in the background noise level across the HF spectrum is a highly distinctive signature of a major space weather event. Noise in the HF bands is largely due to natural atmospheric and galactic sources, but sudden widespread increases typically involve particle energy affecting the Earth’s environment.
This phenomenon is indicated by a coronal mass ejection impact or a solar flare has occurred. A solar flare causes a sudden increase in X-ray flux, which triggers a D-layer absorption event on the sunlit side of Earth, causing the sudden drop in received signal but an increase in background noise (sometimes called a Shortwave Fadeout or SWF). A CME impact, though slower, can cause a similar, prolonged increase in noise as charged particles heat up the atmosphere during a geomagnetic storm.
This topic was automatically created to facilitate community discussion about this exam question. Feel free to share study tips, memory tricks, or additional explanations!