Which of the following is indicated by a sudden rise in radio background noise across a large portion of the HF spectrum?
A temperature inversion has occurred
A coronal mass ejection impact or a solar flare has occurred✓Bonne réponse
Transequatorial propagation on 6 meters is likely
Long-path propagation on the higher HF bands is likely
Explication
The band-wide noise rise comes from solar radio bursts — types II, III and IV — which are emitted at the Sun by the flare and by the shock the eruption drives ahead of it, and which arrive with the light about eight minutes later. The option's word “impact” is imprecise: the arrival of the coronal mass ejection's plasma at Earth occurs one to three days afterwards and produces a geomagnetic disturbance, not broadband HF noise. A temperature inversion is a tropospheric effect acting at VHF and above, and improved transequatorial or long-path conditions do not announce themselves as a rise in the noise floor.