G3A01: How does a higher sunspot number affect HF propagation?

How does a higher sunspot number affect HF propagation?

AHigher sunspot numbers generally indicate a greater probability of good propagation at higher frequencies
BLower sunspot numbers generally indicate greater probability of sporadic E propagation
CA zero sunspot number indicates that radio propagation is not possible on any band
DA zero sunspot number indicates undisturbed conditions

Why Sunspots are a proxy for the sun's ultraviolet and X-ray output, which is what ionizes the F region. More sunspots means a denser F2 layer, a higher critical frequency and therefore a higher maximum usable frequency, so bands like 15, 12 and 10 meters open for long-haul work. At sunspot minimum the ionization drops and HF activity shifts down to 40, 30 and 20 meters.

Watch out A zero sunspot number does not shut down propagation or guarantee quiet conditions: the lower bands still work, and geomagnetic storms from coronal holes can disturb the ionosphere even with a blank sun. Sporadic E is a summer/E-layer phenomenon that is largely independent of the sunspot cycle.

More sunspots, more ionization, higher MUF. High sunspots = the high bands come alive.

HamSandwich explanation, first draft. The question and answers are the NCVEC text.

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