What is solar flux?

Solar flux is a measure of the radio frequency energy emitted directly by the sun. In amateur radio, it is primarily measured at a frequency of 2800 MHz (10.7 cm wavelength), which strongly correlates with solar activity and the ionization levels of the Earth's atmosphere. A higher solar flux value indicates higher levels of solar radiation, meaning a more heavily ionized ionosphere and better HF radio propagation. While sunspots are related to solar activity, solar flux specifically refers to the RF energy itself, making distractors about sunspot counts, magnetic field density, or ionospheric tilt incorrect.