Solar Conditions & Ham Radio Propagation

Solar activity, governed by the solar cycle, impacts radio skywave propagation on Earth. When solar activity is high (such as during solar flares or geomagnetic storms), an increase in sunspots enhances the ionosphere's ability to refract radio waves. Conversely, during periods of low solar activity, a decrease in sunspots diminishes this refractive capacity, negatively impacting global communication. The careful selection of suitable ham bands is therefore crucial to the success of ham radio operations.

Amateur radio operators use solar indices to predict radio wave behavior and adjust communication strategies.

See for example the following banner courtesy of Paul L Herrman, N0NBH:

The banner displays numerical indices, which are explained below:

SFI - Solar Flux, 2800MHz (10.7cm) ↗ (SFU units) correlates with F2-region ionization; higher value better HF conditions.

SN - Daily Sunspot Number is a measure of the solar activity; like SFI it correlates with enhanced F2-region i.e. better HF conditions

K-Index ↗: Geomagnetic Disturbance; good conditions K < 3 | A -Index↗: 24 hours Average; good conditions A < 10

304 Å: Total Solar Radiation at SEM (Solar EUV Monitor) wavelenth: 304 Ångstroms (30.4nm) that affects F-region ionization

Ptn - Proton Flux Density | Elc - Electron Flux Density in the Solar Wind; both impact E-region

Aurora indicates the strength of the ionization of the F-region in the polar regions

MUF Boulder - Maximum Usable Frequency (MHz) at Boulder, CO, USA, updated every 15 minutes.

GeoMag - Calculated - Earth`s Geomagnetic based on K-Index. Updated every 3 hours.

Sig Noise - Calculated every ½ hour: S-units (Solar Wind and Geomagnetic Activity)

The project "Understanding HF Propagation" provides a detailed overview and tutorials on HF propagation.