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Clickable overview of solar activity influencing HF propagation on Earth. Onset times are measured from the occurrence at the Sun’s surface. The mathematical symbol ∩ stands for intersection. The drawing is based on a reading of Paul Harden, NA5N, Solar activity & HF propagation with a “flare” of solar physics, FDIM Symposium, 2005. (Created with GraphvizPDFSVGdot and makefile are available.)

OWF versus MUF

HF propagation prediction is a statistical science.

Sporadic Es layer

When a sporadic Es layer is present, its maximum usable frequency relates to its ordinary critical frequency approximatively as follows:1

\[MU\!F_{E_s} \approx \frac{f_{o,E_s}}{0.188} \approx 5.319\,f_{o,E_s}\]

Plot (updated every 15 minutes) of the critical frequency fo,Es of the sporadic Es layer in the vicinity of where your IP address is thought to be located. The maximum useable frequency of a sporadic Es layer, MU\!F_{E_s} is about 5.319 times the depicted critical frequency f_{o,E_s}. Source: NOAA

Acknowledgements

For the real-time ordinary & extraordinary wave critical frequency of the F2 region (fo,F2 & fx,I), the height of sporadic Es blanketing or screening (hEs) and the real-time the maximum useable frequency (MUF):

For the real-time effective solar sunspot number (SSNe):

References

1.
Emil Pocock, W3EP. Sporadic-E propagation at VHF: A review of progress and prospects. QST. Published online April 1988. https://www.uksmg.org/content/sporade.htm
2.
Global Ionospheric Radio Observatory (GIRO). DIDBase. http://giro.uml.edu/
3.
NorthWest Research Associates, Inc (NWRA). Space weather indices summary. https://spawx.nwra.com/spawx/env_latest.html
5
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