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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.)


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):


1. Global Ionospheric Radio Observatory (GIRO). DIDBase. Available at: http://giro.uml.edu/.

2. NorthWest Research Associates, Inc (NWRA). Space weather indices summary. Available at: https://spawx.nwra.com/spawx/env_latest.html.

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