Space weather Operational Airline Risks Service (SOARS)
Home  |  HF Comms.  |  SatCom/SatNav  |  Radiation  ||  SpW Summary  |  Solar Images  |  Links

HF Communications: D-Region Absorption

Lower/Mid Latitudes Polar Region
Current HF Flags, from IPS
SWF Warning Current HF Fadeout Warning
SWF Event Current HF Fadeout Event
Current Activity Report, from SEC
Range 1 (minor) to 5 (extreme)
NOAA Scale
< Radio Blackouts
Radiation Storm >
(These images update automatically. Click on an image if you want see a larger version.) [Polar Maps]

The HF propagation window shifts in frequency throughout the day and year, depending on local and solar conditions. SWENET provides a 24h high latitude ionospheric forecast for the polar and auroral regions (produced by DIFS).

RF propagation in the HF (High-Frequency) band can be affected by two types of D-Region absorption event - in extreme conditons either type can produce a Radio Blackout: [more]
  • At lower latitudes, X-rays from solar flares can cause a Short Wave Fade (SWF) event - SWF events can only occur on the daytime side of the Earth and persist for the duration of the flare (tens of minutes to hours). A prediction of the effect of this type of event is shown in the SEC HAF Plot (upper plot, left panel); this shows the highest affected frequency based on flare intensity and user location - see also IPS ALF Plot; the X-ray lightcurve (lower plot, left panel) shows current conditions. Alerts related to SWF events (produced by IPS) are also shown (upper table, left panel). [IPS ALF - last major flare]

  • In the polar/auroral zone, protons precipitating down the Earth's magnetic field lines can produce a Polar Cap Absorption (PCA) event - PCA events start within 15 minutes to 2 hours of the flare and last anywhere from about an hour to several days (with an average of around 24 to 36 hours). The intensity of proton precipitation (upper plot, right panel) is a good pointer to the likelyhood of this type of event - also see the proton lightcurve (lower plot, right panel) for current conditions. [Polar Maps] [IPS PCA Report] [IPS - Realtime Riometer]