So what is a Sweep Frequency Event? 
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Sweep Frequency Events (Type II, III, IV and V events) - Energetic solar events often produce characteristic radio "bursts". These bursts are
generated by solar material plunging through the solar corona. Type III and type V events are caused by particles being ejected from the solar
environment at near relativistic speeds. Type II and IV events are caused by slower-moving solar material propagating outward at speeds varying
between approximately 800 and 1600 kilometers per second. Type II and IV radio bursts are of particular importance.

These sweep frequency radio events are signatures of potentially dense solar material which has been ejected from the solar surface. If the region
responsible for these events is well positioned, the expelled solar material may succeed in impacting with the Earth. Such an impact often causes an
SSC followed by Minor to Major geomagnetic storm conditions and significantly degraded radio propagation conditions. It is therefore interesting to
pay attention to events which cause Type II and/or IV radio sweep events, since they may indicate the potential for increased magnetic activity (and
decreased propagation quality) within 48 hours. It should be noted, however, that predicting degraded terrestrial conditions is significantly more
complex than simply observing whether the energetic event had an associated Type II or IV radio sweep. Flare position, proton spectra, flare size,
event duration, event intensity and a host of other variables must be analyzed before a qualitative judgement can be made.

It should also be noted that sweep frequency radio events are capable of producing Short Wave Fades (SWFs) and Sudden Ionospheric Disturbances
(SIDs). Depending on the severity of the event, the duration of SWFs and SIDs may last in excess of several hours with typical values being
approximately 30 minutes. SWFs and SIDs cause absorption of radio signals (due to intense ionization) at frequencies up to and well in excess of 500
MHz. Microwave continuum bursts can affect frequencies up to 30 GHz. Frequencies in the HF region can be completely blacked out for a period of time
during intense energetic events.