The week of 2011 February 13-19 was an extremely active period for solar flares and I recorded more Sudden Ionospheric Disturbances
(SIDs) then than were observed in the previous eight months.
Our observing programme for Sudden Ionospheric Disturbances
(SIDs) continues, with John Cook producing monthly summaries of events reported by a team of six to ten observers.
The observed signal thus depends upon the height of the D layer and the geographical location of the receiver, but when monitoring for Sudden Ionospheric Disturbances
(SIDs) we are only interested in the timings of the start of the event, the time to reach the maximum deviation, and the time for the received radio signal to return to its normal level.