For further information please visit the ips website
A more accurate and up-to date ionogram can be seen by looking at the latest Chilton Ionogram. You need to register and login to the site so I can't reproduce it here.
Historical data in text format can be obtained from sec.noaa.gov, here are quick links to the Chilton and also the Fairford daily text data files. I'm using these to produce the current critical frequency on the comparisons page. I've also added a graphical view of Chilton Data when it is available.
© Nick B. G4IRX. Last update: 17 February 2005 01:07 UTC.