A recurrent coronal hole (CH327) was in an Earth facing position on May 18-19. Another recurrent coronal hole (CH328) rotated into an Earth facing position on May 23-25.
Following a disturbance around 21st May, with the A index at 25, and the K at 5, conditions will have settled down by 23rd May, with the A index at 10 and the K at 3 where it will remain until May 31st with the A rising to 10 and the K index remaining at 3 until 3rd June when the A will drop to 5 and the K to 2.
The Solar Flux, however will drop from 72 to 68 by 25th May until 9th June when it will rise to 70. This is then followed by another rise to 72 by the 12th where it will remain until at least the 16th.
Long distance low and medium frequency (below 2 MHz) propagation along paths north of due west over high and upper middle latitudes is poor. Propagation on long distance northeast-southwest paths is fair.
(From WWM7D.com, NOAA and www.dxlc.com/solar).
Scientists call the ionosphere an extension or a part of the thermosphere. So technically, the ionosphere is not another atmospheric layer, but a region of the atmosphere. The ionosphere represents less than 0.1% of the total mass of the Earth's atmosphere. Even so, it is extremely important!
The upper atmosphere is ionized by solar radiation. Under normal conditions free electrons and ions tend to recombine and a balance is established between electron and ion production and loss.
Ionization processes release energy, which heat up the upper atmosphere. So temperature increases with height in the ionosphere region to the extent that by 150-200km, the Earth's atmosphere is extremely hot compared to surface temperatures.
Different regions of the ionosphere make long distance radio communication possible by reflecting the radio waves back to Earth. It is also home to auroras and the mega-ampere currents that heat the atmosphere at high latitudes during geomagnetically active times. During storms, depletions and enhancements of ionization occur depending on the local time and geographical location.
Aeronomy is a term of recent origin, which is applied to the processes, both physical and chemical, of the ionosphere. From http://www.windows.ucar.edu/ (University Of Michigan)
HF Propagation Predictions For 2008
Here is an interesting website by G4FKH, which has a monthly chart of predicted HF conditions listed by capital cities: http://email@example.com/
See also: http://www.hfradio.org/propagation.html
The New Shortwave Propagation Handbook (Paperback) - by George Jacobs, Theodore J. Cohen, R. B. Rose. The NEW Shortwave Progagation Handbook may well be the only book you'll need on the subject of ionospheric propagation! It is a "must read" for Radio Amateurs, Shortwave Listeners, and radio communicators of any type who need to make the most productive use of the radio spectrum, regardless of the time of day, the season of the year, or the state of the sunspot cycle. It will become your ever-present companion the operating table as you master the art of shortwave radio progagation. (Available from Amazon.com posted from the USA)
Thanks to KF and MET for regular updates.