Saturday, 28 March 2009

April '09

Propagation Forecast
During the second half of March, conditions have remained quite steady with the A index mostly at 5 and the K index at 2. As we enter the A09 period, things are likely to remain the same during April except for the 9th with the A index at 15 and the k index at 4. This should return to normal by April 11th. The Solar flux is likely to remain at a steady 70 during this period.

Modes of propagation
Here is an interesting article explaining modes of radio propagation and how they work:
The three main modes of propagation of electromagnetic waves are:
(a) Ground (or surface) Wave
(b) Ionosphere Wave (Sky Wave)
(c) Tropospheric Wave

Ground-Wave Propagation In ground-wave propagation, the radiated wave follows the surface of the earth. It is the major mode of propagation for frequencies up to about 2MHz. Attenuation of the ground wave increases very rapidly above 2MHz and it may extend for only a few kilometers at frequencies of the order of 15- 20MHz. At very low frequencies the attenuation decreases to such an extent that reliable world-wide communication is possible at all times. The ground wave is not so affected by atmospheric effects or time of day as other modes, particularly at frequencies below about 500 kHz.

Ionospheric Propagation Ionospheric propagation is the 'refraction' (i.e. bending), and hence reflection, of radio waves back to earth by layers of ionised gases as shown in Fig 7.2. It is the normal mode of propagation over the frequency range of about 1MHz to 30MHz.
These layers are the F2 layer (height 300-400km); Fl layer (about 200km) and the E layer (about 120km). At night and in midwinter, the F1 and F2 layers tend to combine into a single layer at a height of about 250km. At about 80km there is a much less distinct layer which is generally known as the D region.
The ionised layers are the result of the ionisation of the oxygen, nitrogen and nitric oxide in the rarefied atmosphere at these heights by X-Ray and ultra-violet radiation of various wavelengths which comes from the sun.
When these gases are ionised the molecules split up into ions and free electrons, and recombine after sunset. This whole region is therefore known as the 'ionosphere'.
The solar radiation which causes the ionisation is continually varying; hence the degree of ionisation varies considerably according to season and time of day. It has also been found that the degree of ionisation is affected by the number of sunspots.
(You can read the full article at:

NOAA Space Weather Prediction Centre Here is a web page featuring the latest solar weather indices including real time maps, solar wind dials and a solar cycle progression chart:

Thanks to Mike Terry and Ken Fletcher for updates. Links to the above articles can be found at.