Description of propagation indexes

Database of historical data of indexes

Sun Spot number

Usually abreviated as SSN. Higher sunspot numbers indicate increased ionizing radiation from the sun which enhances the ionosphere's ability to refract HF signals, The sunspot number can vary from zero to over 200 during the peak of the 11-year solar cycle.

Solar Flux

Usually abreviated as SFI (and often simply as "I"). Measurement of radio signals from the sun. The index is taken once a day at a frequency of 2800 MHz (10.7 cm). Increased radio noise from the sun means more ionizing radiation and correlates with the sunspot number. Solar flux values range from 60 (no sunspots) to 300.

K Indexes

K indexes reflect the geomagnetic conditions (solar particle effects on the earth's magnetic field) and their values range from 0 to 9. Lower numbers mean quieter ionosphere. Trends in the K indexes are important to watch. When K rises you can expect HF propagation conditions to worsen, particularly towards the polar regions. On VHF bands a high K index would mean the possibility of an Aurora openning.

K index: Siebert (1971) defines "K variations are all irregular disturbances of the geomagnetic field caused by solar particle radiation within the 3-h interval concerned. All other regular and irregular disturbances are non K variations. Geomagnetic activity is the occurrence of K variations". K is a local index, describing disturbances in the vicinity of each observatory.

Ks index: Using statistical methods, J. Bartels generated conversion tables to eliminate these disturbances. By applying the conversion tables, a standardized index Ks for each of the 13 selected observatories is determined. In contrast to the K values, the Ks index is expressed in a scale of thirds (28 values:  0o, 0+, 1-, 1o, 1+, 2-, 2o, 2+, ... , 8o, 8+, 9-, 9o). The main purpose of the standardized index Ks is to provide a basis for the global geomagnetic index Kp.

Kp index: Kp is the average of the Ks indexes from a number of "Kp stations" distributed around the globe and gives a "planetary" overview of the geomagnetic activity. 

A Indexes

A indexes are derived from K indexes but converted to a linear scale in gammas (nanoTeslas). They can range from 0 to 400 but it is rare to see it go above 75 o 100. More often you will see A index readings between about 4 and 50. Values below 10 are very desirable for HF commnunications. Higher A numbers can mean excesive absortion of HF radio waves due to increased storm conditions in the ionosphere.

A index: Indicates the disturbances for the last 24 hours in the vicinity of an observatory. It's obtained averaging the eight K indexes and converting the result according to the table below.

ap index: Is the direct result of the conversion of the three-hour Kp index according to the table below.

Ap index: The daily index Ap is obtained by averaging the eight values of ap for each day.

Conversion of geomagnetic Indexes

Ionospheric condition K index A index
Quiet 0-1 0-7
Unsettled 2 8-15
Active 3 16-29
Minor storm 4 30-49
Major storm 5 50-99
Severe storm 6-9 > 99

Kp index ap index
0o 0
0+ 2
1- 3
1o 4
1+ 5
2- 6
2o 7
2+ 9
3- 12
3o 15
3+ 18
4- 22
4o 27
4+ 32
5- 39
5o 48
5+ 56
6- 57
6o 80
6+ 94
7- 111
7o 132
7+ 154
8- 179
8o 207
8+ 236
9- 300
9o 400
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