Bernese GPS Software Version 5.0 - Bernese GNSS Software

Altitude
Hmax
Chapman profile
Ion production rate
Figure 12.1: Chapman curve of ionization rate.
12.2 Theory
Both processes create different layers of ionized gas in different altitudes. The diagram
indicating the number of ions produced as a function of altitude is called a Chapman profile.
This profile, which is a function of the solar zenith angle, is illustrated in Figure 12.1. Due
to the influence of different transportation processes in the ionosphere, the actual electron
concentrations may differ considerably from those estimated from the production layers.
The degree of ionization shows large variations which are correlated with the solar activity;
geomagnetic influences play an important role too. The solar activity may be characterized,
e. g., by the sunspot number, where one observes an 11-year cycle besides an 80–100-year
super-cycle. Figure 12.2 shows the monthly and monthly-smoothed sunspot numbers from
1950 to 2006 (as obtained from http://sidc.oma.be). We see that the most recent ionospheric
maximum must have happened during the years 200–2002 and that currently (2006)
we are approaching again a minimum. The situation will get worse again afterwards, with
increasing sunspot cycle phase.
300
250
200
150
100
50
0
1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005
Figure 12.2: Monthly and monthly-smoothed sunspot numbers.
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