Formation of Ions in the Middle Atmosphere

2 Formation of Ions in the Middle Atmosphere 7.2.1 Effect of Solar Radiation 

Examination of the photoionization thresholds and absorption cross sections for atmospheric constituents shows that the solar radiation capable of producing ionization is primarily absorbed by O2, N2, NO, and 0. Table 7.2 presents the photoionization thresholds for various 

Given the ionization (a) and absorption (K) cross sections of N2, O2, and O for different spectral intervals, the photoionization coefficient can be calculated using the following expression  

Stewart (1970) suggested analytic expressions which can be used to obtain the photoionization coefficients of N2, 02, and O to within 15% 

Wavelength Interval (nm) Very Quiet Sun Quiet Sun Moderate Solar Activity High solar Activity 

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