Figure 1.19: Atmospheric column density Xx in curved atmosphere encountered by a cosmic ray incident under zenith angle 9\ < n/2 to reach point Pi at altitude h. Also shown is the situation for point P2 at 9 > 7t/2 and column density X2, a situation that may arise when h is large.

For zenith angles in excess of tt/2, a situation that may arise in satellite experiments (cf Fig. 1.19), the same authors propose the approximation

The zenith angle dependence of the atmospheric thickness or column density at sea level is illustrated in Fig. 1.20.

For further details concerning atmospheric column densities and attenuation for zenith angles 9 > 7r/2, such as may be relevant at great altitude in conjunction with satellites, the reader is referred to the articles by Swinder (1964) and Brasseur and Solomon (1986). The accuracy of certain approximations for the Chapman function is discussed by Swider and Gardner (1967).

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