For multipath propagation in spherically stratified clear air, the formulas are derived for the phase difference between the direct ray and the multipath ray reflected from an atmospheric layer, and for their arrival angles. With the earth's curvature set to zero, the above formulas will reduce to those currently in use for a plane-stratified atmosphere. With the formulas here derived and the empirical cumulative distribution of refractive index gradients, theoretical expressions for the statistical distributions of the cross-polarization discrimination (XPD) and copolarized attenuation (CPA) are obtained. Furthermore, the relationship between equiprobable values of XPD and CPA is found to be linear. All the above formulas are related to the frequency, the path length, meteorological parameters and cross-polar antenna patterns. The theoretically predicted results for XPD and CPA agree well with experimental data for several paths.