  In this work is obtained new approximation for the yield function Y for
cosmic ray induced ionization in the Earth atmosphere on the basis of simulated
data. The parameterization is obtained using inverse nonlinear problem solution
with afxy(analyze fx=y)-code. Short description of the methods is given. The
found approximation is for primary proton nuclei, inclined up to 70 degrees
zenith angle. This permits to estimate the direct ionization by primary cosmic
rays explicitly. The parameterization is applicable to the entire atmosphere,
from ground level to upper atmosphere. Several implications of the found
parameterization are discussed.
