Cosmic rays are the main source of ions in the atmosphere at altitudes of 5--35 km. The flux of cosmic rays in the atmosphere depends on the site of observation and is controlled by the geomagnetic field. Except for the rare cases of solar proton events and Forbush decreases, cosmic ray flux varies slowly with changes of solar activity level. Thus there is quasi-stationary equilibrium between the ion production and recombination processes. Usually, the equation q=αn2 is used to describe this equilibrium state, where q is the ion production rate, n is the ion concentration, and α is Thompson's coefficient of recombination. However, the joint analysis of data on ion concentration and cosmic ray fluxes observed at various latitudes shows that there is a linear relationship between ion production rate and ion concentration, q=βn, where β is the linear coefficient of ion recombination.¿ 1997 American Geophysical Union