This paper presents a set of basic expressions and parameters to describe the relaxation of ionization in the upper atmosphere and lower ionosphere. Both spatial (diffusion) and chemical loss are included, along with the varying electrical conductivity caused by changing electron density and temperature. In particular, reasonable values for the attachment rates and recombination coefficients at these high altitudes are discussed. Example calculations are given involving studies into red sprites. However, the modeling and parameters are not restricted to these events, and might well be useful in a number of other modeling problems. ¿ 1998 American Geophysical Union