When high power microwaves are transmitted through the atmosphere, air breakdown may occur. This can produce regions of plasma which may distort the microwave beam pattern. There are many variables, such as power level, frequency, pulse duration and altitude, which determine whether or not breakdown can take place. another key variable is the ambient electron concentration, n, in the beam path. The electrons are produced by cosmic ray particles, and so n is a very complicated function of space and time because of the nature of cosmic ray statistics. The proposed research is therefore designed to accomplish four objectives: 1) calculate n based on current knowledge of cosmic ray particles; 2) calculate breakdown fields for the required variables; 3) calculate the effect of the resulting plasmas on beam patterns; and 4) combine 1), 2), and 3) to obtain an algorithm to describe the far field patterns of microwave radiation as a function of the appropriate variables.