Representation of diurnal and geographic variations of ionospheric data by numerical methods

A solution is given to the problem of representing the complex properties of ionospheric characteristics on a worldwide scale, including their diurnal variation, by numerical analysis of ionospheric data as they are obtained from a network of sounding stations, without prior hand operations. The problem is complicated by t wo basic difficulties : (1) the data are affected by noise (random fiuctuation) and (2) t he stations are irregularly positioned in the two space dimensions. The second difficulty is overcome by a general method for construct ing functions orthogonal relative to the distribution of t he stations. Spccial filtering proc esses are employed for t hc optimum separation of noise from real physical variations. The end product of the a nalysis is a table of numerical coeffi cients defining a function r (A, 0, I) of t hrec variables, latit ude (i--), longitude (0) and time (I), which can be used to compute the ionospheric characteristic at any desired location or instant of time. The method applies to any ionospheric characteristic; however, as a means of illustration we use in the present paper only the characteristic, monthly median of t he F2-layer critical frequency (fo F,).