Time-weighted magnetic indices as predictors of ionospheric behaviour

A time-weighted accumulation of the ap index, ap(τ) (Wrenn, 1987; Wrenn et al., 1987, 1989), together with other similar indices, was explored as a predictor of ionospheric behaviour, using ƒ₀F2 data for a selection of locations in Australia and Europe for September and October 1989. All the time accumulated indices showed improved linear correlations, indicative of a response time of the order of about 15 hours. The response time could be decomposed into a lag between respective time series and a persistence time, although the decomposition appeared unnecessary as the persistence time carried the same information. Of the individual indices investigated, aa(τ) appeared best and the auroral oval equatorward edge index (AI index) was poorest, although the differences were not statistically significant. Comparisons between the aa, ap and Kp indices, plus comparisons between different ionospheric parameters showed that forecasting may be improved using different transformations of the data. While these results appear good, further studies using other stations and seasons are warranted to confirm their utility for forecasting.