The prediction of geomagnetic disturbance indices: 1. The elimination of internally predictable variations

Prediction equations for the magnetic character figure Ci are developed by multiple-regression procedures for periods 1, 2, 7, and 27 days in advance. The equations use as predictors only past values of Ci itself. The results indicate that the only consistently useful information for prediction is obtained from various combinations of properly weighted predictors 1, 2, 3, 26, 27, 28, 53, 54, and 55 days before the predicted day. The 1-day prediction equations when applied to a recent set of Ci data (1950–1959) removed all the linearly internally predictable components. The spectrum of the time series remaining after the predictable information was removed closely resembles white noise. This filtered time series is well suited for pilot studies designed to determine the complex underlying physical causes of geomagnetic disturbance.