An Investigation of the Time-Delay between Solar Events and Geomagnetic Disturbances Using a New Method of Superposed Epoch Analysis.

Abstract

A new superposed epoch technique involving an eigen-analysis of the covariance matrix of a set of time series has been used to study the magnetic responses in the polar cap, auroral zone and subauroral zone to the occurrences of solar flares, central meridian passages of coronal holes and disappearing filaments on the Sun. This new technique is superior to the conventional technique of simple averaging in that the dominant common structure in the time series is more clearly identified and that secondary structures can also be extracted. About 6 years of data from 1984 to 1989, extending from solar minimum to solar maximum, have been used in this study. The study showed that the time-delay between the occurrence of solar flares and geomagnetic disturbances is 2-3 days, the delay between the central meridian passage of coronal holes and disturbances is 2-5 days and the delay between the disappearance of filaments and disturbances is 2-6 days. These time-delays, which are based on statistical analysis using the new technique, can serve as guidelines for geomagnetic forecasting.