부산대학교 도서관

The short-term rapid depressions in cosmic-ray (CR) flux intensity, historically referred to as Forbush decreases (FDs), are useful tools for testing some of the numerous hypotheses on space weather. Due to their long-term reliability and automated data acquisition, ground-based CR measurements by neutron monitors (NMs) provide the best direct means of comparing CR intensity variations during FDs with solar-wind disturbances in the vicinity of the Earth. Unfortunately, there is a mixture of high-magnitude FDs and CR diurnal anisotropies of enhanced amplitude during periods of high solar activity. The difficulties of isolating FDs from the superposed effects of diurnal anisotropies cast some doubt on the usefulness of FDs in space-weather studies. Using numerical filtering techniques over two isolated NMs' data (Apatity and Mount Washington) during high solar activity in 1972, we attempt to show that the slowly varying component of CR flux containing the CR anisotropies may be separated from the high-frequency part that contains the FDs. Subsequently, the rapidly varying component is passed to an FD location algorithm for accurate event timing as well as precise quantitative predictions, where the day-to-day amplitudes of the CR diurnal anisotropies are estimated from the slowly varying frequency component of the raw CR data. For effective comparison of event amplitudes and timing, the magnitudes of FDs from raw CR data are also estimated using an FD selection technique. [ABSTRACT FROM AUTHOR]