Cosmic-ray forecasting features for big forbush decreases

Abstract

It is well known that big geomagnetic storms have an adverse influence on technological devices and radio wave propagation. Major geomagnetic storms, associated with Forbush decreases (FDs) in cosmic ray (CR) intensity, have also been found to increase the incidence of some diseases (in particular, the frequency of myocardial infarction increases by 13 ± 1.4%). We discuss here three phenomena that can be used for forecasting FDs: 1) CR intensity increase, of non solar-flare origin, occurring before sudden commencement of a major geomagnetic storm connected with FD (preincrease effect), 2) CR intensity decrease before FD (predecrease effect), 3) change in CR fluctuations before FD. First we investigate several such events by the global survey method for the years 1989–1991. We analyse the behaviour of the isotropic CR intensity and of the 3-dimensional vector of CR anisotropy before FDs, as well as results on CR scintillation of 1-hour and 5-minute data. We discuss a possible procedure of data treatment for future FD-forecasting analyses.