Περίληψη:
Forbush decreases (FDs) are sharp reductions of the cosmic-ray (CR)
intensity, following intense solar activity such as coronal mass
ejections (CMEs) and their corresponding interplanetary shocks. In some
cases, shocks create sudden storm commencements (SSCs) at the Earth’s
magnetosphere with significant interest for space-weather studies.
Preincreases and/or predecreases of CR intensity before the onset of
FDs, known as precursory signals, have been widely examined by many
authors. In this work, an attempt to define precursory signals that are
not related to SSCs is presented. For the present analysis, CR data
recorded by the ground-based Neutron Monitor Network as well as data on
solar flares, CMEs, solar-wind speed, interplanetary magnetic field, and
geomagnetic indices for the years 1969 - 2019 are used. To identify FDs
that present precursors, the adopted criteria are mainly the FD
amplitude (> 2%) and the equatorial CR anisotropy before the onset time
(> 0.8%). The analysis of FDs and the study of their
asymptotic-longitude CR distribution for precursors are based on the
Global Survey Method and the Ring of Stations Method, respectively.
Precursory signals are identified in 17 out of 27 events without SSCs.
Συγγραφείς:
Lingri, D.
Mavromichalaki, H.
Abunina, M.
Belov, A. and
Eroshenko, E.
Daglis, I
Abunin, A.
