We study short period changes in galactic cosmic rays (GCR) intensity and analyze features of its sporadic and recurrent decreases (Forbush effects). We show that the energy spectrum of Forbush effect is suitable for investigating the structure of irregularities of the interplanetary magnetic field, resulting from shock waves and magnetic clouds in the interplanetary space. This study is based on experimental data from neutron monitors and on theoretical modeling of GCR transport.

PACS numbers: 96.40.--z