Magnetic decreases in the interplanetary space

The aim of this paper is to show to the readers the phenomena known as magnetic decreases (MDs) or magnetic holes (MHs). Such structures are regions in interplanetary space, and even into the Earth's magnetosphere, where the ambient magnetic field magnitude is depleted, sometimes drastically. MDs are convected by the solar wind and have been detected in both high and low heliospheric latitudes. MD features are relativelly well known. However, there is not an agreement about a unique theory for their formation. Charged particles/MD nonresonant interactions lead to perpendicular particle diffusion, as a consequence of guiding center displacements.