Polar cap absorption events
From Glossary of Meteorology
polar cap absorption events
(Abbreviated PCA events.) A condition in the polar ionosphere where HF and VHF radio waves are absorbed and LF and VLF radio waves are reflected at lower altitudes than normal. PCA events usually originate from major solar storms that launch energetic protons that reach our outer atmosphere quickly and cause excess ionization that distorts the normal refractive properties of the polar ionosphere.
Term edited 14 August 2018.
