Diffraction of electromagnetic waves by small scale geomagnetic field-aligned density striations

A powerful electromagnetic wave in the ordinary mode transmitted near vertically into the ionospheric F region excites small scale density filaments which are stretched along the geomagnetic field. These striations are associated with a number of electromagnetically driven plasma phenomena, such as anomalous absorption of electromagnetic waves, anomalous heating, and stimulation of electromagnetic emissions. The diffraction of an electromagnetic wave is studied theoretically in a cold plasma as it propagates at small angles to striations which have a small scale across the ambient magnetic field. For a sufficiently high number density of striations the stationary self-consistent wave electric field distribution consists of several independent beams. As a result the pump-induced striations are grouped in independent patches in the plane across the magnetic field. Such bunches of striations may have been detected in in situ measurements from a sounding rocket at Arecibo and as large scale density irregularities observed at Tromso/.