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

A powerful electromagnetic wave in the ordinary mode transmitted near verti cally into the ionospheric F region excites small scale density filaments w hich are stretched along the geomagnetic field. These striations are associ ated with a number of electromagnetically driven plasma phenomena, such as anomalous absorption of electromagnetic waves, anomalous heating, and stimu lation of electromagnetic emissions. The diffraction of an electromagnetic wave is studied theoretically in a cold plasma as it propagates at small an gles to striations which have a small scale across the ambient magnetic fie ld. For a sufficiently high number density of striations the stationary sel f-consistent wave electric field distribution consists of several independe nt beams. As a result the pump-induced striations are grouped in independen t patches in the plane across the magnetic field. Such bunches of striation s may have been detected in in situ measurements from a sounding rocket at Arecibo and as large scale density irregularities observed at Tromso. (C) 2 001 American Institute of Physics.