Geospace Research, Inc.

Space Plasma Physics

  Arecibo Observatory (Puerto Rico) is in the process of recovering its ability to modify the ionospheric plasma with the aid of high-power radio waves transmitted from the ground.  Because of Arecibo's unique midlatitude location and its powerful 430 MHz radar, detailed studies of strong Langmuir tubulence/ion turbulence excited in the plasma are possible over long time periods.  During the initial experiments conducted with the new Arecibo facility, special emphasis will be placed on investigating electron acceleration processes that are linked to the plasma turbulence.

  The figure below shows previous measurements from Arecibo.  It illustrates the temporal evolution of Langmuir and ion turbulence versus altitude for a "cold turn-on" of a high-frequency (5.1 MHz) radio beam in a smooth background plasma. These measurements were made on May 3, 1990 at 21:10:00 local time.  The upper panel shows the intensity of induced Langmuir waves traveling toward the radar, the middle panel depicts the ion turbulence, and the bottom panel shows the Langmuir waves traveling away from the radar.  The upper boundary of the echo is close to the point of radio wave reflection in the plasma.  With increasing time the ionosphere slowly moves upward, and the plasma turbulence follows this trend.  The echo structure below reflection corresponds to maxima in the 5.1 MHz standing wave pattern.