Accession Number : ADP006293

Title :   UHF Radar Backscatter Enhancements from the Topside Ionosphere,

Corporate Author : MASSACHUSETTS INST OF TECH CAMBRIDGE PLASMA FUSION CENTER

Personal Author(s) : Groves, K. M. ; Lee, M. C. ; Foster, J. C.

Report Date : 03 MAY 1990

Pagination or Media Count : 7

Abstract : Intense (about 20 dB) enhancements of the incoherent radar backscatter spectrum from the topside ionosphere have been observed with the Millstone Hill UHF radar; enhancements occurring at the local ion acoustic frequency causing large asymmetries in the measured ion line may be produced by current-driven instabilities. In addition to current-driven processes, we propose the generation of intense ion acoustic turbulence by the nonlinear interaction of Langmuir waves in the ionosphere. Qualitatively, an enhanced Langmuir wave spectrum is produced by the action of suprathermal electrons associated with field-aligned currents. Energy from the enhanced Langmuir waves can then be coupled into ion acoustic models through nonlinear processes. The resulting amplification of the ion modes can be detected by incoherent scatter radars. Analytical and numerical calculations describing the above processes quantitatively will be presented. This newly observed phenomenon is associated with intriguing ionospheric plasma processes. The induced plasma modes have large radar cross-sections give rise to strong backscatter radar echoes. Hence, in the past, they were probably misidentified to be satellite radar returns. From the point of view of space surveillance, it is desirable to identify potential geophysical processes leading to false satellite signals.

Descriptors :   *RADAR REFLECTIONS, INCOHERENT SCATTERING, BACKSCATTERING, ULTRAHIGH FREQUENCY, RADAR CROSS SECTIONS, TARGET ECHOES, SPACE SURVEILLANCE.

Subject Categories : Active & Passive Radar Detection & Equipment

Distribution Statement : APPROVED FOR PUBLIC RELEASE