Accession Number : ADP006530

Title :   The Generation of ULF Waves in the Ionosphere,

Corporate Author : RICE UNIV HOUSTON TX DEPT OF SPACE PHYSICS AND ASTRONOMY

Personal Author(s) : Noble, S. T. ; Gordon, W. E.

Report Date : OCT 1990

Pagination or Media Count : 4

Abstract : One explanation for the generation of HF sidebands during two-frequency heating experiments is based on the interaction between the beat frequency wave and the HF waves. To test this, simultaneous HF sideband and ULF measurements have been made using the facilities at the National Astronomy and Ionosphere Center at Arecibo, Puerto Rico. The ULF measurement technique and recent findings are discussed. At the core of the ULF receiving system are three mutually perpendicular magnetometer sensors. For most studies, only the band 0.5-20 Hz is utilized. Although based upon a limited data set, underdense heating has yielded no signs of ULF production in the ionosphere. This is not surprising, since the achievable field strengths during underdense heating are well below the predicted threshold required for beat frequency wave production. Proposed improvements to the Arecibo HF facility, if undertaken, and the resulting increases in effective radiated power could greatly improve the chances of exciting this mode. Although HF swelling near the reflection height can amplify the fields significantly during overdense heating, no signs of ULF have been observed at these times either. This is possibly a result of geometrical limitations imposed by this type of ionospheric heating.

Descriptors :   *RADIOFREQUENCY GENERATORS, *IONOSPHERIC DISTURBANCES, HEATING, HEIGHT, INTERACTIONS, IONOSPHERE, LIMITATIONS, MAGNETOMETERS, MEASUREMENT, POWER, PRODUCTION, SIDEBANDS, TEST AND EVALUATION, ULTRALOW FREQUENCY, ELECTROMAGNETIC FIELDS, ELECTROMAGNETIC WAVE REFLECTIONS.

Subject Categories : Atmospheric Physics
      Radiofrequency Wave Propagation

Distribution Statement : APPROVED FOR PUBLIC RELEASE