Accession Number:

ADP006500

Title:

Duct Model for the Duty-Cycle Variation of the Plasma-Line Overshoot during Cyclic Heating at Arecibo,

Descriptive Note:

Corporate Author:

COMMUNICATIONS RESEARCH CENTRE OTTAWA (ONTARIO)

Personal Author(s):

Report Date:

1990-10-01

Pagination or Media Count:

5.0

Abstract:

In a recent publication on ionospheric heating by Sulzer et al. 1989 the effects of suddenly changing the duty cycle, during on-off cycling of the HF transmitter, on the plasma-line PL overshoot are strikingly illustrated. When the duty cycle was suddenly decreased, the overshoot lifetime changed gradually over about 1 min from roughly 0.1 s to more than 0.5 s. When the duty cycle was suddenly increased, the lifetime changed gradually from more than 0.5 s to roughly 0.1 s. For a still higher duty cycle, the PL intensity began to Pulsate dramatically. The Langmuir L waves responsible for the PL grow by the parametric-decay instability and propagate in magnetic-field-aligned ionization ducts having a density decrement relative to the ambient density outside the duct. The change in the decrement depends both on the ponderomotive force of the trapped L waves and on heating due to damping of the L waves. When the HF is on, the decrement increases. When the HF is off, the decrement decreases. Rapid decay of the L waves i.e. decay of the overshoot by Landau damping begins when the decrement exceeds a certain level. The duty-cycle observations can be explained with this model.

Subject Categories:

  • Atmospheric Physics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE