Accession Number : ADP006500

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

Corporate Author : COMMUNICATIONS RESEARCH CENTRE OTTAWA (ONTARIO)

Personal Author(s) : Muldrew, D. B.

Report Date : OCT 1990

Pagination or Media Count : 5

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.

Descriptors :   *HEATING, *RADIOFREQUENCY POWER, *ENERGY TRANSFER, *IONOSPHERIC DISTURBANCES, CYCLES, DAMPING, DECAY, DUCTS, INSTABILITY, INTENSITY, IONIZATION, MAGNETIC FIELDS, ELECTRON DENSITY, RADIO TRANSMITTERS, IONOSPHERIC MODELS.

Subject Categories : Atmospheric Physics

Distribution Statement : APPROVED FOR PUBLIC RELEASE