Letter to the Editor: First direct observations of the reduced striations at pump frequencies close to the electron gyroharmonics

[摘要] It is well known that the ionospheric plasmaresponse to high-power HF radio waves changes drastically as the heaterfrequency approaches harmonics of the electron gyrofrequency. These includechanges in the spectrum of the stimulated electromagnetic emission, reduction inthe anomalous absorption of low-power diagnostic waves propagating through theheated volume, and reduction in the large scale F-region heating. Theoreticalmodels as well as previous experimental evidence point towards the absence ofsmall-scale field-aligned plasma density irregularities at pump frequenciesclose to electron gyroharmonics as the main cause of these changes. Resultspresented in this paper are the first direct observations of the reducedstriations at the 3rd gyroharmonic made by the CUTLASS radar. In addition,simultaneous EISCAT observations have revealed that the "enhancedion-line" usually present in the EISCAT ion-line spectrum during the firstfew seconds after heater switch on, persisted at varying strengths while theheater was transmitting at frequencies close to the 3rd electron gyroharmonics.

Key words. Ionosphere (active experiments; ionosphericirregularities) · Radio science (ionospheric physics)

[学科分类] 地球科学(综合)