FUNDAMENTAL AND HARMONIC RADIATION IN TYPE-III SOLAR RADIO-BURSTS

Type III solar radio bursts are investigated by modelling the propagat ion of the electron beam and the generation and subsequent propagation of waves to the observer. Predictions from this model are compared in detail with particle, Langmuir wave, and radio data from the ISEE-3 s pacecraft and with other observations to clarify the roles of fundamen tal and harmonic emission in type III radio bursts. Langmuir waves are seen only after the arrival of the beam, in accord with the standard theory. These waves persist after a positive beam slope is last resolv ed, implying that sporadic positive slopes persist for some time, unre solved but in accord with the predictions of stochastic growth theory. Local electromagnetic emission sets in only after Langmuir waves are seen, in accord with the standard theory, which relies on nonlinear pr ocesses involving Langmuir waves. In the events investigated here, fun damental radiation appears to dominate early in the event, followed an d/or accompanied by harmonic radiation after the peak, with a long-liv ed tail of multiply scattered fundamental or harmonic emission extendi ng long afterwards. These results are largely independent of, but gene rally consistent with, the conclusions of earlier works.