DETECTABILITY OF ELECTROSTATIC DECAY PRODUCTS IN ULYSSES AND GALILEO OBSERVATIONS OF TYPE-III SOLAR RADIO-SOURCES

Recent in situ Ulysses and Galileo observations of the source regions of type III solar radio bursts appear to show an absence of ion acoust ic waves S produced by nonlinear Langmuir wave processes such as the e lectrostatic (ES) decay, in contradiction with earlier ISEE 3 observat ions and analytic theory. This Letter resolves these apparent contradi ctions. Refined analyses of the maximum S-wave electric fields produce d by ES decay and of the characteristics of the Ulysses Wave Form Anal yzer (WFA) instrument show that the bursty S waves observed by ISEE 3 should be essentially undetectable by the Ulysses WFA. It is also show n that the maximum S-wave levels predicted for the Galileo event are l ess than or similar to the instrumental noise level, thereby confirmin g an earlier suggestion. Thus, no contradictions exist between the ISE E 3 and Ulysses/Galileo observations, and no evidence exists against E S decay in the published Ulysses and Galileo data. All available data are consistent with, or at worst not inconsistent with, the ES decay p roceeding and being the dominant nonlinear process in type III bursts.