2-KHZ TO 3-KHZ CONTINUUM EMISSIONS AS POSSIBLE INDICATIONS OF GLOBAL HELIOSPHERIC BREATHING

The main features of 2- to 3-kHz heliospheric emissions are analyzed in the context of a general heliospheric ''breathing'' as inferred from the Voyager 2 solar wind average ram pressure data. Following McNutt (1988) we suggest triggers for the three 3-kHz emission events seen to date, and we obtain good agreement in timing and expected 2f(p) (postshock) frequency for termination shock distances approximately 90 AU. This determination seems to correspond to epochs when the heliosphere is larger than on the average. We suggest that the visibility of the individual 3-kHz events and their observed upward frequency drift are enhanced when the postulated global heliospheric expansion results in formation of a transient. compressed external plasma barrier around the heliopause that prevents for several months the escape of the radiation. We suggest that the 2-kHz emission band is due to typical solar wind density maxima interacting with the termination shock and that the disappearance of that emission after mid-1987 is caused by the 2f(p) (postshock) frequency moving into the 2.4-kHz spacecraft interference band during a period of closer shock distance corresponding to years of lower solar wind ram pressure. From all the events considered, we estimate the average termination shock distance to be in the range 80-90 AU.