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Long‐period dynamic spectrograms of low‐frequency interplanetary radio emissions
Author(s) -
Kurth W. S.,
Gurnett D. A.,
Scarf F. L.,
Poynter R. L.
Publication year - 1987
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl014i001p00049
Subject(s) - spectrogram , physics , interplanetary spaceflight , shock (circulatory) , astrophysics , frequency drift , low frequency , radio spectrum , astronomy , solar wind , plasma , phase (matter) , computer science , medicine , phase locked loop , quantum mechanics , computer vision
In this report we present dynamic spectrograms of the low‐frequency interplanetary radio emissions as observed by Voyagers 1 and 2 from 1983 through mid‐1986. The radio emissions were observed to be most intense in the latter portion of 1983 at 3 kHz but have also been detected at 2 kHz. The emission has been present almost continuously at either 2 or 3 kHz since late 1983. The spectrograms presented herein show that the phenomenon appears almost identically as observed by the two spacecraft separated by more that 10 AU, at least at the higher frequency. One feature revealed by the dynamic spectrograms which had not been noticed previously is a gradual rise in frequency of the 3‐kHz component following the onset of the late 1983 event. These new observations reinforce the conclusion that the low‐frequency emissions are freely propagating radio waves, but the two‐component spectral structure implies that the previous model of emission at twice the plasma frequency at the inner heliosphere shock is inadequate to fully account for the observations. Either an additional source region or source mechanism is suggested.