Open Access
The solar wind velocity determined from Voyager 1 and 2: Low‐Energy Charged Particle measurements in the outer heliosphere
Author(s) -
Kane M.,
Decker R. B.,
Mauk B. H.,
Krimigis S. M.
Publication year - 1998
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/97ja02776
Subject(s) - heliosphere , physics , solar wind , interplanetary medium , plasma , interplanetary spaceflight , astronomy , quantum mechanics
The Voyager 1 and 2 spacecraft are now exploring the outer heliosphere with active field and particle instruments. The primary instrument for the critical plasma bulk flow parameter is the plasma science (PLS) instrument. Unfortunately, on Voyager 1, the spacecraft most likely to first encounter the termination shock and other heliospheric boundaries, the PLS instrument is no longer able to measure plasma flows. In this paper we demonstrate that the Low‐Energy Charged Particle (LECP) detector may, under certain conditions, be used to determine the solar wind plasma flow velocities. We show that higher time resolution radial speeds (daily averages) are obtainable in the downstream regions near interplanetary transient shocks where the ion activity is sufficiently above background levels and where the ion distributions are sufficiently isotropized. Longer‐term (26‐day) averaged speeds are obtainable during lower counting periods, such as during 1980 and 1992, when corotating shocks were prevalent. The Voyager 2 LECP results are in good agreement with known PLS determinations of bulk flow speed from the cold plasma. Using large transient shocks seen during 1989 and 1991 as examples, Voyager 1 calculations indicate slower solar wind speeds near these events despite the higher heliolatitude location of Voyager 1 during this period. During 1992, when Ulysses entered the southern high‐speed stream region, Voyager 1 apparently did not see high‐speed streams at similar northern latitudes. Given the expected activity near the termination shock, our determination of the solar wind speed should serve as an indicator of a Voyager 1 crossing of this shock. The LECP measurements would provide the only determination of bulk flow speed and deviations from the nominal solar wind flow speed at this and other boundaries or shocks encountered by Voyager 1.