Magnetic Field Observations in the Very Local Interstellar Medium by Voyagers 1 and 2

Abstract

Observations of the magnetic field B in the very local interstellar medium (VLISM) were made by Voyager 1 (V1) in the northern hemisphere from 2012 to mid-2021 and by Voyager 2 (V2) in the southern hemisphere from 2018 through 2020. Near 2019.4, V2 observed an abrupt increase in B associated with a pressure front near the heliopause. During 2020, V2 observed an abrupt increase in B at a jump in B that was preceded by electron plasma oscillations and cosmic rays, indicating that it was a shock. The shock was followed by a decrease in B ending ∼50 days later. V2 observed large-scale waves in all three components of B, before and after the shock. The largest- and intermediate-amplitude waves were in the BN and BR component, respectively, indicating that the waves were predominantly transverse several au from the heliopause. It was shown previously that waves near the heliopause were predominantly longitudinal at V1 and V2. Thus, V2 observed a mode transformation process within 10 au of the heliopause in the southern hemisphere, like that observed by V1 in the northern hemisphere. The elevation and azimuthal angles observed by V1 and V2 varied linearly with increasing distance in the VLISM. Voyager 1 observed jumps in B at two shocks and a pressure front, each followed by a decrease in B in a ramp. V1 also observed a fourth jump in B, at 2020.4, but B continued to increase until at least year 2021.5. This long-lasting increase in B was not anticipated.