Observations of the magnetic field and plasma in the heliosheath by Voyager 2 from 2007.7 to 2009.4

Abstract

[1] The density and temperature profiles of the plasma measured by Voyager 2 (V2) behind the termination shock changed abruptly near 2008.6 from relatively large average values and large fluctuations during 2007.7 to 2008.6 (interval A) to relatively low average values and very small-amplitude fluctuations during 2008.6 to 2009.4 (interval B). This paper shows that the change in the magnetic field strength B(t) was less abrupt than the plasma changes, and the fluctuations of the magnetic field strength in interval B were of moderate amplitude, with indications of a quasiperiodic structure in part of the interval. The magnetic field was directed away from the sun (positive polarity) ∼ 78% ± 5% of the time in both interval A and interval B, changing in an irregular way from positive to negative polarities throughout the interval. The polarity distribution indicates that the minimum latitudinal extent of the heliospheric current sheet (HCS) was near V2 throughout the interval, consistent with the extrapolated minimum latitudes of the HCS computed from solar magnetic field observations. Thus, V2 was observing magnetic fields from the southern polar coronal hole most of the time. The distribution of B was lognormal in interval A and Gaussian interval B.

Transition from the Unipolar Region to the Sector Zone: Voyager 2, 2013 and 2014

“…The V2 magnetic field observations from 2007.0 through 2012 have been discussed in previous papers (Burlaga et al 2009(Burlaga et al , 2010Richardson & Burlaga 2013). Figure 1 also includes the new observations for the years 2013 and 2014, which are the main subject of the present paper.…”

“…Nevertheless, Figure 1 shows that there is a broad interval, with no sharp boundaries (for the reasons given above) in which the magnetic field is directed primarily away from the Sun (the unipolar region) from ∼2009.6 to ∼2013.8245. Earlier, Burlaga et al (2009Burlaga et al ( , 2010, based on alimited data set, estimated that V2 was in this unipolar region from ∼2009.5 to at least 2010.3.…”

“…Burlaga et al (2009Burlaga et al ( , 2010 showed that the transition from the sector zone to the unipolar region was caused by the decreasing latitudinal extent of the sector zone. This motion was inferred by Burlaga et al (2009) from variations of the neutral line on the source surface, using the solar magnetic field data from the Wilcox Solar Observatory and the Mount Wilson Observatory data.…”

Coherent Structures at Ion Scales in Fast Solar Wind: Cluster Observations

“…For example, the presence of compressive structures in slow solar wind could be the result of the in- teraction of the wind with the heliospheric current sheet (Burlaga et al 2002;Brooks et al 2015) or be remnant features of large scale coronal structures (Wilcox & Ness 1967;McComas et al 2000). Thanks to Solar Orbiter and Parker Solar Probe, it will be possible to measure the turbulent and structured electric and magnetic fields associated with shocks, reconnection and stochastic energization in unexplored plasma environments, investigating plasma physics in the source regions of both fast and slow wind.…”

Comparison of different analytic heliospheric magnetic field configurations and their significance for the particle injection at the termination shock

“…Burlaga et al 2002;Murphy et al 2002;Mursula 2007;Roberts et al 2007;Mordvinov 2008;Ebert et al 2009) and corresponding modeling (e.g. Burger & Hitge 2004;Giacalone & Jokipii 2004;Burger 2005;Schwadron & McComas 2005;Giacalone et al 2006;Ferreira et al 2007;Burger et al 2008) that can be used to analyze the asymmetry of the HMF have not yet convincingly settled the debate over which of the fields is closest to reality.…”