High-latitude Conic Current Sheets in the Solar Wind

Abstract

We provide observational evidence for the existence of large-scale cylindrical (or conic-like) current sheets (CCSs) at high heliolatitudes. Long-lived CCSs were detected by Ulysses during its passages over the South Solar Pole in 1994 and 2007. The characteristic scale of these tornado-like structures is several times less than a typical width of coronal holes within which the CCSs are observed. CCS crossings are characterized by a dramatic decrease in the solar wind speed and plasma beta typical for predicted profiles of CCSs. Ulysses crossed the same CCS at different heliolatitudes at 2–3 au several times in 1994, as the CCS was declined from the rotation axis and corotated with the Sun. In 2007, a CCS was detected directly over the South Pole, and its structure was strongly highlighted by the interaction with comet McNaught. Restorations of solar coronal magnetic field lines reveal the occurrence of conic-like magnetic separators over the solar poles in both 1994 and 2007. Such separators exist only during solar minima. Interplanetary scintillation data analysis confirms the presence of long-lived low-speed regions surrounded by the typical polar high-speed solar wind in solar minima. Energetic particle flux enhancements up to several MeV/nuc are observed at edges of the CCSs. We built simple MHD models of a CCS to illustrate its key features. The CCSs may be formed as a result of nonaxiality of the solar rotation axis and magnetic axis, as predicted by the Fisk–Parker hybrid heliospheric magnetic field model in the modification of Burger and coworkers.

Simulations of solar wind variations during an 11-year cycle and the influence of north–south asymmetry

“…Finally, we can notice that during maximum, the wind velocity is dropping at the poles in the two hemispheres. This has been observed in Ulysses data and has been interpreted as the presence of high-latitude current sheets (Khabarova et al 2017). Figure 8 displays the Alfvén surface profile at minimum and maximum (respectively left and right panel).…”

“…This has been observed in Ulysses data and has been interpreted as due to the presence of high-latitude current sheets (Khabarova et al. 2017).…”

Symmetries of Magnetic Fields Driven by Spherical Dynamos of Exoplanets and Their Host Stars

“…If the stellar dynamo number D is positive, the activity wave propagates polarwards (e.g., [41]) and activity manifestations are expected to be much more pronounced rather for the Sun. In particular, the conic polar current sheets [42] are expected to be much more pronounced than in solar magnetoshere.…”

Three-Dimensional MHD Modeling of Interplanetary Solar Wind Using Self-Consistent Boundary Condition Obtained from Multiple Observations and Machine Learning

“…We can see that the Ulysses passed a large latitude range from the Southern Hemisphere to the Northern Hemisphere during CR2057 to CR2062, which is very suitable for comparison with our simulation results at high latitudes. The cone-shaped zones with a reduced speed that can be seen in the polar regions may reflect the presence of conic polar current sheets, which are introduced by a previous research [63].…”