Solar Wind Properties In The Outer Heliosphere
Abstract
We examine the solar wind plasma properties in the outer heliosphere making comparisons between recent New Horizons results obtained in a low activity solar cycle to those from Voyager 2 obtained during a more active solar cycle. We examine the radial trends in the solar wind density, temperature, and speed, and examine the relationship between pairs of solar wind parameters. To understand the differences between the solar cycles, we examine the differences in the variability of these solar wind parameters, and the prevalence of speed jumps (shocks). We find that the solar wind density radial profile may decrease at nearly or slightly less than a spherical expansion density profile. However, the temperature profile is well above what would be expected for an adiabatic profile. By comparing outer (New Horizons) and inner (ACE and STEREO) heliospheric solar wind observations, we find the solar wind speed is reduced by 5-7% between 30 and 43 au, and that the solar wind polytropic index ($\gamma$sw) steeply decreases toward zero in the outer heliosphere from 21 to 43 au with a slope of $\sim 0.031 au^{-1}$ Using both this radial variation in $\gamma$sw and the measured amount of interstellar pickup ions, we estimate the slowing in the solar wind and obtain excellent agreement with the observed slowing. For this meeting, we extend these results with new observations to $\sim 47 au$.
- Publication:
-
43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E.871E