Abstract
ABSTRACT One of the key challenges in solar and heliospheric physics is to understand the acceleration of the solar wind. As a super-sonic, super-Alfvénic plasma flow, the solar wind carries mass, momentum, energy, and angular momentum from the Sun into interplanetary space. We present a framework based on two-fluid magnetohydrodynamics to estimate the flux of these quantities based on spacecraft data independent of the heliocentric distance of the location of measurement. Applying this method to the Ulysses data set allows us to study the dependence of these fluxes on heliolatitude and solar cycle. The use of scaling laws provides us with the heliolatitudinal dependence and the solar-cycle dependence of the scaled Alfvénic and sonic Mach numbers as well as the Alfvén and sonic critical radii. Moreover, we estimate the distance at which the local thermal pressure and the local energy density in the magnetic field balance. These results serve as predictions for observations with Parker Solar Probe, which currently explores the very inner heliosphere, and Solar Orbiter, which will measure the solar wind outside the plane of the ecliptic in the inner heliosphere during the course of the mission.
Highlights
The Sun, like most other stars, continuously emits a magnetized plasma in the form of the solar wind (Verscharen, Klein & Maruca 2019)
The Ulysses mission (Wenzel et al 1992; Balogh 1994; Marsden 2001), in operation from 1990 until 2009, plays a special role amongst them due to its unique orbit that led the spacecraft above the Sun’s poles, enabling studies of the solar-wind parameters as functions of heliolatitude. These studies are of great importance to the question of the solar-wind acceleration, since they enable the separation of different solarwind source regions and their relationships to the heliolatitudedependent magnetic-field structure in the corona (Neugebauer 1999)
We find that FL is approximately 1.2 × 10−9 au3 g cm−1 s−2 sr−1 in the Southern polar region (FLS1) and approximately 0.8 × 10−9 au3 g cm−1 s−2 sr−1 in the Northern polar region (FLS3)
Summary
The Sun, like most other stars, continuously emits a magnetized plasma in the form of the solar wind (Verscharen, Klein & Maruca 2019). The Ulysses mission (Wenzel et al 1992; Balogh 1994; Marsden 2001), in operation from 1990 until 2009, plays a special role amongst them due to its unique orbit that led the spacecraft above the Sun’s poles, enabling studies of the solar-wind parameters as functions of heliolatitude. These studies are of great importance to the question of the solar-wind acceleration, since they enable the separation of different solarwind source regions and their relationships to the heliolatitudedependent magnetic-field structure in the corona (Neugebauer 1999).
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