Solar Wind Speed and Temperature Outside 10 AU and the Termination Shock

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Abstract
In this paper we first present a series of pickup proton solar wind solutions following the fluid motion in the upwind direction to show that the wind speed V and temperature T, at a given r outside 10 AU, are primarily functions of the 1 AU wind speed V0. This relationship is attributed to the accumulated effects of the pickup proton process on the heating and deceleration of the solar wind. Because pickup protons are expected to have similar effects on the solar wind at all latitudes in the upwind side of the heliosphere, in the second part of the paper, the two formulae V(r, V0) and T(r, V0) are extended to study the termination shock at 35° latitude. Wang and Sheeley have an empirical model for calculating the 1 AU wind speed V0 from the observed photospheric field. We use the simulated wind speed V0 to calculate V and T outside 60 AU following the fluid motion; then we can study the solar cycle variation of the termination shock. The shock location near 35° is unambiguously dependent on the solar cycle, with a period of approximately 1 solar cycle; the amplitude for variation of the shock location is greater than 50 AU. The new result supports the idea that the first encounter of Voyager 1 with the termination shock may occur during the declining phase of cycle 23. After the first encounter, the spacecraft will cross the shock two more times over a period of 8 years.