MHD Analysis of The Heliopause Scale

Voyager-1 (V1) was at ~122 AU from the Sun in August 2012, and V1 observations in Science papers in 2013 by Stone et al., Krimigis et al., & Burlaga et al. indicated that V1 is now located very near the heliopause. Here, we show by using MHD simulation that the simulated scale of the heliopause along the Sun-V1 line is ~125 AU. Our simulation also shows that the heliopause along the Sun-V2 line is ~105 AU which suggests that V2 is also approaching the heliopause at present time and has a possibility to cross the heliopause in one or two years. For this simulation, we have carefully checked the latitudinal dependence of the solar wind ram-pressure in interplanetary space by comparing Ulysses, OMNI and ACE data in years 1995 to 2009 during which Ulysses provided data, and have confirmed that the solar-wind ram-pressure has no evident latitudinal dependence during the time period of our simulation, although the first Ulysses paper (Philips et al., GRL, 1995) showed that the averaged ram-pressure was 1.4-1.5 times greater in high-latitudes than that in low-latitudes. The absence of the latitudinal dependence of the ram-pressure results in the heliopause scale consistent with V1 observations in our MHD simulation.