Plasma flow in the outer heliosphere due to variations of the solar wind structure at 1 AU in 11-year solar cycle
Abstract
Recent observations at Voyager 1 and 2 in the heliosheath - region of hot subsonic solar wind flow at the heliosphere boundary - show complex and very different plasma flows. Voyager 2 has been observing a constant radial flow 110 km/s indicating that the spacecraft is far from the heliopause. Meanwhile, in 2011 Voyager 1 entered a stagnation region at 120 AU with small/near-zero flow velocity components meaning that Voyager 1 may be very close to the HP. Steady state models of the outer heliosphere do not explain such different flows. These puzzling observational data motivate us to explore different physical effects at the edges of the heliosphere in the models. In this work we focus on time-dependent effects related to 11- year solar cycle. We use a global 3D MHD multi-fluid model of interaction of the solar wind with the local interstellar medium with time-dependent boundary conditions for the supersonic solar wind. Realistic boundary conditions (plasma density and velocity) at 1 AU were obtained from the measurements of intensities of Lyman-alpha emission on SOHO/SWAN, OMNI data (in the ecliptic plane) and interplanetary scintillations data over two full solar cycles. We present results of the time-dependent model and discuss effects of realistic variations of the solar wind parameters on the flow in the heliosheath and in the vicinity of the heliopause. From comparison of model results with the Voyager 1 and 2 observations we found that the solar cycle effects can explain constant radial flow along the Voyager 2 but do not reproduce the decrease of radial flow to zero seen at Voyager 1.
- Publication:
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Solar Heliospheric and INterplanetary Environment (SHINE 2013)
- Pub Date:
- June 2013
- Bibcode:
- 2013shin.confE..67P