Speaker
Description
Solar wind at L1 is modelled by coupling two independent and agnostic domains of the corona and heliosphere. The transition between the two domains occurs when the solar wind becomes supersonic and super-Alfvenic. The heliospheric solar wind is then driven with appropriate boundary conditions at 0.1 AU which are derived from a coronal model. A popular choice for defining the boundary conditions is the Wang-Sheeley-Arges (WSA) model, which provides a magnetic field from a potential model and estimates solar wind velocity through an empirical relationship with the coronal magnetic field. The solar wind is then obtained by coupling the super-Alfvenic boundaries provided by the WSA model to a magnetohydrodynamic (MHD) simulation.
However, while the solar wind emerging from the Sun is evolving in time, heliospheric wind simulations are often simulated using a steady-state approach using a single WSA map or “snapshot” of the Sun. Such steady-state simulations don't capture the Sun's evolving nature and discard information from previous time steps. Previous studies that have modelled a time-dependent solar wind driven using evolving WSA maps have noted the evolution of inverted magnetic field lines and improved lead time forecasting at 1 AU near boundary regions in time-dependent simulations.
Since the MHD solution is driven by super-Alfvenic flows defined by the WSA maps, the boundary conditions play a determining role in any solar wind features that are simulated in time-dependent simulation. Thus, the cadence at which the WSA maps are changed in time to drive the MHD simulation affects the formation of time-dependent features, such as inverted magnetic fields, that are simulated. In our study, we present results from a 2.5D magnetohydrodynamic (MHD) simulation of the heliosphere driven using evolving WSA maps to assess the importance of WSA map cadence on the simulated solar wind parameters.
The simulations show that as compared to steady-state simulations, the magnetic field is inverted with substantially different velocities near the boundaries where the heliospheric current sheet (HCS) is moving across the equatorial plane. Subsequently, we assess the formation of mesoscale density structures in the solar wind and the deviation of the magnetic field angle from a Parker Spiral due to the HCS movement and examine their dependence on the WSA map cadence in the time-dependent simulations. This quantification of the dependence of such structures on the WSA map cadence enables us to distinguish between realistic solar wind structures and simulation artefacts that may be introduced when the simulation boundaries are not updated with sufficient cadence when the HCS is moving rapidly across the equatorial plane. Thus, in this study, we examine magnetic connectivity and density structures in simulations of a more realistic solar wind driven by time-dependent boundaries. The time-dependent solar wind flows are validated by examining their dependence on WSA map cadence thereby allowing the possibility of realistically modelling solar wind properties in the heliosphere.
