OFT / POT3D - WSA / HelioCubed

OFT is a new open-source solar magnetic field flux transport model which will evolve information to the far side of the Sun and its poles and update the model flux with new observations using data assimilation methods. This will provide us with more realistic estimates of the instantaneous global photospheric magnetic field distribution than those available from traditional synoptic maps. This model will take into account the solar rotation and meridional flows, supergranular diffusion, random flux emergence, and new data assimilation approaches. It will provide us with an ensemble of solutions representing the model parameter uncertainties. It will also create sequences of maps at a user-specified cadence for selected time periods.

POT3D is a Fortran code that computes potential field solutions to approximate the solar coronal magnetic field using observed photospheric magnetic fields as a boundary condition. It can be used to generate potential field source surface (PFSS), potential field current sheet (PFCS), and open field (OF) models. It has been (and continues to be) used for numerous studies of coronal structure and dynamics. The code is highly parallelized using MPI and is GPU-accelerated using Fortran standard parallelism (do concurrent) and OpenACC, along with an option to use the NVIDIA cuSparse library. The HDF5 file format is used for input/output.

The WSA model initially extrapolates magnetic field from the photosphere to a source surface, traditionally chosen as 2.5 Rs, using the PFSS model, and further to the inner-heliosphere using Schatten’s current sheet model. Additionally, the model estimates the velocity of the solar wind plasma at the outer boundary using an empirical formula, which depends on a magnetic flux expansion factor and the minimum angular distance to the nearest coronal hole boundary. Above figure shows
the example of radial magnetic field and solar wind velocity boundary maps.

We employ HelioCubed, our inner heliospheric model, to simulate the time-dependent 3D MHD solutions of the solar wind. HelioCubed is a highly parallel, adaptive mesh refinement (AMR) based solver for the hyperbolic, Reynolds-averaged, ideal MHD equations in conservative form. Using the recently built Chombo 4 framework, we employ finite-volume method to solve MHD equations with fourth order of precision in space and time on cubed-sphere grids, which resolves the polar singularity intrinsic in the spherical grid. HelioCubed will utilize the ensemble of OFT-POT3D-WSAmaps as time-dependent boundary conditions with higher spatial resolution. We have also developed a new, data-driven approach for over-imposing CMEs over the background solar wind. (Eg. Singh et al., 2022).