Machine learning-based emulator for the physics-based simulation of
auroral current system
Abstract
Using a machine learning technique called echo state network (ESN), we
have developed an emulator to model the physics-based global
magnetohydrodynamic (MHD) simulation results of REPPU (REProduce Plasma
Universe) code. The inputs are the solar wind time series with date and
time, and the outputs are the time series of the ionospheric auroral
current system in the form of two-dimensional (2D) patterns of
field-aligned current, potential, and conductivity. We mediated a
principal component analysis for a dimensionality reduction of the 2D
map time series. In this study, we report the latest upgraded Surrogate
Model for REPPU Auroral Ionosphere version 2 (SMRAI2) with significantly
improved resolutions in time and space (5 min in time,
~1 degrees in latitude, and 4.5 degrees in longitude),
where the dipole tilt angle is also newly added as one of the input
parameters to reproduce the seasonal dependence. The fundamental
dependencies of the steady-state potential and field-aligned current
patterns on the interplanetary magnetic field (IMF) directions are
consistent with those obtained from empirical models. Further, we show
that the ESN-based emulator can output the AE index so that we can
evaluate the performance of the dynamically changing results, comparing
with the observed AE index. Since the ESN-based emulator runs a million
times faster than the REPPU simulation, it is promising that we can
utilize the emulator for the real-time space weather forecast of the
auroral current system as well as to obtain large-number ensembles to
achieve future data assimilation-based forecast.