Setting Tracing Direction

Perform forward and backward tracing of magnetic field lines.

This example demonstrates how to use the Tracer class to perform forward and backward tracing of magnetic field lines using the set_tracing_direction() method to explicitly set the tracing direction.

Attention

The Tracer class enforces a singleton pattern to manage issues that arise from the underlying mapflpy_fortran object not being thread-safe. As a result, it is recommended to use the Tracer class in single-threaded contexts only viz. instantiating one instance of the class at a time.

import matplotlib.pyplot as plt
import numpy as np

from mapflpy.tracer import Tracer
from mapflpy.utils import plot_traces
from mapflpy.data import fetch_cor_magfiles

Load in the magnetic field files

The fetch_cor_magfiles() function returns a tuple of file paths corresponding to the radial, theta, and phi components of the magnetic field data.

magnetic_field_files = fetch_cor_magfiles()

The Tracer class can be instantiated directly with the magnetic field file paths (along with any additional “mapfl params” as keyword arguments).

For now, the default mapfl configuration is used i.e. DEFAULT_PARAMS.

tracer = Tracer(*magnetic_field_files)

Define launch points in spherical coordinates (r, theta, phi); here we define a ring of points at r=15 Rs around the equatorial plane. The resultant array should have the shape (N, 3), where N is the number of launch points.

rvalues = 15
thetas = np.pi/2
phis = np.linspace(0, 2 * np.pi, 180)

rr, tt, pp = np.meshgrid(rvalues, thetas, phis, indexing='ij')
launch_points = np.column_stack((rr, tt, pp))[0,...]

To explicitly set the tracing direction, use the set_tracing_direction() method – ‘f’ for forward, ‘b’ for backward – before calling the trace() method.

Note

The trace_fwd() and trace_bwd() methods are simply convenience wrappers around this functionality.

tracer.set_tracing_direction('f')
fwd_traces = tracer.trace(launch_points=launch_points)
tracer.set_tracing_direction('b')
bwd_traces = tracer.trace(launch_points=launch_points)

Plot traces using the plot_traces() utility function and adjust the field of view to be 30 Solar Radii in each direction.

Here we plot the forward traces in the default color and the backward traces in red.

ax = plt.figure().add_subplot(projection='3d')
plot_traces(fwd_traces, ax=ax)
plot_traces(bwd_traces, ax=ax, color='red')

FOV = 30.0  # Rsun
for dim in 'xyz':
    getattr(ax, f'set_{dim}lim3d')((-FOV, FOV))
ax.set_box_aspect([1, 1, 1])

plt.show()