Setting the Magnetic Field

Explicitly set the magnetic field files using the TracerMP class.

This example demonstrates how to use explicitly set the TracerMP magnetic field data i.e. br, bt, and bp attributes.

import matplotlib.pyplot as plt

from mapflpy.tracer import TracerMP
from mapflpy.utils import plot_traces
from psi_data import fetch_mas_data

Load in the magnetic field files

The fetch_mas_data() function returns a named tuple of file paths corresponding to the radial, theta, and phi components of the magnetic field data for the requested domain (with fields like cor_br, cor_bt, cor_bp for the coronal domain and hel_br, hel_bt, hel_bp for the heliospheric domain).

magnetic_field_files = fetch_mas_data(domains="cor", variables="br,bt,bp")
hel_magnetic_field_files = fetch_mas_data(domains="hel", variables="br,bt,bp")

The TracerMP class is, for demonstration purposes, instantiated without arguments to illustrate how to set the magnetic field files post-initialization.

Note

As with Tracer, the magnetic field data can be set using the br, bt, and bp attributes, or by passing the file paths to load_fields()

Warning

When setting the magnetic field data with TracerMP, only a filepath can be supplied i.e. not a NumPy array, as with Tracer. This is due to the inter-process communication mechanism used by TracerMP and the prohibitive cost of passing magnetic field data over the pipe.

Here we pass along the n and r parameters to the trace_fwd() and trace_bwd() methods to specify the number of field lines to trace and the starting radius respectively.

with TracerMP(context=CONTEXT) as tracer:
    with TracerMP(context=CONTEXT) as tracer_hel:
        tracer.br = magnetic_field_files.cor_br
        tracer.bt = magnetic_field_files.cor_bt
        tracer.bp = magnetic_field_files.cor_bp

        tracer_hel.load_fields(*hel_magnetic_field_files)
        tracer_hel['domain_r_min_'] = 30

        traces = tracer.trace_fwd(n=128, r=1)
        traces_hel = tracer_hel.trace_bwd(n=32, r=200)

Plot traces using the plot_traces() utility function and adjust the field of view to be 200 Solar Radii in each direction.

ax = plt.figure().add_subplot(projection='3d')
plot_traces(traces, ax=ax)
plot_traces(traces_hel, ax=ax, color='m')

FOV = 200.0  # Rsun
for dim in 'xyz':
    getattr(ax, f'set_{dim}lim3d')((-FOV, FOV))
ax.set_box_aspect([1, 1, 1])

plt.show()