Overplotting HEK feature/event polygons on a map

How to overplot HEK outlines on a map.

import matplotlib.pyplot as plt
import numpy as np

import astropy.units as u
from astropy.coordinates import SkyCoord
from astropy.time import TimeDelta

import sunpy.data.sample
import sunpy.map
from sunpy.coordinates import frames
from sunpy.net import attrs as a
from sunpy.net import hek
from sunpy.physics.differential_rotation import solar_rotate_coordinate
from sunpy.time import parse_time

We start with the sample data.

aia_map = sunpy.map.Map(sunpy.data.sample.AIA_171_IMAGE)

Look for coronal holes detected using the SPoCA feature recognition method:

hek_client = hek.HEKClient()
start_time = aia_map.date - TimeDelta(2*u.hour)
end_time = aia_map.date + TimeDelta(2*u.hour)
responses = hek_client.search(a.Time(start_time, end_time),
                              a.hek.CH, a.hek.FRM.Name == 'SPoCA')

Let’s find the biggest coronal hole within 80 degrees north/south of the equator:

area = 0.0
for i, response in enumerate(responses):
    if response['area_atdiskcenter'] > area and np.abs(response['hgc_y']) < 80.0:
        area = response['area_atdiskcenter']
        response_index = i

Next let’s get the boundary of the coronal hole.

ch = responses[response_index]
p1 = ch["hpc_boundcc"][9:-2]
p2 = p1.split(',')
p3 = [v.split(" ") for v in p2]
ch_date = parse_time(ch['event_starttime'])

The coronal hole was detected at different time than the AIA image was taken so we need to rotate it to the map observation time.

ch_boundary = SkyCoord(
    [(float(v[0]), float(v[1])) * u.arcsec for v in p3],
    obstime=ch_date, observer="earth",
    frame=frames.Helioprojective)
rotated_ch_boundary = solar_rotate_coordinate(ch_boundary, time=aia_map.date)

/home/docs/checkouts/readthedocs.org/user_builds/sunpy/conda/stable/lib/python3.12/site-packages/sunpy/physics/differential_rotation.py:152: SunpyUserWarning: Using 'time' assumes an Earth-based observer.
  warn_user("Using 'time' assumes an Earth-based observer.")

Now let’s plot the rotated coronal hole boundary on the AIA map, and fill it with hatching.

fig = plt.figure()
ax = fig.add_subplot(projection=aia_map)
aia_map.plot(axes=ax, clip_interval=(1, 99.99)*u.percent)
ax.plot_coord(rotated_ch_boundary, color='c')
ax.set_title('{:s}\n{:s}'.format(aia_map.name, ch['frm_specificid']))
plt.colorbar()

plt.show()