Overplotting SRS active region locations on a magnetograms

How to find and plot the location of an active region on an HMI magnetogram.

import matplotlib.pyplot as plt
import numpy as np

from astropy.coordinates import SkyCoord

import sunpy.coordinates
import sunpy.data.sample
import sunpy.map
from sunpy.io.special import srs

For this example, we will start with the sample data. We need an HMI file and use it to create a map, and the SRS table which contains a list of active regions. Both of these data can be downloaded with Fido.

We only need the rows which have ‘ID’ = ‘I’ or ‘IA’. Some tables do not have these columns, so we exit the script if they are not present.

srs_table = srs_table[np.logical_or(srs_table['ID'] == 'I', srs_table['ID'] == 'IA')]

Now we extract the latitudes, longitudes and the region numbers. We make an empty list if there are no ARs.

lats = srs_table['Latitude']
lngs = srs_table['Longitude']
numbers = srs_table['Number']

Let’s plot the results by defining coordinates for each location.

ax = plt.subplot(projection=smap)
smap.plot(vmin=-120, vmax=120)
# As the values are masked arrays, we need to work around that.
c = SkyCoord(lngs.data * lngs.unit, lats.data * lats.unit, frame="heliographic_stonyhurst")
ax.plot_coord(c, 'o')
for i, num in enumerate(numbers):
    ax.annotate(num, (lngs[i].value, lats[i].value),

HMI magnetogram 2011-06-07 06:32:11

Total running time of the script: ( 0 minutes 0.498 seconds)

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