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"""
======================================
Comparing differential-rotation models
======================================
How to compare differential-rotation models.
The example uses the `~sunpy.coordinates.metaframes.RotatedSunFrame` coordinate
metaframe in `sunpy.coordinates` to apply differential rotation to a coordinate.
See :ref:`sunpy-coordinates-rotatedsunframe` for more details on using
`~sunpy.coordinates.metaframes.RotatedSunFrame`.
"""
import matplotlib.pyplot as plt
import astropy.units as u
from astropy.coordinates import SkyCoord
import sunpy.map
from sunpy.coordinates import HeliographicStonyhurst, RotatedSunFrame
from sunpy.data.sample import AIA_335_IMAGE
from sunpy.sun.constants import sidereal_rotation_rate
##############################################################################
# First, we use an AIA observation primarily as a pretty background. We also
# define the meridian using a two-element coordinate array of the south pole
# and the north pole at zero longitude.
aiamap = sunpy.map.Map(AIA_335_IMAGE)
meridian = SkyCoord(0*u.deg, [-90, 90]*u.deg, frame=HeliographicStonyhurst,
obstime=aiamap.date)
##############################################################################
# Next, we calculate the sidereal rotation period of the Sun. This is the
# time for a full rotation relative to an inertial reference frame (e.g.,
# distant stars), as opposed to the synodic period, which is the apparent
# rotation period as seen from an Earth-based observer. Since the Earth
# orbits the Sun in the same direction as the Sun rotates, the Sun appears to
# rotate slower for an Earth-based observer.
sidereal_period = 360*u.deg / sidereal_rotation_rate
print(sidereal_period)
##############################################################################
# We use `~sunpy.coordinates.metaframes.RotatedSunFrame` to rotate the
# meridian by one sidereal period using each of the available
# differential-rotation models. See
# :func:`~sunpy.physics.differential_rotation.diff_rot` for details on each
# model.
rotated_meridian = {}
for model in ['howard', 'snodgrass', 'allen', 'rigid']:
rotated_meridian[model] = SkyCoord(RotatedSunFrame(base=meridian,
duration=sidereal_period,
rotation_model=model))
##############################################################################
# Finally, we plot the differentially rotated meridians over the map, using
# :meth:`~sunpy.map.GenericMap.draw_quadrangle` to conveniently draw a line
# of constant longitude in the original frame between two endpoints. (One
# could instead use :meth:`astropy.visualization.wcsaxes.WCSAxes.plot_coord`,
# but then ``meridian`` would need to consist of a sequence of many points
# spanning all latitudes between the two poles to render as desired.)
# Note that the "rigid" model appears as the meridian again as expected for a
# rotation of exactly one sidereal period.
plt.figure()
aiamap.plot(clip_interval=(0.5, 99.9)*u.percent)
colors = {
'howard': 'red',
'snodgrass': 'green',
'allen': 'yellow',
'rigid': 'white',
}
for model, coord in rotated_meridian.items():
aiamap.draw_quadrangle(coord, edgecolor=colors[model],
label=model.capitalize())
plt.legend()
plt.title(f'{sidereal_period:.2f} of solar rotation')
plt.show()
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