Cartopy issue in polar stereographic projection

Question

The issue only happens with contourf, not with pcolormesh.

How can I fix the discontinuity at longitude=0 (white stripe in the plot)?

Answer 1

A demo code and output plots for the use of .add_cyclic() to solve the problem:

import matplotlib.pyplot as plt
import numpy as np
import cartopy.crs as ccrs
import cartopy.util as cutil

def sample_data(shape=(73, 145)):
    """Return ``lons``, ``lats`` and ``data`` of some fake data."""
    nlats, nlons = shape
    lats = np.linspace(-np.pi / 2, np.pi / 2, nlats)
    # lons is not complete 0-2pi here
    lons = np.linspace(0, -0.1+2 * np.pi, nlons) ## Intended to make it incomplte to use cyclic
    lons, lats = np.meshgrid(lons, lats)
    wave = 0.75 * (np.sin(2 * lats) ** 8) * np.cos(4 * lons)
    mean = 0.5 * np.cos(2 * lats) * ((np.sin(2 * lats)) ** 2 + 2)
    lats = np.rad2deg(lats)
    lons = np.rad2deg(lons)
    data = wave + mean
    return lons, lats, data

fig = plt.figure(figsize=(8, 4))
ax1 = fig.add_subplot(1, 2, 1, projection=ccrs.NorthPolarStereo())
ax2 = fig.add_subplot(1, 2, 2, projection=ccrs.NorthPolarStereo())

lons, lats, data = sample_data()
ax1.contourf(lons, lats, data,
            transform=ccrs.PlateCarree(),
            cmap='nipy_spectral')
ax1.coastlines()
ax1.set_global()

# ----------------------------------------
# add cyclic points to data and longitudes
# latitudes are unchanged
data2, lons2, lats2 = cutil.add_cyclic(data, lons, lats)
# ------------------------------------------------------

ax2.contourf(lons2, lats2, data2,
            transform=ccrs.PlateCarree(),
            cmap='nipy_spectral')
ax2.coastlines()
ax2.set_global()
plt.show()