Zonal mean gallery example

docs/gallery_code/meteorology/plot_zonal_mean.py

@@ -0,0 +1,75 @@
+"""
+Zonal Mean Diagram of Air Temperature
+=====================================
+
+This example demonstrates aligning a linear plot and a cartographic plot using Matplotlib.
+
+"""
+
+import cartopy.crs as ccrs
+import matplotlib.pyplot as plt
+from mpl_toolkits.axes_grid1 import make_axes_locatable
+import numpy as np
+
+import iris
+from iris.analysis import MEAN
+import iris.plot as iplt
+
+
+def main():
+    fname = iris.sample_data_path("air_temp.pp")
+    temperature = iris.load_cube(fname)
+    collapsed_temp = temperature.collapsed("longitude", MEAN)
+
+    # Set y axes with -90 and 90 limits and spacing of 15 per tick.
+    yticks = np.arange(-90, 105, 15)
+    ylim = [-90, 90]
+    fig = plt.figure(figsize=[12, 4])
+    ax1 = fig.add_subplot(111, projection=ccrs.PlateCarree())
+    plt.sca(ax1)
+    im = iplt.contourf(temperature, cmap="RdYlBu_r")
+    ax1.coastlines()
+    ax1.gridlines()
+    ax1.set_xticks([-180, -90, 0, 90, 180], crs=ccrs.PlateCarree())
+    ax1.set_yticks(yticks, crs=ccrs.PlateCarree())
+    ax1.set_title("Air Temperature")
+    ax1.set_ylabel("latitude")
+    ax1.set_xlabel("longitude")
+    ax1.set_ylim(*ylim)
+    divider = make_axes_locatable(ax1)
+
+    # Gives the air temperature bar size, colour and a title.
+    ax2 = divider.new_vertical(
+        size="5%", pad=0.5, axes_class=plt.Axes, pack_start=True
+    )
+    fig.add_axes(ax2)
+    plt.sca(ax2)
+    cbar = plt.colorbar(im, cax=ax2, orientation="horizontal")
+    cbar.ax.set_xlabel("Air Temperature [k]")
+
+    # Round each tick for the third ax to the nearest 20 (ready for use).
+    data_max = collapsed_temp.data.max()
+    x_max = data_max - data_max % -20
+    data_min = collapsed_temp.data.min()
+    x_min = data_min - data_min % 20
+
+    # Plot "collapsed_temp" on the mean graph and set the ticks and titles on the axes.
+    ax3 = divider.new_horizontal(size="30%", pad=0.4, axes_class=plt.Axes)
+    fig.add_axes(ax3)
+    plt.sca(ax3)
+    iplt.plot(collapsed_temp, collapsed_temp.coord("latitude"))
+    ax3.axvline(0, color="k", linewidth=0.5)
+    ax3.set_ylim(*ylim)
+    ax3.set_title("Zonal mean")
+    ax3.set_ylabel("latitude")
+    ax3.set_xlabel("Air Temperature [k]")
+    ax3.yaxis.set_label_position("right")
+    ax3.yaxis.tick_right()
+    ax3.set_yticks(yticks)
+    ax3.set_xlim(x_min, x_max)
+
+    plt.show()
+
+
+if __name__ == "__main__":
+    main()

docs/gallery_tests/test_plot_zonal_mean.py

@@ -0,0 +1,30 @@
+# Copyright Iris contributors
+#
+# This file is part of Iris and is released under the LGPL license.
+# See COPYING and COPYING.LESSER in the root of the repository for full
+# licensing details.
+
+# Import Iris tests first so that some things can be initialised before
+# importing anything else.
+import iris.tests as tests
+
+from .gallerytest_util import (
+    add_gallery_to_path,
+    fail_any_deprecation_warnings,
+    show_replaced_by_check_graphic,
+)
+
+
+class TestGlobalMap(tests.GraphicsTest):
+    """Test the zonal mean gallery code."""
+
+    def test_plot_zonal_mean(self):
+        with fail_any_deprecation_warnings():
+            with add_gallery_to_path():
+                import plot_zonal_mean
+            with show_replaced_by_check_graphic(self):
+                plot_zonal_mean.main()
+
+
+if __name__ == "__main__":
+    tests.main()

docs/src/whatsnew/latest.rst

@@ -25,7 +25,8 @@ This document explains the changes made to Iris for this release
 📢 Announcements
 ================
 
-#. N/A
+#. Welcome to `@TTV-Intrepid`_ who made their first contribution to Iris.
+   The first of many we hope!
 
 
 ✨ Features
@@ -217,6 +218,9 @@ This document explains the changes made to Iris for this release
 #. `@trexfeathers`_ and `@abooton`_ modernised the Iris logo to be SVG format.
    (:pull:`3935`)
 
+#. `@TTV-Intrepid`_ and `@trexfeathers`_ added a gallery example for zonal
+   means plotted parallel to a cartographic plot. (:pull:`4871`)
+
 
 💼 Internal
 ===========
@@ -268,4 +272,5 @@ This document explains the changes made to Iris for this release
 .. _Calendar: https://cfconventions.org/Data/cf-conventions/cf-conventions-1.9/cf-conventions.html#calendar
 .. _Cell Boundaries: https://cfconventions.org/Data/cf-conventions/cf-conventions-1.9/cf-conventions.html#cell-boundaries
 .. _PyData Sphinx Theme: https://pydata-sphinx-theme.readthedocs.io/en/stable/index.html
-.. _setuptools-scm: https://github.com/pypa/setuptools_scm
+.. _setuptools-scm: https://github.com/pypa/setuptools_scm
+.. _@TTV-Intrepid: https://github.com/TTV-Intrepid

lib/iris/tests/results/imagerepo.json

@@ -34,6 +34,7 @@
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     "gallery_tests.test_plot_wind_speed.TestWindSpeed.test_plot_wind_speed.0": "e9e960e996169306c1fe9e96c29e36739e03c06c3d61c07f3da139e1c07f3f01",
     "gallery_tests.test_plot_wind_speed.TestWindSpeed.test_plot_wind_speed.1": "e9e960e996169306c1ee9f96c29e36739653c06c3d61c07f39a139e1c07f3f01",
+    "gallery_tests.test_plot_zonal_mean.TestGlobalMap.test_plot_zonal_mean.0": "b45b30f3c924c9a6869c667cc326cba3cb9634ddc9a634f336738c6634d8c3c4",
     "iris.tests.experimental.test_animate.IntegrationTest.test_cube_animation.0": "fe81c17e817e3e81817e3e81857e7a817e81c17e7e81c17e7a81817e817e8c2e",
     "iris.tests.experimental.test_animate.IntegrationTest.test_cube_animation.1": "fe81857e817e7a85817e7a81857e7e817e81917a7e81817e7a81817e817e843e",
     "iris.tests.experimental.test_animate.IntegrationTest.test_cube_animation.2": "be81817ec17e7a81c17e7e81857e3e803e81817a3e81c17e7a81c17ec97e2c2f",