NCL_conwomap_2.py

This script illustrates the following concepts:

• Drawing a simple filled contour plot

• Selecting a different color map

• Changing the size/shape of a contour plot

See following URLs to see the reproduced NCL plot & script:

• Original NCL script: https://www.ncl.ucar.edu/Applications/Scripts/conwomap_2.ncl

• Original NCL plot: https://www.ncl.ucar.edu/Applications/Images/conwomap_2_lg.png

Import packages:

import numpy as np
import xarray as xr
import cartopy.crs as ccrs
import matplotlib.pyplot as plt
import cmaps

import geocat.datafiles as gdf
import geocat.viz as gv

Read in data:

# Open a netCDF data file using xarray default engine and load the data into xarrays
ds = xr.open_dataset(gdf.get("netcdf_files/cone.nc"))
u = ds.u.isel(time=4)

Plot:

# Generate figure (set its size (width, height) in inches)
plt.figure(figsize=(10, 6))

# Generate axes, using Cartopy
projection = ccrs.PlateCarree()
ax = plt.axes(projection=projection)

# Import an NCL colormap
newcmp = cmaps.gui_default

# Contourf-plot data (for filled contours)
p = u.plot.contourf(ax=ax,
                    vmin=-1,
                    vmax=10,
                    levels=12,
                    cmap=newcmp,
                    add_colorbar=False,
                    transform=projection,
                    extend='neither',
                    add_labels=False)
# Contour-plot data (for borderlines)
u.plot.contour(ax=ax,
               vmin=-1,
               vmax=10,
               levels=12,
               linewidths=0.5,
               colors='black',
               add_colorbar=False,
               transform=projection,
               extend='neither',
               add_labels=False)

# Add horizontal colorbar
cbar = plt.colorbar(p, orientation='horizontal', shrink=0.5, drawedges=True)
cbar.ax.tick_params(labelsize=16)
cbar.set_ticks(np.linspace(0, 9, 10))

# Use geocat.viz.util convenience function to set axes limits & tick values without calling several matplotlib functions
gv.set_axes_limits_and_ticks(ax,
                             xlim=(0, 49),
                             ylim=(0, 29),
                             xticks=np.linspace(0, 40, 5),
                             yticks=np.linspace(0, 25, 6))

# Use geocat.viz.util convenience function to add minor and major tick lines
gv.add_major_minor_ticks(ax,
                         x_minor_per_major=5,
                         y_minor_per_major=5,
                         labelsize=16)

# Use geocat.viz.util convenience function to add titles to left and right of the plot axis.
gv.set_titles_and_labels(ax,
                         lefttitle="Cone amplitude",
                         lefttitlefontsize=18,
                         righttitle="ndim",
                         righttitlefontsize=18,
                         xlabel="X",
                         ylabel="Y",
                         labelfontsize=18)

# Show the plot
plt.show()