NCL_ce_3_2.pyΒΆ

This script illustrates the following concepts:
  • Drawing color-filled contours over a cylindrical equidistant map

  • Selecting a different color map

  • Changing the contour level spacing

  • Turning off contour lines

  • Comparing styles of map tickmarks labels

  • Changing the stride of the colorbar labels

  • Zooming in on a particular area on the map

  • Turning off the addition of a longitude cyclic point

See following URLs to see the reproduced NCL plot & script:
import cartopy.crs as ccrs
import cartopy.feature as cfeature
import geocat.datafiles as gdf
import matplotlib.pyplot as plt

Import packages:

import numpy as np
import xarray as xr
from geocat.viz import cmaps as gvcmaps
from geocat.viz import util as gvutil

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/h_avg_Y0191_D000.00.nc'),
                     decode_times=False)
# Extract a slice of the data
t = ds.T.isel(time=0, z_t=0).sel(lat_t=slice(-60, 30), lon_t=slice(30, 120))

Plot:

# Generate figure (set its size (width, height) in inches)
fig = plt.figure(figsize=(7, 7))

# Generate axes, using Cartopy, drawing coastlines, and adding features
projection = ccrs.PlateCarree()
ax = plt.axes(projection=projection)
ax.coastlines(linewidths=0.5)
ax.add_feature(cfeature.LAND, facecolor='lightgray')

# Import an NCL colormap
newcmp = gvcmaps.BlAqGrYeOrRe

# Contourf-plot data
heatmap = t.plot.contourf(ax=ax,
                          transform=projection,
                          levels=40,
                          vmin=0,
                          vmax=32,
                          cmap=newcmp,
                          add_colorbar=False)

# Add colorbar
cbar = plt.colorbar(heatmap, ticks=np.arange(0, 32, 2))
cbar.ax.set_yticklabels([str(i) for i in np.arange(0, 32, 2)])

# Adjust tick label size
ax.tick_params(labelsize=12)

# Use geocat.viz.util convenience function to set axes parameters without calling several matplotlib functions
# Set axes limits, and tick values
gvutil.set_axes_limits_and_ticks(ax,
                                 xlim=(30, 120),
                                 ylim=(-60, 30),
                                 xticks=np.linspace(-180, 180, 25),
                                 yticks=np.linspace(-90, 90, 13))

# Use geocat.viz.util convenience function to make plots look like NCL plots by using latitude, longitude tick labels
gvutil.add_lat_lon_ticklabels(ax)

# Use geocat.viz.util convenience function to set titles and labels without calling several matplotlib functions
gvutil.set_titles_and_labels(ax,
                             maintitle="15-degree major but no minor ticks",
                             maintitlefontsize=16,
                             lefttitle="Potential Temperature",
                             lefttitlefontsize=14,
                             righttitle="Celsius",
                             righttitlefontsize=14,
                             xlabel="",
                             ylabel="")

# Show the plot
plt.show()
Potential Temperature, 15-degree major but no minor ticks, Celsius

Total running time of the script: ( 0 minutes 0.311 seconds)

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