NCL_xy_7_2.py

An example of a double y plot: two separate line with their own unique axis.

This script illustrates the following concepts:

• Drawing an XY plot with two different Y axes

• Changing the title on the Y axis

• Changing the line dash pattern in an XY plot

• Changing the line color for multiple curves in an XY plot

• Setting the mininum/maximum value of the Y axis in an XY plot

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

• Original NCL script: https://www.ncl.ucar.edu/Applications/Scripts/xy_7.ncl

• Original NCL plot: https://www.ncl.ucar.edu/Applications/Images/xy_7_2_lg.png

Import packages:

import matplotlib.pyplot as plt
import numpy as np
import xarray as xr

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/TestData.xy3.nc"))
# Extract a slice of the data
ds = ds.isel(case=0, time=slice(0, 36))

Plot:

# Generate figure (set its size (width, height) in inches) and axes (with two different y-axes)
fig, ax1 = plt.subplots(figsize=(7, 6.5))

# Plot data
ax1.plot(ds.time, ds.T, color="blue", linestyle="-", linewidth=0.9)

# Usa geocat.viz.util convenience function to add minor and major tick lines
gv.add_major_minor_ticks(ax1, x_minor_per_major=5, labelsize=14)

# Usa geocat.viz.util convenience function to set axes parameters without calling several matplotlib functions
# Set axes limits, and tick values
gv.set_axes_limits_and_ticks(ax1,
                             xlim=(1970, 1973),
                             ylim=(0.0, 16.0),
                             yticks=np.arange(0, 17, 3))

# Usa geocat.viz.util convenience function to set titles and labels without calling several matplotlib functions
gv.set_titles_and_labels(ax1,
                         maintitle="Curves Offset",
                         xlabel=ds.time.long_name,
                         ylabel=f"{ds.T.long_name} [solid]")

# Create second y-axis
ax2 = ax1.twinx()

# Use geocat.viz.util convenience function to add minor and major tick lines
gv.add_major_minor_ticks(ax2, x_minor_per_major=5, labelsize=14)

# Line-plot data
ax2.plot(ds.time,
         ds.P,
         color="red",
         linestyle="--",
         dashes=[6.5, 3.7],
         linewidth=0.9)

# Use geocat.viz.util convenience function to set axes parameters without calling several matplotlib functions
# Set axes limits, and tick values
gv.set_axes_limits_and_ticks(ax2,
                             ylim=(1008.0, 1024.0),
                             yticks=np.arange(1008, 1025, 3))

# Set second y-axis label
ax2.set_ylabel(f"{ds.P.long_name} [dash]", fontsize=16)

# Show the plot
plt.tight_layout()
plt.show()