This script illustrates the following concepts:
  • Draw multiple curves on an XY plot

  • Drawing a Y reference line in an XY plot

  • Filling the areas of an XY curve above and below a reference line

  • Using named colors to indicate a fill color

  • Converting dates from YYYYMM format to floats

  • Creating a main title

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

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

Import packages:

import numpy as np
import xarray as xr
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/"))
dsoik = ds.DSOI_KET
dsoid = ds.DSOI_DEC
date =
num_months = np.shape(date)[0]

# Dates in the file are represented by year and month (YYYYMM)
# representing them fractionally will make ploting the data easier
# This produces the same results as NCL's yyyymm_to_yyyyfrac() function
date_frac = np.empty_like(date)
for n in np.arange(0, num_months, 1):
    yyyy = int(date[n] / 100)
    mon = (date[n] / 100 - yyyy) * 100
    date_frac[n] = yyyy + (mon - 1) / 12


# Generate figure (set its size (width, height) in inches) and axes
plt.figure(figsize=(8, 4))
ax = plt.gca()

# Plot reference line
ax.axhline(y=0, color='grey', linewidth=0.75)

# Plot data
# _labels=False prevents axis labels from being drawn
ax.plot(date_frac, dsoik, color='black', linewidth=0.5)
ax.plot(date_frac, dsoid, color='black')

# Fill above and below the 0 line
ax.fill_between(date_frac, dsoik, where=dsoik > 0, color='red')
ax.fill_between(date_frac, dsoik, where=dsoik < 0, color='blue')

# Use geocat.viz.util convenience function to add minor and major tick lines

# Use geocat.viz.util convenience function to set axes parameters
                                 ylim=(-3, 3),
                                 yticks=np.linspace(-3, 3, 7),
                                 yticklabels=np.linspace(-3, 3, 7),
                                 xlim=(date_frac[0], date_frac[-1]),
                                 xticks=np.linspace(1880, 1980, 6))

# Use geocat.viz.util convenience function to set titles and labels
gvutil.set_titles_and_labels(ax, maintitle="Darwin Southern Oscillation Index")
Darwin Southern Oscillation Index

Total running time of the script: ( 0 minutes 0.850 seconds)

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