Python vector plot

Software requirements:

• Python 3

• matplotlib

• cartopy

• numpy

• xarray

Example script

matplotlib_vectors.py

#!/usr/bin/env python
# coding: utf-8
'''
DKRZ example

Draws vectors on a map.

Content
- used map projection: PlateCarree
- draw vectors
- add vector reference annotation
- save to PNG

-------------------------------------------------------------------------------
2021 copyright DKRZ licensed under CC BY-NC-SA 4.0 <br>
               (https://creativecommons.org/licenses/by-nc-sa/4.0/deed.en)
-------------------------------------------------------------------------------
'''
import xarray as xr
import cartopy.crs as ccrs
import matplotlib.pyplot as plt

def main():
    #-- open data set
    ds = xr.open_dataset('../../data/rectilinear_grid_2D.nc')
    
    #-- generate the figure
    plt.switch_backend('agg')
    
    fig = plt.figure(figsize=(12,6))
    ax  = plt.axes(projection=ccrs.PlateCarree())
    
    #-- add coastlines and grid lines
    ax.coastlines(resolution='50m', linewidth=0.3, color='black')
    ax.gridlines(draw_labels=True, linewidth=0.5, color='gray',
                 xlocs=range(-180,180,30), ylocs=range(-90,90,30))
    
    ax.set_title('Wind velocity', fontsize=10, fontweight='bold')
    
    #-- add vectors to the map; thin out every other vector
    vplot = ax.quiver(ds.lon[::2], ds.lat[::2],
                      ds.u10[0,::2,::2],
                      ds.v10[0,::2,::2],
                      scale_units='xy',
                      scale=2.5,
                      angles='xy',
                      transform=ccrs.PlateCarree())
    
    #-- add vector reference annotation
    vref = ax.quiverkey(vplot, 0.9, 0.905, 20,
                        r'$20 \frac{m}{s}$',
                        labelpos='E',
                        coordinates='figure', zorder=5)
    
    #-- save to PNG
    plt.savefig('plot_matplotlib_vector_rect.png', bbox_inches='tight', dpi=100)


if __name__ == '__main__':
    main()

Plot result: