DKRZ PyNGL Hovmoeller plot

Example script:

#
#  File:
#    hov_1.py
#
#  Synopsis:
#    Default black and white Hovmueller plot.
#
#  Category:
#    contour plot
#
#  Based on NCL example:
#    hov_1.ncl
#
#  Author:
#    Karin Meier-Fleischer
#
#  Date of initial publication:
#    November, 2018
#
#  Description:
#    This example shows how to create a default black and white Hovmueller plot.
#
#  Effects illustrated:
#    o  Creating a Hovmueller plot
#    o  Using text function codes to generate umlauts
#
#  Output:
#     A single visualization is produced.
#
'''
  PyNGL Example:     hov_1.py

  -  Creating a Hovmueller plot
  -  Using text function codes to generate umlauts

'''
from __future__ import print_function
import numpy as np
import os, sys
import Ngl,Nio

#-------------------------------------------------------
#-- Function:    add_titles(wks,plot,resources,title,left,center,right)
#-------------------------------------------------------
def add_titles(wks,plot,title="",left="",center="",right=""):

   vpx = Ngl.get_float(plot,"vpXF")             #-- retrieve value of res.vpXF from plot
   vpy = Ngl.get_float(plot,"vpYF")             #-- retrieve value of res.vpYF from plot
   vpw = Ngl.get_float(plot,"vpWidthF")         #-- retrieve value of res.vpWidthF from plot
   vph = Ngl.get_float(plot,"vpHeightF")        #-- retrieve value of res.vpHeightF from plot

   ymax = vpy+0.08                              #-- we need space for the title and strings

   if(ymax > 0.98):
     print("--> if you can't see the title use res.nglMaximize = False and/or set res.vpYF")

#-- add title
   if(title != ""):
      tires = Ngl.Resources()
      tires.txFontHeightF =  0.018
      tires.txJust        = "CenterCenter"
      tires.txFont        =  22                     #-- Font 22: Helvetica bold
      if(left != "" or center != "" or right != ""):
         y = vpy + 0.07
      else:
         y = vpy + 0.05
      Ngl.text_ndc(wks, title, 0.5, y, tires)

#-- add left, center and/or right string
   txres = Ngl.Resources()
   txres.txFontHeightF = 0.014                  #-- font size for left, center and right string

   y = vpy + 0.035                              #-- y-position

   if(left != ""):
      txres.txJust = "CenterLeft"               #-- text justification
      x = vpx                                   #-- x-position
      Ngl.text_ndc(wks, left, x, y, txres)      #-- add text to wks

   if(center != ""):
      txres.txJust = "CenterCenter"             #-- text justification
      Ngl.text_ndc(wks, center, 0.5, y, txres)  #-- add text to wks

   if(right != ""):
      txres.txJust = "CenterRight"              #-- text justification
      x = vpx+vpw                               #-- x-position
      Ngl.text_ndc(wks, right, x, y, txres)     #-- add text to wks

#-----------------------------------------------------------------------
#-- Function: main
#-----------------------------------------------------------------------
def main():

    #-- data path and file name
    ncarg_root = os.environ.get('NCARG_ROOT')
    diri  = ncarg_root + '/lib/ncarg/data/cdf/'
    fname = 'chi200_ud_smooth.nc'

    #-- open file and read variables
    f     =  Nio.open_file(diri + fname,"r")    #-- open data file
    chi   =  f.variables['CHI'][:,:]            #-- read variable CHI[time,lon]
    lon   =  f.variables['lon'][:]
    time  =  f.variables['time'][:]

    scale =  1.0e6
    chi   =  chi/scale

    #-- create the plot
    wks =  Ngl.open_wks('png','plot_hovmueller')
                                                #-- open workstation
    #-- set resources
    res                       =  Ngl.Resources
    res.nglFrame              =  False
    res.nglMaximize           =  False           #-- maximize plot output

    #res.tiMainString          = 'Default Hovmu~H-13V2F35~H~FV-2H3~ller' #-- title

    res.sfXArray              =  lon            #-- scalar field x
    res.sfYArray              =  time           #-- scalar field y

    res.tiYAxisString         = 'elapsed time'
    res.tmYLLabelFontHeightF  =  0.015

    res.nglPointTickmarksOutward = True         #-- point tickmarks out

    plot = Ngl.contour(wks,chi,res)             #-- draw contours

    #-- delete resources because they will cause warnings (Why?)
    del([res.sfXArray,res.sfYArray,res.tiYAxisString,res.tmYLLabelFontHeightF])

    #-- add the title and left, center and/or right string
    title     = "Default Hovmu~H-13V2F35~H~FV-2H3~ller"
    long_name = f.variables["CHI"].attributes['long_name']
    units     = f.variables["CHI"].attributes['units']

    add_titles(wks,plot,title,left=long_name,right=units)

    #-- advance the frame
    Ngl.frame(wks)

    #-- end
    Ngl.end()

if __name__ == '__main__':
    main()

Result: