Regridding and plotting netcdf file with irregular grid

Question

I am trying to regrid my .nc data with irregular grid with the following code:

from mpl_toolkits.basemap import Basemap
from netCDF4 import Dataset as NetCDFFile
import matplotlib.pyplot as plt
import numpy as np
from scipy.interpolate import griddata

nc = NetCDFFile('test.nc')
lat = nc.variables['latitude'][:]
lon = nc.variables['longitude'][:]
time = nc.variables['time'][:]
ssi = nc.variables['solar_irradiation'][:]

XI = np.arange(46.025, 56.525, 0.05)
YI = np.arange(5.025, 15.525, 0.05)
lat_new, lon_new = np.meshgrid(XI, YI)

new_grid = griddata((lat, lon), ssi, (lat_new, lon_new), method='linear')

It works fine, there are NaN values at lat/lon boxes which are not in the original file. Then I want to plot it using Basemap:

map = Basemap(projection='merc', llcrnrlon=-5., llcrnrlat=35., urcrnrlon=30., urcrnrlat=60., 
resolution='i')
map.drawcountries()
map.drawcoastlines()
x, y = map(XI, YI)
rad = map.contourf(x, y, new_grid)
cb = map.colorbar(rad, "bottom", size="10%", pad="10%")

I am receiving following error: IndexError: too many indices for array: array is 1-dimensional, but 2 were indexed. I know that this means, but I have no clue how to change to code so that it worked the same way. Thank you for every help!