Example Python code
import pygrib
import matplotlib.pyplot as plt
import matplotlib.colors as colors
from mpl_toolkits.basemap import Basemap
from mpl_toolkits.basemap import shiftgrid
import numpy as np
plt.figure(figsize=(12,8))
grib = 'cams_aod.grib' # Set the file name of your input GRIB file
grbs = pygrib.open(grib)
grb = grbs.select()[0]
data = grb.values
# need to shift data grid longitudes from (0..360) to (-180..180)
lons = np.linspace(float(grb['longitudeOfFirstGridPointInDegrees']), \
float(grb['longitudeOfLastGridPointInDegrees']), int(grb['Ni']) )
lats = np.linspace(float(grb['latitudeOfFirstGridPointInDegrees']), \
float(grb['latitudeOfLastGridPointInDegrees']), int(grb['Nj']) )
data, lons = shiftgrid(180., data, lons, start=False)
grid_lon, grid_lat = np.meshgrid(lons, lats) #regularly spaced 2D grid
m = Basemap(projection='cyl', llcrnrlon=-180, \
urcrnrlon=180.,llcrnrlat=lats.min(),urcrnrlat=lats.max(), \
resolution='c')
x, y = m(grid_lon, grid_lat)
cs = m.pcolormesh(x,y,data,shading='flat',cmap=plt.cm.gist_stern_r)
m.drawcoastlines()
m.drawmapboundary()
m.drawparallels(np.arange(-90.,120.,30.),labels=[1,0,0,0])
m.drawmeridians(np.arange(-180.,180.,60.),labels=[0,0,0,1])
plt.colorbar(cs,orientation='vertical', shrink=0.5)
plt.title('CAMS AOD forecast') # Set the name of the variable to plot
plt.savefig(grib+'.png') # Set the output file name
Notes
Changing the grid resolution
Before plotting the field you can use the cdo software to conservatively regrid the data, for example from 0.1˘x0.1˘ to 0.5˘x0.5˘ regular latitude-longitude grid:
cdo -s gencon,grid.R720x360.txt frp_01.grb remapweights.rencon.R3600x1800.to.R720x360.grb cdo -s remap,grid.R720x360.txt,remapweights.rencon.R3600x1800.to.R720x360.grb frp_01.grb frp_05.grb
The content of grid definition file (grid.R720x360.txt) is:
# # gridID 2 # gridtype = lonlat gridsize = 259200 xname = lon xlongname = longitude xunits = degrees_east yname = lat ylongname = latitude yunits = degrees_north xsize = 720 ysize = 360 xfirst = 0.25 xinc = 0.5 yfirst = 89.75 yinc = -0.5
