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GRIB Data Example¶
GRIB format is commonly used to disemminate atmospheric model data. With Xarray and the cfgrib engine, GRIB data can easily be analyzed and visualized.
[1]:
import xarray as xr
import matplotlib.pyplot as plt
To read GRIB data, you can use xarray.load_dataset
. The only extra code you need is to specify the engine as cfgrib
.
[2]:
ds = xr.tutorial.load_dataset('era5-2mt-2019-03-uk.grib', engine='cfgrib')
---------------------------------------------------------------------------
FileNotFoundError Traceback (most recent call last)
<ipython-input-2-783584127f97> in <module>
----> 1 ds = xr.tutorial.load_dataset('era5-2mt-2019-03-uk.grib', engine='cfgrib')
/build/python-xarray-kTVyut/python-xarray-0.15.0/xarray/tutorial.py in load_dataset(*args, **kwargs)
111 open_dataset
112 """
--> 113 with open_dataset(*args, **kwargs) as ds:
114 return ds.load()
115
/build/python-xarray-kTVyut/python-xarray-0.15.0/xarray/tutorial.py in open_dataset(name, cache, cache_dir, github_url, branch, **kws)
76 # May want to add an option to remove it.
77 if not _os.path.isdir(longdir):
---> 78 _os.mkdir(longdir)
79
80 url = "/".join((github_url, "raw", branch, fullname))
FileNotFoundError: [Errno 2] No such file or directory: '/sbuild-nonexistent/.xarray_tutorial_data'
Let’s create a simple plot of 2-m air temperature in degrees Celsius:
[3]:
ds = ds - 273.15
ds.t2m[0].plot(cmap=plt.cm.coolwarm)
---------------------------------------------------------------------------
NameError Traceback (most recent call last)
<ipython-input-3-1c96aded89da> in <module>
----> 1 ds = ds - 273.15
2 ds.t2m[0].plot(cmap=plt.cm.coolwarm)
NameError: name 'ds' is not defined
With CartoPy, we can create a more detailed plot, using built-in shapefiles to help provide geographic context:
[4]:
import cartopy.crs as ccrs
import cartopy
fig = plt.figure(figsize=(10,10))
ax = plt.axes(projection=ccrs.Robinson())
ax.coastlines(resolution='10m')
plot = ds.t2m[0].plot(cmap=plt.cm.coolwarm, transform=ccrs.PlateCarree(), cbar_kwargs={'shrink':0.6})
plt.title('ERA5 - 2m temperature British Isles March 2019')
---------------------------------------------------------------------------
NameError Traceback (most recent call last)
<ipython-input-4-246f01288f90> in <module>
4 ax = plt.axes(projection=ccrs.Robinson())
5 ax.coastlines(resolution='10m')
----> 6 plot = ds.t2m[0].plot(cmap=plt.cm.coolwarm, transform=ccrs.PlateCarree(), cbar_kwargs={'shrink':0.6})
7 plt.title('ERA5 - 2m temperature British Isles March 2019')
NameError: name 'ds' is not defined
---------------------------------------------------------------------------
PermissionError Traceback (most recent call last)
/usr/lib/python3/dist-packages/IPython/core/formatters.py in __call__(self, obj)
339 pass
340 else:
--> 341 return printer(obj)
342 # Finally look for special method names
343 method = get_real_method(obj, self.print_method)
/usr/lib/python3/dist-packages/IPython/core/pylabtools.py in <lambda>(fig)
246
247 if 'png' in formats:
--> 248 png_formatter.for_type(Figure, lambda fig: print_figure(fig, 'png', **kwargs))
249 if 'retina' in formats or 'png2x' in formats:
250 png_formatter.for_type(Figure, lambda fig: retina_figure(fig, **kwargs))
/usr/lib/python3/dist-packages/IPython/core/pylabtools.py in print_figure(fig, fmt, bbox_inches, **kwargs)
130 FigureCanvasBase(fig)
131
--> 132 fig.canvas.print_figure(bytes_io, **kw)
133 data = bytes_io.getvalue()
134 if fmt == 'svg':
/usr/lib/python3/dist-packages/matplotlib/backend_bases.py in print_figure(self, filename, dpi, facecolor, edgecolor, orientation, format, bbox_inches, **kwargs)
2054 # The first save command (to a BytesIO) is just to estimate
2055 # the bounding box of the figure.
-> 2056 result = print_method(
2057 io.BytesIO(),
2058 dpi=dpi,
/usr/lib/python3/dist-packages/matplotlib/backends/backend_agg.py in print_png(self, filename_or_obj, metadata, pil_kwargs, *args, **kwargs)
525
526 else:
--> 527 FigureCanvasAgg.draw(self)
528 renderer = self.get_renderer()
529 with cbook._setattr_cm(renderer, dpi=self.figure.dpi), \
/usr/lib/python3/dist-packages/matplotlib/backends/backend_agg.py in draw(self)
386 self.renderer = self.get_renderer(cleared=True)
387 with RendererAgg.lock:
--> 388 self.figure.draw(self.renderer)
389 # A GUI class may be need to update a window using this draw, so
390 # don't forget to call the superclass.
/usr/lib/python3/dist-packages/matplotlib/artist.py in draw_wrapper(artist, renderer, *args, **kwargs)
36 renderer.start_filter()
37
---> 38 return draw(artist, renderer, *args, **kwargs)
39 finally:
40 if artist.get_agg_filter() is not None:
/usr/lib/python3/dist-packages/matplotlib/figure.py in draw(self, renderer)
1706
1707 self.patch.draw(renderer)
-> 1708 mimage._draw_list_compositing_images(
1709 renderer, self, artists, self.suppressComposite)
1710
/usr/lib/python3/dist-packages/matplotlib/image.py in _draw_list_compositing_images(renderer, parent, artists, suppress_composite)
133 if not_composite or not has_images:
134 for a in artists:
--> 135 a.draw(renderer)
136 else:
137 # Composite any adjacent images together
/usr/lib/python3/dist-packages/matplotlib/artist.py in draw_wrapper(artist, renderer, *args, **kwargs)
36 renderer.start_filter()
37
---> 38 return draw(artist, renderer, *args, **kwargs)
39 finally:
40 if artist.get_agg_filter() is not None:
/usr/lib/python3/dist-packages/cartopy/mpl/geoaxes.py in draw(self, renderer, inframe)
385 self._done_img_factory = True
386
--> 387 return matplotlib.axes.Axes.draw(self, renderer=renderer,
388 inframe=inframe)
389
/usr/lib/python3/dist-packages/matplotlib/artist.py in draw_wrapper(artist, renderer, *args, **kwargs)
36 renderer.start_filter()
37
---> 38 return draw(artist, renderer, *args, **kwargs)
39 finally:
40 if artist.get_agg_filter() is not None:
/usr/lib/python3/dist-packages/matplotlib/axes/_base.py in draw(self, renderer, inframe)
2645 renderer.stop_rasterizing()
2646
-> 2647 mimage._draw_list_compositing_images(renderer, self, artists)
2648
2649 renderer.close_group('axes')
/usr/lib/python3/dist-packages/matplotlib/image.py in _draw_list_compositing_images(renderer, parent, artists, suppress_composite)
133 if not_composite or not has_images:
134 for a in artists:
--> 135 a.draw(renderer)
136 else:
137 # Composite any adjacent images together
/usr/lib/python3/dist-packages/matplotlib/artist.py in draw_wrapper(artist, renderer, *args, **kwargs)
36 renderer.start_filter()
37
---> 38 return draw(artist, renderer, *args, **kwargs)
39 finally:
40 if artist.get_agg_filter() is not None:
/usr/lib/python3/dist-packages/cartopy/mpl/feature_artist.py in draw(self, renderer, *args, **kwargs)
162 except ValueError:
163 warnings.warn('Unable to determine extent. Defaulting to global.')
--> 164 geoms = self._feature.intersecting_geometries(extent)
165
166 # Combine all the keyword args in priority order.
/usr/lib/python3/dist-packages/cartopy/feature/__init__.py in intersecting_geometries(self, extent)
301 """
302 self.scaler.scale_from_extent(extent)
--> 303 return super(NaturalEarthFeature, self).intersecting_geometries(extent)
304
305 def with_scale(self, new_scale):
/usr/lib/python3/dist-packages/cartopy/feature/__init__.py in intersecting_geometries(self, extent)
118 extent_geom = sgeom.box(extent[0], extent[2],
119 extent[1], extent[3])
--> 120 return (geom for geom in self.geometries() if
121 geom is not None and extent_geom.intersects(geom))
122 else:
/usr/lib/python3/dist-packages/cartopy/feature/__init__.py in geometries(self)
283 key = (self.name, self.category, self.scale)
284 if key not in _NATURAL_EARTH_GEOM_CACHE:
--> 285 path = shapereader.natural_earth(resolution=self.scale,
286 category=self.category,
287 name=self.name)
/usr/lib/python3/dist-packages/cartopy/io/shapereader.py in natural_earth(resolution, category, name)
357 format_dict = {'config': config, 'category': category,
358 'name': name, 'resolution': resolution}
--> 359 return ne_downloader.path(format_dict)
360
361
/usr/lib/python3/dist-packages/cartopy/io/__init__.py in path(self, format_dict)
220 else:
221 # we need to download the file
--> 222 result_path = self.acquire_resource(target_path, format_dict)
223
224 return result_path
/usr/lib/python3/dist-packages/cartopy/io/shapereader.py in acquire_resource(self, target_path, format_dict)
408 target_dir = os.path.dirname(target_path)
409 if not os.path.isdir(target_dir):
--> 410 os.makedirs(target_dir)
411
412 url = self.url(format_dict)
/usr/lib/python3.8/os.py in makedirs(name, mode, exist_ok)
211 if head and tail and not path.exists(head):
212 try:
--> 213 makedirs(head, exist_ok=exist_ok)
214 except FileExistsError:
215 # Defeats race condition when another thread created the path
/usr/lib/python3.8/os.py in makedirs(name, mode, exist_ok)
211 if head and tail and not path.exists(head):
212 try:
--> 213 makedirs(head, exist_ok=exist_ok)
214 except FileExistsError:
215 # Defeats race condition when another thread created the path
/usr/lib/python3.8/os.py in makedirs(name, mode, exist_ok)
211 if head and tail and not path.exists(head):
212 try:
--> 213 makedirs(head, exist_ok=exist_ok)
214 except FileExistsError:
215 # Defeats race condition when another thread created the path
/usr/lib/python3.8/os.py in makedirs(name, mode, exist_ok)
211 if head and tail and not path.exists(head):
212 try:
--> 213 makedirs(head, exist_ok=exist_ok)
214 except FileExistsError:
215 # Defeats race condition when another thread created the path
/usr/lib/python3.8/os.py in makedirs(name, mode, exist_ok)
211 if head and tail and not path.exists(head):
212 try:
--> 213 makedirs(head, exist_ok=exist_ok)
214 except FileExistsError:
215 # Defeats race condition when another thread created the path
/usr/lib/python3.8/os.py in makedirs(name, mode, exist_ok)
211 if head and tail and not path.exists(head):
212 try:
--> 213 makedirs(head, exist_ok=exist_ok)
214 except FileExistsError:
215 # Defeats race condition when another thread created the path
/usr/lib/python3.8/os.py in makedirs(name, mode, exist_ok)
221 return
222 try:
--> 223 mkdir(name, mode)
224 except OSError:
225 # Cannot rely on checking for EEXIST, since the operating system
PermissionError: [Errno 13] Permission denied: '/sbuild-nonexistent'
<Figure size 720x720 with 1 Axes>
Finally, we can also pull out a time series for a given location easily:
[5]:
ds.t2m.sel(longitude=0,latitude=51.5).plot()
plt.title('ERA5 - London 2m temperature March 2019')
---------------------------------------------------------------------------
NameError Traceback (most recent call last)
<ipython-input-5-d6577a89d149> in <module>
----> 1 ds.t2m.sel(longitude=0,latitude=51.5).plot()
2 plt.title('ERA5 - London 2m temperature March 2019')
NameError: name 'ds' is not defined