How To Use — wrf-python 1.3.4.1 documentation

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Introduction ¶

The API for wrf-python can be summarized as a variable computation/extraction routine, several interpolation routines, and a few plotting helper utilities. The API is kept as simple as possible to help minimize the learning curve for new programmers, students, and scientists. In the future, we plan to extend xarray for programmers desiring a more object oriented API, but this remains a work in progress.
The five most commonly used routines can be summarized as:
wrf.getvar() - Extracts WRF-ARW NetCDF variables and computes diagnostic variables that WRF does not compute (e.g. storm relative helicity). This is the routine that you will use most often.
wrf.interplevel() - Interpolates a three-dimensional field to a horizontal plane at a specified level using simple (fast) linear interpolation (e.g. 850 hPa temperature).
wrf.vertcross() - Interpolates a three-dimensional field to a vertical plane through a user-specified horizontal line (i.e. a cross section).
wrf.interpline() - Interpolates a two-dimensional field to a user-specified line.
wrf.vinterp() - Interpolates a three-dimensional field to user-specified ‘surface’ levels (e.g. theta-e levels). This is a smarter, albeit slower, version of wrf.interplevel() .
Basic Usage ¶

Computing Diagnostic Variables ¶

The primary use for the wrf.getvar() function is to return diagnostic variables that require a calculation, since WRF does not produce these variables natively. These diagnostics include CAPE, storm relative helicity, omega, sea level pressure, etc. A table of all available diagnostics can be found here: Table of Available Diagnostics .
In the example below, sea level pressure is calculated and printed.
from __future__ import print_function
from netCDF4 import Dataset
from wrf import getvar
ncfile = Dataset("wrfout_d01_2016-10-07_00_00_00")
# Get the Sea Level Pressure
slp = getvar(ncfile, "slp")
print(slp)
Result:
<xarray.DataArray u'slp' (south_north: 1059, west_east: 1799)>
array([[ 1012.220337,  1012.298157,  1012.247864, ...,  1010.132019,
         1009.932312,  1010.067078],
       [ 1012.432861,  1012.444763,  1012.33667 , ...,  1010.1073  ,
         1010.108459,  1010.047607],
       [ 1012.395447,  1012.380859,  1012.417053, ...,  1010.22937 ,
         1010.055969,  1010.026794],
       [ 1009.042358,  1009.069214,  1008.987793, ...,  1019.19281 ,
         1019.144348,  1019.110596],
       [ 1009.224854,  1009.075134,  1008.986389, ...,  1019.071899,
         1019.042664,  1019.061279],
       [ 1009.188965,  1009.107117,  1008.979797, ...,  1018.917786,
         1018.956848,  1019.047485]], dtype=float32)
Coordinates:
    XLONG    (south_north, west_east) float32 -122.72 -122.693 -122.666 ...
    XLAT     (south_north, west_east) float32 21.1381 21.1451 21.1521 ...
    Time     datetime64[ns] 2016-10-07
Dimensions without coordinates: south_north, west_east
Attributes:
    FieldType: 104
    MemoryOrder: XY
    description: sea level pressure
    units: hPa
    stagger:
    coordinates: XLONG XLAT
    projection: LambertConformal(stand_lon=-97.5, moad_cen_lat=38.5000038147,
                                 truelat1=38.5, truelat2=38.5, pole_lat=90.0,
                                 pole_lon=0.0)
Extracting WRF NetCDF Variables¶
In addition to computing diagnostic variables (see Computing Diagnostic Variables),
the wrf.getvar() function can be used to extract regular WRF-ARW output
NetCDF variables.
from __future__ import print_function
from netCDF4 import Dataset
from wrf import getvar
ncfile = Dataset("wrfout_d01_2016-10-07_00_00_00")
p = getvar(ncfile, "P")
print(p)
Result:




    

<xarray.DataArray u'P' (bottom_top: 50, south_north: 1059, west_east: 1799)>
array([[[  1.217539e+03,   1.225320e+03, ...,   9.876406e+02,   1.001117e+03],
        [  1.238773e+03,   1.240047e+03, ...,   1.005297e+03,   9.991719e+02],
        [  9.208594e+02,   9.059141e+02, ...,   1.902922e+03,   1.904805e+03],
        [  9.172734e+02,   9.091094e+02, ...,   1.894375e+03,   1.903422e+03]],
       [[  1.219562e+03,   1.210273e+03, ...,   9.973984e+02,   9.907891e+02],
        [  1.224578e+03,   1.223508e+03, ...,   9.985547e+02,   9.921172e+02],
        [  9.012734e+02,   9.052031e+02, ...,   1.897766e+03,   1.894500e+03],
        [  9.137500e+02,   9.071719e+02, ...,   1.893273e+03,   1.893664e+03]],
       [[  7.233154e+00,   7.224121e+00, ...,   3.627930e+00,   3.613770e+00],
        [  7.226318e+00,   7.358154e+00, ...,   3.725098e+00,   3.634033e+00],
        [  5.354248e+00,   5.406006e+00, ...,   1.282715e+01,   1.264844e+01],
        [  5.295410e+00,   5.177490e+00, ...,   1.256274e+01,   1.257642e+01]],
       [[  2.362061e+00,   2.376221e+00, ...,   1.151367e+00,   1.156982e+00],
        [  2.342529e+00,   2.403809e+00, ...,   1.198486e+00,   1.155273e+00],
        [  1.732910e+00,   1.768799e+00, ...,   4.247070e+00,   4.135498e+00],
        [  1.715332e+00,   1.657227e+00, ...,   4.036377e+00,   4.047852e+00]]], dtype=float32)
Coordinates:
    XLONG    (south_north, west_east) float32 -122.72 -122.693 -122.666 ...
    XLAT     (south_north, west_east) float32 21.1381 21.1451 21.1521 ...
    Time     datetime64[ns] 2016-10-07
Dimensions without coordinates: bottom_top, south_north, west_east
Attributes:
    FieldType: 104
    MemoryOrder: XYZ
    description: perturbation pressure
    units: Pa
    stagger:
    coordinates: XLONG XLAT
    projection: LambertConformal(stand_lon=-97.5, moad_cen_lat=38.5000038147,
                                 truelat1=38.5, truelat2=38.5, pole_lat=90.0,
                                 pole_lon=0.0)
Disabling xarray and metadata¶
Sometimes you just want a regular numpy array and don’t care about metadata.
This is often the case when you are working with compiled extensions.  Metadata
can be disabled in one of two ways.
disable xarray completely
set the meta function parameter to False.
The example below illustrates both.
from __future__ import print_function
from netCDF4 import Dataset
from wrf import getvar, disable_xarray
ncfile = Dataset("wrfout_d01_2016-10-07_00_00_00")
# Disable xarray completely
disable_xarray()
p_no_meta = getvar(ncfile, "P")
print (type(p_no_meta))
enable_xarray()
# Disable by using the meta parameter
p_no_meta = getvar(ncfile, "P", meta=False)
print (type(p_no_meta))
Result:
<type 'numpy.ndarray'>
<type 'numpy.ndarray'>
Extracting a Numpy Array from a DataArray¶
If you need to convert an xarray.DataArray to a numpy.ndarray,
wrf-python provides the wrf.to_np() function for this purpose. Although
an xarray.DataArary object already contains the
xarray.DataArray.values attribute to extract the Numpy array, there is a
problem when working with compiled extensions. The behavior for xarray (and pandas)
is to convert missing/fill values to NaN, which may cause crashes when working
with compiled extensions.  Also, some existing code may be designed to work with
numpy.ma.MaskedArray, and numpy arrays with NaN may not work with it.
The wrf.to_np() function does the following:
If no missing/fill values are used, wrf.to_np() simply returns the
xarray.DataArray.values attribute.
If missing/fill values are used, then wrf.to_np() replaces the NaN
values with the _FillValue found in the xarray.DataArray.attrs
attribute (required) and a numpy.ma.MaskedArray is returned.
from __future__ import print_function
from netCDF4 import Dataset
from wrf import getvar
ncfile = Dataset("wrfout_d01_2016-10-07_00_00_00")
# Get the 3D CAPE, which contains missing values
cape_3d = getvar(ncfile, "cape_3d")
# Since there are missing values, this should return a MaskedArray
cape_3d_ndarray = to_np(cape_3d)
print(type(cape_3d_ndarray))
Result:
<class 'numpy.ma.core.MaskedArray'>
Combining Multiple Files Using the ‘cat’ Method¶
The ‘cat’ (concatenate) method aggregates all files in the sequence along the
‘Time’ dimension, which will be the leftmost dimension for the output array.
To include all of the times, in all of the files, in the output array, set the
timeidx parameter to wrf.ALL_TIMES (an alias for None).  If a single
value is specified for timeidx, then the time index is assumed to be taken from
the concatenation of all times for all files.
It is import to note that no sorting is performed in the wrf.getvar()
routine, so all files in the sequence must be sorted prior to calling this
function.
from __future__ import print_function
from netCDF4 import Dataset
from wrf import getvar, ALL_TIMES
# Creating a simple test list with three timesteps
wrflist = [Dataset("wrfout_d01_2016-10-07_00_00_00"),
           Dataset("wrfout_d01_2016-10-07_01_00_00"),
           Dataset("wrfout_d01_2016-10-07_02_00_00")]
# Extract the 'P' variable for all times
p_cat = getvar(wrflist, "P", timeidx=ALL_TIMES, method="cat")
print(p_cat)
Result:
<xarray.DataArray u'P' (Time: 3, bottom_top: 50, south_north: 1059, west_east: 1799)>
array([[[[  1.21753906e+03,   1.22532031e+03,   1.22030469e+03, ...,
        1.00760156e+03,   9.87640625e+02,   1.00111719e+03],
     [  1.23877344e+03,   1.24004688e+03,   1.22926562e+03, ...,
        1.00519531e+03,   1.00529688e+03,   9.99171875e+02],
     [  1.23503906e+03,   1.23367188e+03,   1.23731250e+03, ...,
        1.01739844e+03,   1.00005469e+03,   9.97093750e+02],
     [  1.77978516e+00,   1.77050781e+00,   1.79003906e+00, ...,
        4.22949219e+00,   4.25659180e+00,   4.13647461e+00],
     [  1.73291016e+00,   1.76879883e+00,   1.77978516e+00, ...,
        4.24047852e+00,   4.24707031e+00,   4.13549805e+00],
     [  1.71533203e+00,   1.65722656e+00,   1.67480469e+00, ...,
        4.06884766e+00,   4.03637695e+00,   4.04785156e+00]]]], dtype=float32)
Coordinates:
    XLONG        (south_north, west_east) float32 -122.72 -122.693 -122.666 ...
    XLAT         (south_north, west_east) float32 21.1381 21.1451 21.1521 ...
  * Time         (Time) datetime64[ns] 2016-10-07 2016-10-07 2016-10-07
    datetime     (Time) datetime64[ns] 2016-10-07T00:00:00 ...
Dimensions without coordinates: bottom_top, south_north, west_east
Attributes:
    FieldType: 104
    MemoryOrder: XYZ
    description: perturbation pressure
    units: Pa
    stagger:
    coordinates: XLONG XLAT
    projection: LambertConformal(stand_lon=-97.5, moad_cen_lat=38.5000038147,
                                 truelat1=38.5, truelat2=38.5, pole_lat=90.0,
                                 pole_lon=0.0)
Combining Multiple Files Using the ‘join’ Method¶
The ‘join’ method combines a sequence of files by adding a new leftmost
dimension for the file/sequence index. In situations where there are multiple
files with multiple times, and the last file contains less times than the
previous files, the remaining arrays will be arrays filled with missing values.
There are checks in place within the wrf-python algorithms to look for these missing
arrays, but be careful when calling compiled routines outside of wrf-python.
In most cases, timeidx parameter should be set to wrf.ALL_TIMES.  If
a timeidx value is specified, then this time index is used when extracting the
variable from each file.  In cases where there are multiple files with multiple
time steps, this is probably nonsensical, since the nth time index for each
file represents a different time.
In general, join is rarely used, so the concatenate method should be used
for most cases.
from __future__ import print_function
from netCDF4 import Dataset
from wrf import getvar, ALL_TIMES
# Creating a simple test list with three timesteps
wrflist = [Dataset("wrfout_d01_2016-10-07_00_00_00"),
           Dataset("wrfout_d01_2016-10-07_01_00_00"),
           Dataset("wrfout_d01_2016-10-07_02_00_00")]
# Extract the 'P' variable for all times
p_join = getvar(wrflist, "P", timeidx=ALL_TIMES, method="join")
print(p_join)
Result:
<xarray.DataArray u'P' (file: 3, bottom_top: 50, south_north: 1059, west_east: 1799)>
array([[[[  1.217539e+03, ...,   1.001117e+03],
         [  9.172734e+02, ...,   1.903422e+03]],
        [[  2.362061e+00, ...,   1.156982e+00],
         [  1.715332e+00, ...,   4.047852e+00]]]], dtype=float32)
Coordinates:
    XLONG     (south_north, west_east) float32 -122.72 -122.693 -122.666 ...
    XLAT      (south_north, west_east) float32 21.1381 21.1451 21.1521 ...
  * file      (file) int64 0 1 2
    datetime  (file) datetime64[ns] 2016-10-07 ...
Dimensions without coordinates: bottom_top, south_north, west_east
Attributes:
    FieldType: 104
    MemoryOrder: XYZ
    description: perturbation pressure
    units: Pa
    stagger:
    coordinates: XLONG XLAT
    projection: LambertConformal(stand_lon=-97.5, moad_cen_lat=38.5000038147,
                                 truelat1=38.5, truelat2=38.5, pole_lat=90.0,
                                 pole_lon=0.0)
Note how the ‘Time’ dimension was replaced with the ‘file’ dimension, due to
numpy’s automatic squeezing of the single element ‘Time’ dimension. To maintain
the ‘Time’ dimension, set the squeeze parameter to False.
from __future__ import print_function
from netCDF4 import Dataset
from wrf import getvar, ALL_TIMES
# Creating a simple test list with three timesteps
wrflist = [Dataset("wrfout_d01_2016-10-07_00_00_00"),
           Dataset("wrfout_d01_2016-10-07_01_00_00"),
           Dataset("wrfout_d01_2016-10-07_02_00_00")]
# Extract the 'P' variable for all times
p_join = getvar(wrflist, "P", timeidx=ALL_TIMES, method="join", squeeze=False)
print(p_join)
Result




    

<xarray.DataArray u'P' (file: 3, Time: 1, bottom_top: 50, south_north: 1059, west_east: 1799)>
array([[[[[  1.217539e+03, ...,   1.001117e+03],
      [  9.172734e+02, ...,   1.903422e+03]],
     [[  2.362061e+00, ...,   1.156982e+00],
      [  1.715332e+00, ...,   4.047852e+00]]]]], dtype=float32)
Coordinates:
    XLONG     (south_north, west_east) float32 -122.72 -122.693 -122.666 ...
    XLAT      (south_north, west_east) float32 21.1381 21.1451 21.1521 ...
  * file      (file) int64 0 1 2
    datetime  (file, Time) datetime64[ns] 2016-10-07 2016-10-07 2016-10-07
Dimensions without coordinates: Time, bottom_top, south_north, west_east
Attributes:
    FieldType: 104
    MemoryOrder: XYZ
    description: perturbation pressure
    units: Pa
    stagger:
    coordinates: XLONG XLAT
    projection: LambertConformal(stand_lon=-97.5, moad_cen_lat=38.5000038147,
                                 truelat1=38.5, truelat2=38.5, pole_lat=90.0,
                                 pole_lon=0.0)
Dictionaries of WRF File Sequences¶
Dictionaries can also be used as input to the wrf.getvar() functions.
This can be useful when working with ensembles.  However, all WRF files in the
dictionary must have the same dimensions.  The result is an array where the
leftmost dimension is the keys from the dictionary.  Nested dictionaries
are allowed.
The method argument is used to describe how each sequence in the dictionary
will be combined.
from __future__ import print_function
from netCDF4 import Dataset
from wrf import getvar, ALL_TIMES
wrf_dict = {"ens1" : [Dataset("ens1/wrfout_d01_2016-10-07_00_00_00"),
                      Dataset("ens1/wrfout_d01_2016-10-07_01_00_00"),
                      Dataset("ens1/wrfout_d01_2016-10-07_02_00_00")],
            "ens2" : [Dataset("ens2/wrfout_d01_2016-10-07_00_00_00"),
                      Dataset("ens2/wrfout_d01_2016-10-07_01_00_00"),
                      Dataset("ens2/wrfout_d01_2016-10-07_02_00_00")]
p = getvar(wrf_dict, "P", timeidx=ALL_TIMES)
print(p)
Result:
<xarray.DataArray 'P' (key_0: 2, Time: 2, bottom_top: 50, south_north: 1059, west_east: 1799)>
array([[[[[  1.217539e+03, ...,   1.001117e+03],
          [  9.172734e+02, ...,   1.903422e+03]],
         [[  2.362061e+00, ...,   1.156982e+00],
          [  1.715332e+00, ...,   4.047852e+00]]]]], dtype=float32)
Coordinates:
    XLONG     (south_north, west_east) float32 -122.72 -122.693 -122.666 ...
    XLAT      (south_north, west_east) float32 21.1381 21.1451 21.1521 ...
  * Time      (Time) datetime64[ns] 2016-10-07 ...
    datetime  (Time) datetime64[ns] 2016-10-07 ...
  * key_0     (key_0) <U6 u'label1' u'label2'
Dimensions without coordinates: bottom_top, south_north, west_east
Attributes:
    FieldType: 104
    MemoryOrder: XYZ
    description: perturbation pressure
    units: Pa
    stagger:
    coordinates: XLONG XLAT
    projection: LambertConformal(stand_lon=-97.5, moad_cen_lat=38.5000038147,
                                 truelat1=38.5, truelat2=38.5, pole_lat=90.0,
                                 pole_lon=0.0)
Interpolating to a Horizontal Level¶
The wrf.interplevel() function is used to interpolate a 3D field to
a specific horizontal level, usually pressure or height.
from __future__ import print_function
from netCDF4 import Dataset
from wrf import getvar, interplevel
ncfile = Dataset("wrfout_d01_2016-10-07_00_00_00")
# Extract the Geopotential Height and Pressure (hPa) fields
z = getvar(ncfile, "z")
p = getvar(ncfile, "pressure")
# Compute the 500 MB Geopotential Height
ht_500mb = interplevel(z, p, 500.)
print(ht_500mb)
Result:
<xarray.DataArray u'height_500_hPa' (south_north: 1059, west_east: 1799)>
array([[ 5882.16992188,  5881.87939453,  5881.81005859, ...,
     5890.14501953,  5890.23583984,  5890.33349609],
   [ 5882.71777344,  5882.17529297,  5882.1171875 , ...,
     5890.37695312,  5890.38525391,  5890.27978516],
   [ 5883.32177734,  5882.47119141,  5882.34130859, ...,
     5890.48339844,  5890.42871094,  5890.17724609],
   [ 5581.45800781,  5580.46826172,  5579.32617188, ...,
     5788.93554688,  5788.70507812,  5788.64453125],
   [ 5580.32714844,  5579.51611328,  5578.34863281, ...,
     5788.15869141,  5787.87304688,  5787.65527344],
   [ 5579.64404297,  5578.30957031,  5576.98632812, ...,
     5787.19384766,  5787.10888672,  5787.06933594]], dtype=float32)
Coordinates:
    XLONG        (south_north, west_east) float32 -122.72 -122.693 -122.666 ...
    XLAT         (south_north, west_east) float32 21.1381 21.1451 21.1521 ...
    Time         datetime64[ns] 2016-10-07
Dimensions without coordinates: south_north, west_east
Attributes:
    FieldType: 104
    units: m
    stagger:
    coordinates: XLONG XLAT
    projection: LambertConformal(stand_lon=-97.5, moad_cen_lat=38.5000038147,
                                 truelat1=38.5, truelat2=38.5, pole_lat=90.0,
                                 pole_lon=0.0)
    level: 500 hPa
    missing_value: 9.96920996839e+36
    _FillValue: 9.96920996839e+36
Vertical Cross Sections¶
The wrf.vertcross() function is used to create vertical cross sections.
To define a cross section, a start point and an end point needs to be specified.
Alternatively, a pivot point and an angle may be used.  The start point,
end point, and pivot point are specified using a wrf.CoordPair object,
and coordinates can either be in grid (x,y) coordinates or (latitude,longitude)
coordinates. When using (latitude,longitude) coordinates, a NetCDF file object or
a wrf.WrfProj object must be provided.
The vertical levels can also be specified using the levels parameter.  If
not specified, then approximately 100 levels will be chosen in 1% increments.
Example Using Start Point and End Point¶
from __future__ import print_function, division
from netCDF4 import Dataset
from wrf import getvar, vertcross, CoordPair
ncfile = Dataset("wrfout_d01_2016-10-07_00_00_00")
# Get the geopotential height (m) and pressure (hPa).
z = getvar(ncfile, "z")
p = getvar(ncfile, "pressure")
# Define a start point and end point in grid coordinates
start_point = CoordPair(x=0, y=(z.shape[-2]-1)//2)
end_point = CoordPair(x=-1, y=(z.shape[-2]-1)//2)
# Calculate the vertical cross section.  By setting latlon to True, this
# also calculates the latitude and longitude coordinates along the cross
# section line and adds them to the 'xy_loc' metadata to help with plotting.
p_vert = vertcross(p, z, start_point=start_point, end_point=end_point, latlon=True)
print(p_vert)
Result:
<xarray.DataArray u'pressure_cross' (vertical: 100, idx: 1798)>
array([[          nan,           nan,           nan, ...,           nan,
              nan,           nan],
   [ 989.66168213,  989.66802979,  989.66351318, ...,  988.05737305,
     987.99151611,  987.96917725],
   [ 959.49450684,  959.50109863,  959.50030518, ...,  958.96948242,
     958.92980957,  958.89294434],
   [  24.28092003,   24.27359581,   24.27034378, ...,   24.24800491,
      24.2486496 ,   24.24947357],
   [  23.2868309 ,   23.27933884,   23.27607918, ...,   23.25231361,
      23.2530098 ,   23.25384521],
   [          nan,           nan,           nan, ...,           nan,
              nan,           nan]], dtype=float32)
Coordinates:
    Time      datetime64[ns] 2016-10-07
    xy_loc    (idx) object CoordPair(x=0.0, y=529.0, lat=34.5279502869, lon=-127.398925781) ...
  * vertical  (vertical) float32 0.0 261.828 523.656 785.484 1047.31 1309.14 ...
Dimensions without coordinates: idx
Attributes:
    FieldType: 104
    description: pressure
    units: hPa
    stagger:
    coordinates: XLONG XLAT
    projection: LambertConformal(stand_lon=-97.5, moad_cen_lat=38.5000038147,
                                 truelat1=38.5, truelat2=38.5, pole_lat=90.0,
                                 pole_lon=0.0)
    orientation: (0.0, 529.0) to (1797.0, 529.0)
    missing_value: 9.96920996839e+36
    _FillValue: 9.96920996839e+36
Example Using Pivot Point and Angle¶
from __future__ import print_function, division
from netCDF4 import Dataset
from wrf import getvar, vertcross, CoordPair
ncfile = Dataset("wrfout_d01_2016-10-07_00_00_00")
# Get the geopotential height (m) and pressure (hPa).
z = getvar(ncfile, "z")
p = getvar(ncfile, "pressure")
# Define a pivot point and angle in grid coordinates, with the
# pivot point being the center of the grid.
pivot_point = CoordPair(x=(z.shape[-1]-1)//2, y=(z.shape[-2]-1)//2)
angle = 90.0
# Calculate the vertical cross section.  By setting latlon to True, this
# also calculates the latitude and longitude coordinates along the line
# and adds them to the metadata to help with plotting labels.
p_vert = vertcross(p, z, pivot_point=pivot_point, angle=angle, latlon=True)
print (p_vert)
Result:




    

<xarray.DataArray u'pressure_cross' (vertical: 100, idx: 1798)>
array([[          nan,           nan,           nan, ...,           nan,
              nan,           nan],
   [ 989.66168213,  989.66802979,  989.66351318, ...,  988.05737305,
     987.99151611,  987.96917725],
   [ 959.49450684,  959.50109863,  959.50030518, ...,  958.96948242,
     958.92980957,  958.89294434],
   [  24.28092003,   24.27359581,   24.27034378, ...,   24.24800491,
      24.2486496 ,   24.24947357],
   [  23.2868309 ,   23.27933884,   23.27607918, ...,   23.25231361,
      23.2530098 ,   23.25384521],
   [          nan,           nan,           nan, ...,           nan,
              nan,           nan]], dtype=float32)
Coordinates:
    Time      datetime64[ns] 2016-10-07
    xy_loc    (idx) object CoordPair(x=0.0, y=529.0, lat=34.5279502869, lon=-127.398925781) ...
  * vertical  (vertical) float32 0.0 261.828 523.656 785.484 1047.31 1309.14 ...
Dimensions without coordinates: idx
Attributes:
    FieldType: 104
    description: pressure
    units: hPa
    stagger:
    coordinates: XLONG XLAT
    projection: LambertConformal(stand_lon=-97.5, moad_cen_lat=38.5000038147,
                                 truelat1=38.5, truelat2=38.5, pole_lat=90.0,
                                 pole_lon=0.0)
    orientation: (0.0, 529.0) to (1797.0, 529.0) ; center=CoordPair(x=899.0, y=529.0) ; angle=90.0
    missing_value: 9.96920996839e+36
    _FillValue: 9.96920996839e+36
from wrf import getvar, vertcross, CoordPair
ncfile = Dataset("wrfout_d01_2016-10-07_00_00_00")
# Get the geopotential height (m) and pressure (hPa).
z = getvar(ncfile, "z")
p = getvar(ncfile, "pressure")
lats = getvar(ncfile, "lat")
lons = getvar(ncfile, "lon")
# Making the same horizontal line, but with lats/lons
start_lat = lats[(lats.shape[-2]-1)//2, 0]
end_lat = lats[(lats.shape[-2]-1)//2, -1]
start_lon = lons[(lats.shape[-2]-1)//2, 0]
end_lon = lons[(lats.shape[-2]-1)//2, -1]
# Cross section line using start_point and end_point.
start_point = CoordPair(lat=start_lat, lon=start_lon)
end_point = CoordPair(lat=end_lat, lon=end_lon)
# When using lat/lon coordinates, you must supply a WRF netcdf file object,
# or a projection object with the lower left latitude and lower left
# longitude points.
p_vert = vertcross(p, z, wrfin=ncfile, start_point=start_point, end_point=end_point, latlon=True)
print(p_vert)
Result:
<xarray.DataArray u'pressure_cross' (vertical: 100, idx: 1798)>
array([[          nan,           nan,           nan, ...,           nan,
              nan,           nan],
   [ 989.66168213,  989.66802979,  989.66351318, ...,  988.05737305,
     987.99151611,  987.96917725],
   [ 959.49450684,  959.50109863,  959.50030518, ...,  958.96948242,
     958.92980957,  958.89294434],
   [  24.28092003,   24.27359581,   24.27034378, ...,   24.24800491,
      24.2486496 ,   24.24947357],
   [  23.2868309 ,   23.27933884,   23.27607918, ...,   23.25231361,
      23.2530098 ,   23.25384521],
   [          nan,           nan,           nan, ...,           nan,
              nan,           nan]], dtype=float32)
Coordinates:
    Time      datetime64[ns] 2016-10-07
    xy_loc    (idx) object CoordPair(x=0.0, y=529.0, lat=34.5279502869, lon=-127.398925781) ...
  * vertical  (vertical) float32 0.0 261.828 523.656 785.484 1047.31 1309.14 ...
Dimensions without coordinates: idx
Attributes:
    FieldType: 104
    description: pressure
    units: hPa
    stagger:
    coordinates: XLONG XLAT
    projection: LambertConformal(stand_lon=-97.5, moad_cen_lat=38.5000038147,
                                 truelat1=38.5, truelat2=38.5, pole_lat=90.0,
                                 pole_lon=0.0)
    orientation: (0.0, 529.0) to (1797.0, 529.0)
    missing_value: 9.96920996839e+36
    _FillValue: 9.96920996839e+36
Example Using Specified Vertical Levels¶
from __future__ import print_function, division
from netCDF4 import Dataset
from wrf import getvar, vertcross, CoordPair
ncfile = Dataset("wrfout_d01_2016-10-07_00_00_00")
# Get the geopotential height (m) and pressure (hPa).
z = getvar(ncfile, "z")
p = getvar(ncfile, "pressure")
lats = getvar(ncfile, "lat")
lons = getvar(ncfile, "lon")
# Making the same horizontal line, but with lats/lons
start_lat = lats[(lats.shape[-2]-1)//2, 0]
end_lat = lats[(lats.shape[-2]-1)//2, -1]
start_lon = lons[(lats.shape[-2]-1)//2, 0]
end_lon = lons[(lats.shape[-2]-1)//2, -1]
# Pressure using start_point and end_point.  These were obtained using
start_point = CoordPair(lat=start_lat, lon=start_lon)
end_point = CoordPair(lat=end_lat, lon=end_lon)
# Specify vertical levels
levels = [1000., 2000., 3000.]
# Calculate the cross section
p_vert = vertcross(p, z, wrfin=ncfile, levels=levels, start_point=start_point, end_point=end_point, latlon=True)
print(p_vert)
Result:
<xarray.DataArray u'pressure_cross' (vertical: 3, idx: 1798)>
array([[ 906.375     ,  906.38043213,  906.39367676, ...,  907.6661377 ,
         907.63006592,  907.59191895],
       [ 804.24737549,  804.26885986,  804.28076172, ...,  806.98632812,
         806.95556641,  806.92608643],
       [ 713.24578857,  713.2722168 ,  713.27886963, ...,  716.09594727,
         716.06610107,  716.03503418]], dtype=float32)
Coordinates:
    Time      datetime64[ns] 2016-10-07
    xy_loc    (idx) object CoordPair(x=0.0, y=529.0, lat=34.5279502869, lon=-127.398925781) ...
  * vertical  (vertical) float32 1000.0 2000.0 3000.0
Dimensions without coordinates: idx
Attributes:
    FieldType: 104
    description: pressure
    units: hPa
    stagger:
    coordinates: XLONG XLAT
    projection: LambertConformal(stand_lon=-97.5, moad_cen_lat=38.5000038147,
                                 truelat1=38.5, truelat2=38.5, pole_lat=90.0,
                                 pole_lon=0.0)
    orientation: (0.0, 529.0) to (1797.0, 529.0)
    missing_value: 9.96920996839e+36
    _FillValue: 9.96920996839e+36
Interpolating Two-Dimensional Fields to a Line¶
Two-dimensional fields can be interpolated along a line, in a manner similar to
the vertical cross section (see Vertical Cross Sections), using the
wrf.interpline() function. To define the line
to interpolate along, a start point and an end point needs to be specified.
Alternatively, a pivot point and an angle may be used.  The start point,
end point, and pivot point are specified using a wrf.CoordPair object,
and coordinates can either be in grid (x,y) coordinates or (latitude,longitude)
coordinates.  When using (latitude,longitude) coordinates, a NetCDF file object or
a wrf.WrfProj object must also be provided.
Example Using Start Point and End Point¶
from __future__ import print_function, division
from netCDF4 import Dataset
from wrf import getvar, interpline, CoordPair
ncfile = Dataset("wrfout_d01_2016-10-07_00_00_00")
# Get the 2m temperature
t2 = getvar(ncfile, "T2")
# Create a south-north line in the center of the domain using
# start point and end point
start_point = CoordPair(x=(t2.shape[-1]-1)//2, y=0)
end_point = CoordPair(x=(t2.shape[-1]-1)//2, y=-1)
# Calculate the vertical cross section.  By setting latlon to True, this
# also calculates the latitude and longitude coordinates along the line
# and adds them to the metadata to help with plotting labels.
t2_line = interpline(t2, start_point=start_point, end_point=end_point, latlon=True)
print(t2_line, "\n")
Result:




    

<xarray.DataArray u'T2_line' (line_idx: 1058)>
array([ 302.07214355,  302.08505249,  302.08688354, ...,  279.18557739,
        279.1998291 ,  279.23132324], dtype=float32)
Coordinates:
    Time      datetime64[ns] 2016-10-07
    xy_loc    (line_idx) object CoordPair(x=899.0, y=0.0, lat=24.3645858765, lon=-97.5) ...
Dimensions without coordinates: line_idx
Attributes:
    FieldType: 104
    description: TEMP at 2 M
    units: K
    stagger:
    coordinates: XLONG XLAT
    projection: LambertConformal(stand_lon=-97.5, moad_cen_lat=38.5000038147,
                                 truelat1=38.5, truelat2=38.5, pole_lat=90.0,
                                 pole_lon=0.0)
    orientation: (899.0, 0.0) to (899.0, 1057.0)
Example Using Pivot Point and Angle¶
from __future__ import print_function, division
from netCDF4 import Dataset
from wrf import getvar, interpline, CoordPair
ncfile = Dataset("wrfout_d01_2016-10-07_00_00_00")
# Get the 2m temperature
t2 = getvar(ncfile, "T2")
# Create a south-north line using pivot point and angle
pivot_point = CoordPair((t2.shape[-1]-1)//2, (t2.shape[-2]-1)//2)
angle = 0.0
# Calculate the vertical cross section.  By setting latlon to True, this
# also calculates the latitude and longitude coordinates along the line
# and adds them to the metadata to help with plotting labels.
t2_line = interpline(t2, pivot_point=pivot_point, angle=angle, latlon=True)
print(t2_line, "\n")
Result:
<xarray.DataArray u'T2_line' (line_idx: 1058)>
array([ 302.07214355,  302.08505249,  302.08688354, ...,  279.18557739,
        279.1998291 ,  279.23132324], dtype=float32)
Coordinates:
    Time      datetime64[ns] 2016-10-07
    xy_loc    (line_idx) object CoordPair(x=899.0, y=0.0, lat=24.3645858765, lon=-97.5) ...
Dimensions without coordinates: line_idx
Attributes:
    FieldType: 104
    description: TEMP at 2 M
    units: K
    stagger:
    coordinates: XLONG XLAT
    projection: LambertConformal(stand_lon=-97.5, moad_cen_lat=38.5000038147,
                                 truelat1=38.5, truelat2=38.5, pole_lat=90.0,
                                 pole_lon=0.0)
    orientation: (899.0, 0.0) to (899.0, 1057.0) ; center=CoordPair(x=899, y=529) ; angle=0.0
from wrf import getvar, interpline, CoordPair
ncfile = Dataset("wrfout_d01_2016-10-07_00_00_00")
t2 = getvar(ncfile, "T2")
lats = getvar(ncfile, "lat")
lons = getvar(ncfile, "lon")
# Select the latitude,longitude points for a vertical line through
# the center of the domain.
start_lat = lats[0, (lats.shape[-1]-1)//2]
end_lat = lats[-1, (lats.shape[-1]-1)//2]
start_lon = lons[0, (lons.shape[-1]-1)//2]
end_lon = lons[-1, (lons.shape[-1]-1)//2]
# Create the CoordPairs
start_point = CoordPair(lat=start_lat, lon=start_lon)
end_point = CoordPair(lat=end_lat, lon=end_lon)
# Calculate the interpolated line.  To use latitude and longitude points,
# you must supply a WRF NetCDF file object, or a projection object along
# with the lower left latitude and lower left longitude points.
# Also, by setting latlon to True, this routine will
# also calculate the latitude and longitude coordinates along the line
# and adds them to the metadata to help with plotting labels.
t2_line = interpline(t2, wrfin=ncfile, start_point=start_point, end_point=end_point, latlon=True)
print (t2_line)
Result:
<xarray.DataArray u'T2_line' (line_idx: 1058)>
array([ 302.07214355,  302.08505249,  302.08688354, ...,  279.18557739,
        279.1998291 ,  279.23132324], dtype=float32)
Coordinates:
    Time      datetime64[ns] 2016-10-07
    xy_loc    (line_idx) object CoordPair(x=899.0, y=0.0, lat=24.3645858765, lon=-97.5) ...
Dimensions without coordinates: line_idx
Attributes:
    FieldType: 104
    description: TEMP at 2 M
    units: K
    stagger:
    coordinates: XLONG XLAT
    projection: LambertConformal(stand_lon=-97.5, moad_cen_lat=38.5000038147,
                                 truelat1=38.5, truelat2=38.5, pole_lat=90.0,
                                 pole_lon=0.0)
    orientation: (899.0, 0.0) to (899.0, 1057.0)
Interpolating a 3D Field to a Surface Type¶
The wrf.vinterp() is used to interpolate a field to a type of surface.
The available surfaces are pressure, geopotential height, theta, and theta-e.
The surface levels to interpolate also need to be specified.
from __future__ import print_function
from netCDF4 import Dataset
from wrf import getvar, vinterp
ncfile = Dataset("wrfout_d01_2016-10-07_00_00_00")
tk = getvar(ncfile, "tk")
# Interpolate tk to theta-e levels
interp_levels = [200, 300, 500, 1000]
interp_field = vinterp(ncfile,
               field=tk,
               vert_coord="eth",
               interp_levels=interp_levels,
               extrapolate=True,
               field_type="tk",
               log_p=True)
print(interp_field)
Result:
<xarray.DataArray u'temp' (interp_level: 4, south_north: 1059, west_east: 1799)>
array([[[ 296.12872314,  296.1166687 ,  296.08905029, ...,  301.71026611,
          301.67956543,  301.67791748],
        [ 296.11352539,  295.95581055,  295.91555786, ...,  301.63052368,
          301.62905884,  301.65887451],
        [ 296.07556152,  295.91577148,  295.88214111, ...,  301.61499023,
          301.60287476,  301.63961792],
        [ 219.11134338,  219.08581543,  219.08602905, ...,  218.29879761,
          218.30923462,  218.3787384 ],
        [ 219.09260559,  219.07765198,  219.08340454, ...,  218.2855072 ,
          218.30444336,  218.37931824],
        [ 219.07936096,  219.08181763,  219.10089111, ...,  218.31173706,
          218.34288025,  218.3687439 ]]], dtype=float32)
Coordinates:
    XLONG         (south_north, west_east) float32 -122.72 -122.693 -122.666 ...
    XLAT          (south_north, west_east) float32 21.1381 21.1451 21.1521 ...
    Time          datetime64[ns] 2016-10-07
  * interp_level  (interp_level) int64 200 300 500 1000
Dimensions without coordinates: south_north, west_east
Attributes:
    FieldType: 104
    MemoryOrder: XYZ
    description: temperature
    units: K
    stagger:
    coordinates: XLONG XLAT
    projection: LambertConformal(stand_lon=-97.5, moad_cen_lat=38.5000038147,
                                 truelat1=38.5, truelat2=38.5, pole_lat=90.0,
                                 pole_lon=0.0)
    vert_interp_type: eth
Lat/Lon <-> XY Routines¶
wrf-python includes a set of routines for converting back and forth between
latitude,longitude space and x,y space.  The methods are wrf.xy_to_ll(),
wrf.xy_to_ll_proj(), wrf.ll_to_xy(), wrf.ll_to_xy_proj().
The latitude, longitude, x, and y parameters to these methods
can contain sequences if multiple points are desired to be converted.




    

Example With Single Coordinates¶
from __future__ import print_function
from netCDF4 import Dataset
from wrf import getvar, interpline, CoordPair, xy_to_ll, ll_to_xy
ncfile = Dataset("wrfout_d01_2016-10-07_00_00_00")
lat_lon = xy_to_ll(ncfile, 400, 200)
print(lat_lon)
x_y = ll_to_xy(ncfile, lat_lon[0], lat_lon[1])
print (x_y)
Result:
<xarray.DataArray u'latlon' (lat_lon: 2)>
array([  28.55816408, -112.67827617])
Coordinates:
  * lat_lon   (lat_lon) <U3 u'lat' u'lon'
    xy_coord  object CoordPair(x=400, y=200)
Dimensions without coordinates: idx
<xarray.DataArray u'xy' (x_y: 2)>
array([400, 200])
Coordinates:
    latlon_coord  object CoordPair(lat=28.5581640822, lon=-112.678276173)
  * x_y           (x_y) <U1 u'x' u'y'
Dimensions without coordinates: idx
from netCDF4 import Dataset
from wrf import getvar, interpline, CoordPair, xy_to_ll, ll_to_xy
ncfile = Dataset("wrfout_d01_2016-10-07_00_00_00")
lat_lon = xy_to_ll(ncfile, [400,105], [200,205])
print(lat_lon)
x_y = ll_to_xy(ncfile, lat_lon[0,:], lat_lon[1,:])
print (x_y)
Result:
<xarray.DataArray u'latlon' (lat_lon: 2, idx: 2)>
array([[  28.55816408,   27.03835783],
       [-112.67827617, -121.36392174]])
Coordinates:
  * lat_lon   (lat_lon) <U3 u'lat' u'lon'
    xy_coord  (idx) object CoordPair(x=400, y=200) CoordPair(x=105, y=205)
Dimensions without coordinates: idx
<xarray.DataArray u'xy' (x_y: 2, idx: 2)>
array([[400, 105],
       [200, 205]])
Coordinates:
    latlon_coord  (idx) object CoordPair(lat=28.5581640822, lon=-112.678276173) ...
  * x_y           (x_y) <U1 u'x' u'y'
Dimensions without coordinates: idx
Mapping Helper Routines¶
wrf-python includes several routines to assist with plotting, primarily for
obtaining the mapping object used for cartopy, basemap, and PyNGL.  For all
three plotting systems, the mapping object can be determined directly from
a variable when using xarray, or can be obtained from the WRF output file(s)
if xarray is turned off.
Also included are utilities for extracting the geographic boundaries
directly from xarray variables.  This can be useful in situations where you
only want to work with subsets (slices) of a large domain, but don’t want to
define the map projection over the subset region.
Cartopy Example Using a Variable¶
In this example, we’re going to extract the cartopy mapping object from a
diagnostic variable (slp), the lat,lon coordinates, and the geographic
boundaries.  Next, we’re going to take a subset of the diagnostic variable
and extract the geographic boundaries.  Some of the variables
will be printed for demonstration.
from __future__ import print_function
from netCDF4 import Dataset
from wrf import getvar, get_cartopy, latlon_coords, geo_bounds
ncfile = Dataset("wrfout_d01_2016-10-07_00_00_00")
# Use SLP for the example variable
slp = getvar(ncfile, "slp")
# Get the cartopy mapping object
cart_proj = get_cartopy(slp)
print (cart_proj)
# Get the latitude and longitude coordinate.  This is usually needed for plotting.
lats, lons = latlon_coords(slp)
# Get the geobounds for the SLP variable
bounds = geo_bounds(slp)
print (bounds)
# Get the geographic boundaries for a subset of the domain
slp_subset = slp[150:250, 150:250]
slp_subset_bounds = geo_bounds(slp_subset)
print (slp_subset_bounds)
Result:
<cartopy.crs.LambertConformal object at 0x115374290>
GeoBounds(CoordPair(lat=25.9246292114, lon=-119.675048828), CoordPair(lat=29.0761833191, lon=-117.46484375))
GeoBounds(CoordPair(lat=25.9246292114, lon=-119.675048828), CoordPair(lat=29.0761833191, lon=-117.46484375))
Cartopy Example Using WRF Output Files¶
In this example, the cartopy mapping object and geographic boundaries
will be extracted directly from the netcdf variable.
from __future__ import print_function
from netCDF4 import Dataset
from wrf import get_cartopy, geo_bounds
ncfile = Dataset("wrfout_d01_2016-10-07_00_00_00")
# Get the cartopy mapping object from the netcdf file
cart_proj = get_cartopy(wrfin=ncfile)
print (cart_proj)
# Get the geobounds from the netcdf file (by default, uses XLAT, XLONG)
# You can supply a variable name to get the staggered boundaries
bounds = geo_bounds(wrfin=ncfile)
print (bounds)
Result:
<cartopy.crs.LambertConformal object at 0x11d3be650>
GeoBounds(CoordPair(lat=21.1381225586, lon=-122.719528198), CoordPair(lat=47.8436355591, lon=-60.9013671875))
Basemap Example Using a Variable¶
In this example, we’re going to extract the basemap mapping object from a
diagnostic variable (slp), the lat,lon coordinates, and the geographic
boundaries.  Next, we’re going to take a subset of the diagnostic variable
and extract the geographic boundaries.  Some of the variables will be
printed for demonstration.
from __future__ import print_function
from netCDF4 import Dataset
from wrf import getvar, get_basemap, latlon_coords, geo_bounds
ncfile = Dataset("wrfout_d01_2016-10-07_00_00_00")
slp = getvar(ncfile, "slp")
# Get the basemap mapping object
bm = get_basemap(slp)
print (bm)
# Get the latitude and longitude coordinate.  This is usually needed for plotting.
lats, lons = latlon_coords(slp)
# Get the geobounds for the SLP variable
bounds = geo_bounds(slp)
print(bounds)
# Get the geographic boundaries for a subset of the domain
slp_subset = slp[150:250, 150:250]
slp_subset_bounds = geo_bounds(slp_subset)
print (slp_subset_bounds)
Result:
<mpl_toolkits.basemap.Basemap object at 0x114d65650>
GeoBounds(CoordPair(lat=21.1381225586, lon=-122.719528198), CoordPair(lat=47.8436355591, lon=-60.9013671875))
GeoBounds(CoordPair(lat=25.9246292114, lon=-119.675048828), CoordPair(lat=29.0761833191, lon=-117.46484375)
Basemap Example Using WRF Output Files¶
In this example, the basemap mapping object and geographic boundaries
will be extracted directly from the netcdf variable.
from __future__ import print_function
from netCDF4 import Dataset
from wrf import get_basemap, geo_bounds
ncfile = Dataset("wrfout_d01_2016-10-07_00_00_00")
# Get the basemap object from the netcdf file
bm = get_basemap(wrfin=ncfile)
print (bm)
# Get the geographic boundaries from the netcdf file
bounds = geo_bounds(wrfin=ncfile)
print (bounds)
Result:
<mpl_toolkits.basemap.Basemap object at 0x125bb4750>
GeoBounds(CoordPair(lat=21.1381225586, lon=-122.719528198), CoordPair(lat=47.8436355591, lon=-60.9013671875))
PyNGL Example Using a Variable¶
In this example, we’re going to extract the basemap mapping object from a
diagnostic variable (slp), the lat,lon coordinates, and the geographic
boundaries.  Next, we’re going to take a subset of the diagnostic variable
and extract the geographic boundaries.  Some of the variables will be
printed for demonstration.
from __future__ import print_function
from netCDF4 import Dataset
from wrf import getvar, get_pyngl, latlon_coords, geo_bounds
ncfile = Dataset("wrfout_d01_2016-10-07_00_00_00")
# Use SLP as the example variable
slp = getvar(ncfile, "slp")
# Get the pyngl resources from the variable
pyngl_resources = get_pyngl(slp)
print (pyngl_resources)
# Get the latitude and longitude coordinate.  This is needed for plotting.
lats, lons = latlon_coords(slp)
# Get the geobounds from the SLP variable
bounds = geo_bounds(slp)
print(bounds)
# Get the geographic boundaries for a subset of the domain
slp_subset = slp[150:250, 150:250]
slp_subset_bounds = geo_bounds(slp_subset)
print (slp_subset_bounds)
Result:




    

<Ngl.Resources instance at 0x114cabbd8>
GeoBounds(CoordPair(lat=21.1381225586, lon=-122.719528198), CoordPair(lat=47.8436355591, lon=-60.9013671875))
GeoBounds(CoordPair(lat=25.9246292114, lon=-119.675048828), CoordPair(lat=29.0761833191, lon=-117.46484375))
PyNGL Example Using WRF Output Files¶
In this example, the basemap mapping object and geographic boundaries
will be extracted directly from the netcdf variable.
from __future__ import print_function
from netCDF4 import Dataset
from wrf import get_pyngl, geo_bounds
ncfile = Dataset("wrfout_d01_2016-10-07_00_00_00")
# Get the pyngl resources from the netcdf file
pyngl_resources = get_pyngl(wrfin=ncfile)
print (pyngl_resources)
# Get the geographic boundaries from the netcdf file
bounds = geo_bounds(wrfin=ncfile)
print (bounds)
Result:
<Ngl.Resources instance at 0x115391f80>
GeoBounds(CoordPair(lat=21.1381225586, lon=-122.719528198), CoordPair(lat=47.8436355591, lon=-60.9013671875))
Moving Nests¶
When a domain nest is moving, the domain boundaries become a function of time when
combining the files using the ‘cat’ method.  When using ‘join’, the domain boundaries
become a function of both file and time. As a result, the methods that
depend on geographic boundaries (wrf.geo_bounds(), wrf.get_basemap(), etc)
will return arrays of objects rather than a single object when multiple times
and/or files are detected in the underlying coordinate variables.
An exception is wrf.get_cartopy(), which contains no geographic
boundary information in the mapping object.  Instead, the
wrf.cartopy_xlim() and wrf.cartopy_ylim() methods can be used to
get the array of matplotlib axes boundaries (returned in the axes projection
coordinates).
Geographic Boundaries with Moving Nest Example¶
In this example, the geographic boundaries are extracted from a sequence
of files that use a moving nest.  The result will be an array of
wrf.GeoBounds objects.
from __future__ import print_function
from glob import glob
from netCDF4 import Dataset as nc
from wrf import getvar, ALL_TIMES, geo_bounds
# Get all the domain 02 files
wrf_filenames = glob("wrf_files/wrf_vortex_multi/wrfout_d02_*")
ncfiles = [nc(x) for x in wrf_filenames]
# SLP is the example variable and includes all times
slp = getvar(ncfiles, "slp", timeidx=ALL_TIMES)
# Get the geographic boundaries
bounds = geo_bounds(slp)
print (bounds)
Result:
[ GeoBounds(CoordPair(lat=21.3020038605, lon=-90.5740585327), CoordPair(lat=29.0274410248, lon=-82.0291671753))
 GeoBounds(CoordPair(lat=21.3020038605, lon=-90.3042221069), CoordPair(lat=29.0274410248, lon=-81.7593231201))
 GeoBounds(CoordPair(lat=21.3020038605, lon=-90.8438949585), CoordPair(lat=29.0274410248, lon=-82.2990036011))
 GeoBounds(CoordPair(lat=21.3020038605, lon=-91.1137390137), CoordPair(lat=29.0274410248, lon=-82.5688400269))
 GeoBounds(CoordPair(lat=21.8039493561, lon=-91.6534042358), CoordPair(lat=29.4982528687, lon=-83.1085205078))
 GeoBounds(CoordPair(lat=22.0542640686, lon=-92.193107605), CoordPair(lat=29.7328338623, lon=-83.6481933594))
 GeoBounds(CoordPair(lat=22.5535621643, lon=-92.7327728271), CoordPair(lat=30.2003688812, lon=-84.1878738403))
 GeoBounds(CoordPair(lat=22.8025398254, lon=-93.0026092529), CoordPair(lat=30.4333114624, lon=-84.4577102661))
 GeoBounds(CoordPair(lat=23.0510597229, lon=-93.2724456787), CoordPair(lat=30.665681839, lon=-84.7275543213))]
Cartopy Mapping with Moving Nest Example¶
In this example, a cartopy mapping object is extracted from a variable
that uses a moving nest.  Since cartopy objects do not include geographic
boundary information, only a single cartopy object is returned.  However,
if the axes xlimits and ylimits are desired, the wrf.cartopy_xlim() and
wrf.cartopy_ylim() functions can be used to obtain the array of
moving boundaries in the axes projected coordinate space.
from __future__ import print_function
from glob import glob
from netCDF4 import Dataset as nc
from wrf import getvar, ALL_TIMES, get_cartopy, cartopy_xlim, cartopy_ylim
# Get all of the domain 02 WRF output files
wrf_filenames = glob("wrf_files/wrf_vortex_multi/wrfout_d02_*")
ncfiles = [nc(x) for x in wrf_filenames]
# Use SLP as the example variable and include all times
slp = getvar(ncfiles, "slp", timeidx=ALL_TIMES)
# Get the cartopy mapping object
cart_proj = get_cartopy(slp)
print (cart_proj)
print ("\n")
# Get the array of axes x-limits
xlims = cartopy_xlim(slp)
print (xlims)
print ("\n")
# Get the array of axes y-limits
ylims = cartopy_ylim(slp)
print (ylims)
Result:
<wrf.projection.MercatorWithLatTS object at 0x13893c9b0>
[[-174999.8505754546, 774999.5806103835]
 [-145000.11853874932, 805000.1608638937]
 [-204999.58261215844, 744999.8485736783]
 [-235000.16286567, 715000.1165369744]
 [-294998.77872227144, 654999.804246759]
 [-355001.6356629085, 595000.34017335]
 [-415000.25151950994, 535000.0278831345]
 [-444999.98355621524, 505000.29584642925]
 [-474999.7155929191, 474999.7155929177]]
[[2424828.507236154, 3374828.14098255]
 [2424828.507236154, 3374828.14098255]
 [2424828.507236154, 3374828.14098255]
 [2424828.507236154, 3374828.14098255]
 [2484829.1182174017, 3434828.972518358]
 [2514829.1041871575, 3464828.196283651]
 [2574829.0041584675, 3524828.8880928173]
 [2604829.1786526926, 3554829.5610342724]
 [2634828.9016262344, 3584828.016406863]]
Basemap Mapping with Moving Nest Example¶
In this example, basemap objects are extracted from a variable that uses a moving
nest.  An array of basemap objects is returned because the
basemap object includes geographic boundary information.
from __future__ import print_function
from glob import glob
from netCDF4 import Dataset as nc
from wrf import getvar, ALL_TIMES, get_basemap
# Get all of the domain 02 WRF output files
wrf_filenames = glob("wrf_files/wrf_vortex_multi/wrfout_d02_*")
ncfiles = [nc(x) for x in wrf_filenames]
# Use SLP as the reference variable and include all times
slp = getvar(ncfiles, "slp", timeidx=ALL_TIMES)
# Get the array of basemap objects
bm = get_basemap(slp)
print (bm)
print ("\n")
Result:
[<mpl_toolkits.basemap.Basemap object at 0x1327bc510>
 <mpl_toolkits.basemap.Basemap object at 0x115a9a790>
 <mpl_toolkits.basemap.Basemap object at 0x115a9a750>
 <mpl_toolkits.basemap.Basemap object at 0x115a9a7d0>
 <mpl_toolkits.basemap.Basemap object at 0x115a9a850>
 <mpl_toolkits.basemap.Basemap object at 0x115a9a8d0>
 <mpl_toolkits.basemap.Basemap object at 0x115a9a950>
 <mpl_toolkits.basemap.Basemap object at 0x115a9a9d0>
 <mpl_toolkits.basemap.Basemap object at 0x115a9aa50>]
PyNGL Mapping with Moving Nest Example¶
In this example, pyngl resource objects are extracted from a variable that uses
a moving nest.  An array of pyngl resource objects is returned because the
pyngl object includes geographic boundary information.
from __future__ import print_function
from glob import glob
from netCDF4 import Dataset as nc
from wrf import getvar, ALL_TIMES, get_pyngl
# Get the domain 02 WRF output files
wrf_filenames = glob("wrf_files/wrf_vortex_multi/wrfout_d02_*")
ncfiles = [nc(x) for x in wrf_filenames]
# Use SLP as the example variable and include all times
slp = getvar(ncfiles, "slp", timeidx=ALL_TIMES)
# Get the array of pyngl resource objects
bm = get_pyngl(slp)
print (bm)
print ("\n")
Result:
[<Ngl.Resources instance at 0x140cd30e0>
 <Ngl.Resources instance at 0x11d3187a0>
 <Ngl.Resources instance at 0x11d3185a8>
 <Ngl.Resources instance at 0x11d3188c0>
 <Ngl.Resources instance at 0x11d318878>
 <Ngl.Resources instance at 0x11d3183f8>
 <Ngl.Resources instance at 0x11d318950>
 <Ngl.Resources instance at 0x11d318a70>
 <Ngl.Resources instance at 0x11d318710>]
Using OpenMP¶
Beginning in version 1.1, the Fortran computational routines in wrf-python make
use of OpenMP directives. OpenMP enables the calculations to use multiple CPU
cores, which can improve performance. In order to use OpenMP features,
wrf-python has to be compiled with OpenMP enabled (most pre-built binary
installations will have this enabled).
The Fortran computational routines have all been built using runtime
scheduling, instead of compile time scheduling, so that the user can choose the
scheduler type within their Python application. By default, the scheduling
type is set to wrf.OMP_SCHED_STATIC using only 1 CPU core, so
wrf-python will behave similarly to the non-OpenMP built versions. For the most
part, the difference between the scheduling types is minimal, with the exception
being the wrf.OMP_SCHED_DYNAMIC scheduler that is much slower due to
the additional overhead associated with it. For new users, using the default
scheduler should be sufficient.
Verifying that OpenMP is Enabled¶
To take advantage of the performance improvements offered by OpenMP, wrf-python
needs to have been compiled with OpenMP features enabled. The example below
shows how you can determine if OpenMP is enabled in your build of wrf-python.
from __future__ import print_function
from wrf import omp_enabled
print(omp_enabled())
Result:
Determining the Number of Available Processors¶
The example below shows how you can get the maximum number of processors
that are available on your system.
from __future__ import print_function
from wrf import omp_get_num_procs
print(omp_get_num_procs())
Result:
Specifying the Number of Threads¶
To enable multicore support via OpenMP, specifying the maximum number
of OpenMP threads (i.e. CPU cores) is the only step that you need to take.
In the example below, wrf.omp_set_num_threads() is used to set the
maximum number of threads to use, and wrf.omp_get_max_threads() is used
to retrieve (and print) the maximum number of threads used.
Although there is an OpenMP routine named wrf.omp_get_num_threads(),
this routine will always return 1 when called from the sequential part of
the program. Use wrf.omp_get_max_threads() to return the value set by
wrf.omp_set_num_threads().
from __future__ import print_function
from wrf import omp_set_num_threads, omp_get_max_threads
omp_set_num_threads(4)
print (omp_get_max_threads())
Result:
Setting a Different Scheduler Type