2. Vertical Interpolation

2.1. Description

This module is used to perform pressure to height conversion in TC-RMW data (netCDF or grb2) by vertically interpolating fields between grids with pressure vertical coordinates. The pressure to height conversion is implemented with linear interpolation. The following fields are required in the input data: relative humidity, surface pressure, and temperature.

2.2. Example

Sample Data

Sample TC-RMW data (in pressure level) is located:

https://dtcenter.ucar.edu/dfiles/code/METplus/METplotpy/tcrmw/tc_rmw_example.nc.gz

Save this data file to a directory of your choosing and cd to your directory:

cd $METCALCPY_DATA_DIR

$METCALCPY_DATA_DIR is the directory where you stored the example data.

Uncompress the data using gunzip:

gunzip tc_rmw_example.nc.gz

You should now have a file: tc_rmw_example.nc

Configuration Files

A configuration file (YAML, with a .yaml extension) is used to define which variables in the input data file (netCDF or grib2) are to be converted from pressure levels to height:

height_from_pressure_tcrmw.yaml:

#
# Filename: height_from_pressure_tcrmw.yaml
#
# Sample YAML configuration file for vertical_interp.py
#
# Author: David Fillmore
# Email:  met_help@ucar.edu
#
# Version    Date
# 0.1.0      2021/08/31    Initial version
#

#
# Set to compute geopotential height from pressure
#
height_from_pressure:
    True

#
# Required fields
#
zero_surface_geopotential:
    True

surface_pressure_name:
    'PRMSL'

temperature_name:
    'TMP'

relative_humidity_name:
    'RH'

#
# Field list to process
#

fields:
    - 'UGRD'
    - 'VGRD'
    - 'TMP'

#
# Vertical coordinate information
#

vertical_coord_type_in:
    'pressure'

vertical_coord_type_out:
    'height'

vertical_dim_name:
    'pressure'

vertical_levels :
    - 100
    - 200
    - 500
    - 1000
    - 2000
    - 3000
    - 4000
    - 5000

vertical_level_units :
    'meter'

This configuration file is located in the $METCALCPY_SOURCE_DIR/examples/ directory, where $METCALCPY_SOURCE_DIR is the location of where you saved the METcalcpy source code.

In this example, the UGRD, VGRD, and TMP variables are selected for conversion (refer to the fields setting in the above configuration file). You may list any other variables as long as they are present in the input data:

e.g.

fields:

  • ‘UGRD’

  • ‘VGRD’

  • ‘TMP’

  • ‘RH’

  • ‘PRMSL’

NOTE: The relative humidity, surface pressure, and temperature fields are required, as they are used to calculate pressure indices.

2.3. Run from the Command Line

A sample Bourne-shell script can be used to convert the pressure level data to height level data:

$METCALCPY_SOURCE_DIR/METcalcpy/examples/height_from_pressure_tcrmw.sh

python ../metcalcpy/vertical_interp.py \
    --datadir $DATA_DIR \
    --input /path/to/input/tc_rmw_example.nc \
    --config height_from_pressure_tcrmw.yaml \
    --output /path/to/output/tc_rmw_dev_test_vertical_interp.nc \
#   --debug

You will need to set the environment variable for the location of the data directory (where the input data resides), the name of the input data, the name of the YAML configuration file, and the name of the output file (output directory and filename). NOTE: If you do not want to see the debug messages, simply delete the line with the –debug. Open the height_from_pressure_tcrmw.sh file using an editor of your choice.

Replace the /path/to/input-data to the actual full path to the directory where you saved the sample data:

e.g.

export DATA_DIR=/users/mydir/data/tcrmw

Replace the /path/to/output to the directory where you want to save your output:

e.g.

--output /users/mydir/tcrmw/output

Where in this example, the /users/mydir/tcrmw/output is the directory where the output should be directed. Replace this with the full path to the desired location for output files.

Uncomment the –debug if additional debug information is desired. This will result in the generation of intermediate netCDF files in the directory specified by the $DATA_DIR environment variable in the height_from_pressure_tcrmw.sh shell script. Create a ‘Debug’ subdirectory in the $DATA_DIR directory. After running the height_from_pressure_tcrmw.sh shell script, numerous netCDF files will be created: a height_from_pressure_debug.nc and numerous files beginning with vertical_interp_debug

Save and close the file.

To perform the conversion, do the following:

  • Make sure you have these required Python packages:

    • Python 3.7

    • metpy 1.1.0

    • netcdf4 1.5.7

    • numpy 1.21.2

    • pint 0.18

    • pyyaml 5.4.1

    • xarray 0.20.1

    • yaml 0.2.5

  • If running in a conda environment, verify that you are running in a conda environment that has the above Python packages installed.

  • cd to the $METCALCPY_SOURCE_DIR/METcalcpy/examples directory

  • run the script, enter the following command:

sh height_from_pressure_tcrmw.sh

This will produce a netCDF file with the filename specified in the height_from_pressure_tcrmw.sh script, in this case it is tc_rmw_example_vertical_interp.nc and will be located in the output directory specified via the $OUTPUT_DIR environment variable. This file contains the converted levels for the fields specified in the height_from_pressure_tcrmw.yaml configuration file.