#!/usr/bin/env python3
'''
Copyright 2023 ECMWF.
This software is licensed under the terms of the Apache Licence Version 2.0
which can be obtained at http://www.apache.org/licenses/LICENSE-2.0
In applying this licence, ECMWF does not waive the privileges and immunities
granted to it by virtue of its status as an intergovernmental organisation
nor does it submit to any jurisdiction.
**************************************************************************
Function : compute_geopotential_on_ml
Author (date) : Cristian Simarro (09/10/2015)
modified: Cristian Simarro (20/03/2017) - migrated to eccodes
Xavi Abellan (03/12/2018) - compatibilty with Python 3
Xavi Abellan (27/03/2020) - Corrected steps in output file
Xavi Abellan (05/08/2020) - Better handling of levels
Xavi Abellan (31/01/2023) - Better handling of steps
Category : COMPUTATION
OneLineDesc : Computes geopotential on model levels
Description : Computes geopotential on model levels.
Based on code from Nils Wedi, the IFS documentation:
https://software.ecmwf.int/wiki/display/IFS/CY41R1+Official+IFS+Documentation
part III. Dynamics and numerical procedures
optimised implementation by Dominique Lucas.
ported to Python by Cristian Simarro
Parameters : tq.grib - grib file with all the levelist
of t and q
zlnsp.grib - grib file with levelist 1 for params
z and lnsp
-l levelist (optional) - slash '/' separated list of levelist
to store in the output
-o output (optional) - name of the output file
(default='z_out.grib')
Return Value : output (default='z_out.grib')
A fieldset of geopotential on model levels
Dependencies : None
Example Usage :
compute_geopotential_on_ml.py tq.grib zlnsp.grib
'''
from __future__ import print_function
import sys
import argparse
import numpy as np
from eccodes import (codes_index_new_from_file, codes_index_get, codes_get,
codes_index_select, codes_new_from_index, codes_set,
codes_index_add_file, codes_get_array, codes_get_values,
codes_index_release, codes_release, codes_set_values,
codes_write)
R_D = 287.06
R_G = 9.80665
def parse_args():
''' Parse program arguments using ArgumentParser'''
parser = argparse.ArgumentParser(
description='Python tool to calculate the Z of the model levels')
parser.add_argument('-l', '--levelist', help='levelist to store',
default='all')
parser.add_argument('-o', '--output', help='name of the output file',
default='z_out.grib')
parser.add_argument('t_q', metavar='tq.grib', type=str,
help=('grib file with temperature(t) and humidity(q)'
'for the model levels'))
parser.add_argument('z_lnsp', metavar='zlnsp.grib', type=str,
help=('grib file with geopotential(z) and Logarithm'
'of surface pressure(lnsp) for the ml=1'))
args = parser.parse_args()
# Handle levelist posibilities
if args.levelist == 'all':
args.levelist = range(1, 138)
elif "to" in args.levelist.lower():
if "by" in args.levelist.lower():
args.levelist = args.levelist.split('/')
args.levelist = list(range(int(args.levelist[0]),
int(args.levelist[2]) + 1,
int(args.levelist[4])))
else:
args.levelist = args.levelist.split('/')
args.levelist = list(range(int(args.levelist[0]),
int(args.levelist[2]) + 1))
else:
args.levelist = [int(l) for l in args.levelist.split('/')]
return args
def main():
'''Main function'''
args = parse_args()
print('Arguments: %s' % ", ".join(
['%s: %s' % (k, v) for k, v in vars(args).items()]))
fout = open(args.output, 'wb')
index_keys = ['date', 'time', 'shortName', 'level', 'step']
idx = codes_index_new_from_file(args.z_lnsp, index_keys)
codes_index_add_file(idx, args.t_q)
if 'u_v' in args:
codes_index_add_file(idx, args.u_v)
values = None
# iterate date
for date in codes_index_get(idx, 'date'):
codes_index_select(idx, 'date', date)
# iterate time
for time in codes_index_get(idx, 'time'):
codes_index_select(idx, 'time', time)
for step in codes_index_get(idx, 'step'):
codes_index_select(idx, 'step', step)
if not values:
values = get_initial_values(idx, keep_sample=True)
if 'height' in args:
values['height'] = args.height
values['gh'] = args.height * R_G + values['z']
if 'levelist' in args:
values['levelist'] = args.levelist
# surface pressure
try:
values['sp'] = get_surface_pressure(idx)
production_step(idx, step, values, fout)
except WrongStepError:
if step != '0':
raise
try:
codes_release(values['sample'])
except KeyError:
pass
codes_index_release(idx)
fout.close()
def get_initial_values(idx, keep_sample=False):
'''Get the values of surface z, pv and number of levels '''
codes_index_select(idx, 'level', 1)
codes_index_select(idx, 'shortName', 'z')
gid = codes_new_from_index(idx)
values = {}
# surface geopotential
values['z'] = codes_get_values(gid)
values['pv'] = codes_get_array(gid, 'pv')
values['nlevels'] = codes_get(gid, 'NV', int) // 2 - 1
check_max_level(idx, values)
if keep_sample:
values['sample'] = gid
else:
codes_release(gid)
return values
def check_max_level(idx, values):
'''Make sure we have all the levels required'''
# how many levels are we computing?
max_level = max(codes_index_get(idx, 'level', int))
if max_level != values['nlevels']:
print('%s [WARN] total levels should be: %d but it is %d' %
(sys.argv[0], values['nlevels'], max_level),
file=sys.stderr)
values['nlevels'] = max_level
def get_surface_pressure(idx):
'''Get the surface pressure for date-time-step'''
codes_index_select(idx, 'level', 1)
codes_index_select(idx, 'shortName', 'lnsp')
gid = codes_new_from_index(idx)
if gid is None:
raise WrongStepError()
if codes_get(gid, 'gridType', str) == 'sh':
print('%s [ERROR] fields must be gridded, not spectral' % sys.argv[0],
file=sys.stderr)
sys.exit(1)
# surface pressure
sfc_p = np.exp(codes_get_values(gid))
codes_release(gid)
return sfc_p
def get_ph_levs(values, level):
'''Return the presure at a given level and the next'''
a_coef = values['pv'][0:values['nlevels'] + 1]
b_coef = values['pv'][values['nlevels'] + 1:]
ph_lev = a_coef[level - 1] + (b_coef[level - 1] * values['sp'])
ph_levplusone = a_coef[level] + (b_coef[level] * values['sp'])
return ph_lev, ph_levplusone
def compute_z_level(idx, lev, values, z_h):
'''Compute z at half & full level for the given level, based on t/q/sp'''
# select the levelist and retrieve the vaules of t and q
# t_level: values for t
# q_level: values for q
codes_index_select(idx, 'level', lev)
codes_index_select(idx, 'shortName', 't')
gid = codes_new_from_index(idx)
if gid is None:
raise MissingLevelError('T at level {} missing from input'.format(lev))
t_level = codes_get_values(gid)
codes_release(gid)
codes_index_select(idx, 'shortName', 'q')
gid = codes_new_from_index(idx)
if gid is None:
raise MissingLevelError('Q at level {} missing from input'.format(lev))
q_level = codes_get_values(gid)
codes_release(gid)
# compute moist temperature
t_level = t_level * (1. + 0.609133 * q_level)
# compute the pressures (on half-levels)
ph_lev, ph_levplusone = get_ph_levs(values, lev)
if lev == 1:
dlog_p = np.log(ph_levplusone / 0.1)
alpha = np.log(2)
else:
dlog_p = np.log(ph_levplusone / ph_lev)
alpha = 1. - ((ph_lev / (ph_levplusone - ph_lev)) * dlog_p)
t_level = t_level * R_D
# z_f is the geopotential of this full level
# integrate from previous (lower) half-level z_h to the
# full level
z_f = z_h + (t_level * alpha)
# z_h is the geopotential of 'half-levels'
# integrate z_h to next half level
z_h = z_h + (t_level * dlog_p)
return z_h, z_f
def production_step(idx, step, values, fout):
'''Compute z at half & full level for the given level, based on t/q/sp'''
# We want to integrate up into the atmosphere, starting at the
# ground so we start at the lowest level (highest number) and
# keep accumulating the height as we go.
# See the IFS documentation, part III
# For speed and file I/O, we perform the computations with
# numpy vectors instead of fieldsets.
z_h = values['z']
codes_set(values['sample'], 'step', int(step))
for lev in sorted(values['levelist'], reverse=True):
try:
z_h, z_f = compute_z_level(idx, lev, values, z_h)
# store the result (z_f) in a field and add to the output
codes_set(values['sample'], 'level', lev)
codes_set_values(values['sample'], z_f)
codes_write(values['sample'], fout)
except MissingLevelError as e:
print('%s [WARN] %s' % (sys.argv[0], e),
file=sys.stderr)
class WrongStepError(Exception):
''' Exception capturing wrong step'''
pass
class MissingLevelError(Exception):
''' Exception capturing missing levels in input'''
pass
if __name__ == '__main__':
main()
