|
1
|
|
|
# Copyright (c) 2008-2017 MetPy Developers. |
|
2
|
|
|
# Distributed under the terms of the BSD 3-Clause License. |
|
3
|
|
|
# SPDX-License-Identifier: BSD-3-Clause |
|
4
|
|
|
"""Contains calculation of various derived indices.""" |
|
5
|
|
|
import numpy as np |
|
6
|
|
|
|
|
7
|
|
|
from .thermo import mixing_ratio, saturation_vapor_pressure |
|
8
|
|
|
from .tools import get_layer |
|
9
|
|
|
from ..constants import g, rho_l |
|
10
|
|
|
from ..package_tools import Exporter |
|
11
|
|
|
from ..units import check_units, units |
|
12
|
|
|
|
|
13
|
|
|
exporter = Exporter(globals()) |
|
14
|
|
|
|
|
15
|
|
|
|
|
16
|
|
|
@exporter.export |
|
17
|
|
|
@check_units('[temperature]', '[pressure]', '[pressure]') |
|
18
|
|
|
def precipitable_water(dewpt, pressure, top=400 * units('hPa')): |
|
19
|
|
|
r"""Calculate precipitable water through the depth of a sounding. |
|
20
|
|
|
|
|
21
|
|
|
Default layer depth is sfc-400 hPa. Formula used is: |
|
22
|
|
|
|
|
23
|
|
|
.. math:: \frac{1}{pg} \int\limits_0^d x \,dp |
|
24
|
|
|
|
|
25
|
|
|
from [Tsonis2008]_, p. 170. |
|
26
|
|
|
|
|
27
|
|
|
Parameters |
|
28
|
|
|
---------- |
|
29
|
|
|
dewpt : `pint.Quantity` |
|
30
|
|
|
Atmospheric dewpoint profile |
|
31
|
|
|
pressure : `pint.Quantity` |
|
32
|
|
|
Atmospheric pressure profile |
|
33
|
|
|
top: `pint.Quantity`, optional |
|
34
|
|
|
The top of the layer, specified in pressure. Defaults to 400 hPa. |
|
35
|
|
|
|
|
36
|
|
|
Returns |
|
37
|
|
|
------- |
|
38
|
|
|
`pint.Quantity` |
|
39
|
|
|
The precipitable water in the layer |
|
40
|
|
|
|
|
41
|
|
|
""" |
|
42
|
|
|
sort_inds = np.argsort(pressure[::-1]) |
|
43
|
|
|
pressure = pressure[sort_inds] |
|
44
|
|
|
dewpt = dewpt[sort_inds] |
|
45
|
|
|
|
|
46
|
|
|
pres_layer, dewpt_layer = get_layer(pressure, dewpt, depth=pressure[0] - top) |
|
47
|
|
|
|
|
48
|
|
|
w = mixing_ratio(saturation_vapor_pressure(dewpt_layer), pres_layer) |
|
49
|
|
|
# Since pressure is in decreasing order, pw will be the negative of what we want. |
|
50
|
|
|
# Thus the *-1 |
|
51
|
|
|
pw = -1. * (np.trapz(w.magnitude, pres_layer.magnitude) * (w.units * pres_layer.units) / |
|
52
|
|
|
(g * rho_l)) |
|
53
|
|
|
return pw.to('millimeters') |
|
54
|
|
|
|
|
55
|
|
|
|
|
56
|
|
|
@exporter.export |
|
57
|
|
|
@check_units('[pressure]') |
|
58
|
|
|
def mean_pressure_weighted(pressure, *args, **kwargs): |
|
59
|
|
|
r"""Calculate pressure-weighted mean of an arbitrary variable through a layer. |
|
60
|
|
|
|
|
61
|
|
|
Layer top and bottom specified in height or pressure. |
|
62
|
|
|
|
|
63
|
|
|
Parameters |
|
64
|
|
|
---------- |
|
65
|
|
|
pressure : `pint.Quantity` |
|
66
|
|
|
Atmospheric pressure profile |
|
67
|
|
|
*args : `pint.Quantity` |
|
68
|
|
|
Parameters for which the pressure-weighted mean is to be calculated. |
|
69
|
|
|
heights : `pint.Quantity`, optional |
|
70
|
|
|
Heights from sounding. Standard atmosphere heights assumed (if needed) |
|
71
|
|
|
if no heights are given. |
|
72
|
|
|
bottom: `pint.Quantity`, optional |
|
73
|
|
|
The bottom of the layer in either the provided height coordinate |
|
74
|
|
|
or in pressure. Don't provide in meters AGL unless the provided |
|
75
|
|
|
height coordinate is meters AGL. Default is the first observation, |
|
76
|
|
|
assumed to be the surface. |
|
77
|
|
|
depth: `pint.Quantity`, optional |
|
78
|
|
|
The depth of the layer in meters or hPa. |
|
79
|
|
|
|
|
80
|
|
|
Returns |
|
81
|
|
|
------- |
|
82
|
|
|
`pint.Quantity` |
|
83
|
|
|
u_mean: u-component of layer mean wind. |
|
84
|
|
|
`pint.Quantity` |
|
85
|
|
|
v_mean: v-component of layer mean wind. |
|
86
|
|
|
|
|
87
|
|
|
""" |
|
88
|
|
|
heights = kwargs.pop('heights', None) |
|
89
|
|
|
bottom = kwargs.pop('bottom', None) |
|
90
|
|
|
depth = kwargs.pop('depth', None) |
|
91
|
|
|
ret = [] # Returned variable means in layer |
|
92
|
|
|
layer_arg = get_layer(pressure, *args, heights=heights, |
|
93
|
|
|
bottom=bottom, depth=depth) |
|
94
|
|
|
layer_p = layer_arg[0] |
|
95
|
|
|
layer_arg = layer_arg[1:] |
|
96
|
|
|
# Taking the integral of the weights (pressure) to feed into the weighting |
|
97
|
|
|
# function. Said integral works out to this function: |
|
98
|
|
|
pres_int = 0.5 * (layer_p[-1].magnitude**2 - layer_p[0].magnitude**2) |
|
99
|
|
|
for i, datavar in enumerate(args): |
|
100
|
|
|
arg_mean = np.trapz(layer_arg[i] * layer_p, x=layer_p) / pres_int |
|
101
|
|
|
ret.append(arg_mean * datavar.units) |
|
102
|
|
|
|
|
103
|
|
|
return ret |
|
104
|
|
|
|
Unidata /
MetPy
