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# Copyright (c) 2008-2017 MetPy Developers. |
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# Distributed under the terms of the BSD 3-Clause License. |
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# SPDX-License-Identifier: BSD-3-Clause |
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"""Contains calculation of various derived indicies.""" |
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import numpy as np |
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from .thermo import mixing_ratio, saturation_vapor_pressure |
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from .tools import get_layer |
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from ..constants import g, rho_l |
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from ..package_tools import Exporter |
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from ..units import check_units, units |
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exporter = Exporter(globals()) |
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@exporter.export |
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@check_units('[temperature]', '[pressure]', '[pressure]') |
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def precipitable_water(dewpt, p, top=400 * units('hPa')): |
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r"""Calculate precipitable water through the depth of a sounding. |
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Default layer depth is sfc-400 hPa. Formula used is: |
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.. math:: \frac{1}{pg} \int\limits_0^d x \,dp |
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from [Tsonis2008]_, p. 170. |
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Parameters |
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---------- |
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dewpt : array-like |
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Atmospheric dewpoint profile |
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p : array-like |
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Atmospheric pressure profile |
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top: `pint.Quantity` |
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The top of the layer, specified in pressure. |
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Returns |
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------- |
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`pint.Quantity` |
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The precipitable water in the layer, in inches |
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""" |
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sort_inds = np.argsort(p[::-1]) |
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p = p[sort_inds] |
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dewpt = dewpt[sort_inds] |
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pres_layer, dewpt_layer = get_layer(p, dewpt, depth=p[0] - top) |
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w = mixing_ratio(saturation_vapor_pressure(dewpt_layer), pres_layer) |
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# Since pressure is in decreasing order, pw will be the negative of what we want. |
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# Thus the *-1 |
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pw = -1. * (np.trapz(w.magnitude, pres_layer.magnitude) * (w.units * pres_layer.units) / |
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(g * rho_l)) |
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return pw.to('millimeters') |
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Unidata /
MetPy
