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59 lines
2.3 KiB
Python
59 lines
2.3 KiB
Python
##
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# This software was developed and / or modified by Raytheon Company,
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# pursuant to Contract DG133W-05-CQ-1067 with the US Government.
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#
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# U.S. EXPORT CONTROLLED TECHNICAL DATA
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# This software product contains export-restricted data whose
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# export/transfer/disclosure is restricted by U.S. law. Dissemination
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# to non-U.S. persons whether in the United States or abroad requires
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# an export license or other authorization.
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#
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# Contractor Name: Raytheon Company
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# Contractor Address: 6825 Pine Street, Suite 340
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# Mail Stop B8
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# Omaha, NE 68106
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# 402.291.0100
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#
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# See the AWIPS II Master Rights File ("Master Rights File.pdf") for
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# further licensing information.
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##
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# ----------------------------------------------------------------
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# Calculate Specific Humidity (g/Kg) from Pressure, Temperature and
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# Relative Humidity.
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# ----------------------------------------------------------------
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from numpy import exp
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from numpy.ma.core import masked_greater
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from numpy.ma.core import masked_values
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from numpy.ma.core import filled
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def execute(*args):
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if len(args) == 2:
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"Calculate specific humidity (SHx) from pressure and vapor pressure"
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# From the old C version:
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# formula is 1000*epsilon*e/(p-(1-epsilon)*e), where
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# p is pressure, e is vapor pressure, and epsilon is the
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# constant 0.622. For evaluation, 622.0 (1000*epsilon) is
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# divided into the constants in the denominator.
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# p is input field 0, e is input field 1. The 100.0 in
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# the first constant is converting mb to pascals.
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P=args[0]
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VPP=args[1]
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oneMinusEpsilon = 0.378
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epsilonTimes1000 = 622
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num = 100.0/epsilonTimes1000 * VPP
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dnm = P - ((oneMinusEpsilon/epsilonTimes1000) * VPP)
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SHx = num / dnm
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return SHx
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else:
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"Calculate specific humidity (SHx) from pressure, temperature, and \
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relative humidity."
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# Get masked arrays so results for out-of-range values aren't generated
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Pma = args[0]
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Tma = args[1]
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RHma = args[2]
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# do the math
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eee = RHma*exp(28.48859-0.0091379024*Tma-6106.396/Tma)
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SHx = eee/(Pma-0.00060771703*eee)
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return SHx
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