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Last change
on this file since 205 was
183,
checked in by aslmd, 14 years ago
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MESOSCALE: PYTHON: added pywrf r39 to act as a reference for futher developments
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File size:
1.0 KB
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| [183] | 1 | ''' |
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| 2 | Useful met formulas |
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| 3 | ''' |
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| 4 | import numpy as n |
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| 5 | import constants as c |
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| 6 | |
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| 7 | def goff_gratch(temperature): |
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| 8 | ''' |
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| 9 | computes saturation water pressure from temperature (in Kelvin) |
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| 10 | ref Smithsonian Tables 1984, after Goff and Gratch 1946 |
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| 11 | usage: |
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| 12 | goff_gratch(temperature) |
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| 13 | ''' |
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| 14 | exponent = \ |
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| 15 | - 7.90298 * (373.16/temperature - 1) \ |
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| 16 | + 5.02808 * n.log10(373.16 / temperature) \ |
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| 17 | - 1.3816e-7 * (10**(11.344 * (1-temperature/373.16)) -1) \ |
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| 18 | + 8.1328e-3 * (10**(-3.49149 * (373.16/temperature-1)) -1) \ |
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| 19 | + n.log10(1013.246) |
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| 20 | return 10**exponent |
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| 21 | |
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| 22 | def water_vapour_pressure_to_mix_ratio(pressure, water_vapour_pressure): |
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| 23 | ''' |
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| 24 | computes the mixing ratio given the total pressure and the water vapour |
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| 25 | partial pressure |
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| 26 | usage: |
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| 27 | water_vapour_pressure_to_mix_ratio(pressure, water_vapour_pressure) |
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| 28 | ''' |
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| 29 | coeff = c.water_molecular_weight / c.air_molecular_weight |
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| 30 | dry_air_pressure = pressure - water_vapour_pressure |
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| 31 | return coeff * water_vapour_pressure / dry_air_pressure |
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