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- vapor_press(variables, missing=1e+20)
- Calculate vapor pressure over liquid water.
Method Arguments:
* variables: A dictionary of input state variables, where for
each key:value pair the key labels what state variable it is
and the value is the state variable. The value is a Numeric
floating point array of any number of dimensions and size.
All state variables must be arrays of the same shape and size.
Argument |variables| can have any number of items. Key values
may be any value, but the values that are understood by this
function include:
+ 'esat': Saturation vapor pressure over water [hPa].
+ 'p': Total pressure [hPa].
+ 'q': Specific humidity [kg/kg].
+ 'r': Mixing ratio [kg/kg].
+ 'RH': Relative humidity (based on esat) [fraction].
* missing: If any array in |variables| has elements that are
missing values, this is the missing value value. Floating
point scalar. Default is 1e+20.
Output:
* Vapor pressure [hPa]. Numeric array of same dimensions and
size as state variables in the argument. If there are any
missing values in output, those values are set to the value
in argument |missing| from the input. If there are missing
values in the output due to math errors and |missing| is set
to None, output will fill those missing values with the MA
default value of 1e+20.
Vapor pressure can be calculated from a variety of different
combinations of state variables. In this function, the follow-
ing combinations are supported:
* Mixing ratio and total pressure,
* Specific humidity and total pressure,
* Relative humidity and saturation vapor pressure over water.
The function will automatically apply the correct equation
depending on what key values are available in the |variables|
dictionary. An error is returned if none of the above combina-
tions are present in |variables|.
References:
* Emanuel, K. A. (1994): Atmospheric Convection. New York, NY:
Oxford University Press, 580 pp.
* Wallace, J. M., and P. V. Hobbs (1977): Atmospheric Science:
An Introductory Survey. San Diego, CA: Academic Press, ISBN
0-12-732950-1, 467 pp.
Example without missing values:
>>> from vapor_press import vapor_press
>>> import Numeric as N
>>> p = N.array([1026.8, 840.2, 640.3, 450.2])
>>> r = N.array([5.5e-3, 5.4e-3, 6.2e-3, 3.9e-3])
>>> e = vapor_press({'p':p, 'r':r})
>>> ['%.9g' % e[i] for i in range(len(e))]
['9.00051379', '7.23209979', '6.31989271', '2.80541885']
Example with missing values:
>>> from vapor_press import vapor_press
>>> import Numeric as N
>>> p = N.array([1026.8, 840.2, 1e+20, 450.2])
>>> r = N.array([5.5e-3, 5.4e-3, 6.2e-3, 3.9e-3])
>>> e = vapor_press({'p':p, 'r':r}, missing=1e+20)
>>> ['%.9g' % e[i] for i in range(len(e))]
['9.00051379', '7.23209979', '1e+20', '2.80541885']
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