Re: Vapor Pressure and Saturated Vapor Pressure

Thanks for the reply.

I am attempting to calculate PenPan from variables in CLM.
Of many variables for PenPan, two I need are: Vapor Pressure and
Saturated Vapor Pressure
but I have yet to find a function in NCL that will calculate them.

My approach was to use the code from the Relhum function. However,
when I search through the 'contributed.ncl' file, the only calculation
I can find for Relhum was with dew point temperature (I do not have
dew point). Yet, the Relhum function calls Pressure, Temperature, and
Mixing Ratio.

I am also checking my work by understanding how NCL contributed
calculates Relhum (I am using Relhum for other processes), as I am
trying to learn how NCL calculates its functions.

Thank you,

-Jonathan

On Apr 13, 2011, at 10:25 PM, Dennis Shea wrote:

> The following is fortran but writing and NCL functio to
> do this would be trivial.
>
> real function esat(t)
> c NCLEND
>
> c include 'lib_dev:[gudoc]edfvaxbox.for/list'
> c g.s. stipanuk 1973 original version.
> c reference stipanuk paper entitled:
> c "algorithms for generating a skew-t, log p
> c diagram and computing selected meteorological
> c quantities."
> c atmospheric sciences laboratory
> c u.s. army electronics command
> c white sands missile range, new mexico 88002
> c 33 pages
> c baker, schlatter 17-may-1982
>
> c this function returns the saturation vapor pressure over
> c water (mb) given the temperature (celsius).
> c the algorithm is due to nordquist, w.s.,1973: "numerical
> approxima-
> c tions of selected meteorlolgical parameters for cloud physics
> prob-
> c lems," ecom-5475, atmospheric sciences laboratory, u.s. army
> c electronics command, white sands missile range, new mexico 88002.
>
> tk = t+273.15
> p1 = 11.344-0.0303998*tk
> p2 = 3.49149-1302.8844/tk
> c1 = 23.832241-5.02808*alog10(tk)
> esat = 10.**(c1-1.3816e-7*10.**p1+8.1328e-3*10.**p2-2949.076/
> tk)
> return
> end
>
> or
>
> C NCLFORTSTART
> real function es(t)
> c NCLEND
>
> c this function returns the saturation vapor pressure es (mb) over
> c liquid water given the temperature t (celsius). the formula
> appears
> c in bolton, david, 1980: "the computation of equivalent potential
> c temperature," monthly weather review, vol. 108, no. 7 (july),
> c p. 1047, eq.(10). the quoted accuracy is 0.3% or better for
> c -35 < t < 35c.
>
> c include 'lib_dev:[gudoc]edfvaxbox.for/list'
> c baker, schlatter 17-may-1982 original version.
>
> c es0 = saturation vapor pressure over liquid water at 0c
>
> data es0/6.1121/
> es = es0*exp(17.67*t/(t+243.5))
> return
> end
>
> ---
> If you have the dw point temperature you can solve for the vapor
> pressure using the following
>
> C NCLFORTSTART
> real function dewpt(ew)
> c NCLEND
>
> c this function yields the dew point dewpt (celsius), given the
> c water vapor pressure ew (millibars).
> c the empirical formula appears in bolton, david, 1980:
> c "the computation of equivalent potential temperature,"
> c monthly weather review, vol. 108, no. 7 (july), p. 1047, eq.(11).
> c the quoted accuracy is 0.03c or less for -35 < dewpt < 35c.
>
> c include 'lib_dev:[gudoc]edfvaxbox.for/list'
> c baker, schlatter 17-may-1982 original version.
>
> enl = alog(ew)
> dewpt = (243.5*enl-440.8)/(19.48-enl)
> return
> end
>
>
>
>
>
>
> On 4/13/11 6:08 PM, jrbuzan wrote:
>> I am attempting to calculate Vapor Pressure and Saturated Vapor
>> Pressure, but I have yet to find a function.
>> My approach was to use the code from the Relhum function. However,
>> when I search through the 'contributed.ncl' file, the only
>> calculation
>> I can find for Relhum was with dew point temperature.
>>
>> Yet, the Relhum function calls Pressure, Temperature, and Mixing
>> Ratio.
>>
>> Any help?
>>
>> -Jonathan
>> _______________________________________________
>> ncl-talk mailing list
>> List instructions, subscriber options, unsubscribe:
>> http://mailman.ucar.edu/mailman/listinfo/ncl-talk

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Received on Thu Apr 14 12:36:48 2011