Re: equivalent potential temperature

From: Dennis Shea <shea_at_nyahnyahspammersnyahnyah>
Date: Mon, 18 May 2009 12:55:27 -0600

David Small wrote:
> Hi,
> Has anyone developed a function that will calculate equivalent potential
> temperature that doesn't assume saturation? Has anyone converted the
> wrf function wrf_eth.ncl to work for input that was not produced by the
> wrf model?
> Thanks,
> Dave Small
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The following is fortran code provided by PROFS.
I am sure it could be implemented in NCL.

real function ept(t,td,p)

c include 'lib_dev:[gudoc]edfvaxbox.for/list'
c baker, schlatter 17-may-1982 original version.

c this function returns the equivalent potential temperature ept
c (celsius) for a parcel of air initially at temperature t (celsius),
c dew point td (celsius) and pressure p (millibars). the formula used
c is eq.(43) in bolton, david, 1980: "the computation of equivalent
c potential temperature," monthly weather review, vol. 108, no. 7
c (july), pp. 1046-1053. the maximum error in ept in 0.3c. in most
c cases the error is less than 0.1c.
c compute the mixing ratio (grams of water vapor per kilogram of
c dry air).

w = wmr(p,td)

c compute the temperature (celsius) at the lifting condensation level.

tlcl = tcon(t,td)
tk = t+273.15
tl = tlcl+273.15
pt = tk*(1000./p)**(0.2854*(1.-0.00028*w))
eptk = pt*exp((3.376/tl-0.00254)*w*(1.+0.00081*w))
ept= eptk-273.15

Dennis J. Shea                  tel: 303-497-1361    |
P.O. Box 3000                   fax: 303-497-1333    |
Climate Analysis Section                             |
Climate & Global Dynamics Div.                       |
National Center for Atmospheric Research             |
Boulder, CO  80307                                   |
USA                        email: shea 'at' |
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Received on Mon May 18 2009 - 12:55:27 MDT

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