Path: utzoo!utgpu!watmath!uunet!lll-winken!uwm.edu!mailrus!rutgers!njin!princeton!phoenix!djboccip
From: djboccip@phoenix.Princeton.EDU (Dennis Joseph Boccippio)
Newsgroups: bionet.agroforestry
Subject: Energy balance ...
Message-ID: <10387@phoenix.Princeton.EDU>
Date: 12 Sep 89 20:47:54 GMT
Reply-To: djboccip@phoenix.Princeton.EDU ()
Organization: Geophysical Fluid Dynamics Laboratory, Princeton
Lines: 36


   Hello, bionet.agroforestry...

   Here's a random call for anyone out there doing energy balance
modeling of terrestrial systems (e.g., soil surface, crop, or forest...)
I am constructing a hydrologic / energy balance model of a local basin
using historical temperature, precipitation, cloud cover, etc. records
and am investigating various methods of estimating evapotranspiration.
Unfortunately, the conventional energy balance equation, when applied
with pre-specified air temperatures, is extremely sensitive to bulk
transfer coefficients in the latent and sensible heat transfer terms,
thus:

           net radiation (down solar + down longwave - up longwave) =
                   sensible heat + latent heat

           sensible heat = H = (Ch) (cp) (u) (Tsurf - Tatm) 
           latent heat   = LE = (const) (Ce) (u) (Qsat - Qair)

           Where Ch, Ce are the bulk transfer coefficients, u is
              windspeed, Tsurf is surface temperature, Q is specific humidity,
              etc.  

   Unfortunately, the bulk transfer / drag coefficients, although
well-known for open-water surfaces, are extremely difficult to compute
over land surfaces, especially when averaging over large areas.

   Has anyone had experience with estimating drag coefficients over
large land / canopy areas, or similar experiences with large scale
energy balance modeling??? Any suggestions, references, etc. would be
really helpful... 

   Thanks in advance...

                                 D.J. Boccippio at GFDL, Princeton