djboccip@phoenix.Princeton.EDU (Dennis Joseph Boccippio) (09/13/89)
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