Hi,
This email discusses the issue of why there are extra heat fluxes in
ocean models with an open water budget, relative to ocean models that
artificially close their water budget (i.e., ocean models employing a
virtual tracer flux). I originally thought it best to have this
discussion off-line, but some contacted me asking to continue online...
Stephen
Stephen Griffies wrote:
Karl and Jonathan,
1/ Regarding pressures: Jonathan, I am fine keeping the original names.
I will report back to the list with this point.
2/ Regarding the temperature fluxes: Jonathan, I am again happy
returning to the names that we originally came up with. More generally,
here are some comments...
The issue of heat fluxes associated with the transfer of mass or volume
across the ocean boundary is a relatively new issue for CMIP. Indeed,
from my understanding, GFDL was perhaps amongst only one or two other
coupled models in AR4 that considered material transport across the
ocean surface associated with E-P+R. Delworth etal (2006) discussed the
point in its heat budget discussion. The remaining coupled models have a
closed water budget for the ocean (i.e., use virtual tracer fluxes). We
are not interested in retaining virtual tracer fluxes, and so had to
consider the implications of opening up the ocean to mass transport with
the atmosphere and land. Doing so adds this extra heat transfer term. We
wish to have a means for CMIP5 to record this term. It is clearly
written in the WGOMD report that virtual flux models will record zero
for this heat.
To reiterate what we have already said: the transport of material
substance (water) across the seawater boundary has an associated
transfer of tracer mass. Correspondingly, there is a transfer of
tracer, including heat, since the water carries a nonzero temperature
and nonzero tracer concentration. For many cases, the water is fresh,
so it only carries a heat. But some river models are being considered
that carry tracer concentration. If we remove water (e.g., through
evaporation), then we remove heat. The heat transfer associated with
phase changes is in ADDITION to the heat associated with mass transport.
Most modelers consider rain falling into the ocean to enter at the SST,
as well as the water evaporating to be at the SST. But how one
specifies the tracer concentration or temperature of the water
transferred across the boundary is not relevant to the discussion. All
I wish to have is the total amount of heat transferred to/from the ocean
with the water mass, referenced to 0C.
As Karl noted, atmospheric models generally do not carry a temperature
for the moisture. But this present limitation of the atmospheric models
should not force us to shut down the ocean's water cycle. That decision
would lead us back to virtual tracer fluxes, which are not desirable
from an oceanographic perspective. Atmospheric modelers inform me that
the non-conservation associated with not carrying temperature of their
moisture is small, so I should quit bothering them with this issue...
Steve
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