Value of bulk heat flux parameterizations for ocean SST prediction
Section snippets
Introduction and motivation
Ocean general circulation model (OGCM) simulations are generally performed using prescribed atmospheric forcing fields, namely, momentum flux (e.g., wind stress) and scalar forcing (e.g., net shortwave and longwave radiation at the sea surface, air temperature and air mixing ratio at 10 m above the sea surface). These forcing fields are typically obtained from archived NWP products. Examples of commonly-used NWP products include the European Centre for Medium-Range Weather Forecasts (ECMWF)
Bulk heat flux approach
The total heat flux (Qnet) at the sea surface can be expressed as follows:where Qsw is the net shortwave radiation at the sea surface, Qlw is the net longwave radiation at the sea surface, Ql is the latent heat flux, and Qs is the sensible heat flux.
All these individual components, and their total, Qnet, are typically available from the archived real-time and re-analysis data sets or from climatologies (ERA-15, ERA-40 and CORE-CNY are used here). Shortwave, Qsw, and longwave,
HYCOM description
The HYbrid Coordinate Ocean Model (HYCOM) is based on a primitive-equation formulation discussed by Bleck (2002), in detail. There have been several HYCOM applications investigating a variety of processes in different ocean basins and enclosed seas. Examples of such studies include the North Atlantic (Chassignet et al., 2003, Halliwell, 2004, Thacker et al., 2004), the Indian Ocean (Han et al., 2004), the tropical Pacific (Shaji et al., 2005), and the Black Sea (Kara et al., 2005a, Kara et al.,
HYCOM SST simulations
In this section, we investigate whether or not monthly mean SSTs obtained from atmospherically-forced HYCOM, which includes the effects of bulk parameterizations in its surface energy balance (see Section 2), is strongly controlled by the near-surface Ta used in the atmospheric forcing. The global HYCOM simulations presented in this paper were performed with no assimilation of any oceanic data except initialization from climatology. There is only weak relaxation to sea surface salinity to keep
Conclusions
The most significant result of this paper is that virtually all applications of the bulk formulae, including a fixed air temperature, does not make the sensible and latent heat behave as though the model SST tracks the near-surface air temperature too strongly. This is demonstrated using an atmospherically-forced OGCM (HYCOM) with no assimilation of any SST and no relaxation to any SST climatology.
Accurate SST simulations in an OGCM depend on how the local changes in SST made by the bulk
Acknowledgments
Two anonymous reviewers are thanked for their comments. The numerical HYCOM simulations were performed under the Department of Defense High Performance Computing Modernization Program on an IBM SP POWER3 at the Naval Oceanographic Office, Stennis Space Center, MS and on a HP/COMPAQ SC45 at the United States Army Engineer Research and Development Center (ERDC), Vicksburg, MS. This research is funded by the Office of Naval Research (ONR) under program element 601153N as part of the NRL 6.1 Global
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