NFLUX Flux Estimates

Surface fluxes at the air-sea interface are used to provide the forcing in ocean model forecasting. Depending on the application of the ocean model, the surface fluxes can be obtained from different sources. The goal of the NRL Ocean Surface Flux (NFLUX) system is to provide gridded surface fluxes over the global ocean in near-real time for operational use. The surface fluxes of interest include the sensible and latent heat fluxes, as well as the longwave and shortwave radiative fluxes. The fluxes produced by NFLUX are compared to fluxes estimated from the current operational model used by the Navy, the Navy Global Environmental Model (NAVGEM), and validated against in situ observations.

The original global surface fields produced by NFLUX include surface air temperature, specific humidity, and scalar wind speed. These fields are generated by 2D variational analyses of (automated) quality controlled in situ and satellite observations with atmospheric model forecasts. The satellite observations include a combination of observed brightness temperatures from the Special Sensor Microwave Imager Sounder (SSMIS), the Advanced Microwave Sounding Unit-A (AMSU-A), and the Advanced Technology Microwave Sensor (ATMS) converted into state parameters and scalar wind speed environmental data records from the WindSat sensor, the Advanced Scatterometer (ASCAT), and the Oceansat-2 Scatterometer (OSCAT). The COARE 3.0 bulk algorithm may then be applied to the surface state parameter fields to produce global estimates of sensible and latent heat fluxes at the air-sea interface.

The NFLUX system has now been expanded to include radiative flux estimates. Both the longwave and shortwave surface radiative fluxes are produced using the Rapid Radiative Transfer Model for Global Circulation Models (RRTM-G). The primary inputs to the RRTM-G are from the Microwave Integrated Retrieval System (MIRS) and include the temperature and moisture profiles, as well as cloud liquid and ice water paths. Additional inputs include global sea surface temperature from daily 10km fields produced by the Naval Oceanographic Office (NAVO), global sea level pressure from an atmospheric model, and a cloud height climatology derived from the International Satellite Cloud Climatology Project (ISCCP).