OAFlux Project Description

The atmosphere interacts with the ocean through the exchange of heat, fresh water, and momentum at the air-sea interface. The air-sea heat exchange includes a number of processes: solar radiation, longwave radiation, sensible heat transfer by conduction and convection, and latent heat release by evaporation of sea surface water. The amount of heat exchange resulting from these radiative and turbulent heat transfer processes is called air-sea heat flux.

The air-sea flux to and from the ocean forces the atmospheric circulation and, at the same time, controls the ocean temperature. There is increasing evidence that the warming trend of ocean temperature has global impacts on climate. However, we cannot make further progress on understanding the mechanisms by which the ocean forces the atmosphere in the absence of good measures of air-sea exchanges.

Direct measurements of air-sea fluxes are too few to contribute directly to the compilation of the flux field on the global-scale. Our knowledge of the mean and variability of global air-sea fluxes has been gained mainly through the parameterizations of observed basic surface meteorological variables (such as wind speed, temperature, humidity, cloud cover, etc.). The observed quantities are obtainable from ship meteorological reports and satellite retrievals. They are also produced from the numerical weather prediction (NWP) models. However, none of the three data sources is error free. Each of them suffers at least one of the four deficiencies: (1) incomplete global coverage, (2) short spanning period, (3) systematic bias, and (4) random error.

The project takes an innovative approach, i.e., to produce a synthesized flux product with improved resolution and improved quality through synthesizing the advantages in existing data sources. Synthesis denotes the process of using an advanced objective analysis approach to combine different data sources with different characteristics. Such a process reduces the errors in data and produces an estimate that has the minimum error variance at the solution.

The objective of the OAFlux project is to produce an enhanced analysis of surface latent, sensible, net shortwave and net longwave radiation fluxes of the global oceans over the past 50 years (from mid-1950s onward). This is to be achieved by an appropriate combination of satellite retrievals, ship reports from Comprehensive Ocean-Atmosphere Data Set (COADS), and surface meteorology from NWP reanalysis outputs by using advanced objective analysis. The target resolution is 1° longitude by 1° latitude and daily for the satellite era (from early 1980s to present) and monthly for the years prior. For detailed descriptions of the project and products, please refer to the project report by Yu et al. (2008).

March 2004: Released the first version. Daily analysis for the Atlantic Ocean (1988-1999).
December 2005: Released the second version. Daily analysis for the global oceans (1981-2002).
January 2008: A 49-year (1958-2006) analysis of latent and sensible heat fluxes, ocean evaporation, and flux-related surface meteorological variables.