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Observing System Products

Ocean-Atmosphere Heat Flux and Ocean Evaporation

Air-sea fluxes, which exchange energy between the ocean and atmosphere, are key climatic processes that influence oceanic and atmospheric circulatation, timing and extent of redistribution of heat from the tropics to the poles, and global and regional precipitation patterns. Precise quantification of energy fluxes, which at certain regions and times can reach tens-to-hundreds of watts/m2, are necessary to close the energy balance of the Earth (i.e., to determine the extent to which the Earth is warming or cooling) to within the few watts/m2 representative of greenhouse warming. Despite the difficulty of deploying and maintaining instruments capable of the requisite accuracy and precision for long periods of time in a hostile ocean environment, numerous measurements of energy fluxes are made on Ocean Reference Stations and Tropical Moored Buoys.

Schematic diagram of the physical exchange processes at the air-sea interface and the upper ocean responses

Schematic diagram of the physical exchange processes at the air-sea interface and the upper ocean responses, with corresponding sensor names shown in red. From Lisan Yu, Sea surface exchanges of momentum, heat, and freshwater determined by satellite remote sensing.

Because heating and cooling vary sharply over the surface of the ocean, it is necessary to evaluate air-sea fluxes with much higher spatial resolution than that possible from just a handful of in situ measurement stations scattered over the ocean surface. To this end, satellite-based observations of sea surface temperatures and near-surface winds are combined with atmospheric humidities inferred from numerical weather prediction models to derive heat fluxes over the ocean. These fluxes are "calibrated" through use of a statistical methodology that combines the sparse but highly accurate network of in situ observations with the geographically dense but less accurate remotely sensed observations.

Utilizing these methods, scientists at the Woods Hole Oceanographic Institution, working in concert with the Ocean Climate Observation Program, have developed and routinely disseminate the Objectively Analyzed Air-Sea Fluxes (OAFlux) product, which provides daily analyses of heat and total energy fluxes over the world's oceans, as well as related fields of wind and humidity.

Heating the ocean surface causes evaporation of sea water, which in turn provides the source of the vast majority of precipitation. Because evaporation is intimately related to heat flux it is possible to utilize the OAFlux data and methodologies to derive an evaporation product, which is also routinely made available to the public by the Woods Hole group.

Additional analyses at the Florida State University Center for Ocean-Atmosphere Prediction Studies focus on improvement of methodologies for deriving ocean-atmosphere fluxes. Flux products include research-quality monthly FSU3 fluxes, based solely on in situ ocean data, and ocean wind products, derived from in situ and satellite data.