Between air and sea

 NCAR scientists Bill Large and Steve Yeager have produced a new analysis of the exchanges of heat, momentum, and moisture between the oceans and atmosphere that should help climate modelers better assess variability on several time scales. In a paper for Climate Dynamics published online in August, they calculated all the air-sea flux components for the period 1984 through 2006, and some components from as far back as 1948.

Bill and Steve corrected global long-term data sets from several sources—including the National Centers for Environmental Prediction reanalysis, the International Satellite Cloud Climatology Project, and NASA’s rainfall-measuring missions—by comparing them to a variety of short-term and regional data sources. With these revisions, they obtained generally higher global winds, lower average atmospheric humidity, less solar radiation in the tropics, and more consistent rainfall than in the original products.

The study also found wide interdecadal variations in the worldwide exchange of heat between air and sea. The global averages ranged from 7.3 watts per square meter (1977–1986) to –0.3 W/m2 (1997–2006), with positive numbers indicating a net downward flux. “Events such as El Niño are reflected in the data as a reduced downward heat flux, because the warmer tropical ocean takes less heat from the atmosphere,” says Bill.

The new flux data were designed to serve as a consistent, balanced forcing for ocean and sea-ice models, but they will also allow scientists to better assess how accurately global models are depicting climate variability from year to year and decade to decade. The research was supported by a NOAA grant and NSF.


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