Enhancement of Tropical Ocean Evaporation and Sensible Heat Flux by Atmospheric Mesoscale Systems

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  • 1 College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon
  • 2 NOAA/Pacific Marine Environmental Laboratory, Seattle, Washington
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Abstract

The enhancement of monthly averaged evaporation by atmospheric mesoscale systems is estimated from long-term hourly observations of surface meteorological data from the Tropical Ocean Global Atmosphere (TOGA) Tropical Atmosphere Ocean (TAO) buoy moorings over the equatorial Pacific Ocean and a bulk aerodynamic flux algorithm developed as a result of the TOGA Coupled Ocean–Atmosphere Response Experiment (COARE). It is shown that mesoscale enhancement is due primarily to the lack of wind steadiness on subsynoptic timescales and is associated with periods of significant precipitation.

The magnitude of the mesoscale enhancement of monthly averaged sea surface evaporation is found to be ∼10% or less of the total. During occasional periods with weak and variable winds over the western Pacific warm pool and the other major precipitation zones in the equatorial Pacific, the mesoscale enhancement of monthly averaged evaporation can reach 30% of the total evaporation.

A similar result is obtained for mesoscale enhancement of diffusive air–sea sensible heat transfer using data from TOGA TAO moorings. However, a comparison of results from the colocated TAO and Improved METeorological measurements (IMET) moorings during TOGA COARE, and results previously reported from a pre COARE cruise in the western Pacific warm pool region, indicate that processes in addition to mesoscale wind variability may be important contributors to the mesoscale enhancement of the sensible heat flux.

It is suggested that the most important effects of atmospheric mesoscale systems on tropical ocean evaporation and sensible heat flux are represented in existing climatologies.

Abstract

The enhancement of monthly averaged evaporation by atmospheric mesoscale systems is estimated from long-term hourly observations of surface meteorological data from the Tropical Ocean Global Atmosphere (TOGA) Tropical Atmosphere Ocean (TAO) buoy moorings over the equatorial Pacific Ocean and a bulk aerodynamic flux algorithm developed as a result of the TOGA Coupled Ocean–Atmosphere Response Experiment (COARE). It is shown that mesoscale enhancement is due primarily to the lack of wind steadiness on subsynoptic timescales and is associated with periods of significant precipitation.

The magnitude of the mesoscale enhancement of monthly averaged sea surface evaporation is found to be ∼10% or less of the total. During occasional periods with weak and variable winds over the western Pacific warm pool and the other major precipitation zones in the equatorial Pacific, the mesoscale enhancement of monthly averaged evaporation can reach 30% of the total evaporation.

A similar result is obtained for mesoscale enhancement of diffusive air–sea sensible heat transfer using data from TOGA TAO moorings. However, a comparison of results from the colocated TAO and Improved METeorological measurements (IMET) moorings during TOGA COARE, and results previously reported from a pre COARE cruise in the western Pacific warm pool region, indicate that processes in addition to mesoscale wind variability may be important contributors to the mesoscale enhancement of the sensible heat flux.

It is suggested that the most important effects of atmospheric mesoscale systems on tropical ocean evaporation and sensible heat flux are represented in existing climatologies.

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