Aircraft Observations of Sea-Surface Turbulent Fluxes Near the California Coast |
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Authors: | John Kalogiros Qing Wang |
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Institution: | (1) Physics Department, Mangalagangotri, Mangalore University, Mangalore, India;(2) Indira Gandhi Centre for Atomic Research, Kalpakkam, India |
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Abstract: | Aircraft turbulence data from the Autonomous Ocean Sampling Network project were analyzed and compared to the Coupled Ocean–Atmosphere
Response Experiment (COARE) bulk parametrization of turbulent fluxes in an ocean area near the coast of California characterized
by complex atmospheric flow. Turbulent fluxes measured at about 35 m above the sea surface using the eddy-correlation method
were lower than bulk estimates under unstable and stable atmospheric stratification for all but light winds. Neutral turbulent
transfer coefficients were used in this comparison because they remove the effects of mean atmospheric conditions and atmospheric
stability. Spectral analysis suggested that kilometre-scale longitudinal rolls affect significantly turbulence measurements
even near the sea surface, depending on sampling direction. Cross-wind sampling tended to capture all the available turbulent
energy. Vertical soundings showed low boundary-layer depths and high flux divergence near the sea surface in the case of sensible
heat flux but minimal flux divergence for the momentum flux. Cross-wind sampling and flux divergence were found to explain
most of the observed discrepancies between the measured and bulk flux estimates. At low wind speeds the drag coefficient determined
with eddy correlation and an inertial dissipation method after corrections were applied still showed high values compared
to bulk estimates. This discrepancy correlated with the dominance of sea swell, which was a usually observed condition under
low wind speeds. Under stable atmospheric conditions measured sensible heat fluxes, which usually have low values over the
ocean, were possibly affected by measurement errors and deviated significantly from bulk estimates. |
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