83rd Annual

Tuesday, 11 February 2003: 2:28 PM
Air-Sea Heat Exchange along the Northern Sea Surface Temperature Front in the Eastern Tropical Pacific
Nicolai Thum, Oregon State University, Corvallis, OR; and S. K. Esbensen, D. B. Chelton, and M. J. McPhaden
The atmospheric response to the oceanic forcing in the eastern Pacific along the northern equatorial sea surface temperature (SST) front is investigated in terms of sensible and latent heat flux during the 6-month period from 28 July 1999 through 27 January 2000 and the 7-month period from 28 June 2000 through 27 January 2001. Of particular interest is the atmospheric boundary layer (ABL) response to oceanic Tropical Instability Waves (TIWs) that distort the SST front during May through January in normal years. In previous studies, time series of surface heat fluxes clearly show the influence of TIWs but the relationship to spatial patterns of SST and wind speed has been inferred only from sparse in situ data.

In this study, satellite observations are used as a basis for compositing in situ data from moorings to compensate for the lack of a spatially dense mooring array. The variability in the position of the SST front caused by westward propagating TIWs enables fixed mooring locations to measure the atmospheric boundary layer response from a large range of locations relative to the front. The satellite data enable determination of the precise location of the mooring relative to the front. The advantage of this strategy is the recurring measurement of the ABL response to the SST front over the thirteen month period considered here.

The results indicate that the TIW-induced perturbations of sensible heat flux are spatially shifted in phase towards the east relative to the perturbations of SST. The maximum fluxes of sensible heat are not centered directly over the warmest water, but are shifted towards the portion of the frontal region where a disequilibrium boundary layer is expected due to the advection of colder air from the equatorial region. The latent heat flux pattern is approximately in phase with the SST, with only a slight shift to the east. The changes of sensible and latent heat fluxes across the SST front have typical magnitudes of about 12 Wm-2 and 125 Wm-2, respectively.

The sensible and latent heat flux patterns are interpreted in two complementary ways: (1) as an atmospheric response to the change of oceanic forcing as air flows across the SST front; and (2) as the atmospheric response to westward propagating TIWs along the SST front.

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