COMPARISON OF SEA-SURFACE FLUX MEASURED BY INSTRUMENTED AIRCRAFT AND SHIP DURING SOFIA AND SEMAPHORE EXPERIMENTS

Citation
P. Durand et al., COMPARISON OF SEA-SURFACE FLUX MEASURED BY INSTRUMENTED AIRCRAFT AND SHIP DURING SOFIA AND SEMAPHORE EXPERIMENTS, J GEO RES-O, 103(C11), 1998, pp. 25125-25136
Citations number
43
Categorie Soggetti
Oceanografhy,"Geosciences, Interdisciplinary","Astronomy & Astrophysics","Geochemitry & Geophysics","Metereology & Atmospheric Sciences
Journal title
JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS
ISSN journal
21699275 → ACNP
Volume
103
Issue
C11
Year of publication
1998
Pages
25125 - 25136
Database
ISI
SICI code
2169-9275(1998)103:C11<25125:COSFMB>2.0.ZU;2-5
Abstract
Two major campaigns (Surface of the Oceans, Fluxes and Interactions wi th the Atmosphere (SOFIA) and Structure des Echanges Mer-Atmosphere, P roprietes des Heterogeneites Oceaniques : Recherche Experimentale (SEM APHORE)) devoted to the study of ocean-atmosphere interaction were con ducted in 1992 and 1993, respectively, in the Azores region. Among the various platforms deployed, instrumented aircraft and ship allowed th e measurement of the turbulent flux of sensible heat, latent heat, and momentum. From coordinated missions we can evaluate the sea surface f luxes from (1) bulk relations and mean measurements performed aboard t he ship in the atmospheric surface layer and (2) turbulence measuremen ts aboard aircraft, which allowed the flux profiles to be estimated th rough the whole atmospheric boundary layer and therefore to be extrapo lated toward the sea surface level. Continuous ship fluxes were calcul ated with bulk coefficients deduced from inertial-dissipation measurem ents in the same experiments, whereas aircraft fluxes were calculated with eddy-correlation technique. We present a comparison between these two estimations. Although momentum flux agrees quite well, aircraft e stimations of sensible and latent heat flux are lower than those of th e ship. This result is surprising, since aircraft momentum flux estima tes are often considered as much less accurate than scalar flux estima tes. The various sources of errors on the aircraft and ship flux estim ates are discussed. For sensible and latent heat flux, random errors o n aircraft estimates, as well as variability of ship flux estimates, a re lower than the discrepancy between the two platforms, whereas the m omentum flu?: estimates cannot be considered as significantly differen t. Furthermore, the consequence of the high-pass filtering of the airc raft signals on the flux values is analyzed; it is weak at the lowest altitudes flown and cannot therefore explain the discrepancies between the two platforms but becomes considerable at upper levels in the bou ndary layer. From arguments linked to the imbalance of the surface ene rgy budget, established during previous campaigns performed over land surfaces with aircraft, we conclude that aircraft heat fluxes are prob ably also under-estimated over the sea.