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
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.