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Martin Flügge
,
Mostafa Bakhoday Paskyabi
,
Joachim Reuder
,
James B. Edson
, and
Albert J. Plueddemann

Abstract

Direct covariance flux (DCF) measurements taken from floating platforms are contaminated by wave-induced platform motions that need to be removed before computation of the turbulent fluxes. Several correction algorithms have been developed and successfully applied in earlier studies from research vessels and, most recently, by the use of moored buoys. The validation of those correction algorithms has so far been limited to short-duration comparisons against other floating platforms. Although these comparisons show in general a good agreement, there is still a lack of a rigorous validation of the method, required to understand the strengths and weaknesses of the existing motion-correction algorithms. This paper attempts to provide such a validation by a comparison of flux estimates from two DCF systems, one mounted on a moored buoy and one on the Air–Sea Interaction Tower (ASIT) at the Martha’s Vineyard Coastal Observatory, Massachusetts. The ASIT was specifically designed to minimize flow distortion over a wide range of wind directions from the open ocean for flux measurements. The flow measurements from the buoy system are corrected for wave-induced platform motions before computation of the turbulent heat and momentum fluxes. Flux estimates and cospectra of the corrected buoy data are found to be in very good agreement with those obtained from the ASIT. The comparison is also used to optimize the filter constants used in the motion-correction algorithm. The quantitative agreement between the buoy data and the ASIT demonstrates that the DCF method is applicable for turbulence measurements from small moving platforms, such as buoys.

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I. A. Renfrew
,
R. S. Pickart
,
K. Våge
,
G. W. K. Moore
,
T. J. Bracegirdle
,
A. D. Elvidge
,
E. Jeansson
,
T. Lachlan-Cope
,
L. T. McRaven
,
L. Papritz
,
J. Reuder
,
H. Sodemann
,
A. Terpstra
,
S. Waterman
,
H. Valdimarsson
,
A. Weiss
,
M. Almansi
,
F. Bahr
,
A. Brakstad
,
C. Barrell
,
J. K. Brooke
,
B. J. Brooks
,
I. M. Brooks
,
M. E. Brooks
,
E. M. Bruvik
,
C. Duscha
,
I. Fer
,
H. M. Golid
,
M. Hallerstig
,
I. Hessevik
,
J. Huang
,
L. Houghton
,
S. Jónsson
,
M. Jonassen
,
K. Jackson
,
K. Kvalsund
,
E. W. Kolstad
,
K. Konstali
,
J. Kristiansen
,
R. Ladkin
,
P. Lin
,
A. Macrander
,
A. Mitchell
,
H. Olafsson
,
A. Pacini
,
C. Payne
,
B. Palmason
,
M. D. Pérez-Hernández
,
A. K. Peterson
,
G. N. Petersen
,
M. N. Pisareva
,
J. O. Pope
,
A. Seidl
,
S. Semper
,
D. Sergeev
,
S. Skjelsvik
,
H. Søiland
,
D. Smith
,
M. A. Spall
,
T. Spengler
,
A. Touzeau
,
G. Tupper
,
Y. Weng
,
K. D. Williams
,
X. Yang
, and
S. Zhou

Abstract

The Iceland Greenland Seas Project (IGP) is a coordinated atmosphere–ocean research program investigating climate processes in the source region of the densest waters of the Atlantic meridional overturning circulation. During February and March 2018, a field campaign was executed over the Iceland and southern Greenland Seas that utilized a range of observing platforms to investigate critical processes in the region, including a research vessel, a research aircraft, moorings, sea gliders, floats, and a meteorological buoy. A remarkable feature of the field campaign was the highly coordinated deployment of the observing platforms, whereby the research vessel and aircraft tracks were planned in concert to allow simultaneous sampling of the atmosphere, the ocean, and their interactions. This joint planning was supported by tailor-made convection-permitting weather forecasts and novel diagnostics from an ensemble prediction system. The scientific aims of the IGP are to characterize the atmospheric forcing and the ocean response of coupled processes; in particular, cold-air outbreaks in the vicinity of the marginal ice zone and their triggering of oceanic heat loss, and the role of freshwater in the generation of dense water masses. The campaign observed the life cycle of a long-lasting cold-air outbreak over the Iceland Sea and the development of a cold-air outbreak over the Greenland Sea. Repeated profiling revealed the immediate impact on the ocean, while a comprehensive hydrographic survey provided a rare picture of these subpolar seas in winter. A joint atmosphere–ocean approach is also being used in the analysis phase, with coupled observational analysis and coordinated numerical modeling activities underway.

Open access