Aircraft-based observations of air–sea turbulent ﬂuxes around the British Isles
Cook, P. A. and Renfrew, I. A. (2014) Aircraft-based observations of air–sea turbulent ﬂuxes around the British Isles. Quarterly Journal of the Royal Meteorological Society, 141 (686). pp. 139-152. ISSN 1477-870X
To link to this article DOI: 10.1002/qj.2345
Observations of turbulent ﬂuxes of momentum, heat and moisture from low-level aircraft data are presented. Fluxes are calculated using the eddy covariance technique from ﬂight legs typically ∼40 m above the sea surface. Over 400 runs of 2 min (∼12 km) from 26 ﬂights are evaluated. Flight legs are mainly from around the British Isles although a small number are from around Iceland and Norway. Sea-surface temperature (SST) observations from two on-board sensors (the ARIES interferometer and a Heimann radiometer) and a satellite-based analysis (OSTIA) are used to determine an improved SST estimate. Most of the observations are from moderate to strong wind speed conditions, the latter being a regime short of validation data for the bulk ﬂux algorithms that are necessary for numerical weather prediction and climate models. Observations from both statically stable and unstable atmospheric boundary-layer conditions are presented. There is a particular focus on several ﬂights made as part of the DIAMET (Diabatic inﬂuence on mesoscale structures in extratropical storms) project. Observed neutral exchange coefﬁcients are in the same range as previous studies, although higher for the momentum coefﬁcient, and are broadly consistent with the COARE 3.0 bulk ﬂux algorithm, as well as the surface exchange schemes used in the ECMWF and Met Ofﬁce models. Examining the results as a function of aircraft heading shows higher ﬂuxes and exchange coefﬁcients in the across-wind direction, compared to along-wind (although this comparison is limited by the relatively small number of along-wind legs). A multi-resolution spectral decomposition technique demonstrates a lengthening of spatial scales in along-wind variances in along-wind legs, implying the boundary-layer eddies are elongated in the along-wind direction. The along-wind runs may not be able to adequately capture the full range of turbulent exchange that is occurring because elongation places the largest eddies outside of the run length.