Physical Oceanography, Vol. 17, No. 1, 2007
FIELD MEASUREMENTS OF THE VERTICAL SHEARS FOR A DRIFT CURRENT
V. A. Dulov,
V. N. Kudryavtsev,
V. I. Shrira,
V. E. Smolov,
and A. N. Bol’shakov
We describe the procedure of field experiments aimed at measuring the vertical profiles of the
vectors of a drift current with the help of quasi-Lagrangian drifters. We present the data on the
vertical shears of the current at depths of
obtained under the conditions of neutral strati-
fication in the upper
5-m layer of the sea in the presence of weak and moderate winds. The cor-
respondence of the obtained data to the concept according to which the subsurface layer of the
sea is regarded as a near-wall turbulent layer with Ekman current located below is analyzed. A
conclusion is made that the results of measurements correspond, on the average, to the classical
concepts demonstrating both the region of logarithmic sublayer and its transition into the Ekman
The processes running on the sea surface and in the upper layer of the ocean (several meters in depth) play
an extremely important role in the global ocean–atmosphere system [1, 2]. In particular, they are responsible for
the exchange of momentum, energy, and substances between the ocean and atmosphere. Hence, a broad circle of
problems of climatic and routine simulation requires the application of adequate parametrizations of the ex-
change processes. The exchange processes in the ocean involve the wind waves, turbulence, and drift currents
characterized by their own vertical profiles. However, their relative role in the processes of momentum and heat
exchange, as well as the correlation between these processes, remain unclear despite persistent efforts of numer-
ous researchers [2–4]. The relatively slow advance in this field is explained by the following inherent difficul-
ties: the realization of comprehensive and precise in-situ measurements is still beyond the existing technical
possibilities and, at the same time, any further advances in theoretical simulation require new physical ideas.
According to the classical concepts, the subsurface boundary layer is regarded as a near-wall turbulent layer
subjected to the action of Earth’s rotation. Therefore, it is expected that the vertical profile of current velocity
near the surface is logarithmic and, with depth, turns into the Ekman spiral specified by the coefficient of turbul-
ent viscosity at the corresponding depth [2, 3]. However, the presence of wind waves most likely violates this
simple picture. In the course of numerous in-situ investigations [4–7, etc.], it was demonstrated that the inten-
sity of turbulence in the upper layer significantly exceeds the predictions of the theory of near-wall turbulence.
This disagreement was explained by the generation of turbulence as a result of breaking of the wind waves. The
analysis of the in-situ data on the shears of a drift current performed in  revealed the deviations of the current
profile from the logarithmic law caused by the influence of wave breaking in a layer of thickness 1
k, where k
is the wave number of the spectral peak of surface waves. Parallel with breaking, there exist some other possible
mechanisms of influence of waves on the phenomenon of turbulence in the upper layer . Thus, in particular,
the role of wave motions in the generation of turbulence remains unclear. Note that, in the pioneer works carried
Marine Hydrophysical Institute, Ukrainian Academy of Sciences, Sevastopol.
Keele University, Keele, UK.
Translated from Morskoi Gidrofizicheskii Zhurnal, No.
32–44, January–February, 2007. Original article submitted August 19,
2005; revision submitted September 20, 2005.
0928-5105/07/1701–0029 © 2007 Springer Science+Business Media, Inc. 29