Statistical signature of the surface waves in the wind over the ocean

The surface waves at sea substantially perturb the mean

flow and distort the wind turbulence in the marine

atmospheric boundary layer. The perturbation is

responsible for the wind-wave momentum and energy

transfer, but also, by moving the refractive

inhomogeneities in the air, it influences the

propagation pattern of electromagnetic signals. While

the spatio-temporal structure of this perturbation

allows to identify the mechanism of wind-wave

interaction, the perturbation's statistical composition

determines the intensity, phase, and angle of arrival

variation of the signals being transmitted. In the past,

extensive effort has been devoted to studying the

influence of the turbulent motion on signal

(radio-frequency, optical, acoustic)

propagation. However, because of the limited

observational and theoretical information regarding the

wave signature in the wind, virtually nothing has been

known about the surface wave influence on signal

transmission.

In this work we present meteorological field data

collected over the coastal Atlantic in the summer of

2003 during the Coupled Boundary Layers Air-Sea Transfer

(CBLAST) experiment. The data persuasively demonstrate

that especially in low-wind conditions, rather prevalent

at sea, the surface waves modulation dominates the

motion in the marine atmospheric boundary layer. We

invoke a linear model for wave-mean flow interaction to

describe the spatio-temporal structure of the wave

signature and we establish a connection between the

statistics of the surface motion and that of the

wave-induced fields in the atmosphere. Both these are

further used to express the characteristic functions of

the velocity and pressure, as well as the characteristic

function of two-point velocity differences. We observe

that the wave effects depend distinctly on the vertical

coordinate, thus none of the considerations for

isotropy, commonly invoked in studies of turbulence, is

applicable. Similar approach and results apply to the

statistics of wave motion in the boundary layer of the

upper ocean, which influences the propagation of

acoustic signals.