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An experimental measurement of all three components of the velocity and vorticity vectors, as well as the temperature and its gradient, and potential vorticity, has been described using four acoustic anemometers. Anemometers were placed at vertices of a tetrahedron, the horizontal base of which was a rectangular triangle with equal legs, and the upper point was exactly above the top of the right angle. The distance from the surface to the tetrahedron its base was 5.5 m, and the lengths of legs and a vertical edge were 5 m. A covariance–correlation matrix for turbulent variations in all measured values has been calculated. In the daytime horizontal and vertical components of the helicity are of the order of–0.03 and +0.01 m s –2 , respectively. The nighttime signs remain unchanged, but the absolute values are several times smaller. The cospectra and spectral correlation coefficients have been calculated for all helicity components. The time variations in the components of “instantaneous” helicity and potential vorticity are demonstrated.
Koprov et al. (2015) studied this question.