C.R.T. Displays of Wind Eddies and Some Lagrangian Deductions from a Vortex Model of Turbulence

Abstract

The concept of atmospheric turbulence in a two-dimensional field as a mixture of circular eddies of different diameters and circulation velocities is considered, and from this an argument is presented to show how the frequency of air fluctuations relative to the mean flow (the Lagrangian) is related to that measured at a fixed point. A technique described in earlier papers by the author, for presenting wind fluctuations at various positions in the field as vectors correspondingly arranged on a cathode-ray tube, is used for examining the plausibility of the theory, and some supporting evidence is given in the form of multi-vector oscillograms. It is argued that, in narrow bands, the ratio of fixed point (Eulerian) to Lagrangian frequencies is inversely proportional to the intensity of turbulence and may be calculated from fixed point measurements. A practical method of measuring the ratio has been tried and statistical results covering a range of wind speeds, frequencies and atmospheric stabilities are given. Within the frequency range 0.06?2.2 cycle min?1, the ratio varies from 2 in unstable conditions to 12 in stable conditions.