The spectrum of waves and turbulence at the tropopause

Abstract

Aircraft measurements of winds, temperatures, and composition were conducted with a high‐altitude aircraft in the tropopause region above Northern Wales during May and June 2000. Observations on 6 June 2000 along three vertically stacked horizontal flight legs show fluctuations due to both gravity waves and turbulence. Horizontal kinetic energy spectra determined from the measurements extend to 3 m in wavelength, the smallest scales yet available at these heights. The vertical wind spectrum for strong turbulence is considerably different in both shape and intensity from the non‐turbulent spectrum. A sharp knee in the turbulent spectrum at 100 m wavelength is associated with the equipartition of kinetic energy in three dimensions. At other scales the vertical motions are relatively suppressed. A wave with 500 m wavelength was found, and provides a transition between the turbulent and non‐turbulent cases.