Articles | Volume 17, issue 12
Research article
30 Jun 2017
Research article |  | 30 Jun 2017

Case study of wave breaking with high-resolution turbulence measurements with LITOS and WRF simulations

Andreas Schneider, Johannes Wagner, Jens Faber, Michael Gerding, and Franz-Josef Lübken

Abstract. Measurements of turbulent energy dissipation rates obtained from wind fluctuations observed with the balloon-borne instrument LITOS (Leibniz-Institute Turbulence Observations in the Stratosphere) are combined with simulations with the Weather Research and Forecasting (WRF) model to study the breakdown of waves into turbulence. One flight from Kiruna (68° N, 21° E) and two flights from Kühlungsborn (54° N, 12° E) are analysed. Dissipation rates are of the order of 0. 1 mW kg−1 (∼ 0.01 K d−1) in the troposphere and in the stratosphere below 15 km, increasing in distinct layers by about 2 orders of magnitude. For one flight covering the stratosphere up to ∼ 28 km, the measurement shows nearly no turbulence at all above 15 km. Another flight features a patch with highly increased dissipation directly below the tropopause, collocated with strong wind shear and wave filtering conditions. In general, small or even negative Richardson numbers are affirmed to be a sufficient condition for increased dissipation. Conversely, significant turbulence has also been observed in the lower stratosphere under stable conditions. Observed energy dissipation rates are related to wave patterns visible in the modelled vertical winds. In particular, the drop in turbulent fraction at 15 km mentioned above coincides with a drop in amplitude in the wave patterns visible in the WRF. This indicates wave saturation being visible in the LITOS turbulence data.

Short summary
Wave breaking is studied with a combination of high-resolution turbulence observations with the balloon-borne instrument LITOS and mesoscale simulations with the WRF model. A relation between observed turbulent energy dissipation rates and the occurrence of wave patterns in modelled vertical winds is found, which is interpreted as the effect of wave saturation. The change of stability plays less of a role for mean dissipation for the flights examined.
Final-revised paper