High-Resolution Observations of Turbulence Distributions Across Tropopause Folds

Abstract

In this study, we interpret two vertical turbulence measurements. We acquired these uninterrupted high-resolution dissipation rate profiles with the balloon-borne instrument LITOS (Leibniz Institute Turbulence Observations in the Stratosphere) from velocity measurements using a spectral technique. The meteorological situation is characterized using ECMWF’s integrated forecast system (IFS) as breaking Rossby waves showing significant tropospheric jets and a developed tropopause fold. In both cases, dissipation rates in the shear zone above the upper-tropospheric jet are three orders of magnitude larger than below, reaching severe turbulence strengths (1,000 mW kg−1) in a deep tropopause fold and moderate turbulence strengths in a medium tropopause fold (10 mW kg−1). These turbulent spots are shown to create a tripole shaped pattern of PV modification across the tropopause. Furthermore, tracer-tracer correlations exhibit mixing of tropospheric and stratospheric air masses in the medium-fold case. While the strength of turbulence corresponds to the depth of the tropopause fold, its asymmetric vertical distribution is possibly related to the tropopause fold life cycle. The observed asymmetry in the vertical turbulence distribution is consistent across both tropopause folds and in overall agreement with measured Richardson numbers. In the medium-fold case however, it is neither expected from conceptual models nor from Richardson numbers in the IFS. This calls for further field campaigns to investigate the role of turbulence and its implications for the meteorological understanding as well as for aviation safety.