High-Resolution Simulations of Observed Cases of Lower-Stratospheric Turbulence

Tropopause jet streams often constitute approximate cruising altitudes for commercial airliners. However meteorological conditions near the tropopause can be conducive turbulence. Such turbulence encountered near the tropopause sometimes results in enroute adjustments from approximate tropopause level to altitudes located within the upper troposphere or lower stratosphere, respectively. Though horizontal wind magnitudes are typically maximized near the tropopause, layers of strong vertical shear conducive to turbulence often extend for up to several km (~10 kft) above or beneath it. In the upper troposphere the situation is often exacerbated by small static stability, which can also promote turbulence. Though static stability is larger in the lower stratosphere, this enhanced static stability can support gravity waves that under certain conditions can initiate turbulence. For instance, Lane and Sharman (2008) demonstrated in idealized simulations that the strength and depth of turbulence resulting from gravity wave breaking in the lower stratosphere were strongly influenced by the combined effects of environmental static stability and vertical shear.

In the current research we discuss more detailed WRF simulations of observed cases of lower stratospheric turbulence occurring in different meteorological situations. These cases include one (5 April 2022) where the turbulence was associated with strong flow over the Rockies. A second case was observed during the DCOTTS (Dynamics and Chemistry of the Summer Stratosphere) experiment on 31 May – 1 June 2022. In that case, simulated turbulence was associated with small-scale gravity waves along the tropopause, which were triggered by nearby deep convection and extended into the lower stratosphere. Simulations of this case are compared with observations along the DCOTTS flight track and will be discussed at the conference. Several other cases have been identified where lower-stratospheric turbulence occurred along DCOTTS flight tracks and are currently being simulated.

This research is partially in response to requirements and funding by the Federal Aviation Administration (FAA). The views expressed are those of the authors and do not necessarily represent the official policy or position of the FAA.

Reference:

Lane, T. P., and R. D. Sharman, 2008: Some influences of background flow conditions on the generation of turbulence due to gravity wave breaking above deep convection. J. Appl. Meteor. Climatol., 47, 2777-2796.