Environment and mechanisms of severe turbulence in a midlatitude cyclone

For one region, where turbulence was isolated and short lived, simulations revealed breaking of similar to 100-km horizontal-wavelength lower-stratospheric gravity waves in the exit region of a UTLS jet streak as the most likely mechanism for the observed turbulence. Although similar waves occurred in a simulation without convection, the altitude at which wave breaking occurred in the control simulation was strongly affected by UTLS outflow from distant deep convection.

In the other analyzed region, turbulence was more persistent and widespread. There, overturning waves of much shorter 5-10-km horizontal wavelengths occurred within layers of gradient Richardson number < 0.25, which promoted Kelvin-Helmholtz instability associated with strong vertical shear in different horizontal locations both above and beneath the convectively enhanced UTLS jet.