The role of gravity wave breaking in a case of upper-level near-cloud turbulence

Here, the mechanisms associated with the observed moderate-to-severe turbulence during the evolution of this convective system are examined. Comparison between aircraft-observed eddy dissipation rate data with satellite and radar shows that a majority of turbulence reports are located on the south side and outside of a nocturnal mesoscale convective system (MCS), relatively large distances from the active convective regions.

Simulations show that divergent storm-induced upper-level outflow reduces the environmental flow on the south side of the MCS, while on the north and northwest side it enhances the environmental flow. This upper-level storm outflow enhances the vertical shear near the flight levels and contributes to mesoscale reductions in Richardson number to values that support turbulence. In addition to the role of the MCS-induced outflow, high-resolution simulations (1.1-km horizontal grid spacing) show that turbulence is largely associated with a large-amplitude gravity wave generated by the convective system, which propagates away from it.