High-resolution numerical simulations of gravity wave-induced turbulence in association with an upper-level jet system

Clear-air turbulence (CAT) is frequently observed in the vicinity of upper-level jet streaks. Such turbulence generations coincide with the occurrence of gravity waves at approximately the same location ? on the north-east side of a jet exit region. These observations point to a possible chain-reacting relationship between an upper-level jet, gravity waves, and CAT. However, an upper-level jet system, representing a synoptic-scale feature, typically possesses a scale on an order of thousands kilometers, whereas gravity waves, as mesoscale phenomena, span scales from a few kilometers to a few hundred kilometers. Turbulence is categorized as a micro-scale feature whose spatial scale ranges from a few meters to a few hundred meters. Turbulence at atmospheric boundary layers is typically treated as subscale motions, and thus is parameterized in the atmospheric numerical models. CAT, on the other hand, is neither directly simulated nor parameterized in any of the typical atmospheric models.

In this study, we present simulations of CAT generation using high-resolution numerical models with multi-nested domains. The simulation starts with a balanced upper-level jet. Mesoscale gravity waves are generated as the tropospherical baroclinicity intensifies. These gravity waves experience scale contraction and eventually break, resulting in turbulent flow in the upper troposphere.