HIGH-RESOLUTION Numerical Simulation of Gravity Wave-induced Turbulence In Association With An Upper-level Jet System

Abstract

Clear-air turbulence (CAT) is frequently observed in the vicinity of upper-level jet streaks. Such turbulence generation coincides with the occurrence of gravity waves at approximately the same location ? on the northeast side of the jet exit region. These observations point to a possible chain-reaction relationship between an upper-level jet, gravity waves, and CAT. However, an upperlevel jet system, representing a synopticscale feature, typically possesses a scale on the order of several thousand kilometers, whereas gravity waves, as mesoscale phenomena, span scales from a few kilometers to a few hundred kilometers, and 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 a high-resolution numerical model with multi-nested domains. The simulation starts with a balanced upper-level jet. Mesoscale gravity waves are generated as a result of the intensification of tropospheric baroclinicity. These gravity waves experience scale contraction and eventually break, resulting in turbulent flow in the upper troposphere.