Inertia-gravity wave energy and instability drive turbulence: evidence from a near-global high-resolution radiosonde dataset

The inertia-gravity wave (IGW), Kelvin–Helmholtz instability (KHI) and turbulence in the lower free atmosphere are tightly linked through complex dynamical processes and their interactions profoundly shape the energy and mass transfer processes, but they remain largely unidentified. Here the near-global distributions of IGW energy, KHI (indicated by the critical value of Richardson number, Ri ), and turbulence in the free atmosphere are investigated based on 5 years (2016–2020) of high-resolution radiosonde data. A poleward decrease can be detected in IGW energy density, as well as in the occurrence frequencies of KHI and turbulence. Their maxima occur at 15 km above ground level (AGL) at low latitudes but move to 5 km AGL at high latitudes, with notable latitudinal and seasonal variations. Over the contiguous United States, spatial distributions in KHI and turbulence frequencies agree well with moderate-or-greater turbulence frequency gathered from pilot reports. Vertically, the turbulence dissipation rate follows a log-normal distribution. Notably, a half of burst turbulence exists in the regime of Ri larger than 1 instead of 1/4, beyond or even far beyond what is known as the critical value of 1/4. Positive correlations have been extensively uncovered between IGW energy and KHI frequency, KHI and turbulence frequencies, wave energy dissipation and turbulence frequency, which indicate that IGW and KHI could be major drivers for the occurrence of turbulence in the free atmosphere. These findings could advance our understanding of the physical connection from medium-scale IGWs to small-scale turbulence and are theoretically valuable for aircraft safety.