Spatiotemporal Characteristics Of Atmospheric Turbulence Over China Estimated Using Operational High-Resolution Soundings

Large-scale in situ observations are sorely lacking, leading to poor understanding of nationwide atmospheric turbulence over China. Nevertheless, high-resolution soundings have become available starting in 2011, providing a unique opportunity to investigate turbulence across China. Here, we calculated the mean turbulence dissipation rate (epsilon) from radiosonde measurements across China for the period 2011-2018 using Thorpe analysis. The atmospheric layers that had stronger turbulence indicated by larger epsilon generally came with larger Thorpe length but with smaller Brunt-Vaisala frequency. Overall, the clear-air epsilon in the free atmosphere exhibited large spatial variability with a 'south-high north-low' pattern. Large clear-air epsilon values were observed in both the lower stratosphere (LS) and upper troposphere (UT), especially over the Tibetan Plateau (TP) and its neighboring regions with complex terrain likely due to large-amplitude mountain waves. Particularly, less frequent but more intense clear-air turbulence was observed in both lower troposphere (LT) and UT over the TP, while more frequent, less intense clear-air turbulence was found in northern China. The all-sky turbulence considering the moist-saturation effects was much stronger in the troposphere, notably in southern China where convective clouds and precipitation oftentimes dominated. In the vertical direction, the altitude of peak clear-air epsilon in the troposphere was found to decrease poleward, broadly consistent with the meridional gradient of tropopause height in the Northern Hemisphere. A double-peak mode stood out for the profiles of clear-air epsilon at midlatitudes to the north of 30 degrees N in winter: one peak was at altitudes of 15-18 km, and another at altitudes of 5-8 km. The strong shear instabilities around the westerly jet stream could account for the vertical bimodal structures. The seasonality of epsilon was also pronounced, reaching maxima in summer and minima in winter. Our results may help understand and avoid clear-air turbulence, as related to aviation safety among other issues.