Research On The Spatiotemporal Characteristics And Influencing Factors Of Turbulence In The Free Atmosphere Of China

Turbulence carries the exchange of mass and energy in the atmosphere,and can also reflect the dynamic and thermal processes in the atmosphere.However,due to the lack of large-scale high-resolution measured data,the study on the spatiotemporal characteristics of turbulence in free atmosphere and the reasons for these characteristics is limited.In this paper,we calculated the turbulence dissipation rate()from highresolution soundings that from 120 stations across China for the period 2011–2018 by Thorpe analysis.The spatiotemporal characteristics of which represents the turbulence intensity in the numerical model were given,and the reasons for these distributions are also discussed.The main conclusions are as follows:(1)Although the clear-air turbulence has a large spatial variability,it showed“south-high north-low” pattern in the horizontal distribution,and the turbulence in the upper troposphere is stronger.In the troposphere,the frequency of turbulence in northern China was higher while the intensity was weaker.The frequency of turbulence at the edge of the Tibet Plateau(TP)is lower but the average intensity is stronger than that of other areas at the same latitude,which may be likely due to the orographicallyinduced convection and mountain-wave breaking.The turbulence considering the moist saturation effect is stronger than the clear-air turbulence,especially in southern China where convective clouds and precipitation dominate.In the vertical direction,the altitude of the peak clear-air 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 at mid-latitudes to the north of 30°N in winter.The strong shear instabilities around the westerly jet stream could account for the vertical bimodal structures.The seasonality of was also pronounced,reaching maxima in summer and minima in winter.(2)Turbulent dissipation rate showed a Gaussian distribution from the statistical results.The atmosphere with lower stability has a larger turbulent dissipation rate,which also corresponds to a larger Thorpe scale.The numerical range of the observed turbulent dissipation rate is consistent with the theoretical value and is also similar to the results that from other regions using the same mothed.(3)The upper-level turbulence in the mid-latitude region had a significant increasing trend during the period 1980 to 2019.This may be due to the increase in the meridional temperature gradient in the upper troposphere,which leads to an increase in vertical wind shear around the jet stream.The predictions from CMIP6 models showed that the zonal wind speed and turbulence in the upper troposphere in mid-latitudes will increase in the context of global warming.