Characteristics of Atmospheric Turbulence Retrieved From High Vertical‐Resolution Radiosonde Data in the United States
Résumé
n this study, we estimate atmospheric turbulence in the free atmosphere in terms of the Thorpe scale (LT) and eddy dissipation rate (ε) using US high vertical‐resolution radiosonde data (HVRRD) over 4 years (2012.9‐2016.8) at 68 operational stations. In addition, same calculations are conducted for 12 years (2005.10‐2017.9) at 4 stations among the 68 stations. These HVRRD have a vertical resolution of approximately 5 m and extend to an altitude of approximately 33 km, and thus, turbulence can be retrieved in the entire troposphere and lower stratosphere. There are thicker and stronger turbulent layers in the troposphere than in the stratosphere, with mean ε values of 1.84 × 10−4 m2<:sup>s−3 and 1.37 × 10−4 m2s−3 in the troposphere and stratosphere, respectively. The vertical structure of ε exhibits strong seasonal variations, especially in the upper troposphere and lower stratosphere (UTLS), with the largest ε values in summer and the smallest in winter. In the horizontal distribution of ε, large ε is seen mainly above the mountainous region in the troposphere, but this pattern is not seen in the stratosphere. Although ε is estimated by the square of LT multiplied by the cube of the Brunt‐Väisälä frequency (N), the regions of large ε are matched with large LT regions where N is relatively small. For the time series of ε near the tropopause for 12 years at 4 stations, an annual variation is prominent at all stations without significant interannual variations. There is, however, a slightly increasing trend of ε at 2 stations.
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