Interactive comment on “ Statistical variations of lower atmospheric turbulence and roles of inertial gravity waves at a middle latitude radiosonde site

This manuscript estimates turbulent energy dissipation rates from the potential temperature derived from the radiosonde data applying the Thorpe displacement technique which has been previously developed in studies of oceanic turbulence and adapted to the atmosphere. With the multiple atmospheric parameters simultaneously measured with radiosonde, the authors present an interesting comparison between energy dissipation rates and Richardson number as well as the gravity waves on a statistical basis. The findings are encouraging.

Abstract. Activities about turbulence and gravity waves are crucial for the understanding of 23 the dynamical processes in the lower atmosphere. Thus, this study presents the long-term 24 variations of turbulence and their associations with the Richardson number Ri and gravity 25 waves by using a high-resolution radiosonde dataset from Miramar Nas (32.8° N, 117.1° W). 26 Seasonal cycles and lognormal distribution are the two main characteristics of turbulence. 27 The amount of turbulence can be increased where Ri exceeds any critical value, which 28 suggests that the threshold Ri may not be an optimal predictor of the existence of turbulence, 29 whereas a low Ri can lead to large and abundant turbulent energy dissipation rates. In general, 30 dissipation rates from the radiosonde quantitatively agree with results from the neighboring 31 MST radar given by Nastrom and Easton (2005), whereas an encouraging argument is 32 reached in terms of the diffusion rate. The propagating gravity waves in the lower atmosphere, 33 especially in the middle troposphere and the tropopause regions, can reduce Ri. Therefore, 34 enhanced turbulent mixing is expected. Other roles of gravity waves in turbulent flow are that 35 breaking waves and the temporal variations of waves may be occasionally transferred to 36 turbulence and can roughly estimate dissipation rates at different heights.

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Tropospheric and lower stratospheric turbulence is attracting considerable interest due to 51 its important role in determining dynamic atmospheric and stratosphere-troposphere  (Sharman et al., 2012). Therefore, much attention has been paid over the 55 past decades to the variation and generation of turbulence. 56 Experimental observations, such as radar and sounding, are fundamental to the 57 comprehensive understanding of the characteristics of turbulence. Radar observations with 58 large power-aperture and high spatial resolution are necessary for the accurate detection of 59 turbulent air according to the assumption that the Bragg scale lies within the inertial subrange 60 of turbulence (Wilson et. al., 2005). VHF radars are the most widely adopted among the  and should be rare in the free atmosphere, and the other is dynamical instability (0≤Ri<1/4), 85 which tends to excite weak turbulence (Thorpe, 1973 its association with the Thorpe sorting process can reveal the correlations between turbulence, 104 local instabilities, and gravity waves and summarize long-term turbulence trends.

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By employing the Thorpe sort method for examining the distribution of turbulence and    deviation of the temperature noise. ς should be less than a threshold if the noise is severe, 176 and the critical value is typically set to 1.5; false overturns are rejected when TNR is introduced to determine the overall quality of * θ and defined as where n is the number of data points. We follow Kantha and Hocking (2011) where N is the Brunt-Väisälä frequency deduced from the sorted monotonic potential  The wind shear S is estimated by zonal and meridional wind components, that is,  generally consistent with radiosonde findings, but significant differences can be noted from 9 311 km to 12 km. This discrepancy can be interpreted as follows. Dissipation rates from radars 312 are resolved from the wind spectrum but understood by unstable overturn from a Thorpe sort.

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Furthermore, an encouraging argument can be found between the Thorpe-resolved diffusion 314 rates and those from radar. 315 Figure 6 shows the histogram densities of the dissipation rates that match 1 4 Ri < , Ri ≥ , respectively, and it appears to be more abundant and vigorous when Ri is lower.  profile is removed as the background from each measurement raw profile. Then, the residual 336 profile is filtered by a high-pass filter to extract gravity wave perturbations. Given that the 337 vertical wavelengths of low atmospheric gravity waves are typically shorter than 10 km, the 338 cut-off vertical wavelength of the high-pass filter is chosen to be 10 km. Then, a low-pass 339 filter with a wavelength of 1 km is applied to the residual components to exclude the 340 influence of eddies. Finally, the filtered profile can be seen as gravity wave perturbations.

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The total gravity energy density E , that is, kinetic energy density plus potential energy 342 density, can be calculated from the zonal wind perturbation ( ′ u ), meridional wind 343 perturbation ( ′ v ), and temperature perturbation ( ′ T ): where T is monthly averaged background temperature, g is gravity acceleration; and  is that breaking gravity waves may directly generate turbulence. Figure 8(