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Abstract One-second U.S. high vertical-resolution radiosonde data (HVRRD) contain two different sets of temperature data—the raw data and the processed data. The processed data have been subject to radiation corrections, which have been well documented, and smoothing, the details of which are proprietary to the radiosonde manufacturers. We have tried to characterize this smoothing by computing the root-mean-square (rms) of normalized temperature perturbations derived from removing a second-degree polynomial fit for altitude segments (Δz) from 100 m to 5 km. We find that for Δz= 100 m, rms values are larger at higher altitudes, are larger in the raw data than in the processed data, and are larger during daytime than during nighttime, for both the raw and processed data. The rms values and their daytime to nighttime differences are larger in the raw data than in the processed data. As Δzincreases toward 5 km, the geographical patterns of rms over the contiguous United States from both the raw and processed data start resembling previously published gravity wave total energy patterns obtained from the older 6-s U.S. radiosonde data. An example is shown of a discontinuity in the small-scale rms values when radiosonde instrumentation is changed, so it is concluded that small-scale temperature fluctuations will be different for different radiosonde instruments. Examples are shown of enhanced small-scale rms temperature values indicative of turbulence resulting from gravity wave critical levels and from enhanced gravity waves due to seasonal maxima in convection. Significance StatementWe have characterized the variability of the raw and processed temperature profiles of the U.S. high vertical resolution radiosonde data for various vertical scales. We have argued that sources of small-scale fluctuations in the processed data include turbulence and the radiation effects which have not been accounted for in the current derivation of the processed data. Temperature fluctuations of larger scales correspond to those from gravity waves. We have shown an example of a discontinuity in small-scale fluctuations at a radiosonde station when the instrumentation was changed. These results suggest that temperature fluctuations resulting from varying amounts of solar radiation falling on the temperature sensor as the radiosonde instrumentation swings and rotates should be evaluated for each radiosonde system. 

Abstract Atmospheric turbulence plays a key role in the mixing of trace gases and diffusion of heat and momentum, as well as in aircraft operations. Although numerous observational turbulence studies have been conducted using campaign experiments and operational data, understanding the turbulence characteristics particularly in the free atmosphere remains challenging due to its small-scale, intermittent, and sporadic nature, along with limited observational data. To address this, turbulence in the free atmosphere is estimated herein based on the Thorpe method by using operational high vertical-resolution radiosonde data (HVRRD) with vertical resolutions of about 5 or 10 m across near-global regions, provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) via the U.S. National Centers for Environmental Information (NCEI) for 6 years (October 2017–September 2023). Globally, turbulence is stronger in the troposphere than in the stratosphere, with maximum turbulence occurring about 6 km below the tropopause, followed by a sharp decrease above. Seasonal variations show strong tropospheric turbulence in summer and weak turbulence in winter for both hemispheres, while the stratosphere exhibits strong turbulence during spring. Regional analyses identify strong turbulence regions over the South Pacific and South Africa in the troposphere and over East Asia and South Africa in the stratosphere. Notably, turbulence information can be provided in regions and high altitudes that are not covered by commercial aircraft, suggesting its potential utility for both present and future high-altitude aircraft operations. 

Abstract Thorpe analysis has been used to study turbulence in the atmosphere and ocean. It is clear that Thorpe analysis applied to individual soundings cannot be expected to give quantitatively reliable measurements of turbulence parameters because of the instantaneous nature of the measurement. A critical aspect of this analysis is the assumption of the linear relationship C = LO/LT between the Thorpe scale LT, derived from the sounding measurements, and the Ozmidov scale LO. It is the determination of LO that enables determination of the dissipation rate of turbulence kinetic energy ε. Single atmospheric and oceanic soundings cannot indicate either the source of turbulence or the stage of its evolution; different values of C are expected for different turbulence sources and stages of the turbulence evolution and thus cannot be expected to yield quantitatively reliable turbulence parameters from individual profiles. The variation of C with the stage of turbulence evolution is illustrated for direct numerical simulation (DNS) results for gravity wave breaking. Results from a DNS model of multiscale initiation and evolution of turbulence with a Reynolds number Re (which is defined using the vertical wavelength of the primary gravity wave and background buoyancy period as length and time scales, respectively) of 100 000 are sampled as in sounding of the atmosphere and ocean, and various averaging of the sounding results indicates a convergence to a well-defined value of C, indicating that applying Thorpe analysis to atmospheric or oceanic soundings and averaging over a number of profiles gives more reliable turbulence determinations. The same averaging study is also carried out when the DNS-modeled turbulence is dominated by turbulence growing from the initial instabilities, when the turbulence is fully developed, when the modeled turbulence is decaying, and when the turbulence is in a still-later decaying stage. These individual cases converge to well defined values of C, but these values of C show a large variation resulting from the different stages of turbulence evolution. This study gives guidance as to the accuracy of Thorpe analysis of turbulence as a function of the number of profiles being averaged. It also suggests that the values of C in different environments likely depend on the dominant turbulence initiation mechanisms and on the Reynolds number of the environment.