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

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