We use a database of direct numerical simulations to evaluate parametrizations for energy dissipation rate in stably stratified flows. We show that shear-based formulations are more appropriate for stable boundary layers than commonly used buoyancy-based formulations. As part of the derivations, we explore several length scales of turbulence and investigate their dependence on local stability.

The high-fidelity modeling of optical turbulence is critical to the design and operation of a new class of emerging highly-sophisticated astronomical telescopes and adaptive optics instrumentation. In this study, we perform retrospective simulations of optical turbulence over the Hawaiian islands using a mesoscale model. The simulated results are validated against thermosonde data. We focus on turbulence in the free atmosphere, above the atmospheric boundary layer. The free-atmosphere is particularly important for adaptive optics performance and for sky coverage calculations and hence has significant impact on performance optimisation and scheduling of observations. We demonstrate that a vertical grid spacing of 100 m or finer is needed to faithfully capture the intrinsic variabilities of observed clear air turbulence. This is a particularly timely study because the next generation of Extremely Large Telescopes are currently under construction and their associated suite of instruments are in the design phase. Knowledge of the expected accuracy of optical turbulence simulations and real-time forecasts will enable the design teams to i) test and develop instrument designs and ii) formulate operational procedure.

We analyzed several multiyear wind speed datasets from 4 different geographical locations. The probability density functions of wind ramps from all these sites revealed remarkably similar shapes. The tails of the probability density functions are much heavier than a Gaussian distribution, and they also systematically depend on time increments. Quite interestingly, from a purely statistical standpoint, the characteristics of the extreme ramp‐up and ramp‐down events are found to be almost identical. With the aid of extreme value theory, we describe several other inherent features of extreme wind ramps in this paper.

In this study, we explore several integral and outer length scales of turbulence which can be formulated by using the dissipation of temperature fluctuations () and other relevant variables. Our analyses directly lead to simple yet non-trivial parameterizations for both spatially-averaged and the structure parameter of temperature (C 2 T). For our purposes, we make use of high-fidelity data from direct numerical simulations of stratified channel flows.

Kolmogorov’s 1941 hypothesis on local isotropy is only applicable for scales smaller than the outer length scales (OLS). By utilizing data from direct numerical simulations and wind tunnel experiments, we quantify OLS in stratified flows.