Non-Gaussian statistics of large-scale fields are routinely observed in data from atmospheric and oceanic campaigns and global models. Recent direct numerical simulations (DNSs) showed that large-scale intermittency in stably stratified flows is due to the emergence of sporadic, extreme events in the form of bursts in the vertical velocity and the temperature. This phenomenon results from the interplay between waves and turbulent motions, affecting mixing. We provide evidence of the enhancement of the classical small-scale (or internal) intermittency due to the emergence of large-scale drafts, connecting large- and small-scale bursts. To this aim we analyze a large set of DNSs of the stably stratified Boussinesq equations over a wide range of values of the Froude number ($Fr\approx 0.01-1$). The variation of the buoyancy field kurtosis with $Fr$ is similar to (though with smaller values than) the kurtosis of the vertical velocity, both showing a non-monotonic trend. We present a mechanism for the generation of extreme vertical drafts and vorticity enhancements which follows from the exact equations for field gradients.
Estimating Intermittency Exponent in Neutrally Stratified Atmospheric Surface Layer Flows: A Robust Framework based on Magnitude Cumulant and Surrogate Analyses
On the large-scale vertical velocity intermittency of turbulent wall flows
University of California, Irvine（加州大学尔湾分校）；Politecnico di Torino（都灵理工大学）；University of Sydney（悉尼大学）；Italian Institute for Environmental Protection and Research (ISPRA)（意大利环境保护与研究研究所）；University of Pennsylvania（宾夕法尼亚大学）；Princeton University（普林斯顿大学）；Duke University（杜克大学）
Machine-Learned Closure of URANS for Stably Stratified Turbulence: Connecting Physical Timescales & Data Hyperparameters of Deep Time-Series Models
National Center for Computational Sciences, Oak Ridge National Laboratory（橡树岭国家实验室国家计算科学中心）；University of Massachusetts Amherst（马萨诸塞大学阿默斯特分校）；University of Washington（华盛顿大学）；DoD HPCMP PET/GDIT（美国国防部高性能计算现代化计划项目执行办公室/通用动力信息技术公司）
Scaling laws and local enhancements of buoyancy flux in stratified turbulent flows
CNRS, École Centrale de Lyon, INSA Lyon, Université Claude Bernard Lyon 1, LMFA（法国国家科学研究中心、里昂中央理工学院、里昂国立应用科学学院、克洛德·贝尔纳里昂大学、流体力学与声学实验室）；Dipartimento di Fisica, Università della Calabria（卡拉布里亚大学物理系）；Leibniz Institute of Atmospheric Physics, University of Rostock（罗斯托克大学大气物理研究所）；French American Center for Theoretical Sciences, CNRS, KITP, University of California, Santa Barbara（美法理论科学中心、法国国家科学研究中心、加州大学圣塔芭芭拉分校KITP）；Laboratoire de Physique, Ecole Normale Supérieure de Lyon and CNRS（里昂高等师范学校物理实验室及法国国家科学研究中心）；Max Planck Institute for Dynamics and Self-Organization（马克斯·普朗克动力学与自组织研究所）；National Center for Atmospheric Research（美国国家大气研究中心）；Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Departamento de Física（布宜诺斯艾利斯大学理学院物理系）；CONICET - Universidad de Buenos Aires, Instituto de Física Interdisciplinaria y Aplicada (INFINA)（阿根廷国家科学研究委员会-布宜诺斯艾利斯大学交叉与应用物理研究所）；Cooperative Institute for Research in the Atmosphere（大气研究合作研究所）
