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 –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.

在来自大气和海洋运动以及全球模型的数据中经常观察到大尺度场的非高斯统计。最近的直接数值模拟 (DNS) 表明，稳定分层流的大规模间歇性是由于垂直速度和温度爆发形式的零星极端事件的出现。这种现象是由波浪和湍流运动之间的相互作用引起的，影响了混合。我们提供了由于连接大尺度和小尺度爆发的大尺度吃水的出现而增强经典小尺度（或内部）间歇性的证据。为了这个目的，我们分析了大量的稳定分层 Boussinesq 方程的 DNS，在广泛的弗劳德数值范围内–1)。浮力场峰度随Fr的变化与垂直速度的峰度相似（尽管值小于），均呈现非单调趋势。我们提出了一种产生极端垂直气流和涡度增强的机制，它遵循场梯度的精确方程。