  Understanding rare events in turbulence provides a basis for the science of
extreme weather, for which the atmosphere is modeled by Navier-Stokes equations
(NSEs). In solutions of NSEs for isotropic fluids, various quantities, such as
fluid velocities, roughly follow Gaussian distributions, where extreme events
are prominent only in small-scale quantities associated with the
dissipation-dominating length scale or anomalous scaling regime. Using
numerical simulations, this study reveals another universal promotion mechanism
at much larger scales if three-dimensional fluids accompany strong
two-dimensional anisotropies, as is the case in the atmosphere. The dimensional
crossover between two and three dimensions generates prominent fat-tailed
non-Gaussian distributions with intermittency accompanied by colossal
chain-like structures with densely populated self-organized vortices
(serpentinely organized vortices (SOV)). The promotion is caused by a sudden
increase of the available phase space at the crossover length scale. Since the
discovered intermittency can involve much larger energies than those in the
conventional intermittency in small spatial scales, it governs extreme events
and chaotic unpredictability in the synoptic weather system.
