Naslov
Determining Wave–Turbulence Interactions in the Stable Boundary Layer

Autori
Nappo, C. ; Sun, J. ; Mahrt, L. ; Belušić, D.

Izvornik
Bulletin of the American Meteorological Society (0003-0007) 95 (2014), 1; ES11-ES13

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
Wave–Turbulence Interactions ; Stable Boundary Layer

Sažetak
Internal gravity waves not only effectively influence global atmospheric circulations in the middle and upper atmosphere, but also generate turbulence in the stably stratified atmospheric boundary layer, which leads to the transport of momentum, heat, aerosols, and biogenic and anthropogenic gases. Although some progress has been made in parameterizing gravity waves in global models, difficulties in calculating them still exist due to nonlinear wave effects and wave interactions with turbulence, especially near the ground. One of the most challenging problems facing atmospheric modelers is the parameterization of turbulence and gravity waves in the stable planetary boundary layer (PBL). Currently numerical models perform much worse for the stably stratified nocturnal PBL than the daytime convective PBL. The structure of the stable PBL has often been studied, including its dependence on the Richardson number, turbulence intermittency, surface inhomogeneity, decoupling of the surface layer from the upper PBL, density currents (katabatic flows), mesoscale motions, low-level jets, and gravity waves. At any time, all these effects can be present, especially under strongly stable conditions when turbulence appears intermittently. The impact of simple terrain features can become complex under stable conditions. A lack of understanding of the momentum and energy exchanges through the PBL is the major obstacle for model parameterization. Numerical models lack realistic physical processes to generate turbulence once the PBL becomes very stable. This can result in unrealistic “run-away cooling” problems. A practical way to avoid the problem is to modify the turbulence mixing in models to maintain a certain level of energy and momentum flux when the flow stability becomes too strong to support active turbulence. This is accomplished by specifying minimal friction velocity or by using the so-called long-tail formulation of the stability function under strongly stable atmospheric conditions. The long- tail parameterization comes with undesirable consequences such as boundary layers that are too deep and surface temperatures that are too high.

Izvorni jezik
Engleski

Znanstvena područja
Geofizika

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