Climate Process Team on Internal Wave–Driven Ocean Mixing

Abstract

O cean turbulence influences the transport of heat, freshwater, dissolved gases such as CO 2 , pollutants, and other tracers. It is central to understanding ocean energetics and reducing uncertainties in global circulation and simulations from climate models. The dissipation of turbulent energy in stratified water results in irreversible diapycnal (across density surfaces) mixing. Recent work has shown that the spatial and temporal inhomogeneity in diapycnal mixing may play a critical role in a variety of climate phenomena. Hence, a quantitative understanding of the physics that drive the distribution of diapycnal mixing in the ocean interior is fundamental to understanding the ocean's role in climate.Diapycnal mixing is very difficult to accurately parameterize in numerical ocean models for two reasons. The first one is due to the discrete representation of tracer advection in directions that are not perfectly aligned with isopycnals, which can result in numerically induced mixing from truncation errors that is larger than observed diapycnal mixing (Griffies et al. 2000;Ilıcak et al. 2012). The second reason is related to the intermittency of turbulence, which is generated by complex and chaotic motions that span a large space-time range. Furthermore, this mixing is driven by a wide range of processes with distinct governing physics that create a rich global geography [see MacKinnon et al. (2013c) for a review]. The difficulty is also related to the relatively sparse direct sampling of ocean mixing, whereby sophisticated ship-based measurements are generally required to accurately characterize ocean mixing processes. Nonetheless, we have sufficient evidence from theory, process models, laboratory experiments, and field measurements to conclude that away from ocean boundaries (atmosphere, ice, or the solid ocean bottom), diapycnal mixing is largely related to the breaking of internal gravity waves, which have a complex dynamical underpinning and associated geography. The study summarizes recent advances in our understanding of internal wave-driven turbulent mixing in the ocean interior and introduces new parameterizations for global climate ocean models and their climate impacts.

The Global Mode‐2 M2 Internal Tide

“…Therefore, we should resolve the internal tide's multimodal structure in order to quantify the fate of internal tides. The information may be useful to examine the near‐field and far‐field tidal dissipation (Jayne & Laurent, , Klymak et al, , St. Laurent et al, ), with a long‐term goal of parameterization of the tide‐driven ocean mixing in the global ocean (MacKinnon et al, ).…”

Long‐Range Radiation and Interference Pattern of Multisource M2 Internal Tides in the Philippine Sea

“…The vertical variations in internal tide propagation and dissipation have been too complex to understand until now due to the high expense of such measurements and limited field observations (Kerry et al, ). A well‐depicted horizontal propagation path is an important step toward correctly parameterizing the spatial distribution of diapycnal mixing in the global domain (MacKinnon et al, ). Furthermore, multiwave interference processes are widespread in the open ocean because of the long‐range propagation and numerous source distributions (Zhao et al, ).…”

The Impact of Topographic Steepness on Tidal Dissipation at Bumpy Topography

“…These waves propagate both vertically and horizontally, carrying wave energy away from their generation site [2]. When the waves break, that energy can be used for turbulent mixing of heat and salt.…”

“…While internal tides are generated on horizontal scales of order 1-100 km, and break through overturning on much smaller scales, global climate models typically have resolutions of order 10-100 km, allowing resolution of the generation and propagation of only the large-scale internal tides and none of the wave-breaking and mixing processes [2]. The diapycnal mixing that results from internal tide breaking must therefore be parameterized.…”