41 research outputs found
Interacting internal waves explain global patterns of interior ocean mixing
Across the stable density stratification of the abyssal ocean, deep dense
water is slowly propelled upward by sustained, though irregular, turbulent
mixing. The resulting mean upwelling is key to setting large-scale oceanic
circulation properties, such as heat and carbon transport. It is generally
accepted that in the ocean interior, this turbulent mixing is caused mainly by
breaking internal waves, which are predominantly generated by winds and tides,
interact nonlinearly, thereby fluxing energy down to ever smaller scales, and
finally become unstable, break and mix the water column. This paradigm forms
the conceptual backbone of the widely used Finescale Parameterization. This
formula estimates small-scale mixing from the readily observable internal wave
activity at larger scales and theoretical scaling laws for the downscale
nonlinear energy flux, but has never been fully explained theoretically. Here,
we close this gap using wave-wave interaction theory with input from both
localized high-resolution experiments and combined global observational
datasets. We find near-ubiquitous agreement between our predictions, derived
from first-principles alone, and the observed mixing patterns in the global
ocean interior. Our findings lay the foundations for a new type of wave-driven
mixing parameterization for ocean general circulation models that is entirely
physics-based, which is key to reliably represent climate states that differ
substantially from today's
Thank You to Our 2022 Peer Reviewers
On behalf of the journal, AGU, and the scientific community, the editors of Geophysical Research Letters would like to sincerely thank those who reviewed manuscripts for us in 2022. The hours reading and commenting on manuscripts not only improve the manuscripts, but also increase the scientific rigor of future research in the field. With the advent of AGU\u27s data policy, many reviewers have also helped immensely to evaluate the accessibility and availability of data, and many have provided insightful comments that helped to improve the data presentation and quality. We greatly appreciate the assistance of the reviewers in advancing open science, which is a key objective of AGU\u27s data policy. We particularly appreciate the timely reviews in light of the demands imposed by the rapid review process at Geophysical Research Letters. We received 6,687 submissions in 2022 and 5,247 reviewers contributed to their evaluation by providing 8,720 reviews in total. We deeply appreciate their contributions in these challenging times
Climate Process Team on internal wave–driven ocean mixing
Author Posting. © American Meteorological Society, 2017. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Bulletin of the American Meteorological Society 98 (2017): 2429-2454, doi:10.1175/BAMS-D-16-0030.1.Diapycnal mixing plays a primary role in the thermodynamic balance of the ocean and, consequently, in oceanic heat and carbon uptake and storage. Though observed mixing rates are on average consistent with values required by inverse models, recent attention has focused on the dramatic spatial variability, spanning several orders of magnitude, of mixing rates in both the upper and deep ocean. Away from ocean boundaries, the spatiotemporal patterns of mixing are largely driven by the geography of generation, propagation, and dissipation of internal waves, which supply much of the power for turbulent mixing. Over the last 5 years and under the auspices of U.S. Climate Variability and Predictability Program (CLIVAR), a National Science Foundation (NSF)- and National Oceanic and Atmospheric Administration (NOAA)-supported Climate Process Team has been engaged in developing, implementing, and testing dynamics-based parameterizations for internal wave–driven turbulent mixing in global ocean models. The work has primarily focused on turbulence 1) near sites of internal tide generation, 2) in the upper ocean related to wind-generated near inertial motions, 3) due to internal lee waves generated by low-frequency mesoscale flows over topography, and 4) at ocean margins. Here, we review recent progress, describe the tools developed, and discuss future directions.We are grateful to U.S. CLIVAR for their leadership in instigating and facilitating the Climate Process Team program. We are indebted to NSF and NOAA for sponsoring the CPT series.2018-06-0
Climate Process Team On Internal Wave-Driven Ocean Mixing
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
Climate Process Team on Internal-Wave Driven Ocean Mixing
Diapycnal mixing plays a primary role in the thermodynamic balance of the ocean, and consequently, in oceanic heat and carbon uptake and storage. Though observed mixing rates are on average consistent with values required by inverse models, recent attention has focused on the dramatic spatial variability, spanning several orders of magnitude, of mixing rates in both the upper and deep ocean. Climate models have been shown to be very sensitive not only to the overall level but to the detailed distribution of mixing; sub-grid-scale parameterizations based on accurate physical processes will allow model forecasts to evolve with a changing climate. Spatio-temporal patterns of mixing are largely driven by the geography of generation, propagation and destruction of internal waves, which are thought to supply much of the power for turbulent mixing. Over the last five years and under the auspices of US CLIVAR, a NSF and NOAA supported Climate Process Team has been engaged in developing, implementing and testing dynamics-base parameterizations for internal-wave driven turbulent mixing in global ocean models. The work has primarily focused on turbulence 1) near sites of internal tide generation, 2) in the upper ocean related to wind-generated near inertial motions, 3) due to internal lee waves generated by low-frequency mesoscale flows over topography, and 4) at ocean margins. Here we review recent progress, describe the tools developed, and discuss future directions
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Global Patterns of Diapycnal Mixing from Measurements of the Turbulent Dissipation Rate
The authors present inferences of diapycnal diffusivity from a compilation of over 5200 microstructure
profiles. As microstructure observations are sparse, these are supplemented with indirect measurements of
mixing obtained from (i) Thorpe-scale overturns from moored profilers, a finescale parameterization applied to
(ii) shipboard observations of upper-ocean shear, (iii) strain as measured by profiling floats, and (iv) shear and
strain from full-depth lowered acoustic Doppler current profilers (LADCP) and CTD profiles. Vertical profiles
of the turbulent dissipation rate are bottom enhanced over rough topography and abrupt, isolated ridges. The
geography of depth-integrated dissipation rate shows spatial variability related to internal wave generation,
suggesting one direct energy pathway to turbulence. The global-averaged diapycnal diffusivity below 1000-m
depth is O(10⁻⁴) m² s⁻¹ and above 1000-m depth is O(10⁻⁵) m² s⁻¹. The compiled microstructure observations
sample a wide range of internal wave power inputs and topographic roughness, providing a dataset with which
to estimate a representative global-averaged dissipation rate and diffusivity. However, there is strong regional
variability in the ratio between local internal wave generation and local dissipation. In some regions, the depth-integrated
dissipation rate is comparable to the estimated power input into the local internal wave field. In a few
cases, more internal wave power is dissipated than locally generated, suggesting remote internal wave sources.
However, at most locations the total power lost through turbulent dissipation is less than the input into the local
internal wave field. This suggests dissipation elsewhere, such as continental margins