Variations of the global net air–sea heat flux during the “hiatus” period (2001–10)

Author Posting. © American Meteorological Society, 2016. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 29 (2016): 3647-3660, doi:10.1175/JCLI-D-15-0626.1.An assessment is made of the mean and variability of the net air–sea heat flux, Qnet, from four products (ECCO, OAFlux–CERES, ERA-Interim, and NCEP1) over the global ice-free ocean from January 2001 to December 2010. For the 10-yr “hiatus” period, all products agree on an overall net heat gain over the global ice-free ocean, but the magnitude varies from 1.7 to 9.5 W m−2. The differences among products are particularly large in the Southern Ocean, where they cannot even agree on whether the region gains or loses heat on the annual mean basis. Decadal trends of Qnet differ significantly between products. ECCO and OAFlux–CERES show almost no trend, whereas ERA-Interim suggests a downward trend and NCEP1 shows an upward trend. Therefore, numerical simulations utilizing different surface flux forcing products will likely produce diverged trends of the ocean heat content during this period. The downward trend in ERA-Interim started from 2006, driven by a peculiar pattern change in the tropical regions. ECCO, which used ERA-Interim as initial surface forcings and is constrained by ocean dynamics and ocean observations, corrected the pattern. Among the four products, ECCO and OAFlux–CERES show great similarities in the examined spatial and temporal patterns. Given that the two estimates were obtained using different approaches and based on largely independent observations, these similarities are encouraging and instructive. It is more likely that the global net air–sea heat flux does not change much during the so-called hiatus period.This paper is funded in part by the NOAA Climate Observation Division, Climate Program Office, under Grant NA09OAR4320129 and by the NOAA MAPP Climate Reanalysis Task Force Team under Grant NA13OAR4310106. The study was initiated when X. Liang was a postdoc at MIT, where he was supported in part by the NSF through Grant OCE-0961713, by NOAA through Grant NA10OAR4310135, and by the NASA Physical Oceanography Program through ECCO.2016-11-1

Influence of Mesoscale Eddies on the Deep Ocean Dynamics over the East Pacific Rise near 10N

Mesoscale eddies are ubiquitous in the World Ocean and dominate the energy content on subinertial time scales. However, due to a lack of in situ data from the deep ocean, most previous work has focused on signals near the sea-surface, that is, the signals of mesoscale eddies in the deep ocean and their influence on the deep ocean dynamics have not yet been intensively studied. In this thesis, the connections between mesoscale eddies and deep ocean dynamical processes, including low-frequency flows, internal waves and ocean mixing, are examined using observations from a collection of moored instruments located near the crest of the East Pacific Rise (EPR) between 9 and 10N. First, the relationship between mesoscale eddies and subinertial flows in the deep ocean over the EPR were examined. The subinertial velocities at depth are significantly correlated with geostrophic near-surface currents, which are dominated by westward-propagating mesoscale eddies. It is concluded that the subinertial velocity near the EPR crest is a super-position of velocities associated with eddies propagating westward across the ridge and "topographic flows". Second, the relationship between subinertial flows and internal waves were investigated. The observations reveal subinertial modulations of internal waves, particularly near-inertial oscillations and internal tides. These subinertial modulations are highly correlated with the subinertial flows in the deep ocean. Third, based on a finescale parameterization model, the deep ocean diapycnal diffusivity over the ridge crest was estimated. The estimated diapycnal diffusivity shows variation on the subinertial time scale. In particular, the measurements imply a significant increase in diapycnal diffusivity near the seafloor during episodes of increased subinertial flow. Fourth, combined with previous numerical and theoretical studies, the observations imply energy transfer near the crest of the EPR from low-frequency flows, including mesoscale eddies, to near-inertial oscillations, turbulence and mixing. Considering the ubiquitousness of mesoscale eddies in the ocean, it is expected that the circulation near other portions of the global mid-ocean ridge system is similarly dominated by mesoscale variability and topographic effects. This is particularly important for dispersal of larvae and geochemical tracers associated with hydrothermal sources that are found primarily along the crest of mid-ocean ridges. Also, the observed eddy-modulated mixing is expected to be useful for validating and improving numerical-model parameterizations of turbulence and mixing in the ocean. Furthermore, since the frequency and intensity of mesoscale eddies depend on the state of the climate, the observed eddy modulation of deep ocean mixing connects climate change and climate variability to physical and biogeochemical dynamics in the deep ocean and implies an unexplored feedback mechanism potentially affecting the global climate system

Global ocean vertical velocity from a dynamically consistent ocean state estimate

Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 122 (2017): 8208–8224, doi:10.1002/2017JC012985.Estimates of the global ocean vertical velocities (Eulerian, eddy-induced, and residual) from a dynamically consistent and data-constrained ocean state estimate are presented and analyzed. Conventional patterns of vertical velocity, Ekman pumping, appear in the upper ocean, with topographic dominance at depth. Intense and vertically coherent upwelling and downwelling occur in the Southern Ocean, which are likely due to the interaction of the Antarctic Circumpolar Current and large-scale topographic features and are generally canceled out in the conventional zonally averaged results. These “elevators” at high latitudes connect the upper to the deep and abyssal oceans and working together with isopycnal mixing are likely a mechanism, in addition to the formation of deep and abyssal waters, for fast responses of the deep and abyssal oceans to the changing climate. Also, Eulerian and parameterized eddy-induced components are of opposite signs in numerous regions around the global ocean, particularly in the ocean interior away from surface and bottom. Nevertheless, residual vertical velocity is primarily determined by the Eulerian component, and related to winds and large-scale topographic features. The current estimates of vertical velocities can serve as a useful reference for investigating the vertical exchange of ocean properties and tracers, and its complex spatial structure ultimately permits regional tests of basic oceanographic concepts such as Sverdrup balance and coastal upwelling/downwelling.National Science Foundation Grant Numbers: OCE-1736633 , OCE-1534618 , OCE-0961713; National Oceanic and Atmospheric Administration Grant Number: NA10OAR43101352018-04-2

Three-Dimensional Distribution of Turbulent Mixing in the South China Sea*

A three-dimensional distribution of turbulent mixing in the South China Sea (SCS) is obtained for the first time, using the Gregg–Henyey–Polzin parameterization and hydrographic observations from 2005 to 2012. Results indicate that turbulent mixing generally increases with depth in the SCS, reaching the order of 10[superscript −2] m[superscript 2] s[superscript −1] at depth. In the horizontal direction, turbulence is more active in the northern SCS than in the south and is more active in the east than the west. Two mixing “hotspots” are identified in the bottom water of the Luzon Strait and Zhongsha Island Chain area, where diapycnal diffusivity values are around 3 × 10[superscript −2] m[superscript 2] s[superscript −1]. Potential mechanisms responsible for these spatial patterns are discussed, which include internal tide, bottom bathymetry, and near-inertial energy

Triangular algebras with nonlinear higher Lie n-derivation by local actions

This paper was devoted to the study of the so-called nonlinear higher Lie n-derivation of triangular algebras $\mathcal{T}$, where $n$ is a nonnegative integer greater than two. Under some mild conditions, we proved that every nonlinear higher Lie n-derivation by local actions on the triangular algebras is of a standard form. As an application, we gave a characterization of higher Lie $n$-derivation by local actions on upper triangular matrix algebras, block upper triangular matrix algebras and nest algebras, respectively

Hidden upwelling systems associated with major western boundary currents

© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Liao, F., Liang, X., Li, Y., & Spall, M. Hidden upwelling systems associated with major western boundary currents. Journal of Geophysical Research: Oceans. 127, (2022): e2021JC017649, https://doi.org/10.1029/2021jc017649.Western boundary currents (WBCs) play an essential role in regulating global climate. In contrast to their widely examined horizontal motions, less attention has been paid to vertical motions associated with WBCs. Here, we examine vertical motions associated with the major WBCs by analyzing vertical velocity from five ocean synthesis products and one eddy-resolving ocean simulation. These data reveal robust and intense subsurface upwelling systems, which are primarily along isopycnal surfaces, in five major subtropical WBC systems. These upwelling systems are part of basin-scale overturning circulations and are likely driven by meridional pressure gradients along the western boundary. Globally, the WBC upwelling contributes significantly to the vertical transport of water mass and ocean properties and is an essential yet overlooked branch of the global ocean circulation. In addition, the WBC upwelling intersects the oceanic euphotic and mixed layers, and thus likely plays an important role in ocean biological and chemical processes by transporting nutrients, carbon and other tracers vertically inside the ocean. This study calls for more research into the dynamics of the WBC upwelling and their role in the ocean and climate systems.X. Liang is supported by the National Science Foundation through Grants OCE-2021274, OCE-2122507, and the Alfred P. Sloan Foundation through Grant FG-2019-12536. M. Spall is supported through the National Science Foundation Grants OCE-1947290 and OCE-2122633