Based on an extensive dataset obtained from multiple individual ship-based samplings of mesoscale eddies (2006-2023), interactions between mesoscale eddies and internal waves are analyzed. Theory predicts that anticyclonic mesoscale eddies shift the effective Coriolis frequency for near-inertial waves (NIW) locally in regions of strong relative vorticity towards subinertial frequencies,...
Mesoscale structures are key dynamical features of the ocean. They are associated with a variety of short lived and small-scale dynamics linked to physical, biological, and chemical processes at the submesoscale, such as cascading energy, impacting ocean stratification, and guiding ocean carbon and oxygen uptake. In the high latitudes, the spatial extent of the mesoscale is only tens of...
In the power spectrum, the upper and deep parts of the Kuroshio Extension have distinctly different peaks. The former peaks around 200 days, while the latter is mainly at the intraseasonal band. How the upper meandering jet links the deep intraseasonal eddy current then makes an issue. In this study, it is investigated using the outputs from a 1/10° ocean general circulation model. The...
The oceans circulation redistributes heat, salt, biota, dissolved gases, microplastics, and sediments on Earth. The interior ocean, 100 - 1000 m above the sloping seafloor, moves on average mainly with the deeper seafloor to its left in the Northern Hemisphere and to its right in the Southern Hemisphere. It has not been addressed how bottom friction and the steepness of the seafloor affect...
Tropical precipitation and organized convection have a global influence in the form of extratropical teleconnections. The main source for these stationary Rossby wave trains is believed to be vortex stretching by the divergent outflow of convection. We present the tropical zonal-mean momentum budget from reanalysis data and use a Helmholtz decomposition as a diagnostic tool. In contrast to...
The coupled nature of the ocean-atmosphere system frequently makes understanding the direction of causality difficult in ocean-atmosphere interactions. This study presents a method to decompose turbulent heat fluxes into a component which is directly forced by atmospheric circulation, and a residual which is assumed to be primarily `ocean-forced'. This method is applied to the North Atlantic...
Eurasian teleconnection pattern (EU) and its two variants (EU1 and EU2) are the representative wintertime atmospheric teleconnections over Eurasian continent. They are mainly indicative of the local features and closely related to other teleconnection patterns. What are the major interannual climate modes over mid-high latitude Eurasia in boreal winter is still an open question. With the ERA5...
The three-dimensional (3D) currents and hydrography over the eastern Canadian shelf (ECS) are affected significantly by atmospheric forcing and freshwater discharges from rivers and low salinity waters associated with ice/snow melting at high latitudes. A significantly large knowledge gap exists in our understanding of temporal and spatial variability in the 3D circulation and...
This study examines sea level variations beyond monthly time scales during 2008-2016 in the northeast Pacific, using the solution of the 1/36-deg NE Pacific regional model combined with tide gauge and gridded altimeter data, and surface atmospheric forcing. Main results are:
(1) Along a zonal section extending westward from the Tofino tide gauge on Vancouver Island, sea level variations...
Warm Atlantic Water is resulting in significant retreat of marine terminating glaciers in Northwest Greenland. We use the FESOM ocean model, together with observations of salinity, temperature, and bathymetry from NASA’s Ocean Melting Greenland mission, and Mankoff’s discharge estimates to understand the pathways of Atlantic Water towards these glaciers. Using the model we explore the role of...
This study investigates the specific circulation anomalies that have sustained the low Antarctic sea ice state since 2016. Firstly, we find a significant strengthening and southward shift in the Ferrel Cell (FC) during 2016–2022, resulting in a marked increase in southward transport of heat and moisture. Secondly, this enhanced FC is closely associated with a stronger circumpolar wave pattern...
The intraseasonal variability of the tropical eastern boundary upwelling region in the Atlantic Ocean is investigated using multiyear mooring and satellite data. Pronounced oscillations of alongshore velocity and sea level off Angola at periods of about 90 and 120 days are observed. Similar spectral peaks are detected along the equator suggesting an equatorial forcing via equatorial and...
The Synergistic Observing Network for Ocean Prediction (SynObs) project (https://oceanpredict.org/synobs) seeks to find synergies between ocean observations and ocean prediction through a multi-system approach to an Observing System Experiment (OSE). Best estimates and predictions of the location of eddies, ocean sound speed profiles, ocean currents and ocean water masses are important ocean...
The coupling of the upper mixed layer with the thermocline is investigated in a planetary geostrophic model. Assuming that submesoscale instabilities lead to a rectified effect of geostrophic eddies on the (late winter) mixed layer depth D, and that the mesoscale eddy field is stronger where the thermocline (depth G) is larger, a parameter (r) coupling D to G is identified. Inclusion of this...
Observational and modelling studies of the tropical ocean mixed layer have shown a dominate role of the vertical diffusive heat flux due to turbulent mixing for maintaining sea surface temperature in the tropical Atlantic. Progress has been made in identifying ocean processes responsible for enhancing turbulent mixing in the upper stratified ocean including near-inertial waves and Tropical...
The Atlantic meridional overturning circulation (AMOC) is a key feature of the oceanic circulation and has a big impact on regional weather and global climate. As the characteristics of the northward return flow of the AMOC crossing the equator are crucial for deep water formation at high latitudes in the North Atlantic, the AMOC variability in the South Atlantic is of particular interest....
The eastern equatorial Atlantic hosts a productive marine ecosystem that relies on upward supply of nitrate, the main limiting nutrient in this region. The annual peak in surface chlorophyll occurs in boreal summer, roughly coincident with increased easterly winds. Enhanced turbulence is expected with increased winds. However, upward nitrate supply by mixing requires this turbulence to act on...
It has been shown that the Equatorial Intermediate Current (EIC) in the Pacific Ocean, which is a westward current along the equator at intermediated depth (from 500m to at least 2000 m), has a basin-wide zonally uniform structure. In addition to the EIC, intraseasonal variability (ISV) has also been observed near the equator at 1000 m depth with significant amplitude in the eastern Pacific...
The amplitude of El Niño/Southern Oscillation (ENSO) varied considerably over the last 140 years. We find that the difference between high and low ENSO-amplitude periods results mainly from the number of strong Eastern Pacific (EP) El Niños, while Central Pacific (CP) El Niños and La Niña events do not contribute much. Further, the asymmetry of ENSO, i.e. SST anomalies during El Niño being...
The present study has determined the anticyclonic and cyclonic circulations of wave energy in the western and eastern parts, respectively, of the tropical-subtropical Pacific Ocean in each hemisphere. In terms of directionality, these wave energy circulation patterns contrast sharply with those in the Indian and Atlantic Oceans where wave energy circulation is cyclonic in the western part of...
co-authors: Martin Claus, Jufen Lai and Xiaoting Zhu
In the 1970's and 80's, Jim O'Brien's group at Florida State University showed that linear, reduced-gravity shallow water models have skill at capturing and interpreting ENSO events. At that time, the models were driven by estimates of the surface wind stress derived from ship measurements and were verified using sea level measured at...
Atmosphere and ocean dynamics are dictated by balanced flows, such as mesoscale eddies, but determining a precise balanced state remains challenging in the presence of its nonlinear coupling with the unbalanced flows, such as internal gravity waves. This results in nonlinear internal wave generation by spontaneous loss of balance, that challenges the conundrum of the existence of an invariant...
The Boussinesq approximation is commonly made in ocean general circulation models (OGCMs). As a consequence, the model ocean is incompressible and conserves volume, but not mass. It has been argued that these consequence introduce errors at the noise level of coarse OGCMs, but that non-Boussinesq modeling is preferable simply for tidiness. Here, we use the height-pressure coordinate...
The difference between eastern and western boundary pressures is strongly constrained by the zonal wind stress via the balance of angular momentum, and the meridional derivative of boundary pressure represents the bottom pressure torque, closely related to boundary current transport. Here, we use the analytical solutions available due to the Stommel and Munk models to investigate the behaviour...
Observing subsurface temperatures in the ocean can be challenging due to their natural sparsity, leading to considerable uncertainties in model-based estimates. As a result, historical assessments of ocean heat content (OHC) often suffer from distortions and biases. In this research, we explore the feasibility of employing physics-informed neural networks (PINNs) to reconstruct subsurface...
Ocean models have unresolved processes and scales, normally associated with processes that model resolution or model physics cannot account for. For systems initialized to observations, one also has unconstrained scales, scales that cannot be constrained by the observational network. Ensemble systems, through accessing the full parameter space with Monte Carlo methods, are one method to...
Deep learning has proven to be a valuable tool to represent subgrid processes in climate models, but most application cases have so far used idealized settings and deterministic approaches. Here, we develop ensemble and stochastic parameterizations with calibrated uncertainty quantification to learn subgrid convective and turbulent processes and surface radiative fluxes of a...
Scale analysis based on coarse-graining has recently been proposed as an alternative to Fourier analysis for the analysis of eddy-rich ocean simulation data. It requires interpolation to a regular grid for data on general meshes, especially for the output of unstructured-mesh models. We propose an alternative coarse-graining method based on implicit filters using powers of discrete Laplacians....
This study investigates the variability of Atlantic Meridional Overturning Circulation (AMOC) using both density and traditional z frameworks in the AWI-CM climate model. By prioritizing the density framework, we aim to understand which water mass transformations cause the AMOC change. These transformations are seen as diapycnal velocities through given isopycnal surfaces, and their...
The volume transport of the Antarctic Circumpolar Current is typically described in textbooks as set by a combination of wind and buoyancy forcing. However, results of eddy-permitting numerical ocean models contradict this statement, instead indicating minimal sensitivity of circumpolar volume transport to the magnitude of the surface wind stress. A simple theoretical model is developed,...
The Southern Ocean provides dominant contributions to global ocean heat and carbon uptake, which is widely interpreted as resulting from its unique upwelling and circulation. Here we show a large asymmetry in these contributions, with the Southern Ocean accounting for 83%±33% of global heat uptake versus 43%±3% of global ocean carbon uptake over the historical period in state-of-the-art...
Decadal variability in subpolar North Atlantic Ocean heat content is strongly influenced by the atmosphere. Seasonal and annual atmospheric disturbances leave a lasting impact on the ocean for several years due to the ocean's substantial thermal inertia. These atmospheric perturbations first generate anomalous air-sea heat fluxes and wind patterns, rapidly modifying upper ocean temperatures (a...
Understanding the uncertainty of a state is not only important in assessing the forecast of that state, but also of interest in its own right from a physical point of view. Within the information theoretic framework, uncertainty is conveniently measured in terms of Shannon entropy, which we denote by H henceforth. For the atmosphere-ocean system, however, H is in general computationally...
