scholarly journals Altimetry-Based Diagnosis of Deep-Reaching Sub-Mesoscale Ocean Fronts

Fluids ◽  
2020 ◽  
Vol 5 (3) ◽  
pp. 145
Author(s):  
Lia Siegelman ◽  
Patrice Klein ◽  
Andrew F. Thompson ◽  
Hector S. Torres ◽  
Dimitris Menemenlis
Keyword(s):  
Finite Size ◽  
Elephant Seal ◽  
Ocean Fronts ◽  
Velocity Gradients ◽  
Lack Of Information ◽  
Frontal Dynamics ◽  
In Situ Observations ◽  
Circumpolar Current ◽  
The Antarctic

Recent studies demonstrate that energetic sub-mesoscale fronts (10–50 km width) extend in the ocean interior, driving large vertical velocities and associated fluxes. However, diagnosing the dynamics of these deep-reaching fronts from in situ observations remains challenging because of the lack of information on the 3-D structure of the horizontal velocity. Here, a realistic numerical simulation in the Antarctic Circumpolar Current (ACC) is used to study the dynamics of submesocale fronts in relation to velocity gradients, responsible for the formation of these fronts. Results highlight that the stirring properties of the flow at depth, which are related to the velocity gradients, can be inferred from finite-size Lyapunov exponent (FSLE) at the surface. Satellite altimetry observations of FSLE and velocity gradients are then used in combination with recent in situ observations collected by an elephant seal in the ACC to reconstruct frontal dynamics and their associated vertical velocities down to 500 m. The approach proposed here is well suited for the analysis of sub-mesoscale-resolving datasets and the design of future sub-mesoscale field campaigns.

scholarly journals Estimating the Four-Dimensional Structure of the Southern Ocean Using Satellite Altimetry

2011 ◽  
Vol 28 (4) ◽  
pp. 548-568 ◽  
Author(s):  
A. J. S. Meijers ◽  
N. L. Bindoff ◽  
S. R. Rintoul
Keyword(s):  
Southern Ocean ◽  
Satellite Altimetry ◽  
Velocity Structure ◽  
Velocity Fields ◽  
Optimal Interpolation ◽  
Dimensional Structure ◽  
Strongly Correlated ◽  
Circumpolar Current ◽  
The Antarctic

Abstract A gravest empirical mode (GEM) projection of temperature and salinity fields over the circumpolar Southern Ocean is presented and is used in combination with satellite altimetry to produce gridded, full-depth, time-evolving temperature, salinity, and velocity fields. Optimal interpolation of historical hydrography, including Argo floats, is used to produce GEM projections of the circumpolar temperature and salinity fields. Parameterizing these fields by dynamic height allows the use of altimetric SSH values from 1992–2006 to create synoptic temperature and salinity fields at weekly intervals on a ⅓° grid at 36 depth levels. The satellite-derived temperature and salinity fields generally capture over 90% of the property variance below the thermocline, with RMS residuals of 1.16°C and 0.132 in salinity at the surface, decreasing to less than 0.45°C and 0.05 below 500 dbar. The combination of altimetry with the GEM fields allows the resolution of the subsurface structure of the filamentary fronts and eddy features. Velocity fields derived from the time-evolving temperature and salinity fields reproduce the Antarctic Circumpolar Current (ACC) velocity structure well, and are strongly correlated (r > 0.7) with in situ measurements from current meters and drifters, with RMS velocity residuals of 4.8–14.8 cm−1 in the Subantarctic Front.

Mesoscale frontal dynamics: shaping the environment of primary production in the Antarctic Circumpolar Current

2002 ◽  
Vol 49 (18) ◽  
pp. 3735-3769 ◽  
Author(s):  
Volker H Strass ◽  
Alberto C Naveira Garabato ◽  
Raymond T Pollard ◽  
Haika I Fischer ◽  
Inga Hense ◽  
...  
Keyword(s):  
Primary Production ◽  
Antarctic Circumpolar Current ◽  
Frontal Dynamics ◽  
Circumpolar Current ◽  
The Antarctic

scholarly journals Performance of Satellite-Based Evapotranspiration Models in Temperate Pastures of Southern Chile

Water ◽  
2020 ◽  
Vol 12 (12) ◽  
pp. 3587
Author(s):  
Italo Moletto-Lobos ◽  
Cristian Mattar ◽  
Jonathan Barichivich
Keyword(s):  
Water Footprint ◽  
Southern Chile ◽  
Productivity Losses ◽  
Lack Of Information ◽  
Irrigation Practice ◽  
Average Water ◽  
In Situ Observations ◽  
Temperate Pastures ◽  
Sustainable Irrigation

Farmers in the temperate zone of southern Chile have started to irrigate historically rainfed pastures during recent years to reduce dairy productivity losses against increasingly severe summer droughts. The lack of information on pasture water requirements (i.e., evapotranspiration), however, hampers the implementation of efficient irrigation programs. Here, we use in-situ observations to evaluate the skill of four remote sensing Surface Energy Balance (SEB) models and two satellite-based global evapotranspiration products (PML_V2 and GLEAM) to estimate actual evapotranspiration (ETa) of pastures in southern Chile during 2014–2017. Daily ETa measured at an evaluation site over the period ranges between 1.2 mm and 6.2 mm day−1 during the growing season (October–March), with an annual maximum of about 4.8 mm day−1 in January and a minimum 0.6 mm day−1 in June. Only the Simplified SEB (SEBS) model and its operational variant (SSEBop) and the PML_V2 global evapotranspiration product perform well, capturing 63–79% of the variance of in-situ evapotranspiration with an error between 0.75 mm day−1 and 1.1 mm day−1. The readily available PML_V2 product can be used as a convenient way to determine average water footprint of pastures and the two SEBs models can be implemented to monitor irrigation requirements in near-real time from field to regional scales. These results demonstrated a high potential of satellite observations for monitoring evapotranspiration and quantify the water footprint of pastures in southern Chile for a sustainable irrigation practice.

Modification of phytoplankton group diversity over submesoscale fronts

2021 ◽  
Author(s):  
Clément Haëck ◽  
Marina Levy ◽  
Laurent Bopp ◽  
Roy El Hourany
Keyword(s):  
Total Biomass ◽  
Phytoplankton Diversity ◽  
Total Phytoplankton ◽  
Frontal Dynamics ◽  
In Situ Observations ◽  
Underlying Mechanisms ◽  
Group Diversity ◽  
Reflectance Data ◽  
Phytoplankton Group

<p>Over large parts of the ocean, submesoscale fronts are known to enhance total phytoplankton abundance because they are the location of intense vertical transport of nutrients. Disparate in situ observations suggest that such frontal dynamics not only affects the total biomass of phytoplankton, but also significantly modifies its composition. Here we make use of a newly developed algorithm able to distinguish a set of phytoplankton-specific pigments to statistically explore the change in phytoplankton community composition over basin-wide regions. We use 15 years of SST and reflectance data from the MODIS sensor on the Aqua satellite, at 1km and daily resolutions and focus on the oligotrophic North Atlantic subtropical gyre and on the more productive gulf stream region. We locate submesoscale fronts by computing an index quantifying SST patchiness. Our results confirm that submesoscale fronts are collocated with elevated Chlorophyll-a concentration and show significant changes in phytoplankton composition. These results underline the influence of submesocale dynamics on phytoplankton diversity, and stress the need to better understand the underlying mechanisms.</p>

Characterization of the ocean mesoscale eddies in the Antarctic Circumpolar Current from in situ, model and remotely sensed data

2020 ◽  
Author(s):  
Yuri Cotroneo ◽  
Lavinia Patara ◽  
Milena Menna ◽  
Pierpaolo Falco ◽  
Jan Klaus Rieck ◽  
...  
Keyword(s):  
Antarctic Circumpolar Current ◽  
Mesoscale Eddies ◽  
Ocean Dynamics ◽  
Joint Analysis ◽  
Spatial And Temporal Variability ◽  
The South ◽  
Eddy Characteristics ◽  
Circumpolar Current ◽  
The Antarctic

<p>Mesoscale variability and associated eddy fluxes play crucial roles in the ocean dynamics, transport of water mass properties and ecology of the upper ocean. In the Southern Hemisphere, where the nearly zonal flow of the Antarctic Circumpolar Current (ACC) acts as a barrier to the direct poleward transport toward the Antarctica, the eddy flux across the ACC is the main mechanism that guarantees the heat budget and distributes physical and biogeochemical properties between subtropical and polar regions. We focused on a high dynamical region located between the South-West Indian Ridge and the South Pacific Ridge. In this area, the interaction between the ACC and the major bathymetric features produces relatively large values of eddy kinetic energy and eddy heat fluxes as well as a relevant forcing for the ACC path.</p><p>The aim of this study is to evaluate the actual efficiency of mesoscale eddies to exchange heat and other properties across the different ACC fronts and to describe the vertical properties of the eddies, their tracks and evolution. To this end, we used in-situ and satellite data in conjunction with a hindcast simulation from 1958 to 2018 performed with a 1/10° ocean biogeochemistry model.</p><p>Eddies are identified and tracked in both the model output and altimetry data while their thermohaline properties and vertical extension are described using model outputs and in situ data, which include available repeated XBT sections (i.e. New Zealand – Antarctica and Hobart – Antarctica) and Argo float profiles located inside these structures.</p><p>Thanks to the joint analysis of model and observational data, we are able to 1) assess the ability of the 1/10° ocean model of simulating the eddy field properties, and to 2) better interpret the spatial and temporal variability of the observed eddy characteristics in the larger and longer framework of the ocean simulation.</p>

Consistency of observed sea surface height changes, bottom pressure changes and temperature, salinity variations in a South Atlantic transect of the Antarctic Circumpolar Current

2020 ◽  
Author(s):  
Alisa Yakhontova ◽  
Roelof Rietbroek ◽  
Jens Schröter ◽  
Nadja Jonas ◽  
Christina Lück ◽  
...  
Keyword(s):  
Antarctic Circumpolar Current ◽  
Sea Surface Height ◽  
South Atlantic ◽  
Sea Surface ◽  
Ocean Bottom ◽  
Bottom Pressure ◽  
Satellite Gravimetry ◽  
Circumpolar Current ◽  
The Antarctic

<p>Improved estimates of temperature, salinity, and sea surface height changes are computed from radar altimetry, satellite gravimetry and Argo profiles, and validated by the in situ ocean bottom pressure measurements in a South Atlantic transect of the Antarctic Circumpolar current. Using satellite gravimetry and altimetry observations, separate contributions to the global sea level can be estimated, but a regional solution is more challenging. Furthermore, Argo derived steric sea level change suffers from spatio-temporal sampling problems, and some signals are not well captured, e.g. in the deeper ocean below 2000m, around the boundary currents, in the Arctic or in the shelf/coastal regions. Jointly processing radar altimetry, Argo and data from the Gravity Recovery and Climate Experiment (GRACE), would allow to correct the deficiencies of the individual datasets, and produce observation based estimates of consistent temperature, salinity and sea surface height changes. In order to pave the way for an advanced joint inversion scheme that additionally resolves for temperature and salinity, the observation equations are formulated which link the satellite observations to temperature and salinity at depth. Observations in the South Atlantic region are compared with simulations from the FESOM model in terms of variability and the model data is used to find the spatial coherence of the signals at the sites with the surrounding ocean. The experiment is performed in the Southern Atlantic Ocean, where the estimates can be validated using an array of in situ ocean bottom pressure observations.</p>

scholarly journals Subantarctic and Polar Fronts of the Antarctic Circumpolar Current and Southern Ocean Heat and Freshwater Content Variability: A View from Argo

2016 ◽  
Vol 46 (3) ◽  
pp. 749-768 ◽  
Author(s):  
Donata Giglio ◽  
Gregory C. Johnson
Keyword(s):  
Southern Ocean ◽  
Antarctic Circumpolar Current ◽  
Potential Temperature ◽  
Local Maximum ◽  
Potential Density ◽  
Argo Data ◽  
Circumpolar Current ◽  
The Antarctic ◽  
Ekman Upwelling

AbstractArgo profiling floats initiated a revolution in observational physical oceanography by providing numerous, high-quality, global, year-round, in situ (0–2000 dbar) temperature and salinity observations. This study uses Argo’s unprecedented sampling of the Southern Ocean during 2006–13 to describe the position of the Antarctic Circumpolar Current’s Subantarctic and Polar Fronts, comparing and contrasting two different methods for locating fronts using the same dataset. The first method locates three fronts along dynamic height contours, each corresponding to a local maximum in vertically integrated shear. The second approach locates the fronts using specific features in the potential temperature field, following Orsi et al. Results from the analysis of Argo data are compared to those from Orsi et al. and other more recent studies. Argo spatial resolution is not adequate to resolve annual and interannual movements of the fronts on a circumpolar scale since they are on the order of 1° latitude (Kim and Orsi), which is smaller than the resolution of the gridded product analyzed. Argo’s four-dimensional coverage of the Southern Ocean equatorward of ~60°S is used to quantify variations in heat and freshwater content there with respect to the time-mean front locations. These variations are described during 2006–13, considering both pressure and potential density ranges (within different water masses) and relations to wind forcing (Ekman upwelling and downwelling).

Sign in / Sign up

Export Citation Format

Share Document