The hidden geometry of ocean flows

We introduce a new global Lagrangian descriptor that is applied to flows with general time dependence (altimetric datasets). It succeeds in detecting simultaneously, with great accuracy, invariant manifolds, hyperbolic and non-hyperbolic flow regions.Comment: 4 pages, 4 figure

Altimetric sampling and mapping procedures induce spatial and temporal aliasing of the signal – characteristics of these aliasing effects in the Mediterranean Sea

International audienceThis study deals with spatial and temporal aliasing of the sea surface signal and its restitution with altimetric maps of Sea Level Anomalies (SLA) in the Mediterranean Sea. Spatial and temporal altimetry sampling, combined with a mapping process, are unable to restore high-frequency (HF) surface variability. In the Mediterranean Sea, it has been shown that signals whose intervals are less than 30–40 days are largely underestimated, and the residual HF restitution signal contains characteristic errors which make it possible to identify the spatial and temporal sampling of each satellite. The origin of these errors is relatively complex. Three main effects are involved: the sampling of the HF long-wavelength (LW) signal, the correction of this signal's aliasing and the mapping procedure. – The sampling depends on the characteristics of the satellites considered, but generally induces inter-track bias that needs to be corrected before the mapping procedure is applied. – Correcting the aliasing of the HF LW signal, carried out using a barotropic model output and/or an empirical method, is not perfect. In fact, the baroclinic part of the HF LW signal is neglected and the numerical model's capabilities are limited by the spatial resolution of the model and the forcing. The empirical method cannot precisely control the corrected signal. – The mapping process, which is optimised to improve restitution of mesoscale activity, does not propagate the LW signal far from the satellite tracks. Even though these residual errors are very low with respect to the total signal, their signature may be visible on maps of SLAs. However, these errors can be corrected by more careful consideration of their characteristics in terms of spatial distribution induced by altimetric along-track sampling. They can also be attenuated by increasing the altimetric spatial coverage through the merging of different satellites. Ultimately, the HF signal, which is missing in maps of SLA, can be completed using a numerical model in order to estimate the total surface signal. The barotropic HF (<30 days) component accounts for nearly 10% of the total variability. Locally, it contributes nearly 25% of the total variance

High resolution 3-D temperature and salinity fields derived from in situ and satellite observations

This paper describes an observation-based approach that efficiently combines the main components of the global ocean observing system using statistical methods. Accurate but sparse in situ temperature and salinity profiles (mainly from Argo for the last 10 yr) are merged with the lower accuracy but high-resolution synthetic data derived from satellite altimeter and sea surface temperature observations to provide global 3-D temperature and salinity fields at high temporal and spatial resolution. The first step of the method consists in deriving synthetic temperature fields from altimeter and sea surface temperature observations, and salinity fields from altimeter observations, through multiple/simple linear regression methods. The second step of the method consists in combining the synthetic fields with in situ temperature and salinity profiles using an optimal interpolation method. Results show the revolutionary nature of the Argo observing system. Argo observations now allow a global description of the statistical relationships that exist between surface and subsurface fields needed for step 1 of the method, and can constrain the large-scale temperature and mainly salinity fields during step 2 of the method. Compared to the use of climatological estimates, results indicate that up to 50% of the variance of the temperature fields can be reconstructed from altimeter and sea surface temperature observations and a statistical method. For salinity, only about 20 to 30% of the signal can be reconstructed from altimeter observations, making the in situ observing system essential for salinity estimates. The in situ observations (step 2 of the method) further reduce the differences between the gridded products and the observations by up to 20% for the temperature field in the mixed layer, and the main contribution is for salinity and the near surface layer with an improvement up to 30%. Compared to estimates derived using in situ observations only, the merged fields provide a better reconstruction of the high resolution temperature and salinity fields. This also holds for the large-scale and low-frequency fields thanks to a better reduction of the aliasing due to the mesoscale variability. Contribution of the merged fields is then illustrated to describe qualitatively the temperature variability patterns for the period from 1993 to 2009

Sea level budget over 2003-2008: A reevaluation from GRACE space gravimetry, satellite altimetry and Argo

0921-8181From the IPCC 4th Assessment Report published in 2007, ocean thermal expansion contributed by similar to 50% to the 3.1 mm/yr observed global mean sea level rise during the 1993-2003 decade, the remaining rate of rise being essentially explained by shrinking of land ice. Recently published results suggest that since about 2003, ocean thermal expansion change, based on the newly deployed Argo system, is showing a plateau while sea level is still rising, although at a reduced rate (similar to 2.5 mm/yr). Using space gravimetry observations from GRACE, we show that recent years sea level rise can be mostly explained by an increase of the mass of the oceans. Estimating GRACE-based ice sheet mass balance and using published estimates for glaciers melting, we further show that ocean mass increase since 2003 results by about half from an enhanced contribution of the polar ice sheets - compared to the previous decade - and half from mountain glaciers melting. Taking also into account the small GRACE-based contribution from continental waters (<0.2 mm/yr), we find a total ocean mass contribution of similar to 2 mm/yr over 2003-2008. Such a value represents similar to 80% of the altimetry-based rate of sea level rise over that period. We next estimate the steric sea level (i.e., ocean thermal expansion plus salinity effects) contribution from: (1) the difference between altimetry-based sea level and ocean mass change and (2) Argo data. Inferred steric sea level rate from (1) (similar to 0.3 mm/yr over 2003-2008) agrees well with the Argo-based value also estimated here (0.37 mm/yr over 2004-2008). Furthermore, the sea level budget approach presented in this study allows us to constrain independent estimates of the Glacial Isostatic Adjustment (GIA) correction applied to GRACE-based ocean and ice sheet mass changes, as well as of glaciers melting. Values for the CIA correction and glacier contribution needed to close the sea level budget and explain GRACE-based mass estimates over the recent years agree well with totally independent determinations. (C) 2008 Elsevier B.V. All rights reserved

Operational oceanography in support to indicator reporting

Operational Oceanography (OO) has now emerged to a stage that allows the design, development and execution of marine core services tailored to user requirements. As such it is also feasible to provide routine production of environmental and climate indicators. Indicators are synthetic indices of environmental changes at various temporal and spatial scales. In this paper we outline the possible contribution and strengthening of existing indicator reporting based on OO products followed by a discussion of the relevance of such improved reporting for marine environmental policy implementation and regulation. In particular, it capitalizes on the main achievements of the Marine Environment and Security of the European Area (MERSEA) project, the outcome of a European Marine Monitoring and Assessment (EMMA) workshop on the connection between operational oceanography and the European Marine Strategy (EMS) Directive and the regular European Environmental Agency (EEA) assessment reports

Assessing the impact of observations on ocean forecasts and reanalyses: Part 2, Regional applications

The value of global (e.g., altimetry, satellite sea-surface temperature, Argo) and regional (e.g., radars, gliders, instrumented mammals, airborne profiles, biogeochemical) observation-types for monitoring the mesoscale ocean circulation and biogeochemistry is demonstrated using a suite of global and regional prediction systems and remotely-sensed data. A range of techniques is used to demonstrate the value of different observation-types to regional systems and the benefit of high- resolution and adaptive sampling for monitoring the mesoscale circulation. The techniques include Observing System Experiments, Observing System Simulation Experiments, adjoint sensitivities, representer matrix spectrum, observation footprints, information content and spectral analysis. It is shown that local errors in global and basin-scale systems can be significantly reduced when assimilating observations from regional observing systems

Use of satellite observations for operational oceanography: recent achievements and future prospects

The paper gives an overview of the development of satellite oceanography over the past five years focusing on the most relevant issues for operational oceanography. Satellites provide key essential variables to constrain ocean models and/or serve downstream applications. New and improved satellite data sets have been developed and have directly improved the quality of operational products. The status of the satellite constellation for the last five years was, however, not optimal. Review of future missions shows clear progress and new research and development missions with a potentially large impact for operational oceanography should be demonstrated. Improvement of data assimilation techniques and developing synergetic use of high resolution satellite observations are important future priorities

Impairing flow-mediated endothelial remodeling reduces extravasation of tumor cells

Tumor progression and metastatic dissemination are driven by cell-intrinsic and biomechanical cues that favor the growth of life-threatening secondary tumors. We recently identified pro-metastatic vascular regions with blood flow profiles that are permissive for the arrest of circulating tumor cells. We have further established that such flow profiles also control endothelial remodeling, which favors extravasation of arrested CTCs. Yet, how shear forces control endothelial remodeling is unknown. In the present work, we aimed at dissecting the cellular and molecular mechanisms driving blood flow-dependent endothelial remodeling. Transcriptomic analysis of endothelial cells revealed that blood flow enhanced VEGFR signaling, among others. Using a combination of in vitro microfluidics and intravital imaging in zebrafish embryos, we now demonstrate that the early flow-driven endothelial response can be prevented upon specific inhibition of VEGFR tyrosine kinase and subsequent signaling. Inhibitory targeting of VEGFRs reduced endothelial remodeling and subsequent metastatic extravasation. These results confirm the importance of VEGFR-dependent endothelial remodeling as a driving force of CTC extravasation and metastatic dissemination. Furthermore, the present work suggests that therapies targeting endothelial remodeling might be a relevant clinical strategy in order to impede metastatic progression.</p

GlobCurrent : Multisensor synergy for surface current estimation

The GlobCurrent project (http://www.globcurrent.org) aims to: (i) advance the quantitative estimation of ocean surface currents from satellite sensor synergy; and (ii) demonstrate impact in user-led scientific, operational and commercial applications that, in turn, will improve and strengthen the uptake of satellite measurements. It is often demonstrated that sharp gradients in the sea surface temperature (SST) and current fields and the ocean surface chlorophyll-a distribution are spatially correlated with the sea surface roughness anomaly fields at small spatial scales, in the sub-mesocale (1-10 km) to the mesoscale (30-80 km). At the larger mesoscale range (>50 km), information derived from radar altimeters often depict the presence of coherent structures and eddies. The variability often appears largest in regions where the intense surface current regimes (>100 - 200 km) are found. These 2dimensional structures manifested in the satellite observations represent evidence of the upper ocean (~100-200 m) dynamics. Whereas the quasi geostrophic assumption is valid for the upper ocean dynamics at the larger scale (>100 km), possible triggering mechanisms for the expressions at the mesoscale-to-submesoscale may include spiraling tracers of inertial motion and the interaction of the wind-driven Ekman layer with the quasi-geostrophic current field. This latter, in turn, produces bands of downwelling (convergence) and upwelling (divergence) near fronts. A regular utilization of the sensor synergy approach with the combination of Sentinel-3, Sentinel-2 and Sentinel-1 together with other satellite missions will provide a highly valuable data set for further research and development to better relate the 2-dimensional surface expressions and the upper ocean dynamics