Puertos del Estado, Madrid, Spain
Predicting in a turbulent environment: The Iberian-Biscay-Ireland Copernicus Marine Forecasting System
The present study is aimed at intercomparing the ocean physical daily forecast and 10-year (2002-2012) reanalysis products provided by the Iberia-Biscay-Ireland Monitoring and Forecasting Center (IBI-MFC), in the framework of the Copernicus Marine Environment Monitoring Service (CMEMS), over an overlapping 9-month period (April-December 2011). These two products differ in their spatial resolution and in the use of an observational data assimilation scheme in the reanalysis. Both modeled solutions are compared at regional and local scale against several observational data sources. At regional scale, the forecast and reanalysis show realistic patterns in the area of study. However, at finer scales the results highlight better performances of the 1/36º forecast in coastal areas and the 1/12º reanalysis over open waters. The comparison emphasizes the possible benefits of the data assimilation scheme in areas away from the coastline, but also its limitations in complex coastal regions. Spatial resolution seems to play a key role in such areas, especially around the Iberian Peninsula, where the higher resolution forecast brings in general better results than the coarser resolution reanalysis. The study suggests that the observational data assimilation represents a crucial step towards improving the performance of regional modeled solutions, as long as the spatial resolution is kept at fine-enough meshes in order to prevent higher uncertainties in coastal and shelf areas.
The concept of data assimilation encompasses the various methodologies used to blend the information from observations and model outputs to provide a suitable model solutions incorporating data from observations and able to initialize the ocean model. Since the pioneering failure of the first meteorological application of data assimilation in 1922, much has been understood about model filtering, initialization and interpolation procedures. The optimal solution of the data assimilation problem is based on the Bayes theorem, which allows to calculate the probability distribution of the model states conditioned by the observed state. However, closed optimal solutions of the Bayes theorem exist only for linear models. For non-linear models, only approximate solutions do exist, and a richness of sub-optimal methods have been proposed in the last twenty years. Each sub-optimal approach differs on the strategy used to beat the curse of dimensionality. A review of these approaches in given here.
Many unicellular algae, which compose phytoplankton, are able to swim. Some species have simple orientation mechanisms allowing them to swim against gravity towards the photic zone. A standard mechanistic model allows to account for several experimental observations as resulting from the balance between fluid torque and directed vertical motion, the so-called gyrotaxis. I will discuss how (turbulent) fluid motion and gyrotactic motility can generate patchy distributions.
Institut de Ciències del Mar (CSIC), Barcelona, Spain
Reconstruction of ocean currents from existing satellite observations: the challenge of high resolution dynamics
Infrared and visible satellite observations have revealed that the ocean surface is crowded with eddies with scales O(10 -100 km) and submesoscale structures, like fronts and filaments, with scales O(1-10 km). Satellite infrared measurements of Sea Surface Temperature (SST) have resolutions high enough to observe submesoscales (~1 km), and the existence of multiple platforms with infrared sensors can provide observations of the same area with temporal samplings of less than 6 h. The key problem to be addressed is the extraction of quantitative dynamical information at the scales of interest from existing observations. Indeed, along-track altimetric measurements of Sea Surface Heights (SSH) are very well suited to quantify across-track currents. However, the spatial resolution of derived 2D velocities is restricted to scales above 100-150 km and the limited number of altimeters can lead to errors in the location of currents. To overcome the previous constrains, new theoretical frameworks that model the dynamics of the upper ocean have been proposed. Here, we discuss the strengths and weakness of dynamical approaches like the Surface Quasi-Geostrophic (SQG) equations to retrieve the three-dimensional dynamics of the ocean, as well as other approaches that exploit the synergy between SST and SSH measurements to provide enhanced 2D surface currents. Recent results showing the current capabilities to retrieve the velocity field at scales of the order of 10 km will be also shown.
Lanotte, Alessandra S.
CNR-Istituto di Scienze dell'Atmosfera e del Clima, Lecce, Italy
Modelling Oceanic Dispersion : an application to the Lagrangian Transport in the Sicily Channel
A correct description of Lagrangian dispersion in the ocean has great relevance, but it is a delicate task because of the finite space and time resolution of the circulation models. These are mostly affected by two main limitations: i) unresolved scale motions, and mesoscale motions that are largely smoothed out at scales close to the grid spacing; (ii) poorly resolved time variability in the profiles of the horizontal velocities in the upper layer. In the talk, I will discuss how we can use observations to improve numerical modeling of dispersion processes. As an application, I will discuss a case of Lagrangian transport in the Central Mediterranean Region.
LOPS, IRD, Brest, France
Small Scales of variability of the Sea Surface Salinity: a regional and global survey.
C. Maes (Laboratoire d’Océanographie Physique et Spatiale–LOPS) in collaboration with L. Rousselet, S. Guimbard, K Drushka, A. Doglioli, N. Kolodziejczyk, N. Reul, G. Charria, J. Reagan, B. Blanke, E. Martinez, A. Petrenko, J. Boutin and I. Ansorge Recent research, mostly from numerical simulations at very high resolution, suggests that mesoscale and submesoscale variability and the associated exchange processes are not independent but coupled in a subtle but important way, which includes a variety of potential mechanisms for the nonlinear transfer of energy between different scales. Consequently, new and high-resolution global observations of upper ocean motions are required to make progress in the critical areas of the mesoscale and submesoscale variability and their associated upper-ocean lateral and vertical exchange processes. The goal here will be to provide a regional and global survey of the small scales of variability of the SSS field with typical range from 10 to 100 km, that could be observed from in situ observations, and mainly shipboard thermosalinographs (TSGs). Salinity variability at these scales also has implications for the validation of satellite-based measurements, characterized by a spatial footprint of 50-150 km. Different oceanic areas will be investigated to give an
United States Naval Academy, Annapolis, MD, USA
SPace of Eulerian MeasureS (SPEMS) application to Oceanographic Flows
Through the application of multiple Eulerian measures of a fluid flow, a measurement space is created which is comprised of one axis for each measurement, where currently at least six Eulerian measures are being applied to oceanographic flows. The SPace of Eulerian MeasureS (SPEMS) is analyzed using high dimensional cluster analysis, where the data for the flows aggregate into clusters, which can then be interpreted more traditionally as gyres, steady flow, turbulence, hyperbolicity, etc... A novel approach to correlating the clusters from the SPEMS with Lagrangian techniques will be presented. Areas of interest include the mouth of the Chesapeake Bay and the Kuroshio.
Unique datasets have been collected by field campaigns that released from Antarctica super-pressure balloons capable of drifting for months in the lower southern stratosphere during the springs of 2005 and 2010. The existence of these datasets provided a major motivation for Lagrangian studies of this region of the atmosphere wherein the “Antarctic Ozone Hole” forms. In this presentation we review the results of our analyses that used this data complemented by modeling studies to examine the transport inside the strong circumpolar vortex that characterizes the region during spring and the kinematics of the large-scale (Rossby) waves that perturb the vortex. The data analysis applied by the first time to the stratospheric flow the Lagrangian descriptor known as the function M (e. g. Madrid and Mancho 2009). The modeling approach was based on the simulation by a conceptual numerical model of the flow both inside the vortex from realistic initial conditions. The results obtained have demonstrated that the function M provides a sharp depiction of key Lagrangian features of a highly transient flow, presented plausible routes of large-scale horizontal transport across the vortex edge, highlighted the importance of lobe dynamics as a transport mechanism across the Antarctic polar vortex, and identified episodes of planetary (Rossby) wave breaking both inside and outside the vortex. The modeling studies showed how hyperbolic trajectories can be used to detect kinematic structures associated Rossby wave breaking. Current research focuses on the interannual variability of the winter-to-summer transition in the southern stratosphere.
Transport properties of nonautonomous dynamical systems over a finite-time interval can be described within a probabilistic framework. Of particular interest are coherent sets. These are time-dependent macroscopic structures that hardly mix with the rest of phase space over the considered time span. Such behavior can be observed in many real-world phenomena, including the polar vortex, gyres and eddies in the ocean as well as thermal plumes in convection. Coherent sets can be efficiently detected and approximated within a transfer operator based approach and by recently developed clustering techniques. In this talk, we discuss the theory and numerics of coherent sets constructions and demonstrate their properties in a number of example systems. This is joint work with Gary Froyland (UNSW Australia).
University of Santiago de Compostela, University of Santiago de Compostela., Spain
Atmospheric rivers and their contribution to a 40-year Lagrangian “climatology”
The transport of moisture from the tropics to mid-latitudes is not continuous and uniform, but rather intermittent. More than 90% of poleward water vapor is transported by narrow and elongated structures (longer than 2000 km and narrower than 1000 km). These structures, referred to as Atmospheric Rivers (ARs), are a key process for the latent heat redistribution and atmospheric mixing. They are responsible for extreme precipitation and flood events as they approach coastal areas. Based on an integrated water vapor flux obtained from the ERA-Interim database, AR events have been clearly identified with attracting Lagrangian Coherent Structures (LCS) (Chaos 25, 063105 (2015)). From a Lagrangian point of view, the attracting LCS accumulates water vapor in front of the pattern moving towards the east. Given that ARs over the Atlantic and Pacific Ocean appear as coherent filaments of water vapor with a persistence time of several days up to a week and they occur periodically, we will address their contribution to the atmospheric mixing in the troposphere. To that end, a 40-year Lagrangian “climatology” based on the calculation of Finite-Time Lyapunov Exponents (FTLE) has been calculated. Different geophysical drivers as ENSO and ARs were identified in the FTLE climatology. Our results suggest that ARs contribution to the atmospheric mixing ranges from 15 to 25%.
Ramos, Antonio G.
Universidad de las Palmas de Gran Canaria, Las Palmas, Spain
Lagrangian path planning for the first Autonomous Underwater Vehicles in transoceanic missions: The new boundaries of the operational oceanography
Unmanned Underwater Vehicles (UUVs) are used in Oceanography due to their relative low cost and wide range of capabilities. Gliders change their buoyancy in order to dive and climb, describing a vertical saw tooth route. These diplacements produce an effective although low horizontal speed which makes the glider strongly sensitive to the ocean dynamics. In order to control the glider path its heading is adapted by using information obtained from verified 4D current data sets. In particular from these data, Lagrangian descriptors have supplied potentially useful paths for piloting the RU-29 Challenger glider in the first South Atlantic Circunnavigation crossing flight (760 days-sea, 17400 km) held from 16 th January 2013 to 31 st March 2016). A description of the Challenger glider mission is found at http://challenger.marine.rutgers.edu/ . Invariant manifolds of hyperbolic trajectories were obtained from the real time 4D current fields (1o/12) forecast (+5 days) provided by the european marine forecasting system COPERNICUS in the South Atlantic domain during the last quarter of the mission (1500km far from S Africa). Manifolds outputs were then compared with the ground true paths and the ground currents provided by RU29 when surfaced (every 14 hours). Preliminary results reported by the glider at its arrival at Cape Town (end of March, 2016), showed that the strong Agulhas current/mixing dynamics, was not captured by any of the 5 current models (Copernicus, Hycom, Oscar, NRTOFS, Glory) used for the comparison. Prior to this stage however (December 2015-mid March 2016) the manifolds obtained from the COPERNICUS current fields showed a high percentage of confident good routes that were confirmed by the ground true flying paths reported by the glider nearing the South African ZEE border (10 th March 2016). The preliminary combination of the glider data with the invariant manifolds suggests a potentially useful tool for gliders path planning in future long range transoceanic glider missions (Indian Ocean 2017-). Keywords: South Atlantic Crossing. Autonomous Underwater Vehicles (AUVs). Path planning. Lagrangian Descriptors. Hyperbolic Trajectories. Decision Support.
NERSC, Bergen, Norway
Challenges in observation and modelling of Arctic climate change
It is a major challenge to develop an integrated Arctic Observation System that is required to understand and predict the changes in the Arctic climate system. There are numerous ongoing efforts to extend and improve existing systems in the different regions of the Arctic. Satellite earth observation data plays an increasingly important role in such observing system, because the amount of EO data for observing the global climate and environment grows year by year. In situ observing systems are much more limited due to logistical constraints and cost limitations. The sparseness of in situ data is therefore the largest gap in the overall observing system.. The development of a sustainable Arctic observing system requires coordination, mobilization and cooperation between the existing European and international infrastructures (in-situ and remote including space-based) the modelling communities and relevant stakeholder groups. An integrated Arctic Observation System will enable better-informed decisions and better-documented processes within key sectors (e.g. local communities, shipping, tourism, fishing), in order to strengthen the societal and economic role of the Arctic region and support the EU strategy for the Arctic and related maritime and environmental policies.