Fiat lux – Shedding new light on derivatives markets.

Not so long ago, we policymakers thought we knew just what challenges we were facing for Europe to better take advantage of globalisation through a more sustainable model: these were climate change and a rapidly ageing society. However, since 2007 we have also learnt that there was another area requiring a deep sustainability check: the financial system. What started in 2007 as a credit crisis in the US market for subprime mortgages turned into a full-blown global fi nancial crisis in 2008, following Lehman’s default and has taken us near to a sovereign debt crisis as countries face the fiscal consequences of financial instability, on top of large public indebtedness. This highlights the importance of the financial system for society as a whole and, therefore, the political imperative of mending it so that finance serves the real economy – not the other way around. We therefore need to put in place a new set of rules and principles ensuring a stable and sustainable financial system. Without this our whole economy will be impeded from prospering again and we will not be able to address the challenges outlined above.

Sources, fate, and pathways of Leeuwin Current water in the Indian Ocean and Great Australian Bight: A Lagrangian study in an eddy-resolving ocean model

The Leeuwin Current is the dominant circulation feature in the eastern Indian Ocean, transporting tropical and subtropical water southward. While it is known that the Leeuwin Current draws its water from a multitude of sources, existing Indian Ocean circulation schematics have never quantified the fluxes of tropical and subtropical source water flowing into the Leeuwin Current. This paper uses virtual Lagrangian particles to quantify the transport of these sources along the Leeuwin Current's mean pathway. Here the pathways and exchange of Leeuwin Current source waters across six coastally bound sectors on the south-west Australian coast are analyzed. This constitutes the first quantitative assessment of Leeuwin Current pathways within an offline, 50 year integration time, eddy-resolving global ocean model simulation. Along the Leeuwin Current's pathway, we find a mean poleward transport of 3.7 Sv in which the tropical sources account for 60-78% of the transport. While the net transport is small, we see large transports flowing in and out of all the offshore boundaries of the Leeuwin Current sectors. Along the Leeuwin Current's pathway, we find that water from the Indonesian Throughflow contributes 50-66% of the seasonal signal. By applying conditions on the routes particles take entering the Leeuwin Current, we find particles are more likely to travel offshore north of 30°S, while south of 30°S, particles are more likely to continue downstream. We find a 0.2 Sv pathway of water from the Leeuwin Current's source regions, flowing through the entire Leeuwin Current pathway into the Great Australian Bight

Wind Forced Variability in Eddy Formation, Eddy Shedding, and the Separation of the East Australian Current

The East Australian Current (EAC), like many other subtropical western boundary currents, is believed to be penetrating further poleward in recent decades. Previous observational and model studies have used steady state dynamics to relate changes in the westerly winds to changes in the separation behavior of the EAC. As yet, little work has been undertaken on the impact of forcing variability on the EAC and Tasman Sea circulation. Here using an eddy‐permitting regional ocean model, we present a suite of simulations forced by the same time‐mean fields, but with different atmospheric and remote ocean variability. These eddy‐permitting results demonstrate the nonlinear response of the EAC to variable, nonstationary inhomogeneous forcing. These simulations show an EAC with high intrinsic variability and stochastic eddy shedding. We show that wind stress variability on time scales shorter than 56 days leads to increases in eddy shedding rates and southward eddy propagation, producing an increased transport and southward reach of the mean EAC extension. We adopt an energetics framework that shows the EAC extension changes to be coincident with an increase in offshore, upstream eddy variance (via increased barotropic instability) and increase in subsurface mean kinetic energy along the length of the EAC. The response of EAC separation to regional variable wind stress has important implications for both past and future climate change studies

Optimal adjustment of the atmospheric forcing parameters of ocean models using sea surface temperature data assimilation

In ocean general circulation models, near-surface atmospheric variables used to specify the atmospheric boundary condition remain one of the main sources of error. The objective of this research is to constrain the surface forcing function of an ocean model by sea surface temperature (SST) data assimilation. For that purpose, a set of corrections for ERAinterim (hereafter ERAi) reanalysis data is estimated for the period of 1989–2007, using a sequential assimilation method, with ensemble experiments to evaluate the impact of uncertain atmospheric forcing on the ocean state. The control vector of the assimilation method is extended to atmospheric variables to obtain monthly mean parameter corrections by assimilating monthly SST and sea surface salinity (SSS) climatological data in a low resolution global configuration of the NEMO model. In this context, the careful determination of the prior probability distribution of the parameters is an important matter. This paper demonstrates the importance of isolating the impact of forcing errors in the model to perform relevant ensemble experiments. <br><br> The results obtained for every month of the period between 1989 and 2007 show that the estimated parameters produce the same kind of impact on the SST as the analysis itself. The objective is then to evaluate the long-term time series of the forcing parameters focusing on trends and mean error corrections of air–sea fluxes. Our corrections tend to equilibrate the net heat-flux balance at the global scale (highly positive in ERAi database), and to remove the potentially unrealistic negative trend (leading to ocean cooling) in the ERAi net heat flux over the whole time period. More specifically in the intertropical band, we reduce the warm bias of ERAi data by mostly modifying the latent heat flux by wind speed intensification. Consistently, when used to force the model, the corrected parameters lead to a better agreement between the mean SST produced by the model and mean SST observations over the period of 1989–2007 in the intertropical band

Interactions between the Somali Current eddies during the summer monsoon: insights from a numerical study

International audienceThree hindcast simulations of the global ocean circulation differing by resolution (1/4 or 1/12°) or parametrization or atmospheric forcing are used to describe the interactions between the large anticyclonic eddies generated by the Somali Current system during the Southwest Monsoon. The present investigation of the Somalian coherent eddy structures allows us to identify the origin and the subsequent development of the cyclones flanked upon the Great Whirl (GW) previously identified by Beal and Dono-hue (2013) in satellite observations and to establish that similar cyclones are also flanked upon the Southern Gyre (SG). These cyclones are identified as potential actors in mixing water masses within the large eddies and offshore the coast of Somalia. All three simulations bring to light that during the period when the Southwest Monsoon is well established, the SG moves northward along the Somali coast and encounters the GW. The interaction between the SG and the GW is a collision without merging, in a way that has not been described in observations up to now. During the collision the GW is pushed to the east of Socotra Island, sheds several smaller patches of anticyclonic vorticity, and often reforms into the Socotra Eddy, thus proposing a formation mechanism for that eddy. During this process the GW gives up its place to the SG. This process is robust throughout the three simulations

Transfer of particulate matter from the Northwestern Mediterranean continental margin: Variability and controlling factors

International audienceLong-term observations of monthly downward particle fluxes and hourly currents and temperaturewere initiated in 1993 in two canyons of the continental margin of the Gulf of Lion. The goals of thissurvey were to estimate its contribution to the CO 2 global budget and to understand the role offorcing factors in the control of present-day particle exchange across this margin. A previousstatistical analysis of the long-term time series suggested that variability in the transfer of particulatematter to the deep ocean could be the result of the effect of the meandering of the Northern Currentand by dense water formation in winter rather than variations in the sources of matter. Numericalsimulations have been carried out to consider these hypotheses. A model is used to examine theimpact of local atmospheric forcing (wind stress, heat fluxes, precipitation–evaporation budget) onthe variability of the oceanic circulation and of mass fluxes within the canyons from December toApril, for five consecutive years between 1996 and 2001. Results show an east-west gradient of massexport on the shelf and a positive correlation between anomalies of dense water formation rates andinterannual variability of particle fluxes. However, in the eastern part of the Gulf, the simulated massexport from the shelf is not significant, even during a winter of strong convection, when the measuredparticle fluxes are at maxima. Moreover, although the model suggests that the dense water formationcould be the major hydrodynamic forcing factor, this process is not sufficient to completely explainthe space and time variations of observed particle fluxes, especially at depth

Simultaneous mm/X-ray intraday variability in the radio-quiet AGN MCG+08-11-11

Most of the Active Galactic Nuclei (AGN) are radio-quiet (RQ) and, differently from radio-loud (RL) AGN, do not show signature of large-scale and powerful jets. The physical origin of their radio emission remains then broadly unclear. The observation of flat/inverted radio spectra at GHz frequencies seems to support however the presence of an unresolved synchrotron self-absorbed region in the close environment of the supermassive black hole. Its size could be as small as that of the X-ray corona. Since synchrotron self absorption decreases strongly with frequency, these sources need to be observed in the millimetric (mm) domain. We report here a 12h simultaneous mm-X-ray observation of the RQ AGN MCG+08-11-11 by NOEMA and NuSTAR. The mm flux shows a weak but clear increase along the pointing with a fractional variability of $2.0\pm0.1$\%. The 3-10 keV flux of NuSTAR also increases and shows a fractional variability of $7.0\pm1.5$\%. A structure function analysis shows a local maximum in the mm light curve corresponding to 2-3\% of variability on timescale of $\sim2\times10^4$ seconds (100-300 $R_g$ light crossing time). Assuming an optically thick mm emitting medium, this translates into an upper limit of its size of $\sim$1300 $R_g$. The observation of fast variability in radio-mm and X-ray wavelengths, as well as a similar variability trend, well support the mm emission to be emitted by a region close, and potentially related to, the X-ray corona like an outflow/weak jet.Comment: Accepted in A&A Letters. 5 pages main text, 3 pages of appendices, 12 figure