Monthly mean wind stress and Sverdrup transport in the North Atlantic: A comparison of the Hellerman-Rosenstein and Isemer-Hasse climatologies

The monthly mean wind stress climatology of Hellerman and Rosenstein (HR) is compared with the climatology of Isemer and Hasse (IH), which represents a version of the Bunker atlas (BU) for the North Atlantic based on revised parameterizations. The drag coefficients adopted by IH are 21% smaller than the values of BU and HR, and the calculation of wind speed from marine estimates of Beaufort force (Bft) is based on a revised Beaufort equivalent scale similar to the scientific scale recommended by WMO. The latter choice significantly increases wind speed below Bft 8, and effectively counteracts the reduction of the drag coefficients. Comparing the IH stresses with HR reveals substantially enhanced magnitudes in the trade wind region throughout the year. At 15°N the mean easterly stress increases from about 0.9 (HR) to about 1.2 dyn cm−1 (IH). Annual mean differences are smaller in the region of the westerlies. In winter, the effect due to the reduced drag coefficient dominates and leads to smaller stress values in IH; during summer season the revision of the Beaufort equivalents is more effective and leads to increased stresses. Implications of the different wind stress climatologies for forcing the large-scale ocean circulation are discussed by means of the Sverdrup transport streamfunction (ψs): Throughout the subtropical gyre a significant intensification of ψs takes place with IH. At 27°N, differences of more than 10 Sv (1 Sv ≡ 106 m3 s−1) are found near the western boundary. Differences in the seasonality of ψs are more pronounced in near-equatorial regions where IH increase the amplitude of the annual cycle by about 50%. An eddy-resolving model of the North Atlantic circulation is used to examine the effect of the different wind stresses on the seasonal cycle of the Florida Current. The transport predicted by the numerical model is in much better agreement with observations when the circulation is forced by IH than by HR, regarding both the annual mean (29.1 Sv vs 23.2 Sv) and the seasonal range (6.3 Sv vs 3.4 Sv)

Multifractal analysis of oceanic chlorophyll maps remotely sensed from space

International audiencePhytoplankton patchiness has been investigated with multifractal analysis techniques. We analyzed oceanic chlorophyll maps, measured by the SeaWiFS orbiting sensor, which are considered to be good proxies for phytoplankton. Multifractal properties are observed, from the sub-mesoscale up to the mesoscale, and are found to be consistent with the Corssin-Obukhov scale law of passive scalars. This result indicates that, within this scale range, turbulent mixing would be the dominant effect leading to the observed variability of phytoplankton fields. Finally, it is shown that multifractal patchiness can be responsible for significant biases in the nonlinear source and sink terms involved in biogeochemical numerical models

Human Gamma Oscillations during Slow Wave Sleep

Neocortical local field potentials have shown that gamma oscillations occur spontaneously during slow-wave sleep (SWS). At the macroscopic EEG level in the human brain, no evidences were reported so far. In this study, by using simultaneous scalp and intracranial EEG recordings in 20 epileptic subjects, we examined gamma oscillations in cerebral cortex during SWS. We report that gamma oscillations in low (30–50 Hz) and high (60–120 Hz) frequency bands recurrently emerged in all investigated regions and their amplitudes coincided with specific phases of the cortical slow wave. In most of the cases, multiple oscillatory bursts in different frequency bands from 30 to 120 Hz were correlated with positive peaks of scalp slow waves (“IN-phase” pattern), confirming previous animal findings. In addition, we report another gamma pattern that appears preferentially during the negative phase of the slow wave (“ANTI-phase” pattern). This new pattern presented dominant peaks in the high gamma range and was preferentially expressed in the temporal cortex. Finally, we found that the spatial coherence between cortical sites exhibiting gamma activities was local and fell off quickly when computed between distant sites. Overall, these results provide the first human evidences that gamma oscillations can be observed in macroscopic EEG recordings during sleep. They support the concept that these high-frequency activities might be associated with phasic increases of neural activity during slow oscillations. Such patterned activity in the sleeping brain could play a role in off-line processing of cortical networks

Large-Scale Cortical Dynamics of Sleep Slow Waves

Slow waves constitute the main signature of sleep in the electroencephalogram (EEG). They reflect alternating periods of neuronal hyperpolarization and depolarization in cortical networks. While recent findings have demonstrated their functional role in shaping and strengthening neuronal networks, a large-scale characterization of these two processes remains elusive in the human brain. In this study, by using simultaneous scalp EEG and intracranial recordings in 10 epileptic subjects, we examined the dynamics of hyperpolarization and depolarization waves over a large extent of the human cortex. We report that both hyperpolarization and depolarization processes can occur with two different characteristic time durations which are consistent across all subjects. For both hyperpolarization and depolarization waves, their average speed over the cortex was estimated to be approximately 1 m/s. Finally, we characterized their propagation pathways by studying the preferential trajectories between most involved intracranial contacts. For both waves, although single events could begin in almost all investigated sites across the entire cortex, we found that the majority of the preferential starting locations were located in frontal regions of the brain while they had a tendency to end in posterior and temporal regions

Extracorporeal Membrane Oxygenation for Severe Acute Respiratory Distress Syndrome associated with COVID-19: An Emulated Target Trial Analysis.

RATIONALE: Whether COVID patients may benefit from extracorporeal membrane oxygenation (ECMO) compared with conventional invasive mechanical ventilation (IMV) remains unknown. OBJECTIVES: To estimate the effect of ECMO on 90-Day mortality vs IMV only Methods: Among 4,244 critically ill adult patients with COVID-19 included in a multicenter cohort study, we emulated a target trial comparing the treatment strategies of initiating ECMO vs. no ECMO within 7 days of IMV in patients with severe acute respiratory distress syndrome (PaO2/FiO2 <80 or PaCO2 ≥60 mmHg). We controlled for confounding using a multivariable Cox model based on predefined variables. MAIN RESULTS: 1,235 patients met the full eligibility criteria for the emulated trial, among whom 164 patients initiated ECMO. The ECMO strategy had a higher survival probability at Day-7 from the onset of eligibility criteria (87% vs 83%, risk difference: 4%, 95% CI 0;9%) which decreased during follow-up (survival at Day-90: 63% vs 65%, risk difference: -2%, 95% CI -10;5%). However, ECMO was associated with higher survival when performed in high-volume ECMO centers or in regions where a specific ECMO network organization was set up to handle high demand, and when initiated within the first 4 days of MV and in profoundly hypoxemic patients. CONCLUSIONS: In an emulated trial based on a nationwide COVID-19 cohort, we found differential survival over time of an ECMO compared with a no-ECMO strategy. However, ECMO was consistently associated with better outcomes when performed in high-volume centers and in regions with ECMO capacities specifically organized to handle high demand. This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/)

Les deux visages de la concentration industrielle : efficacité et rente de situation

[fre] Depuis le début des années quatre-vingt, la concentration industrielle s'est nettement renforcée. . Aujourd'hui, la concentration est synonyme d'une plus grande ouverture sur l'extérieur, d'une plus forte intensité capitalistique, d'un effort de recherche plus important et d'une meilleure qualification des salariés. En bref, la . concentration dynamise les performances industrielles. Certes, les groupes des secteurs les plus concentrés dégagent les marges les plus élevées. Mais ces rentes de situation sont doublement limitées. D'une part, elles sont attractives et favorisent ainsi une certaine déconcentration. D'autre part, l'internationalisation des marchés inhérente au processus de concentration tend à les réduire. [eng] The Two Aspects of Industrial Concentration : Efficiency and Situational Rent - Since the early eighties, industrial concentration has noticeably intensified. . Nowadays, industrial concentration is synonymous with greater access to foreign markets, a higher capital intentity, more efforts devoted to research and better-qualified wage-earners. In short, concentration boosts industrial performance. . Of course, groups belonging to the most concentrated sectors draw the highest margins. But the situational rents are limited in two ways. On the one hand, because they are attractive, they favor some kind of déconcentration. On the other hand, the internationalization of the markets inherent in the combining process tends to reduce situational rents. [spa] Las dos caras de la concentración industrial: eficacidad y renta de situación - . el inicio de los años ochenta, la concentración industrial se reforzó considerablemente. Hoy en día, la concentración surge como sinónimo de una mayor apertura hacia el exterior, de una intensidad capitahsta más fuerte, de un esfuerzo de investigación más importante y de una mejor calificación de los asalariados. En resumen, la concentración dinamiza los buenos resultados industrials. Ciertamente, en los grupos de los sectores de mayor concentración se desprenden las márgenes de ganancias más elevadas. Pero esas rentas de situación son doblemente limitadas. Por una parte, son atractivas, favoreciendo de ese modo, una cierta desconcentración. Por otra parte, la internacionalización de los mercados, inherente al proceso de concentración, tiene tendencia a reducirlas.

21st century climate change scenario for the Mediterranean using a coupled Atmosphere-Ocean Regional Climate Model

International audienceThe SAMM (Sea Atmosphere Mediterranean Model) has been developed to study the climate evolution of the Mediterranean and European regions for the 21st Century. SAMM is a new concept of AORCM (Atmosphere-Ocean Regional Climate Model), where a global atmosphere model is locally coupled with a regional ocean circulation model. It consists of the global spectral AGCM ARPEGE-Climate model, whose variable resolution is maximum in the Mediterranean region (50 km), which has been coupled to the Mediterranean Sea limited area OGCM OPAMED (10 km). A 140-year numerical experiment starting in 1960 was run with the AORCM. Up to year 2000, forcing was prescribed from observed values, whereas forcing following a SRES-A2 scenario was applied beyond 2000. In order to ensure the model stability, a simple monthly heat flux correction on air-sea exchanges was applied. The present-climate validation proves that the AORCM is comparable to the state-of-the-art European Atmosphere Regional Climate Models (ARCM) at the same resolution. At first order, the climate change impact over Europe simulated by the AORCM is comparable with ARCM simulations. However the AORCM significantly amplifies the climate change signal over large parts of Europe with respect to the corresponding ARCM: the warming is higher in all seasons and in many areas of Europe (up to 25% of the signal), winters are wetter over northern Europe and summers drier over southern and eastern Europe (up to 50% of the signal). These differences are highly significant and the choice between coupled and non-coupled regional models could be an additional source of uncertainty when evaluating the climate change response over Europe. The factors responsible for these differences are discussed. Among them, the response of the Mediterranean SST, better simulated by the high resolution Mediterranean Sea model of the AORCM, seems to be preponderant. Further mechanism studies and model inter-comparisons are however required to legitimate the present results

Generation of Rossby waves off the Cape Verde Peninsula: the role of the coastline

In December 2002 and January 2003 satellite observations of chlorophyll showed a strong coastal signal along the west African coast between 10 and 22° N. In addition , a wavelike pattern with a wavelength of about 750 km was observed from 20 December 2002 and was detectable for 1 month in the open sea, southwest of the Cape Verde Peninsula. Such a pattern suggests the existence of a locally generated Rossby wave which slowly propagated westward during this period. This hypothesis was confirmed by analysing sea surface height provided by satellite altimeter during this period. To decipher the mechanisms at play, a numerical study based on a reduced-gravity shallow-water model has first been conducted. A wind burst, broadly extending over the region where the offshore oceanic signal is observed, is applied for 5 d. A Kelvin wave quickly develops along the northern edge of the cape, then propagates and leaves the area in a few days. Simultaneously, a Rossby wave whose characteristics seem similar to the observed pattern forms and slowly propagates westward. The existence of the peninsula limits the extent of the wave to the north. The spatial extent of the wind burst determines the extent of the response and correspondingly the timescale of the phenomenon (about 100 d in the present case). When the wind burst has a large zonal and small meridional extent, the behaviour of a wave to the north of the peninsula differs from that to the south. These results are corroborated and completed by an analytical study of a linear reduced-gravity model using a non-Cartesian coordinate system. This system is introduced to evaluate the potential impact of the coastline shape. The analytical computations confirm that a period of around 100 d can be associated with the observed wave considering the value of the wavelength ; they also show that the role of the coastline remains moderate at such timescales. By contrast, when the period becomes shorter (smaller than 20-30 d), the behaviour of the waves is modified because of the shape of the coast. South of the peninsula, a narrow band of sea isolated from the rest of the ocean by two critical lines appears. Its meridional extent is about 100 km and Rossby waves could propagate there towards the coast