Chronic flooding events due to sea-level rise in French Guiana

As sea levels are rising, the number of chronic flooding events at high tide is increasing across the world coastlines. Yet, many events reported so far either lack observational evidence of flooding, or relate to coastal areas where ground subsidence or oceanic processes often enhance climate change-induced sea-level rise (SLR). Here we present observational and modelling evidence of high-tide flooding events that are unlikely to occur without SLR in French Guiana, where sea-level rise rates are close to the global average and where there is no significant ground subsidence. In particular, on 16 October 2020, a well-documented flooding event happened in Cayenne under calm weather conditions. Our probabilistic assessment of daily maximum water levels superimposed on SLR shows that this event can be modelled and is a consequence of SLR. As sea levels will continue to rise, we show that the number, severity and extent of such high-tide flooding events will increase across several urban areas of French Guiana, with an evolution depending on the topography. As concerns are growing regarding the economic impacts and adaptation challenges of high-tide chronic events across the world, our study provides new evidence that this early impact of SLR is emerging now

Projections of tropical cyclone rainfall over land with an Eulerian approach: Case study of three islands in the West Indies

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ENSO feedbacks and associated time scales of variability in a multimodel ensemble

International audienceThe background state of the equatorial Pacific determines the prevalence of a "slow" recharge oscillator-type ENSO over a "fast" quasi-biennial surface-driven ENSO. The first is controlled to a large extent by the thermocline feedback, whereas the latter is related to enhanced zonal advective feedback. In this study, dynamical diagnostics are used to investigate the relative importance of these two feedbacks in the Coupled Model Intercomparison Project and its relation with the differences in ENSO-like variability among the models. The focus is on the role of the mean oceanic surface circulation in controlling the relative weight of the two feedbacks. By the means of an intermediate-type ocean model of the tropical Pacific "tuned" from the coupled general circulation model (CGCM) outputs, the contribution of the advection terms (vertical versus zonal) to the rate of SST change is estimated. A new finding is that biases in the advection terms are to a large extent related to the biases in the mean surface circulation. The latter are used to infer the dominant ENSO feedback for each CGCM. This allows for the classification of the CGCMs into three groups that account for the dominant feedback process of the ENSO cycle: horizontal advection (mainly in the western Pacific), vertical advection (mainly in the eastern Pacific), and the combination of both mechanisms. Based on such classification, the analysis also reveals that the models exhibit distinctive behavior with respect to the characteristics of ENSO: for most models, an enhanced (diminished) contribution of the zonal advective feedback is associated with faster (slower) ENSO and a tendency toward a cooler (warmer) mean state in the western-to-central Pacific Ocean. The results support the interpretation that biases in the mean state are sustained/maintained by the privileged mode of variability associated with the dominant feedback mechanism in the models. In particular, the models having a dominant zonal advective feedback exhibit significant cold SST asymmetry (or negative skewness) in the western equatorial Pacific

Correction to: Future changes in Atlantic hurricanes with the rotated-stretched ARPEGE-Climat at very high resolution

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Equatorially forced intraseasonal propagations along the Peru-Chile coast and their relation with the nearshore eddy activity in 1992-2000: A modeling study

International audienceA regional eddy-resolving oceanic model spanning the 1992-2000 period is used to study the influence of 50 to 80 day intraseasonal equatorial Kelvin waves (IEKW) on mesoscale eddy activity off the west coast of Peru and northern and central Chile. The model is shown to realistically simulate nearshore intraseasonal sea level variability, poleward propagation of equatorially forced coastal trapped waves along the coastal waveguide, and offshore variability related to mesoscale eddies and Rossby waves (RW). In agreement with linear theory, RW are confined equatorward of ˜12°S in the 50-80 days period range. South of that critical latitude, westward propagation is dominated by energetic mesoscale signals resulting mainly from coastal flow instability. Sensitivity experiments to the open boundary conditions are then used to estimate to what extent eddy activity is impacted by the remote equatorial forcing. A coastal increase in eddy kinetic energy related to the energetic 60 day IEKW activity present in the open boundary forcing is evidenced and is largest off northern Peru, whereas no major changes are observed offshore. Additional regional simulations with different open boundary conditions corroborate our findings and suggest that this limited effect of IEKW on the offshore eddy kinetic energy may be a robust feature

Sensitivity of the Humboldt Current system to global warming: a downscaling experiment of the IPSL-CM4 model

International audienceThe impact of climate warming on the seasonal variability of the Humboldt Current system ocean dynamics is investigated. The IPSL-CM4 large scale ocean circulation resulting from two contrasted climate scenarios, the so-called Preindustrial and quadrupling CO2, are downscaled using an eddy-resolving regional ocean circulation model. The intense surface heating by the atmosphere in the quadrupling CO2 scenario leads to a strong increase of the surface density stratification, a thinner coastal jet, an enhanced Peru-Chile undercurrent, and an intensification of nearshore turbulence. Upwelling rates respond quasi-linearly to the change in wind stress associated with anthropogenic forcing, and show a moderate decrease in summer off Peru and a strong increase off Chile. Results from sensitivity experiments show that a 50% wind stress increase does not compensate for the surface warming resulting from heat flux forcing and that the associated mesoscale turbulence increase is a robust feature

Future changes in Atlantic hurricanes with the rotated-stretched ARPEGE-Climat at very high resolution

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Atmospheric Drivers of Oceanic North Swells in the Eastern Caribbean

Large wintertime ocean swells in the Caribbean, known as north swells, generate high surf and expose communities, ecosystems, and infrastructure to hazardous conditions. Empirical orthogonal functions and cluster analyses using ERA5 reanalysis swell data are performed to characterize north swells in the eastern Caribbean and to establish a ranked list of historical events. ERA5 atmospheric and swell data are used to create basin-scale sea-level pressure, surface wind and swell composites for north swell events of different magnitudes. Additionally, storm events are identified in the mid-latitude North Atlantic Ocean. North swells are predominantly generated by storms that intensify off the North American east coast. However, there is a subset of moderately sized swells associated with a westward-located high-pressure system in the North Atlantic. While lower sea-level pressure and stronger surface winds are important for generating larger swells, the location of the low-pressure center and storm track as well the zonal speed of the storm are critical in the development of large eastern Caribbean north swells. The largest such events are associated with storms located comparatively further southeast, with a more zonal trajectory, and slower zonal speed. Large storms located further northwest, with a more southwest to northeast trajectory, and faster zonal speeds are associated with weaker north swells or in many cases, no significant north swell in the eastern Caribbean

Similarities and Contrasts in Time-Mean Striated Surface Tracers in Pacific Eastern Boundary Upwelling Systems: The Role of Ocean Currents in Their Generation

Eastern boundary upwelling systems feature strong zonal gradients of physical and biological properties between cool, productive coastal oceans and warm, oligotrophic subtropical gyres. Zonal currents and jets (striations) are therefore likely to contribute to the transport of water properties between coastal and open oceanic regions. For the first time, multi-sensor satellite data are used to characterize the time-mean signatures of striations in sea surface temperature (SST), salinity (SSS), and chlorophyll-a (Chl-a) in subtropical eastern North/South Pacific (ENP/ESP) upwelling systems. In the ENP, tracers exhibit striated patterns extending up to ~2500 km offshore. Striated signals in SST and SSS are highly correlated with quasi-zonal jets, suggesting that these jets contribute to SST/SSS mesoscale patterns via zonal advection. Striated Chl-a anomalies are collocated with sea surface height (SSH) bands, a possible result of mesoscale eddy trains trapping nutrients and forming striated signals. In the ESP, the signature of striations is only found in SST and coincides with the SSH bands, consistently with quasi-zonal jets located outside major zonal tracer gradients. An interplay between large-scale SST/SSS advection by the quasi-zonal jets, mesoscale SST/SSS advection by the large-scale meridional flow, and eddy advection may explain the persistent ENP hydrographic signature of striations. These results underline the importance of quasi-zonal jets for surface tracer structuring at the mesoscale