Influence of El Niño on the variability of global shoreline position

Coastal zones are fragile and complex dynamical systems that are increasingly under threat from the combined effects of anthropogenic pressure and climate change. Using global satellite derived shoreline positions from 1993 to 2019 and a variety of reanalysis products, here we show that shorelines are under the influence of three main drivers: sea-level, ocean waves and river discharge. While sea level directly affects coastal mobility, waves affect both erosion/accretion and total water levels, and rivers affect coastal sediment budgets and salinity-induced water levels. By deriving a conceptual global model that accounts for the influence of dominant modes of climate variability on these drivers, we show that interannual shoreline changes are largely driven by different ENSO regimes and their complex inter-basin teleconnections. Our results provide a new framework for understanding and predicting climate-induced coastal hazards

On the influence of the Galapagos Islands on the Humboldt Current System

International audienceRecent studies have shown that water masses which compose the poleward Peru-Chile Undercurrent (PCUC) and the equatorward Peru Coastal Current are influenced by the mean state and variability of the Equatorial Under Current (EUC) and of the South Equatorial Current. Several modeling studies emphasized that EUC intensity is strongly affected by the topographic barrier formed by the Galapagos Islands (GI) and the spatial resolution of the model, which can reduce the eastward flow and the associated cold bias usually present in the cold tongue in the majority of CGCMs. Consequently, the archipelago appears to be a key element connecting the Equatorial Pacific and the Humboldt Current System. A ROMS (Regional Oceanic Model System) model configuration was designed to address the role of the small scale topography of the GI on the dynamics of the area. The employed methodology was quite simple: 2 climatological simulations (15 years after spin ups) were run, one including the archipelago with a 1/6° resolution, the other one excluding all bathymetric features above 3000m depth in the vicinity of GI. The main investigated questions are how the model spatial fine resolution impacts the Eastern Pacific mean state, seasonal variability, meso-scale dynamics in the region and the EUC/PCUC pathways, which are studied using Lagrangian diagnostics. The influence of these islands on the propagation of equatorial and coastally trapped Kelvin waves, and on the reflection of Rossby waves is also diagnosed. Because of the role of these waves on the surface and sub-surface water properties off South America coast, the possible rectification of Tropical eastern Pacific mean state through nonlinear processes and changes in waves propagation features, namely changes in vertical stratification, is also investigated

On the influence of the Galapagos Islands on the Humboldt Current System

International audienceRecent studies have shown that water masses which compose the poleward Peru-Chile Undercurrent (PCUC) and the equatorward Peru Coastal Current are influenced by the mean state and variability of the Equatorial Under Current (EUC) and of the South Equatorial Current. Several modeling studies emphasized that EUC intensity is strongly affected by the topographic barrier formed by the Galapagos Islands (GI) and the spatial resolution of the model, which can reduce the eastward flow and the associated cold bias usually present in the cold tongue in the majority of CGCMs. Consequently, the archipelago appears to be a key element connecting the Equatorial Pacific and the Humboldt Current System. A ROMS (Regional Oceanic Model System) model configuration was designed to address the role of the small scale topography of the GI on the dynamics of the area. The employed methodology was quite simple: 2 climatological simulations (15 years after spin ups) were run, one including the archipelago with a 1/6° resolution, the other one excluding all bathymetric features above 3000m depth in the vicinity of GI. The main investigated questions are how the model spatial fine resolution impacts the Eastern Pacific mean state, seasonal variability, meso-scale dynamics in the region and the EUC/PCUC pathways, which are studied using Lagrangian diagnostics. The influence of these islands on the propagation of equatorial and coastally trapped Kelvin waves, and on the reflection of Rossby waves is also diagnosed. Because of the role of these waves on the surface and sub-surface water properties off South America coast, the possible rectification of Tropical eastern Pacific mean state through nonlinear processes and changes in waves propagation features, namely changes in vertical stratification, is also investigated

On the influence of the Galapagos Islands on the Humboldt Current System

International audienceRecent studies have shown that water masses which compose the poleward Peru-Chile Undercurrent (PCUC) and the equatorward Peru Coastal Current are influenced by the mean state and variability of the Equatorial Under Current (EUC) and of the South Equatorial Current. Several modeling studies emphasized that EUC intensity is strongly affected by the topographic barrier formed by the Galapagos Islands (GI) and the spatial resolution of the model, which can reduce the eastward flow and the associated cold bias usually present in the cold tongue in the majority of CGCMs. Consequently, the archipelago appears to be a key element connecting the Equatorial Pacific and the Humboldt Current System. A ROMS (Regional Oceanic Model System) model configuration was designed to address the role of the small scale topography of the GI on the dynamics of the area. The employed methodology was quite simple: 2 climatological simulations (15 years after spin ups) were run, one including the archipelago with a 1/6° resolution, the other one excluding all bathymetric features above 3000m depth in the vicinity of GI. The main investigated questions are how the model spatial fine resolution impacts the Eastern Pacific mean state, seasonal variability, meso-scale dynamics in the region and the EUC/PCUC pathways, which are studied using Lagrangian diagnostics. The influence of these islands on the propagation of equatorial and coastally trapped Kelvin waves, and on the reflection of Rossby waves is also diagnosed. Because of the role of these waves on the surface and sub-surface water properties off South America coast, the possible rectification of Tropical eastern Pacific mean state through nonlinear processes and changes in waves propagation features, namely changes in vertical stratification, is also investigated

On the influence of the Galapagos Islands on the Humboldt Current System

International audienceRecent studies have shown that water masses which compose the poleward Peru-Chile Undercurrent (PCUC) and the equatorward Peru Coastal Current are influenced by the mean state and variability of the Equatorial Under Current (EUC) and of the South Equatorial Current. Several modeling studies emphasized that EUC intensity is strongly affected by the topographic barrier formed by the Galapagos Islands (GI) and the spatial resolution of the model, which can reduce the eastward flow and the associated cold bias usually present in the cold tongue in the majority of CGCMs. Consequently, the archipelago appears to be a key element connecting the Equatorial Pacific and the Humboldt Current System. A ROMS (Regional Oceanic Model System) model configuration was designed to address the role of the small scale topography of the GI on the dynamics of the area. The employed methodology was quite simple: 2 climatological simulations (15 years after spin ups) were run, one including the archipelago with a 1/6° resolution, the other one excluding all bathymetric features above 3000m depth in the vicinity of GI. The main investigated questions are how the model spatial fine resolution impacts the Eastern Pacific mean state, seasonal variability, meso-scale dynamics in the region and the EUC/PCUC pathways, which are studied using Lagrangian diagnostics. The influence of these islands on the propagation of equatorial and coastally trapped Kelvin waves, and on the reflection of Rossby waves is also diagnosed. Because of the role of these waves on the surface and sub-surface water properties off South America coast, the possible rectification of Tropical eastern Pacific mean state through nonlinear processes and changes in waves propagation features, namely changes in vertical stratification, is also investigated

ENSO's non-stationary and non-Gaussian character: the role of climate shifts

El Niño Southern Oscillation (ENSO) is the dominant mode of climate variability in the Pacific, having socio-economic impacts on surrounding regions. ENSO exhibits significant modulation on decadal to inter-decadal time scales which is related to changes in its characteristics (onset, amplitude, frequency, propagation, and predictability). Some of these characteristics tend to be overlooked in ENSO studies, such as its asymmetry (the number and amplitude of warm and cold events are not equal) and the deviation of its statistics from those of the Gaussian distribution. These properties could be related to the ability of the current generation of coupled models to predict ENSO and its modulation. <br><br> Here, ENSO's non-Gaussian nature and asymmetry are diagnosed from in situ data and a variety of models (from intermediate complexity models to full-physics coupled general circulation models (CGCMs)) using robust statistical tools initially designed for financial mathematics studies. In particular α-stable laws are used as theoretical background material to measure (and quantify) the non-Gaussian character of ENSO time series and to estimate the skill of ``naïve'' statistical models in producing deviation from Gaussian laws and asymmetry. The former are based on non-stationary processes dominated by abrupt changes in mean state and empirical variance. It is shown that the α-stable character of ENSO may result from the presence of climate shifts in the time series. Also, cool (warm) periods are associated with ENSO statistics having a stronger (weaker) tendency towards Gaussianity and lower (greater) asymmetry. This supports the hypothesis of ENSO being rectified by changes in mean state through nonlinear processes. The relationship between changes in mean state and nonlinearity (skewness) is further investigated both in the Zebiak and Cane (1987)'s model and the models of the Intergovernmental Panel for Climate Change (IPCC). Whereas there is a clear relationship in all models between ENSO asymmetry (as measured by skewness or nonlinear advection) and changes in mean state, they exhibit a variety of behaviour with regard to α-stability. This suggests that the dynamics associated with climate shifts and the occurrence of extreme events involve higher-order statistical moments that cannot be accounted for solely by nonlinear advection

Different controls of tropical cyclone activity in the Eastern Pacific for two types of El Niño

The El Niño-Southern Oscillation (ENSO) is known to have different modes of expression, characterized by different dynamics and spatial anomalies patterns: the Eastern Pacific (EP) and Central Pacific (CP) El Niño. The main region of influence of the former is located in the Eastern Pacific, while CP events have a stronger signature of ocean/climate anomalies in the Central West Pacific. This leads to distinctive oceanic and atmospheric signatures that likely have different influences on tropical cyclone (TC) activity in the Eastern Pacific, the second most active region in the world. In this study we investigate the respective role of oceanic and atmospheric conditions on TC formation and intensification in the Eastern Pacific associated with these two flavors of ENSO. We find that the oceanic control, through meridional redistribution of subsurface heat, is the main driver of TC activity during the hurricane season following EP events. In contrast, atmospheric conditions tend to be destructive to TC intensification after those events. The altered atmospheric circulation, in particular the reduction of vertical wind shear and the increase in relative humidity, tends to be more influential in controlling TC activity post CP events. However, unlike for subsurface heat, these changes in atmospheric conditions are not statistically distinct between these two ENSO flavors - although they are consistent across all atmospheric data sets tested. Overall, unlike after EP El Niño events, the hurricane season activity following a CP event is not significantly different from neutral or even La Niña years

ENSO's non-stationary and non-Gaussian character : the role of climate shifts

El Nino Southern Oscillation (ENSO) is the dominant mode of climate variability in the Pacific, having socio-economic impacts on surrounding regions. ENSO exhibits significant modulation on decadal to inter-decadal time scales which is related to changes in its characteristics (onset, amplitude, frequency, propagation, and predictability). Some of these characteristics tend to be overlooked in ENSO studies, such as its asymmetry (the number and amplitude of warm and cold events are not equal) and the deviation of its statistics from those of the Gaussian distribution. These properties could be related to the ability of the current generation of coupled models to predict ENSO and its modulation. Here, ENSO's non-Gaussian nature and asymmetry are diagnosed from in situ data and a variety of models (from intermediate complexity models to full-physics coupled general circulation models (CGCMs)) using robust statistical tools initially designed for financial mathematics studies. In particular alpha-stable laws are used as theoretical background material to measure (and quantify) the non-Gaussian character of ENSO time series and to estimate the skill of "naive" statistical models in producing deviation from Gaussian laws and asymmetry. The former are based on non-stationary processes dominated by abrupt changes in mean state and empirical variance. It is shown that the alpha-stable character of ENSO may result from the presence of climate shifts in the time series. Also, cool (warm) periods are associated with ENSO statistics having a stronger (weaker) tendency towards Gaussianity and lower (greater) asymmetry. This supports the hypothesis of ENSO being rectified by changes in mean state through nonlinear processes. The relationship between changes in mean state and nonlinearity (skewness) is further investigated both in the Zebiak and Cane (1987)'s model and the models of the Intergovernmental Panel for Climate Change (IPCC). Whereas there is a clear relationship in all models between ENSO asymmetry (as measured by skewness or nonlinear advection) and changes in mean state, they exhibit a variety of behaviour with regard to alpha-stability. This suggests that the dynamics associated with climate shifts and the occurrence of extreme events involve higher-order statistical moments that cannot be accounted for solely by nonlinear advection

Tropical origins of the Pacific meridional mode associated with the nonlinear interaction of ENSO with the annual cycle

The Pacific Meridional Mode (PMM) has long been associated with extra-tropical air-sea coupling processes, which are thought to influence the development of El Nino-Southern Oscillation (ENSO). Here we show that the PMM on seasonal to interannual timescales is closely associated with a newly proposed tropical mode known as the ENSO Combination mode (C-mode), which arises from the nonlinear interaction between ENSO and the background annual cycle in the deep tropics. The PMM exhibits a remarkable resemblance with the C-mode in atmospheric patterns, spectral characteristics, and local impacts. Based on a simple Hasselmann-type model, we further demonstrate that the C-mode-related atmospheric anomalies can effectively drive PMM-like sea surface temperature anomalies. As the C-mode captures seasonally modulated ENSO characteristics, the seasonal-to-interannual PMM variability could naturally establish a connection with ENSO, thereby offering an alternative explanation for the observed relationship between PMM and ENSO. Previous studies demonstrated that the Pacific Meridional Mode (PMM) is driven by the extratropical climate systems, which can impact the development of El Nino-Southern Oscillation (ENSO) events in the tropics. In our study, we establish a close connection between the PMM on seasonal-to-interannual timescales and a tropical atmospheric mode arising from the nonlinear interaction between ENSO and the background annual cycle (the ENSO Combination mode, C-mode). The C-mode closely resembles the PMM in terms of atmospheric patterns and spectral characteristics. We further demonstrate that the C-mode could drive a PMM-like SST pattern in the tropical Pacific. Consequently, we suggest that the PMM on seasonal-to-interannual timescales has tropical origins, thereby offering an alternative explanation for the relationship between the conventional PMM index and the mature phase of ENSO. The spatiotemporal features of Pacific Meridional Mode (PMM) on seasonal-to-interannual timescales exhibit a remarkable resemblance with those of the tropical combination modeC-mode-related atmospheric anomalies are capable of inducing PMM-like sea surface temperature changes in the tropical PacificEl Nino-Southern Oscillation (ENSO)'s interaction with the annual cycle manifests in PMM-related air-sea conditions, which explains the observed ENSO-PMM linkag