Regional Circulation Model Research Articles

Enhancing decadal snowfall forecasts in the Mediterranean mountains through informed atmospheric variability and climate data

ABSTRACT Forecasting decadal-scale snowfall, crucial for global water management, is challenging due to the complex interplay of environmental factors. This study projects the number of snowfall days (NSD) up to 2060, using the extensive time-series data from the Montevergine Observatory, southern Italy (1884-2022). We pioneered an innovative statistical model, accounting for antecedent time-lags, and exogenous support from the Teleconnection-Climate Pattern Index, incorporating large-scale (Arctic Oscillation) and smaller-scale (temperature) forcings. Our projections reveal the influence of decadal and multidecadal oscillations throughout the forecast period and suggest an increase in NSD after 2030, notably shifting in the 2040s to 2050s, averaging from about 20 to 30 snowfall days annually. The frequency of snowfall deficit years (reaching -1 standard deviation) remains, however, high in the first part of the forecast. Despite the limitation of a single-site study, this trend is consistent with projections from various regional circulation models for increased extreme snowloads in Italy.

Deep Mesoscale and Submesoscale Circulations Around the Atlantis II Seamount

AbstractThis study investigates the complex interactions between the North Atlantic Current (NAC) and the New England Seamount chain, focusing on the Atlantis II seamount. Employing a high‐resolution submesoscale permitting regional ocean circulation model nested within a basin‐wide simulation, it explores three distinct periods, each 2 weeks long, showcasing varied deep mesoscale and submesoscale circulations around the seamount. The analysis includes Eulerian statistics and Lagrangian particle tracing experiments to explore the transport and mixing impacts of the highly dynamic flow around the seamount. The results reveal significant density variations across the water column, attributed to the seamount's influence on local ocean currents. Specifically, mesoscale and submesoscale vortices, a seamount wake, and lee waves form during periods of increased near‐bottom current flow. These findings highlight the critical role of topographic features in modulating oceanic flows and ocean mixing, which have implications, among others, for nutrient distribution, acoustic propagation, and climate modeling. The variety and variability of the mesoscale and submesoscale circulations that arise in response to the variability in the NAC strength and position in relation to the New England Seamount Chain demonstrate the difficulty in extrapolating general behaviors from isolated observational campaigns.

Effects of global change on snakebite envenoming incidence up to 2050: a modelling assessment

Human activities are driving climate, land cover, and population change (global change), and shifting the baseline geographical distribution of snakebite. The interacting effects of global change on snakes and communities at risk of snakebite are poorly understood, limiting capacity to anticipate and manage future changes in snakebite risk. In this modelling study, we projected how global change will affect snakebite envenoming incidence in Sri Lanka, as a model system that has a high incidence of snakebite. We used the shared socioeconomic pathway (SSP) scenario analysis framework to integrate forecasts across the domains of: climate change (historical trend from WorldClim plus three underlying regional circulation models [RCMs] in the Coordinated Regional Downscaling Experiment-South Asia repository, with two emissions pathways [representative concentration pathways RCP4.5 and RCP8.5]); land cover change (Dyna-CLUE model); and human population density change (based on Gridded Population of the World data) from Jan 1, 2010 to Dec 31, 2050. Forecasts were integrated under three different development scenarios: a sustainability pathway (SSP1 and no further emissions), a middle-of-the-road pathway (SSP2 and RCP4.5), and a fossil-fuelled pathway (SSP5 and RCP8.5). For SSP2 and SSP5, we nested three different RCMs (CNRM-CM5, GFDL-CCM3, and MPI-ESM-LR; mean averaged to represent consensus) to account for variability in climate predictions. Data were used as inputs to a mechanistic model that predicted snakebite envenoming incidence based on human-snake contact patterns. From 2010 to 2050, at the national level, envenoming incidence in Sri Lanka was projected to decrease by 12·0-23·0%, depending on the scenario. The rate of decrease in envenoming incidence was higher in SSP5-RCP8.5 than in SSP1 and SSP2-RCP4.5. Change in envenoming incidence was heterogenous across the country. In SSP1, incidence decreased in urban areas expected to have population growth, and with land cover changes towards anthropised classes. In SSP2-RCP4.5 and SSP5-RCP8.5, most areas were projected to have decreases in incidence (SSP5-RCP8.5 showing the largest area with incidence reductions), while areas such as the central highlands and the north of the country showed localised increases. In the model, decreases occurred with human population growth, land use change towards anthropised classes (potentially shifting occupational risk factors), and decreasing abundance of some snake species, potentially due to global warming and reduced climatic and habitat suitability, with displacement of some snake species. Snakebite envenoming incidence was projected to decrease overall in the coming decades in Sri Lanka, but with an apparent emerging conflict with sustainability objectives. Therefore, efforts to mitigate snakebite envenoming incidence will need to consider the potential impacts of sustainability interventions, particularly related to climate and land use change and in areas where increases in incidence are projected. In view of global change, neglected tropical diseases and public health issues related to biodiversity, such as snakebite, should be managed collaboratively by both environment and health stakeholders. UK Medical Research Council.

Environmental risk assessment of coastal dredging based on clustering of meteocean forcing

Dredging and dumping in-situ sediments is a fundamental operation for most coastal engineering projects and coastal defense projects, such as the construction of breakwaters, beach nourishment and land reclamation. Future projections in terms of coastal hazard suggest that coastal protection and land reclamation project will be more and more frequent. In this context, the assessment of the environmental and socio-economic impact of the risk induced by dredging is a fundamental step during both the design stage and the operational management. Most of the standard practices and available risk assessment frameworks rely on the numerical prediction of the sediment plume in the large field driven by coastal circulations forced by tides, winds and waves. In this study, we formulated a new risk assessment framework based on an unsupervised machine learning clustering algorithm, K-means clustering, for generating representative meteocean scenarios subsequently used to force a regional circulation model. Moreover, we introduced three criteria of hazard/risk based on the spatial and temporal evolution of the suspended sediment concentration that explained different environmental impacts and two new methods to synthetically present the risk values. The major improvement of the present framework is that the final probability of risk fully describes the statistics in terms of hydrodynamic and dredging conditions.This framework presents the probability analysis of risk spatial distribution based on representative hydrodynamic conditions and dredging scenarios, which is a major improvement of this study compared with previous risk assessment strategies that were unable to predict quantified dredging risk before field construction. Finally, to demonstrate the potentiality of the risk assessment framework, we applied this methodology to the Hong Kong Water and Pearl River Estuary (China) as a pilot case.

Effects of open boundary bias correction and data assimilation in a regional ocean circulation model for the East Sea

Effects of open boundary bias correction and data assimilation in a regional ocean circulation model for the East Sea

Performance study of ray-based ocean acoustic tomography methods for estimating submesoscale variability in the upper ocean.

Ocean acoustic tomography (OAT) methods aim at estimating variations of sound speed profiles (SSP) based on acoustic measurements between multiple source-receiver pairs (e.g., eigenray travel times). This study investigates the estimation of range-dependent SSPs in the upper ocean over short ranges (<5 km) using the classical ray-based OAT formulation as well as iterative or adaptive OAT formulations (i.e., when the sources and receivers configuration can evolve across successive iterations of this inverse problem). A regional ocean circulation model for the DeSoto Canyon in the Gulf of Mexico is used to simulate three-dimensional sound speed variations spanning a month-long period, which exhibits significant submesoscale variability of variable intensity. OAT performance is investigated in this simulated environment in terms of (1) the selected source-receivers configuration and effective ray coverage, (2) the selected OAT estimator formulations, linearized forward model accuracy, and the parameterization of the expected SSP variability in terms of empirical orthogonal functions, and (3) the duration over which the OAT inversion is performed. Practical implications for the design of future OAT experiments for monitoring submesoscale variability in the upper ocean with moving autonomous platforms are discussed.

Оценка точности воспроизведения метеорологических характеристик по модели WRF для акватории Каспийского моря

The paper presents the accuracy estimates for the simulation of meteorological characteristics obtained from the WRF model with a spatial resolution of 6 km adapted for the Caspian Sea. It was used to simulate meteorological characteristics using various parameterizations of physical processes available in the WRF model. The model was verified using data from coastal weather stations for 2021. It was found that the best results in reproducing meteorological characteristics are achieved using the Thompson graupel scheme as a parameterization of physical processes, the Tiedtke scheme as a parameterization of convection, the RRTMG scheme as a parameterization of long-wave and short-wave radiation, the MYJ scheme as a boundary layer parameterization, and the Noah Land-Surface Model as a surface layer parameterization. An analysis of the simulation results versus observational data from weather stations showed that the model correctly reproduces the modulus and direction of wind speed, air temperature, and sea-level pressure. It was found that the model correctly reproduces not only the average characteristics of wind speed, but also its extreme values, which is especially important when modeling storm surges in the Caspian Sea. Keywords: Caspian Sea, regional nonhydrostatic atmosphere circulation model, numerical methods

Climate Change Effects on Rainfall Intensity–Duration–Frequency (IDF) Curves for the Lake Erie Coast Using Various Climate Models

This study delved into the analysis of hourly observed as well as future precipitation data in the towns of Willoughby and Buffalo on the Lake Erie Coast to examine the variations in IDF relationships over the 21st century. Several regional climate models (RCMs) and general circulation models (GCMs) from the Coupled Model Intercomparison Project (CMIP) Phases 5 and 6 were used. The study evaluated three RCMs with historical and Representative Concentration Pathway (RCP) 8.5 scenarios for each CMIP5 and three GCMs with historical and Shared Socioeconomic Pathways (SSPs) (126, 245, 370, and 585) scenarios for each CMIP6. The results suggested that the town of Willoughby would experience an increase of 9–46%, whereas Buffalo would experience an upsurge of 6–140% in the hourly precipitation intensity under the worst-case scenarios of RCP8.5 for CMIP5 and SSP585 for CMIP6. This increase is expected to occur in both the near (2020–2059) and far future (2060–2099), with a return period as low as 2 years and as high as 100 years when compared to the baseline period (1980–2019). The analysis indicated an increased range of 9–39% in the near future and 20–55% in the far future for Willoughby, while the Buffalo region may experience an increase of 2–95% in the near future and 3–192% in the far future as compared to the baseline period. In contrast to CMIP6 SSP585 models, CMIP5 RCP8.5 models predicted rainfall with an intensity value that is up to 28% higher in the town of Willoughby, while the reverse was true for the Buffalo region. The findings of this study are expected to be helpful for the design of water resource infrastructures.

Tracing Atlantic water transit times in the Arctic Ocean: Coupling reprocessing-derived 236U and colored dissolved organic matter to distinguish different pathways

The Fram Strait is a key region for investigating the exchange of Atlantic water with the Arctic Ocean. Uranium-236 (236U) from the two European nuclear reprocessing plants (NRPs) at La Hague and Sellafield provides a unique fingerprint in Atlantic water which can be used for studying its circulation patterns in the Arctic Ocean. And NRPs-derived 236U (236UNRPs) can be identified by its 233U/236U signature. In this study, we use colored dissolved organic matter (CDOM) absorption to constrain the selection of three Atlantic branch waters that carried different inputs of 236UNRPs in Fram Strait. This can potentially provide better estimates of transit times of Atlantic waters in the Arctic Ocean. High CDOM levels (a350≥0.35 m−1) in Fram Strait reflect the passage of Atlantic water transported to the Arctic by the Norwegian Coastal Current (NCC) and its extension and subsequently along the Siberian continental slope and shelf where the Ob, Yenisei and Lena rivers supply terrestrial organic matter with significantly high CDOM content. Conversely, low CDOM water represents Atlantic water that has remained off the shelf. Based on CDOM absorption, potential temperature (Θ), potential density (σΘ) and 236U concentration, the path of a given body of Atlantic water could be inferred and an appropriate NRPs input function constrained so that transit times could be estimated. Our results indicate that Arctic High CDOM Water (a350≥0.35 m−1) sourced from the NCC and Barents Sea Branch Water (BSBW) in the Barents Sea Opening has an average of 7–27 yrs transit time in the upper ∼200 m of the western shelf of the Fram Strait. Atlantic Low CDOM Water (a350<0.35 m−1, Θ>2°C) sourced from the Fram Strait Branch Water (FSBW) has a short pathway from the eastern Fram Strait. Arctic Low CDOM / High 236U Water (a350<0.35 m−1, Θ≤2°C, σΘ≤27.97 or 236U concentration ≥15 × 106 atom/L) sourced from the BSBW and the FSBW has an average of 22–28 yrs transit time. These findings demonstrate how combining measurements of CDOM with 236UNRPs can improve the robustness in estimation of transit times of different Atlantic water pathways in the Arctic Ocean. There are limited ways to empirically derive estimates and the values provided offer unique data for comparison with estimates from regional circulation models.

Large sex differences in vulnerability to circulatory-system disease under current and future climate in Bucharest and its rural surroundings

Circulatory-system diseases (CSDs) are responsible for 50–60% of all deaths in Romania. Due to its continental climate, with cold winters and very warm summers, there is a strong temperature dependence of the CSD mortality. Additionally, within its capital Bucharest, the urban heat island (UHI) is expected to enhance (reduce) heat (cold)-related mortality. Using distributed lag non-linear models, we establish the relation between temperature and CSD mortality in Bucharest and its surroundings. A striking finding is the strong temperature-related response to high urban temperatures of women in comparison with men from the total CSDs mortality. In the present climate, estimates of the CSDs attributable fraction (AF) of mortality at high temperatures is about 66% higher in Bucharest than in its rural surroundings for men, while it is about 100% times higher for women. Additionally, the AF in urban areas is also significantly higher for elderly people, and for those with hypertensive and cerebrovascular diseases than in the rural surroundings. On the other hand, in rural areas, men but especially women are currently more vulnerable with respect to low temperatures than in the urban environment. In order to project future thermal-related mortality, we have used five bias-corrected climate projections from regional circulation models under two climate-change scenarios, RCP4.5 and RCP8.5. Analysis of the temperature-mortality associations for future climate reveals the strongest signal under the scenario RCP8.5 for women, elderly people as well as for groups with hypertensive and cerebrovascular diseases. The net AF increase is much larger in urban agglomeration for women (8.2 times higher than in rural surroundings) and elderly people (8.5 times higher than in rural surroundings). However, our estimates of thermal attributable mortality are most likely underestimated due to the poor representation of UHI and future demography.

Investigating the Role of Bias Correction Methods and Climate Models on Water Budget of Büyük Menderes Basin

Büyük Menderes Basin is one of the largest basins in Turkey, with almost half of the basin area utilized for agricultural purposes. The amount of water allocated to the agricultural areas in the basin corresponds to 80% of water use in the watershed. Hence, the impact of climate change on the water supply in the Büyük Menderes Basin will be significant for the basin. In this study, we model the effects of climate change on the water budget (water supply and demand balance) of the Büyük Menderes Basin using the Water and Evaluation and Planning (WEAP) tool. Future precipitation, temperature, and evaporation data for the basin are attained from outputs of the HadGEM2-ES global circulation model (GCM), along with CNRM-CM5.1 and GFDL-ESM2M regional circulation models (RCM) for RCP 4.5 and RCP 8.5 scenarios. Subsequently, the study applies different statistical bias correction methods (Linear Scaling (LS), Distribution Mapping (DM), Local Precipitation Scaling (PLIS), and Power Transformation of Precipitation (PTP) for raw outputs of GCMs and RCMs and analyzes the changes in outcomes of projected climate data and the impact of changes on the hydrology of the basin using the WEAP model. For this analysis, calibrated and validated WEAP model for the 12 reservoirs of Büyük Menderes Basin is used to understand the impact of different bias correction methods on reservoir levels.

El Niño‐Related Stratification Anomalies Over the Continental Slope Off Oregon in Summer 2014 and 2015: The Potential Vorticity Advection Mechanism

AbstractOver the continental slope off Oregon at the US West Coast, at 44.6°N, vertical stratification is found to be anomalously weak in July–August of 2014 and 2015 both in a regional ocean circulation model and conductivity–temperature–depth (CTD) profile observations. To understand the responsible mechanism, we focus on the layer between the isopycnal surfaces σθ = 26.5 and 26.25 kg m−3 that is found between depths 100 and 300 m and represents material properties characteristic of the slope poleward undercurrent and shelf‐slope exchange. This layer thickness, about 50 m on average, can be twice as large during the above‐mentioned periods. In the 2009–2018 model analysis, this anomaly is revealed over the continental slope only in summers 2014 and 2015 and only off the Oregon and Washington coasts (40°–47°N). The stratification anomaly is explained as the effect of advection of the seasonal along‐slope potential vorticity (PV) gradient by an anomalously strong poleward slope current. In the annual cycle, the zone of strong along‐slope PV gradient is found between 40° and 47°N, supported by the local upwelling that results in the injection of the large PV in the bottom boundary layer over the shelf followed by its offshore transport in the slope region. The positive along‐slope current anomaly propagates to Oregon with coastally trapped waves as part of the El Niño oceanic response and can be up to 0.1 m s−1. Advection by this anomalous poleward current results in transporting the seasonal PV gradient earlier in the season than on average.

Simulated seasonal oceanographic changes and their implication for the small pelagic fisheries in the Java Sea, Indonesia

Small pelagic fisheries in the Java Sea (JS) contributes to about 26.6% of the total marine fisheries resources, where their spatial-temporal variation is controlled by seasonal oceanographic changes. This study aims to investigate a relationship between seasonal reversal circulation and number of light-fishing vessels (VBD) dispersion that capture small pelagic fishes, using multi-datasets from a regional ocean circulation model, satellite-derived datasets, and pelagic fish landing datasets between 2010 and 2020. The model demonstrates that main axis of eastward (westward) monsoon current that brings warmer and fresher (cooler and saltier) water, confines much closer along the northern Java (southern Kalimantan) during the northwest (southeast) monsoon period. These changes are followed unprecedentedly by southward (northward) shift of VBD and high abundance of euryhaline (stenohaline) fish species. This new evidence implies that reversal monsoon current and surface component of Makassar Throughflow play a significant role on delineating potential small pelagic fishing ground and fish productions.

Potential Impacts of Climate Change on Surface Water Resources in Arid Regions Using Downscaled Regional Circulation Model and Soil Water Assessment Tool, a Case Study of Amman-Zerqa Basin, Jordan

Water scarcity, aggravated by climate change impacts, threatens all sectors in arid regions and hampers sustainable development plans. This work aims to assess the potential impacts of climate change on surface water resources of Amman-Zerqa Basin, Jordan, using the Soil Water Assessment Tool model (SWAT) and outputs from the Downscaled Regional Circulation Model. Future scenarios were developed based on combining two Representative Concentration Pathways (RCPs 4.5 and 8.5). A reference scenario from 1973 to 2015 was used to compare the current climate with future climates and their impacts on hydrological processes. Hydrologic modeling outputs showed very good performance ratings for calibration and validation periods. Statistical bias correction of the Downscale Regional Circulation Model (GCM) indicated that linear scaling for precipitation data was the best-performing bias correction method, along with variance scaling and distribution mapping methods for minimum and maximum temperature, respectively. The coupled future model simulations indicated a reduction in crucial water balance components under all modeled scenarios. The simulated reductions range between 3.7% and 20.7% for precipitation, 22.3–41.6% for stream flow, 25.0–47.0% for surface runoff, 0.5–13.4% for evapotranspiration, and 21.5–41.4% for water yield, from conservative to the severe scenario, respectively. In conclusion, spatial analyses indicated the presence of three zones of impact. Thus, future climate and hydrological adaptation measures should focus on the provided zoning.

A nonhydrostatic oceanic regional model, ORCTM v1, for internal solitary wave simulation

Abstract. The Oceanic Regional Circulation and Tide Model (ORCTM), including a nonhydrostatic dynamics module which can numerically reproduce internal solitary wave (ISW) dynamics, is presented in this paper. The performance of a baroclinic tidal simulation is also examined in regional modeling with open boundary conditions. The model control equations are characterized by three-dimensional and fully nonlinear forms considering incompressible Boussinesq fluid in Z coordinates. The pressure field is decomposed into the surface, hydrostatic, and nonhydrostatic components on the orthogonal curvilinear Arakawa-C grid. The nonhydrostatic pressure determined by the intermediate velocity divergence field is obtained via solving a three-dimensional Poisson equation based on a pressure correction method. Model validation experiments for ISW simulations with the topographic change in the two-layer and continuously stratified ocean demonstrate that ORCTM has a considerable capacity for reproducing the life cycle of internal solitary wave evolution and tide–topography interactions.

Inherent bias correction is necessary for weather data of global and regional circulation models

Inherent bias correction is necessary for weather data of global and regional circulation models

Simulated circulation and trajectory analysis in the Makassar Strait

Makassar Strait conveys the main Indonesian Throughflow (ITF) pathway, as part of the global thermohaline circulation transferring heat and freshwater fluxes from the Pacific Ocean to the Indian Ocean. Dynamics and variability of the ITF and the monsoon winds system influence significantly marine ecosystem in the Indonesian Seas. The study aims to analyze sea surface circulation patterns and particle trajectories in the Makassar Strait by developing a simulation of the CROCO’s 1/36º regional general circulation model between 2017-2018. The results revealed the dynamics of near-surface layer (0 – 50 m depth) varied seasonally. The magnitude of surface current was about 0.6 m/s during the peak of northwest monsoon (NWM) flowing northward and reverse southward during the peak of southeast monsoon (SEM). The magnitude of the current intensified up to 1 m/s in the subsurface at Labani Channel and persistent flows to the southward. The thermocline transport volume was maximum during SEM with average transport about -11.00 (±1.54) Sv. The analysis shows that the particles near Balikpapan coast spreaded slowly to the north, then rotating at the center of the strait and spreaded according to the NWM and SEM.

Circulation and stratification drivers during the summer season in the upwelling bay of Paracas (Peru): A modelling study

The circulation and stratification in the shallow semi-enclosed bay of Paracas located downstream of the main upwelling cell off the Peruvian coast were studied during the summer season using a regional circulation model and in situ observations. A downscaling strategy based on a series of three embedded grids, from 10 km to 500 m resolution in the bay allows to take into account the influence of remote perturbations on the bay dynamics. Debiased surface winds from a high-resolution regional atmospheric model were used to force the model. The shortwave absorption depth was parameterized using satellite measurements of surface chlorophyll.Sensitivity experiments to the model forcing and parameterizations were performed to investigate the impact of the wind diurnal variability, tidal forcing, freshwater discharge from a nearby river and shortwave absorption depth on the bay stratification. Results show that: debiasing the wind intensity reduced the model cold bias in the bay and increase the stratification; a shallow shortwave absorption depth induced a cooling of the subsurface water, increasing the stratification; freshwater discharge from the Pisco river north of the bay increased slightly the stratification in the bay during days of weak wind. The high sensitivity of the bay stratification to the atmospheric forcing calls for the need to use more realistic wind forcing products.The circulation in the bay under strong (>5.5 m s−1) and weak (<3 m s−1) winds was also examined. The summer circulation during strong upwelling-favorable wind conditions was characterized by northward surface currents transporting the bay surface waters outward and subsurface currents transporting cold deeper waters into the bay along its western shore. During weak wind conditions, the current is outward in the bottom layer and a surface southward current related to the poleward undercurrent flowing over the continental slope and shelf transported warm waters into the bay, generating a cyclonic circulation in the bay.

IMPACT OF CLIMATE CHANGE ON THE SUGAR CANE IRRIGATION WATER DEMAND IN THE GRAMAME RIVER WATERSHED

Climate change is a recurring theme as it impacts various sectors of society, including water resources, reflecting directly on human beings' activities. In this context, the objective of this study was to assess the impacts produced by climate change on the sugarcane water demands for irrigation in four municipalities within the Gramame River watershed. For this, the irrigation water demand was estimated from the calculation of the evapotranspiration of the sugarcane culture. The temperature data used in these estimates were obtained from the projections of three Regional Circulation Models: ICHEC-EC-EARTH-RCA4, MPI-ESM-LR-RCA4, and MPI-ESM-LR-REMO2009 taken from the Coordinated Regional Climate Downscaling (CORDEX). These demands were estimated for two intervals of years (2006-2037 and 2038-2069) and for two greenhouse gas emission scenarios, RCP 4.5 and RCP 8.5. The patterns of the temperature projections of the three models were evaluated and corrected in order to reduce uncertainties. The results indicate that the MPI-ESM-LR-REMO2009 model was the one that best represented the temperature in the current climate (1961-2005). Furthermore, the increase in temperature due to climate change affects irrigation water demand in the near future (2006-2037) with slight effects, and in the distant future (2038-2069) with stronger impacts.

Slope and Shelf Flow Anomalies Off Oregon Influenced by the El Niño Remote Oceanic Mechanism in 2014–2016

AbstractOutputs of the regional ocean circulation model are analyzed to demonstrate the measurable impact of the El Niño remote oceanic forcing mechanism along the US West Coast during the major heat wave period of 2014–2016. The 2‐km horizontal resolution model, based on the Regional Ocean Modeling System (ROMS), was run for the period of 2009–2018. Though the model does not assimilate observations, it performs well by comparison with time series data explaining observed variability on temporal scales from several days to seasonal and interannual. The El Niño‐related oceanic anomalies provided by a global state estimate are introduced in the regional model at the southern boundary at 24N. These propagate alongshore with coastally trapped waves (CTWs) and influence the variability off Oregon (41°–46°N). In particular, CTWs are evident in the subsurface along‐slope current, vs, and in the depth of the 26.5 kg m−3 isopycnal surface over the slope, z26.5. In summer 2014 and 2015, vs anomalies are positive (northward) and z26.5 anomalies are negative (deeper) along the US West Coast. In addition to the CTW patterns, z26.5 anomalies also exhibit slow‐moving features associated with undercurrent widening, separation, and subsurface eddy variability. Over the Oregon shelf, El Niño conditions contributed to the sharp weakening of the southward alongshore current throughout the water column in July 2014 and 2015, despite the near‐average southward, upwelling‐favorable winds.