Regional Ocean Modeling System Research Articles

Assessing the destructiveness of tropical cyclones induced by anthropogenic aerosols in an atmosphere–ocean coupled framework

Abstract. Intense tropical cyclones (TCs) can cause catastrophic damage to coastal regions after landfall. Recent studies have linked the devastation associated with TCs to climate change, which induces favorable conditions, such as increasing sea-surface temperature, to supercharge storms. Meanwhile, environmental factors, such as atmospheric aerosols, also impact the development and intensity of TCs, but their effects remain poorly understood, particularly coupled with ocean dynamics. Here, we quantitatively assess the aerosol microphysical effects and aerosol-modified ocean feedbacks during Hurricane Katrina using a cloud-resolving atmosphere–ocean coupled model: Weather Research and Forecasting (WRF) in conjunction with the Regional Ocean Model System (ROMS). Our model simulations reveal that an enhanced storm destructive power, as reflected by larger integrated kinetic energy, heavier precipitation, and higher sea-level rise, is linked to the combined effects of aerosols and ocean feedbacks. These effects further result in an expansion of the storm circulation with a reduced intensity because of a decreasing moist static energy supply and enhancing vorticity Rossby wave outward propagation. Both accumulated precipitation and storm surge are enhanced during the mature stage of the TC with elevated aerosol concentrations, implying exacerbated flood damage over the polluted coastal region. The ocean feedback following the aerosol microphysical effects tends to mitigate the vertical mixing cooling in the ocean mixing layer and offsets the aerosol-induced storm weakening by enhancing cloud and precipitation near the eyewall region. Our results highlight the importance of accounting for the effects of aerosol microphysics and ocean-coupling feedbacks to improve the forecast of TC destructiveness, particularly near the heavily polluted coastal regions along the Gulf of Mexico.

Modelling the impacts of a large marine turbine array in the Cozumel Channel

Ocean renewable energies are a promising alternative to meet the growing energy demand. Due to the intense, persistent and relatively constant unidirectional flow, the Cozumel Channel (CC) in the Caribbean Sea is considered one of the most favorable global sites for the potential exploitation of ocean current energy. In this paper we use the Regional Ocean Modelling System (ROMS) to simulate the effects of a large number of individual turbines (5277) on the marine environment at a regional scale. A couple of two-way nested grids were used to extend the horizontal resolution from 30 m to ∼3600 m. The impacts of the turbines on circulation, water temperature, sea surface high (SSH), sediment transport and upwelling events, were analyzed. An improved estimate of the average power generated was also performed, which includes the disruption of the currents by the turbines. The results suggest that the installation of a large number of marine turbines would cause severe flow disturbances in the CC and neighboring regions, changing several aspects of the ecosystem. While the number and characteristics of the marine turbines might seem excessive, this study could serve as a benchmark to determine thresholds in the size of future turbine farms in the region.

Contrasting Central Equatorial Pacific Oxygen Isotopic Signatures of the 2014/2015 and 2015/2016 El Niño Events

AbstractPaleoclimate reconstructions of El Niño/Southern Oscillation (ENSO) behavior often rely on oxygen isotopic records from tropical corals (δ18O). However, few reef‐based observations of physical conditions during El Niño events exist, limiting our ability to interpret coral δ18O. Here we present physical and geochemical measurements from Palmyra Atoll (5.9°N, 162.1°W) from 2014–2017, along with a data assimilation product using the isotope‐enabled Regional Ocean Modeling System (isoROMS). Coral δ18O signals are comparably strong in 2014–2015 and 2015–2016; notably, over 50% of the signal is driven by seawater δ18O, not temperature. If a constant seawater δ18O:salinity relationship were present, this would imply a comparable salinity anomaly during both events. However, salinity changes are much larger during 2014–2015, indicating a highly nonstationary relationship. isoROMS then shows that advection strongly influences δ18O during both the 2014–2015 and 2015–2016 El Niño, driving differences in the salinity/seawater δ18O relationship. This demonstrates the need for considering ocean dynamics when interpreting coral δ18O.

Development of a high-resolution marine ecosystem model for predicting the combined impacts of ocean acidification and deoxygenation

An approach was developed to help evaluate and predict the combined effects of ocean acidification and deoxygenation on calcifying organisms along the coast of Japan. The Coastal and Regional Ocean COmmunity (CROCO) modeling system was set up to couple the Regional Ocean Modeling System (ROMS) to the Pelagic Interaction Scheme for Carbon and Ecosystem Studies (PISCES) biogeochemical model and used to reproduce physical and biochemical processes in the area around Miyako Bay, Iwate Prefecture, Japan. Future scenario cases were also set up, which used initial and boundary conditions based on Future Ocean Regional Projection (FORP) simulations. Present day simulations were able to reproduce the general features of observed physical and biochemical parameters, except for some rapid decreases in salinity, pH and aragonite saturation state (Ωarag). This suggests that more local factors which have not been introduced into the model, such as submarine groundwater discharge, may be involved, or that river inputs may be underestimated. Results of the future projections suggest a significant impact of global warming and ocean acidification on calcifying organisms for the worst case of climate change under the Representative Concentration Pathway (RCP) 8.5 scenario. In particular, it is feared that values of Ωaragwould approach the critical level for calcifying organisms (Ωarag< 1.1) throughout the year, under which decreased larval shell lengths and malformation have been observed experimentally for the locally grownHaliotis discus hannai(Ezo Abalone) species. However, these findings may not be true for a different coastal locality, and this study highlights and continues to stress the importance of developing model setups capable of incorporating both regional and local factors affecting ocean acidification and deoxygenation.

Roles of thermal advection in setting the Southern Ocean warming pattern

AbstractThe Southern Ocean is the major region of global ocean heat gain. Most of the heat gain is concentrated in the region of the Antarctic Circumpolar Current (ACC), but SST within the ACC only exhibits a slight increase. Ocean circulation plays a fundamental role in setting the pattern of temperature response to global warming. In this study, a 1/4° Southern Ocean eddy‐permitting model configured based on the Regional Ocean Modeling System is used to study the role of ocean in setting the warming pattern, by examining the response of ocean temperature and heat budget terms to a uniform air–sea heat flux (Qnet) increase. As Qnet increases by a constant value, the SST increases, but with a smaller value within the ACC region. Consequently, more heat flux in the ACC region is induced from the atmosphere to the ocean through thermal adjustment. Heat budget analyses suggest that the surface warming induced by vertical diffusion is largely offset by the cooling effect of heat advection, especially within the ACC region; however, in the subsurface, the effect of vertical diffusion becomes slight, and heat advection dominates the temperature change and induces warming in the ACC region. These results highlight the importance of heat advection in setting the temperature response pattern to air–sea heat flux increase: by transporting more heat from the surface to the deep ocean, the SST increase within the ACC region becomes smaller, and this induces more heat flux from the atmosphere to the ocean and thus makes the ACC region become a major region of heat gain.

Weak constraint 4D-Var data assimilation in the Regional Ocean Modeling System (ROMS) using a saddle-point algorithm: Application to the California Current Circulation

The saddle-point formulation of weak constraint 4-dimensional variational (4D-Var) data assimilation has been developed for the Regional Ocean Modeling System (ROMS), and is applied here to the California Current System (CCS). Unlike the conventional primal and dual forcing formulation of weak constraint 4D-Var, the saddle-point formulation can be efficiently parallelized in time, leading to a substantial decrease in wall-clock run time. The performance of the ROMS saddle-point 4D-Var algorithm is assessed here and compared to that of the dual forcing formulation which is the current standard in ROMS. While the rate of convergence of the saddle-point formulation is slower than the dual forcing formulation, the increase in computational speed due to time-parallelization can more than compensate for the additional inner-loop iterations required by the saddle-point algorithm in the CCS configuration considered here. Further gains in performance can be achieved by running the 4D-Var inner-loop iterations at reduced resolution and/or reduced arithmetic precision. The results presented here indicate that in high performance computing environments with large numbers of available compute cores, the saddle-point formulation of 4D-Var could significantly reduce the run-time compared to the dual forcing formulation for large data assimilation problems.

Transport of the Tumen River water to the Far Eastern Marine Reserve (Posyet Bay) based on in situ, satellite data and Lagrangian modeling using ROMS current velocity output

We study physical mechanisms of the Tumen River water transport in the area of the Posyet Bay (Peter the Great Bay, Sea of Japan). This study is based on the satellite and in situ measurements, and numerical simulation of advection of river water by the current velocity simulated by Regional Ocean Model System (ROMS). The importance of this study is in identification of the reasons of the transport of pollutants into the area of the Far Eastern Marine Reserve. The results of the study showed that such reasons are wind currents and mesoscale cyclonic eddies. These eddies were originally detected on satellite imagery and CTD and bio-optical measurements. The anomalies in the form of spots of the chlorophyll a (CHL) increased concentration were detected on satellite images in fall 2009. The oceanographic sections of CTD and bio-optical measurements through the anomalies show that they are cyclonic eddies. These eddies consist of two cores — upper and lower. The upper core is filled with river waters with low salinity, high values of CHL and colored dissolved organic matter content (CDOM). The lower core is filled with cold saline waters. The ROMS results show that eddies are generated as a result of symmetrical and centrifugal instabilities.

Optimal initial errors related to the prediction of the vertical thermal structure and their application to targeted observation: A 3-day hindcast case study in the northern South China Sea

This 3-day hindcast case study focuses on the effects of the initial errors, a non-negligible factor in oceanic prediction, on VTS prediction in the NSCS and provides scientific guidance on observation design through targeted observation. Based on the Conditional Nonlinear Optimal Perturbation (CNOP) approach and the Regional Ocean Modeling System, the impact of optimal initial errors (OIEs) on the 3-day VTS prediction is estimated and their nonlinear evolution mechanism is clarified. The OIEs, horizontally distributed along the 1000 m isobath and vertically confined within the upper 50 m, experience non-localized evolution and cause a rapid increase in the root mean square errors by about 100 times during the prediction period. Eddy energetics analysis indicates that barotropic instabilities constitute a key factor in the evolution of the OIEs. In addition, sensitive areas are identified for targeted observation based on the vertically integrated total energy of the OIEs. Sensitive experiments demonstrate that the prediction errors caused by random initial errors in the sensitive areas are larger than those in other nearby areas. Observing system simulation experiments (OSSEs) further suggest that eliminating the initial errors in sensitive areas can improve VTS prediction by over 50%. This study reveals the patterns and growth dynamic mechanism of CNOP-type OIEs in 3-day VTS prediction in the NSCS and provides scientific guidance for operational observation design.

Evaluating Alternate Methods of 4D-Var Data Assimilation in a Coupled Hydrodynamic—Four-Component Biogeochemical Model of the California Current System

Assimilating biogeochemical (BGC) data into ocean models using traditional four-dimensional variational data assimilation (4D-Var) includes the technical challenge of constructing tangent-linear (TLM) and adjoint (ADJ) models corresponding to the non-linear BGC model. This hurdle can be time-consuming, particularly for non-linear BGC models experiencing active development, with regular updates to functional types or representation of key BGC processes. We evaluate two alternate approaches that greatly simplify TLM and ADJ construction and eliminate the need for code updates when the underlying, non-linear BGC model changes. One form of model-reduced data assimilation represents BGC interactions as a linear combination of orthogonal modes; we use empirical orthogonal functions and refer to this as the BioEOFs method. The second approach treats BGC variables as passive tracers that experience advection and diffusion by TLM and ADJ physics over an assimilation cycle, but are biochemically inactive. We evaluate the efficacy of these methods in a realistically configured, data-assimilative implementation of the Regional Ocean Modeling System with a simple nutrient–phytoplankton–zooplankton–detritus (NPZD) BGC model for the U.S. west coast. In a series of sequential data-assimilative model cycles, observations of temperature, salinity, sea-level anomaly, and phytoplankton biomass constrain the modeled state over the period spanning January–June 2019. We perform the assimilation in both physical and logarithmic-transformed space and compare results of the two approximate methods to traditional 4D-Var using TLM and ADJ models with BGC processes corresponding explicitly to the BGC model. While the full-adjoint 4D-Var results in the best correction to phytoplankton fields for analyses and forecasts, the BioEOFs and passive-tracer approaches also significantly reduce the model-observation misfit compared to a non-assimilative run and do so at reduced computational expense. The passive tracer performs generally better than BioEOFs, whose corrections exhibit large-scale structure across the domain. While the most accurate state estimate will result from development and application of the full TLM and ADJ, the log-transformed passive-tracer approach may be a viable alternative for performing BGC 4D-Var for state estimation when a full-adjoint option is not yet available.

Simulation of seasonal transport of microplastics and influencing factors in the China Seas based on the ROMS model

Elucidating the mechanisms governing microplastic transport and spatial distribution in offshore waters is essential to microplastic control. However, current research on microplastic transport in the China Seas is largely restricted to small-scale investigations, which do not provide a comprehensive result. Therefore, in this study, we used the Regional Ocean Modeling System (ROMS) combined with the Lagrangian Transport (LTRANS v.2) model to investigate how microplastics are transported around the China Seas during different seasons and under climatological river discharge. Our findings showed that the microplastic pathways and spatial distributions exhibit marked seasonal variations controlled by circulation patterns in the China Seas, river discharge values, and the characteristics of the microplastic materials. Floating microplastics exhibited the longest transport distance in summer, when microplastics from the Pearl River could be transported up to 1375.8 km through the Tokara and Tsushima straits. The heavy pollution areas in summer were located in the South Yellow Sea and East China Sea, mainly resulting from the contribution of the Yangtze River (>66%). In autumn and winter, more than three-quarters of the microplastics beached off the south-central Chinese coast. In addition, simulating the vertical velocity of the water prolonged the time required for microplastics to reach the open ocean, thereby reducing the amount of microplastics entering the Pacific Ocean by 6% compared to the simulation without the vertical velocity of the water in summer. Microplastics with higher densities were generally transported shorter distances. The transmission distances of PET and PS were two orders of magnitude smaller than that of PE. This study enhances knowledge of the sources and fates of offshore microplastics and provides scientific support for offshore microplastic control.

Parameterizing Subglacial Discharge in Modeling Buoyancy Driven Flow in Tidewater Glacier Fjords

AbstractIn tidewater glacier fjords, subglacial discharge drives a significant mixing mechanism near glacier fronts and drives a strong exchange flow. Numerous studies (Cowton et al., 2015, https://doi.org/10.1002/2014jc010324; Slater et al., 2017, https://doi.org/10.1002/2016gl072374) have utilized a parameterization for buoyant plume theory to force fjord scales systems, but neglect to parameterize the outflowing of the plume away from the glacial wall after it has reached its neutral density. In this study, a new model framework, ROMS‐ICEPLUME, is developed to parameterize the rising and initial outflowing stage of subglacial discharge plumes in the Regional Ocean Modeling System. The coupled model applies a novel parameterization algorithm to prescribe the velocity and vertical extent of the outflowing plume, which reduces numerical instability and improves model performance. The model framework is tested with a quasi‐realistic forcing using observations of a subglacial discharge plume hydrographic surveys collected from a Greenland fjord. We find that the new model framework is able to reproduce the strong outflowing plume and the compensating inflow at depth, with a spatial structure that correlates well with in‐situ observations. On the other hand, the model framework without the new parameterization algorithm fails to capture the outflowing plume structure. Thus, our new framework for parameterizing subglacial discharge plumes is an improvement from previous coupled model frameworks, and is a promising tool toward advancing our understanding of circulation in tidewater glacier fjords.

Two-Dimensional Numerical Simulation of Tide and Tidal Current of Eight Major Tidal Constituents in the Bohai, Yellow, and East China Seas

Numerical simulations of the eight major tidal constituents (M2, S2, K1, O1, N2, K2, P1, and Q1) in the Bohai, Yellow and East China Seas (BYES) were conducted using the Regional Ocean Modeling System (ROMS) based on altimeter products from X-TRACK. Tidal harmonic constants and two-dimensional tidal current data with a spatial resolution of 1/12° were obtained. To validate the simulation results (SRs), harmonic constants from altimeters and tide gauges, two sea level anomaly time series, and velocity observations from 12 current meters were utilized. Additionally, data from five tidal models were used for comparison. The validation and comparison results demonstrated the accuracy of SR, especially when compared with coastal tide gauge data where SR performs exceptionally well. The cotidal charts and tidal current ellipses obtained through SR exhibited good continuity and consistency with the previous studies, effectively reflecting the tidal characteristics of the BYES. The SR can serve as a valuable reference and support for tidal-related fields in the BYES, including the supplement and verification of ocean measurements and the calculation of reference planes for ocean engineering.

Multiscale hydrodynamics modeling reveals the temperature moderating role of the Northern Red Sea Islands

A growing interest in the hydrodynamics of the Red Sea has been observed since the beginning of the 21st century. However, the interaction between the Gulf of Suez (GOS) and the Red Sea along with possible natural mitigation mechanisms of heat stress on its southern coral reef zones have not been adequately investigated. This study evaluated different Regional Ocean Modeling System (ROMS) simulations of the Red Sea using a nesting approach in the southern parts of the GOS to elucidate the three-dimensional nature of thermal variability. The developed regional ROMS model simulated the general circulation patterns and sea surface temperature on the TSUBAME 3.0 supercomputer operated by the Tokyo Institute of Technology. Ultimately, remotely sensed satellite data of Sea Surface Temperature (SST) spanning the period 2016–2020 were used to validate the regional model results. A further challenge posed by the scarcity of distributed depth-varying temperature data on the northern islands' region was overcome by using an offline nesting approach (i.e., incorporating boundary conditions from the parent domain) to simulate the local 3-D thermal regimes. Intriguingly, the results of the nested model scenarios confirmed unique northern islands-enhanced thermal moderating mechanisms where islands act as barriers to the impacts of the relatively warmer water originating from the eastern boundary current. Additionally, this study introduces a new approach to applying higher-resolution models to the precise spatial and temporal representation of thermal indices in a way that surpasses the widely adopted remote sensing approaches. In short, multiscale modeling provides a valuable approach for assessing the thermal regimes around one of the most precious marine ecosystems in the world.

Intelligent path planning algorithm of Autonomous Underwater Vehicle based on vision under ocean current

AbstractAutonomous Underwater Vehicle (AUV) is an important tool for intelligent ocean applications, which can be applied to detect underwater environment and search target. Path planning is the key technology to realize AUV intelligence, which has important research significance. Aiming at the dynamic path planning problem, the Regional Ocean Modeling System (ROMS) was first applied to the AUV three‐dimensional (3D) dynamic path planning, and a Gate Recurrent Unit Proximal Policy Optimization with Local Vision (GPPO‐LV) model based on local vision is proposed. The 3D ocean current environment is constructed based on the ROMS simulation data. The local vision matrix is constructed based on underwater images, and the features of local vision are extracted using convolutional neural network. Furthermore, Gate Recurrent Unit (GRU) network is used to mine the hidden information between observation states. Finally, the Actor network for strategy output and the Critical network for action value evaluation are constructed, and strategies are optimized in the process of interaction with the environment. The experiment shows that under various unknown environments, AUV can carry out real‐time path planning under real ocean current data, and has good obstacle avoidance ability.

The impact of LNG offshore terminal on sea temperature and sea currents in the northern Adriatic Sea

The aim of this paper is to simulate the impact of a potential offshore LNG terminal on sea temperature (in autumn and spring/ summer) and sea currents (in autumn/winter) at three different depths (at the sea surface, at 25 m depth and at the seabed) in the northern Adriatic Sea from 14 November 2015 to 06 August 2016 using the Regional Ocean Modelling System (ROMS) model. The location of the potential offshore LNG terminal Istria (in the northern Adriatic Sea) was selected using the visual PROMETHEE method. The potential LNG terminal uses seawater for LNG heating and the seawater cooled to a temperature of 9°C returns to the marine environment. Although the differences in sea temperature with and without the discharge fit within normal temperature ranges, the simulations show that the discharge changed the speed and direction of sea currents at the sea surface not only in the wider northern Adriatic, but in the entire Adriatic. This is probably due to the specific circulation in the Adriatic, where cold water affects the geostrophic balance, an important part of the circulation field that depends on density (a function of salinity and temperature). Atmospheric conditions in the broader vicinity of the LNG terminal would also be affected by redistribution of air-sea fluxes due to changes in surface temperature. Changes in circulation would alter environmental conditions by redistributing nutrients, oxygen, etc. Further multi-year simulations of changes in the circulation system are needed, but other physical parameters (density, salinity, river inflow...) should also be included in the simulations to determine the cumulative impact of a potential LNG terminal on the marine environment.

Summertime discontinuity of Western Boundary Current in the Bay of Bengal during contrasting Indian Ocean Dipole events of 2008 and 2010

The East India Coastal Current (EICC), the Western Boundary Current (WBC) in the Bay of Bengal (BOB) is continuous northward and southward during pre- and post-Indian Summer Monsoon (ISM), respectively. The discontinuity in EICC occurs during ISM (June–September) when the boundary current remains inconsistent with various cyclonic and anticyclonic eddies in presence of a southward flow from 21°N and a northward flow from 10°N along the boundary. The variations in this summertime EICC discontinuity during the contrasting Indian Ocean Dipole (IOD) events of 2008 (positive) and 2010 (negative) are investigated here. The study uses a 1/12° Regional Ocean Modelling System (ROMS) simulation, available observations and reanalysis data. The study reveals that the strong coastal Kelvin and reflected Rossby waves during 2010, supported by strong winds in the equatorial Indian Ocean, helped to strengthen the spring and winter time continuous EICC. The continuous EICC remained very weak with the weaker equatorial remote forcing signals in 2008. The southward and northward flows from 21°N and 10°N, respectively were much stronger during 2010 ISM. However, strong eddy activities along the boundary reduced these two flows in 2008. The year 2010 showed relatively weak, but well-distributed eddy activity over the whole western BOB during ISM. Conversely, pronounced eddy activity near the western boundary with high eddy kinetic energy accumulation increases the inconsistency in boundary current flow during ISM of 2008. Therefore, the study suggests that the contrasting IOD modes have significant and complementary influence on WBC discontinuity in the BOB.

Effect of western Pacific current uncertainties on the forecasting of eddy shedding from the Kuroshio loop into the South China Sea: A case study

The process of eddy shedding from the Kuroshio loop current (LC) into the South China Sea via the Luzon Strait is highly variable and significantly controlled by the uncertainties in the Western Pacific (WP) currents. This study investigates the forecast of a strong eddy shedding event from the Kuroshio LC during the winter 2016–2017 using the regional ocean modeling system and ensemble Kalman filter assimilation method. Experiments are conducted to explore the sensitivity of forecasts to the assimilation of satellite sea surface height anomaly data from different key regions of the WP, such as the subtropical countercurrent (STCC) and Northern Equatorial Current (NEC) regions. The results indicate that the improved forecast performance of the strong Kuroshio LC eddy shedding event is mainly attributed to assimilation in the STCC region and partly owing to assimilation in the NEC region. Specifically, assimilation in the STCC region reproduces a westward-propagating cyclonic eddy that collides with the Kuroshio in the Luzon Strait, blocking the Kuroshio northward flow and causing Kuroshio LC eddy shedding. Furthermore, assimilation in the NEC region enhances the simulation of the weak Kuroshio background current, which further facilitates the formation of a strong Kuroshio background LC and the occurrence of Kuroshio LC eddy shedding.

Development and Application of an Infragravity Wave (InWave) Driver to Simulate Nearshore Processes

AbstractInfragravity waves are key components of the hydro‐sedimentary processes in coastal areas, especially during extreme storms. Accurate modeling of coastal erosion and breaching requires consideration of the effects of infragravity waves. Here, we present InWave, a new infragravity wave driver of the Coupled Ocean‐Atmopshere‐Waves‐Sediment Transport (COAWST) modeling system. InWave computes the spatial and temporal variation of wave energy at the wave group scale and the associated incoming bound infragravity wave. Wave group‐varying forces drive free infragravity wave growth and propagation within the hydrodynamic model of the coupled modeling system, which is the Regional Ocean Modeling System (ROMS) in this work. Since ROMS is a three‐dimensional model, this coupling allows for the combined formation of undertow currents and infragravity waves. We verified the coupled InWave‐ROMS with one idealized test case, one laboratory experiment, and one field experiment. The coupled modeling system correctly reproduced the propagation of gravity wave energy with acceptable numerical dissipation. It also captured the transfer of energy from the gravity band to the infragravity band, and within the different infragravity bands in the surf zone, the measured three‐dimensional flow structure, and dune morphological evolution satisfactorily. The idealized case demonstrated that the infragravity wave variance depends on the directional resolution and horizontal grid resolution, which are known challenges with the approach taken here. The addition of InWave to COAWST enables novel investigation of nearshore hydro‐sedimentary dynamics driven by infragravity waves using the strengths of the other modeling components, namely the three‐dimensional nature of ROMS and the sediment transport routines.

Improving sea surface temperature in a regional ocean model through refined sea surface temperature assimilation

Abstract. Infrared (IR) and passive microwave (PMW) satellite sea surface temperature (SST) retrievals are valuable to assimilate into high-resolution regional ocean forecast models. Still, there are issues related to these SSTs that need to be addressed to achieve improved ocean forecasts. Firstly, satellite SST products tend to be biased. Assimilating SSTs from different providers can thus cause the ocean model to receive inconsistent information. Secondly, while PMW SSTs are valuable for constraining models during cloudy conditions, the spatial resolution of these retrievals is rather coarse. Assimilating PMW SSTs into high-resolution ocean models will spatially smooth the modeled SST and consequently remove finer SST structures. In this study, we implement a bias correction scheme that corrects satellite SSTs before assimilation. We also introduce a special observation operator, called the supermod operator, into the Regional Ocean Modeling System (ROMS) four-dimensional variational data assimilation algorithm. This supermod operator handles the resolution mismatch between the coarse observations and the finer model. We test the bias correction scheme and the supermod operator using a setup of ROMS covering the shelf seas and shelf break off Norway. The results show that the validation statistics in the modeled SST improve if we apply the bias correction scheme. We also find improvements in the validation statistics when we assimilate PMW SSTs in conjunction with the IR SSTs. However, our supermod operator must be activated to avoid smoothing the modeled SST structures on spatial scales smaller than twice the PMW SST footprint. Both the bias correction scheme and the supermod operator are easy to apply, and the supermod operator can easily be adapted for other observation variables.

Storm Surge Inundation Modulated by Typhoon Intensities and Tracks: Simulations Using the Regional Ocean Modeling System (ROMS)

Storm surges are one of the most severe marine hazards, causing fatalities and devastating infrastructure. It is important to conduct research on storm surge hazards to achieve disaster avoidance and the protection of local populations. In this study, the Regional Ocean Modeling System (ROMS) was used to develop a framework to simulate the inundation (using the wet/dry method) of land in Ningbo, China during an extreme typhoon storm surge. The baseline simulation with the realistic typhoon intensity and track was well validated by meteorological and ocean tidal observations. Using reanalysis and an asymmetric typhoon wind field from the Holland model as atmospheric forcing, we presented different storm surge inundation scenarios regarding various intensities and tracks. The results revealed that typhoon storm surges are significantly affected by both the intensities and tracks of typhoons. Specifically, when Ningbo was located in the navigable semicircle, increasing the typhoon intensity not only resulted in the total inundation area of the whole study area from 108.57 km2 to 139.97 km2, but also led to significant negative storm surges in some sea areas. When Ningbo was exposed to the dangerous semicircle of the intensified typhoon, the storm surge along the coast of the Xiangshan Bay could exceed 4 m, amplifying the total inundation area to 245.41 km2. Thus, it was evident that the location of the impacted region within the typhoon’s wind field plays a critical role in determining the severity of the storm surge. These results provide valuable suggestions for storm surge disaster prevention and mitigation for local governments.