Hybrid Coordinate Ocean Model Research Articles

The impact of internal tides and gravity waves on key acoustic parameters and acoustic transmission loss near the Amazon shelf

Upper ocean variability depends on tides and wind forcing. The barotropic tide creates baroclinic internal tides and internal gravity waves (IGWs) that can propagate long distances and dissipate, impacting mixed layer and thermocline depths, vertical thermal gradients, and mixing. In the last decade, there has been an effort to include tidal motions in global HYCOM (HYbrid Coordinate Ocean Model). Here, we look at the impacts of tidally driven motions on acoustic propagation along the Amazon shelf by comparing acoustic transmission loss and key acoustic parameters in 1/25 deg Global HYCOM model runs with and without tides. Acoustic runs were performed at mid-frequencies using Bellhop3D at depths above and below the sonic-layer depth (SLD). Key acoustic parameters assessed include the SLD and vertical sound-speed gradients. Although the impacts of the internal waves and tides on acoustics are intermingled with the effects of other stochastic ocean processes (e.g., mesoscale eddies, fronts, and atmospheric forcing), timeseries analysis indicates that there is acoustic sensitivity to tidally forced variability. These ocean-acoustic results can be used for future development of machine learning algorithms to model coupled oceanographic and acoustical processes.

Intraseasonal variability of the Indonesian throughflow associated with the Madden-Julian Oscillation

Intraseasonal variability (20–90 days) of the Indonesian Throughflow (ITF), which is primarily forced by the Madden-Julian Oscillation (MJO), is investigated using a high-resolution global ocean reanalysis and satellite altimeter data. Previous studies show that during the MJO active phase, downwelling Kelvin waves generated in the central equatorial Indian Ocean propagate along the coast of Sumatra and Java islands, affecting the ITF transport at exit passages in the Indonesian Seas and Makassar Strait. However, the intraseasonal variation of the ITF transport through these straits over the MJO life cycle, especially during the suppressed phase, has not been quantified. To quantify the ITF transport associated with the MJO, composites of ITF transport through major straits in the Indonesian Seas are constructed using a 0.08° global HYbrid Coordinate Ocean Model (HYCOM) reanalysis. A prominent reduction of ITF transport through major straits is found during the MJO active phase, and a transport enhancement comparable to the reduction is evident during the suppressed phase. As a result, the net effect of the MJO on the mean ITF transport is very small due to the cancellation of the enhancement and reduction. The magnitude of the MJO-associated ITF transport variation through all ITF exit passages is about 6 Sv, which is about 50% of the total transport. While the propagation of coastal Kelvin waves during the MJO active phase and their impact on ITF transport is clearly evident in the composite, such Kelvin wave influence on ITF transport is not clearly detected during the suppressed phase. This suggests that anomalous winds over the Maritime Continent (MC) area are mostly responsible for the ITF variation during the suppressed phase in many MJO events. Yet, during some MJO events, remotely-forced upwelling Kelvin waves and their significant impact on the ITF transport are evident during the MJO suppressed phase.

Generalized Kalman Filter and Ensemble Optimal Interpolation, Their Comparison and Application to the Hybrid Coordinate Ocean Model

In this paper, we consider a recently developed data assimilation method, the Generalized Kalman Filter (GKF), which is a generalization of the widely-used Ensemble Optimal Interpolation (EnOI) method. Both methods are applied for modeling the Atlantic Ocean circulation using the known Hybrid Coordinate Ocean Model. The along-track altimetry data taken from the Archiving, Validating and Interpolating Satellite Oceanography Data (AVISO) were used for data assimilation and other data from independent archives of observations; particularly, the temperature and salinity data from the Pilot Research Array in the Tropical Atlantic were used for independent comparison. Several numerical experiments were performed with their results discussed and analyzed. It is shown that values of the ocean state variables obtained in the calculations using the GKF method are closer to the observations in terms of standard metrics in comparison with the calculations using the standard data assimilation method EnOI. Furthermore, the GKF method requires less computational effort compared to the EnOI method.

Generation mechanism of the counter-wind South China Sea Warm Current in winter

A 22-year (1994–2015) HYbrid Coordinate Ocean Model (HYCOM) global reanalysis is used to study the generation mechanism of the counter-wind characteristic of the South China Sea Warm Current (SCSWC) in winter seasons. Our analysis clearly demonstrates that the counter-wind SCSWC in winter is driven by wind relaxation. An Extended Empirical Orthogonal Function (EEOF) analysis of the hourly Sea Surface Height (SSH) and wind stresses reveals that the most dominant SSH mode is an Ekman mode. When the wind relaxes, the Ekman transport anomaly is offshore and generates a favorable cross-shore SSH slope for the northeastward surface currents over the continental shelf mainly by geostrophic balance. The alongshore pressure gradient force also increases when the wind relaxes, and dominates the weak wind stresses to push the alongshore water northeastwards. We also identify the region south of Taiwan Strait as the origin of the SCSWC, instead of the Hainan Island or Gulf of Tonkin, Vietnam due to the dominant Ekman dynamics.

Simulated zonal current characteristics in the southeastern tropical Indian Ocean (SETIO)

Abstract. Detailed ocean currents in the southeastern tropical Indian Ocean adjacent to southern Sumatran and Javan coasts have not been fully explained because of limited observations. In this study, zonal current characteristics in the region have been studied using simulation results of a 1/8∘ global hybrid coordinate ocean model from 1950 to 2013. The simulated zonal currents across three meridional sections were then investigated using an empirical orthogonal function (EOF), where the first three modes account for 75 %–98 % of the total variance. The first temporal mode of EOF is then investigated using ensemble empirical mode decomposition (EEMD) to distinguish the signals. This study has revealed distinctive features of currents in the South Java Current (SJC) region, the Indonesian Throughflow (ITF)–South Equatorial Current (SEC) region, and the transition zone between these regions. The vertical structures of zonal currents in southern Java and offshore Sumatra are characterized by a one-layer flow. Conversely, a two-layer flow is observed in the nearshore and transition regions of Sumatra. Current variation in the SJC region has peak energies that are sequentially dominated by semiannual, intraseasonal, and annual timescales. Meanwhile, the transition zone is characterized by semiannual and intraseasonal periods with pronounced interannual variations. In contrast, interannual variability associated with El Niño–Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) modulates the prominent intraseasonal variability of current in the ITF–SEC region. ENSO has the strongest influence at the outflow ITF, while the IOD's strongest influence is in southwestern Sumatra, with the ENSO (IOD) leading the current by 4 months (1 month). Moreover, the contributions (largest to smallest) of each EEMD mode at the nearshore of Java and offshore Sumatra are intraseasonal, semiannual, annual, interannual, and long-term fluctuations. The contribution of long-term variation (19.2 %) in the far offshore eastern Indian Ocean is larger than the interannual (16.3 %) and annual (14.7 %) variations. Future studies should be conducted to investigate this long-term variation.

OCEANIC DISPERSAL MODEL OF GREEN TURTLE HATCHLINGS IN THE SOUTH CHINA SEA

High-resolution ocean circulation models have increased our understanding of the movement and distribution of worldwide ocean currents, which were previously unknown and difficult to study. The metabolic expenditure data obtained through open-flow respirometric analysis was put into an energy budget context by comparing it to their available reserved energy in the body upon entering the swimming life phase. We modeled the dispersal range of green turtle hatchling from Chagar Hutang in various monsoon season using the particle-tracking program Ichthyop v3.2 and ocean surface current output from HYCOM (Hybrid Coordinate Ocean Model). The prediction distribution suggests that ocean current variability determines their movements into different dispersal areas. The simulated hatchlings are distributed north into the Gulf of Thailand during the Southwest monsoon, while during the Northeast monsoon, the simulated hatchlings travel south into the Java Sea. By quantifying hatchlings potential energy, they can swim a distance of 116 km and can last up to 7 days. Green turtle hatchlings from Chagar Hutang reached offshore water of Kelantan State and Terengganu waters near Tenggol Island on Day 7. These findings highlight areas of high priority for conservation, as habitat crucial for an endangered sea turtle species during a critical period of early development.

Dispersal modeling of octopoda paralarvae in the Gulf of Mexico

AbstractThe dynamics and population structure of octopus species in the Gulf of Mexico (GoM) can be studied by analyzing dispersal paralarvae mechanisms. Accordingly, this study focused on understanding octopus paralarval dispersal using numerical modeling. A Lagrangian approach was implemented using the transport model ICHTHYOP and surface currents from a GoM simulation of the HYbrid Coordinate Ocean Model (HYCOM). We modeled the dispersal of four octopus species from the GoM (Octopus “vulgaris”, Octopus insularis, Macrotritopus defilippi, and Amphioctopus burryi), considering two regions as the source of larvae in the southern GoM, namely the Yucatan shelf and the Veracruz coastal waters. Additionally, an environmental suitability analysis was incorporated using the maximum entropy (MaxEnt) model to establish potential settlement areas under the influence of the water masses’ thermal conditions. The simulation results supported the hypothesis that the abundances recorded in the GoM were influenced by the fertility (egg‐laying) of each species, surface water circulation (the Loop Current, eddies, and wind), and sea surface temperature. Greater dispersal was obtained throughout the GoM for Yucatan species O. “vulgaris”, registering the highest settlement rates. In contrast, in Veracruz, O. insularis dispersed and settled only in the western portion of the GoM. The relevance of the ecological descriptors proposed to influence the dispersal and abundance of octopods throughout the GoM's coastal waters are discussed.

Trace metal distributions and fluxes in the Taiwan Strait

The Taiwan Strait plays an important role as a corridor for the transport of water and chemicals between the South China Sea and the East China Sea, two of the largest marginal seas in the world, while receiving terrestrial material from land masses on both sides. In this study, we report on trace metal results in multiple cross-Strait transects during surveys of trace metal distributions and fluxes that reached from the northern South China Sea to the southern East China Sea. Plumes of elevated trace metal concentrations off the mainland China coast and off the northwest coast of Taiwan were documented to reach into the Taiwan Strait. Combining trace metal data with current velocity, obtained from HYbrid Coordinate Ocean Model (HYCOM), trace metal fluxes through multiple cross-sections in the Taiwan Strait were calculated. Seasonal variability in terrestrial source strength and current patterns in the Taiwan Strait dictated trace metal fluxes in different parts of the Strait. The northward fluxes were smaller during northeastern monsoon in the fall/winter because of the greater southward Chinese Coastal Current, which carried terrestrial trace metal sources in its water into the Taiwan Strait. Some trace metals had strong linear relationships with salinity within plume extensions, within a few tens of kilometers off a major river mouth. Results show that varying monsoon-induced water transports led to distinctively different trace metal distributions and fluxes at different times and through different transects across the Taiwan Strait.

The features of the coastal fronts in the Eastern Guangdong coastal waters during the downwelling-favorable wind period

A coastal front was detected in the eastern Guangdong (EGD) coastal waters during a downwelling-favorable wind period by using the diffuse attenuation coefficient at 490 nm (Kd(490)). Long-term satellite data, meteorological data and hydrographic data collected from 2003 to 2017 were jointly utilized to analyze the environmental factors affecting coastal fronts. The intensities of the coastal fronts were found to be associated with the downwelling intensity. The monthly mean Kd(490) anomalies in shallow coastal waters less than 25 m deep along the EGD coast and the monthly mean Ekman pumping velocities retrieved by the ERA5 dataset were negatively correlated, with a Pearson correlation of − 0.71. The fronts started in October, became weaker and gradually disappeared after January, extending southwestward from the southeastern coast of Guangdong Province to the Wanshan Archipelago in the South China Sea (SCS). The cross-frontal differences in the mean Kd(490) values could reach 3.7 m−1. Noticeable peaks were found in the meridional distribution of the mean Kd(490) values at 22.5°N and 22.2°N and in the zonal distribution of the mean Kd(490) values at 114.7°E and 114.4°E. The peaks tended to narrow as the latitude increased. The average coastal surface currents obtained from the global Hybrid Coordinate Ocean Model (HYCOM) showed that waters with high nutrient and sediment contents in the Fujian and Zhejiang coastal areas in the southern part of the East China Sea could flow into the SCS. The directions and lengths of the fronts were found to be associated with the flow advection.

Oil spill trajectory prediction assessment using multi model ocean currents - case study of MT Dawn Oil spill 2017

Abstract 684276 An assessment was carried out to judge the performance of the modeled ocean currents in oil spill trajectory prediction. Ocean circulation is the key factor in determining the drift pattern of the spilled marine oil pollutant. General National Oceanic and Atmospheric Administration Operational Modeling Environment (GNOME), an oil spill trajectory model, in diagnostic mode was set for simulating drift pattern of Heavy Fuel Oil (HFO). On 28 January 2017, 0345 hrs, Indian Standard Time (IST), approximately 196.4 MT of HFO was spilled due to vessel collision. The oil spill model was set and run during 28-Jan-2017 to 05-Feb-2017 with 196 tons of HFO. Wind velocity fields were obtained from European Centre for Medium-Range Weather Forecasts (ECMWF). The modeled ocean currents were obtained from High resolution Operational Ocean Forecasting and reanalysis System (HOOFS) with two model set ups such as Indian ocean (IO) and Bay Of Bengal (BOB). Ocean current pattern were also obtained from Hybrid Co-ordinate Ocean Model (HYCOM) and Global Ocean Data Assimilation System (GODAS) based Modular Ocean Model (GM4P1). The oil drift patterns were simulated individually for the spillage due to MT Dawn vessel, by forcing GNOME with the above said wind and ocean currents. Radar data obtained for 29-Jan-2017, from Sentinel -1A was processed for detecting oil slicks. The respective drift patterns obtained were compared individually with the oil slick signatures of Sentinel -1A on 29-Jan-2017. It was found that the drift pattern obtained while using the ocean currents of HOOFS_BOB was in better agreement with that of the observed slicks. Unlike other oil drift patterns, offshore spread of the slicks are well captured while using the ocean currents of HOOFS_BOB. This paper illustrates the method of oil spill trajectory prediction using various ocean currents and validating the simulated drift with the ground truth. It also emphasize the need of using various modeled ocean currents in assessing the performance of oil spill trajectory model.

Sensitivity Analysis of OTEC-CC-MX-1 kWe Plant Prototype

The Mexican Caribbean Sea has potential zones for Ocean Thermal Energy Conversion (OTEC) implementation. Universidad del Caribe and Instituto de Ciencias del Mar y Limnologia, with the support of the Mexican Centre of Innovation in Ocean Energy, designed and constructed a prototype OTEC plant (OTEC-CC-MX-1 kWe), which is the first initiative in Mexico for exploitation of this type of renewable energy. This paper presents a sensitivity analysis whose objective was to know, before carrying out the experimental tests, the behavior of OTEC-CC-MX-1 kWe regarding temperature differences, as well as the non-possible operating conditions, which allows us to assess possible modifications in the prototype installation. An algorithm was developed to obtain the inlet and outlet temperatures of the water and working fluid in the heat exchangers using the monthly surface and deep-water temperature data from the Hybrid Coordinate Ocean Model and Geographically Weighted Regression Temperature Model for the Mexican Caribbean Sea. With these temperatures, the following were analyzed: fluctuation of thermal efficiency, mass flows of R-152a and water and power production. By analyzing the results, we verified maximum and minimum mass flows of water and R-152a to produce 1 kWe during a typical year in the Mexican Caribbean Sea and the conditions when the production of electricity is not possible for OTEC-CC-MX-1 kWe.

Near-Inertial Waves Induced by Typhoon Megi (2010) in the South China Sea

Near-inertial waves (NIWs) are a kind of internal wave, which are usually generated by synoptic wind forcing and play an important role in the oceanic energy budget. However, the lack of in situ observations limits our understanding of NIWs to some extent. Through a comparison with in situ observations, in this study, we first showed that the hybrid coordinate ocean model reanalysis results could reasonably reproduce the typhoon-induced NIWs, and we then adopted these data to investigate the NIWs induced by typhoon Megi in 2010 in the South China Sea (SCS). The results indicate that Megi-induced near-inertial kinetic energy was mainly concentrated in the SCS Basin. In the vertical direction, Megi-induced NIWs could propagate to 1000 m depth. The damping and modal content of Megi-induced NIWs were site-dependent: In the region near Megi’s track, NIWs were dominated by the first three baroclinic modes and damped quickly; whereas in two zones to the west of the Luzon Island and Luzon Strait, the e-folding time of Megi-induced NIWs could be longer than 20 days and higher modes (mode-4 to mode-7) were enhanced several days after the passage of Megi. Possible mechanisms of these phenomena were also explored in this study.

Bio-Physical Changes in the Gulf of Mexico During the 2018 Hurricane Michael

We investigate the impacts of one of the strongest recorded hurricanes to have hit the Florida Panhandle, Hurricane Michael (2018), on the upper ocean using a suite of satellite data, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> profiles, and outputs from the HYbrid Coordinate Ocean Model (HYCOM). Strong, low-level cyclonic winds associated with the hurricane generated strong Ekman suction that propagated ahead of the hurricane and caused changes in the surface and subsurface ocean. Following the passage of Hurricane Michael, a 3 °C drop in sea surface temperature (SST) was accompanied with a 4–5 mg <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}^{-3}$ </tex-math></inline-formula> increase in chlorophyll-a concentration. In the subsurface, a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 15$ </tex-math></inline-formula> m mixed layer deepening preceded upward displacements of the isotherms and cooling of the mixed layer. The impact of hurricane conditions on sea surface salinity (SSS) was localized and influenced by competing processes, with upwelling of salty subsurface water increasing SSS and enhanced precipitation decreasing SSS. During the peak of the hurricane, the impact of upwelling was greater than that of enhanced precipitation and, thus, SSS increased. Further away from the upwelling centers, hurricane-influenced precipitation, and river runoff freshened SSS.

Impact of mesoscale eddies on the source funnel of sediment trap measurements in the South China Sea

The mooring tethered time-series sediment traps (TS-traps) collect sinking particles in the ocean, enabling the estimation of biological pump (BP) efficiency based on the assumption of vertical settling. However, the advection of sea water can disperse particles over long distance during the sinking process, introducing uncertainties into the estimates of BP efficiency. In the South China Sea, mesoscale eddies generate significant lateral transport above the mesopelagic zone, which has a large impact on the collecting area and source funnel of TS-traps. We studied the role of eddies in the lateral transport of sinking particles using a Lagrangian Particle Tracking Model (LPTM) which was forced by three-dimensional currents of eddy composites derived from the global Hybrid Coordinate Ocean Model (HYCOM). The eddy reanalysis using the HYCOM outputs was validated using occurrence, genesis and dissipation statistics of eddies. Backward particle tracking was performed at three stations located in the northern, central and southwestern SCS, respectively. The results indicate that the vertical sinking assumption is invalid when the particle sinking velocity is relatively low. Furthermore, the fraction of surface sources from the edge of the eddies depends on both the sinking velocity and seasonal variability of the background current. The eddy current controls the movement of particles within the eddy, and many of the particles with a sinking velocity <80 m d−1 can be transported from the edge to the eddy center. The source funnel within the mesoscale eddy is tilted vertically, leading to an asymmetrical distribution of the particle source around the trap location. Finally, for slow-sinking particles, trap-collected particles could originate from the subsurface located tens to hundreds of kilometers away from the trap location. Overall, our results highlight the role of mesoscale eddies in interpreting trap measurements.

MJO-Induced Intraseasonal Mixed Layer Depth Variability in the Equatorial Indian Ocean and Impacts on Subsurface Water Obduction

AbstractChange of oceanic surface mixed layer depth (MLD) is critical for vertical exchanges between the surface and subsurface oceans and modulates surface temperature variabilities on various time scales. In situ observations have documented prominent intraseasonal variability (ISV) of MLD with 30–105-day periods in the equatorial Indian Ocean (EIO) where the Madden–Julian oscillation (MJO) initiates. Simulation of Hybrid Coordinate Ocean Model (HYCOM) reveals a regional maximum of intraseasonal MLD variability in the EIO (70°–95°E, 3°S–3°N) with a standard deviation of ~14 m. Sensitivity experiments of HYCOM demonstrate that, among all of the MJO-related forcing effects, the wind-driven downwelling and mixing are primary causes for intraseasonal MLD deepening and explain 83.7% of the total ISV. The ISV of MLD gives rise to high-frequency entrainments of subsurface water, leading to an enhancement of the annual entrainment rate by 34%. However, only a small fraction of these entrainment events (&lt;20%) can effectively contribute to the annual obduction rate of 1.36 Sv, a quantification for the amount of resurfacing thermocline water throughout a year that mainly (84.6%) occurs in the summer monsoon season (May–October). The ISV of MLD achieves the maximal intensity in April–May and greatly affects the subsequent obduction. Estimation based on our HYCOM simulations suggests that MJOs overall reduce the obduction rate in the summer monsoon season by as much as 53%. A conceptual schematic is proposed to demonstrate how springtime intraseasonal MLD deepening events caused by MJO winds narrow down the time window for effective entrainment and thereby suppress the obduction of thermocline water.

The Navy's Earth System Prediction Capability: A New Global Coupled Atmosphere‐Ocean‐Sea Ice Prediction System Designed for Daily to Subseasonal Forecasting

AbstractThis paper describes the new global Navy Earth System Prediction Capability (Navy‐ESPC) coupled atmosphere‐ocean‐sea ice prediction system developed at the Naval Research Laboratory (NRL) for operational forecasting for timescales of days to the subseasonal. Two configurations of the system are validated: (1) a low‐resolution 16‐member ensemble system and (2) a high‐resolution deterministic system. The Navy‐ESPC ensemble system became operational in August 2020, and this is the first time the NRL operational partner, Fleet Numerical Meteorology and Oceanography Center, will provide global coupled atmosphere‐ocean‐sea ice forecasts, with atmospheric forecasts extending past 16 days, and ocean and sea ice ensemble forecasts. A unique aspect of the Navy‐ESPC is that the global ocean model is eddy resolving at 1/12° in the ensemble and at 1/25° in the deterministic configurations. The component models are current Navy operational systems: NAVy Global Environmental Model (NAVGEM) for the atmosphere, HYbrid Coordinate Ocean Model (HYCOM) for the ocean, and Community Ice CodE (CICE) for the sea ice. Physics updates to improve the simulation of equatorial phenomena, particularly the Madden‐Julian Oscillation (MJO), were introduced into NAVGEM. The low‐resolution ensemble configuration and high‐resolution deterministic configuration are evaluated based on analyses and forecasts from January 2017 to January 2018. Navy‐ESPC ensemble forecast skill for large‐scale atmospheric phenomena, such as the MJO, North Atlantic Oscillation (NAO), Antarctic Oscillation (AAO), and other indices, is comparable to that of other numerical weather prediction (NWP) centers. Ensemble forecasts of ocean sea surface temperatures perform better than climatology in the tropics and midlatitudes out to 60 days. In addition, the Navy‐ESPC Pan‐Arctic and Pan‐Antarctic sea ice extent predictions perform better than climatology out to about 45 days, although the skill is dependent on season.

An assessment Indonesia’s Ocean Thermal Energy Conversion (OTEC) as an electrical energy resource

The primary source of Indonesian electricity still has a dependence on the availability of fossil energy, which is limited in its presence and has non-renewable properties. It is necessary for alternative energy research as a renewable source of electrical power to replace energy sources that cannot be renewed. The one of energy is ocean thermal energy conversion, in which the technology is based on the thermal energy difference between surface temperatures and deepsea water to produce electricity. The research aimed to assess the power potential generated by utilizing the vertical sea temperature in some Indonesian waters. The survey method was used to collect secondary data from the HYbrid Coordinate Ocean Model. The process was completed with the conversion of OTEC to produce the electric base on the model applied by Rauchenstein. This model calculated the net power production of an OTEC plant as a function of water temperature and chilled water pipe length with the potential OTEC power generated for a closed cycle power plant of 100 MW / 150 MW gross power. The study found an average temperature difference of 20 °C at a depth of ≥500 m. Based on the seasonally mean, the highest potential of power was in the Papua of 174 MW during transitional season 2. The lowest value was assessed in Southeast Sulawesi of 82.09 MW in the southeast season. The highest electricity potential for annual average has been obtained in Papua with 168.33 MW and the lowest around 97.69 MW in North Sulawesi.

Rain-induced characteristics in C- and X-band synthetic aperture radar observations of tropical cyclones

ABSTRACT This work focused on the rain-induced characteristics of synthetic aperture radar (SAR) at the C- and X-bands. Six SAR images were collected in tropical cyclones: four C-band dual-polarized Sentinel-1 (S-1) images during the 2016 hurricane season and two vertical–vertical) polarized TerraSAR-X (TS-X) images of Hurricane Sandy (2012). Wind speeds were retrieved from the S-1 images at the vertical–horizontal polarization channel, and winds from the TS-X images were obtained from the Hurricane Research Division of the National Oceanic and Atmospheric Administration . Simultaneously, Tropical Rainfall Measuring Mission (TRMM) rain rates, current data from the HYbrid Coordinate Ocean Model and wave spectra simulated by the WAVEWATCH-III (WW3) model were collocated. The three-scale backscattering model was employed to simulate the normalized radar cross-section (NRCS)without considering the rain effect, yielding a 2.21-dB root mean square errorand 2.23-dB for S-1 and TS-X, respectively. The difference between model-simulated and observed NRCS was analysed using the TRMM rain rate. The results indicate a linear relationship of the difference at the X-band with the TRMM rain rate, while the difference at the C-band exhibited a ‘V’ relationship with the TRMM rain rate. It was also discovered that the difference at the X-band decreased with increasing wind speed, while the difference at the C-band increased with increasing wind speed.

Validation of Oil Trajectory and Fate Modeling of the Deepwater Horizon Oil Spill

Trajectory and fate modeling of the oil released during the Deepwater Horizon blowout was performed for April to September of 2010 using a variety of input data sets, including combinations of seven hydrodynamic and four wind models, to determine the inputs leading to the best agreement with observations and to evaluate their reliability for quantifying exposure of marine resources to floating and subsurface oil. Remote sensing (satellite imagery) data were used to estimate the amount and distribution of floating oil over time for comparison with the model’s predictions. The model-predicted locations and amounts of shoreline oiling were compared to documentation of stranded oil by shoreline assessment teams. Surface floating oil trajectory and distribution was largely wind driven. However, trajectories varied with the hydrodynamic model used as input, and was closest to observations when using specific implementations of the HYbrid Coordinate Ocean Model modeled currents that accounted for both offshore and nearshore currents. Shoreline oiling distributions reflected the paths of the surface oil trajectories and were more accurate when westward flows near the Mississippi Delta were simulated. The modeled movements and amounts of oil floating over time were in good agreement with estimates from interpretation of remote sensing data, indicating initial oil droplet distributions and oil transport and fate processes produced oil distribution results reliable for evaluating environmental exposures in the water column and from floating oil at water surface. The model-estimated daily average water surface area affected by floating oil &amp;gt;1.0 g/m2 was 6,720 km2, within the range of uncertainty for the 11,200 km2 estimate based on remote sensing. Modeled shoreline oiling extended over 2,600 km from the Apalachicola Bay area of Florida to Terrebonne Bay area of Louisiana, comparing well to the estimated 2,100 km oiled based on incomplete shoreline surveys.

Structure and Dynamics of the Ras al Hadd Oceanic Dipole in the Arabian Sea

The Ras al Hadd oceanic dipole is a recurrent association of a cyclone (to the northeast) and of an anticyclone (to the southwest), which forms in summer and breaks up at the end of autumn. It lies near the Ras al Hadd cape, southeast of the Arabian peninsula. Its size is on the order of 100 km. Along the axis of this dipole flows an intense jet, the Ras al Had jet. Using altimetric data and an eddy detection and tracking algorithm (AMEDA: Angular Momentum Eddy Detection and tracking Algorithm), we describe the life cycle of this oceanic dipole over a year (2014–2015). We also use the results of a numerical model (HYCOM, the HYbrid Coordinate Ocean Model) simulation, and hydrological data from ARGO profilers, to characterize the vertical structure of the two eddies composing the dipole, and their variability over a 15 year period. We show that (1) before the dipole is formed, the two eddies that will compose it, come from different locations to join near Ras al Hadd, (2) the dipole remains near Ras al Hadd during summer and fall while the wind stress (due to the summer monsoon wind) intensifies the cyclone, (3) both the anticyclone and the cyclone reach the depth of the Persian Gulf Water outflow, and (4) their horizontal radial velocity profile is often close to Gaussian but it can vary as the dipole interacts with neighboring eddies. As a conclusion, further work with a process model is recommended to quantify the interaction of this dipole with surrounding eddies and with the atmosphere.