A combination of multiple data sources has been used to study the characteristics of internal solitary waves (ISWs) in the Gulf of Oman (GoO). Water column stratification in the Gulf has been ...examined using field observations and World Ocean Atlas 2018 datasets. The spatiotemporal distribution of ISWs has been obtained from satellite images obtained by means of Synthetic Aperture Radar (SAR) and optical sensors taken from 2018 to 2020. The mechanisms of ISW generation in the GoO have been studied using the data revealed from different available sources. The results show that there are annually two major typical stratifications in the GoO throughout the year, strong stratification in May through September and weak stratification during other months. Dispersion relations corresponding to these types of stratification have been obtained with acceptable accuracy for both deep and shallow regions. The spatiotemporal distribution of ISWs demonstrates that the western and southern regions of the GoO are the hotspots for generation of ISWs in this basin. Several mechanisms of ISW generation in the GoO are discussed including tide, eddies, lee waves, and atmospheric perturbation; the latter one is, apparently, responsible for the appearance of large-amplitude ISWs.
Dye, B.; Jose, F., and Allahdadi, M.N., 2020. Circulation dynamics and seasonal variability for the Charlotte Harbor Estuary, Southwest Florida coast. Journal of Coastal Research, 36(2), 276–288. ...Coconut Creek (Florida), ISSN 0749-0208. A hydrodynamic model was developed and validated for the Charlotte Harbor estuarine system, located in SW Florida, to elucidate freshwater fluxes within the system's various inlets during diverse hydrologic conditions. Fresh water entering the system not only varies seasonally but also, because of regulatory fresh water, releases controlling water levels within an upstream lake. The unnatural freshwater releases have been found to negatively affect the system's ecology, in particular within the Caloosahatchee River portion of the system. Neither the flood nor ebb phase exhibits uniform dominance in flushing the system's four major passes. Boca Grande Pass and Big Carlos Pass were mostly ebb dominant, whereas San Carlos Bay was largely flood dominant; neither phase dominated at Captiva Pass. The similarities and/or contradictions of these results in comparison to former field and modeling results are mainly attributed to the differences between the freshwater sources and environmental forces corresponding to each study that forces a different mass-balance condition over the estuary-bay system and, thereby, at each individual inlet. A Lagrangian particle tracking study revealed particles released within the Peace River during different hydrological conditions were comparably transported regardless of freshwater inputs and predominate wind direction. In contrast, particles released within the Caloosahatchee River were flushed into the Gulf of Mexico within 10 days during a usually wet El Niño, dry (November–April) season period whereas during the summer wet (May–October) season released particles remained in the estuary for a longer period (13 days), ultimately resulting in their further transport into Pine Island Sound and Matlacha Pass. The results also demonstrate the effect of freshwater river inputs and wind on the travel time of the neutrally buoyant particles within the estuarine system. The hydrodynamic and coupled particle tracking model serve as the first step in a forthcoming larval transport modeling study.
Simulating WAves Nearshore (SWAN) on a structured grid over the Louisiana shelf in the northern Gulf of Mexico is used to evaluate the performance of three different classes of formulations for ...quantifying wind input and whitecapping dissipation. The formulations include Komen based on the mean spectral parameters, Westhuysen based on the saturation concept of the wave groups, and the most recent observation-based physics package ST6. The evaluation was implemented for two summer months (July and August 2015) to assess these formulations for a low wave energy period. The modeling area consists of the Louisiana inner shelf with the offshore open boundary located beyond the continental shelf. The model was forced using the spatially variable Climate Forecast System Reanalysis (CFSR) wind field and wave parameters obtained from the NOAA’s WAVEWATCH-III (WWIII) model along the open boundaries. Simulated wave parameters and spectra regarding each formulation were evaluated and compared with measured wave data at NDBC stations; comparisons showed that the most appropriate formulation for the simulation of low energy waves for the study area to be ST6. The e performance of each whitecapping formulation was described by examining 1D/2D spectra and the source term balance at different met-ocean conditions during the simulation period. It was also shown that the inaccuracies in the input wind field and boundary conditions can substantially contribute to the model inaccuracy.
The Bay of Bengal and Arabian Sea are annually exposed to severe tropical cyclones, which impose massive infrastructure damages and cause the loss of life in coastal regions. Cyclone Shaheen ...originally generated in the Bay of Bengal in 2021 and translated a rare east-to-west path toward the Arabian Sea. Although the cyclone’s wind field can be obtained from reanalysis datasets such as ERA5 (fifth generation European Centre for Medium-Range Weather Forecasts), the wind speed cannot be reproduced with realistic details in the regions close to the center of cyclone due to spatial resolution. In this study, to address this problem, the high-resolution advanced Weather Research and Forecasting (WRF) model is used for simulation of Shaheen’s wind field. As a critical part of the study, the sensitivity of the results to the planetary boundary layer (PBL) parameterization in terms of the track, intensity, strength and structure of the cyclone Shaheen is investigated. Five experiments are considered with five PBL schemes: Yonsei University (YSU); Mellor–Yamada–Janjić (MYJ); Mellor–Yamada–Nakanishi–Niino level 2.5 (MYNN); Asymmetric Convective Model version 2 (ACM2); Quasi-Normal Scale Elimination (QNSE). The track, intensity, and strength of the experiments are compared with the wind fields obtained from the Joint Typhoon Warning Centre (JTWC) dataset. The results imply the high dependency of the track, intensity, and strength of the cyclone to the PBL parameterization. Simulated tracks with non-local PBL schemes (YSU and ACM2) outperformed those of the local PBL schemes (MYJ, MYNN, and QNSE), especially during the rapid intensification phase of Shaheen before landfall. The YSU produced highly intensified storm, while the ACM2 results are in better agreement with the JTWC data. The most accurate track was obtained from the ERA5 data; however, this dataset overestimated the spatial size and underestimated the wind speed. The WRF model using either YSU or ACM2 overestimated the wind speed compared to that of the altimeter data. The YSU and ACM2 schemes were able to reproduce the observed increase in wind speed and pressure drop at in situ stations. The wind data from EAR5 and cyclone parametric model were applied to the SWAN model to simulate the wave regime in the Arabian Sea during the time that Shaheen was translating across the region. Janssen formulation for wind input and whitecapping dissipation source terms in combination with both ERA5 and hybrid wind were used and the minimum combined error in the prediction of significant wave height (Hs) and zero up-crossing wave period (Tz) was examined. The maximum significant wave height for hybrid wind is higher than that of ERA5, while the cyclone development was successfully inferred from the wave field of the hybrid data.
Cold fronts are meteorological phenomena that impact the northern Gulf of Mexico, mostly between the fall and spring seasons. On average, they pass the region every 3–7 days, with a duration ranging ...between 24 and 74 h. In the present study, a high-resolution FVCOM model with an unstructured mesh was used to simulate the effect of the fall cold front winds on water column mixing over the Louisiana shelf, which is often stratified in the summer, leading to hypoxia. Numerical experiments were conducted for October 2009, a period with five consecutive cold front events. Winds from an offshore station forced the model, while climatological temperature/salinity profiles prepared by NOAA for September were used for model initialization. The model performance was evaluated by comparing it with the surface current measurements at two offshore stations, and the results showed a good agreement between the model results and observations. Shelf mixing and stratification were investigated through examining the simulated sea surface temperature as well as the longitudinal and cross-shelf vertical sections. Simulation results showed a significant effect on shelf mixing, with the mixed layer depth increasing from the initial values of 5 m to 25 m at the end of simulation at different parts of the shelf, with maximum mixed layer depths corresponding to the peak of cold fronts. The buoyancy frequency, Richardson number, and the average potential energy demand (APED) for mixing the water column were used to quantify the stratification at two selected locations over the shelf. Results showed that all these parameters almost continuously decreased due to mixing induced by cold front wind events during this time. At the station off the Terrebonne Bay with a water depth of 20 m, the water column became fully mixed after three of the cold front events, with Richardson numbers smaller than 0.25 and approaching zero. This continued mixing trend was also proven by obtaining a decreasing trend of APED from 100 to 5 kg/m.s2 with several close to zero energy demand values.
Studying mixing and re-stratification during and after hurricanes have important implications for the simulation of circulation and bio-geochemical processes in oceanic and shelf waters. Numerical ...experiments using FVCOM on an unstructured computational mesh were implemented to study the direct effect of hurricane winds on the mixing and temperature redistribution of the stratified Louisiana shelf during Hurricane Katrina (2005), as well as the post-storm re-stratification timescale. The model was forced by Katrina’s wind stress obtained from a combination of H-Wind database and NCEP model. The climatological profiles of temperature and salinity for August (the month in which Katrina occurred) from the world ocean atlas (WOA, 2013) were used as the pre-storm conditions over the shelf. Model results for sea surface temperature (SST) and mixed layer depth (MLD) were validated versus SST data from an optimally interpolated satellite product, and the MLD was calculated from the heat budget equation of the mixed layer. Model results were used to examine the temporal and spatial responses of SST and MLD over the shelf to Katrina. Results showed that intense mixing occurred within 1–1.1 RMW (RMW is the radius of maximum wind for Katrina), with turbulent mixing as the dominant mixing force for regions far from the eye, although upwelling was an important contributor to modulating SST and MLD. During the peak of Katrina and for the shelf regions severely affected by the hurricane wind, three distinct temperature zones were formed across the water column: an upper mixed layer, a transition zone, and a lower upwelling zone. Shelf re-stratification started from 3 h to more than two weeks after the landfall, depending on the distance from the track. The mixing during Hurricane Katrina affected the seasonal summertime hypoxic zone over the Louisiana shelf and likely contributed to the water column re-oxygenation.
The category 5-equivalent tropical Cyclone Gonu (2007) was the strongest cyclone to enter the northern Arabian Sea and Gulf of Oman. The impact of this cyclone on the sea surface temperature (SST) ...cooling and deepening of the mixed layer was investigated herein using an optimally interpolated (OI) cloud-free sea surface temperature (SST) dataset, climatological profiles of water temperature, and data from Argo profilers. SST data showed a maximum cooling of 1.7–6.5 °C during 1–7 June 2007 over the study area, which is similar to that of slow- to medium-moving cyclones in previous studies. The oceanic heat budget equation with the assumptions of the dominant turbulent mixing effect was used to establish relationships between SST and mixed layer depth (MLD) for regions that were directly affected by cyclone-induced turbulent mixing. The relationships were applied to the SST maps from satellite to obtain maps of MLD for 1–7 June, when Gonu was over the study area. Comparing with the measured MLD from Argo data showed that this approach estimated the MLDs with an average error of 15%, which is an acceptable amount considering the convenience of this approach in estimating MLD and the simplifications applied in the heat budget equation. Some inconsistencies in calculating MLD were attributed to use of climatological temperature profiles that may not have appropriately represented the pre-cyclone conditions due to pre-existing cold/warm core eddies. Estimation of the diapycnal diffusion that quantified the turbulent mixing across the water column showed consistent temporal and spatial variations with the calculated MLDs.
Numerical experiments were conducted using the finite volume community ocean model (FVCOM) to study the impact of the initial density stratification on simulated currents over the Louisiana shelf ...during Hurricane Katrina. Model results for two simulation scenarios, including an initially stratified shelf and an initially non-stratified shelf, were examined. Comparison of two simulations for two-dimensional (2D) currents, the time series of current speed, and variations of cross-shore currents across different sections showed that the smallest differences between simulated currents for these two scenarios occurred over highly mixed regions within 1 radius of maximum wind (RMW) under the hurricane. For areas farther from the mixed zone, differences increased, reaching the maximum values off Terrebonne Bay. These large discrepancies correspond to significant differences between calculated vertical eddy viscosities for the two scenarios. The differences were addressed based on the contradictory behavior of turbulence in a stratified fluid, as compared to a non-stratified fluid. Incorporation of this behavior in the Mellor-Yamada turbulent closure model established a Richardson number-based stability function that was used for estimation of the vertical eddy viscosity from the turbulent energy and macroscale. The results of this study demonstrate the necessity for inclusion of shelf stratification when circulation modeling is conducted using three-dimensional (3D) baroclinic models. To achieve high-accuracy currents, the parameters associated with the turbulence closures should be calibrated with field measurements of currents at different depths.
The southeastern segment of the Caspian Sea (CS) along the Iranian coast, which has a very gentle inner shelf slope, underwent rapid beach evolution in response to water level changes. Based on ...satellite altimetry data, the CS basin has experienced an accelerated water level fall drop in recent years, leading to an increase in the rate of shoreline changes. The shoreline dynamics and morphodynamics of the Amirabad coastal zone, Gorgan Bay, Miankaleh Spit, and Gomishan Lagoon are evaluated here to determine morphological changes of the study area. Landsat-TM/ETM+/OLI moderate spatial resolution products were acquired at unequal intervals between 1994 and 2015 to monitor the coastal changes using Geographic Information System (GIS) tools. The Digital Shoreline Analysis System (DSAS), a GIS software extension, has been used for estimation of the shoreline rate of change through several approaches, including End Point Rate (EPR), Linear Regression Rate (LRR), and Weighted Linear Regression (WLR). The results show that both Gorgan Bay and Gomishan Lagoon have significantly decreased in size during recent years, mainly due to the fall of the CS water level. Results also show that water level drop of the CS, along with net eastward littoral transport, resulted in the growing of the Miankaleh Spit. Further analysis based on the wave climate in the southeast CS and net estimated longshore sediment transport indicates that the littoral drift contributed to ~ 6% of the total annual elongation of the Miankaleh Spit during the study period.
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