Numerical Circulation Research Articles

Fusion of Lagrangian drifter data and numerical model outputs for improved assessment of turbulent dispersion

Abstract. Transport and dispersion processes in the ocean are crucial, as they determine the lifetime and fate of biological and chemical quantities drifting with ocean currents. Due to the complexity of the coastal ocean environment, numerical circulation models have difficulties to accurately simulate highly turbulent flows and dispersion processes, especially in highly energetic tidal basins such as the eastern English Channel. A method of improving the results of coastal circulation modeling and tracer dispersion in the Dover Strait is proposed. Surface current velocities derived from Lagrangian drifter measurements in November 2020 and May 2021 were optimally interpolated in time and space to constrain a high-resolution coastal circulation MARS model, with careful attention given to selecting ensemble members composing the model covariance matrix. The space–time velocity covariances derived from model simulations were utilized by the optimal interpolation algorithm to determine the most likely evolution of the velocity field under constraints provided by Lagrangian observations and their error statistics. The accuracy of the velocity field reconstruction was evaluated at each time step. The results of the fusion of model outputs with surface drifter velocity measurements show a significant improvement (by ∼ 50 %) of the model capability to simulate the drift of passive tracers in the Dover Strait. Optimized velocity fields were used to quantify the absolute dispersion in the study area. The implications of these results are important, as they can be used to improve existing decision-making support tool or design new tools for monitoring the transport and dispersion in a coastal ocean environment.

Моделирование влияния вариаций солнечной активности на глобальную атмосферную циркуляцию

In this study, we continue a series of works devoted to modeling and studying the sensitivity of global atmospheric dynamic processes to variations in solar emissions during the 11-year solar activity (SA) cycle. We focus on studying the response of meridional atmospheric circulation in the middle atmosphere to changes in thermosphere characteristics with changes in SA. For this purpose, numerical simulations of the general atmospheric circulation were carried out using the nonlinear numerical circulation model of the middle and upper atmosphere MUAM. The main mechanism of the influence of thermospheric disturbances on the underlying layers is assumed to be a change in the conditions of propagation and reflection of planetary waves (PWs) due to changes in SA. Changes in temperature, zonal and meridional wind are shown to localize along waveguides, demonstrating the significant role of PWs in transmitting thermospheric disturbances, caused by changes in SA, to the middle atmosphere. The magnitude of changes in meridional circulation can reach 10 % in the northern stratosphere between SA maxima and minima.

Modeling the impact of solar activity variations on global atmospheric circulation

In this study, we continue a series of works devoted to modeling and studying the sensitivity of global atmospheric dynamic processes to variations in solar emissions during the 11-year solar activity (SA) cycle. We focus on studying the response of meridional atmospheric circulation in the middle atmosphere to changes in thermosphere characteristics with changes in SA. For this purpose, numerical simulations of the general atmospheric circulation were carried out using the nonlinear numerical circulation model of the middle and upper atmosphere MUAM. The main mechanism of the influence of thermospheric disturbances on the underlying layers is assumed to be a change in the conditions of propagation and reflection of planetary waves (PWs) due to changes in SA. Changes in temperature, zonal and meridional wind are shown to localize along waveguides, demonstrating the significant role of PWs in transmitting thermospheric disturbances, caused by changes in SA, to the middle atmosphere. The magnitude of changes in meridional circulation can reach 10 % in the northern stratosphere between SA maxima and minima.

Multiple thermal Atlantic Meridional Overturning Circulation thresholds in the intermediate complexity model Bern3D

Abstract. Variations in the Atlantic Meridional Overturning Circulation (AMOC) are associated with Northern Hemispheric and global climate shifts. Thermal thresholds of the AMOC have been found in a hierarchy of numerical circulation models, and there is an increasing body of evidence for the existence of highly sensitive AMOC modes where small perturbations can cause disproportionately large circulation and hence climatic changes. We discovered such thresholds in simulations with the intermediate-complexity Earth system model Bern3D, which is highly computationally efficient, allowing for studying this non-linear behaviour systematically over entire glacial cycles. By simulating the AMOC under different magnitudes of orbitally paced changes in radiative forcing over the last 788 000 years, we show that up to three thermal thresholds are crossed during glacial cycles in Bern3D and that thermal forcing could have destabilised the AMOC repeatedly. We present the circulation and sea ice patterns that characterise the stable circulation modes between which this model oscillates during a glacial cycle and assess how often and when thermal forcing could have preconditioned the Bern3D AMOC for abrupt shifts over the last 788 kyr.

The sandpaper theory of flow–topography interaction for homogeneous shallow-water systems

Recent studies reveal the dramatic impact of seafloor roughness on the dynamics and stability of broad oceanic flows. These findings motivate the development of parameterizations that concisely represent the effects of small-scale bathymetric patterns in theoretical and coarse-resolution numerical circulation models. The previously reported quasi-geostrophic ‘sandpaper’ theory of flow–topography interaction a priori assumes gentle topographic slopes and weak flows with low Rossby numbers. Since such conditions are often violated in the ocean, we now proceed to formulate a more general model based on shallow-water equations. The new version of the sandpaper model is validated by comparing roughness-resolving and parametric simulations of the flow over a corrugated seamount.

Mean circulation and its seasonal cycle on the West Florida Shelf as evidenced by multi-decadal time series of moored currents and winds

Time series from a moored array of current velocity and surface meteorological sensors, some with record lengths as long as 25 years, are used to describe both the long-term mean circulation and its seasonal variations on the West Florida Continental Shelf (WFS). The moorings are part of the University of South Florida's Coastal Ocean Monitoring and Prediction System (USF-COMPS), a network of ocean observing assets along with numerical circulation models, all used to describe and understand physical and ecological processes on the WFS. These USF-COMPS observations reveal a coherent, shelf-wide mean circulation pattern with depth-averaged flow directed alongshore and down-coast. The vertical structure and the seasonal variations further describe an inner-shelf, wind-driven upwelling region separated from a deeper-ocean influenced offshore downwelling region by a coastal jet. By adding to the record lengths from previous analyses, the statistics are shown to be robust, with the inferences drawn from shorter records being borne out by the present longer-term analyses.

The Respondence of Wave on Sea Surface Temperature in the Context of Global Change

Several aspects of global climate change, e.g., the rise of sea level and water temperature anomalies, suggest the advantages of studying wave distributions. In this study, WAVEWATCH-III (WW3) (version 6.07), which is a well-known numerical wave model, was employed for simulating waves over global seas from 1993–2020. The European Centre for Medium-Range Weather Forecasts (ECMWF), Copernicus Marine Environment Monitoring Service (CMEMS), current and sea level were used as the forcing fields in the WW3 model. The validation of modelling simulations against the measurements from the National Data Buoy Center (NDBC) buoys and Haiyang-2B (HY-2B) altimeter yielded a root mean square error (RMSE) of 0.49 m and 0.63 m, with a correlation (COR) of 0.89 and 0.90, respectively. The terms calculated by WW3-simulated waves, i.e., breaking waves, nonbreaking waves, radiation stress, and Stokes drift, were included in the water temperature simulation by a numerical circulation model named the Stony Brook Parallel Ocean Model (sbPOM). The water temperature was simulated in 2005–2015 using the high-quality Simple Ocean Data Assimilation (SODA) data. The validation of sbPOM-simulated results against the measurements obtained from the Array for Real-time Geostrophic Oceanography (Argo) buoys yielded a RMSE of 1.12 °C and a COR of 0.99. By the seasonal variation, the interrelation of the currents, sea level anomaly, and significant wave heights (SWHs) were strong in the Indian Ocean. In the strong current areas, the distribution of the sea level was consistent with the SWHs. The monthly variation of SWHs, currents, sea surface elevation, and sea level anomalies revealed that the upward trends of SWHs and sea level anomalies were consistent from 1993–2015 over the global ocean. In the Indian Ocean, the SWHs were obviously influenced by the SST and sea surface wind stress. The rise of wind stress intensity and sea level enlarges the growth of waves, and the wave-induced terms strengthen the heat exchange at the air–sea layer. It was assumed that the SST oscillation had a negative response to the SWHs in the global ocean from 2005–2015. This feedback indicates that the growth of waves could slow down the amplitude of water warming.

Variations of temperature, salinity and oxygen of the Baltic Sea for the period 1950 to 2020

Variations of temperature, salinity and oxygen of the Baltic Sea on interannual to decadal timescales were studied for the period from 1950 to 2020. Both observational data and the output of a numerical circulation model of the Baltic Sea were analyzed. In addition, we investigated the influence of atmospheric parameters and river runoff on the observed hydrographic variations. Variability of sea surface temperature (SST) closely follows that of air temperature in the Baltic on all timescales examined. Interannual variations of SST are significantly correlated with the North Atlantic Oscillation in most parts of the sea in winter. The entire water column of the Baltic Sea has warmed over the period 1950 to 2020. The trend is strongest in the surface layer, which has warmed by 0.3–0.4°C decade−1, noticeably stronger since the mid-1980s. In the remaining water column, characterized by permanent salinity stratification in the Baltic Sea, warming trends are slightly weaker. A decadal variability is striking in surface salinity, which is highly correlated with river runoff into the Baltic Sea. Long-term trends over the period 1950–2020 show a noticeable freshening of the upper layer in the whole Baltic Sea and a significant salinity increase below the halocline in some regions. A decadal variability was also identified in the deep layer of the Baltic Sea. This can be associated with variations in saltwater import from the North Sea, which in turn are influenced by river runoff: fewer strong saltwater inflows were observed in periods of enhanced river runoff. Furthermore, our results suggest that changes in wind speed have an impact on water exchange with the North Sea. Interannual variations of surface oxygen are strongly anti-correlated with those of SST. Likewise, the positive SST trends are accompanied by a decrease in surface oxygen. In greater depths of the Baltic Sea, oxygen decrease is stronger, which is partly related to the observed increase of the vertical salinity gradient.

Hillsborough bay inflow modification study: An application of the Tampa Bay Coastal Ocean Model

With a large salinity gradient existing between the rivers and the ocean, the saline environment of an estuary is crucial to its ecosystem functionality. For Tampa Bay, the Howard F. Curren Advanced Wastewater Treatment Plant (HFCAWTP) presently yields an outflow of nearly freshwater to the Hillsborough Bay portion of Tampa Bay. In order to estimate the potential impact that the removal of this outflow may have on the salinity and flow fields of Hillsborough Bay, as part of the Tampa Augmentation Project, both numerical circulation model and Knudsen theorem applications are made. The numerical model study compares the instantaneous and nontidal, mean estuarine circulation and salinity distributions for the Hillsborough Bay on the basis of the HFCAWTP outflow being either included with, or excluded from, the freshwater inflows. It is found that the potential reduction of the treated reclaimed water inflow to the bay from the HFCAWTP will not significantly affect the circulation or the salinity distributions of Hillsborough Bay or of the larger Tampa Bay. The estimation through a Knudsen theorem application shows an 0.13 psu increase of salinity after removing the HFCAWTP outflow when averaged within Hillsborough Bay. Thus, both approaches demonstrate that the effects of HFCAWTP outflow removal are very small when compared with variations that occur naturally.

Local And Deep-Ocean Forcing Effects on the West Florida Continental Shelf Circulation and Ecology

We review the evolution of knowledge on the forcing of the west Florida continental shelf by a combination of local winds and deep-ocean influences, and we provide application examples regarding the relationships between the shelf responses to these forcing functions and certain ecological phenomena, including blooms of the harmful alga,Karenia brevis, recruitment of gag juveniles and how Deepwater Horizon hydrocarbons may have affected west Florida reef fish and the shoreline. Our approach employs a coordinated set of observations and numerical circulation model simulations, wherein the observations, by providing reasonable veracity checks on the model simulations, allow for further dynamical analyses that would otherwise be unavailable from the observations alone. For the case of local forcing only, we provide two dynamically consistent definitions of the inner-shelf and outer-shelf regions, and for the case of deep-ocean forcing, we show how the west Florida shelf geometry (with regard to certain geophysical fluid dynamics principles) can result in the entire shelf region being impacted by the Gulf of Mexico Loop Current. Thus, we help to explain why the west Florida shelf experiences large inter-annual variations in shelf ecology, providing impetus for further interdisciplinary study.

The genesis of Rare-alkali metal enrichment in the geothermal anomalies controlled by faults and magma along the northern Yadong-Gulu rift

Geothermal water from the hot springs in the Yadong-Gulu rift (YGR) of southern Tibet is extremely enriched in rare-alkali metal (RAM) elements; however, the mechanism of enrichment has long been debated. Much attention has been given to the deep melting magma of the YGR, but no direct evidence indicates whether and how it is connected to the RAM anomaly of hot springs. Determining the mechanism of RAM enrichment and its variations with the time and space of hot springs will contribute to the exploration of the hydrothermal metallogenic systems. This paper presents numerical hydrothermal numerical circulation models constrained by the geological data and the geophysical structure of the YGR. The results illustrate that the depths of boundary faults control the anomalous temperatures of hot springs. High-temperature springs (such as Yangbajing) could be induced by deep faults extending to the middle crust, whereas magma at a depth greater than 10 km has a limited effect on geothermal anomalies. Secondary faults define the extent of hydrothermal circulation and further determine the distribution of thermal anomalies across the rift. We simulate the enrichment and distribution of RAMs from a deep magma source. The pathways of RAMs from the source are consistent with hydrothermal circulation. RAM concentrations are lower in infiltrating groundwater and higher in ascending hot water. In general, deep faults control the hydrothermal circulation of geothermal groundwater. Deep faults and magma further constrain the distribution of RAM anomalies.

Modeling Iceberg Longevity and Distribution During Heinrich Events

AbstractDuring the last glacial period (120–12 ka), the Laurentide ice sheet discharged large numbers of icebergs into the North Atlantic. These icebergs carried sediments that were dropped as the icebergs melted, leaving a record of past iceberg activity on the floor of the subpolar North Atlantic. Periods of significant iceberg discharge and increased ice‐rafted debris (IRD) deposition, are known as Heinrich Events. These events coincide with global climate change, and the melt from the icebergs involved is frequently hypothesized to have contributed to these changes in climate by adding a significant volume of cold, fresh water to the North Atlantic. Using an iceberg model coupled with the Massachusetts Institute of Technology Global Circulation Model numerical circulation model, we explore the various factors controlling iceberg drift and rates of melt that influence the spatial patterns of IRD deposition during Heinrich Events. In addition to clarifying the influence of sea surface temperature and wind on the path of an armada of icebergs, we demonstrate that the same volume of ice can produce very different patterns of iceberg drift simply by altering the size of icebergs involved. We note also a significant difference in the seasonal locations of icebergs, influenced primarily by the changing winds, and show that the spatial patterns of IRD for Heinrich Event 1 most closely corresponds to where icebergs are located during the summer months. Consistent with proxy evidence, the ocean must be several degrees colder than temperatures estimated for the Last Glacial Maximum in order for icebergs to travel the distance implied by Heinrich Layers.

ТЕСТИРОВАНИЕ И КОРРЕКТИРОВКА БАТИМЕТРИИ НА КООРДИНАТНОЙ СЕТКЕ ОЗЕРА ИССЫК-КУЛЬ

The available bathymetry data of the Issyk-Kul Lake from different sources are analyzed and corrected for mutual consistency and deviation from the GPS coordinates on the shoreline. As a result, a gridded bathymetry of the Lake with 360×360 m bin size suitable for use in numerical circulation models is compiled and made available on the Internet for free download.

Demons in the North Atlantic: Variability of Deep Ocean Ventilation

AbstractTranslation of atmospheric forcing variability into the ocean interior via ocean ventilation is an important aspect of transient climate change. On a seasonal timescale in the subtropics, this translation is mediated by a so‐called “Demon” that prevents access to all except late‐winter mixed‐layer water. Here, we use an eddy‐permitting numerical circulation model to investigate a similar process operating on longer (interannual) timescales in the subpolar North Atlantic. We find that variations in atmospheric forcing are mediated in their translation to the ocean interior, with year‐to‐year changes in the late‐winter mixed layer depth being the critical factor. The signature of persistent strong atmospheric forcing driving deep mixed layers is preferentially ventilated to the interior when the forcing is ceased. Susceptibility to this effect depends on the location and density of subduction—with the rate at which newly ventilated water escapes its region of subduction being the crucial factor.

Studying the Fluxes of the Marine Ecosystem Components from the Northwestern Shelf to the Deep Part of the Black Sea

Purpose. The study represents analysis of the features of the Black Sea ecosystem components transfer from the northwestern shelf to the deep-sea part and its dependence on circulation in the sea upper layer. Methods and Results. The fluxes of water mass, nutrients and bioproduction from the shelf zone to the deep part of the sea were calculated using the current fields and biogeochemical ones resulted from the reanalysis, which, in its turn, was carried out due to the Black Sea ecosystem model including assimilation of remote sensing data both in the numerical circulation model and in the biogeochemical block. Numerical modeling permitted to calculate the fluxes through three sections that bound the shelf zone (by the capes Kaliakra and Chersonesus, and along the 200 m isobath). Behavior of the RIM Current jet and, consequently, direction and magnitude of the flows through the boundaries of the northwestern shelf depend on the wind stress vorticity over the western part of the Black Sea. The type of circulation with the intense RIM Current jet pressed to the shelf edge, is characterized by the pattern of distribution of the inorganic nitrogen and phytoplankton surface concentration as a narrow strip of its high values along the Black Sea western and partially southern coasts. When the RIM Current jet is weak or moves from the shelf edge (that corresponds to the low values of the wind stress vorticity) the increased concentration values are located on the northwestern shelf. Conclusions. Direction, magnitude and character of horizontal distribution of the nutrient and bioproduction fluxes are determined mainly by circulation in the sea upper layer. The magnitude of these flows is significantly affected by difference between the nutrient and bioproduction concentrations in the shelf zone and in the deep part of the Black Sea.

Issledovaniye potokov komponentov morskoy ekosistemy s severo-zapadnogo shel'fa v glubokovodnuyu chast' Chernogo morya

Purpose. The study represents analysis of the features of the Black Sea ecosystem components transfer from the northwestern shelf to the deep-sea part and its dependence on circulation in the sea upper layer. Methods and Results. The fluxes of water mass, nutrients and bioproduction from the shelf zone to the deep part of the sea were calculated using the current fields and biogeochemical ones resulted from the reanalysis, which, in its turn, was carried out due to the Black Sea ecosystem model including assimilation of remote sensing data both in the numerical circulation model and in the biogeochemical block. Numerical modeling permitted to calculate the fluxes through three sections that bound the shelf zone (by the capes Kaliakra and Chersonesos, and along the 200 m isobath). Behavior of the RIM Current jet and, consequently, direction and magnitude of the flows through the boundaries of the northwestern shelf depend on the wind stress vorticity over the western part of the Black Sea. The type of circulation with the intense RIM Current jet pressed to the shelf edge, is characterized by the pattern of distribution of the inorganic nitrogen and phytoplankton surface concentration as a narrow strip of its high values along the Black Sea western and partially southern coasts. When the RIM Current jet is weak or moves from the shelf edge (that corresponds to the low values of the wind stress vorticity) the increased concentration values are located on the northwestern shelf. Conclusions. Direction, magnitude and character of horizontal distribution of the nutrient and bioproduction fluxes are determined mainly by circulation in the sea upper layer. The magnitude of these flows is significantly affected by difference between the nutrient and bioproduction concentrations in the shelf zone and in the deep part of the Black Sea

Impacts of a Major Mississippi River Freshwater Diversion on Suspended Sediment Plume Kinematics in Lake Pontchartrain, a Semi-enclosed Gulf of Mexico Estuary

MODIS satellite imagery and in situ water measurements were used to quantify inorganic sediment concentration (ISC) and, subsequently, sediment plume motion and evolution during the 2016 diversion of the Mississippi River through the Bonnet Carre Spillway (BCS) within Lake Pontchartrain (LP) estuary in Louisiana, USA. Satellite images revealed that sediment plume areal distribution was closely linked to BCS discharge rate. The plume flowed eastward along the southern LP coastline at an average speed of ~ 0.3 m s−1 during the first week of the event and attained its maximum areal extent (~ 1117 km2; 68% of the total LP area) on 23 January. In an attempt to examine the plume kinematics and potential sediment resuspension impacts, wind information was also assessed. Following BCS closure, the prevailing wind direction, but not wind speed, corresponded to significant differences in LP ISC. LP was further subdivided into four separate quadrants to assess relationships between ISC within each quadrant to BCS discharge rate and winds. While the BCS was open, the plume’s eastward motion was associated with a high correlation (r2 = 0.93) between BCS discharge and ISC in the southeast quadrant. However, the weak relationship (r2 = 0.42) between BCS discharge and ISC in the northwest quadrant was attributed to influences from other tributaries. These results will benefit future research regarding impacts of freshwater diversions on coastal and estuarine processes that are sensitive to sediment influx by providing a satellite-based sediment map time series that can be used to help validate numerical circulation and sediment transport models.

Performance Comparisons on Parallel Optimization of Atmospheric and Ocean Numerical Circulation Models Using KISTI Supercomputer Nurion System

The characteristics of the 5th Supercomputer Nurion Knights Landing (KNL) system of the Korea Institute of Science and Technology Information (KISTI) were analyzed by developing ultra-high resolution atmospheric and ocean numerical circulation models. These models include the Weather Research and Forecasting System (WRF), Regional Ocean Modeling System (ROMS), and Unstructured Grid Finite Volume Community Ocean Model (FVCOM). Ideal and real-case experiments were simulated for each model according to the number of parallelized cores used for comparing performances. Identical experiments were performed on a general multicore system (Skylake and a general cluster system) for a performance comparison with the Nurion KNL system. Although the KNL system has more than twice as many cores per node as the Skylake system, the KNL system demonstrated 1/3 of the performance rate of the Skylake system. However, the performance rate of the Nurion KNL system was approximately 43% for all experiments. Reducing the number of cores per node in the KNL system by half (36 cores) is the most efficient method when the total number of cores is less than 256 cores, while it is more economical to use all cores when using more than 256 cores. In all experiments, the performance was continuously improved even for a maximum core experiment (1024 cores), thereby indicating that the KNL system can effectively simulate ultra-high resolution numerical circulation models.

On PSI Interactions in Internal Gravity Wave Fields and the Decay of Baroclinic Tides

AbstractBarotropic tidal oscillations over seafloor topography generate baroclinic tides that may be damped in turn via nonlinear triad interactions with internal gravity waves, fueling the ambient wave field. We derive the kinetic equations for this tidal damping and the energy transfer to the ambient wave field and compute damping times and energy transfer rates for the M2 tide and a Garrett–Munk-like ambient wave field. We show that parametric subharmonic instability (PSI) interactions are important, where the tide interacts resonantly with two background waves, each of half the tidal frequency. PSI is restricted to the latitude belt 28.8°N/S and yields under typical conditions damping times of about 20 days for tides with low vertical wavenumber. Damping times decrease with equivalent mode number j roughly as 1/j2. Outside the critical latitudes PSI is not possible, and damping times are from one to two orders of magnitude larger. The energy transfer to the ambient wave field is concentrated at half the tidal frequency ω at all latitudes within the critical latitude belt. Outside, the transfer is much smaller and peaks at ω + f and N. An estimation of the tidal spectral transfer on the global scale is hampered by insufficient knowledge of the baroclinic energy distribution over the vertical modes. Using results from a numerical circulation model with tidal forcing, we find an energy transfer from the tide to the ambient wave field of typically 0.3 TW, about half of what is currently proposed for the conversion of barotropic to baroclinic energy.

The impact of sea level rise on maritime navigation within a large, channelized estuary

ABSTRACT Vessel handling guidelines in Tampa Bay have been developed and refined over many years to prevent vessel groundings, collisions, and other maritime incidents. These guidelines restrict navigation based upon vessel characteristics such as vessel length, draft, displacement, and destination, often in conjunction with tidal levels and current speeds. A numerical circulation model of the Tampa Bay estuary was used to examine the occurrence frequency of the most common limiting current speeds within the main shipping channel under four sea level rise (SLR) scenarios ranging from 0.25 to 2 m. Near the bay mouth, the occurrence of limiting speeds generally decreased with SLR, but farther up the channel it increased, mostly due to changes in the M2 tide, with contributions from other primary tides. The relative occurrence of slack water, the lowest of the limiting speeds, was most sensitive to SLR, with absolute changes in occurrence ~50%. Higher speed limits had smaller relative changes. A methodology is developed using data from the Automatic Identification System that identifies vessel traffic potentially impacted by SLR and changing tidal currents. Some implications of reduced tidal currents for port and vessel traffic management are discussed.