Eddy Structures Research Articles

Modeling of Barotropic Tide off the Southeastern Coast of the Kamchatka Peninsula in View of the Accuracy of Global Tidal Models in the Northwest Pacific Ocean

This study introduces the development and implementation of a regional numerical finite-volume model FESOM–C, specifically designed to accurately compute barotropic tidal dynamics in the Pacific waters adjacent to the southeastern region of the Kamchatka Peninsula. The dynamics of principal harmonics of the semidiurnal M2 and diurnal K1 tidal constituents are replicated, as well as the total tide, which encompasses 12 constituents. The computed results, obtained using a detailed unstructured grid, are interpreted through the Long-wave approach. The FESOM–C regional model revealed the variability of harmonic constants of tide and current characteristics within the shelf and canyon-cut continental slope, due to topographic scattering of tidal waves. The assessment includes the estimation of maximum currents and eddy structures associated with residual tidal circulation on the shelf and continental slope. To investigate the influence of varying open boundary conditions, sensitivity experiments have been conducted using data from two state-of-the-art global tidal models FES2014 and TPXO9. The findings reveal that the regional model’s solution exhibits only minimal dependency on this choice, and it aligns well with the limited available tidal data. Interestingly, the global models themselves demonstrate significant disparities in the tidal currents. Furthermore, we assess the accuracy of global tidal model solutions in a broader region encompassing the Sea of Okhotsk, as well as the Pacific waters along the Kuril Islands and the Kamchatka Peninsula. This assessment utilizes a verified database of tidal harmonic constants derived from the Soviet and British tide tables. While the average errors in tidal heights calculations remain minor and closely approximate officially declared values, certain areas within the region exhibit notable discrepancies in the outputs of the global models. These discrepancies are site-specific and vary depending on the particular model and tidal harmonic under consideration. This underscores the need for caution when applying results from global tidal models at the regional scale. Meanwhile, the importance of advancing regional tidal dynamics modeling remains evident.

Three-Dimensional Structure of Oceanic Mesoscale Eddies

Mesoscale eddies contribute to the global oceanic energy budget and cascade; they induce substantial mass and heat transport, thus playing a key role in the global climate system. The three-dimensional (3D) structures of mesoscale eddies should be studied in order to quantify their impact. In this paper, mesoscale eddies are reviewed from the perspective of their horizontal and vertical structures, temporal evolution, and fine structures. The universal 3D structure of mesoscale eddies is revealed via observations, and findings show that their tendency to achieve lowest-energy or minimum-dissipation states shapes their lowest-order coherent structure. Recent efforts also push forward to the higher-order structure of eddies: The understanding of horizontal structures is gradually evolving from symmetric to asymmetric, and the vertical structure based on separable variable assumption and vertical mode decomposition should further take the eddy vertical alignment and tilt into account. The temporal evolution of mesoscale eddies’ 3D structure is in a dynamical balance influenced by multiple competitive factors, such as eddies’ self-sustaining ability, background gradient and deformation, and generation of submesoscale fine structures. The submesoscale processes associated with mesoscale eddies have been intensively studied in recent years, and they should be considered as a fine-scale part of the 3D structure of eddies rather than separate instability processes. This review hopes to provide the readers with an enlightening, yet not thorough, review of the development of mesoscale eddies’ structures and brings up potential topics and unresolved difficulties for further research and development.

Submesoscale Eddy Structures of Lake Ladoga According to Sentinel-1 Radar Data for a Warm Period of 2019–2022

Submesoscale Eddy Structures of Lake Ladoga According to Sentinel-1 Radar Data for a Warm Period of 2019–2022

On the Vertical Structure of Mesoscale Eddies in the Kuroshio‐Oyashio Extension

AbstractVertical structure of mesoscale eddies is key to the eddy‐induced heat/material transport that further affects the climate and marine ecosystem. This study explores the vertical structure of mesoscale eddies in the Kuroshio‐Oyashio Extension region (KOE) and its underlying dynamics. By applying the hierarchical ascending classification to the observational and reanalysis data sets, we classify mesoscale eddies with three distinct kinds of vertical structures. Each kind of eddies exhibits clear spatial aggregation along a distinct zonal band. Eddies have core depths of 100–300 m in the northern part of the KOE and core depths of 300–500 m and 0–100 m in the southern. The eddy splitting or merging does not introduce new kind of eddy vertical structure but causes large intra‐kind variability. The different kinds of eddy vertical structures can be partially accounted for by the baroclinic instabilities at the eddy generation sites and local adjustment process.

Evolution of Different Types of Eddies Originating from Different Baroclinic Instability Types

This paper investigates the evolution of global eddies and various types of eddies originating from baroclinic instability (BCI) by utilizing satellite altimetry, Argo profiles, and climatology datasets. The structure of global eddies with regard to potential temperature anomalies experiences downward propagation and spreading from the periods of eddy growth to stabilization. However, from the eddy’s stabilization to the decay period, the process of spreading primarily occurs horizontally, and this process is usually accompanied by weakening. By comparing the evolution of eddies in three typical regions dominated by distinct types of BCI, we found that the basic properties of eddies related to different BCI types evolve similarly; however, there are notable differences in their vertical structures and evolution. Eddies associated with Phillips + Charney_s-type, Charney_s-type, and Eady-type BCIs exhibit dual-core, single-core, and dual-core structures, respectively. In particular, the intrusion of the Okhotsk cold water mass into the Northwest Pacific region forms cold-core anticyclonic eddies, resulting in AEs that are significantly distinct from the rest of the ocean. The evolution of surface-layer cores closely resembles that of the global eddies, while the decay of subsurface and bottom-layer cores is comparably sluggish. Additionally, we examine the impact of local oceanic stratification conditions on eddy decay and determine that stronger vertical gradients result in more vigorous eddy decay, accounting for the concentration of eddies at depths where vertical gradients are weaker during their evolution.

Variations and Depth of Formation of Submesoscale Eddy Structures in Satellite Ocean Color Data in the Southwestern Region of the Peter the Great Bay

The aim of this study was to develop methods for determining the most significant contrasts in satellite ocean color data arising in the presence of a submesoscale eddy structure, as well as to determine the corresponding depths of the upper layer of the sea where these contrasts are formed. The research was carried out on the example of the chain of submesoscale eddies identified in the Tumen River water transport area in the Japan/East Sea. MODIS Aqua/Terra satellite data of the remotely sensed reflectance (Rrs) and Rrs band ratio at various wavelengths, chlorophyll-a concentration, and, for comparison, sea surface temperature (sst) were analyzed. Additionally, the results of ship surveys in September 2009 were used to study the influence of eddy vertical structure on the obtained remote characteristics. The best characteristic for detecting the studied eddies in satellite ocean color data was the MODIS chlor_a standard product, which is an estimate of chlorophyll-a concentration obtained by a combination of the three-band reflectance difference algorithm (CI) for low concentrations and the band-ratio algorithm (OCx) for high concentrations. At the same time, the weakest contrasts were in sst data due to similar water heating inside and outside the eddies. The best eddy contrast-to-noise ratio according to Rrs spectra is achieved at 547 nm in the spectral region of seawater with maximum transparency and low relative errors of measurements. The Rrs at 678 nm and associated products may be a significant characteristic for eddy detection if there are many phytoplankton in the eddy waters. The maximum depth of the remotely sensed contrast formation of the considered eddy vertical structure was ~6 m, which was significantly less than the maximum spectral penetration depth of solar radiation for remote sensing, which was in the 14–17 m range. The results obtained can be used to determine the characteristics that provide the best contrast for detecting eddy structures in remotely sensed reflectance data and to improve the interpretation of remote spectral ocean color data in the areas of eddies activity.

Airborne Radar Doppler Spectrum Width as a Scale-Dependent Turbulence Metric

Abstract High-resolution airborne cloud Doppler radars such as the W-band Wyoming Cloud Radar (WCR) have, since the 1990s, investigated cloud microphysical, kinematic, and precipitation structures down to 30-m resolution. These measurements revolutionized our understanding of fine-scale cloud structure and the scales at which cloud processes occur. Airborne cloud Doppler radars may also resolve cloud turbulent eddy structure directly at 10-m scales. To date, cloud turbulence has been examined as variances and dissipation rates at coarser resolution than individual pulse volumes. The present work advances the potential of near-vertical pulse-pair Doppler spectrum width as a metric for turbulent air motion. Doppler spectrum width has long been used to investigate turbulent motions from ground-based remote sensors. However, complexities of airborne Doppler radar and spectral broadening resulting from platform and hydrometeor motions have limited airborne radar spectrum width measurements to qualitative interpretation only. Here we present the first quantitative validation of spectrum width from an airborne cloud radar. Echoes with signal-to-noise ratio greater than 10 dB yield spectrum width values that strongly correlate with retrieved mean Doppler variance for a range of nonconvective cloud conditions. Further, Doppler spectrum width within turbulent regions of cloud also shows good agreement with in situ eddy dissipation rate (EDR) and gust probe variance. However, the use of pulse-pair estimated spectrum width as a metric for turbulent air motion intensity is only suitable for turbulent air motions more energetic than the magnitude of spectral broadening, estimated to be <0.4 m s−1 for the WCR in these cases. Significance Statement Doppler spectrum width is a widely available airborne radar measurement previously considered too uncertain to attribute to atmospheric turbulence. We validate, for the first time, the response of spectrum width to turbulence at and away from research aircraft flight level and demonstrate that under certain conditions, spectrum width can be used to diagnose atmospheric turbulence down to scales of tens of meters. These high-resolution turbulent air motion intensity measurements may better connect to cloud hydrometeor process and growth response seen in coincident radar reflectivity structures proximate to turbulent eddies.

Dynamic Structure of Eddies of the Brazil‐Malvinas Confluence Zone Revealed by Direct Measurements and Satellite Altimetry

AbstractThe goal of this work is to study the dynamical structure of eddies of the Brazil‐Malvinas Confluence zone (BMC eddies) using direct velocity measurements carried out by Shipborne Acoustic Doppler Current Profiler during five oceanographic cruises performed in 2016–2022. In total, in situ data of 13 BMC eddies, including nine anticyclones and four cyclones are available. These data show that the orbital velocity in such eddies can reach 189 cm/s and their vertical structure is highly barotropic. In several eddies, the velocities exceeding 100 cm/s are observed down to a depth of 560 m and at a depth of 800 m they are still higher than 80 cm/s. The spatial structure of velocity and horizontal shear in the eddies is strongly asymmetric, with higher velocities in the southern part near the intense thermohaline BMC front. Altimetry data show qualitative agreement with in situ data, but underestimate the horizontal velocity shear and the maximum velocities at the periphery of the BMC eddies. We also use satellite altimetry and Argo float measurements to study these eddies, and estimate their impact on the thermohaline structure. The analysis shows that the eddies with orbital velocities exceeding 100 cm/s cause intense temperature and salinity anomalies reaching 7–9°C and 1 psu in anticyclones and −4°C and 0.8 psu in cyclones at 100–300 m depth.

Estimating Three‐Dimensional Structures of Eddy in the South Indian Ocean From the Satellite Observations Based on the isQG Method

AbstractBy incorporating the high‐resolution satellite remote sensing sea surface temperature (SST) with low‐resolution sea level anomaly and sea surface salinity (SSS), this study explores the reconstructability of the three‐dimensional (3D) eddy structures via the “interior + surface quasigeostrophic” (isQG) method in the South Indian Ocean. We apply the incorporation of high‐resolution SST to improve the spatial resolution of the reconstruction. We also propose a correction scheme for density reconstruction within the mixed layer to offset the absence of mixed layer dynamics in the SQG framework. Comparison against the in situ observations demonstrates a satisfactory reconstructability for subsurface velocity and density anomalies. Statistically, the zonal velocity reconstructability outperforms its meridional counterpart and the corresponding velocity phase. The reconstructed shallow‐layer velocity exhibits a superior skill in eddy‐active regions, when compared with drogued drifter observations. Reconstructed subsurface velocities reproduce the spatial structures of eddy‐induced velocity anomaly along the GO‐SHIP observation transect, although present smaller magnitudes. Results demonstrate the potential applicability of the isQG method for reconstructing mesoscale eddies, particularly in the ocean at mid‐to‐high latitudes, where subsurface dynamics are strongly influenced by barotropic and the first baroclinic modes. With the upcoming high‐advanced satellite observations, the isQG framework is expected to achieve better subsurface estimations.

Enhanced Dissipation of Internal Tides in a Mesoscale Baroclinic Eddy

Abstract The dissipation of low-mode internal tides as they propagate through mesoscale baroclinic eddies is examined using a series of numerical simulations, complemented by three-dimensional ray tracing calculations. The incident mode-1 internal tide is refracted into convergent energy beams, resulting in a zone of reduced energy flux in the lee of the eddy. The dissipation of internal tides is significantly enhanced in the upper water column within strongly baroclinic (anticyclonic) eddies, exhibiting a spatially asymmetric pattern, due to trapped high-mode internal tides. Where the eddy velocity opposes the internal tide propagation velocity, high-mode waves can be trapped within the eddy, whereas high modes can freely propagate away from regions where eddy and internal wave velocities are in the same direction. The trapped high modes with large vertical shear are then dissipated, with the asymmetric distribution of trapping leading to the asymmetric distribution of dissipation. Three-dimensional ray tracing solutions further illustrate the importance of the baroclinic current for wave trapping. Similar enhancement of dissipation is also found for a baroclinic cyclonic eddy. However, a barotropic eddy is incapable of facilitating robust high modes and thus cannot generate significant dissipation of internal tides, despite its strong velocities. Both energy transfer from low to high modes in the baroclinic eddy structure and trapping of those high modes by the eddy velocity field are therefore necessary to produce internal wave dissipation, a conclusion confirmed by examining the sensitivity of the internal tide dissipation to eddy radius, vorticity, and vertical scale. Significance Statement The oceanic tides drive underwater waves at the tidal frequency known as internal tides. When these waves break, or dissipate, they can lead to mixing of oceanic heat and salt which impacts the ocean circulation and climate. Accurate climate predictions require computer models that correctly represent the distribution of this mixing. Here we explore how an oceanic eddy, a swirling vortex of order 100–400 km across, can locally enhance the dissipation of oceanic internal tides. We find that strong ocean eddies can be hotspots for internal tide dissipation, for both clockwise and anticlockwise rotating vortices, and surface-enhanced eddies are most effective at internal tide dissipation. These results can improve climate model representations of tidally driven mixing, leading to more credible future predictions.

Two-phase modeling of fluid injection inside subcutaneous layer of skin

The motivation of this present theoretical investigation comes from the delivery of various drugs and vaccines through subcutaneous injection (SCI) to the human body. In the SCI procedure, a medical person takes a big pinch of skin of the injection applicable area of a patient to pull the subcutaneous layer (SCL) from the underlying muscle layer to smooth the execution of the procedure. Generally, the human skin, particularly SCL, is a heterogeneous and anisotropic living material. The major constituents of the SCL are adipose cells or fat cells and interstitial fluid. These adipose cells are oriented in such a way that the hydraulic conductivity of the SCL exhibits anisotropy. Consequently, one can adopt the field equations of mixture theory to describe the continuum nature of SCL. This mathematical modeling involves a perturbation technique where the small aspect ratio of the SCL provides a valid perturb parameter. This study highlights the issue of the mechanical response of the adipose tissue in terms of the anisotropic hydraulic conductivity variation, the viscosity of the injected drug, the mean depth of subcutaneous tissue, etc. In particular, the computed stress fields can measure the intensity of pain experienced by a patient after this procedure. Also, this study discusses the biomechanical impact of the creation of one or more eddy structure(s) due to the high pressure developed, increased tissue anisotropy, fluid viscosity, etc., within the area of applying injection.

Analysis of the vortical flow in a cyclone using four vortex identification methods

This paper analyzes the vortex flow field and performance of a solid-gas cyclone separator using computational fluid dynamics (CFD) by employing the Reynolds stress turbulence model (RSM) and Eulerian-Lagrangian particle tracking scheme for particle diameter (d) range of 0.1 to 8 μm. The complex structure of vortices is analyzed using the vorticity method, λ2-criterion, Q-criterion, and Ω-method. The results demonstrate that the presence of helical guide vanes (HGVs) enhances the centrifugal force applied to the solid particles and fluid velocity up to 4.4 times compared to the conventional cyclone. It is revealed that the λ2, Q, and Ω methods provide more details of eddy structure in the inner and outer layers of the isovortex surfaces than the vorticity method. Besides, the vortex core diameter can be estimated by all vortex identification methods.

Three-Dimensional Climatological Structures of the Arabian Sea Eddies and Eddy-Induced Flux

Three-Dimensional Climatological Structures of the Arabian Sea Eddies and Eddy-Induced Flux

On the reductions of airfoil–turbulence noise by curved wavy serrations

The present study provides an extensive experimental investigation into the use of curved sinusoidal (or wavy) trailing-edge (TE) serrations as a passive means for augmenting the airfoil broadband noise reduction over a broad range of frequencies. The curved sinusoidal TE serrated airfoils with parameters i = 20°, h/Co = 0.167, λ/Co = 0.134, and R/Co = 0.334 provide significant noise reduction benefits of about 4 dB with respect to the wider uniform serrations (i.e., λ/Co = 0.2), particularly from mid- to high-frequency ranges, where i, Co, h, λ, and R are the inclination angle, mean chord, serration amplitude, serration wavelength, and radius of curvature, respectively. Also, they provide an additional noise reduction of about 2.5 dB with respect to the narrow uniform serrations (i.e., λ/Co = 0.033), particularly from mid- to high-frequency ranges. On the whole, the curved sinusoidal TE serrations having an inclination angle of i = 15° and i = 20° could offer an average additional noise reduction benefit of about 1 and 2 dB for the range of frequencies from 1 to 10 kHz at all jet velocities. The normalized sound reduction (ΔPWL′) provided by the curved sinusoidal TE serrated airfoils show linear dependence with the modified Strouhal number for all jet speeds. Furthermore, the sound power reduction performance provided by curved sinusoidal TE serrations follows a modified Strouhal number scaling law from mid- to high-frequency ranges, which indicates their universal behavior on the noise reduction performance. The flow near the TE of the curved sinusoidal TE serrated airfoil undergoes multiple breakups, thus leading to non-uniform acoustic radiation throughout the span. The flow structures along the curvature undergo large-scale disintegration due to the presence of the inclination section in the curved sinusoidal TE serration. Thus, the granular structure of the turbulent eddies is fragmented into the fine length scales due to the presence of multiple breakups near the TE of the curved wavy serrations. Furthermore, the inclined portion of the curved wavy TE serration increases the disruption of the vortex shedding and reduces the velocity fluctuations, which reduces the surface pressure fluctuations close to the TE and, hence, the far-field noise.

The Aerodynamic Characteristics of a Rotating Cylinder Based on Large-Eddy Simulations

The cylindrical flow around a cylinder is present in several engineering problems. Moreover, the flow pattern around a rotating cylinder is more complex than that around a cylinder. In this paper, a rotating cylinder at different speed ratios is investigated by means of large-eddy simulations. In particular, the lift coefficient CL, drag coefficient CD, lift-to-drag ratio k, Strouhal number St, the flow field in each section, and the three-dimensional eddy structure are compared at different speed ratios. In addition, the effects of an end disk on the aerodynamic loads and flow field of the rotating cylinder were investigated. The results showed that, in the absence of an end disk, CL increased, CD increased and then decreased, k increased and then decreased, and St increased and then decreased as the speed ratio increased. The turnaround occurs for each parameter at a speed ratio of n = 2, and vortex shedding is suppressed at this speed ratio. Notably, the tip vortex at the free end was not suppressed. The CL, CD, and k values of the cylinder when adding the end disk were greater than those of the normal cylinder. For example, when the speed ratio is 3, the lift coefficient is increased by 27%, the drag coefficient is increased by 24%, and the lift-to-drag ratio is increased by 23% after adding the end plate. In addition, the vortex structure at the free end differed substantially. This study provides a systematic method to evaluate the aerodynamic loads and flow field changes around a cylinder, laying the foundation for solving the problems of cylinder flow and rotating cylinder flow.

Generation of Cold Anticyclonic Eddies and Warm Cyclonic Eddies in the Tropical Oceans

Abstract Mesoscale eddies are ubiquitous features of the global ocean circulation. Traditionally, anticyclonic eddies are thought to be associated with positive temperature anomalies while cyclonic eddies are associated with negative temperature anomalies. However, our recent study found that about one-fifth of the eddies identified from global satellite observations are cold-core anticyclonic eddies (CAEs) and warm-core cyclonic eddies (WCEs). Here we show that in the tropical oceans where the probabilities of CAEs and WCEs are high, there are significantly more CAEs and WCEs in summer than in winter. We conduct a suite of idealized numerical model experiments initialized with composite eddy structures obtained from Argo profiles as well as a heat budget analysis. The results highlight the key role of relative wind-stress-induced Ekman pumping, surface mixed layer depth, and vertical entrainment in the formation and seasonal cycle of these unconventional eddies. The relative wind stress is found to be particularly effective in converting conventional eddies into CAEs or WCEs when the surface mixed layer is shallow. The abundance of CAEs and WCEs in the global ocean calls for further research on this topic.

Characteristics of submesoscale eddy structures within mesoscale eddies in the Gulf of Mexico from 1/48° ECCO estimates

Submesoscale oceanic structures (<10-20 km) such as eddies and fronts are often difficult to describe given the influence of the mesoscale. In order to characterize the surface signatures of submesoscale structures, we utilize a custom spatial filtering function to separate the meso- and large-scale sea surface height (SSH) signal from the small scale SSH signal of 1/48° high resolution estimates provided by NASA’s Estimating the Circulation and Climate of the Oceans (ECCO) project. In this study, we use ECCO estimates from a 14-month global simulation between September 2011 and November 2012 with a 2 km horizontal grid spacing in the Gulf of Mexico. We then use an eddy detection and tracking algorithm to identify persistent circular features on both scales, giving rise to an atlas of submesoscale eddy-like variabilities (SEVs). We briefly investigate the geographic and temporal variability of SEVs as a whole before collocating SEVs inside mesoscale eddies, allowing us to evaluate the characteristics of internal SEVs and the impact of SEVs on mesoscale eddies. We find that SEVs, both anticyclonic and cyclonic, are ubiquitous inside mesoscale eddies with lifetimes longer than a week, accounting for an average of 10-20% of the spatial area and eddy kinetic energy of mesoscale eddies. We also show that internal SEVs are persistently associated with temperature and salinity anomalies in both eddy centers and edges of up to 0.1 °C and 0.05 psu, with anticyclonic internal SEVs being warmer and fresher while cyclonic internal SEVs are colder and saltier. Finally, we examine the life cycle of an anticyclonic Loop Current eddy, demonstrating that the number and intensity of internal SEVs within increases as the eddy approaches separation from the Loop Current until a maximum is obtained just after separation. In light of forthcoming submesoscale SSH observations from NASA’s Surface Water and Ocean Topography (SWOT) mission, our results showcase the variability of submesoscale eddy structures and their possible implications for biogeochemical cycling, the inverse energy cascade, and Loop Current prediction techniques.

Capture of colloidal fine suspended particle by aquatic vegetation under rainfall

The capture of colloidal fine suspended particles by vegetation plays an important role in water quality of the shallow aquatic system under rainfall. Quantifying impact of rainfall intensity and vegetation condition on this process remains poorly characterized. In this study, the colloidal particle capture rates under three rainfall intensities, four vegetation densities and with submerged or emergent vegetation were investigated in different travel distance in a laboratory flume. Considering vegetation as porous media, non-Darcy's law with rainfall as a source term, was coupled with colloid first-order deposition model, to simulate the particle concentration changes with time, determining the particle deposition rate coefficient (kd), representing capture rate. We found that the kd increased linearly with rainfall intensity; but increased and then decreased with vegetation density, suggesting the existence of optimum vegetation density. The kd of submerged vegetation is slightly higher than emergent vegetation. The single collector efficiency (η) showed the same trend as kd, suggesting colloid filtration theory well explained the impact of rainfall intensity and vegetation condition. Flow hydrodynamic enhanced the kd trend, e.g., the theoretical strongest flow eddy structure represented in the optimum vegetation density. This study is helpful for the design of wetland under rainfall, to remove colloidal suspended particles and the hazardous material, for the protection of the downstream water quality.

Simulating Atmospheric Characteristics and Daytime Astronomical Seeing Using Weather Research and Forecasting Model

The present study is aimed at the development of a novel empirical base for application to ground-based astronomical telescopes. A Weather Research and Forecasting (WRF) model is used for description of atmospheric flow structure with a high spatial resolution within the Baikal Astrophysical Observatory (BAO) region. Mesoscale vortex structures are found within the atmospheric boundary layer, which affect the quality of astronomical images. The results of simulations show that upward air motions in the lower atmosphere are suppressed both above the cold surface of Lake Baikal and inside mesoscale eddy structures. A model of the outer scale of turbulence for BAO is developed. In this work, we consider the seeing parameter that represents the full width at half-maximum of the point spread function. Optical turbulence profiles are obtained and daytime variations of seeing are estimated. Vertical profiles of optical turbulence are optimized taking into account data from direct optical observations of solar images.

High‐Resolution Gridded Temperature and Salinity Fields From Argo Floats Based on a Spatiotemporal Four‐Dimensional Multigrid Analysis Method

AbstractThe shortage of in situ ocean observations greatly limits the development of gridded ocean subsurface environmental analysis products. Fully using the correlated information of the observations in time and space is an appropriate approach to this problem. Here we adopt a method of spatiotemporal four‐dimensional multigrid analysis. A weekly gridded Argo product is also constructed in the Northwest Pacific Ocean (0°–40°N, 120°–152°E) from 2005 to 2020, with a horizontal resolution of 0.5° × 0.5° and 65 layers in the upper 1,500 m. Then, the gridded Argo product is evaluated by using in situ Argo floats, satellite altimeter data, the Tropical Atmosphere Ocean/Triangle Trans‐Ocean Buoy Network (TAO/TRITON), high‐resolution shipboard observations and some global gridded Argo products. Compared with in situ Argo floats, the reconstructed fields retain the spatiotemporal information of Argo floats well. The maximum vertical root mean square errors of temperature and salinity between the gridded Argo product and in situ Argo floats are less than 0.47°C and 0.06 psu respectively. In addition, the product agrees well with independent observations of satellite altimeter data, TAO/TRITON. Compared with shipboard observations, the product can well reflect the structure of mesoscale eddies and detect some small‐scale water masses. Compared with global gridded Argo products, our product retains more mesoscale features and has spatiotemporal correlation.