Mixed Layer Research Articles

Influence of cavity and ramp layout on combustion performance in a strut-based scramjet combustor

The computational analysis focuses on the flow performance of a wall-mounted cavity and ramp within DLR scramjet model operating in a reacting flow environment. The analysis encompasses a base setup aligned with DLR experiments, along with suggested configurations featuring different lower wall cavity depth and a fixed upper wall ramp. The 2-D Reynolds-Averaged Navier-Stokes approach (RANS) combined with Shear Stress Transport (SST) k-ω turbulence model, which incorporates single-step reaction chemistry, is utilized in steady-flow simulations. Subsequently, the unsteady-flow computations are completed using the Delayed Detached Eddy Simulation (DDES) with the SST k-ω turbulence model as a continuation of RANS analysis to compute and observe the coherent structures by using data driven methods. To examine shock structures and their associations with shear layer mixing characteristics, the cavity and ramp are positioned downstream of the strut. Inclusion of the cavity and ramp increase the number of shock waves in the flow substantially. Accordingly, complete combustion occur earlier than in the baseline model which is accompanied by a subtle increase in total pressure loss. Due to intense interactions between shock waves and shear layers, combustion zone widens laterally as the cavity displaces the shock train downstream of the strut injector. DDES results are processed to observe the dynamics and the coherent structures employing Dynamic Mode Decomposition (DMD) and Spectral Proper Orthogonal Decomposition (SPOD) methods. Both analysis show that the recirculation zone proceeds into the core engine with the progressive deepening of the cavity leading to a consequential stationary combustion.

The Effect of Y Addition on Oxidation Resistance of Bulk W-Cr Alloys

The self-passivating tungsten-based alloy W-11.4Cr-0.6Y (in wt.%) is a potential plasma-facing material for the first wall of future fusion reactors, which has been shown to suppress oxidation of tungsten and withstand temperatures of up to 1000 °C. In this study, the effect of Y addition on the microstructure and oxidation behavior of W-11.4Cr alloy at 1000 °C is analyzed by comparing it with W-11.4Cr-0.6Y, both prepared using identical synthesis routes. While the binary W-Cr alloy already exhibits improved oxidation resistance over pure W due to the formation of an outer Cr2WO6 layer, it still shows a tendency for spallation and, hence, is not protective. A continuous passivating chromia layer is only obtained with the addition of Y, and we demonstrate that it results in a 50-fold decrease in the oxide growth rate and eliminates the preferred growth of the oxide at edges seen in the binary alloy. Although a porous, complex oxide scale containing mixed oxide layers and WO3 is formed in both cases, the addition of Y results in lower porosity, which makes the oxide scale more adherent.

Model Sensitivity Analysis for Coastal Morphodynamics: Investigating Sediment Parameters and Bed Composition in Delft3D

Numerical simulation of sediment transport and subsequent morphological evolution rely on accurate parameterizations of sediment characteristics. However, these data are often not available or are spatially and/or temporally limited. This study approaches the problem of limited sediment grain-size data with a series of simulations assessing model sensitivity to sediment parameters and initial bed composition configurations in Delft3D, leading to improved modeling practices. A previously validated Delft3D sediment transport and morphology model for Dauphin Island, Alabama, USA, is used as the benchmark case. A method for the generation of representative sediment grain sizes and their spatially varying distributions is presented via end-member analysis of in situ surficial sediment samples. Derived sediment classes and their spatial distributions are applied to two sensitivity case simulations with increasing bed composition complexity. First, multiple sediment classes are applied in a single fully mixed layer, regardless of sediment type. Second, multiple sediment classes are applied in a thin, fully mixed transport layer with underlayers containing only the non-cohesive sediment classes below. Simulations were carried out in a probabilistic, Delft3D MorMerge configuration to capture long-term morphology change for 10 years. We found there is sensitivity to the inclusion of additional sediment classes and sediment distribution made evident in bed level and morphology change. Inclusion of highly mobile fine sediments altered model results in each sensitivity case. The model was also found to be sensitive to initial bed composition in terms of bed level and morphology change, with notable differences between sensitivity cases on decadal timescales, indicating an armoring effect in the second sensitivity case, which used the transport and underlayer bed configuration. The results of this study offer guidance for numerical modelers concerned with sediment behavior in coastal and estuarine environments.

Habitat suitability modeling of loggerhead sea turtles in the Central-Eastern Mediterranean Sea: a machine learning approach using satellite tracking data

Understanding how sea turtle species move through the environment and respond to environmental features is fundamental for sustainable ecosystem management and effective conservation. This study investigates the habitat suitability of the loggerhead sea turtle (Caretta caretta) in the Adriatic and Northern Ionian Seas (Central-Eastern Mediterranean) by developing and validating a multidisciplinary framework that leverages machine learning to investigate movement patterns collected by satellite tags Argos satellite tags. Satellite tracking data, enriched with sixteen environmental variables from the Copernicus Marine Service and EMODnet-bathymetry, were analyzed using Random Forest models, obtaining an accuracy of 80.9% when classifying presence versus pseudo-absence of loggerhead sea turtles. As main findings, sea bottom depth, surface chlorophyll (chl-a), and mixed layer depth (MLD) were identified as the most influential features in the habitat suitability of these specimens. Moreover, statistically significant differences, evaluated using t-test statistics, were found between coastal and pelagic locations, for the different seasons, in mixed layer depth, chl-a, 3D-clorophyll, salinity and phosphate. Although based on a limited sample of tagged animals, this study demonstrates that the distribution patterns of loggerhead sea turtles in Mediterranean coastal and pelagic areas are primarily influenced by sea water features linked to productivity and, consequently, to potential prey abundance. Additionally, this multidisciplinary framework presents a replicable approach that can be adapted for various species and regions.

Global distribution prediction and ecological conservation of basking shark (Cetorhinus maximus) under integrated impacts

Global climate change presents substantial threats to marine ecosystems, with particularly profound impacts on widely distributed migratory species. The basking shark (Cetorhinus maximus), the second-largest fish species, faces significant conservation challenges due to overfishing, habitat degradation, and climate change, necessitating urgent research to address knowledge gaps in its spatial distribution and interactions with changing marine environments. This study employs various environmental variables and distribution data to construct a global species distribution model for basking sharks, predicting their distribution patterns under current and future climate scenarios. The results indicate that chlorophyll, sea surface temperature, silicate and mixed layer depth are the primary factors determining habitat suitability for basking sharks. Under high-emission scenarios (Shared Socioeconomic Pathway, SSP5–8.5), our model predicts a shift toward the higher latitudes of the northern hemisphere in basking shark habitats, including temperate and sub-Arctic waters. Ecological corridor analysis identifies critical migratory pathways and pinch points, emphasizing the importance of incorporating the effects of climate change and human activities in the formulation of conservation strategies. The finding underscores the importance of integrated conservation strategies, highlighting how positive human interventions can aid in accurately identifying critical ecological corridors to ensure the long-term survival of the basking shark. Adaptive, science-based conservation measures are crucial to mitigating the effects of climate change and human activities, supporting the resilience of marine ecosystems.

The influence of the shock-to-reshock time on the Richtmyer–Meshkov instability in reshock

Experiments on the Richtmyer–Meshkov instability (RMI) in a dual driver vertical shock tube (DDVST) are described. An initially planar, stably stratified membraneless interface is formed by flowing air from above and sulfur hexafluoride from below the interface location using the method of Jones & Jacobs (Phys. Fluids, vol. 9, issue 1997, 1997, pp. 3078–3085). A random three-dimensional, multi-modal initial perturbation is imposed by vertically oscillating the gas column to produce Faraday waves. The DDVST design generates two shock waves, one originating above and one below the interface, with these shocks having independently controllable strengths and interface arrival times. The shock waves have nominal strengths of $M_L=1.17$ and $M_H=1.18$ for the shock wave originating in the light and heavy gas, respectively, with these strengths chosen to result in arrested bulk interface motion following reshock. The influence of the length of the shock-to-reshock time, as well as the order of shock arrival, on the post-reshock RMI is examined. The mixing layer width grows according to $h\propto t^\theta$ , where $\theta _H=0.36\pm 0.018$ (95 %) and $\theta _L=0.38\pm 0.02$ (95 %) for heavy and light shock first experiments, respectively, indicating no strong dependence on the order of shock wave arrival. Volume integrated specific turbulent kinetic energy (TKE) in the mixing layer versus time is found to decay according to $E_{tot}/\bar {\rho }\propto t^p$ with $p_H=-0.823\pm 0.06$ (95 %) and $p_L=-1.061\pm 0.032$ (95 %) for heavy and light shock first experiments, respectively. Notably, the 95 % confidence intervals do not overlap. Analysis on the influence of the shock-to-reshock time on turbulent length scales, transition criteria, spectra and mixing layer anisotropy are also presented.

Impacts of Typhoons on the Evolution of Surface Anticyclonic Eddies into Subsurface Anticyclonic Eddies in the Northwestern Subtropical Pacific Ocean

In this study, we investigated the impacts of typhoons on the transformation of anticyclonic eddies (AEs) into subsurface anticyclonic eddies (SAEs) in the northwestern subtropical Pacific Ocean (NWSP) based on an ocean reanalysis product and multiple satellite observations. Results suggest that while the heavy precipitation and strong positive wind stress curl (WSC) induced by the passage of typhoons may be two main driving factors that transformed shallow mixed layer depth (MLD) AEs (i.e., those shallower than 50 m at the eddy core) into SAEs, the latter played a greater role in such transformation. In addition, shallow MLD AEs with a less depressed isopycnal structure near the eddy center before the passage of typhoons were more likely to be transformed into SAEs under the impacts of typhoons. The likely timing of such transformation may be within 9 days after the passage of typhoons. For deep MLD AEs (i.e., those deeper than 80 m at the eddy core), the impacts of typhoons may be much less prominent below the mixed layer. Based on a diagnostic analysis of the vertical potential vorticity (PV) flux at the surface, we examined the mechanism and dynamic processes involved in the transformation of deep MLD AEs into SAEs under the impacts of typhoons. Results show that while typhoons played a positive role in maintaining low PV within deep MLD AEs, which was favorable for further transformation into SAEs, the diabatic process associated with the net air–sea heat flux was the crucial favorable condition for the transformation of deep MLD AEs into SAEs.

Spatio-temporal variations of the heat fluxes at the ice-ocean interface in the Bohai Sea

Thermodynamic process between the ice and the ocean plays a critical role in the evolution of sea-ice growth and melting in marginal seas. At the ice-ocean interface, the oceanic heat flux and the conductive heat flux transmitted through the ice layer jointly determine the latent heat flux driving the phase change (i.e., ice freezing/melting). In this study, the determination of two important thermal parameters in the ice module of the HAMSOM ice-ocean coupled model, namely the mixed layer thickness and the heat exchange coefficient at the ice-ocean interface, has been adjusted to improve the model performance. Spatio-temporal variations of heat fluxes at the ice-ocean interface in the Bohai Sea are investigated, based on the validated sea ice simulation in the 2011/2012 ice season. The relationships between the interfacial heat fluxes and oceanic and atmospheric conditioning factors are identified. We found that the surface conductive heat flux through ice shows short-term fluctuations corresponding to the atmospheric conditions, the magnitude of these fluctuations decreases with depth in the ice layer, likely due to reduced influence from atmospheric conditions at greater depths. Atmospheric conditions are the key controlling factors of the conductive heat flux through ice, while the oceanic heat flux is mainly controlled by the oceanic conditions (i.e., mixed layer temperature). Spatially, the value of the oceanic heat flux is larger in the marginal ice zone with relatively thin ice than in the inner ice zone with relatively thick ice. In the Bohai Sea, when ice is growing, heat within the ice layer is transferred upward from the ice base, and the heat is losing at the ice-ocean interface. This heat loss in the inner ice zone is obviously greater than that in the marginal ice zone. Whereas when ice is melting, the opposite is true.

Quantifying the Role of Ocean Dynamics in SST Variability across GCMs and Observations

Abstract Midlatitude SSTs forced by mesoscale oceanic processes can affect the large-scale atmosphere, pointing to the ocean’s crucial role outside the tropics. Previous studies have shown oceanic mesoscale processes’ effect on global and regional climate variability. This study quantifies the local contribution of ocean dynamics to mixed-layer temperature across the globe by directly estimating the ocean heat flux divergence resolved by state-of-the-art ocean reanalysis, eddy-resolving, and eddy-parameterized versions of two U.S. national climate models and indirectly from air–sea flux satellite-based estimates. Our results show that the eddy-resolving climate simulations resolve mixed-layer temperature variances that are larger and closer to those inferred from observations than both their eddy-parameterized counterparts and ECCO over much of the extratropics. The observations and the eddy-resolving models indicate a more significant role of ocean dynamics in the mixed-layer temperature variability than the surface fluxes over most extratropics compared to their eddy-parameterized versions. A frequency domain analysis shows that the better-resolved ocean mesoscale and thermal gradients enhance the variance over a time scale from 2 months to 30 years. Results show agreement in the ocean’s contribution among satellite-based estimates, ocean reanalysis products, and ocean eddy-resolving simulations. At the same time, differences emerge for ECCO and the eddy-parameterized models, suggesting that surface fluxes account for a larger fraction of the mixed-layer temperature variability in most of the extratropics.

An evaluation of morphometrical trends in a population of Woodringina hornerstownensis Olsson, 1960 (Foraminifera) reveals the role of intraspecific variations for paleoceanographical studies

The foraminiferal species Woodringina hornerstownensis is stratigraphically limited between the stages Danian and Selandian and was adapted to inhabit the mixed layer water column. We present a case study based on morphometry of W. hornerstownensis recovered in upper Danian strata (biozone P2) in the Pernambuco-Paraiba Basin at the Poty quarry. The morphometric data, associated with abundance and geochemical indicators, point to (i) an increase in size towards the top of the studied interval, associated with the shallowing-upward trend of the Maria Farinha Formation, and (ii) an increase in size directly related to the increase in abundance. By integrating and incorporating a specific variation of W. hornerstownensis into abundance parameters, we conclude that the shell increase appears to be consistent. Our results suggest that the increase in size responds to environmental optimum conditions for the species W. hornerstownensis. In a broader context, our work demonstrates the usefulness of morphometric indicators and the significance of intraspecific variation when interpreting macroecological patterns. Keywords: planktic foraminifera, paleoceanography, intraspecific variation, upper Danian, South Atlantic Ocean.

Impact of phytoplankton, CDOM, and suspended sediments on the vertical attenuation of light, changing heat content and circulation on a continental shelf: A modelling study of the Great Barrier Reef

Solar radiation propagating through the water column is scattered and absorbed by optically active constituents in the ocean, in particular phytoplankton, coloured-dissolved organic matter (CDOM), suspended inorganic particulate matter (SPIM) and detritus. These wavelength-dependent processes affect the vertical distribution of heating in the water column and its stratification. The continental shelf north-east of Australia, containing the Great Barrier Reef (GBR), is characterised by highly seasonal and intermittent freshwater inputs leading to large sediment and nutrient discharges that strongly impact the water optical properties. While this complex mixture of optically active constituents is known to affect water clarity and the euphotic zone depth in the river plumes, its impact on the ocean circulation and thermal balance is still unclear at the scale of the GBR. In this study, we use a hydrodynamic-optical-biogeochemical ocean model to investigate the feedback between heat absorption by phytoplankton, CDOM and suspended sediments and ocean dynamics in the GBR region. The results show that the attenuation of the vertical heat flux due to phytoplankton, CDOM and SPIM concentrations is stronger on the continental shelf and dominated by the absorption and scattering from suspended sediments. The presence of absorbing constituents in the water column drives a temperature increase at the surface and a decrease below the mixed layer with stronger stratification and greater heat losses to the atmosphere. Inshore, the ocean heat content increases by up to 1% due to optically active constituents. Offshore, absorption by optically active constituents near the surface is compensated by less absorption underneath the mixed layer resulting in a decrease in the ocean heat content of the top 500 m. We find that considering a spatially- and temporally-variable vertical attenuation of heat due to multiple optically-active components improves hydrodynamic model skill. This study highlights the importance of the impact of water clarity and its spatial variability on hydrodynamic processes.

Research on the oxidation behavior and oxidation mechanism of NiCrAl-bentonite abradable seal coatings at 650 °C

To study the oxidation behavior and microstructure transformation mechanism of NiCrAl-bentonite abradable seal coatings (ASCs), the NiCrAl-bentonite ASCs were prepared on GH4169 substrate with NiAl as the bonding layer, and the oxidation experiments were carried out at 650 °C at different time (24 h, 48 h, 72 h, 96 h, 144 h, 192 h). The evolution of surface, interior, and interface microstructure of the coating with different oxidation time was analyzed through X-ray diffractometer (XRD) and scanning electron microscope (SEM). The results indicated that the microstructure changes of the coating surface were as follows: the initiation of spot-like oxide → the growth of acicular oxide → the production of continuous oxidation film → the generation of NiO. The internal microstructure changes of the coating were as follows: the formation of Cr oxide layer → the formation of mixed oxide layer. The microstructure changes of the coating's interface were as follows: the initiation and growth thickening of the oxide layer. Element diffusion and oxygen partial pressure controlled the overall oxidation behavior of the coating. The formation of NiO and α-Al2O3 on the surface of coating after oxidation for 192 h at 650 °C had a bad effect on the service performance of the coating.

Inkjet printing of mixed layers comprising multinary semiconductor quantum dots and charge transport materials for light‐emitting diode displays

AbstractQuantum dots (QDs) are important luminescent structures with applications in wide‐color‐gamut displays requiring exceptional color reproducibility. Multinary semiconductor QDs are expected to serve as eco‐friendly materials to replace conventional QDs owing to the narrow spectral widths and tunable bandgaps of these QDs. However, the application of multinary QDs, which tend to exhibit defect‐related emissions, to QD light‐emitting diode (QLED) displays will require electroluminescence to be obtained from QLEDs incorporating inkjet‐printed emitting layers. The present work examines QLEDs exhibiting vibrant color emissions based on blue‐emitting Zn–Se–Te QDs, green‐emitting Ag–In–Ga–S QDs, and red‐emitting Ag–Cu–In–Ga–S QDs. Each such QLED contains QD emitting layers comprising a mixture of charge transport materials. The spectra obtained from these RGB QLEDs fabricated by spin‐coating show very high color purity. Passive matrix QLED displays incorporating these QDs are also fabricated by inkjet printing to demonstrate the high color purity that can be obtained from multinary QDs in displays. In conjunction with passive matrix driving, these displays produce clear moving images with vibrant electroluminescence originating from the multinary QDs. The present results indicate that these QDs have significant potential for utilization in wide‐color‐gamut displays.

Aerobic and anaerobic poise of white swimming muscles of the deep-diving scalloped hammerhead shark: comparison to sympatric coastal and deep-water species

Scalloped hammerhead sharks (Sphyrna lewini) routinely perform rapid dives to forage on mesopelagic prey. These deep dives consist of intensive swimming followed by recovery periods in the surface mixed layer. Swimming muscle temperature profiles suggest that S. lewini suppresses gill function as a means to reduce convective heat loss during dives into cool water. Such intensive swimming behavior coupled with reduced respiration prompted us to test whether the aerobic and anaerobic metabolic capacities of the white swimming muscle tissue of this species are greater than those of other shark species from the same region. The activities of key enzymes used in aerobic and anaerobic metabolism provide an indirect indicator of the metabolic potential (“poise”) of a tissue. Here we measured the maximal activities [international units (µmol substrate converted to product per min, U) per gram of wet tissue mass at 10°C] of the citric acid cycle enzymes citrate synthase (CS) and malate dehydrogenase (MDH) and glycolytic enzymes pyruvate kinase (PK) and lactate dehydrogenase (LDH) from white swimming muscle of S. lewini. Enzyme activities, and ratios of these enzyme activities that indicate relative indexes of aerobic to anaerobic capacity, were compared to those measured in three sympatric coastal carcharhinid sharks and two deep-dwelling species, Echinorhinus cookei and Hexanchus griseus. This is the first report of swimming-muscle enzyme activity for these deep-dwelling species. In comparison to the other species, S. lewini had significantly higher activities of both LDH and MDH in the white muscle, and a higher MDH/CS ratio. The high LDH activities suggest that the white muscle of S. lewini relies on relatively high rates of anaerobic ATP production, with would result in build up of high lactate levels, during deep foraging dives. High MDH activity in S. lewini white muscle suggests the potential for lactate levels to be rapidly reduced when aerobic conditions are restored while in the surface mixed layer between dives. These biochemical characteristics may enable S. lewini to swim rapidly while suppressing gill function during deep dives and thereby exploit a very different ecological niche from sympatric shark species (e.g., coastal carcharhinids) and hunt more rapidly via faster swimming for deep-water prey compared to species that permanently inhabit deep depths.

The cause of an extreme sea surface warming in the midlatitude western North Pacific during 2012 summer

This study investigated an extreme sea surface warming in the midlatitude western North Pacific (MLWNP) during the summer of 2012. The 2012 extreme event was characterized by warm sea surface temperature anomaly (SSTA) extending from the East/Japan Sea to central North Pacific. The SSTA box–averaged over the MLWNP (130–180°E, 33–50°N) in 2012 ranked as the third warmest in recent four decades, which has caused intense marine heatwaves in this region. During the summer of 2012, a positive Indian Ocean Dipole event co-occurred with El Niño, favoring anomalous moisture transport between the two basins that caused enhanced convection in the South China and Philippine Seas and western–to–central subtropical Pacific. The enhanced convective activities triggered two meridional atmospheric Rossby wave trains to form strong atmospheric blocking high–pressure systems in the MLWNP. This reduced the total cloud cover and surface wind speed, enhancing insolation and reducing the release of latent heat flux. In addition, the weakened wind strengthened the stratification and shoaled the mixed layer. As a result, the increased net heat flux into the ocean accompanied by a shallower mixed layer contributed to the upper ocean warming in the MLWNP. Meanwhile, the North Pacific was dominated by a negative phase of Pacific Decadal Oscillation (PDO), significantly contributing to warm SSTAs in the MLWNP in 2012. Consequently, the 2012 extreme warming in the MLWNP was the results of the combination of atmospheric Rossby waves and PDO. Our study highlighted the roles of high–frequency atmospheric teleconnection and low–frequency PDO in extreme sea surface warming in the MLWNP.

Large eddy simulation of the combined effect of heat fluxes and wave forcing of summer monsoon on a diurnal ocean mixed layer in the north Arabian Sea

Large eddy simulation of the combined effect of heat fluxes and wave forcing of summer monsoon on a diurnal ocean mixed layer in the north Arabian Sea

Ocean-scale patterns of environment and climate changes driving global marine phytoplankton biomass dynamics.

Effects of marine environment and climate changes on phytoplankton dynamics in global oceans have received increasing attention but remain a mystery. This study used a comprehensive approach combining correlation and information flow to explore relationships among phytoplankton biomass, marine environment, and climate forcing based on global observations over the past multi-decadal period. Correlation and causality between phytoplankton biomass and environmental factors exhibit spatial asymmetry-regions where environmental factors directly drive biomass variations were concentrated in oceanic currents and subtropical circulations. Temperature, light, and mixed layer depth show pronounced influences on global phytoplankton interdecadal variations. Climate forcing over interdecadal timescales directly affects phytoplankton biomass in the equatorial Pacific, South Pacific, and Indian Oceans, with more uncertain biomass variability in the equatorial Pacific due to multiple climate events. Our findings revealed that environment and climate changes directly affect phytoplankton interdecadal variability only in specific regions at the oceanic scale.

Dakar Niño under global warming investigated by a high-resolution regionally coupled model

Abstract. In this study, we investigated interannual variability in sea surface temperature (SST) along the northwestern African coast, focusing on strong Dakar Niño and Niña events and their potential alterations under the RCP8.5 emission scenario for global warming, using a high-resolution regional coupled model. Our model accurately reproduces the SST seasonal cycle along the northwestern African coast, including its interannual variability in terms of amplitude, timing, and the position of maximum variability. Comparing Dakar Niño variability between the 1980–2010 and 2069–2099 periods, we found that it intensifies under a warmer climate without changing its location and timing. The intensification is more pronounced during Dakar Niñas (cold SST events) than during Dakar Niños (warm SST events). In the future, SST variability will be correlated with ocean temperature and vertical motion at deeper layers. The increase in Dakar Niño variability can be explained by the larger variability in meridional wind stresses, which is likely to be amplified in the future by enhanced land–sea thermal contrast and associated sea-level-pressure anomalies extending from the Iberian Mediterranean area. A heat budget analysis of the mixed layer suggests that surface heat flux and horizontal-advection anomalies are comparably important for Dakar Niño and Niña events in the present climate. However, the future intensification of Dakar Niños and Niñas is likely to be driven by surface heat flux (latent heat flux and shortwave radiation). While horizontal- and vertical-advection anomalies also contribute to the intensification, their roles are secondary.

Impact of axial strain on linear, transitional and self-similar turbulent mixing layers

Impact of axial strain on linear, transitional and self-similar turbulent mixing layers

A Preliminary Study on The Causes of the "Triple-peak" La Niña During 2020-2022

The 2020-2022 triple-peak La Niña is the first consecutive three-year La Niña event in this century. In order to investigate the similarities and differences between this event and the other observed bimodal and triple events, this study uses synthetic and regression analysis, empirical orthogonal function decomposition, and mixed layer heat budget diagnosis to compare other events with this one in terms of location of anomalous negative sea surface temperature (SST), anomalous wind direction, and mixed layer heat budget. In the previous bimodal events, the centers of SST negative anomalies were both in the (5°S-5°N, 180°-120°W) region; there were anomalous northerly and westerly winds east of 140°W, and the negat precipitation anomalies were distributed along north of the equator. In contrast, the peak position of the second negative SST anomaly in this event is more eastward and southward; the anomalous easterlies continue from 120°E to the eastern boundary of the basin, and there is an anomalous southerlies in the eastern part of the basin. To further investigate the role of the anomalous easterlies and southerlies, this study calculates the mixed layer heat budget in key region. Corresponding to the latitudinal (longitudinal) wind anomalies, the latitudinal (longitudinal) temperature advection dominates the robust difference between the bimodal event and this triple-peak event. The anomalous easterlies and southerlies in the equatorial Pacific are favorable to the appearance of the third La Niña year in this event. This study is important in understanding the dynamics of triple-peak La Niña events, and will facilitate the forecast of such event.