Frontogenesis and Frontolysis of a Cold Filament Driven by the Cross-Filament Wind and Wave Fields Simulated by a Large Eddy Simulation

The variations of the frontogenetic trend of a cold filament induced by the cross-filament wind and wave fields are studied by a non-hydrostatic large eddy simulation. Five cases with different strengths of wind and wave fields are studied.The results show that the intense wind and wave fields further break the symmetries of submesoscale flow fields and suppress the levels of filament frontogenesis. The changes of secondary circulation directions—that is, the conversion between the convergence and divergence of the surface cross-filament currents with the downwelling and upwelling jets in the filament center—are associated with the inertial oscillation. The filament frontogenesis and frontolysis caused by the changes of secondary circulation directions may periodically sharpen and smooth the gradient of submesoscale flow fields.The lifecycle of the cold filament may include multiple stages of filament frontogenesis and frontolysis.

Influence of the upper mixed layer depth on Langmuir turbulence characteristics

The upper mixed layer depth(h)has a significant seasonal variation in the real ocean and the low-order statistics of Langmuir turbulence are dramatically influenced by the upper mixed layer depth.To explore the influence of the upper mixed layer depth on Langmuir turbulence under the condition of the wind and wave equilibrium,the changes of Langmuir turbulence characteristics with the idealized variation of the upper mixed layer depth from very shallow(h=5 m)to deep enough(h=40 m)are studied using a non-hydrostatic large eddy simulation model.The simulation results show that there is a direct entrainment depth induced by Langmuir turbulence(h_(LT))within the thermocline.The normalized depthaveraged vertical velocity variance is smaller and larger than the downwind velocity variance for the ratio of the upper mixed layer to a direct entrainment depth induced by Langmuir turbulence h/h_(LT)<1 and h/h_(LT)>1,respectively,indicating that turbulence characteristics have the essential change(i.e.,depth-averaged vertical velocity variance(DAVV)DADV for Langmuir turbulence)between h/h_(LT)<1 and h/h_(LT)>1.The rate of change of the normalized depth-averaged low-order statistics for h/h_(LT)<1 is much larger than that for h/h_(LT)>1.The reason is that the downward pressure perturbation induced by Langmuir cells is strongly inhibited by the upward reactive force of the strong stratified thermocline for h/h_(LT)<1 and the eff ect of upward reactive force on the downward pressure perturbation becomes weak for h/h_(LT)>1.Hence,the upper mixed layer depth has significant influences on Langmuir turbulence characteristics.

Impact of Sea-Level-Rise and Human Activities in Coastal Regions:An Overview

Coastal regions are becoming increasingly vulnerable to flooding because of accelerating sea-level-rise(SLR),local ground subsidence,and the changes in topography and morphology.Moreover,coastal areas are usually highly urbanized and increased human activities have an effect on the stability and preservation of the environment.For instance,the growing demand for new lands to accommodate the population and the industrial facilities in China has required the design and the deployment of land-reclamation projects from the ocean,with a marked impact on fragile coastal eco-systems.Specifically,the Yangtze River and Pearl River Estuary,two major estuaries of the world,have long been subject to intensive human activities over the past decades.Long-term ground subsidence evolution,topographic changes,and morphological variation of the coastal regions have drawn great attention.This paper provides an overview of well-established Earth Observation(EO)remote sensing(RS)technologies that are employed to continuously monitor the changes of urbanized regions.The combined use of EO-based DInSAR analyses along with the knowledge of the geomorphology of the coastal regions allows a more precise picture of the SLR risk in the investigated coastal regions.In this paper,we will concentrate on remote sensing technologies that allow the gathering of heterogeneous information,such as those based on the use of synthetic aperture radar(SAR),satellite altimeters and tide gauge data.We will underline how human activities trigger changes in the living environment of coastal zones and the associated risks for the population.Observed coastline changes,coastal regions terrain subsidence,and offshore bathymetry have a pronounced effect on the increasing risk of flooding.Accordingly,we also present insights into some inundation model projections employed for evaluating the potential flooding risk in coastal regions.

Compact mid-infrared dual-comb spectrometer over 3-4μm via intra-pulse difference frequency generation in LiNbO_(3) waveguides

The mid-infrared optical frequency comb is a powerful tool for gas sensing.In this study,we demonstrate a simple midinfrared dual-comb spectrometer covering 3±4μm in Li Nb O_(3)waveguides.Based on a low-power fiber laser system,the mid-infrared comb is achieved via intra-pulse difference frequency generation in the Li Nb O_(3)waveguide.We construct pre-chirp management before supercontinuum generation to control spatiotemporal alignment for pump and signal pulses.The supercontinuum is directly coupled into a chirped periodically poled Li Nb O_(3)waveguide for the 3±4μm idler generation.A mid-infrared dual-comb spectrometer based on this approach provides a 100 MHz resolution over25 THz coverage.To evaluate the applicability for spectroscopy,we measure the methane spectrum using the dualcomb spectrometer.The measured results are consistent with the HITRAN database,in which the root mean square of the residual is 3.2%.This proposed method is expected to develop integrated and robust mid-infrared dual-comb spectrometers on chip for sensing.

Frequency comb generation from the ultraviolet to mid-infrared region based on a three-stage cascaded PPLN chain

Optical frequency combs(OFCs)have enabled significant opportunities for high-precision frequency metrology and high-resolution broadband spectroscopy.Although nonlinear photonics chips have the capacity of frequency expansion for OFCs,most of them can only access the limited bandwidths in the partial infrared region,and it is still hard to satisfy many measurement applications in the ultraviolet-to-visible region.Here,we demonstrate a compact broadband OFC scheme via the combination of three χ(2) nonlinearities in a three-stage periodically poled lithium niobate(PPLN)chain.With a supercontinuum spectrum OFC delivered into the PPLN chain,the intra-pulse diffidence frequency generation,optical parametric amplification,and high-order harmonic generation were carried out in sequence.It is crucial that the harmonics of the 1st–10th orders are simultaneously obtained with an offset-free OFC spectrum from 0.35 to 4.0μm.In view of the great potential for integration and spectral expansion,this wideband frequency comb source will open a new insight for the valuable applications of two-dimensional material analysis,biofluorescence microscopy,and nonlinear amplitude-phase metrology.

Remote sensing study of wetlands in the Pearl River Delta during 1995-2015 with the support vector machine method

In recent years, experienced rapid economic the Pearl River Delta has growth which may create a substantial burden to its ecology. In this study, the wetlands of the Pearl River Delta are investigated. Through the use of remote sensing methods, we analyze spatial and temporal variations of wetlands in this area over the past twenty years. The support vector machine （SVM） method is proven to be an effective approach for classifying the wetlands of the Pearl River Delta, and the total classifica- tion resolution reaches 94.94% with a Kappa coefficient exceeding 0.94, higher than other comparable analysis methods. Our results show that wetland areas were reduced by 36.9% during the past twenty years. The change detection analysis method shows that there was a 95.58% intertidal zone change to other land-use types, most of which （57.12%） was converted to construction land. In addition, farmland was reduced by 54.89% during the past twenty years, 47.19% of which was changed to construction land use. The inland water area increased 19.02%, but most of this growth （18.77%） was converted from the intertidal zone.

Remote sensing observations of phytoplankton increases triggered by successive typhoons

Phytoplankton blooms in the Western North Pacific, triggered by two successive typhoons with different intensities and translation speeds under different pre-existing oceanic conditions, were observed and analyzed using remotely sensed chlorophyll-a （Chl-a）, sea surface temperature （SST）, and sea surface height anomaly （SSHA） data, as well as typhoon parameters and CTD （conductivity, temperature, and depth） profiles. Typhoon Sinlaku, with relatively weaker intensity and slower translation speed, induced a stronger phytoplankton bloom than Jangrni with stronger intensity and faster translation speed （Chl-a〉0.18 mg-m-3 versus Chl- a〈 0.15 mg.m-3） east of Taiwan Island. Translation speed may be one of the important mechanisms that affect phytoplankton blooms in the study area. Pre-existing cyclonic circulations provided a relatively unstable thermodynamic structure for Sinlaku, and therefore cold water with rich nutrients could be brought up easily. The mixed-layer deepening caused by Typhoon Sinlaku, which occurred first, could have triggered an unfavorable condition for the phytoplankton bloom induced by Typhoon Jangmi which followed afterwards. The sea surface temperature cooling by Jangmi was suppressed due to the presence of the thick upper-ocean mixed-layer, which prevented the deeper cold water from being entrained into the upper-ocean mixed layer, leading to a weaker phytoplankton augment. The present study sug- gests that both wind （including typhoon translation speed and intensity） and pre-existing conditions （e.g., mixed- layer depths, eddies, and nutrients） play important roles in the strong phytoplankton bloom, and are responsible for the stronger phytoplankton bloom after Sinlaku＇s passage than that after Jangmi＇s passage. A new typhoon- influencing parameter is introduced that combines the effects of the typhoon forcing （including the typhoon intensity and translation speed） and the oceanic pre- condition. This parameter shows that the forcing effect of Sinlaku was stronger than that of Jangmi.

An ultraviolet to visible scheme to estimate chromophoric dissolved organic matter absorption in a Case-2 water from remote sensing reflectance

In a typical Case-2 coastal water environment(here,the Pearl River Estuary(PRE),China),chromophoric dissolved organic matter(CDOM)and suspended particulates dominate the water optical properties,and CDOM fluorescence contributes considerably to surface water reflectance.In this paper,an ultraviolet(UV)to visible scheme to retrieve CDOM absorption(ag)is developed based on a set of in situ observations.First,the CDOM UV absorption and spectral slope(Sg)are derived directly from the visible remote sensing reflectance;then the Sg is extrapolated to obtain the spectrum from UV to visible spectral range.This algorithm performs well,with an overall mean absolute percent difference(MAPD)of^30%,~5%and^6%for the estimation of ag in 250–450 nm,Sg over 250–400 nm,and 250–700 nm,respectively.The effectiveness and stability of the algorithm is further demonstrated in capturing the distribution pattern of CDOM absorption in the PRE from satellite ocean color imagery with multiple spatial and spectral resolution,namely:the Visible Infrared Imaging Radiometer Suite(VIIRS)(750 m/Multispectral),the Ocean and Land Color Instrument(OLCI)(300 m/Multispectral),the Hyperspectral Imager for the Coastal Ocean(HICO)(100 m/Hyperspectral),and the Landsat 8 Operational Land Imager(OLI)(30 m/Multispectral).The UV to visible scheme can benefit the CDOM absorption estimation in two aspects:1)it is free from the disturbance of suspended matter;2)it avoids uncertainties caused by the low signalto-noise ratio(SNR)of ag measurements in the visible range.The algorithm is effective in revealing multiple scales of variation of CDOM absorption from ocean color observations.

Multi-regional observations and validation of the M_(3)ocean tide

Improved determinations of the oft-ignored third-degree ocean tides can yield better accuracy for tidal predictions,numerical model solutions,and geodesy.While only a small part of tidal range,these components can be larger at certain coastal locations due to shelf resonances and other effects.Here,we discuss observations of the M3lunar terdiurnal tide using 9-year windowed tidal harmonic analyses at 157 tide gauges compares to a global assimilation model(TPXO9v5a),with a focus on the Western Pacific and the European Shelf.TPXO9v5a does well in estimating the observed M_(3)amplitudes and phase lags in most regions,though determinations in coastal zones and in morphologically complex areas are coarse and often inaccurate.We also employ a shallow-water model(MARS)on the European Shelf,which can yield localized improvement over TPXO.In five subregions of the European Shelf,regional root-mean-squared-errors(RMSEs)are lower(and thus a better fit)at three locations for TPXO for amplitudes,and three for phase lags,with MARS simulations being a better fit in the other subregions.We also show that some locations have experienced significant long-term increases and/or decreases in the M_(3)amplitude over time,likely related to resonance changes under sea level rise(SLR)which can modulate the oceanic response to astronomical forcing.This hypothesis is explored for Europe using the MARS model by applying various sea level rise scenarios,showing that the directionality(positive or negative)of the long-term changes in M_(3)amplitudes over time match the model results for more than half of our validation stations.

Introduction to the Special Issue： Coastal and Marginal Sea Studies

1 Introduction As an important part of the ocean system, the coastal and marginal sea （CMS） is a junction between land and the open ocean where the ocean-land interaction occurs, and also it is the area with substantial marine- economic activities for many countries. The development of marine economics greatly affects the CMS environment and causes deteriorating environmental problems. The study on the CMS helps to understand how the land and ocean interact, and how the marine environment responses to the land system change resulting from economic developments in coastal regions. Therefore, deeply understanding physical properties of the CMS is of great importance not only in the earth science study, but for marine environmental protection.