Spatio-Temporal Analysis of Sea Surface Temperature in the East China Sea Using TERRA/MODIS Products Data

Sea surface temperature (SST) is an important parameter in determining the atmospheric and oceanic circulations, and satellite thermal infrared remote sensing can obtain the SST with very high spatio-temporal resolutions. The study first validated the accuracy of TERRA MODIS SST daytime and nighttime products with the timing SST measurements from the ships in the East China Sea (ECS) in February, May, August and November, 2001, and then the daily variation of daytime and nighttime SST difference was analyzed. Using 16-year MODIS SST monthly products data from February 2000 to January 2016, when all SST monthly products in February, May, August and November were averaged respectively, the seasonal spatial distribution pattern of SST in the ECS was discovered. After monthly sea surface temperature anomaly was finally processed by the empirical orthogonal function (EOF), the interannual variability of SST in the ECS was discussed. The results show that the MODIS SST daily products have a good accuracy with a mean absolute percentage error (MAPE) below 5%. The SST difference between day and night is the largest in winter, followed by spring, then for autumn and the smallest in summer, while the diurnal SST difference is very low for the same season in the different seas. The SST in the ECS displays the obvious seasonal spatial distribution pattern, in which the SST of winter is gradually increasing from north to south, while local temperature difference is the largest for 26.5°C in a year. In comparison, the SST in summer tends uniform and the difference is not more than 5°C in the whole sea. From the EOF analysis of SST anomaly, the interannual variability of SST in the ECS is affected by the East Asian monsoon, the latitudinal difference of solar radiation, the offshore circulation and the submarine terrain

Rotated Spectral Principal Component Analysis (rsPCA) for Identifying Dynamical Modes of Variability in Climate Systems.

Spectral PCA (sPCA), in contrast to classical PCA, offers the advantage of identifying organized spatiotemporal patterns within specific frequency bands and extracting dynamical modes. However, the unavoidable trade-off between frequency resolution and robustness of the PCs leads to high sensitivity to noise and overfitting, which limits the interpretation of the sPCA results. We propose herein a simple nonparametric implementation of sPCA using the continuous analytic Morlet wavelet as a robust estimator of the cross-spectral matrices with good frequency resolution. To improve the interpretability of the results, especially when several modes of similar amplitude exist within the same frequency band, we propose a rotation of the complex-valued eigenvectors to optimize their spatial regularity (smoothness). The developed method, called rotated spectral PCA (rsPCA), is tested on synthetic data simulating propagating waves and shows impressive performance even with high levels of noise in the data. Applied to global historical geopotential height (GPH) and sea surface temperature (SST) daily time series, the method accurately captures patterns of atmospheric Rossby waves at high frequencies (3-60-day periods) in both GPH and SST and El Niño-Southern Oscillation (ENSO) at low frequencies (2-7-yr periodicity) in SST. At high frequencies the rsPCA successfully unmixes the identified waves, revealing spatially coherent patterns with robust propagation dynamics

Inner Shelf Circulation in Coastal Virginia: A Data Assimilation Approach

The primary objective of this dissertation is to describe the tidal and subtidal flow patterns over the inner shelf of the Delmarva Peninsula, located in the Mid-Atlantic Bight of the United States (36.6–38.0 N), north of the Chesapeake Bay. The objective is pursued with a combination of direct measurements and numerical assimilative techniques. The dynamic balance of the study area is little known, and the distribution of tidal properties has not been described for this area since very rough descriptions in the 1950\u27s. Hydrographic and current velocity profiles from four regional cruises in the inner shelf were used to study the area. The tidal and subtidal fields were studied using data assimilation techniques on a numerical model. The model described the spatial and temporal dynamics of the area and included vertically averaged shallow water equations. Current velocity measurements were assimilated into the model using the adjoint method. Concurrent predicted sea level data from inside the Chesapeake Bay were also assimilated in order to incorporate the sea level signal in the model. Measured current velocities were not able to represent adequately the tidal signal in the location of sea level stations, except for one cruise. In turn, sea level data were not able to recover shipboard current measurements. A weighted combination of both data sources and a regularization term that penalized vorticity, gave the best results in terms of minimizing the root mean square error of un-assimilated information. The mean circulation obtained over the inner shelf was less than 10 cm s−1 and oriented along shelf. The mean flow and elevation reflected semigeostrophic dynamics with along shore pressure gradient balanced by friction and rotation, and cross shore pressure gradient balanced by rotation. The mean flow and elevation had spatial scales of 15–40km in the along shelf direction. The across shelf direction presented smaller scales (3–5 km). In terms of tidal flows, the semidiurnal constituent was dominant, with magnitudes of 30 cm s−1. The diurnal constituent was less than 10 cm s−1. The propagation of the semidiurnal tide could be explained as combination of a Kelvin and a Poincaré wave that transform into a coastal trapped Kelvin wave as it moves into the Chesapeake Bay

Investigating Physical Processes Associated With Chesapeake Bay and Changjiang Estuary

Coastal and estuaries are landforms that not only have great impacts on large marine ecosystem, but also play a significant role in moderating or aggravating natural hazards and erosion risks that are expected to increase with climate change. This dissertation explores some of the concerns associated with coasts and coastal systems. In the second chapter, a thirty seven year wave hindcast (1979-2015) in Chesapeake Bay using NCEP\u27s Climate Forecast System Reanalysis (CFSR) wind is presented. The long-term significant wave heights are generated by the third-generation nearshore wave model SWAN, which is validated using the wave height measurements at buoy stations inside the bay. Validation results show a good agreement between simulations and measurements. Statistical analyses on the simulated wave heights are carried out. Firstly, an Empirical Orthogonal Function (EOF) analysis is performed to study the temporal and spatial variability of significant wave heights in the bay. Secondly, the long-term changing trends of extreme wave heights are examined using regression analysis and empirical cumulative distribution function approach, which reveal a steady increase of extreme wave heights in most parts of the Chesapeake Bay in the past several decades. Finally, extreme value analyses based on generalized extreme value and generalized Pareto distribution functions are applied to evaluate design wave heights with different return periods. The effects of key parameters including threshold value, time span and data length on the design wave heights are extensively studied. Through the comparisons of different distribution functions evaluated by Bayesian Information Criterion and Akaike Information Criterion, it is found that Gamma distribution function and generalized extreme value analysis provide the best fit for annual and monthly data, while generalized Pareto distribution function gives the best fit when peak-over-threshold analysis is conducted. In the third chapter, sediment deposition in the north passage of the Changjiang Estuary, where the Deep-water Navigation Channel (DNC) is located, has been studied. To understand the suspended sediment dynamics and the effects of sediment-induced stratification on sediment flux in the navigational channel, field data on tidal ow and suspended sediment concentration (SSC) are collected and analyzed in this study. It is shown that net sediment transport is dominated by ebb currents in the study area. The net sediment flux is generally toward the ocean and the maximum value is found to be in the middle reach of the passage. In the lower reach of the passage, the net sediment flux is landward in the lower layer and seaward in the upper layer of the water column due to the two-layer feature of the estuarine circulation. Advective flux plays a significant role in transport of sediment in upper and middle reach of the passage by carrying 70~100% of the suspended sediment. However, this amount is reduced to 30~60% in lower reach of the passage where tidal effects become more important. The suspended sediment induced stratification in the north passage is examined by calculating eddy viscosity. It is found that suspended sediment can reduce eddy viscosity by 10~30%. The highest depth-averaged SSC is located in the middle reach of the north passage, where the averaged SSC is 4~15 times higher than that in the upper reach. In this region, bed shear stress is larger at ebb while SSC is higher at food. It is inferred that suspended sediments in the DNC during food are partially transported from a neighboring shoal, which plays an important role in sediment dynamics in the north passage

Thirty-three years of ocean benthic warming along the U.S. Northeast Continental Shelf and Slope : patterns, drivers, and ecological consequences

© The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Journal of Geophysical Research: Oceans 122 (2017): 9399–9414, doi:10.1002/2017JC012953.The U.S. Northeast Continental Shelf is experiencing rapid warming, with potentially profound consequences to marine ecosystems. While satellites document multiple scales of spatial and temporal variability on the surface, our understanding of the status, trends, and drivers of the benthic environmental change remains limited. We interpolated sparse benthic temperature data along the New England Shelf and upper Slope using a seasonally dynamic, regionally specific multiple linear regression model that merged in situ and remote sensing data. The statistical model predicted nearly 90% of the variability of the data, resulting in a synoptic time series spanning over three decades from 1982 to 2014. Benthic temperatures increased throughout the domain, including in the Gulf of Maine. Rates of benthic warming ranged from 0.1 to 0.4°C per decade, with fastest rates occurring in shallow, nearshore regions and on Georges Bank, the latter exceeding rates observed in the surface. Rates of benthic warming were up to 1.6 times faster in winter than the rest of the year in many regions, with important implications for disease occurrence and energetics of overwintering species. Drivers of warming varied over the domain. In southern New England and the mid-Atlantic shallow Shelf regions, benthic warming was tightly coupled to changes in SST, whereas both regional and basin-scale changes in ocean circulation affect temperatures in the Gulf of Maine, the Continental Shelf, and Georges Banks. These results highlight data gaps, the current feasibility of prediction from remotely sensed variables, and the need for improved understanding on how climate may affect seasonally specific ecological processes.John D. and Catherine T. MacArthur Foundation Grant Number: 14–106159-000-CFP; National Aeronautics and Space Administration Grant Number: NNX14AP62

ESTIMATING SURFICIAL SEAFLOOR SEDIMENT PROPERTIES USING AN EMPIRICAL ORTHOGONAL DECOMPOSITION ON ACOUSTIC BACKSCATTER WAVEFORM PROPERTIES

Seafloor classification and environmental assessment in shallow marine waters are crucial to habitat mapping, coastal management policies and maintaining navigational waterways. There are existing methods for remotely estimating some bottom properties, but the large variety of desired measured sediment properties frequently leads to insufficient quantifiable data to support marine policy decisions. This problem is exacerbated by the highly variable bottom composition of typical coastal and estuarine environments. In this work, field observations from an Odom Echotrac vertical-incidence echosounder with a 200 khz transducer were used to estimate seafloor sediment characteristics in regions with variable bottom types. Observations were obtained in water depths ranging 0.5-24 m of the Little Bay, New Hampshire, during February and March, 2013. Backscatter waveforms (the acoustic return representing the first interaction with the bottom) were analyzed and their properties compared to sediment grain size distributions. These comparisons showed varied degrees of predictive capability and require subjective a priori selection. In an effort to better capture the collective effects of seafloor sediment\u27s composition on acoustic returns, empirical orthogonal functions (EOF\u27s) were computed from an ensemble of seven waveform properties and compared with observed surficial sediment size fractions, bulk density, and porosity. A simple logarithmic model relating first mode EOF spatial variability to observed mud fractions explained 43% of the variability and well estimated the spatial pattern of mud across the bay (RMS errors in mud fraction of 10-15%) from deep channels (with no mud) to high concentrations of mud on the shallower flats near the sides of the estuary. This method produced greater coverage and higher resolution predictions of mud fraction than could be obtained using traditional sediment measuring techniques. Deviations from the model are shown to be correlated with lower sediment porosity most likely due to river inflow from the Bellamy River draining into the Bay. Application of the model coefficients to new data obtained in the Great Bay in 2014 with the same sonar and acoustic settings, showed similar predicted mud fractions with RMS errors of 11.9 and 13.2% along two surveyed lines. This empirical analysis provides a first order objective means to interpret acoustic backscatter, an important step towards a widespread quantitative assessment of shallow water seafloor sediments

Settlement of blue crab postlarvae in western North Atlantic estuaries

We quantified variability in daily settlement of blue crab postlarvae (megalopae) on identical artificial settlement substrates at up to 6 sites concurrently over a broad geographic expanse (similar to 1300 km) of the western North Atlantic (Delaware-South Carolina, USA). The 4-year study encompassed the blue crab recruitment season (generally July-November) from 1989-1992. Regional settlement was characterized by: (1) constant low levels of daily settlement punctuated by significantly non-random, episodic peaks of variable duration and intensity with peaks collectively accounting for at least half the total annual settlement at a site; (2) spatial and temporal variability leading to a general lack of coherence between sites in a given year and across years within a site; (3) occasional coherence in patterns between sites during a given year, suggesting linkages in regional processes affecting settlement; and, (4) significant semilunar patterns of episodic settlement pulses at the York River and Charleston-Harbor sites over a 4-year period. Thus, regional settlement patterns exhibit both consistent (i.e., semilunar periodicity, episodic pulses) and variable (i.e., temporal and spatial variation) elements, which are likely due to a combination of stochastic and deterministic processes. Such patterns may impart an ecological advantage to crabs settling en masse (i.e., reduced encounter rate with predators through predator swamping) or at continuous low levels (i.e., below a density-dependent threshold) during the recruitment season. An identical study illustrated that settlement in Gulf of Mexico estuaries exhibited similarly episodic and highly variable patterns. Daily mean and total annual settlement were up to a hundred-fold greater for gulf than Atlantic Coast estuaries implying population limitation by post-settlement processes in the gulf and greater recruitment limitation in the Atlantic. These studies emphasize the merit of conducting research over a broad geographic range using standardized techniques to attempt meaningful ecological comparisons

Simulation of hydrodynamics and sediment transport patterns in Delaware Bay

This research seeks to increase understanding of hydrodynamic processes influencing the salinity intrusion and sediment transport patterns by simulating the complex flows in Delaware Estuary. For this purpose, a three-dimensional numerical model is developed for the tidal portion of the Delaware Estuary using the UnTRIM hydrodynamic kernel. The model extends from Trenton, NJ south past the inlet at Cape May, NJ and incorporates a large portion of the continental shelf.The simulation efforts are focused on summer 2003. A variable, harmonically decomposed, water level boundary condition of three diurnal (K1, Q1, O1) and four semidiurnal (K2, S2, N2, M2) components are used to regenerate the observed tidal signals in the bay. The effect of forcing by the Chesapeake Bay through the Chesapeake-Delaware canal is also modeled. The major forcings such as inflow and wind is used to better reproduce the observed characteristics.Various turbulence closure models are compared for use in Delaware Estuary to best represent the salinity intrusion patterns. In particular, seven different turbulence closures, five of which are two-equation closure models, are used for comparison. Four of these models are implemented in the UnTRIM hydrodynamic code using Generic Length Scale (GLS) approach that mimics the models through its parameter combinations. The original Yamada Mellor level 2.5 code is used as the fifth one.The water levels are compared with data available from National Oceanic and Atmospheric Administration observation stations. Harmonic analysis to observations and simulations are performed. All turbulence models perform similar in performance representing the tidal conditions.Salinity time series data is available at Ship John Shoal Light Station for the 62 day simulation period. In addition to the time series data, a survey performed by University of Delaware along the main shipping channel in June 2003 is available. Simulation with different turbulence closures yielded substantially different results. Among the seven closures compared, the k −ε parameterization of GLS is found to best represent the observed salinity characteristics.The k −ε model is used in the sediment transport modeling. The model results are compared to the available sediment data from a survey performed in spring 2003. The location of turbidity maximum is accurately identified by k −ε model.Ph.D., Civil, Architectural & Environmental Engineering -- Drexel University, 200