Ming Li

Bio: Ming Li is an academic researcher from University of Maryland Center for Environmental Science. The author has contributed to research in topics: Estuary & Fractional Brownian motion. The author has an hindex of 46, co-authored 291 publications receiving 7044 citations. Previous affiliations of Ming Li include City University of Hong Kong & National University of Singapore.

Vertical swimming behavior influences the dispersal of simulated oyster larvae in a coupled particle-tracking and hydrodynamic model of Chesapeake Bay

Abstract: Because planktonic organisms have swimming speeds that are orders of magnitude lower than horizontal current velocities, it is unclear whether behavior of weak-swimming bivalve larvae could influence dispersal distance, encounters with suitable habitat, or subpopulation connec- tivity. We used a numerical approach to investigate whether these processes could be affected by species-specific differences in larval vertical swimming behavior of 2 oyster species (Crassostrea vir- ginica and C. ariakensis) in Chesapeake Bay, a partially mixed estuary. A coupled particle-tracking and hydrodynamic model was forced with observed winds and freshwater flow and included the best available estimate of present-day oyster habitat. Model scenarios were conducted with hydrody- namic predictions from June to September, 1995 to 1999, to simulate a range of environmental con- ditions. Simple larval swimming behaviors were parameterized for the 2 oyster species with results from preliminary laboratory experiments and literature. To isolate the effect of circulation, settlement habitat, and larval behavior on the spatial trajectories of particles, vertical swimming velocity was the only biological process represented in the model; egg production and larval growth were not included. Differences in larval swimming behavior had significant consequences for particle trans- port in Chesapeake Bay by influencing dispersal distances, transport success, and the degree of con- nectivity between 'subpopulations' in different tributaries. Most particles (>96%) did not return to the same reef on which they were released, and there were behavior-dependent differences in spa- tial patterns of the 'source' and 'sink' characteristics of oyster reefs. Simulated larval behavior had greater influence on spatial patterns of transport success than did interannual differences in circula- tion patterns. These model results have implications for fisheries management and oyster restoration activities.

Fractal Time Series—A Tutorial Review

Abstract: Fractal time series substantially differs from conventional one in its statistic properties. For instance, it may have a heavy-tailed probability distribution function (PDF), a slowly decayed autocorrelation function (ACF), and a power spectrum function (PSD) of type. It may have the statistical dependence, either long-range dependence (LRD) or short-range dependence (SRD), and global or local self-similarity. This article will give a tutorial review about those concepts. Note that a conventional time series can be regarded as the solution to a differential equation of integer order with the excitation of white noise in mathematics. In engineering, such as mechanical engineering or electronics engineering, engineers may usually consider it as the output or response of a differential system or filter of integer order under the excitation of white noise. In this paper, a fractal time series is taken as the solution to a differential equation of fractional order or a response of a fractional system or a fractional filter driven with a white noise in the domain of stochastic processes.

Spatial and temporal variations in sediment grain size in tidal wetlands, Yangtze Delta: On the role of physical and biotic controls

Abstract: To examine the spatial and temporal variability of sediment grain size in exposed tidal wetlands with ample sediment supply, we sampled sediments and measured hydrodynamics, accretion/erosion rates, and vegetation characteristics in the Yangtze Delta. Sediment grain size exhibited a landward/upward decreasing trend. This trend is mainly attributed to attenuation of hydrodynamics. A 630-day series of daily surface sediment sampling at a fixed site on an unvegetated intertidal flat revealed significant seasonal and storm-cyclic changes in grain size. This temporal variability was related to alternating accretion/erosion events, with erosion associated with coarser grain size. Such temporal dynamics were not present in vegetation, where sediment remained fine grained throughout the year. In the marsh, vegetation cover enables the trapping of fine-grained sediments in the following ways: (a) adherence of suspended sediments onto plants; (b) deposition of suspended sediments stimulated by attenuation of hydrodynamics through plant obstruction; and (c) prevention of resuspension of fine-grained deposits due to the protection of the plant canopy. The influence of vegetation on sediment grain size was clearly seen when comparing sediment trapped by different vegetation types and seasonal patterns of trapped sediment on different vegetation canopy densities. The relatively high plant biomass of the recently introduced Spartina alterniflora enhanced the trapping effect, whereas plant degradation due to buffalo grazing reduced the trapping effect. We conclude that for exposed tidal wetlands with ample sediment supply such as the Yangtze Delta, the spatial and temporal variability of sediment grain size is governed predominantly by physical controls on the unvegetated flat and predominantly by biophysical interaction of hydrodynamics and vegetation in the salt marsh, rather than by sediment supply.

Simulations of Chesapeake Bay estuary: Sensitivity to turbulence mixing parameterizations and comparison with observations

Abstract: [1] Regional Ocean Modeling System (ROMS) is used to develop a new three-dimensional hydrodynamic model for the Chesapeake Bay estuary. Hindcast simulations are conducted for 2 years with markedly different annual river discharges and are compared with time series measurements and high-resolution hydrographic data. The model shows skill in reproducing observed temporal variability in sea level height, salinity, and subtidal current. The agreement with observations is better in the normal runoff year 1997 than in the high runoff year 1996. The model qualitatively reproduces the along-channel and cross-channel salinity distributions during low-to-medium runoff periods. However, during high runoff periods it predicts weaker stratification and a more diffuse halocline than shown by observations. This model/data discrepancy is related to the deficiency of turbulent mixing parameterizations in strong stratification. We have experimented with four turbulence closure schemes (Mellor-Yamada/k-kl, k-ɛ, k-ω, and KPP models) in ROMS but found little difference in the model results. However, vertical stratification shows a strong sensitivity to the background diffusivity. The vertical diffusivity inferred from the model is found to be set by the background diffusivity except in the surface and bottom boundary layers where the turbulence schemes produce similar diffusivity distributions. Among the schemes explored, KPP and k-kl scheme with a background diffusivity of 10−5 or 10−6 m2 s−1 provide the best simulations of the Chesapeake Bay estuary. Both the model sensitivity study and model/data comparison highlight the importance of obtaining a more realistic parameterization for turbulence mixing in a strong pycnocline.

The Coupled Boundary Layers and Air–Sea Transfer Experiment in Low Winds

Abstract: The Office of Naval Research's Coupled Boundary Layers and Air–Sea Transfer (CBLAST) program is being conducted to investigate the processes that couple the marine boundary layers and govern the exchange of heat, mass, and momentum across the air–sea interface. CBLAST-LOW was designed to investigate these processes at the low-wind extreme where the processes are often driven or strongly modulated by buoyant forcing. The focus was on conditions ranging from negligible wind stress, where buoyant forcing dominates, up to wind speeds where wave breaking and Langmuir circulations play a significant role in the exchange processes. The field program provided observations from a suite of platforms deployed in the coastal ocean south of Martha's Vineyard. Highlights from the measurement campaigns include direct measurement of the momentum and heat fluxes on both sides of the air–sea interface using a specially constructed Air–Sea Interaction Tower (ASIT), and quantification of regional oceanic variability over sca...

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Numerical study of convection observed during the Winter Monsoon Experiment using a mesoscale two-dimensional model [presentation]

Abstract: Abstract A two-dimensional version of the Pennsylvania State University mesoscale model has been applied to Winter Monsoon Experiment data in order to simulate the diurnally occurring convection observed over the South China Sea. The domain includes a representation of part of Borneo as well as the sea so that the model can simulate the initiation of convection. Also included in the model are parameterizations of mesoscale ice phase and moisture processes and longwave and shortwave radiation with a diurnal cycle. This allows use of the model to test the relative importance of various heating mechanisms to the stratiform cloud deck, which typically occupies several hundred kilometers of the domain. Frank and Cohen's cumulus parameterization scheme is employed to represent vital unresolved vertical transports in the convective area. The major conclusions are: Ice phase processes are important in determining the level of maximum large-scale heating and vertical motion because there is a strong anvil componen...

Projected Gradient Methods for Nonnegative Matrix Factorization

Abstract: Nonnegative matrix factorization (NMF) can be formulated as a minimization problem with bound constraints. Although bound-constrained optimization has been studied extensively in both theory and practice, so far no study has formally applied its techniques to NMF. In this letter, we propose two projected gradient methods for NMF, both of which exhibit strong optimization properties. We discuss efficient implementations and demonstrate that one of the proposed methods converges faster than the popular multiplicative update approach. A simple Matlab code is also provided.

Larval Dispersal and Marine Population Connectivity

Abstract: Connectivity, or the exchange of individuals among marine populations, is a central topic in marine ecology. For most benthic marine species with complex life cycles, this exchange occurs primarily during the pelagic larval stage. The small size of larvae coupled with the vast and complex fluid environment they occupy hamper our ability to quantify dispersal and connectivity. Evidence from direct and indirect approaches using geochemical and genetic techniques suggests that populations range from fully open to fully closed. Understanding the biophysical processes that contribute to observed dispersal patterns requires integrated interdisciplinary approaches that incorporate high-resolution biophysical modeling and empirical data. Further, differential postsettlement survival of larvae may add complexity to measurements of connectivity. The degree to which populations self recruit or receive subsidy from other populations has consequences for a number of fundamental ecological processes that affect population regulation and persistence. Finally, a full understanding of population connectivity has important applications for management and conservation.