Quanan Zheng

Bio: Quanan Zheng is an academic researcher from University of Maryland, College Park. The author has contributed to research in topics: Sea surface temperature & Internal wave. The author has an hindex of 34, co-authored 163 publications receiving 20319 citations. Previous affiliations of Quanan Zheng include National Science Foundation & University of Delaware.

A study of long-term sea level variability in the East China Sea

Abstract: From the analyses of the satellite altimeter Maps of Sea Level Anomaly (MSLA) data, tidal gauge sea level data and historical sea level data, this paper investigates the long-term sea level variability in the East China Sea (ECS). Based on the correlation analysis, we calculate the correlation coefficient between tidal gauge and the closest MSLA grid point, then generate the map of correlation coefficient of the entire ECS. The results show that the satellite altimeter MSLA data is effective to observe coastal sea level variability. An important finding is that from map of correlation coefficient we can identify the Kuroshio. The existence of Kuroshio decreases the correlation between coastal and the Pacific sea level. Kurishio likes a barrier or a wall, which blocks the effect of the Pacific and the global change. Moreover, coastal sea level in the ECS is mainly associated with local systems rather than global change. In order to calculate the long-term sea level variability trend, the empirical mode decomposition (EMD) method is applied to derive the trend on each MSLA grid point in the entire ECS. According to the 2-D distribution of the trend and rising rate, the sea level on the right side of the axis of Kuroshio rise faster than in its left side. This result supports the barrier effect of Kuroshio in the ECS. For the entire ECS, the average sea level rose 45.0 mm between 1993 and 2010, with a rising rate of (2.5±0.4) mm/a which is slower than global average. The relatively slower sea level rising rate further proves that sea level rise in the ECS has less response to global change due to its own local system effect.

Mechanisms of SAR Imaging of Shallow Water Topography of the Subei Bank

Abstract: In this study, the C-band radar backscatter features of the shallow water topography of Subei Bank in the Southern Yellow Sea are statistically investigated using 25 ENVISAT (Environmental Satellite) ASAR (advanced synthetic aperture radar) and ERS-2 (European Remote-Sensing Satellite-2) SAR images acquired between 2006 and 2010. Different bathymetric features are found on SAR imagery under different sea states. Under low to moderate wind speeds (3.1~6.3 m/s), the wide bright patterns with an average width of 6 km are shown and correspond to sea surface imprints of tidal channels formed by two adjacent sand ridges, while the sand ridges appear as narrower (only 1 km wide), fingerlike, quasi-linear features on SAR imagery in high winds (5.4~13.9 m/s). Two possible SAR imaging mechanisms of coastal bathymetry are proposed in the case where the flow is parallel to the major axes of tidal channels or sand ridges. When the surface Ekman current is opposite to the mean tidal flow, two vortexes will converge at the central line of the tidal channel in the upper layer and form a convergent zone over the sea surface. Thus, the tidal channels are shown as wide and bright stripes on SAR imagery. For the SAR imaging of sand ridges, all the SAR images were acquired at low tidal levels. In this case, the ocean surface waves are possibly broken up under strong winds when propagating from deep water to the shallower water, which leads to an increase of surface roughness over the sand ridges.

New insight into the South China Sea: Rossby normal modes

Abstract: The South China Sea (SCS), the largest marginal sea of the Northwest Pacific Ocean, is characterized by frequent occurrence of energetic mesoscale eddies. The eddy diameters range from 100 to 300 km. The eddy lifespan varies from several days to several months with the longest time of seven months (Zheng et al., 2017). The eddy disturbance reaches down to the ocean bottom layer. Before 2011, eddies in the SCS were treated as a single process. Thus, their generation was individually attributed to various mechanisms, such as the Kuroshio intrusion, local winds and disturbances from the Pacific (Wang and Chern, 1987; Li et al., 1998; Wang et al., 2003; Hu and Kawamura, 2004; Xie et al., 2011; Zheng et al., 2011). Since 2011, some investigators have found that eddies in the SCS behaved as grouped phenomena. Nan et al. (2011) observed three long-lived anticyclonic eddies appearing as an eddy train along 18°N in the northern SCS in summer 2007, and suggested the frontal instability of the local current as their generation mechanism. Zheng et al. (2014) found that there is internal coherence among alternatingly distributed anticyclonic and cyclonic eddies in the SCS, and suggested existence of 2-D standing wave modes in the SCS deep basin. Recently, Xie et al. 1 adopted theories of the Rossby normal modes in the enclosed ocean basin to analyze 2-D distribution patterns of the sea level anomaly (SLA) in the SCS deep basin. Their results give a new insight into the SCS eddy dynamics. The Rossby normal mode solutions to the linear potential vorticity equation on the β-plane for a rectangular ocean basin with a zonal length L (0≤x≤L), a meridional width l (0≤y≤l), and a uniform depth are

Vector empirical orthogonal function modes of the ocean surface wind variability derived from satellite scatterometer data

Abstract: Ocean surface winds derived from NSCAT, QuikSCAT and ERS-1/2 scatterometer observations during a period from January 1992 to April 2000 were analyzed using the vector empirical orthogonal function (VEOF) method. With the boreal winter and summer oscillation, the first VEOF is dominated by the Indian and East Asian monsoons and also shows an annual cycle of the trade winds. The second VEOF represents the boreal autumn and spring oscillation, and reveals a transition state between winter and summer. The third VEOF indicates the wind variability associated with El Nino Southern Oscillation (ENSO) events, because the temporal mode has a high correlation coefficient of 0.8 with the Southern Oscillation Index (SOI). Furthermore, the third mode reveals the teleconnection of the Indian monsoon and wind variability over high latitude oceans, such as the Aleutian Low system, with ENSO events.

A new type of internal solitary waves with a re-appearance period of 23 h observed in the South China Sea

Abstract: A new type of internal solitary waves with a re-appearance period of 23 h observed in the South China Sea CHEN Liang1, 2, 3, ZHENG Quanan4, XIONG Xuejun2, 3*, YUAN Yeli1, 2, 3, XIE Huarong2, 3 1 College of Oceanic and Atmospheric Sciences, Ocean University of China, Qingdao 266100, China 2 The First Institute of Oceanography, State Oceanic Administration, Qingdao 266061, China 3 Functional Laboratory for Regional Oceanography and Numerical Modeling, Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao 266237, China 4 Department of Atmospheric and Oceanic Science, University of Maryland, College Park, Maryland 20742, USA

The empirical mode decomposition and the Hilbert spectrum for nonlinear and non-stationary time series analysis

Abstract: A new method for analysing nonlinear and non-stationary data has been developed. The key part of the method is the empirical mode decomposition method with which any complicated data set can be dec...

Ensemble empirical mode decomposition: a noise-assisted data analysis method

Abstract: A new Ensemble Empirical Mode Decomposition (EEMD) is presented. This new approach consists of sifting an ensemble of white noise-added signal (data) and treats the mean as the final true result. Finite, not infinitesimal, amplitude white noise is necessary to force the ensemble to exhaust all possible solutions in the sifting process, thus making the different scale signals to collate in the proper intrinsic mode functions (IMF) dictated by the dyadic filter banks. As EEMD is a time–space analysis method, the added white noise is averaged out with sufficient number of trials; the only persistent part that survives the averaging process is the component of the signal (original data), which is then treated as the true and more physical meaningful answer. The effect of the added white noise is to provide a uniform reference frame in the time–frequency space; therefore, the added noise collates the portion of the signal of comparable scale in one IMF. With this ensemble mean, one can separate scales naturall...

Variational Mode Decomposition

Abstract: During the late 1990s, Huang introduced the algorithm called Empirical Mode Decomposition, which is widely used today to recursively decompose a signal into different modes of unknown but separate spectral bands. EMD is known for limitations like sensitivity to noise and sampling. These limitations could only partially be addressed by more mathematical attempts to this decomposition problem, like synchrosqueezing, empirical wavelets or recursive variational decomposition. Here, we propose an entirely non-recursive variational mode decomposition model, where the modes are extracted concurrently. The model looks for an ensemble of modes and their respective center frequencies, such that the modes collectively reproduce the input signal, while each being smooth after demodulation into baseband. In Fourier domain, this corresponds to a narrow-band prior. We show important relations to Wiener filter denoising. Indeed, the proposed method is a generalization of the classic Wiener filter into multiple, adaptive bands. Our model provides a solution to the decomposition problem that is theoretically well founded and still easy to understand. The variational model is efficiently optimized using an alternating direction method of multipliers approach. Preliminary results show attractive performance with respect to existing mode decomposition models. In particular, our proposed model is much more robust to sampling and noise. Finally, we show promising practical decomposition results on a series of artificial and real data.

Accumulation and fragmentation of plastic debris in global environments.

Abstract: One of the most ubiquitous and long-lasting recent changes to the surface of our planet is the accumulation and fragmentation of plastics. Within just a few decades since mass production of plastic...

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...