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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.


Papers
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Journal ArticleDOI
TL;DR: In this paper, the vector empirical orthogonal function (VEOF) method was used to process the wind data set and extract principal modes of the wind fields, which can lead to better understanding of ENSO events.
Abstract: The variation of the Walker circulation is closely related to the onset of El Nino-Southern Oscillation (ENSO) events [Kousky, 1984], so observing the Walker circulation can lead to better understanding of ENSO events. Wind data from the NASA Scatterometer (NSCAT), Quick Scatterometer (QuikSCAT), and European Remote Sensing Satellite-1/2 (ERS-1/2) were merged into one data set in a 1°×1° grid covering a period from January 1992 to December 2000. The study region was confined to the tropical oceans between 20°S and 20°N. The vector empirical orthogonal function (VEOF) method [Hardy and Walton, 1978] was used to process the wind data set and extract principal modes of the wind fields.

5 citations

Journal ArticleDOI
TL;DR: In this paper, the authors observed two packets of orderly wave clouds on two sides of Hainan Island in the South China Sea and found new evidence of the coexistence of both upstream and downstream solitary wavetrains generated in the real atmosphere by land topographic disturbances.
Abstract: From a true colour image of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) onboard the Orbview-2 satellite, we observed two packets of orderly wave clouds on two sides of Hainan Island in the South China Sea. A packet of 23 wave clouds stretches southward from the island. A second packet of more than 20 wave clouds stretches north-eastward off the north-east coast of the island. The concave orientation of the wave cloud lines implies that both packets are propagating away from the island. A chart of geopotential height and velocity at 850 mbar shows a south-westerly air flow over the island; hence the two wave cloud packets propagate upstream and downstream, simulta- neously. Thus, we have found new evidence of the coexistence of both upstream and downstream solitary wavetrains generated in the real atmosphere by land topographic disturbances. Comparison with theoretical results supports this conclusion.

5 citations

Journal ArticleDOI
TL;DR: In this paper, a new type of overshoot phenomenon is identified, which occurs at gravity-capillary wavelengths, is practically a function of local wind stress only and is referred to as the Overshoot phenomenon of the third kind.
Abstract: Laboratory measurements using both wave probes (contact and optical) and radar confirm the existence of a new type of overshoot phenomenon in the wind-wave development processes. This type of overshoot, which occurs at gravity-capillary wavelengths, is practically a function of local wind stress only. It is named the overshoot phenomenon of the third kind. With the existence of this overshoot it becomes obvious that the assumed simple power-law relationship between the rms value of surface slope at a fixed wavelength and the wind stress is untenable. Since such a relationship is one of the key assumptions invoked in the development of algorithms used in scatterometry, the published scatterometer data are reexamined, pointing out the implications of this overshoot phenomenon. Recommendations for improvement of the performance of the scatterometer are also made in light of this new understanding of the wind-wave development processes.

5 citations

Journal ArticleDOI
TL;DR: In this article, a pattern recognition method and a spatial integration filtering method have been developed to analyze satellite altimeter sea surface elevation anomaly (SSEA) data for the tropical Pacific Ocean.

5 citations


Cited by
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Journal ArticleDOI
TL;DR: In this paper, a new method for analysing nonlinear and nonstationary data has been developed, which is the key part of the method is the empirical mode decomposition method with which any complicated data set can be decoded.
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...

18,956 citations

Journal ArticleDOI
TL;DR: 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.
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...

6,437 citations

Journal ArticleDOI
TL;DR: This work proposes an entirely non-recursive variational mode decomposition model, where the modes are extracted concurrently and is a generalization of the classic Wiener filter into multiple, adaptive bands.
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.

4,111 citations

Journal ArticleDOI
TL;DR: Global plastics production and the accumulation of plastic waste are documented, showing that trends in mega- and macro-plastic accumulation rates are no longer uniformly increasing and that the average size of plastic particles in the environment seems to be decreasing.
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...

4,044 citations

01 Jan 1989
TL;DR: In this article, 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.
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...

3,813 citations