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Zhu X.-H.,State Key Laboratory of Satellite Ocean Environment DynamicsSecond Institute of Oceanography
Journal of Geophysical Research C: Oceans | Year: 2015

Temperature variations caused by a typhoon were measured in the northern part of Hiroshima Bay by four coastal acoustic tomography (CAT) systems. The horizontal distributions of depth-averaged temperature from 0 to 8 m were mapped at 10 min intervals between the 11 and 25 September 2013. The horizontal distributions of a coastal upwelling and the associated diurnal internal tides were reconstructed well by regularized inversion based on the grid segmented method, using one-way travel time data along five successful sound transmission lines. Station-to-station ranges were corrected in such a way that sound speed (determined from one-way travel time data) was equal to sound speed calculated from a couple of CTD (conductivity-temperature-depth) data sets on each transmission line. In addition, all station positions were adjusted to make focal points at the geographical positions of the transducers. The corrections increased the accuracy of temperature measurements to make temperature errors as small as 0.073-0.079°C. The high accuracy made it possible to map the temperature structure with a variation range of less than 0.5°C. An upwelling grew from 16 to 17 September, due to a typhoon-derived northerly wind. The diurnal internal tide resonated with the semidiurnal external tide, which was pronounced after the upwelling decayed (18 September), around the time the spring tide occurred. The upwelling and mixing fractions were formulated. These fractions increased continuously as the upwelling grew. Complete mixing was observed during the upwelling's mature phase. © 2015. American Geophysical Union.


Yan Y.,State Key Laboratory of Satellite Ocean Environment DynamicsSecond Institute of Oceanography | Wang G.,State Key Laboratory of Satellite Ocean Environment DynamicsSecond Institute of Oceanography | Wang C.,National Oceanic and Atmospheric Administration | Su J.,State Key Laboratory of Satellite Ocean Environment DynamicsSecond Institute of Oceanography
Journal of Geophysical Research C: Oceans | Year: 2015

Low-salinity water with two cores is found off West Luzon Island in the South China Sea (SCS) during summer. A series of salinity observations and model results show that the low-salinity water begins to appear in June, reaches its lowest salinity in September, and disappears after October. Rainfall associated with the summer monsoon impinging on the Philippine mountain ranges plays an important role in the formation of the low-salinity water, while upward Ekman pumping of high-salinity subsurface water caused by the strong winter monsoon is important for its disappearance. Variation in mixed layer depth is responsible for the formation of the two cores of the low-salinity water, while advection also contributes. The study further demonstrates that the low-salinity water has considerable interannual variability associated with El Niño-Southern Oscillation (ENSO): during the summer of the decaying year of an El Niño, an anticyclonic wind anomaly occurs in the SCS. The anticyclonic wind anomaly is associated with a northeasterly anomaly south of 18°N, reducing precipitation and causing salting of the low-salinity water off West Luzon Island. The situation is reversed during the summer of the decaying year of a La Niña. © 2015. American Geophysical Union. All Rights Reserved.


Shen Z.,State Key Laboratory of Satellite Ocean Environment DynamicsSecond Institute of Oceanography | Tang Y.,University of Northern British Columbia
Journal of Advances in Modeling Earth Systems | Year: 2015

The ensemble Kalman particle filter (EnKPF) is a combination of two Bayesian-based algorithms, namely, the ensemble Kalman filter (EnKF) and the sequential importance resampling particle filter (SIR-PF). It was recently introduced to address non-Gaussian features in data assimilation for highly nonlinear systems, by providing a continuous interpolation between the EnKF and SIR-PF analysis schemes. In this paper, we first extend the EnKPF algorithm by modifying the formula for the computation of the covariance matrix, making it suitable for nonlinear measurement functions (we will call this extended algorithm nEnKPF). Further, a general form of the Kalman gain is introduced to the EnKPF to improve the performance of the nEnKPF when the measurement function is highly nonlinear (this improved algorithm is called mEnKPF). The Lorenz '63 model and Lorenz '96 model are used to test the two modified EnKPF algorithms. The experiments show that the mEnKPF and nEnKPF, given an affordable ensemble size, can perform better than the EnKF for the nonlinear systems with nonlinear observations. These results suggest a promising opportunity to develop a non-Gaussian scheme for realistic numerical models. © 2014. The Authors.


Mao Z.,State Key Laboratory of Satellite Ocean Environment DynamicsSecond Institute of Oceanography | Pan D.,State Key Laboratory of Satellite Ocean Environment DynamicsSecond Institute of Oceanography | Tang C.L.,Bedford Institute of Oceanography | Tao B.,State Key Laboratory of Satellite Ocean Environment DynamicsSecond Institute of Oceanography | And 7 more authors.
Journal of Geophysical Research: Oceans | Year: 2016

The concentration of total suspended matter (TSM) at the sea surface is derived from satellite data using a complex proxy TSM model in East China Sea from 1997 to 2008. The structure of the mean TSM image is similar to that of the topography, indicating that the distribution of the surface concentration is strongly related to the water depth. A dynamic sediment model (DSM) is constructed to relate the TSM concentration at the sea surface with suspended sediment at the benthic boundary layer, the Rouse number, and the water depth. The DSM model is improved through iteration with a convergence identified by the mean relative difference between two adjacent bottom TSM images which becomes smaller with the more iterations and the value is less than 1% after 50 iterations. The performance of the DSM model is validated by satellite-measured concentration with a mean relative error of 5.2% for the monthly mean images. The DSM model is used to deduce the bottom TSM concentration at the benthic boundary layer and the distribution of the Rouse number. The spatial distribution of the sea surface TSM concentration is determined predominately by both the bottom suspended sediment concentration and water depth. The temporal variation of the sea surface concentration mainly depends upon the Rouse number in the water column. Our result shows that the discharge of the Changjiang River can change the distribution of the Rouse number to form a band-shaped region in the Changjiang Estuary. The DSM model provides a framework for understanding some of the mechanisms of the formation and variation of the primary TSM plume and the secondary plume in the ECS. The primary TSM plume corresponds approximately to the region with depth shallower than 20 m and the secondary plume corresponds to the region with depths between 20 and 50 m. © 2016. American Geophysical Union. All Rights Reserved.


Yan X.,Chinese Academy of Sciences | Zhu X.-H.,State Key Laboratory of Satellite Ocean Environment DynamicsSecond Institute of Oceanography | Pang C.,Chinese Academy of Sciences | Zhang L.,Chinese Academy of Sciences
Journal of Geophysical Research: Oceans | Year: 2016

Using satellite altimeter data and a long-term altimetric transport index for the Kuroshio inflow northeast of Taiwan, the effects of mesoscale eddies on the Kuroshio volume transport (KVT) at the East Taiwan Channel and the branching pattern of the Kuroshio east of Taiwan are investigated at scales from those of individual events to interannual timescales. Both anticyclonic and cyclonic eddies are found to be able either to strengthen or weaken the KVT, depending on the relative strength of mass convergence and divergence produced upstream and downstream of the eddies. The major factor influencing the intensity of the Kuroshio inflow is the meridional location of the eddies. For single eddy events, the KVT is significantly correlated with the latitude of the eddy's center, the correlations being 0.44 and -0.48 for anticyclonic and cyclonic eddies, respectively. For dipole eddy events, when the direction angle falls in the interval 40-150° (240-300°), the KVT anomaly tends to be positive (negative). Furthermore, low KVT events generally correspond to the formation of the Ryukyu Current branch, which is also generated from strong mass divergence produced by the eddies. In addition, on interannual timescales, the variation of KVT is closely related to the relative number of anticyclonic to cyclonic eddies west of 125°E, with a correlation of 0.5. © 2016. American Geophysical Union. All Rights Reserved.


Zhao R.,State Key Laboratory of Satellite Ocean Environment DynamicsSecond Institute of Oceanography | Zhu X.-H.,State Key Laboratory of Satellite Ocean Environment DynamicsSecond Institute of Oceanography
Journal of Geophysical Research: Oceans | Year: 2016

During the winter of 2015-2016, the strongest El Niño event of the twenty-first century occurred. At the same time, volume transport (VT) time series of the South China Sea western boundary current (SCSWBC) exhibited a minimum value of 3.7 Sv (1 Sv=1 × 106 m3 s-1) toward the southwest, indicating the weakest strength ever recorded in boreal winter (from November to February). The South China Sea (SCS) cyclonic gyre, inferred from the satellite-derived surface absolute geostrophic current, was significantly reduced. It was considered that the weakened wind stress curl (negative anomaly) over the SCS resulting from an anticyclone over the Philippine Sea played an essential role. The anticyclone arose from a Rossby-wave response to a negative sea surface temperature anomaly in the northwest Pacific. This idea is further supported by composite analysis, which shows that during El Niño (La Niña) winter, negative (positive) wind stress curl anomalies prevail in the Philippine Sea and the SCS; thus, the wind stress curl over the SCS is reduced (strengthened), leading to a weaker (stronger) SCS cyclonic gyre and SCSWBC. The mean VT of SCSWBC is 4.7 Sv (5.6 Sv), which is smaller (larger) than 5.2 Sv in normal years. This study provides robust observational evidence from long-term in situ volume transport monitoring that El Niño can have a significant impact on the SCSWBC through an atmosphere-bridged teleconnection. © 2016. American Geophysical Union. All Rights Reserved.

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