Coastal upwelling along the north coast of Papua New Guinea and SST cooling over the pacific warm pool: A case study for the 2002/03 El Niño event

We investigate an overlooked mechanism—coastal upwelling—for sea surface temperature (SST) cooling in the western side of the mean location of the Pacific warm pool (WSWP: 5°S–5°N, 140°E–150°E) prior to El Niño onset. We analyze various observed data such as the TRIangle Trans-Ocean buoy Network (TRITON) moored buoy data, Conductivity-Temperature-Depth (CTD) data, satellite data and a hindcast experiment output by a high-resolution ocean general circulation model (OGCM). We focus on the precondition of the 2002/03 El Niño event, for which many datasets are available. Relatively cool water upwelled along the north coast of Papua New Guinea (PNG) during December 2001, prior to the onset of the 2002/03 El Niño event, and then spread out over a wider area to the northeast. Simultaneously, strong west-northerly surface winds occur along the north coast. Heat budget analysis of TRITON buoy data in the WSWP reveals that negative zonal heat advection due to eastward current is the main factor for cooling the mixed layer in the WSWP in contrast to the warming effect of the surface heat flux during the period. This cooling requires a source of colder water to the west. Similar analysis of OGCM outputs also suggests that the upwelled relatively cool water along the PNG north coast, and its northeastward extension to the equatorial region, contributes to cooling of the surface water over the WSWP mainly via negative zonal heat advection. Similar mechanisms are confirmed also for the 1982/83 and 1997/98 El Niño events by analyses of OGCM outputs and historical SST data. The low SST in the WSWP generated a positive zonal SST gradient together with high SST east of the WSWP. It may contribute to enhancement of the westerly surface wind in this region, leading to the onset of the 2002/03 El Niño event.     

Bathymetry enhancement by altimetry-derived gravity anomalies in the East Sea (Sea of Japan)

The gravity-geologic method (GGM) was used to enhance the bathymetry of the East Sea (Sea of Japan) with satellite altimetry-derived free-air gravity anomalies and shipborne depth measurements. By comparison with the bathymetry model of Smith and Sandwell’s (SAS) approach (1994), GGM was found to have an advantage with short wavelength (≤12 km) components, while SAS better predicts longer wavelength (≥25 km) components, despite its dependency on density contrast. To mitigate this limitation, a tuning density contrast of 10.25 g/cm³ between seawater and the seafloor was primarily estimated by the downward continuation method and then validated by the check points method with GGM. Similarly, SAS is limited by the “A” value in low-pass part of the Wiener filter, which defines the effective range of the wavelength components on bathymetry. As a final result, we present an enhanced GGM bathymetry model by integrating all available data.     

Trend and dynamic cause of sediment particle size on the adjacent continental shelf of the Yangtze Estuary

Based on the measured data in recent 20 years, the variation trends of the median grain size of the surface sediment, the sand-silt boundary and the mud area on the adjacent continental shelf of the Yangtze Estuary were analyzed in depth, and the effects of natural mechanism and human activities were discussed. The results show that:(1) In recent years(2006-2013), the median grain size of sediment and the distribution pattern of grouped sediments in the adjacent continental shelf area to the Yangtze Estuary have presented no obvious change compared with those before 2006;(2) The median diameter of the surface sediment in the continental shelf area displayed a coarsening trend with the decrease of sediment discharge from the basin and the drop in suspended sediment concentration in the shore area;(3) In 2004-2007, the sand-silt boundary in the north part(31°30′N) of the continental shelf area presented no significant changes, while that in the south part(31°30′S) moved inwards; In 2008-2013, both the sand-silt boundaries in the north and south parts of the continental shelf area moved inwards, mainly due to the fact that in the dry season, a relatively enhanced hydrodynamic force of the tides was generated in the Yangtze River, as well as a decreased suspended sediment concentration and a flow along the banks in North Jiangsu;(4) The mud area where the maximum deposition rate is found in the Yangtze Estuary, tends to shrink due to the drop in sediment discharge from the basin, and the decrease in suspended sediment concentration in the shore area and erosion in the delta. Moreover, it tended to shift to the south at the same time because the implement of the training works on the deep-water channel of the North Passage changed the split ratio between the North and South Passages with an increase in the power of the discharged runoff in the South Passage.     

Managing land-use effects on Northland dune lakes: lessons from the past

The Northland region of New Zealand includes numerous high-value, macrophyte-dominated dune lakes. Recent water policy reforms offer limited guidance on managing for aquatic macrophytes. In addition, dune lake histories are poorly known as regular monitoring dates to 2005 AD. Here, ca. 4000 years of lake functional behaviour is reconstructed from sedimentary archives in two Northland dune lakes (Humuhumu and Rotokawau). Results demonstrated that macrophyte dominance is sensitive to catchment erosion and hydrological drawdown. Degradation of macrophyte communities occurred in the nineteenth and twentieth centuries, earlier at Lake Humuhumu than Lake Rotokawau (post-1880 AD and post-1930 AD, respectively). In both lakes, increased erosional influx reduced macrophyte productivity, before later increases to wider trophic state (post-1970 AD). Lake-level decline is linked to increased nutrient loading at Lake Rotokawau but less so, Lake Humuhumu which is more strongly groundwater-fed. In Northland dune lakes, water-level reduction and erosional influx from land use have driven macrophyte degradation.     

High-frequency ocean radar derived characteristics of sea surface currents in the Ariake Sea,Japan

Composite analysis was conducted using high-frequency radar data obtained during 2006–2015 in order to gain a better understanding of the current field in the Ariake Sea. The seasonally averaged surface current in the Ariake Sea was directed southward in all seasons, except around river mouths during summer. Heavy rainfall enhanced the outflow along the eastern coast of the Shimabara Peninsula from Isahaya Bay to the southern area 2–5 days after heavy rainfall. Spring–neap differences were clearly seen in the southward current along the Shimabara Peninsula. Interannual variation in the M₂ tidal current amplitude was synchronized with the lunar nodal cycle.     

Free Vibration Analysis of Symmetrically Laminated Composite Plates on Elastic Foundation and Coupled with Stationary Fluid

Free vibration analysis of symmetrically laminated composite plates resting on Pasternak elastic support and coupled with an ideal, incompressible and inviscid fluid is the objective of the present work. The fluid domain is considered to be infinite in the length direction but bounded in the depth and width directions. In order to derive the eigenvalue equation, Rayleigh-Ritz method is applied for the fluid-plate-foundation system. The efficiency of the method is proved by comparison studies with those reported in the open literature. At the end, parametric studies are carried out to examine the impact of different parameters on the natural frequencies.     

Optimization Design of Minimum Total Resistance Hull Form Based on CFD Method

In order to reduce the resistance and improve the hydrodynamic performance of a ship, two hull form design methods are proposed based on the potential flow theory and viscous flow theory. The flow fields are meshed using body-fitted mesh and structured grids. The parameters of the hull modification function are the design variables. A three-dimensional modeling method is used to alter the geometry. The Non-Linear Programming (NLP) method is utilized to optimize a David Taylor Model Basin (DTMB) model 5415 ship under the constraints, including the displacement constraint. The optimization results show an effective reduction of the resistance. The two hull form design methods developed in this study can provide technical support and theoretical basis for designing green ships.     

Experimental Study on Sloshing Characteristics in the Elastic Tank Based on Morlet Wavelet Transform

Hydroelastic effect of sloshing is studied through an experimental investigation. Different excitation frequencies are considered with low-fill-depth and large amplitude. Morlet wavelet transform is introduced to analyze the free surface elevations and sloshing pressures. It focuses on variations and distributions of the wavelet energy in elastic tanks. The evolutions of theoretical and experimental wavelet spectra are discussed and the corresponding Fourier spectrums are compared. Afterwards, average values of the wavelet spectra are extracted to do a quantitative study at various points. From the wavelet analysis, sloshing energies are mainly distributed around the external excitation frequency and expanded to high frequencies under violent condition. In resonance, experimental wavelet energy of the elevation in elastic tanks is obviously less than that in the rigid one; for sloshing pressures, the elastic wavelet energy close to the rigid one and conspicuous impulse is observed. It recommends engineers to concern the primary natural frequency and impulsive peak pressures.     

Lateral Bearing Capacity of Modified Suction Caissons Determined by Using the Limit Equilibrium Method

The modified suction caisson (MSC) adds a short-skirted structure around the regular suction caissons to increase the lateral bearing capacity and limit the deflection. The MSC is suitable for acting as the offshore wind turbine foundation subjected to larger lateral loads compared with the imposed vertical loads. Determination of the lateral bearing capacity is a key issue for the MSC design. The formula estimating the lateral bearing capacity of the MSC was proposed in terms of the limit equilibrium method and was verified by the test results. Parametric studies on the lateral bearing capacity were also carried out. It was found that the lateral bearing capacity of the MSC increases with the increasing length and radius of the external skirt, and the lateral bearing capacity increases linearly with the increasing coefficient of subgrade reaction. The maximum lateral bearing capacity of the MSC is attained when the ratio of the radii of the internal compartment to the external skirt equals 0.82 and the ratio of the lengths of the external skirt to the internal compartment equals 0.48, provided that the steel usage of the MSC is kept constant.