This paper investigates the impact of the Madden-Julian Oscillation (MJO) on the diurnal cycle of rainfall over the western Maritime Continent during the austral summer. For this purpose, cyclostationary empirical orthogonal function analysis is applied to the tropical rainfall measuring mission rain rate and the Japanese Reanalysis-25 data for the period 1998–2008. The real-time multivariate MJO index by Wheeler and Hendon (Mon Wea Rev 132:1917–1932, 2004) is adopted to define the intensity and the phase of MJO. It is demonstrated that the hourly maximum rain rate over the domain tends to increase when convectively active phase of MJO approaches the Maritime Continent. In contrast, the hourly maximum rain rate tends to decrease when convectively suppressed phase of MJO resides over the region. The changes in the rain rate due to MJO differ over the ocean and the land. This difference is the greatest when the MJO is in the mature stage. Throughout the day during this stage, terrestrial rain rates show minimum values while diurnally varying oceanic rain rates record maximum values. Thus, precipitation becomes more intense in the morning over the Java Sea and is weakened in the evening over Borneo and Sumatra during the mature stage of MJO. During the decaying stage of MJO over the Maritime Continent, the diurnal cycle of precipitation weakens significantly over the ocean but only weakly over land. Analyses suggest that the anomalous lower level winds accompanied by MJO interact with the monsoonal flow over the Maritime Continent. Westerlies induced by MJO convection in the mature stage are superimposed on the monsoonal westerlies over the equator and increase wind speed mainly over the Java Sea due to the blocking effect of orography. Mountainous islands induce flow bifurcation, causing near-surface winds to converge mainly over the oceanic channels between two islands. As a result, heat flux release from the ocean to the atmosphere is enhanced by the increased surface wind resulting in instability as described in the wind-induced surface heat exchange mechanism. This may contribute to heavy rainfall over the Java Sea in the morning during the mature stage. On the other hand, convergence and vertical velocity over the islands, which play important roles in inducing nighttime rainfall, tend to be weak in the evening during the mature stage of MJO. Strong westerlies arising from MJO and the seasonal flow during the mature stage tend to interrupt convergence over islands. This interruption of convergence by MJO gives rise to decreased rain rates over the land regions. 相似文献
The influence of clay dispersion method on dewatering behaviour of a run-of-mine bentonite was examined to better understand the roles of calcium–sodium ion exchange and overall electrolyte concentration on the suppression of swelling and subsequent stabilisation of the clay. As with previous work, controlled dispersion of the clay directly into a swelling suppressing environment was observed to yield order of magnitude improvements in dewatering behaviour [de Kretser, R.G., Scales, P.J. and Boger, D.V., 1997. Improving clay-based tailings disposal: a case study on coal tailings. AIChE Journal. 43 (7), 1894–1903.]. The calcium ion, even after normalisation for its valence, yielded significantly better clay stabilisation performance than the sodium ion indicating the greater benefit afforded via divalent ion-exchange driven controlled dispersion. However the results also highlighted a synergistic effect of the double layer suppression effect on the efficacy of ion-exchange mediated controlled dispersion through simultaneous swelling suppression and structure preservation during the transient process of ion exchange on hydration. Studies of controlled dispersion in dual ion, Na+ and Ca2+, systems illustrated that although the efficacy of controlled dispersion deteriorated with an increase in the Na+ to Ca2+ ratio, even small amounts of calcium character could generate significant improvements in dewaterability over the pure sodium case. This result was relevant in terms of defining an operational window for the commonly used, but sparingly soluble calcium source, gypsum where the low deliverable calcium level could be more than offset by the controlled dispersion benefits of maintaining a higher overall salinity level. Based on the results presented, the potential impact of practical implementation of a controlled dispersion framework within a mineral processing operation was illustrated via numerical modelling of the operation of a steady state thickener. 相似文献
Tarap peel (TP) and oxalic-acid-modified Tarap peel (TP-OX) were used to remove brilliant green (BG) dye from aqueous solution. Surface modification of TP suggested that functional groups such as carboxyl, hydroxyl and amino were involved in the adsorption of BG onto TP. Parameters such as effects of pH, contact time, ionic strength, initial dye concentration and temperature were included to study the adsorption of BG onto TP and TP-OX. Adsorption isotherm models were used to investigate the adsorption process, while kinetics models were used to provide insight into the adsorption mechanisms. Optimised contact time of 2 h with no pH adjustment was used. Adsorption of BG onto TP was best fitted to the Freundlich model, while experimental data for TP-OX are best described by the Tempkin model. The maximum adsorption capacities were determined as 174 and 275 mg g?1 for TP and TP-OX, respectively. Thermodynamics study indicated the endothermic nature of adsorptions of BG onto both adsorbents. According to kinetics study, the adsorption mechanisms on both adsorbents followed pseudo-second-order model, and film diffusion might have major role in the adsorption process. 相似文献
Diatom densities in the surface water and dinoflagellate cysts in bottom sediments of Gwangyang Bay were studied to determine
changes in the phytoplankton community structure in response to anthropogenic eutrophication and to assess the use of dinoflagellate
cysts as indicators of coastal eutrophication. Our results show that, in nutrient-enriched environments, diatoms are particularly
benefited from the nutrients supplied and, as a consequence, heterotrophic dinoflagellates that feed on the diatoms can be
more abundant than autotrophic dinoflagellates. In short-core sediment records, a marked shift in autotrophic–heterotrophic
dinoflagellate cyst compositions occurred at a depth of approximately 9–10 cm corresponding to the timing of the 1970s industrialization
around Gwangyang Bay. This tentatively indicates that diatom and dinoflagellate communities here have undergone a considerable
change mainly due to increased nutrient loadings from both domestic sewage effluent and industrial pollution. Our study suggests
a possible potential use of dinoflagellate cysts in providing retrospective information on the long-term effects of coastal
eutrophication. 相似文献
Since the discovery of hydrothermal vents in the late 1970s, deep-sea hydrothermal vent fields have attracted great attention as biological hotspots. However, compared with other ocean ridges, the structure and function of microbial communities inhabiting vent fields in the Central Indian ridge (CIR) remain understudied. Here, we provide for the first time 16S rRNA gene-based comparative metagenomic analysis of the sediment-associated microbial communities from three newly discovered vent fields in the CIR. Sediment samples collected in the Invent B, Invent E and Onnuri vent fields varied in geochemical properties, elemental concentrations and associated microbial communities. Proteobacteria (Gammaproteobacteria) was the dominant phylum in Invent B and Onnuri vent fields. In contrast, Invent E mainly consisted of Chloroflexi and Euryarchaeota. Predicted functional profiling revealed that the microbial communities in the three vents are dominated by chemoheterotrophic functions. In addition, microbial communities capable of respiration of sulfur compounds, nitrification, nitrite oxidation, methylotrophy, and methanotropy were found to be the main chemolithoautotrophs. Compared to other vent fields, Invent E showed a predominance of archaeal methanogens suggesting it exhibits slightly different geochemistry. Multivariate analysis indicated that the biogeochemical and trace metal differences are reflected in the sediment microbial compositions of the three vent fields. This study expands our current understanding of the microbial community structure and potential ecological functions of the newly discovered hydrothermal vent fields in the CIR.
This study examined tidal modification and change in tidal currents caused by the construction of the Saemangeum dike, based
on field observations and a numerical model. The Saemangeum dike was completed in April 2006, enclosing an estuarine area
along the mid-western coast of South Korea. After closure of the dike, the tidal range outside the dike decreased slightly
but significantly, while the inside tidal range decreased drastically. The numerical model results show that the dike construction
has influenced tidal energy propagation and the tidal system in the Yellow Sea. The tidal current speed near the dike decreased
abruptly following closure of the dike, except in front of the sluice gates. Since completion of the dike, outflow water discharged
from the sluice gates has longer residence times due to the weakened tidal current; the change in the tidal current field
has also caused greater northward expansion of outflow water. The sluice gates release fresher water, which spreads over the
sea surface mainly by inertial momentum near the gate; this water is then gradually mixed with sea water farther from the
gate. The less saline, possibly more contaminated outflow impacts the marine environment near the Saemangeum dike. Controlling
the discharge and gate-opening timing can partially mitigate these impacts on the marine environment. 相似文献
Settlement of the surrounding soil due to surcharge placement may give rise to negative skin friction developed in piles. In this paper, a simple discrete element approach using subgrade reaction method is proposed to analyse negative skin friction on single piles. The pile is embedded in a two-layer soil where the upper soil layer undergoes consolidation while the lower soil layer acts as a stiffer bearing stratum. Two different and uncoupled deformation modes, one at the pile shaft and the other at the pile toe have been assumed in the determination of the soil stiffness. The effects of a compressible bearing stratum and embedment length of the pile in the bearing stratum are considered in the analysis. This simple approach is verified by comparison with rigorous methods of modelling the soil as an elastic continuum. Three reported case histories are analysed and the computed results are shown to be in reasonable agreement with the field measurements. 相似文献