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811.
Previous studies suggest that the atmospheric precursor of El Ni ?no–Southern Oscillation(ENSO) in the extratropical Southern Hemisphere(SH) might trigger a quadrapole sea surface temperature anomaly(SSTA) in the South Pacific and subsequently influence the following ENSO. Such a quadrapole SSTA is referred to as the South Pacific quadrapole(SPQ).The present study investigated the relationships between the atmospheric precursor signal of ENSO and leading modes of atmospheric variability in the extratropical SH [including the SH annular mode(SAM), the first Pacific–South America(PSA1) mode, and the second Pacific–South America(PSA2) mode]. The results showed that the atmospheric precursor signal in the extratropical SH basically exhibits a barotropic wavenumber-3 structure over the South Pacific and is significantly correlated with the SAM and the PSA2 mode during austral summer. Nevertheless, only the PSA2 mode was found to be a precursor for the following ENSO. It leads the SPQ-like SSTA by around one month, while the SAM and the PSA1 mode do not show any obvious linkage with either ENSO or the SPQ. This suggests that the PSA2 mode may provide a bridge between the preceding circulation anomalies over the extratropical SH and the following ENSO through the SPQ-like SSTA. 相似文献
812.
A simple method to extract tropical monsoon forests using NDVI based on MODIS data: A case study in South Asia and Peninsula Southeast Asia 总被引:1,自引:0,他引:1
Distribution of monsoon forests is important for the research of carbon and water cycles in the tropical regions. In this paper, a simple approach is proposed to map monsoon forests using the Normalized Difference Vegetation Index(NDVI) derived from the Moderate Resolution Imaging Spectroradiometer(MODIS) data. Owing to the high contrast of greenness between wet season and dry season, the monsoon forest can be easily discriminated from other forests by combining the maximum and minimum annual NDVI. The MODIS-based monsoon forest maps(MODMF) from 2000 to 2009 are derived and evaluated using the ground-truth dataset. The MODMF achieves an average producer accuracy of 80.0% and the Kappa statistic of 0.719. The variability of MODMF among different years is compared with that calculated from MODIS land cover products(MCD12Q1). The results show that the coefficient of variation of total monsoon forest area in MODMF is 7.3%, which is far lower than that in MCD12Q1 with 24.3%. Moreover, the pixels in MODMF which can be identified for 7 to 9 times between 2001 and 2009 account for 53.1%, while only 7.9% of MCD12Q1 pixels have this frequency. Additionally, the monsoon forest areas estimated in MODMF, Global Land Cover 2000(GLC2000), MCD12Q1 and University of Maryland(UMD) products are compared with the statistical dataset at national level, which reveals that MODMF has the highest R2 of 0.95 and the lowest RMSE of 14 014 km2. This algorithm is simple but reliable for mapping the monsoon forests without complex classification techniques. 相似文献
813.
814.
Land surface emissivity is known to be affected by land cover, surface roughness, and soil moisture. In this study we used land surface emissivity data from National Aeronautics and Space Administration's Advanced Microwave Scanning Radiometer for Earth Observing Systems for 2003 to 2007 to detect areas of significant emissivity change and identify its potential causes. Data distribution of annual emissivity averages on a global scale revealed that the western coastlines of the continents, deserts, and the polar areas showed the lowest emissivity values, whereas the higher emissivity values were concentrated in large cities, heavily forested areas, and large mountain ranges. A two-tailed Z test was then used to identify regions that showed statistically significant changes at the 99 percent confidence interval. At the regional scale, three regions that showed statistically significant annual change values at the 99 percent confidence interval—the Iranian Plateau, the La Plata basin, and the Indus basin—were then isolated. An analysis of variance was then performed to determine whether the variability was due to phenomena across the region or within each region. In the La Plata River basin, areas of significant negative emissivity change (≤–0.0156) were noted, which are associated with deforestation, whereas the areas of significant emissivity gain (≥0.0165) were concentrated in floodplains. In the Indus basin and Iranian Plateau, the significant negative emissivity change was associated with variations in surface wetness. Using emissivity as an indicator of land surface properties can assist in more detailed analysis of changes on the surface of the earth. 相似文献
815.
816.
The East Asian Summer Monsoon (EASM) exerts considerable influences on the climate in China. Studying kinetic energy sources of monsoon circulation from the perspective of energetics is critical important to understand monsoon variability and relevant mechanism. The traditional theory of Available Potential Energy (APE) and relevant studies were reviewed, and some limitations of the APE theory in studying regional effective energy cycle and transformation were discussed. A new theory of Perturbation Potential Energy (PPE) of atmospheric circulation, which can be applicable to the study of energy cycle and transformation of regional circulation systems,was introduced. The advantage of the PPE theory in studying regional effective energy cycle and conversion was discussed, and some advances in the role of the PPE in variability of the EASM were further reviewed. At the end, some important scientific open questions about the application of the PPE to investigations of EASM variability in future were summarized as follows: spatial-temporal characteristics and dominant modes of PPE at seasonal-interannual timescale over the EASM region, and their relationships with the EASM and lower boundary forcings; the physical processes and relevant mechanisms on how lower boundary forcings affecting the kinetic energy of EASM circulation through the key link of PPE; the preceding PPE signals associated with EASM variations, relevant underlying mechanisms, and predictability of the preceding PPE signals as well. 相似文献
817.
818.
819.
E. Hong C. M. Herbert A. M. Yeneneh T. K. Sen 《International Journal of Environmental Science and Technology》2016,13(11):2629-2638
Significant amount of slurry waste is produced from mineral processing plants globally constituting high levels of both kaolin and sand in aqueous suspension. Large quantities of slurry and mine tailings require efficient handling, transportation and storage system. The transportation and treatment of kaolin–sand slurry is dependent on its rheological behaviour which is a function of temperature, total solid concentration and pH. In this study, the effects of total solid concentration, pH and temperature on rheological behaviour of kaolin–sand mixture were investigated. These parameters were varied to analyse the viscosity, yield stress, flow index and shear force requirements of the mixed kaolin–sand suspension as a function of these varying parameters. Experimental rheological investigation conducted on rotational stress-controlled rheometer equipped with Peltier concentric cylinder system showed that the kaolin–sand mixture suspension is shear thickening in nature. The shear stress-rate rheograms for the kaolin–sand suspension can be modelled by the Herschel–Bulkley model with high levels of accuracy for pH range of 4–11, temperature range of 20–50 °C and solid concentration of 5–50 %. Solid concentration of the suspension was found to significantly affect the rheological behaviour of the mixture where higher kaolin–sand slurry concentration resulted in greater viscosity and the trend becoming less predictable for solid concentration greater than 50 % by weight. pH was another factor affecting the rheological behaviour of kaolin–sand slurry. pH of 3 or less resulted in the dramatic increase of viscosity of the suspension possibly due to the isoelectric point of the mixture system found between pH of 3 and 4. 相似文献
820.