Sand storms: CFD analysis of Reynolds stress and collision stress of particles near sand bed

Sand storm is a serious environmental threat to humans. Sand particles are transported by saltation and suspension, causing soil erosion in one place and deposition in another. In order to prevent and predict sand storms, the causes and the manners of particle motions must be studied in detail. In this paper a standard k-epsilon model is used for the gas phase simulation and the discrete element method (DEM) is used to predict the movements of particles using an in-house procedure. The data are summarized in an Eulerian-Eulerian regime after simulation to get the statistical particle Reynolds stress and particle collision stress. The results show that for the current case the Reynolds stress and the air shear stress predominate in the region 20-250 mm above the initial sand bed surface. However, in the region below 3 mm, the collision stress must be taken into account in predicting particle movement. (C) 2010 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.

A 10,000 year record of dune activity；dust storms；and severe drought in the central Great Plains

IEECAS SKLLQG

The evolution of chemical components of aerosols at five monitoring sites of China during dust storms

IEECAS SKLLQG

Chemical composition of dust storms in Beijing and implications for the mixing of mineral aerosol with pollution aerosol on the pathway

IEECAS SKLLQG

Using the RBFN model and GIS technique to assess wind erosion hazard of inner Mongolia, China

Soil wind erosion is the primary process and the main driving force for land desertification and sand-dust storms in and and semi-arid areas of Northern China. While many researchers have studied this issue, this study quantified the various indicators of soil wind erosion, using the GIS technology to extract the spatial data and to construct a RBFN (Radial Basis Function Network) model for Inner Mongolia. By calibrating sample data of the different levels of wind erosion hazard, the model parameters were established, and then the assessment of wind erosion hazard. Results show that in the southern parts of Inner Mongolia wind erosion hazards are very severe, counties in the middle regions of Inner Mongolia vary from moderate to severe, and in eastern are slight. Comparison of the results with other research shows conformity with actual conditions, proving the reasonability and applicability of the RBFN model. Copyright (C) 2007 John Wiley & Sons, Ltd.

Sedimentary features of the Yangtze River-derived along-shelf clinoform deposit in the East China Sea

A predominant sigmoidal clinoform deposit extends from the Yangtze River mouth southwards 800 kin along the Chinese coast. This clinoform is thickest (similar to 40m) between the 20 and 30 m isobaths and progressively thins offshore, reaching water depths of 60 and 90 m and distances up to 100 km offshore. Clay mineral, heavy metal, geochemical and grain-size analyses indicate that the Yangtze River is the primary source for this longshore-transported clinoform deposit. Pb-210 chronologies show the highest accumulation rates (> 3 cm/yr) occur immediately adjacent to the Yangtze subaqueous delta (north of 30 degrees N), decreasing southward alongshore and eastward offshore. The interaction of strong tides, waves, the China Coastal Current, winter storms, and offshore upwelling appear to have played important roles in trapping most Yangtze-derived sediment on the inner shelf and transporting it to the south. (c) 2006 Elsevier Ltd. All rights reserved.

Speed ambiguity in hurricane wind retrieval from SAR imagery

Under strong ocean surface wind conditions, the normalized radar cross section of synthetic aperture radar (SAR) is dampened at certain incident angles, compared with the signals under moderate winds. This causes a wind speed ambiguity problem in wind speed retrievals from SAR, because two solutions may exist for each backscattered signal. This study shows that the problem is ubiquitous in the images acquired by operational space-borne SAR sensors. Moreover, the problem is more severe for the near range and range travelling winds. To remove this ambiguity, a method was developed based on characteristics of the hurricane wind structure. A SAR image of Hurricane Rita (2005) was analysed to demonstrate the wind speed ambiguity problem and the method to improve the wind speed retrievals. Our conclusions suggest that a speed ambiguity removal algorithm must be used for wind retrievals from SAR in intense storms and hurricanes.

Effects of winds, tides and storm surges on ocean surface waves in the Sea of Japan

Ocean surface waves are strongly forced by high wind conditions associated with winter storms in the Sea of Japan. They are also modulated by tides and storm surges. The effects of the variability in surface wind forcing, tides and storm surges on the waves are investigated using a wave model, a high-resolution atmospheric mesoscale model and a hydrodynamic ocean circulation model. Five month-long wave model simulations are inducted to examine the sensitivity of ocean waves to various wind forcing fields, tides and storm surges during January 1997. Compared with observed mean wave parameters, results indicate that the high frequency variability in the surface wind filed has very great effect on wave simulation. Tides and storm surges have a significant impact on the waves in nearshores of the Tsushima-kaihyo, but not for other regions in the Sea of Japan. High spatial and temporal resolution and good quality surface wind products will be crucial for the prediction of surface waves in the JES and other marginal seas, especially near the coastal regions.

中低纬度变化磁场的暴时特征研究

Magnetic storm is a kind of severe disturbances in the whole solar-earth electromagnetic space. It has significant effects on communication, electric power, oil transport pipe and human activities in space. Therefore, magnetic storms are worth for applications systems, not only being a favorable issue for scientists. In this paper, the spatial and temporal distributions of the magnetic fields produced by the magnetosphere-ionosphere current systems during storms are studied. Four parts are included in this paper decomposion of different disturbances with different origins, topological structure of the ring current, the asymmetric characteristics of the ring current, and the statistic peculiarities of the day-to-day variability (DTD) of Sq. 1 The decomposition of magnetic disturbances at mid-low latitudes and its evolutions during storms Transient variations in the geomagnetic field recorded at mid-low latitudes mainly include the storm-time variation (Dst), solar quiet daily variation (Sq) and disturbance daily variation (SD). With the data of the geomagnetic meridian chain observatories in China, 25 storms during the period of 1997 to 1999 have been analyzed. According to the features of different variations, a method of “three-steps decomposition” is developed by using the method of Natural Orthogonal Components (NOC), Correlation Analysis and Fourier Analysis to separate those three components in turn. The results show that, the first eigenmode by the MNOC clearly describing the special distribution and temporal evolution of storm-time variation, in addition, Correlation Analysis and Fourier Analysis offer a useful method to extract the Sq and SD variations. The latitudinal shift of the Sq current focus seems to be the principal reason of the day-to-day variaitons in the daily range of Sq. The magnitude of SD reaches a maximum during the main phase, and then gradually decreases. 2 The topology structure of the ring current during storms Both the mechanism of the ring current and the geomagnetic data suggest that the central plane of the ring current is declining to the geomagnetic equator plane with a tilt angle δ. Using the H and Z component data at two stations in a meridian chain, we deduce a new parameter describing the invariable peculiarity of different storms. Then the δ angle is calculated by using the data from a meridian chain and tested with the ERC model. Finally the deduced tilt angles are used to modify Dst index. 3 The asymmetric characteristics of the ring current during storms The variations of the geomagnetic field at mid-low latitudes show a significant dawn-dusk asymmetry, resulting from the superposition of the fields from the symmetric ring current and the partial ring current. On the basis of the data from the 20°E, 30°E meridian chains and 30°N latitudinal chain, the dawn-dusk asymmetry is investigated by using three methods, namely, statistic analysis, ring current model calculation and typical event analysis. This characteristic implies the asymmetry of the spatial distribution of the ring current. In addition, during the main phase after the sudden commencement (SC), H field increases and reaches maximum around noontime, implying the effect of the Chapman-Ferraro current. 4 The statistic characteristics of the day-to-day variability and its mechanism The day-to-day variability of the geomagnetic Sq field is studied by using the magnetic data from a meridian chain of magnetometers along 120° E longitude. The method of NOC is applied to separate the Sq variation from complicated disturbances. The first eigenmode with the largest eigenvalue represents fairly well the Sq variation with a conspicuous day-to-day variability in the daily range. For the stations on the same north- or south-side of the Sq current system focus, the day-to-day variations show a positive correlation. In contrast, for the stations on the different sides of the Sq focus, they show a negative correlation, suggesting an important role of latitudinal shift of the Sq current system focus to the day-to-day variability of the Sq daily range. The Sq daily range is correlated with the magnetic indices Ap and Dst in a peculiar way: on some severe disturbed days, noticeably enhancements of the Sq are observed, implying increases of the ionospheric conductivities and/or tidal wind velocities; on other severe disturbed days, however, dramatically reduced Sq variations occur, suggesting dominant effects of the ‘disturbance dynamo’ process.