Dust supply from river floodplains: the case of the lower Huang He (Yellow River) recorded in a loess–palaeosol sequence from the Mangshan Plateau

The Mangshan Plateau is located on the south bank of the Huang He (Yellow River) just west of the city of Zhengzhou, well outside the Loess Plateau in central China. Mixing models of the grain‐size data indicate that the loess deposits are mixtures of three loess components. Comparison of the mixing model with existing models established for a series of loess–palaeosol sequences from the Loess Plateau indicates that the Mangshan loess has been supplied from a proximal dust source, the Huang He floodplain, during major dust outbreaks. The high accumulation rates, the composition of the loess components, and especially the high proportions of a sandy loess component support this. Owing to the exceptionally high accumulation rates, the Mangshan grain size, magnetic susceptibility and carbonate records provide a high‐resolution archive of environmental and climate change. Copyright © 2008 John Wiley & Sons, Ltd.     

Laboratory studies of the interaction of carbon monoxide with water ice

The interaction of carbon monoxide (CO) with vapour-deposited water(H₂O) ices has been studied using temperature programmed desorption (TPD) and Fourier transform reflection-absorption infrared spectroscopy (FT-RAIRS) over a range of astrophysically relevant temperatures. Such measurements have shown that CO desorption from amorphous H₂Oices is a much more complex process than current astrochemical models suggest. Re-visiting previously reported laboratory experiments (Collings et al., 2003), a rate model has been constructed to explain, in a phenomenological manner, the desorption of CO over astronomically relevant time scales. The model presented here can be widely applied to a range of astronomical environments where depletion of CO from the gas phase is relevant. The model accounts for the two competing processes of CO desorption and migration, and also enables the entrapment of some of the CO in the ice matrix and its subsequent release as the water ice crystallises and then desorbs. The astronomical implications of this model are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Characterization of microbial communities associated with African desert dust and their implications for human and ecosystem health

Desert winds aerosolize several billion tons of soil-derived dust each year, including concentrated seasonal pulses from Africa and Asia. Huge dust events create an atmospheric bridge over continents and oceans, and eject a large pulse of soil-associated microorganisms into the atmosphere. These dust events might therefore have a role in expanding the biogeographical range of some microorganisms by facilitating rare long-distance dispersal events. The goal of this study is to characterize the microbes associated with African dust events and determine if they pose a risk to humans or downwind ecosystems. Air samples were collected by vacuum filtration in a source region （Mali, West Africa） during dust events and plated on R2A media to culture microorganisms. These organisms were compared to those in similar samples collected in the Caribbean during Saharan/Sahelian dust events. A high-volume liquid impinger is currently being tested in Barbados, collecting aerosol samples during African dust events. Over 100 bacteria and fungi （19 genera of bacteria and three genera of fungi） have been characterized from source region dust events.     

Regional characteristics of dust events in China

The regional characteristics of dust events in China has been mainly studied by using the data of dust storm, wind-blown sand and floating dust from 338 observation stations through China from 1954 to 2000. The results of this study are as follows: (1) In China, there are two high frequent areas of dust events, one is located in the area of Minfeng and Hotan in the South Xinjiang Basin, the other is situated in the area of Minqin and Jilantai in the Hexi Region. Furthermore, the spatial distributions of the various types of dust events are different. The dust storms mainly occur in the arid and semiarid areas covering the deserts and the areas undergoing desertification in northern China. Wind-blown sand and floating-dust not only occur in the areas where dust storms occur, but also extend to the neighboring areas. The range of wind-blown sand extends northeastward and southeastward, but floating-dust mainly extends southeastward to the low-latitude region such as the East China Plain and the area of the middle and lower reaches of the Yangtze River. Compared with wind-blown sand, the floating-dust seldom occurs in the high latitude areas such as North Xinjiang and Northeast China. (2) The affected areas of dust storms can be divided into seven sub-regions, that is, North Xinjiang Region, South Xinjiang Region, Hexi Region, Qaidam Basin Region, Hetao Region, Northeastern China Region and Qinghai-Xizang (Tibet) Region. The area of the most frequent occurrence of dust storms and floating-dust is in South Xinjiang Region, and of wind-blown sand in the Hexi Region. In general, the frequency of dust events in all the seven regions shows a decreasing tendency from 1954 to 2000, but there are certain differences between various dust events in different regions. The maximum interannual change and variance of dust events during this time happened in South Xinjiang Region and Hexi Region. The dust events generally occur most frequently in April in most parts of China. The spring occurred days of dust events occupied 60-70% of the whole year in Hetao Region and Northeastern China Region. However, in South Xinjiang Region and North Xinjiang Region, which was less affected by monsoon climate, dust events may occur at any time of the year, less than 50% of the events in this region occur during spring. In the remaining three regions 50-60% of the dust events occur in spring of a year.     

Magnetostratigraphy and palaeoclimate of Red Clay sequences from Chinese Loess Plateau

Two Red Clay profiles near Xi’an and Xifeng were investigated in an attempt to determine magnetostratigraphic and palaeoclimatic records. The results show that aeolian dust accumulation and the related East Asia palaeomonsoon system had begun by 6.5 Ma, and it is deduced that the Tibetan Plateau had reached a significant elevation at that time. The late Tertiary palaeoclimatic history of the Red Clay as reflected by magnetic susceptibility is reconstructed during the period of 6.5–2.5 Ma. Stepwise increase in susceptibility of aeolian dust accumulation appears to have a close correlation to the uplift processes of the Tibetan Plateau. The remarkable increase of aeolian dust accumulation at 3.2 Ma appears to be due to the influence of global ice volume on the East Asia monsoon. Palaeomonsoon variation during the late Tertiary as recorded in the Red Clay sequences from the Chinese Loess Plateau can be regarded as the product of a number of interacting factors, such as uplift of the Tibetan Plateau, solar radiation, global ice volume, etc. Project supported by the National Natural Science Foundation of China and the Foundation of Xi’an Laboratory of Loess and Quaternary Geology, Chinese Academy of Sciences.     

沈阳地区沙尘天气分析

本文总结了沈阳地区沙尘天气的时空分布特点，从天气条件、地表自然条件(沙源)两方面分析了沈阳地区沙尘天气的成因，总结了沈阳地区预报沙尘天气时应参考的5个因素。     

北京地区两次沙尘(暴)天气过程对比分析

通过对 2 0 0 0年 4月 6日和 4月 9日北京地区两次沙尘 (暴 )天气过程的对比分析认为 :蒙古气旋型和不伴有气旋的西北槽型所造成的北京沙尘天气的严重程度不同 ;沙源地区中低层较强上升运动的主要作用是将当地沙尘垂直输送到空中 ,然后在70 0hPa较强西北气流的引导下将卷起的沙尘水平输送到下游地区 ;不稳定层结又加强了沙尘天气 ;沙尘暴区上空z 螺旋度分布的特征是高层为负值 ,低层为正值 ,对流层中低层螺旋度正的大值区与卫星云图显示的沙尘暴区具有较好的一致性 ,对沙尘暴的预报有一定的指示意义     

Vertical dynamic and thermodynamic characteristics of urban lower boundary layer and its relationship with aerosol concentration over Beijing

By utilizing observational data from a 325 m tower of the Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences (CAS) on March 19-29, 2001 and August 11-25, 2003, a comprehensive study was conducted on the vertical dynamical and thermodynamic characteristics of the urban lower boundary layer (ULBL) and its relationship with aerosol concentration over Beijing. Firstly, a comparative analysis was made on the gradient data (wind, temperature and humidity), ultrasonic data (atmospheric turbulences) and air-quality observations at different tower heights (47, 120 and 280 m). Secondly, a diagnosis was made to reveal the major features of normalized variances of velocity and temperature, turbulence kinetic energy as well as their relationship with aerosol concentrations. Furthermore, the characteristics of the ULBL vertical structure and the TSP concentration/distribution variations during a sand/dust weather process were also analyzed. The outcome of the study showed that under unstable stratification, the normalized variances of velocity (σu/u*, σv/u*, σw/u*) and temperature (σT/T*) at 47 and 120 m heights fit the Monin-Obukhov similarity (MOS) framework and the fitting formulas were given out accordingly. According to the stratification parameter (z′/L), the stable ULBL could be divided into 2 zones. With z′/L<0.1, it was a weakly stable zone and MOS framework was applicable. The other was a highly stable zone with z′/L>0.1 and the normalized velocity variances tended to increase along with higher stability, but it remained constant for normalized temperature variances. At daytime, the near-surface layer includes two heights of 47 and 120 m, while 280 m has been above it. The ULBL analysis in conjunction with a sand/dust weather process in Beijing in March 2001 indicated that the maximum concentration of Total Suspended Particulates (TSP) at 320 m reached 913.3 μg/m3 and the particles were transported from the upper to lower ULBL, which was apparently related to the development process of a low-level jet and its concomitant strong sinking motion.     

2014年4月大气环流和天气分析

2014年4月大气环流特征为,北半球极涡呈单极型分布,中心位于喀拉海北端附近;亚洲大陆东部高压脊强度偏强,导致4月我国气温较常年同期(11.0℃)偏高1.1℃,为1961年同期以来第五高值。东亚大槽强度和位置、南支系统和西北太平洋副热带高压接近常年平均状况。4月全国平均降水量为43.7 mm,比常年同期略偏少。月内,江南南部和华南等地出现短时强降水、雷雨大风等强对流天气;北方地区出现多次沙尘天气过程;此外,部分站次出现极端高温、极端降温事件。