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SUMMARY The relationship between climate and the magnetic properties of surface soils on the Chinese Loess Plateau (CLP) have been widely used to provide the basis for palaeoclimatic reconstruction, based on the underlying loess/palaeosol sequences. To date, however, there are few investigations of variations in the magnetic properties of surface soils on the Tibetan Plateau (TP), especially on the southern TP. Therefore, it remains unclear whether magnetic properties could be used as proxies for palaeoclimatic reconstruction in the region. In this study, environmental magnetic parameters and bulk sediment grain-size measurements were made on a set of surface samples from the Yarlung Zangbo River Basin (YZRB), on the southern TP, and their environmental significance was evaluated. The results reveal spatial differences in the magnetic properties of the surface soils, likely caused by regional climatic factors. The input of primary magnetic minerals is the driver of the magnetic properties of the samples from the western (Gar-Saga) part of the YZRB, where the magnetic variations are controlled by the influence of wind intensity on the local source material. However, the samples from the eastern region (Gongga-Nyingchi) are significantly affected by the topographic and sedimentary conditions, and there is no relationship between the magnetic properties and climate. The samples from the central part of the study area (Saga-Gongga) show obvious signs of a pedogenic influence on magnetic properties and ultrafine superparamagnetic (SP) and single domain (SD) ferrimagnetic minerals dominate the magnetic susceptibility. Combined with the variation of grain size, this implies the influence of wind intensity and pedogenesis contribute to the magnetic enhancement. However, the pedogenic intensity closely related to precipitation and temperature could offer the possibility of using sedimentary magnetic properties for palaeoclimatic reconstruction. Furthermore, the existence of a distinct pedogenic alteration boundary in the Saga area is consistent with the location of the Indian summer monsoon, which may be the dominant control on the pedogenic intensity.

The mid-latitude Westerlies (MLW) are one of the most important atmospheric circulation systems in the Northern Hemisphere, exerting a huge influence on the climate of the region downwind, and thus on vegetation, water resources, and human wellbeing. However, the seasonal variation of the MLW during the Holocene is not yet been fully understood, especially when its contribution is the most important. Here, we used end-member (EM) modeling analysis of the grain-size distributions of a high-altitude aeolian sedimentary sequence (4452 m a.s.l.) from the Yarlung Zangbo River valley in the southern Tibetan Plateau to reveal variations in the winter MLW during the Holocene. Analysis of seasonal differences in modern atmospheric circulation suggests that the southern Tibetan Plateau was heavily influenced by the mid-latitude Westerlies at the 400, 500, and 600 hPa levels in winter, while it was seldom influenced at these levels in summer. Four grain-size end-members are identified, representing distinct aerodynamic environments, of which EM1 (modal grain size 8.1 μm) can be used as a proxy of the winter MLW. A reconstruction of the variation of the winter MLW during the Holocene based on EM1 revealed that a weaker winter MLW occurred during the Early to Middle Holocene, and a stronger winter MLW during the Middle to Late Holocene. Overall, we suggest that this change in the winter MLW was closely related to the insolation/temperature/pressure gradient between low and high latitudes in the Northern Hemisphere.

Aeolian processes have been studied extensively at low elevations, but have been relatively little studied at high elevations. Aeolian sediments are widely distributed in the Yarlung Zangbo River basin, southern Tibetan Plateau, which is characterized by low pressure and low temperature. Here, we comprehensively analyzed the wind regime using data since 1980 from 11 meteorological stations in the study area, and examined the interaction between the near-surface wind and aeolian environment. The wind environment exhibited significant spatial and temporal variation, and mean wind speed has generally decreased on both annual and seasonal bases since 1980, at an average of 0.181 m/(s·10a). This decrease resulted from the reduced contribution of maximum wind speed, and depended strongly on variations of the frequency of sand-driving winds. The drift potential and related parameters also showed obvious spatial and temporal variation, with similar driving forces for the wind environment. The strength of the wind regime affected the formation and development of the aeolian geomorphological pattern, but with variation caused by local topography and sediment sources. The drift potential and resultant drift direction were two key parameters, as they quantify the dynamic conditions and depositional orientation of the aeolian sediments. Wind affected the spatial variation in sediment grain size, but the source material and complex topographic effects on the near-surface wind were the underlying causes for the grain size distribution of aeolian sands. These results will support efforts to control aeolian desertification in the basin and improve our understanding of aeolian processes in high-elevation environments.

Surface solar radiation is affected by many random mutation factors, which makes the ultra-short-term prediction face great challenges. In this paper, the surface radiation observation station in the northwest (Dunhuang) desert area with broad PV prospects is selected as the research object. The input parameters of the test sample are: cloud forecast value, reflectivity and brightness temperature value of a satellite cloud image closest to the forecast time. The MATLAB software is used to model the prediction program and to predict the surface solar radiation in the next 10 minutes. A combined algorithm of satellite cloud images and neural network is applied to predict surface solar radiation for the next 10 minutes and is compared with the measured surface solar radiation. The model is a lightweight calculation model, it satisfies the calculation precision of engineering requirements. The results show that the diurnal variation trend of measured and predicted radiation values is basically the same. Among them, the prediction accuracy of the model for cloudy days is higher, while for snowy days with more abrupt changes, the prediction error of abrupt points is larger. The model can provide reference for ultra-short-term prediction of surface radiation.

The atmospheric mechanisms responsible for the loess grain‐size variations in central Asia are less clear, and an increasing number of studies have found that the coarse‐grained component is likely supplied by the surface circulation rather than by the westerlies (westerlies circulation). In this study, we attempt to determine the atmospheric dynamics patterns in the Afghan‐Tajik Basin during the past 800 kyr, based on the coarse grain‐size fraction of loess, combined with a study of modern dust transport processes. We suggest that the coarse grain‐size fraction can be used to indicate the intensity of near‐surface winds, while on glacial‐interglacial time scales, the variations of loess grain size in Tajikistan are dominated by Northern Hemisphere ice volume via its effect on the strength of the Siberian High. In addition, we suggest that atmospheric greenhouse gases concentration affected the loess grain size during interglacials via their influence on the temperature of southern high latitudes.

The Holocene Climate Optimum (HCO) was an important interval in the development of human civilization and has been the focus of many paleoclimatic studies. However, there are significant regional differences in the timing of the HCO due to the complex response of regional climates to insolation changes, associated with internal feedbacks within the climate system. Here, we present the results of a study of magnetic and geochemical properties of loess-paleosol sequences from across mid-latitude Asia, with the aim of assessing differences in the timing of the HCO. The HCO generally occurred after ~5 ka in Tajikistan and Xinjiang; during 5–2.5 ka in the western Chinese Loess Plateau (CLP); and during ~8–2.5 ka in the central CLP. This asynchroneity reflects differences in the response of regional climates to global climate change. Specifically, the difference in timing between the central and western CLP may have been related to shifts in the position of the East Asian summer monsoon rain belt, due to the changing longitudinal position of the Western Pacific Subtropical High, together with changes in the east-west thermal gradient in the equatorial Pacific (i.e. shifts between La Nina and El Nino conditions).

Eolian sediments are widely distributed and are one of the most important geological archives of past climatic changes. For example, the degree of pedogenic development of loess is widely used as an indicator of precipitation amount. However, in the case of arid lands, characterized by drought conditions and where potential evaporation is much higher than precipitation, it is unclear whether precipitation is the sole factor dominating pedogenic development, or whether temperature is also an important factor affecting for pedogenic development. In this study, we compared variations in pedogenic development of sequences of Holocene eolian sediments in arid basins and humid high mountains in Northwest China to assess the role of precipitation and temperature in soil development. The results indicate that the variation trend of pedogenic development was similar in both arid basins and high mountains, with weak development in the early Holocene and gradually increasing development into the late Holocene. In addition, combining both temperature and moisture records reveals that the weakest soil development was in the early Holocene when the climate was warm and dry and the strongest soil development was in the late Holocene when the climate was warm and humid. Overall, our results reveal that precipitation was the dominant climatic factor controlling changes in pedogenic development in the study area.

K-feldspar pIRIR dating was used to establish a chronological framework for the KS15-05 loess section in the Yili Basin, northern Xinjiang Province, China, in arid central Asia. The reliability of the dating results was verified from the luminescence characteristics and internal checks. The chronology was used to calculate mass accumulation rates (MARs) for the section and the paleoclimatic proxies of grain size and magnetic susceptibility were also analyzed. The high dust accumulation patterns during the last glacial maximum in Yili Basin are consistent with those of the Chinese Loess Plateau (CLP). On a millennial-scale, the Bolling-Allerod (B/A) interstadial is clearly reflected in the KS15-05 section by the variation of the 2–10 μm grain-size fraction, suggesting the influence of the Westerlies which dominate the modern atmospheric circulation of the region. However, the B/A interstadial is poorly recorded in grain-size records of the CLP and this disparity may provide additional information about the nature of the transmission of climate signals from the North Atlantic region to Asia. Specifically, the zonal transmission of the B/A warm signal to the CLP may have been obscured by the cooling effect of High-latitude cold air to the north of the CLP.

Central Asia comprises a vast area of arid terrain which has an important impact on the global climate system. Although still debated, the pattern of climatic variations in central Asia is regionally distinctive and does not appear to be strongly related to changes in insolation. To understand the climatic evolution of central Asia, as well as its forcing mechanisms, it is necessary to characterize variations in the Westerlies, which have had a major influence on climate change in the region. Past variations in the Westerlies are commonly reconstructed from records of the composition, grain-size and mass accumulation rate (MAR) of loess and the eolian component of lacustrine sediments which are commonly mixed by the signal of surface atmospheric circulation. Here we present the results of grain-size analysis of a section of last glacial and Holocene loess deposits in the Tien Shan Mountains. The results indicate that the strength of the Westerlies was weakest during the last deglacial and early Holocene (16–6 ka), strongest during the mid-Holocene (6–3.1 ka), and moderate during the late Holocene (3.1–0 ka). By comparison with an independent record of humidity, we propose that the Westerlies were an important driver of moisture variations in central Asia, with strong Westerlies circulation resulting in high precipitation and vice versa during the past 16 kyr.

The pattern of changes in Holocene moisture conditions in the southern Tibetan Plateau (TP) and the associated driving mechanism are still controversial. Here, we present the results of an analysis of an aeolian sedimentary sequence from the Yarlung Zangbo River valley in the southern TP, which potentially provides a record of changes in moisture conditions during the Holocene, and hence changes in the atmospheric circulation process. Optically stimulated luminescence dating with the single-aliquot regeneration protocol was used to establish the chronology for the sequence, and geochemical and granulometric measurements were used to reconstruct the Holocene moisture history. The results indicate that moisture conditions were strongly influenced by the early Holocene maximum in summer insolation (30°N) and hence by the Indian summer monsoon (ISM), under which the weathering intensity was relatively high. However, at ∼7.6 ka the climate abruptly became drier, probably due to the weakening of the ISM. Subsequently, with the further decrease in summer insolation and increase in winter insolation, the variations in ISM-related moisture delivery to the southern TP were regulated by the enhanced winter mid-latitude Westerlies (MLW), resulting in increasing weathering intensity. Thus, the Holocene evolution of moisture conditions in the southern TP was mainly controlled by changes in the relative intensities of the ISM and the winter MLW, which depended on the variations of summer and winter insolation at 30°N. Overall, our results provide an improved understanding of the driving mechanism of climate change in the southern TP during the Holocene.

The East Asian summer monsoon (EASM) and East Asian winter monsoon (EAWM) are major drivers of environmental conditions in East Asia. However, due to the lack of high-resolution EAWM records, the phase relationship between the EASM and EAWM during the Holocene epoch is still debated. Here, we use magnetic and grain-size measurements from a sequence of aeolian sediments from the eastern edge of the Mu Us Desert to track the history of the EASM and EAWM from 7.5 to 2.5 ka. The results show that both the EASM and EAWM exhibit a similar long-term weakening trend during this interval. In view of the stable glacial boundary conditions and the significantly decreased rates of atmospheric CO 2 rise since the mid-Holocene, we suggest that orbitally-induced insolation was the major cause of the weakening of both the EASM and EAWM. Decreasing summer insolation and increasing winter insolation reduced the thermal contrast between the ocean and the Asian continent in both summer and winter time, resulting in the weakening of both monsoon systems during the mid- to late Holocene.

The expansion of poisonous plants can change vegetation community structures and affect grassland ecosystem service values. Stellera chamaejasme is one of the most important poisonous plants and has rapidly expanded in the arid areas of Northwest China in recent decades. The objective of this study was to elucidate the expansion process and model of an S. chamaejasme population. Therefore, we classified the S. chamaejasme population into five classes based on coverage: 31–40%, 41–50%, 51–60%, 61–70% and 71–80%. We investigated the spatial distribution patterns and the size compositions of S. chamaejasme under different coverages. The results show that the spatial distribution pattern of S. chamaejasme under low coverage (31–40%) at all study scales (0–100 cm) was random; the spatial distribution pattern translated to a clumped distribution from a random distribution at some scales, and the clumped distributions gradually became obvious, with coverage increasing from 41–50% to 61–70%; the spatial distribution tended to be random at all study scales when coverage was increased further (71–80%). However, the spatial distribution patterns were closely related to the size composition of the S. chamaejasme population. In particular, the quantity of older individuals had a significant impact on the variation of the spatial distribution patterns of S. chamaejasme. The spatial distribution pattern varied from a random distribution to a clumped distribution and then returned to a random distribution with increasing coverage (from 31–40% to 71–80%), and this may indicate that the S. chamaejasme patches experienced patch formation and extension and merged with each other.

Previous studies from the central and eastern Chinese Loess Plateau (CLP) showed that the S5-1 paleosol, which corresponding to Marine Isotope Stage (MIS) 13, was the strongest developed during the last million years, suggesting extremely strong East Asian summer monsoon (EASM). However, evidence shows that regional diversity exists in the relative intensity of the S5-1 soil formation. In this study, we first verify systematically the S5-1 soil development across the whole CLP by using numerous loess records. We then examine the spatial variation of the magnetic susceptibility of different loess-paleosol sections to identify the spatial change of the EASM intensity during MIS-13. We also compare the loess records with other monsoon records in China. Our results show that, in central CLP, S5-1 is indeed the strongest developed as suggested by previous studies, whereas in the western CLP, it is weakly developed and the S4 paleosol developed during MIS-11 is the strongest. As compared to MIS-11, the northern front of the EASM during MIS-13 didn’t penetrate into western CLP, but was located more northerly and eastward. Based on sea surface temperature records in the tropical Pacific, we suggest that the temporal and spatial abnormal variation of the EASM during MIS-13 could be related to a strong La Nina or La Nina-like climate condition. Under such condition, the Western Pacific Subtropical High (WPSH) becomes weaker and retreats more northeastward, leading to more precipitation in the mid-east region of northern China but less rainfall in the western inland.

Competition is a common phenomenon among plant communities, especially among natural communities. It is an important factor in biology and plant–plant interactions has inspired an increasing concern in recent years. The investigation of inter-specific competition is useful to reveal the mechanism in plant growth and reproduction of organisms. Plant root systems play an important role in uptake of water and nutrients from soil for plant growth. However, it is still a divergent topic about the regulating mechanism between root morphological variations and competition. The spatial distribution, morphology of plant roots and above-ground growth can be influenced by inter-specific interactions. Their morphology characteristics and structure distribution were studied to reveal the adaptive mechanism of roots system in the soil environment. The deWit series experiments were conducted to study the relationship between relative competitive ability immixture and monoculture along seven levels of density at the experiment station of Shiyang river in Sunan country of Gansu province in 2010 (latitude 37°58′26′′N, longitude 101°47′ 34′′E). It was carried out to analyze inter-specific interaction between Avena sativa L . and Vicia villosa Roth. Taking the roots both A. sativa L. and V. villosa Roth as the research object, the WinRHZO was used to measure the changes of root length, diameter, surface area and so on. To evaluate the competitive responses and the competitive effects of target plants, the plant combinations with A. sativa L. and V. villosa Roth were established in plots in seven replacement grass–legume combinations (monoculture of A. sativa L . and V. villosa Roth, and mixed culture of A. sativa L . and V. villosa Roth with the ratios: 8:2, 6:4, 5:5, 4:6, 2:8). Four indexes of Relative yield (RY), relative yield total (RYT), Aggressivity (AG) and Relative crowding coefficient (RCC) were used to measure competition performances of inter-specific competition, and inter-superiority during different phonological period. The results showed that RY y , RY m and RYT of each seeding group was less-than 1 from seeding stage to mature stage, the degree of inter-specific competition was stronger than intra-specific, A. sativa L . and V. villosa Roth obviously showed hostile relations, however, the competitive superiority of two species has significant difference. From seeding stage to tillering stage, the RCC y of group B and group E was bigger than 1, RCC m was less-than 1 and the AG was bigger than 0, so the competitive power of A. sativa L . was stronger than V. villosa Roth, A. sativa L . gain advantage in the competition by increasing the root length and advancing the nutrient absorption ability, the competitive power of other groups cannot be judged. From jointing stage to seeding stage, the RCC y of group A, C and D was less-than 1, RCC m was bigger than 1 and the AG was bigger than 0, so the competitive power of V. villosa Roth was stronger than A. sativa L . , which was caused by increasing the number of A. sativa L . root, so the advantage in the competition gradually declined. Two species responded the transforming of inter-specific relationship well by adjusting the root morphology plasticity.

The O-3 uptake in 17 adult trees of six urban species was evaluated by the sap flow-based approach under free atmospheric conditions. The results showed very large species differences in ground area scaled whole-tree ozone uptake (F-O3), with estimates ranging from 0.61 +/- 0.07 nmol m(-2) s(-1) in Robinia pseudoacacia to 4.80 +/- 1.04 nmol m(-2) s(-1) in Magnolia liliiflora. However, average F-O3 by deciduous foliages was not significantly higher than that by evergreen ones (3.13 vs 2.21 nmol m(-2) p = 0.160). Species of high canopy conductance for 03 (G(O3)) took up more 03 than those of low G(O3), but that their sensitivity to vapour pressure deficit (D) were also higher, and their F-O3 decreased faster with increasing D, regardless of species. The responses of F-O3 to D and total radiation led to the relative high flux of O-3 uptake, indicating high ozone risk for urban tree species. (C) 2011 Elsevier Ltd. All rights reserved.

Transpiration patterns of Aesculus chinensis in relation to explanatory variables in the microclimatic, air quality, and biological phenomena categories were measured in Beijing, China using the thermal dissipation method. The highest transpiration rate measured as the sap flux density of the trees took place from 10:00 am to 13:00 pm in the summer and the lowest was found during nighttime in the winter. To sort out co-linearity, principal component analysis and variation and hierarchical partitioning methods were employed in data analyses. The evaporative demand index (EDI) consisting of air temperature, soil temperature, total radiation, vapor pressure deficit, and atmospheric ozone (O3), explained 68% and 80% of the hourly and daily variations of the tree transpiration, respectively. The independent and joint effects of EDI variables together with a three-variable joint effect exerted the greatest influences on the variance of transpiration rates. The independent effects of leaf area index and atmospheric O3 and their combined effect exhibited minor yet significant influences on tree transpiration rates.

Bistability and bifurcation of the transmitted light from a Fabry-Perot cavity containing carbon disulphide liquid have been studied experimentally. With polarized molecules instead of Eichler et al.'s, electron-hole pairs, the experimental results have been simulated successfully, also the possibility of observing chaos in experiment and pulse compression by an FP resonator is discussed.