Gobi Area Research Articles

Early Paleozoic oceanic inliers and reconstruction of accretionary tectonics in the Middle Gobi region, Mongolia: Evidence from SHRIMP zircon U-Pb dating and geochemistry

The ophiolites that occur as inliers among the Late Paleozoic formations in the Middle Gobi area are crucial for understanding the tectonic evolution of South Mongolia. In this paper, we conducted detailed studies on the Namdain hundy ophiolite to provide some constraints on the Early Paleozoic evolution of the Middle Gobi region in Mongolia. The ophiolite mainly consists of ultramafic rocks (carbonatation), plagiogranite, metagabbro, basalt and chert. The metagabbro and plagiogranite from Namdain hundy ophiolite yielded SHRIMP zircon U-Pb ages of 528±7Ma and 519±5Ma, respectively. Though most of the volcanic rocks of this ophiolite show supra-subduction zone (SSZ) affinity, samples with OIB and N-MORB geochemical features were also identified, indicating genesis in a forearc setting. The granodiorite intruding into the Namdain hundy ophiolite yielded a SHRIMP zircon U-Pb age of 491±3Ma, which constrained the upper age limit of ophiolite emplacement. This granodiorite shows adakitic geochemical affinity, attesting to the existence of Cambrian paleo - subduction in South Mongolia. Based on the available data so far, we suggest the Middle Gobi area comprises of the Manlay accretion complex, the island arc and the Biluutiin ovoo back-arc basin. The spatial configuration of these three tectonic belts suggests that the polarity of the paleo-ocean subduction was from south to north in the Early Paleozoic, forming a trench-arc-basin system south of the Central Mongolia microcontinent.

Insights into a dust event transported through Beijing in spring 2012: Morphology, chemical composition and impact on surface aerosols

Multiple approaches were used to investigate the evolution of surface aerosols in Beijing during the passage of a dust event at high altitude, which was from the Gobi areas of southern Mongolia and covered a wide range of North China. Single particle analysis with electron microscope showed that the majority of coarse particles were mineral ones, and most of them were in the size range of 1–7μm with a peak of number concentration at about 3.5μm. Based on elemental composition and morphology, the mineral particles could be classified into several groups, including Si-rich (71%), Ca-rich (15%), Fe-rich (6%), and halite-rich (2%), etc., and they were the main contributors to the aerosol optical depth as the dust occurred. The size distributions of surface aerosols were significantly affected by the dust intrusion. The average number concentration of accumulation mode particles during the event was about 400cm−3, which was much lower than that in heavily polluted days (6300cm−3). At the stage of floating dust, the number concentration of accumulation mode particles decreased, and coarse particles contributed to total volume concentration of particulate matter as much as 90%. The accumulation mode particles collected in this stage were mostly in the size range of 0.2–0.5μm, and were rectangular or spherical. They were considered to be particles consisting of ammonium sulfate. New particle formation (NPF) was observed around noon in the three days during the dust event, indicating that the passage of the dust was probably favorable for NPF.

Aeolian sediment transport over gobi: Field studies atop the Mogao Grottoes, China

Abstract This paper reports on field studies of aeolian sediment transport over a rough surface-gobi atop the Mogao Grottoes, China, in relation to sediment entrainment, saltation mass flux and transport rate prediction. Wind speeds were measured with five cup anemometers at different heights and sediment entrainment and transport measured with horizontal and vertical sediment traps coupled to weighing sensors, where sediment entrainment and transport were measured synchronously with wind speeds. Four sediment transport events, with a measurement duration ranging between 2.5 and 11 h, were studied. The entrainment threshold determined by the horizontal sediment trap varied between 0.28 and 0.33 m s−1, and the effect of non-erodible roughness elements-gravels increased the entrainment threshold approximately by 1.8 times compared to a uniform sand surface. Unlike the non-monotone curve shape of sediment flux density profile over gobi measured in wind tunnels, the flux density profile measured in the field showed an exponential form. Aeolian sediment transport over gobi could be predicted by an Owen-type saltation model: q = A ρ / gu ∗ ( u ∗ 2 - u ∗ t 2 ) , where q is sediment transport rate, A is a soil-related dimensionless factor, u ∗ is the friction velocity, u ∗ t is the threshold friction velocity, g is the gravitational acceleration, ρ is the air density. This study indicates that the sediment flux sampling using horizontal and vertical sediment traps coupled to weighing sensors provides a practical method to determine values for A in this model that can provide good estimates of sediment transport rates in gobi areas.

Ecological Functions of PV Power Plants in the Desert and Gobi

Abstract: Photovoltaic (PV) power generation is an emerging energy industry that is developing rapidly. A number of PV power plants have been established in the desert and Gobi areas in northwest China in recent years. Is there any ecological significance to the establishment of PV power plants? If yes, what is it? This paper tries to find the answer by analyzing meteorological data from the Hexi Corridor as well as the observational data of light and vegetation in the Minqin desert area. The results show that the solar energy converted from 1 m2 of PV panels is equivalent to the solar energy that is utilized by 260.75 m2 of desert plants in the desert area. In China, there is vast area of desert and Gobi, with frequent dust storms and aeolian sand, as well as rich sunlight resources. Therefore, to develop the PV industry in the desert and Gobi regions will not only create considerable economic benefits, but will also be of great ecological significance. On the one hand, PV can effectively regulate thermo...

Late Paleozoic magmatic record of Middle Gobi area, South Mongolia and its implications for tectonic evolution: Evidences from zircon U–Pb dating and geochemistry

Late Paleozoic subduction–accretion complexes occur widely in Middle Gobi area and provide a good opportunity for unraveling the Paleozoic tectonic evolution of South Mongolia. The magmatic rocks in the Tsavchir hudug district mainly consist of rhyolites and volcaniclastic rocks. The rhyolites show enrichment in LREE and LILE and negative Nb, Ta and Ti anomalies, indicating genesis in the subduction zone. A rhyolite sample from the Tsavchir hudug region yielded a SHRIMP 206Pb/238U zircon age of 315±4Ma (MSWD=0.79, n=15). The andesite overlying the Namdain hundy Early Paleozoic ophiolite shows adakite geochemical features, and the two andesite samples yielded SHRIMP 206Pb/238U zircon ages of 325±3Ma (MSWD=1.6, n=14) and 319±4Ma (MSWD=0.56, n=13), respectively, suggesting that the Carboniferous island arc formed on the basis of Early Paleozoic accretionary complex. The granodiorite sample that intrudes the Early Paleozoic accretion complex with adakite geochemical features yielded a SHRIMP 206Pb/238U zircon age of 333±4Ma (MSWD=1.6, n=16), representing the Late Paleozoic island arc intrusive. The SHRIMP U–Pb analyses for the tuff sandstones that occur associated with Early Paleozic oceanic inliers in Middle Gobi area suggest detrital zircons mainly stem from the Devonian–Carboniferous arc. The age data obtained from the ophiolite (528–509Ma) and tuff sandstone indicate the accretion in Middle Gobi area lasted from Early Paleozoic to Late Paleozoic for at least ca. 200Ma, suggesting the ocean of the accretionary complex was the major Paleo-Asain ocean basin. The subduction related magmatic belt in Middle Gobi area includes both Early Paleozoic and Late Paleozoic island arc activities, which is consistent with the accretion duration time obtained from accretionary complex and also attests the argument of major Paleo-Asain ocean basin.

Ambient Noise Tomography in Central‐South Mongolia

AbstractRelying on cooperation projects in Mongolia, “Observation and modeling on the geomagnetic, gravitational field and deep structure in the Far East Areas”, we got dense seismic array data in the area for the first time. By using the vertical component of continuous data, recorded by 69 broadband seismic stations from Aug. 2011 to Jul. 2013 in south‐central Mongolia (103.5°E–111.5° E, 43°N–49°N), we calculated the inter‐station Empirical Green functions (EGFs) from cross‐correlation. In addition, a time‐frequency analysis based on a continuous wavelet transform was used to extract the Rayleigh wave phase velocity dispersion curves. Through quality control and manually screening, we finally obtained a total number of 1478 phase velocity dispersion curves at periods ranging from 6 s to 30 s. The Ditmar & Yanovskaya method was utilized to obtain phase velocity maps of the Rayleigh wave at periods of 6∼30 s in the study area. Checkerboard tests showed that the tomographic results had a high resolution of 0.5° ×0.5°. The results revealed that the phase velocity maps of Rayleigh waves have a small perturbation of about ±2%. A phase velocity map with a short period (e. g. 6 s) was imaged with high‐speed anomalies corresponding to the mountain ranges in the north and low‐speed anomalies coinciding with the sedimentary basin and Gobi Desert in the central‐south region. As the period (15 s, 20 s) increased, the imaging still showed a high‐velocity zone (HVZ) in the north and low‐velocity zone (LVZ) in the central‐south. However, the effect of the phase velocity distribution controlled by the surface geological structure was significantly weaker. The phase velocity maps with a long period (e.g. 30 s) showed an HVZ in the north that expanded further to the south than those with shorter periods (e.g., 15 s and 20 s), which is associated with the thinner crust in the south compared to that in the north. On those maps with long periods (e.g., 20 s, 30 s), there were significant differences between the northern and southern sides of Main Mongolian Lineament (MML), indicating that MML was not only a boundary for the topography and tectonics, but also for the crustal structure. The Middle Gobi area always showed an LVZ at periods from 6 s to 30 s, which could have been related to Cenozoic volcanism, while the Hangay‐Hentey basin was always imaged with an HVZ, which could have been associated with the old, stable layers in the north.

Characteristics of the disastrous wind-sand environment along railways in the Gobi area of Xinjiang, China

Based on detailed long-term data of wind regimes collected from typical ventilation sites along the railways in the Gobi area of Xinjiang, this study systematically analyzes the characteristics of the disastrous wind-sand environment along the railways by combining gradient sand sampling data collected by a wind-drift sand monitoring system and site survey data. Wind direction and speed rose diagrams revealed the prevailing wind direction in each wind area along the railways, and this is the wind direction from which the maximum frequency of sandstorms occurred. Drift potential characteristic parameters (RDP, RDD) and the direction variability (RDP/DP) showed that each wind area along the Gobi railway featured a long wind period, with strong power in a single wind direction. The special geological environment of the Gobi determines the wind-drift sand that features gravel of large grain size and unsaturation, which are different from the wind-drift sand in deserts. With increasing wind velocity, the density of the wind-drift sand increased steadily; however, at a certain critical value, the density surged. This study on the wind-sand environment of the Gobi has significance for railway safety. The critical value of wind velocity corresponded to an abrupt increase in the wind-drift sand density and should be taken into account during the planning process of railway safety passage, since this will lead to a decrease in frontal visual distance, and an associated decrease in safety. Additionally, the specific features of wind-drift sand activities, such as the abruptness and higher than usual sand height, should be considered during the process of designing sand-damage-control engineering measures.

Ecological Significance of the Sand Wedge In the Extra-Arid Gobi Area

The sand wedge was widely found, by field survey, to lie within the Gobi on the top of the Mogao Grottoes. The characteristics of its shape, size, structure, and ecological function were investigated. This original sand wedge was of a special type; formed in an arid environment, and with a multi-level fractal structure. The width range of main wedge was from 30 to 60 cm and its depth was about 50 cm, where the width of the irregular polygon matrix was about 60 to 160 cm. Meanwhile, the features of this sand wedge, including mechanical composition, salinity, and water content differed greatly from its matrix. The salt content in the sand wedge was 0.86 g · kg−1, correspondingly, that of the matrix reached 4.56 g · kg−1. The sand wedge can absorb plentiful rainfall and retain it for a long time, which can benefit plant survival. However, the higher salt content of the matrix would dissolve under eluviation, which plays an important role in pruning roots. These double functions of higher water content in the wedge and salt pruning in the matrix have made the main roots of vegetation grow inside the sand wedge only. Thus, the net shape structure of sand wedge was vital to vegetation distribution in the Gobi and the formation of the associated geomorphologic landscape. At the same time, the sand wedge formed a crucial habitat for small animals, thus was the last surviving such enclave in the extreme aridity of the Gobi ecosystem.

Retrieving soil moisture in arid area based on MODIS data

In order to study the spatial and temporal distribution and the change of soil moisture in the lower reaches of the Heihe River Basin,the authors used the MODIS data products and the soil moisture data measured from the field data and adopted the thermal inertia to calculate the apparent thermal inertia( ATI). Then ATI and soil moisture were used to build the experience model by regression analysis. At last the soil moisture in the lower reaches of Heihe River Basin was successfully retrieved by this model. The results indicate that using MODIS products provided by NASA could predigest the retrieval parameters,reduce the complexity of soil moisture retrieval and ensure the application in the large or middle- sized region. The ATI mean of sand is larger than that of loam and clay,the ATI of clay and loam is relatively large and scattered. The ATI mean of the oasis area is larger than that of the gobi and desert area. The proposed thermal inertia model can reliably monitor the soil moisture within the soil depth of 20 cm.

Particle size variation of aeolian dune deposits in the lower reaches of the Heihe River basin, China

The grain-size characteristics of aeolian dune and Gobi sands in the lower reaches of the Heihe River desert basin (Ejina) of northwestern China in central Asia were investigated, aimed at a sedimentological study of the dune sediments and their response to aeolian processes and source area. Grain-size parameters (mean, standard deviation, skewness, and kurtosis) were determined for sand samples from dune crests, interdunes and Gobi areas. The aeolian dunes are mainly composed of medium and fine-grained sand. Sorting improves with decreasing grain size. A clear relationship occurs between skewness and sorting in that sands become progressively zero-skewed (SK1≈0) as sorting improves, suggesting that improved sorting is accomplished by loss of both relatively coarser and finer grains in the desert. In comparison with many other desert areas, the dunes in the Ejina are composed of relatively coarse sands, are poorly sorted and relatively platykurtic. In log-probability grain-size distributions, most dune sands in the Ejina are composed of two distinctive saltation populations truncated at about 1.8ϕ and 2.5ϕ. This represents two differing aeolian transport conditions and presumably produces two separate saltation populations in opposite air-flow directions. Sand dunes exhibit grain size and sorting patterns in which sands become finer, better sorted, and more finely skewed from interdune to crest, which is a similar pattern to that in the Namib Desert. This pattern can be best explained by differential movement of sand in creep and saltation populations. At a regional scale, dune sands tend to become finer from southwest to northeast in the desert basin, which coincides with the basin hydrological setting but not with the compound direction of the basin wind system. It appears that local-scale factors, such as hydrological processes and source materials, rather than regional aeolian processes, are responsible for the grain-size variations of dune sands in the Ejina desert.

Computational fluid dynamics evaluation of the effect of different city designs on the wind environment of a downwind natural heritage site

Disturbance in wind regime and sand erosion deposition balance may lead to burial and eventual vanishing of a site. This study conducted 3D computational fluid dynamics (CFD) simulations to evaluate the effect of a proposed city design on the wind environment of the Crescent Spring, a downwind natural heritage site located in Dunhuang, Northwestern China. Satellite terrain data from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Digital Elevation Model (DEM) were used to construct the solid surface model. Steady-state Reynolds Averaged Navier-Stokes equations (RANS) with shear stress transport (SST) k-ω turbulence model were then applied to solve the flow field problems. Land-use changes were modeled implicitly by dividing the underlying surface into different areas and by applying corresponding aerodynamic roughness lengths. Simulations were performed by using cases with different city areas and building heights. Results show that the selected model could capture the surface roughness changes and could adjust wind profile over a large area. Wind profiles varied over the greenfield to the north and over the Gobi land to the east of the spring. Therefore, different wind speed reduction effects were observed from various city construction scenarios. The current city design would lead to about 2 m/s of wind speed reduction at the downwind city edge and about 1 m/s of wind speed reduction at the north of the spring at 35-m height. Reducing the city height in the north greenfield area could efficiently eliminate the negative effects of wind spee. By contrast, restricting the city area worked better in the eastern Gobi area compared with other parts of the study area. Wind speed reduction in areas near the spring could be limited to 0.1 m/s by combining these two abatement strategies. The CFD method could be applied to simulate the wind environment affected by other land-use changes over a large terrain.

Deformation Monitoring and Evaluating Technology for Subgrade of Unballasted Track on Lan-Xin Passenger Dedicated Line

Lanzhou-Xinjiang passenger dedicated line is the first high speed railway on chinas northwestern Gobi where the temperature range is large and the wind is huge. Most road section of Lan-Xin passenger dedicated line is subgrade. This paper researches the ballastless track subgrade settlement observation scheme and assessment method on area where climatic conditions is harsh and geologic conditions is complex. The result shows that: the observation accuracy of subgrade settlement tests satisfies the requirement by using Layered settlement instrument, intelligent static force level and high-accuracy Hydraulic settlement instrument; Subgrade lies upon bedrock or Gobi soil with great bearing capacity in gale area, and distance between observation sections could be increased seemly. The space between observation sections generally should be less than 100m in areas where bedrock exposed, thick gravel soil distribute commonly; the distance between observation sections should be less than 50m in pre-mountain Alluvial-pluvial plain areas; hyperbolic method adapt the estimate of subgrade settlement on Gobi area, and the correlation coefficient is 0.97; Subgrade settlement deformation curve converges quickly and the settlement value after 40 days reaches 85% of ultimate settlement.

Shallow groundwater dynamics and its driving forces in extremely arid areas: a case study of the lower Heihe River in northwestern China

Shallow groundwater is an important source of water for the maintenance and restoration of ecosystems in arid environments, which necessitates a deeper understanding of its complex spatial and temporal dynamics driven by hydrological processes. This study explores the dominant hydrological processes that control the shallow groundwater dynamics in the Gobi Desert-riparian-oasis system of the lower Heihe River, a typical arid inland river basin located in northwestern China. The groundwater level and temperature were monitored in 14 shallow wells at 30-min intervals during the 2010–2012 period. After combining this information with meteorological and hydrological data, a comprehensive analysis was conducted to understand the dynamic behaviour of the shallow groundwater system and to determine the dominant factors that control the groundwater flow processes. The results of the study indicate notably large temporal and spatial variations in both the groundwater level and temperature. Noticeable fluctuations in the groundwater level (0.5–1 m) and temperature (4–8 °C) were observed in the riparian zone, evidencing a clear river influence. In comparison, the groundwater fluctuations in the Gobi Desert were more stable (the annual variations of the water table were less than 0.5 m, and the water temperature varied by no more than 2 °C). Strong variations in the groundwater table (1.5–5.0 m/year) and temperature (1.5–6.5 °C), mainly caused by surface flood irrigation and groundwater pumping, were observed in the oasis area. The investigated sites were categorized into three types that reflect the dominant hydrological processes: (1) the riparian zone, dominated by riverbank filtration and groundwater evapotranspiration; (2) the Gobi Desert area, controlled by groundwater evaporation and lateral recharge; and (3) the oasis area, dominated by groundwater evapotranspiration as well as surface–groundwater interactions caused by human activities. Copyright © 2012 John Wiley & Sons, Ltd.

The Yingba shear zone on the Sino-Mongolian border: Southwestern extension of the Zuunbayan Fault from Mongolia to China and implications for Late Mesozoic intracontinental extension in Eastern Asia

Major strike-slip and normal faults are prominent features of Eastern Asia during the Meso-Cenozoic and they are critical to understanding the intracontinental deformation. Among others, the northeast-striking Zuunbayan Fault in southeastern Mongolia is usually documented as a strike-slip fault, but it may be a normal fault during the Late Mesozoic. However, its southwestern extension from Mongolia to China is still uncertain. The northeast-striking Yingba shear zone in western Inner Mongolia, China, just lies in the place where the Zuunbayan Fault probably strikes through southwestward. The gentle northwest-dipping foliation and lineation and top-to-the-northwest shear sense in the granitic mylonite indicate that the Yingba shear zone is a northwest-dipping, low-angle normal fault. The mylonitization occurred mainly at 400–500°C, as a result of the Early Cretaceous intracontinental extension, as bounded by the zircon U–Pb ages of 145Ma from two deformed (pre-tectonic) pegmatite veins and of 134Ma from one undeformed (post-tectonic) pegmatite vein, all of which definitely crosscut the shear zone. The Yingba normal faulting was coeval with the Late Mesozoic extensional phase of the Zuunbayan Fault in southeastern Mongolia, which is characterized by northwest-dip and NW–SE extension from at least 155 to 126Ma. Therefore, the Yingba shear zone is considered as the southwestern segment of the Zuunbayan Fault in China. The Late Mesozoic intracontinental extension, which was possibly triggered by the Jurassic thrusting in the South Gobi area of Mongolia, generated the Yingba shear zone and the Yagan metamorphic core complex on the Sino-Mongolian border.

Remote sensing temporal and spatial patterns of evapotranspiration and the responses to water management in a large irrigation district of North China

To deal with water resources crisis caused by climate change and intensified human activities, the Hetao Irrigation District of Inner Mongolia in North China has been experiencing rehabilitation for water-saving since 1999. This has significantly changed its regional hydrological cycle and thus water use patterns over different land use types. In this paper, Surface Energy Balance Algorithm for Land (SEBAL) model fed with MODIS data was applied in Hetao area from 2000 to 2010 to examine the spatial and temporal patterns of evapotranspiration (ET). The SEBAL estimated ET agreed well with that from other methods in the study area. The results indicate that inter-annual variability in ET over agricultural land, water body, woodland and irrigated grassland are primarily explained by the variation of reference ET. So it is with the seasonal variability in agricultural land ET on monthly basis. However, the inter-annual variations of ET over sandy land, Gobi desert and mountain areas are mainly controlled by precipitation. Over the study period, a reduction in river water diversion for irrigation has not reduced the agricultural land ET, indicating no significant impact on agricultural production. But ET over the non-irrigated grassland tends to decrease, which was likely caused by declining groundwater table in recent years.

Study on the Wind-Sand Flow Movement Characteristics and the Shielding Effect of the Wind-Break Wall along the Railway in Gobi Area

Based on the large number of field surveys and long-term monitoring data of Hongceng, Hongliu and MengliuDong monitoring points, the wind-sand flow movement characteristics along the railway in Gobi area was analyzed. The shielding effect of the wind-break wall was evaluated by the methods of numerical simulation and field test. Conclusions drawn as followings: the wind-sand flow movement in Gobi area is characterized by stable of direction, seasonal, high-velocity,long-term,and shorting of starting-up time and moresand content. Numerical simulation shows that the wind flow form a large vortex region on the leeward side of wall, the flow field elements occurs significant changes. Both field test data and numerical simulations indicated that 3.0m height of wind-break wall meet the requirement of shielding wind-sand flow.

Magnetic properties of surface soils in the Chinese Loess Plateau and the adjacent Gobi areas, and their implication for climatic studies

Sixty-two surface soil samples, collected along a precipitation gradient in the Loess Plateau and the Alxa Plateau area, northwest China, were analyzed using environmental magnetic parameters (χlf, χfd%, χARM, SIRM, HIRM, SOFT, and back field IRM), grain size, and weight loss on ignition. The results show that the magnetic mineral assemblage in the surface soil is dominated by magnetite and maghemite, with some hematite. Cross plots of χfd% vs. χARM/SIRM indicate that the main magnetic grain sizes in the surface soils are pseudo single domain (PSD) and multidomain (MD). The samples from the Alxa area are dominated by magnetic minerals with a larger grain size while those from the Loess Plateau are dominated by magnetic minerals with a finer grain size. The main magnetic minerals in the surface soil of the Loess Plateau originate from both the aeolian dust and pedogenic processes, with the later dominating. Compared to magnetic susceptibility, frequency-dependent magnetic susceptibility has a stronger correlation with precipitation in this large area of complex geology and topography. This result is not consistent with previous studies and we suggest that caution is needed when using magnetic susceptibility as an indicator of environmental change in arid regions.

LOSA-M2 aerosol Raman lidar

The scanning LOSA-M2 aerosol Raman lidar, which is aimed at probing atmosphere at wavelengths of 532 and 1064 nm, is described. The backscattered light is received simultaneously in two regimes: analogue and photon-counting. Along with the signals of elastic light scattering at the initial wavelengths, a 607-nm Raman signal from molecular nitrogen is also recorded. It is shown that the height range of atmosphere probing can be expanded from the near-Earth layer to stratosphere using two (near- and far-field) receiving telescopes, and analogue and photon-counting lidar signals can be combined into one signal. Examples of natural measurements of aerosol stratification in atmosphere along vertical and horizontalpaths during the expeditions to the Gobi Desert (Mongolia) and Lake Baikal areas are presented.

Research on threshold friction velocities during dust events over the Gobi Desert in northwest China

[1] Dust emission generated by wind erosion is the largest source of tropospheric aerosols. The Gobi Desert in northwest China has one of highest dust storm frequencies in northeast Asia. In this paper, a simple method is proposed to distinguish local dust emissions. A lag correlation coefficient Rlag of wind speed and dust concentration is introduced. Using observational data obtained from a 20 m monitoring tower in the Gobi Desert, the characteristics of dust concentration and friction velocities u* during various dust emission periods were investigated. The threshold friction velocities u*t were estimated to be 0.34–0.42 m/s over the Gobi area for four local dust events in April 2006. The values of u*t were slightly smaller than those in previous results, but they were proven to be reasonable through validation based on additional dust events in April 2008 over the same area.

GSPAC water movement in extremely dry area

Under an extremely arid condition, a PVC greenhouse was built on the top of Mogao Grottoes in gobi area. The results of 235-day constant extraction of condensed water on the greenhouse film and soil water content showed that 2.1 g/(m 2 ⋅d) groundwater moved up and exported into the soil, and a phreatic water evaporation existed in the extreme dry area where the groundwater is buried deeper than 200 m. After a prolonged export, the soil water content in the greenhouse was not lower but obviously higher than the original control ones. According to the monitored parameters including relative humidity and absolute humidity of soil, and temperature outside and inside the greenhouse, it was found that there is the available condition and mechanism for the upward movement of groundwater, and also it can be sure that the ex- ported water was not from the soil and atmosphere outside the greenhouse. Phreatic water, an important source for soil water, interacts with atmosphere moisture via soil respiration. Soil salinity also has important effects on soil water movement and spatial-temporal heterogeneity. The extremely dry climate, terrestrial heat and change of upper soil temperature are the fundamental driving forces of water transportation and phreatic water evaporation in the Groundwater-Soil-Plant-Atmosphere Continuum (GSPAC) system.