Jianjun Qu

Grain size characteristics of dune sands in the central Taklimakan Sand Sea

Abstract Compared with the sand grain size of the other sand seas, central Taklimakan Sand Sea has some of the finest sands seen globally. The dunes are composed of fine and very fine sands with a diameter between 2.00 and 4.00 φ (0.25–0.063 mm). There are differences in the grain size distributions for different dune types. Mean grain size of the compound/complex crescent dune sands is 3.08 φ; the compound dome dunes 3.21 φ; the compound/complex linear dune sands between 2.63 and 3.41 φ; and the star dunes 2.81 φ. From the northern edge of the sand sea towards southern edge, the components of fine and very fine sands increase, closely related to the wind regimes, time scale for dune development, and underlying sediments. Compared with the foregoing, there are some differences for the compound/complex linear dunes in the centre of Taklimakan. Though the pattern of coarser crests does exist, the sorting parameters indicate that the sands on the west flank of compound/complex linear dunes are better sorted than that on the east flank and crest. Sampling on the superimposed dunes developed on the surface of the complex linear dunes suggests that the patterns of finer crest, coarser crest all existed in central Taklimakan. Under the conditions of low energy wind regime when fine sand is available, the frequency of the pattern for finer crest and better sorting will increase. Sampling on the simple crescent dunes developed on the interdunes suggests that the simple dunes are developed originally with nearly the same grain size distributions and parameters. With the development of the dunes and evolution of the dune morphology, the grain size distributions of the dune sands varied under the actions of the wind regimes, time scale and underlying sediments.

Measurements of dust deposition in Gansu Province, China, 1986¿2000

Abstract Dust samples, collected monthly for 15 years from 50 urban sites in 10 cities in Gansu Province, China, provide information on modern rates of dust deposition in the desert and Gobi areas and in the Loess Plateau. Dust deposition is highest during spring months and lowest during autumn months, in both the desert and Gobi areas and the Loess Plateau. There is a significant positive correlation between dust deposition and dust event, and an inverse correlation between dust deposition and precipitation. The 15-year mean maximums in the desert and Gobi areas and the Loess Plateau are 498.64 and 327.02 t km −2 year −1 , respectively, and the mean minimums are 290.22 and 180.86 t km −2 year −1 , respectively. Drought may have a widespread, major influence on the modern rates of the dust deposition.

Sand sea activity and interactions with climatic parameters in the Taklimakan Sand Sea, China

An analysis is undertaken of the temporal and spatial variability of climatic parameters including precipitation, potential evaporation and wind regimes that control the aeolian activity in the Taklimakan Sand Sea. Mobility index is calculated according to the mode that Lancaster (J. Arid Environ. 14 (1988) 233) suggested. Our results show that there are apparent temporal and spatial variations for this mobility index. The annual aeolian activity varies in phase with the number of windy days, precipitation and potential evaporation. Dune development is highly consistent with distribution of the mobility index. The mobility index shows that the Taklimakan Sand Sea experienced high aeolian sand activity during the 1960s and mid-1980s, and then related sand transport was reduced from the mid-1980s to the late 1990s. The mobility index cycle cannot be obtained because the available meteorological data cover only short periods. Such an approach will require longer research combined with field observations of sand movement.

Dynamic processes of a simple linear dune--a study in the Taklimakan Sand Sea, China

Samples of dune sands, surveys of the morphology and field measurements of wind velocity and direction of a simple linear dune in Taklimakan Sand Sea show that the airflow and sand flux vary with the change of wind direction on the dune surface. Decrease of the airflow stress on the lee flank does not result in much decrease of the sand flux because of the low threshold shear velocities and the airflow conditions. There are no significant relations between the sand flux on the lee flank and the angle of incidence of the airflow. The low threshold shear velocities and the maintenance of the sand flux at the lee flank are the main mechanisms keeping the linear shape of the dunes. Measurements of the sand flux shows that it reaches a maximum on the crest of the dune. The grain size of the transported sands has some differences compared to that of the dune surface. The sands transported are finer than that on the dune surface, but better sorted under the influence of the medium to low wind activity. The field experiment results exhibit that it is possible for the dunes to be shaped as linear dunes during the processes of accumulation and elongation.

Research on an optimal site selection model for desert photovoltaic power plants based on analytic hierarchy process and geographic information system

Optimal site selection for desert photovoltaic power plants is important to energy output and involves a multicriteria evaluation of many factors. This paper analyzes the factors influencing desert photovoltaic power station site selection and establishes an optimal site selection model for desert photovoltaic power plants using an analytic hierarchy process and geographic information system technology. We selected a typical desert area in northwestern China as the research location to test the model. Validation results were ideal, and the model successfully displayed the optimal site for desert photovoltaic power plants, from which the most suitable site for desert photovoltaic power plants could be selected.

The Effect of Air Density on Sand Transport Structures and the Adobe Abrasion Profile: A Field Wind-Tunnel Experiment Over a Wide Range of Altitude

Aeolian sand transport results from interactions between the surface and the airflow above. Air density strongly constrains airflow characteristics and the resulting flow of sand, and therefore should not be neglected in sand transport models. In the present study, we quantify the influence of air density on the sand flow structure, sand transport rate, adobe abrasion profiles, and abrasion rate using a portable wind-tunnel in the field. For a given wind speed, the flow’s ability to transport sand decreases at low air density, so total sand transport decreases, but the saltation height increases. Thus, the damage to human structures increases compared with what occurs at lower altitudes. The adobe abrasion rate by the cloud of blowing sand decreases exponentially with increasing height above the surface, while the wind erosion and dust emission intensity both increase with increasing air density. Long-term feedback processes between air density and wind erosion suggest that the development of low-altitude areas due to long-term deflation plays a key role in dust emission, and will have a profound significance for surface Aeolian processes and geomorphology.

Key evidence of the role of desertification in protecting the underlying permafrost in the Qinghai-Tibet Plateau.

Previous research has shown that the temperature of underlying permafrost decreases after the ground surface is covered with sand. No significant conclusions have yet been drawn that explain why this happens, because the heat transfer mechanism effects of the sand layer on the underlying permafrost remain unclear. These mechanisms were studied in the present work. We found that the upward shortwave radiation flux of the Qinghai-Tibet Plateau ground surface with a sand layer covering was higher than that of the surface without sand; thus, the atmospheric heat reflected by the sand layer is greater than that reflected by the surface without sand. Therefore, the net radiation of the surface with the sand layer is lower than that of the surface without sand, which reduces the heat available to warm the sand layer. Because sand is both a porous medium and a weak pervious conductor with poor heat conductivity, less heat is conducted through the sand layer to the underground permafrost than in soil without the sand deposition layer. This phenomenon results in a decrease in the ground temperature of the permafrost under the sand layer, which plays a key role in protecting the permafrost.

Building Chinese wind data for Wind Erosion Prediction System using surrogate US data

Wind erosion is a global problem, especially in arid and semiarid regions of the world, which leads to land degradation and atmosphere pollution. The process-based Wind Erosion Prediction System (WEPS), developed by the USDA, is capable of simulating the windblown soil loss with changing weather and field conditions and different manmade management scenarios (Hagen 1991; Hagen 2004; Tatarko et al. forthcoming). Erosion in WEPS is driven by stochastically generated hourly wind data by the WINDGEN program, which is more appropriate than using measured data directly, and thus hourly wind data for the entire day are needed to build the statistical database (Donk et al. 2005). The current version of WEPS contains wind data for 2,718 stations within the United States. When running WEPS, wind data from the nearest station, from a station assigned to a polygon region or interpolated from nearby stations, can be used (Wagner forthcoming). Another database, named CLIGEN, which contains other climate information, including daily temperature, precipitation, solar radiation, etc., is also needed for the WEPS simulation. There is a great potential to extend WEPS to other countries and regions, such as China, which has a similar area, latitude location, and climate diversity to the United States.

Numerical evaluation of the scale problem on the wind flow of a windbreak

The airflow field around wind fences with different porosities, which are important in determining the efficiency of fences as a windbreak, is typically studied via scaled wind tunnel experiments and numerical simulations. However, the scale problem in wind tunnels or numerical models is rarely researched. In this study, we perform a numerical comparison between a scaled wind-fence experimental model and an actual-sized fence via computational fluid dynamics simulations. The results show that although the general field pattern can be captured in a reduced-scale wind tunnel or numerical model, several flow characteristics near obstacles are not proportional to the size of the model and thus cannot be extrapolated directly. For example, the small vortex behind a low-porosity fence with a scale of 1:50 is approximately 4 times larger than that behind a full-scale fence.

Quantitative analysis on the dynamic characteristics of megadunes around the Crescent Moon Spring, China

The Crescent Moon Spring is a precious natural heritage. However, the dynamic characteristics of megadunes around the Crescent Moon Spring are not well known. This paper quantitatively studied the characteristics and changes of megadunes around the Crescent Moon Spring by interpreting aerial photographs taken in 1985 and 2004 and analysing the dune crestlines and the wind data collected from 2011 to 2012. Results revealed that pyramid dunes were formed by a complex wind regime. The Crescent Moon Spring was not buried by shifting sands because of the stable wind regime and relative stability of pyramid dunes. The crestlines of the dunes around the spring moved northward between 1985 and 2004. The south-facing slip faces were also exposed to wind erosion, whereas the other faces were under deposition, thus indicating that the southerly wind was relatively enhanced. Limiting the scale of tall windbreaks and architectures in the Dunhuang oasis at the north of the spring was necessary to maintain the dynamic equilibrium of the wind regime and sand transport.