Study on Dune Morphology in Computer Mapping Based on 3S Technology

Take the parabolic dune of Hobq desert in Inner Mongolia as research object. Based on the GIS platform by using differential GPS data and spatial interpolation to generate DEM, then using Multi-periods high resolution images to acquire the environmental background, at the same time combine with regional wind regime and vegetation condition to measure and analyze the morphology of the parabolic dune. The result shows that the parabolic dune showed U shape in plane, and dune arms point to the west which was also wind direction. The windward slope of longitudinal profile is gentler, while leeward slope is steeper. And cross section wasn’t symmetric. The dune’s average moving speed is 11.76 m/yr. Desert ridge line’s medial axis direction is WNW-ESE, in accord with the direction of prevailing wind and resultant drift potential. Artemisia Ordosicas mainly distribute on leeward slope, two arms, and the plane ground between them, and the annual average vegetation coverage decreased 0.95%. In the long-term effect of resultant wind, the dune keeps moving forward and Artemisia Ordosica between two arms show gradual natural stage recovery which presented zonal distribution. 3S technology has already become important research method in modern Aeolian sand morphology.

Study on Surface and Internal Humidity of Dunes in the Southwestern Margin of the Taklimakan Desert

Greening on the edge of desert is an effective way to prevent and control desertification. This paper studies the humidity characteristics of sand samples collected from the surface and interior of dunes in the southwestern edge of the Taklimakan Desert, whose geographic coordinates are 39°43’37” – 39°43’41” N, 78°43’02” – 78°43’09” E. The humidity of sand samples at vertical depths under five different surface positions of windward slope bottom, windward slope middle, windward slope top, leeward slope middle and leeward slope bottom was studied. On the surface of the sand at different locations and at the same depth under the surface, the sand humidity is greater closer to the bottom of the slope, for both windward slope and leeward slope. The humidity gradient values on the surface and at different depths on different positions of the dunes are obtained. Finally, recommendations are provided for effective ways to prevent desertification in the desert edge of Kashgar.

Research on Micro-terrain Classification of Transmission Line Galloping

Micro-terrain and micro-weather have an important impact on transmission line galloping. In order to carry out galloping prediction of micro-terrain, the classification of galloping micro-terrain is studied in this work. Firstly, we collect historical data of 1537 galloping points from the State Grid Corporation of China, and select 208 galloping points located in the micro-terrain area by analyzing the altitude and the topographic relief characteristics around each galloping point. Then the galloping micro-terrain types are extracted by Empirical Orthogonal Function method, the first four spatial modes of galloping micro-terrain are the windward slope of east-west mountain area, the windward slope of north-south mountain area, the independent hill, and the saddle back of mountain/hill. Finally, the regional characteristics of typical micro-terrain are analyzed according to the actual lines.

Vortex heat transfer enhancement in the separated flow near structured dimpled surfaces

The numerically discovered phenomena of abnormal enhancement of the separated flow in the inclined oval-trench dimple (OTD) and the flow acceleration in the dimpled narrow channel are substantiated experimentally. The analysis of turbulent flow around a deep OTD on the plate and on the channel wall show that within the inclination angle range from 25° to 85°, the pressure drop is seen between the zones of stagnation on the windward slope and of rarefaction in the place where a tornado-like vortex is generated. The velocity field measurements in the narrow channel with two rows of inclined OTDs at the inclination angles of ±45° and ±135° reveal that the shear flow with a maximum velocity in front of the dimple entrance is formed in the flow core. This maximum shear flow velocity exceeds the maximum velocity in the plane-parallel channel.

The Role of Aging and Wind in Inducing Death and/or Growth Reduction in Korean Fir (Abies Koreana Wilson) on Mt. Halla, Korea

The purpose of this study was to investigate the role of strong winds and aging in the death and/or decline in the growth of Korean fir on Mt. Halla in Korea. Bangeoreum (BA-S), Jindalrebat (JD-E), and Youngsil (YS-W) on the southern, eastern, and western slopes of Mt. Halla (ca. 1600 and 1700 m a.s.l.) were selected for the study. The site chronologies were established using more than 10 living Korean firs at each site. Additionally, to date the years and seasons of death of standing/fallen dead Korean firs, 15/15, 14/15, and 10/10 trees were selected at BA-S, JD-E, and YS-W, respectively. After adjusting the age with the period of growth up to the sampling point, the oldest Korean fir found among the living trees was 114 years old at JD-E and the oldest fir among the dead trees was 131 years old at JD-E. Besides this, most of the trees at BA-S and JD-E were found to have died between 2008 and 2015, and at irregular intervals between 1976 and 2013 at YS-W. Also, the maximum number of trees, that is, 62.7% died between spring and summer, followed by 20.9% between summer and autumn, and 16.4% between autumn of the current year and spring of the following year. Abrupt growth reductions occurred at BA-S and JD-E, and have become more significant in recent years, whereas at YS-W, the abrupt growth reduction and recovery occur in a cyclic order. The intensity and frequency of the typhoons increased from 2012, and this trend was in-line with the increased number of abrupt growth reductions at BA-S and JD-E. Therefore, the typhoons of 2012 are considered as the most likely influencing factor in death and/or growth reduction in Korean firs. In contrast, the decline in the growth of the Korean firs located on the windward slope (YS-W) showed a relationship with winds stronger than 25–33 m/s.

Simulations in the Topography Effects of Tianshan Mountains on an Extreme Precipitation Event in the Ili River Valley, China

Xinjiang is located in an arid and semi-arid climate region in China, but Xinjiang Ili river valley is more humid, with higher precipitation intensity and precipitation, which is closely related to the role of the Tianshan Mountains. In this paper, through the NCRP 1° × 1° reanalysis data and the conventional observation data of the Ili River Valley in Xinjiang, the terrain sensitivity experiment conducted by the WRF model is used to analyze the short-term extreme precipitation event of the Ili River Valley from 18–19 of May 2017, to reveal the influence of Tianshan Mountains on the extreme precipitation event of the Ili River Valley. The results show that: (1) The reduction or removal of the terrain will cause a wide range of wind field changes, weaken the vertical upward movement of the windward slope, and the accumulation of water vapor before the windward slope will also be reduced; a large-scale change of the terrain will also affect the direction of water vapor transportation. These effects together lead to a decrease or increase in regional precipitation. (2) “Fuzzy” (smooth) terrain will affect the precipitation simulated by changing the local vertical movement and water vapor transport, which shows that the WRF model’s accurate description of the terrain structure characteristics of mountainous areas is beneficial to accurately simulate the precipitation process on the windward slope area.

Characteristics of Summer Hourly Extreme Precipitation Events and Its Local Environmental Influencing Factors in Beijing under Urbanization Background

Studies on urban extreme precipitation and its influencing factors are significant for prevention and reduction of meteorological disasters; however, few studies focus on hourly extreme precipitation (HEP) events due to the limitation of observation. By using the summer hourly precipitation data in Beijing from 1980 to 2020, the spatial distribution and temporal variation of HEP as well as its local environmental influencing factors are investigated. It is found that both summer precipitation amount and frequency of HEP are affected by topography, with high values in windward slope area. The summer precipitation amount of HEP is 160–200 mm, accounting for 42–47% of the annual summer precipitation amount, while the frequency proportion of HEP is only 5.5–6.0%. Although the summer precipitation amount and frequency in Beijing both decrease in the past 41 years, those for HEP present an opposite trend mainly due to the increasing HEP since 2003 and this is a phenomenon worthy of attention. A similar bimodal pattern in diurnal variation is found for the summer precipitation amount and frequency of HEP, with two peaks in 19–22 LT and 01–05 LT, respectively, indicating that HEPs are more concentrated in the evening and early morning especially in urban area. Moreover, the urbanization process of Beijing is consistent with the change trend of HEP, implying that the stronger the urban heat island intensity (UHI), the higher the probability of HEP. Furthermore, the convergence lines of terrain are also conducive to local heavy rainfall, and lower tropospheric stability (LTS) and convective available potential energy (CAPE) as well as aerosols may also affect HEP in Beijing.

On the relationship of aeolian relief, microrelief and wind direction with the concentration of dust aerosol in the near-surface layer

<p>Saltations, secondary knock-out of particles, and their rolling over the surface in the abrasion process are the main source of micron- and submicron-sized particles near the surface [1]. Zones with different aerosol generation rates and wiping dynamics emerge around growing aeolian structures [3,4]. On the leeward slope, larger particles remain in the embedding zone and abrasion is less active. On the windward slope, fractions of smaller size accumulate in the zone of cascade capture of layers by wind [2], and abrasion is predominant.</p><p> </p><p>The occurrence of aeolian forms varies in time depending on their height. Three areas are considered: 1-3 m, 1-3 cm, <1 cm. The effect of changes in wind direction at intervals of a few hours changes the length of zones near aeolian structures. Thus, the cascade trapping zone expands and the accumulation zone narrows. Aeolian microstructures on the surface of the windward slope decrease the length of the cascade capture zone, leaving structures with a height > 1 cm almost unchanged.</p><p> </p><p>We consider a sample of data from summer field measurements obtained in the evening with close values of air temperature (30-32°C) and wind speeds (6.1-6.5 m/s). Observations were made on a perennial patch of unfixed sands about 1.5 km long and 200-300 m wide at 5 km to the west of Naryn Khuduk settlement (Kalmykia, 2010-2020). The lines of dune ridges for this area extend approximately in the latitudinal direction.</p><p> </p><p>Based on the empirical functions of aerosol size and mass distribution, the classification related to the wind direction in relation to the line of windward and leeward slopes connection was obtained. When the wind direction changes from frontal to tangential along the slopes, mass concentrations of coarse aerosol fraction increase. This can be related to the processes of chipping for newly involved large particles from the layers of the leeward slope setting zone. The phenomenon is also illustrated by the observed emergence on the surface of a ripple with a ridge spacing of 10-30 cm during the next day of a micro-ridge with a period of 1-2 cm. For the windward slope line change model [5], it was obtained that the fraction of detached particles decreases with the growth of new structures. The presence of aeolian ripples [6] and larger particles generally reduces the fraction of particles moving in the wind flow.  There is weakening of wiping intensity at collision and reduction of concentration of submicron particles as a result, as compared to the case of absence of developed microrelief. The type of aerosol distribution function is influenced by the size of the embedding and cascade trapping zones and the composition of the layer of particles involved in collisions and displacements near the surface.</p><p>The study was supported by the Russian Science Foundation project 20-17-00214.</p><p> </p><p>1.Houser C.A., Nickling W.G. Sedimentology. 48(2). 255,. (2001)</p><p>2.Chepil W.S. Soil Science  60(4) 305.(1945)</p><p>3.Anderson R. Sedimentology 34, 943 (1987).</p><p>4.Hoyle R., Woods A. Phys. Rev. E 56, 6861 (1997).</p><p>5.Malinovskaya E.A. Izvestiya. Atmospheric and Oceanic Physics 55(2) 218 (2019)</p><p>6. Malinovskaya E. et al. EGU2019-3693-1 (2019)</p><p> </p>

Optimization of Scanning Scheme for Low-height Vegetation Survey Based on Terrestrial Laser Scanning - A Case Study on the Restored Sand Land, Southern Qinghai-Tibetan Plateau

Background: In recent decades, vegetation surveys based on terrestrial laser scanning (TLS) have developed rapidly, especially on the forest inventory, but few studies have been conducted to the low-height vegetation. Because of the high investigation cost and subjectivity, it is impending to provide a scientific scanning scheme based on the TLS for the low-height vegetation survey (e.g. shrub, grassland, and meadow) in eco-fragile region (e.g. Qinghai-Tibetan Plateau). Method: In this study, we extracted the vegetation parameter i.e., number, height (H), and crown width (CW) of the two sample plots to evaluate the integrity of the data collected by TLS, on the restored sand land in southern Qinghai-Tibetan Plateau. We assessed the difference between the scanning mode of single-scan (SS) and multiple-scan (MS), and evaluated the influence of terrain fluctuation (windward slope, leeward slope, and the peak of slope) on the determination of scanning spots.Results: The results showed that: (1) the accuracy of vegetation parameter extracted by the mode of SS was mainly affected by the occlusion and the distance from central scanning spot, the RMSE of vegetation parameters is the smallest (RMSEH = 0.186 m; RMSECW = 0.208 m) within 20 m from the central scanning spot. (2) For the MS mode, in addition to the central scanning spot, the scanning spot located at the peak of the slope is the most important, which was the connection of combining the data of windward slope and leeward slope.Conclusion: To sum up, the scientific layout of scanning spot is the key to collecting data by TLS efficiently, and topography is the main factor affecting the layout of scanning spot. Since occlusion effect cannot be avoided, it can only be compensated by setting up more scanning points. Secondly, the accuracy of different sensors will has influence on the distance between adjacent scanning spots.

Wind Tunnel Measurements of Surface Shear Stress on an Isolated Dune Downwind a Bridge

As part of a comprehensive environmental assessment of the Dun-Gel railway project located in Dunhuang city, Gansu Province, China, a wind tunnel experiment was proposed to predict surface shear stress changes on a sand dune when a bridge was built upstream it. The results show that the length of the wall shear stress shelter region of a bridge is about 10 times of the bridge height (H). In the cases that the interval of the bridge and sand dune (S) is less than 5 H, normalized wall shear stress on the windward crest is decreased from 1.75 (isolated dune) to 1.0 (S = 5.0 H, measured downwind bridge pier) and 1.5 (S = 5.0 H, measured in the middle line of two adjacent bridge piers). In addition, the mean surface shear stress in the downstream zone of the sand dune model is reduced by the bridge pier and is increased by the bridge desk. As for the fluctuation of surface shear stress ( ζ ) on the windward crest, ζ decreases from 1.3 (in the isolated dune case) to 1.2 (in the case S = 5.0 H, measured just downwind the pier) and increases from 1.3 (in the isolated dune case) to 1.6 (in the cases S = 5.0 H, in the middle of two adjacent piers). Taking the mean and fluctuation of surface shear stress into consideration together, we introduce a parameter ψ ranging from 0 to 1. A low value indicates deposition and a high value indicates erosion. On the windward slope, the value of ψ increases with height (from 0 at toe to 0.98 at crest). However, in the cases of S = 1.5 H, ψ is decreased by the bridge in the lower part of the sand dune at y = 0 and is increased at y = L/2 compared with the isolated dune case. In other cases, the change of ψ on the windward slope is not as prominent as in the case of S = 1.5 H. Downstream the sand dune, erosion starts in a point that exists between x = 10 H and 15 H in all cases.