Controlling factors of plant community composition with respect to the slope aspect gradient in the Qilian Mountains

Slope aspect can affect soil temperature and soil type distribution, which, in turn, is likely to influence plant community composition. Three Qilian mountains, located in the northeastern part of the Qinghai–Tibetan Plateau, China, with four distinct slope aspects including south‐facing (SF), southwest‐facing (SW), northwest‐facing (NW), and north‐facing (NF) slope aspects, were studied to investigate the impact of slope aspect on plant assemblages. The results indicated that the environmental conditions were favorable under the NF and NW slope aspects as the soil water, soil organic carbon (SOC), and soil total nitrogen (STN) contents were significantly higher, and soil temperature (ST) and soil bulk density (SBD) were significantly lower than under the SF and SW aspects. Under all slope aspects, however, SOC, STN, and soil total phosphate in the top 0.2 m of topsoil accounted for about 60% of its total quantity, to a soil depth of 0.6 m. The plant communities on the SF and SW slopes were found to be primarily composed of Poa pratensis, Potentilla anrisena, and Carex aridula. In contrast, the plant community on the NW slope was mainly composed of Kobresia humilis, Carex crebra, and Potentilla bifurca, while on the NF slope it was mainly composed of Picea crassifolia, Carex scabrirostris, and Polygonum macrophyllum. The order of the influence of environmental factors on species distributions was ST > SBD > sand > STN. Results suggest that the slope aspect has an important role in the regulation of the soil environment and plant assemblages and that ST and SBD were the main factors influencing plant community composition. Furthermore, evidence from this study suggests that these mountains will become increasingly vulnerable to global warming. Thus, the plant community composition on these mountains must be monitored continuously in order to allow for strategic adaptive management

Diurnal Variations of Surface Fluxes and Boundary Layer over Tibetan Plateau (Session 3: In-site Flux Observation studies)

During the GAME-Tibet IOP, surface eddy fluxes were directly measured at four stations as well as radiation fluxes. These flux data were summarized and compared in the diurnal and seasonal basis. Another important issue is the interaction between the surface fluxes and the atmospheric boundary layer. It is clearly observed in sensible heat flux and mixed layer development, and mixed layer during the daytime leads to large amplitude of diurnal variation in surface wind speed

Increasing compound drought and hot event over the Tibetan Plateau and its effects on soil water

Climate extremes, such as droughts and hot events, are expected to become more frequent and intense as the Earth’s climate continues to change. Indeed, they will likely pose increasingly serious threats to both humanity and the sustainability of natural ecosystems. Compound climate extremes may significantly impact regions sensitive to climate change, such as the Tibetan Plateau (TP), although there is currently a notable lack of research on compound extreme drought and hot events (CEDHs) that affect this region. We employed the copula model using the standardized precipitation index (SPI), standardized temperature index (STI), and standardized soil moisture index (SSMI) to explore patterns of changes in CEDHs and assess the risk of soil water scarcity under CEDHs. Our results showed that the probability of CEDHs increased significantly across the TP over time, mainly due to hot events becoming more common. The conditional probability of soil water scarcity (SSMI  0.8) increased by 81.8% and 21.4% over time compared with those under individual hot and dry conditions, respectively. Our findings have important implications for mitigating the impacts of CEDHs under future global warming scenarios

Multi-Parameter Optimization of Heat Dissipation Structure of Double Disk Magnetic Coupler Based on Orthogonal Experimental Design

The existing heat dissipation research on double disk magnetic couplers ignores the coupling influence of electromagnetic temperature–stress and other multiphysics fields, and the error between the calculation and analysis results and the measured values is large. Therefore, a multi-parameter optimization method for heat dissipation structures of double disk magnetic couplers based on orthogonal experimental design is proposed. Based on the double disk magnetic coupler model, a three-dimensional finite element model based on fluid–solid–heat coupling is established, with the axial air gap length, input motor speed, the thickness of the permanent magnet in the magnetizing direction, the thickness of the copper plate, the number of fins of the heat dissipation plate and the length of the fins of the heat dissipation plate as design variables. Six-factor and three-level simulation experiments are designed with the minimum temperature of the heat dissipation plate as the objective function, and additionally, orthogonal experiments were designed according to the actual working conditions by selecting the optimal combination of parameters and modifying the model to perform physical tests. The results show that the variables that have the most significant impact on heat dissipation performance from high to low are as follows: axial air gap length, input motor speed, the length of the fins of the heat dissipation plate, the thickness of the permanent magnet in the magnetizing direction, the number of fins of the heat dissipation plate and the thickness of the copper plate. The increase in axial air gap length can effectively reduce the temperature rise, and the maximum decrease can reach 9.76%. Under the same conditions, the input motor speeds are set to 300 r/min, 400 r/min, 500 r/min, 600 r/min and 700 r/min, respectively, and the simulation results are in good agreement with the physical test results, with a maximum error of 4.8%. The error between the simulation result and the physical test result is only 1.9% under the optimal combination of parameters obtained by the orthogonal experiment, which verifies the correctness of the optimization model. In conclusion, the study is of reference significance for the parameter optimization of the heat dissipation structure of the double disk magnetic coupler

Actual and Reference Evapotranspiration in a Cornfield in the Zhangye Oasis, Northwestern China

Evapotranspiration (ET) is an important component of the surface energy balance and water cycle, especially in arid and semiarid regions. The characteristics of the actual evapotranspiration (ETa), which was calculated using the eddy covariance method, and the reference evapotranspiration (ET0), which was estimated using the Food and Agriculture Organisation (FAO) Penman–Monteith method, were analysed. This work focussed on the seasonal variations in evapotranspiration and crop coefficient (Kc) above the heterogeneous canopy of an arid oasis ecosystem in a cornfield of the Zhangye oasis in northwestern China. The results showed that in 2008, the total net radiation (Rn) was 2457.73 MJ∙m−2 and that the rainfall was 117 mm. The average wind velocity, air temperature, and specific humidity, which were observed 2 m above the ground surface, were 1.23 m∙s−1, 7.07 °C, and 3.66 g∙kg−1, respectively. The total ETa and ET0 were 654.69 mm and 1039.92 mm, respectively; thus, the ET0 was higher than the ETa. The difference between the ET0 and ETa was high in summer and autumn, and low in winter and spring. The ETa was greatly influenced by irrigation events, whereas the ET0 was not influenced by irrigation. The ETa and ET0 were both greatly influenced by meteorological elements. The Kc values were less than 0.5 outside of the maize-growing stage and greater than 0.5 during the entire maize-growing stage (from 20 April to 22 September 2008). The Kc values were 0.63, 0.75, 0.78, 0.76, 0.61 and 0.71 at the seedling, shooting, heading, filling, and maturity stages and the entire growth stage, respectively

☑Under a wait / Role of Patchy Snow Cover on the Planetary Under a waitBoundary Layer Structure during Late Winter Observed in the Central Tibetan Plateau

The one-dimensional structure of a daytime planetary boundary layer (PBL) with shallow cloud development was captured by intensive sonde observation during the late winter season at the central Tibetan Plateau (TP), and its relationship to patchy snow cover conditions was revealed. The diurnal change of potential temperature was evident in the atmosphere up to 1 km above ground, indicating PBL development, and frequent cloud formation in the afternoon and night over the PBL was confirmed by the increase of relative humidity in the sonde data profile and abrupt decrease of brightness temperature in the satellite images. Day-to-day changes of PBL and nighttime stable layer developments were dependent on the speed of the sub-tropical jet stream prevailing 5 km above the surface and the changing of snow cover conditions after snowfall events. Numerical simulations confirmed that the increase of land-surface albedo, imitating the continuous snow covers, could suppress the PBL and cloud development. The positive feedback of land-atmosphere interactions through the PBL development on patchy snow cover and re-distribution process of shallow and dry snow cover were discussed.著者から連絡があったら公

Analysis and inhibition of radial electromagnetic force in composite magnetic coupler

Abstract A new inhibition method was proposed for the problem of harmonic of radial electromagnetic force during the operation of the composite magnetic coupler. In order to suppress its radial electromagnetic force, a radial permanent magnet rotor eccentricity method is proposed, and a three‐dimensional finite element model is established. Based on the Maxwell tensor method, the radial electromagnetic force of the composite magnetic coupler is analysed, and the mathematical expression of its radial electromagnetic force is established, Maxwell stress tensor was used to analyse the radial electromagnetic force in a composite magnetic coupler and to establish the mathematical equation for the radial electromagnetic force. In order to suppress the radial electromagnetic force, a method based on rotor eccentricity in a radial permanent magnet was proposed. A prototype of a composite magnetic coupler with a rated power of 5 kW was designed to test its output torque under load. The results showed that the simulated curve was consistent with the tested curve, with a maximum numerical error of 8.9%. The tested values of the output torque before and after eccentricity were compared, and the results showed that the output torque remained basically unchanged after the eccentric structure was adopted and that the torque pulsation was significantly reduced

Topographical and Thermal Forcing in Favorable Circulation Pattern to Early Spring Precipitation over the Southeastern Tibetan Plateau

During the boreal spring (March–May), the precipitation that occurs from March over the southeastern Tibetan Plateau (TP) can account for 20–40% of the total annual amount. The origin of this phenomenon has not been clearly understood from a climatological perspective. In this study, the role of topographical and thermal forcing on the precipitation over the southeastern TP in early spring (March) was investigated through sensitivity numerical simulations based on general circulation model. The simulated results show the favorable circulation and static stability to early spring precipitation over the southeastern TP when the model is simultaneously forced by realistic topography, zonal symmetric radiative equilibrium temperature, and diabatic heating over the TP and its surrounding areas. The quasi-stationary wave pattern over the Eurasian continent forced by realistic and TP topographical forcing leads to prolonged low pressure and intensified zonal winds over the southeastern TP due to quasi-steady wave activities. Thermal forcing experiments reveals that sensible heating over the southeastern TP not only strengthens the cyclonic circulation, ascending motion and statically unstable over the southeastern TP through thermal adaptation and the Sverdrup balance, but also triggers an anticyclone at upper tropospheric level extending from north of the Bay of Bengal to the eastern TP, which further favors precipitation over the southeastern TP. This work will provide useful background information for spring climate prediction over the TP

Topographical and Thermal Forcing in Favorable Circulation Pattern to Early Spring Precipitation over the Southeastern Tibetan Plateau

During the boreal spring (March–May), the precipitation that occurs from March over the southeastern Tibetan Plateau (TP) can account for 20–40% of the total annual amount. The origin of this phenomenon has not been clearly understood from a climatological perspective. In this study, the role of topographical and thermal forcing on the precipitation over the southeastern TP in early spring (March) was investigated through sensitivity numerical simulations based on general circulation model. The simulated results show the favorable circulation and static stability to early spring precipitation over the southeastern TP when the model is simultaneously forced by realistic topography, zonal symmetric radiative equilibrium temperature, and diabatic heating over the TP and its surrounding areas. The quasi-stationary wave pattern over the Eurasian continent forced by realistic and TP topographical forcing leads to prolonged low pressure and intensified zonal winds over the southeastern TP due to quasi-steady wave activities. Thermal forcing experiments reveals that sensible heating over the southeastern TP not only strengthens the cyclonic circulation, ascending motion and statically unstable over the southeastern TP through thermal adaptation and the Sverdrup balance, but also triggers an anticyclone at upper tropospheric level extending from north of the Bay of Bengal to the eastern TP, which further favors precipitation over the southeastern TP. This work will provide useful background information for spring climate prediction over the TP