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981.
A mesoscale Planetary Boundary Layer (PBL) model with a simple turbulence closure scheme based on the turbulence kinetic energy (TKE) equation and the dissipation () equation is used to simulate atmospheric flow over mesoscale topography. Comparative studies with different parameterizations suggest that with a proper closure assumption for turbulence dissipation, the E-model can simulate the circulation induced by the mesoscale topography with results similar to those obtained using the E- model. On the other hand, the first-order closure using O'Brien's cubic interpolation for eddy diffusivities (K) generally produces much larger K profiles in the stable and the unstable regions, which is believed to be due to the overprediction of the height of the PBL. All models with the TKE equation yield quite similar ensemble mean fields, which are found to be little sensitive to the closure assumption for turbulence dissipation, though their predicted magnitudes of TKE and K may differ appreciably. A discussion on the diurnal evolution of the mesoscale topography-induced circulation and the spatial variations of the turbulence fluxes in the surface layer is also given based on the E- model results. 相似文献
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983.
984.
The temporal variability of 210Po and 210Pb was examined in the overlying water of the Zhubi Coral Reef flat to detect nutrient-like behavior of 210Po. Different mechanisms influencing their geochemical behaviors were observed. Excess 210Po relative to 210Pb revealed an additional input of 210Po other than in situ production from 210Pb. The 210Po input comes from the reef flat sediment through diffusion. The diffusion contributes 62% of the total 210Po. This diffusion of 210Po directly highlights its nutrient-like behavior. No input, but the slight removal, of 210Pb was observed. Fractionation factors indicate that particulate matter prefers to adsorb 210Po rather than 210Pb. In combination with particulate composition, 210Po diffusion was closely related to organic matter. These results reveal that 210Po might be a potential tracer for quantifying nutrient recycling in the Coral Reef system. 相似文献
985.
利用常规观测资料、ERA5再分析资料、FY-2G卫星TBB数据和双偏振雷达资料等,对2022年6月29日浙江省金华地区一次强对流过程的环境条件与中尺度特征进行了分析。结果表明:1) 充沛的不稳定能量、较低的抬升凝结高度和中等强度的0—3 km垂直风切变为此次强对流过程的发生发展提供了良好环境条件。2) 触发机制主要为边界层辐合线;低层强烈辐合、高层强烈辐散的配置,为对流提供了良好的动力条件;源源不断的水汽供应和水汽辐合,致使暴雨天气的产生和维持。3) 降雹时刻风暴单体雷达回波具有高反射率因子、高垂直累积液态含水量、旁瓣回波、大于55 dBz强回波伸展高度超过-20 ℃层、回波悬垂结构和有界弱回波区等特征;双偏振参量对应较小的差分反射率和较大的差分相移率,湿雹特征明显。 相似文献
986.
Zhiteng?YuEmail author Jiabiao?LiEmail author Weiwei?Ding Jie?Zhang Aiguo?Ruan Xiongwei?Niu 《Marine Geophysical Researches》2017,38(1-2):85-104
The Southwest Subbasin (SWSB) is an abyssal subbasin in the South China Sea (SCS), with many debates on its neotectonic process and crustal structure. Using two-dimensional seismic tomography in the SWSB, we derived a detailed P-wave velocity model of the basin area and the northern margin. The entire profile is approximately 311-km-long and consists of twelve oceanic bottom seismometers (OBSs). The average thickness of the crust beneath the basin is 5.3 km, and the Moho interface is relatively flat (10–12 km). No high velocity bodies are observed, and only two thin high-velocity structures (~7.3 km/s) in the layer 3 are identified beneath the northern continent-ocean transition (COT) and the extinct spreading center. By analyzing the P-wave velocity model, we believe that the crust of the basin is a typical oceanic crust. Combined with the high resolution multi-channel seismic profile (MCS), we conclude that the profile shows asymmetric structural characteristics in the basin area. The continental margin also shows asymmetric crust between the north and south sides, which may be related to the large scale detachment fault that has developed in the southern margin. The magma supply decreased as the expansion of the SWSB from the east to the west. 相似文献
987.
988.
Ji Yang Ying-Xi Zuo Zheng LOU Jing-Quan Cheng Qi-Zhou Zhang Sheng-Cai Shi Jia-Sheng Huang Qi-Jun Yao Zhong Wang 《天体物理学报》2013,(12):1493-1508
As the highest, coldest and driest place in Antarctica, Dome A provides exceptionally good observing conditions for ground-based observations over terahertz wavebands. The 5 m Dome A Terahertz Explorer (DATES) has been proposed to explore new terahertz windows, primarily over wavelengths between 350 and 200 pm. DATE5 will be an open-air, fully-steerable telescope that can function by unmanned operation with remote control. The telescope will be able to endure the harsh polar environment, including high altitude, very low temperature and very low air pressure. The unique specifications, including high accuracies for surface shape and pointing and fully automatic year-around remote operation, along with a stringent limit on the periods of on-site assembly, testing and maintenance, bring a number of challenges to the design, construction, assembly and operation of this telescope. This paper intro- duces general concepts related to the design of the DATE5 antenna. Beginning from an overview of the environmental and operational limitations, the design specifications and requirements of the DATE5 antenna are listed. From these, major aspects on the conceptual design studies, including the antenna optics, the backup structure, the pan- els, the subreflector, the mounting and the antenna base structure, are explained. Some critical issues of performance are justified through analyses that use computational fluid dynamics, thermal analysis and de-icing studies, and the proposed approaches for test operation and on-site assembly. Based on these studies, we conclude that the specifications of the DATE5 antenna can generally be met by using enhanced technological approaches. 相似文献
989.
990.
Marc?Hesse Timothy?L.?GroveEmail author 《Contributions to Mineralogy and Petrology》2003,146(1):10-27
We have investigated the near liquidus phase relations of a primitive absarokite from the Mascota region in western Mexico. Sample M.102 contains ~11.6 wt% MgO, Mg#=0.73 and the lava contains Fo90 olivine phenocrysts, indicating near equilibrium with the mantle. High-pressure experiments on a synthetic analogue of the absarokite composition containing low and high H2O abundances of (~2 and ~5 wt%, respectively) were performed in a piston cylinder apparatus over the pressure range of 1.2 to 2.0 GPa. The composition containing ~2 wt% H2O is multiply saturated with olivine and orthopyroxene at 1.6 GPa and 1,400 °C. At the same pressure, clinopyroxene appears 30 °C below the liquidus. At an H2O content of ~5 wt% the multiple saturation with olivine and orthopyroxene occurs at 1.7 GPa and 1,300 °C. Assuming a batch-melting process, we suggest that the primitive absarokite was segregated from a depleted lherzolite or harzburgite residue at ~50 km, placing the depth of origin well within the mantle wedge beneath the Jalisco Block. A low degree (<5 %wt%) batch-melt of an original metasomatized depleted lherzolite or harzburgite source would contain the observed trace element abundances found in M.102. The liquidus phase relations are not consistent with the presence of non-peridotitic veins at the depth of last equilibration. Therefore, we propose that the Mascota absarokites segregated at an apparent melt fraction of less than 5% from a depleted peridotitic source. Melting first began at a greater depth as a small degree H2O- and trace element- rich melt of a metasomatized peridotite that ascended into the overlying wedge and re-equilibrated with shallower, hotter mantle.Editorial responsibility: J. Hoefs 相似文献