Impact of surface variations on the momentum flux above the urban canopy

Based on the momentum flux–wind profile relationship of the Monin–Obukhov Similarity (MOS) theory, the observational data from the urban boundary layer field campaign in Nanjing are used to calculate the friction velocity ( $ {u_*} $ ) at the top of the urban canopy and the calculated results are evaluated. The urban surface roughness parameters (the roughness length z ₀ and zero-plane displacement height z _d) are estimated with the Ba method (Bottema’s morphological method). Two different regimes are employed for the calculations. In the homogeneous approach, z ₀ and z _d are averagely derived from the surface elements in the whole study area; while in the heterogeneous approach, z ₀ and z _d are locally derived from the surface elements in the corresponding upwind fetches (or source areas). The calculated friction velocities are compared to the measurement data. The results show that the calculated friction velocities from the heterogeneous approach are in better agreement with the observed values than those from the homogeneous approach are. This study implies that the local roughness parameters can properly represent the dynamical heterogeneity of urban surface, and its application can significantly improve the performance of parameterizations based on the MOS theory in the urban roughness sublayer.     

一次冷涡过程降水的微物理机制分析

该文分析了一次冷涡天气过程中云微物理量的分布特征、降水粒子的增长机制及云下雨滴的蒸发效应。主要结果为：云系由低层暖性Sc云和冷性主体As云组成。As云底高2 km,云顶高大于5 km,云中存在比较大的过冷水区,–11.2 ℃时的过冷水含量0.21 g·m-3,但过冷水的含量分布极不均匀,大于0.05 g·m-3的过冷水区连续分布的宽度87%小于2.4 km,不利于云中冰晶的连续凇附增长;同时云下雨滴的蒸发效应大,直径小于1.0 mm的雨滴难以落到地面,因此本次过程只产生弱的降水。     

IC-D新型脉冲标定电路的设计与应用——华北地区遥测地震台网联网论文续七

介绍了一种适用于遥测地震台网台站钟控脉冲标定的IC-D新型脉冲标定电路.     

Structural Setting of Strong Earthquakes in the Huabei Area of China

— Using P and S arrival times, which occurred within the Huabei seismic network, we carried out a tomographic inversion and compared results with the earthquake catalogue of the last 1000?years in the area. The results are as follows:¶1) The hypocenters of most of the strong shocks are distributed in the transitional zones between high- and low-velocity areas in the crust, especially at edges of high-velocity blocks.¶2) Strong shocks predominantly lie above low-velocity blocks, or in transitional zones between low- and high-velocity areas, in the lower crust.¶3) The tectonic settings for the Tangshan and the Sanhe-Pingu earthquakes are similar. Both are not known near large fault belts, and in zones with a sharp lateral velocity gradient.¶4) The Ninghe, Tangshan and Luanxia earthquakes are located in high-velocity blocks that differ in size and depth. This difference can explain the focal depth distribution of the Tangshan earthquake sequence, i.e., earthquakes are shallower in the northeastern Luanxian area but deeper in the southwestern Ninghe area.     

Fast and dynamic generation of linear octrees for geological bodies under hardware acceleration

In the application of 3D Geoscience Modeling,we often need to generate the volumetric representations of geological bodies from their surface representations.Linear octree,as an efficient and easily operated volumetric model,is widely used in 3D Geoscience Modeling.This paper proposes an algorithm for fast and dynamic generation of linear octrees of geological bodies from their surface models under hardware acceleration.The Z-buffers are used to determine the attributes of octants and voxels in a fast way,a...     

A new framework for evaluating along-wind responses of a transmission tower

In this paper, an analytical framework to evaluate the along-wind-induced dynamic responses of a transmission tower is presented. Two analytical models and a new method are developed: (1) a higher mode generalized force spectrum (GFS) model of the transmission tower is deduced; (2) an analytical model that includes the contributions of the higher modes is further derived as a rational algebraic formula to estimate the structural displacement response; and (3) a new approach, applying load with displacement (ALD) instead of force, to solve the internal force of transmission tower is given. Unlike conventional methods, the ALD method can avoid calculating equivalent static wind loads (ESWLs). Finally, a transmission tower structure is used as a numerical example to verify the feasibility and accuracy of the ALD method.     

On the Mechanism of Air Pollutant Removal in Two-Dimensional Idealized Street Canyons: A Large-Eddy Simulation Approach

Flow resistance, ventilation, and pollutant removal for idealized two-dimensional (2D) street canyons of different building-height to street-width (aspect) ratios $AR$ are examined using the friction factor $f$ , air exchange rate (ACH), and pollutant exchange rate (PCH), respectively, calculated by large-eddy simulation (LES). The flows are basically classified into three characteristic regimes, namely isolated roughness, wake interference, and skimming flow, as functions of the aspect ratios. The LES results are validated by various experimental and numerical datasets available in the literature. The friction factor increases with decreasing aspect ratio and reaches a peak at $AR = 0.1$ in the isolated roughness regime and decreases thereafter. As with the friction factor, the ACH increases with decreasing aspect ratio in the wake interference and skimming flow regimes, signifying the improved aged air removal for a wider street canyon. The PCH exhibits a behaviour different from its ACH counterpart in the range of aspect ratios tested. Pollutants are most effectively removed from the street canyon with $AR = 0.5$ . However, a minimum of PCH is found nearby at $AR = 0.3$ , at which the pollutant removal is sharply weakened. Besides, the ACH and PCH are partitioned into the mean and turbulent components to compare their relative contributions. In line with our earlier Reynolds-averaged Navier–Stokes calculations (Liu et al., Atmos Environ 45:4763–4769, 2011), the current LES shows that the turbulent components contribute more to both ACH and PCH, consistently demonstrating the importance of atmospheric turbulence in the ventilation and pollutant removal for urban areas.     

The effect of seafloor topography in the Southern Ocean on tabular iceberg drifting and grounding

Antarctic tabular icebergs are important active components in the ice sheet-ice shelf-ocean system. Seafloor topography is the key factor that affects the drifting and grounding of icebergs, but it has not been fully investigated. This study analyzes the impact of seafloor topography on the drifting and grounding of Antarctic tabular icebergs using Bedmap-2 datasets and iceberg route tracking data from Brigham Young University. The results highlight the following points. (1) The quantitative distributions of iceberg grounding events and the tracking points of grounded icebergs are mainly affected by iceberg draft and reach their peak values in sea water with depths between 200 m and 300 m. The peak tracking point number and linear velocity of free-drifting icebergs are found in the Antarctic Slope Front (water depth of approximately 500 m). (2) The area of possible grounding regions of small-scale icebergs calved from ice shelf fronts accounts for 28% of the sea area at water depths less than 2000 m outside the Antarctic coastline periphery (3.62 million km²). Their spatial distribution is mainly around East Antarctica and the Antarctic Peninsula. The area of possible grounding regions of large tabular icebergs with long axes larger than 18.5 km (in water depths of less than 800 m) accounts for 74% of the sea area. (3) The iceberg drifting velocity is positively correlated with ocean depth in areas where the depth is less than 2000 m (R=0.85, P<0.01). This result confirms the effect of water depth variations induced by seafloor topography fluctuations on iceberg drifting velocity.     

容量法测定水样中硫酸根

本文对EDTA滴定过量Pb间接测定SO_4~(2-)的方法作了改进。加入乙醇抑制PbSO_4沉淀的溶解,使滴定不需分离沉淀而直接进行。用六次甲基四胺调节控制pH为5.2—5.4,可避免大量共存Ca~(2+)、Mg~(2+)的干扰。改进后的方法简单、快速,准确度和精密度均好,可适用SO_4~(2-)含量高于1mg/L的天然水分析。