Comparison of a Spectral Bin and Two Multi-Moment Bulk Microphysics Schemes for Supercell Simulation:Investigation into Key Processes Responsible for Hydrometeor Distributions and Precipitation

There are more uncertainties with ice hydrometeor representations and related processes than liquid hydrometeors within microphysics parameterization(MP)schemes because of their complicated geometries and physical properties.Idealized supercell simulations are produced using the WRF model coupled with“full”Hebrew University spectral bin MP(HU-SBM),and NSSL and Thompson bulk MP(BMP)schemes.HU-SBM downdrafts are typically weaker than those of the NSSL and Thompson simulations,accompanied by less rain evaporation.HU-SBM produces more cloud ice(plates),graupel,and hail than the BMPs,yet precipitates less at the surface.The limiting mass bins(and subsequently,particle size)of rimed ice in HU-SBM and slower rimed ice fall speeds lead to smaller melting-level net rimed ice fluxes than those of the BMPs.Aggregation from plates in HU-SBM,together with snow–graupel collisions,leads to a greater snow contribution to rain than those of the BMPs.Replacing HU-SBM’s fall speeds using the formulations of the BMPs after aggregating the discrete bin values to mass mixing ratios and total number concentrations increases net rain and rimed ice fluxes.Still,they are smaller in magnitude than bulk rain,NSSL hail,and Thompson graupel net fluxes near the surface.Conversely,the melting-layer net rimed ice fluxes are reduced when the fall speeds for the NSSL and Thompson simulations are calculated using HU-SBM fall speed formulations after discretizing the bulk particle size distributions(PSDs)into spectral bins.The results highlight precipitation sensitivity to storm dynamics,fall speed,hydrometeor evolution governed by process rates,and MP PSD design.

Analysis on the Doppler Radar Materials of A Typical Supercell Hailstorm

Based on basic reflectivity of Doppler radar,radial velocity and wind shear result calculated via radial velocity,a typical supercell hailstorm was analyzed.It was found that strong echo appeared in the middle level of volume scan during the beginning of storm and the converging radial wind indicated the increasing echo;with the development of storm,the converging radial wind increased gradually and tended to extend vertically,which reveals that the influx of warm and damp air provides enough vapor and heat.In the fastigium of storm,bounded weak echo region and V-shape gap can be observed;moreover,there was a mesocyclone in the radial velocity field.Vertical shear reflected environment field that wind rotated in clockwise with the increase of height,warm and damp influx at low altitude,the dry and cold air diverging at high altitude and the spatial distribution of ascending air flow at the middle level;during the dispersing of storm,the divergence of radial wind transformed to lower level gradually and its convergence reduced with strong echo disappeared.

Analysis of Supercell Storm Structure and Mesocyclone Parameters

By using the high spatial and temporal resolution Jinan Doppler Weather Radar data and Jinan,Xingtai sounding data,the radar signature and mesocyclone parameters of 54 supercells during 2003-2008 were analyzed.The results showed that the probability of a supercell forming would be higher when SI (showalter index) ≤ -2℃,K (K index) ≥ 30℃ and 0-6 km wind shear>15 m/s.The supercell storms can generally be divided into two categories,namely,type of isolation and mosaic type.To the type of isolation,the max reflectivity,cell-based VIL,max reflectivity height,cell top,mesocyclone base and top were significantly higher than the mosaic type.Isolation-type supercells had significantly higher probability of hail,lower probability of gale than the mosaic category.The mesocyclone attribute differences between isolation-type and mosaic type supercells determined the differences of storm structures and severe weather phenomenon.

丰田4A-FE型发动机的改进

较详细介绍了丰田公司对4A-FE型1.6升4缸发动机所进行的改进,从而提高了全部转速范围内的性能和燃油经济性。例如,采用了爆震控制装置、怠速控制装置和燃油蒸发污染物排放控制系统等。通过改进燃油控制系统,使得发动机更加省油。

Cr_2O_3在a-Fe_2O_3中固溶量的测定

本文采用X射线晶胞参数法,测定了Cr2O3在a-Fe2O3中的固溶量,其相对误差为2.08%,是一行之有效的方法,本方法简单易行,准确度高。

Sensitivities of Tornadogenesis to Drop Size Distribution in a Simulated Subtropical Supercell over Eastern China

ABSTRACT Numerical simulations with the Advanced Regional Prediction System （ARPS） model were performed to investigate the impact of microphysical drop size distribution （DSD） on tornadogenesis in a subtropical supercell thunderstorm over Anhui Province, eastern China. Sensitivity experiments with different intercept parameters of rain, hail and snow DSDs in a Lin-type microphysics scheme were conducted. Results showed that rain and hail DSDs have a significant impact on the simulated storm both microphysically and dynamically. DSDs characterized by larger （smaller） intercepts have a smaller （larger） particle size and a lower （higher） mass-weighted mean fall velocity, and produce relatively stronger （weaker） and wider （narrower） cold pools through enhanced （reduced） rain evaporation and hail melting processes, which are then less favorable （favorable） for tornadogenesis. However, tornadogenesis will also be suppressed by the weakened mid-level mesocyclone when the cold pool is too weak. When compared to a U.S. Great Plain case, the two microphysical processes are more sensitive to DSD variations in the present case with a higher melting level and deeper warm layer. This suggests that DSD-related cloud microphysics has a stronger influence on tornadogenesis in supercells over the subtropics than the U.S. Great Plains.

基于A-F双临界值法的外卖骑手多维影响因素研究

从工作环境与压力、权益保障、职业发展、个人能力、就业稳定性、就业满意度六个方面构建就业脆弱性评价体系,利用各地区外卖骑手的调查数据,采用A-F双临界值法对外卖骑手就业脆弱状况进行分析。研究表明:当k为0.3时,样本骑手约有70%表现出多维就业脆弱性,专送骑手比众包骑手的就业脆弱性程度更加严重;事故率、工作时间、社会保险、升职和加薪可能性是影响骑手就业脆弱性的主要因素;分组研究表明,青少年骑手、美团公司骑手的就业脆弱性程度更高。基于研究结论,提出了提高骑手就业质量的相关建议。研究内容对促进平台经济的发展以及我国外卖骑手职业发展具有一定的理论价值和现实意义。

Investigating Lightning Characteristics through a Supercell Storm by Comprehensive Coordinated Observations over North China

Electrical characteristics of an isolated supercell storm observed on 13 June 2014 over Beijing were investigated using lightning data obtained from the Beijing Lightning Network,radar reflectivity,and hydrometeor retrievals during the 6-h lifetime.Positive cloud-to-ground(+CG)lightning took a high percentage of CG lightning.Before and during a hail event,+CG lightning was more frequent than negative cloud-to-ground(-CG)lightning,except that+CG lightning took a high percentage at the beginning and in the dissipating stage.After the hail event ended,-CG lightning dominated and reached its maximum value.An analysis of hydrometeors retrieved by X-band polarimetric radar revealed that the discharge concentrated in the convective region with graupel particles and hailstones,whereas graupel,snow and ice crystals in the stratiform region.Lightning radiation sources were located mainly in the convective region,some of which were distributed along a gradient of radar reflectivity from the convective region to the stratiform region.The indication is that the supercell demonstrated an inverted tripole charge structure before the hail event,which converted to a normal tripole structure after the hail event.

Radar-based Characteristics and Formation Environment of Supercells in the Landfalling Typhoon Mujigae in 2015

This study presents the radar-based characteristics and formation environment of supercells spawned by the tornadic landfalling Typhoon Mujigae(2015)in October 2015.More than 100 supercells were identified within a 24-hour period around the time of the typhoon’s landfall,of which three were tornadic with a rotational intensity clearly stronger than those of non-tornadic supercells.The identified supercells were concentrated within a relatively small area in the northeast quadrant beyond 140 km from the typhoon center.These supercells were found more likely to form over flat topography and were difficult to maintain in mountainous regions.During the study period,more supercells formed offshore than onshore.The mesocyclones of the identified supercells were characterized by a small diameter generally less than 5 km and a shallow depth generally less than 4 km above ground level.An environmental analysis revealed that the northeast quadrant had the most favorable conditions for the genesis of supercell in this typhoon case.The nondimensional supercell composite parameter(SCP)and entraining-SCP(E-SCP)were effective in separating supercell from non-supercell environment.Even though the atmosphere in the typhoon’s northeast quadrant was characterized by an E-SCP/SCP value supportive of supercell organization,orography was an impeditive factor for the supercell development.These findings support the use of traditional parameters obtained from midlatitude supercells to assess the supercell potential in a tropical cyclone envelope.

Characteristics of Radar Echo Parameters and Microphysical Structure Simulation of a Short-Time Heavy Precipitation Supercell

By using the conventional observations, radar data, NCEP/NCAR FNL 1°×1° reanalysis data and numerical simulation data and with the construction and calculation of radar echo parameters, this paper presents the structural characteristics and physical processes of a short-time heavy precipitation supercell that occurred in the squall line process in Shanxi Province on 24 June 2020. The results show that this squall line event occurred in front of a surface cold front,combined with infiltration of low-level cold air and continuous increase of near-surface humidity in the afternoon. The surface mesoscale convergence line and mesoscale dew point front contributed to the development and systemization of the squall line by a large degree. The short-time extremely heavy precipitation in Pingshun County was caused by the development of a supercell from thunderstorm cells on the front side of the squall line. The characteristics of sharp increase in vertical integral liquid water content, persistent increase in reflectivity factor and continuous rise in the echo top height appeared about 23 min earlier than the severe precipitation, which has qualitative indicating significance for the nowcasting of short-time heavy precipitation. A quantitative analysis of the radar echo parameters suggests that the“sudden drop”of FV40was a precursor signal of cells’ coalescence and rapid development to the mature stage. The areal change of the echo core at the 6 km height was highly subject to the merging and developing of cells, the rapid change of hydrometeor particles in clouds and the precipitation intensity. Changes in the cross-sectional area of convective cells at different heights can indirectly reflect the changes of liquid particles and ice particles in clouds, which is indicatively meaningful for predicting the coalescing and developing-to-maturing of cells and heavy precipitation 30-45 min earlier.A comprehensive echo parameter prediction model constructed by the random forest principle can predict the magnitude of short-time heavy precipitation 40-50 min in advance. Numerical simulation reveals that large amounts of water vapor existed in the near-surface atmosphere, and that the cells rapidly obtained moisture from the ambient atmosphere and developed rapidly through maternal feeding. The cold cloud zone was narrow, upright and had a high stretch height. The upward motion in clouds was strong and deep, and very rich in liquid water content. The graupel particles had a large vertical distribution range, the coexistence area of graupel and snow was large, the height of raindrops was close to the surface with a wide horizontal scale, and the precipitation efficiency was high. These may be the important elements responsible for the occurrence of the short-time heavy precipitation that exceeded historical extreme values. On the basis of the above analyses, a comprehensive parameter(CP) prediction model is worked out, which can estimate the developing trend of supercells and the intensity of short-time heavy precipitation about 1 h in advance.

Growth of High Magnetic a-Fe2O3 and Fe3O4 Nanowires via an Oxide Assisted Vapor-Solid Process

We describes a controllable synthesis procedure for growing a-Ee2O3 and Ee3O4 nanowires. High magnetic hematite a-Fe2O3 nanowires are successfully grown on Fe0.5Ni0.5 alloy substrates via an oxide assisted vapor-solid process. Experimental results also indicate that previous immersion of the substrates in a solution of oxalic acid causes the grown nanowires to convert gradually into magnetite （Fe3O4） nanowires. Additionally, the saturated state of Fe3O4 nanowires is achieved as the oxalic acid concentration reaches 0.75 mol/L. The average diameter and length of nanowires expands with an increasing operation temperature and the growth density of nanowires accumulates with an increasing gas flux in the vapor-solid process. The growth mechanism of a-Fe2O3 and Fe3O4 nanowires is also discussed. The results demonstrate that the entire synthesis of nanowires can be completed within 2 h.

企业跨国并购中的财务风险分析及防范——基于腾讯收购supercell的案例分析

随着经济全球化的不断发展,越来越多的企业选择跨国并购作为进入国际市场,融入全球经济的主要手段。但由于缺乏经验、并购流程不规范等原因,跨国并购也给我国企业带来了诸多的风险,整体成功率不高。因此,本文以腾讯收购supercell为例,总结企业在跨国并购中容易遇到的财务风险,并就如何应对风险给出相应的建议,期望能为我国企业的跨国并购有所帮助。

5A-FE电控发动机实验台的开发

电控发动机技术应用了大量的电子元器件、集成电路,使维修难度越来越大。为了使学生能够充分的理解电控系统的工作原理,掌握故障诊断的基本思路,达到排除故障的目的。经过我单位专业教师的共同努力,在丰田5A-FE发动机的基础上,开发了能够真实反映发动机运行工况,并能设置模拟故障的实验台。本文介绍了5A-FE电控发动机实验台的设计方案,对实验台机架的结构设计做了说明,同时详细的阐述了实验台控制电路的设计制作。

Analysis on Three-dimensional Structure and Echo Characteristic Quantity of a Supercell Storm

[Objective] The research aimed to study three-dimensional structure and echo characteristic quantity of a supercell storm in central Gansu on May 30,2005.[Method] By monitoring data of Lanzhou CINRAD/CC Doppler radar,the three-dimensional structure characteristics of a rare supercell storm which happened in central Gansu on May 30,2005 were analyzed.We tried to reveal three-dimensional structure and echo characteristic index of supercell storm in the northeast of Qinghai-Tibet Plateau,and find reason of rare heavy hail appearance.[Result] The large-scale strong storm was formed by the common effect of Mongolia cold vortex,low-level jet and ground cold front.When the development of main echo was mature,on reflectivity factor map,it presented obvious inverted 'V' shaped structure in left front of low-level storm,typical hooked and 'person'-type echo characteristics in the right rear.The bounded weak echo zone(vault) in low level corresponded with strong echo overhanging body in high level.It surpassed 60 dBz in the strong reflectivity factor zone.It presented one weak meso-cyclone on corresponding radial velocity map.The jumped increase characteristic of VIL could be as one of indices for judging that hail started to grow.Almost all storms(VILD ≥4.0 g/m3) had more obvious indication significance than VIL for judging heavy hail(diameter ≥20 mm).[Conclusion] The research provided reference for nowcasting of strong convection weather and artificial hail suppression.

Nd-Fe-B/a-Fe双相纳米复合永磁材料的发展及研究进展

简要分析稀土永磁材料的发展,及当前状况下Nd-Fe-B/a-Fe双相纳米复合永磁材料的研究方向,对我国的稀土永磁材料展望。

Lithium-ion mobility in layered oxides Li_(2)Ca_(1.5)Nb_(3)O_(10),Li_(2)Ca_(1.5)TaNb_(2)O_(10)and Li_(2)Ca_(1.5)Ta_(2)NbO_(10),enhanced by supercell formation

The formation of a supercell and its impact on lithium-ion conductivity have been studied through synthesis of three layered oxides,Li_(2)Ca_(1.5)Nb_(3)O_(10),Li_(2)Ca_(1.5)TaNb_(2)O_(10)and Li_(2)Ca_(1.5)Ta_(2)NbO_(10),related to Ruddlesden-Popper structure-type.Neutron diffraction experiments show that these materials feature a supercell,which is significantly larger(√2a×√2b×1c)than that of a typical RuddlesdenPopper oxide.Electrochemical impedance spectroscopy shows that the formation of the new supercell is associated with enhanced lithium-ion conductivity of these materials as compared with the Sranalogue,Li_(2)Sr_(1.5)Nb_(3)O_(10),which lacks the supercell.In addition,a systematic trend is observed in the ionic conductivity:Li_(2)Ca_1.5Ta_(2)NbO10<Li_(2)Ca_(1.5)TaNb_(2)O_(10)<Li_(2)Ca_(1.5)Nb_(3)O_(10).The Arrhenius analysis in the temperature range 25–400°C shows that activation energy for the temperature-dependent rise in conductivity follows a similar trend.Detailed analyses of real and imaginary components of impedance,dielectric properties,tangent loss,and complex modulus show the systematic increase in lithium-ion mobility.The dielectric values mirror the same trend as ionic conductivity,where the most conductive material shows the highest dielectric properties.In addition,the same trend is observed in the peak and dispersion of dielectric loss and complex modulus as a function of angular frequency,indicating a systematic rise in lithium-ion mobility.This fundamental study is aimed at exploring the impact of structural modifications on ionic conductivity in solids.

Mesocyclone Evolution and Differences between Isolated and Embedded Supercells

A total of 61 supercells with mesocyclones lasting for at least 6 volume scans were investigated. These storm parameters and mesocyclone parameters were counted and compared to determine the salient differences between isolated supercells and embedded supercells in different regions. The results showed that the mesocyclone parameters had different evolution characteristics in three stages of mesocyclone. The storm parameters, mesocyclone parameters and severe weather phenomenon had significantly differences between isolated supercells and embedded supercells. The mesocyclone parameter differences determined the differences in the reflectivity structure and weather phenomenon. The higher base and top of mesocyclone for isolated supercells indicated that the isolated supercells had higher maximum reflectivity, maximum reflectivity height, cell-based vertically integrated liquid and top of storm cell, and significantly higher probability of hail or large hail than the embedded supercells. The descending lower base of mesocyclone at its mature stage in the region of Jianghuai Plain indicated that the supercells in this region had a higher probability of mesocyclone-induced tornado.

Analyses and Forecasts of a Tornadic Supercell Outbreak Using a 3DVAR System Ensemble

As part of NOAA＇s ＂Warn-On-Forecast＂ initiative, a convective-scale data assimilation and prediction system was developed using the WRF-ARW model and ARPS 3DVAR data assimilation technique. The system was then evaluated using retrospective short-range ensemble analyses and probabilistic forecasts of the tornadic supercell outbreak event that occurred on 24 May 2011 in Oklahoma, USA. A 36-member multi-physics ensemble system provided the initial and boundary conditions for a 3-km convective-scale ensemble system. Radial velocity and reflectivity observations from four WSR-88 Ds were assimilated into the ensemble using the ARPS 3DVAR technique. Five data assimilation and forecast experiments were conducted to evaluate the sensitivity of the system to data assimilation frequencies, in-cloud temperature adjustment schemes, and fixed- and mixed-microphysics ensembles. The results indicated that the experiment with 5-min assimilation frequency quickly built up the storm and produced a more accurate analysis compared with the 10-min assimilation frequency experiment. The predicted vertical vorticity from the moist-adiabatic in-cloud temperature adjustment scheme was larger in magnitude than that from the latent heat scheme. Cycled data assimilation yielded good forecasts, where the ensemble probability of high vertical vorticity matched reasonably well with the observed tornado damage path. Overall, the results of the study suggest that the 3DVAR analysis and forecast system can provide reasonable forecasts of tornadic supercell storms.

COMPARISONS BETWEEN DOPPLER AND SIMULATED FEATURES OF A SUPERCELL

Firstly, typical features of a supercell, which occurred in Guangzhou on August 11, 2004, are discussed by using the new generation weather radar data. V-notch, finger-echo, weak echo region, overfiang and echo-wall are observed from reflectivity products. A vertical cross section of the radial velocity is made along the direction of the low-level inflow and across the maximum reflectivity core, which displays a part of strong updraft and downdraft. Secondly, a 3-D convective storm model is used to simulate the supercell. The maximum reflectivity and the core thickness of the simulated radar echo are 75 dBz and 14km, respectively. These values are more than the counterparts that are detected by radar. The reason is that attenuation is not calculated in the model. The wind field structure is also given when the storm is the strongest. Divergence, caused by thunderstorm outflow, is in the low level. In the middle and high level, convergence is dominant, but the plume is not simulated at the top. Finally, the evolution of the simulated vertical motion is documented. The interaction between the environmental wind and the updraft, which is formed by the convergence on the ground at the beginning, makes the storm stronger. Then, downdraft occurs and grows. When it becomes dominant, the supercell collapses.

Surface Modification of a-Fe Metal Particles by Chemical Surface Coating

The structure of a-Fe metal magnetic recording particles coated with silane coupling agents have been studied by TEM, FT-IR, EXAFS, Mossbauer. The results show that a close, uniform, firm and ultra thin layer, which is beneficial to the magnetic and chemical stability, has been formed by the cross-linked chemical bond Si-O-Si. And the organic molecule has chemically bonded to the particle surface, which has greatly affected the surface Fe atom electronic structure. Furthermore, the covalent bond between metal particle surface and organic molecule has obvious effect on the near edge structure of the surface Fe atoms.