1969—2020年夏季山东极端暴雨事件的时空特征及其影响环流分型

利用山东省84个气象台站的逐日降水资料、美国国家环境预测中心和国家大气研究中心(National Centers for Environmental Prediction and National Center for Atmospheric Research, NCEP/NCAR)逐日再分析资料以及中国气象局(CMA)热带气旋资料中心的CMA最佳路径数据集,对1969—2020年夏季(6—8月)发生在山东的857例极端暴雨事件(Extreme rainstorm events, EREs)的时空分布特征及影响环流分型进行了分析。结果表明:山东夏季EREs主要集中在7和8月,8月极端暴雨降水量占当月总降水量的比值最大,可达53.5%。山东夏季极端暴雨降水量以及极端暴雨发生日数呈现不显著的增加趋势,8月的增加趋势最明显。使用经验正交函数分解对影响山东夏季EREs的大气环流系统进行分型,发现影响山东夏季出现EREs的环流系统主要有4类,其中,影响ERE最多的环流系统是北方气旋型,约占事件总频次的33.1%;其次是高空急流型,占比约11.3%;南方气旋型和热带气旋型的环流型影响相当,出现的概率分别为9.7%和9.4%。

盛夏亚洲大陆上空急流变化的两类模态及其与东亚大气环流异常的联系

基于NCEP/NCAR月平均再分析资料,利用EOF分解方法揭示出1960-2019年7-8月亚洲大陆上空西风急流变化的两类主要模态,并利用合成方法研究了两类模态与东亚大气环流异常的联系及其气候效应。研究结果表明,夏季亚洲大陆上空西风急流变化的第一模态为纬向风以急流轴为界南北的反位相变化,主要表现为急流整体的南北移动;第二模态为纬向风以青藏高原为界在东西方向上的反相变化,主要表现为急流轴的西南(西北)-东北(东南)向倾斜,该结论不同于以往大多数研究将第二模态定义为急流的强度变化。通过对大气环流异常的分析发现,急流的南北移动对应南亚高压同步的南北移动以及西太平洋副热带高压范围的变化,急流向南移动时,南亚高压脊线偏南,同时西太平洋副热带高压向南扩张,急流向北移动时则相反,该模态主要影响亚洲地区40°N以南的降水异常以及贝加尔湖一带、东亚和南亚的温度异常。第二模态即纬向风以青藏高原为界的反相变化主要伴随着南亚高压强度的东西振荡,急流轴呈西南(西北)-东北(东南)向倾斜时,南亚高压东侧(西侧)位势高度增强,该模态与西亚高纬度地区、中亚以及印度半岛的降水异常有关。此外,第二模态具有一定的特殊性,可影响整个欧亚大陆的气温,并呈现双偶极子型的异常分布。

泰山地形对一次副高边缘大暴雨过程影响的观测分析

利用区域加密自动气象站、雷达、风廓线及卫星等观测资料,分析了2022年秋季山东一次极端大暴雨事件中泰山山脉周围的降水分布及其产生这种分布的可能原因。结果表明:(1)这次山东大暴雨事件发生在对流层中、低层为强盛偏南气流的背景下,强降水时段集中在2022年10月1日23时至2日02时(北京时,下同),100 mm等雨量线呈“反弓形”横亘在泰山北侧与西侧,并各自伴有超170 mm的降水中心,而泰山南侧降水反而明显偏弱。(2)大暴雨分布带与地面上的中尺度涡旋-辐合线对应:泰山西侧的中尺度涡旋是山脉北侧冷性绕流与南侧暖性绕流相遇而形成的,导致泰山西侧出现强降水中心,降水呈单峰型;山脉北侧的辐合线长时间维持与重建过程,造成泰山北侧降水时间更长,累计降水量更大,小时降水量呈双峰型。(3)泰山北侧观测站的两个降水峰值与雷达反射率因子的两条平行回波带对应:位于泰山北坡处于长时间准静止状态的第一条回波带,与泰山北侧水平涡度环流的上升支气流对应,其形成机制是夜间具有强垂直切变特征的越山西南低空急流和近地面层受到山脉阻滞的东北气流构成的水平涡度强烈发展和维持的结果;第二条降水回波带与弱冷空气云系对应,当其靠近泰山北侧时受到越山西南低空气流背风坡上升支的影响,出现雷达反射率因子增强现象,与之对应的地面风场特征表征为辐合线的重建过程。(4)在泰山西侧,地面辐合线在低空冷空气的驱动下向东南方向移动,致使回波带逐渐演变成“反弓形”,造成强雨带也呈“反弓形”分布;而泰山南侧处于具有强烈垂直切变低空急流形成的水平涡度的下沉支控制下,因而降水量相较泰山北侧和西侧明显偏小。

反循环气动潜孔锤进气端分流引射接头设计及结构参数分析

为解决反循环气动潜孔锤在钻进过程中岩石重复破碎及排渣效率低下的问题,笔者基于NGQ-320反循环气动潜孔锤设计了进气端分流引射接头。该接头可实现潜孔锤供气量的动态调节,其引射结构可以将部分压缩气体引入中心通道,对井底流场产生泵吸作用的同时改善冲击机构的动力供给;同时采用CFD技术研究了分流引射接头局部流场,分析了喷射孔夹角、喷射孔开口深度、喷射孔直径和喷射孔偏转角度等参数对中心通道抽吸性能的影响,确定了各项结构参数的较优取值。结果表明,分流引射接头在喷射孔开口深度320~330 mm、喷射孔夹角30°~35°、喷射孔直径12 mm、喷射孔偏转角11°~13°的情况下具有较好的抽吸性能。

Flight control of a flying wing aircraft based on circulation control using synthetic jet actuators

To achieve the nice stealth performance and aerodynamic maneuverability of a Flying Wing Aircraft(FWA),a longitudinal aerodynamic control technology based on circulation control using trailing-edge synthetic jet actuators was proposed without the movement of rudders.Effects on the longitudinal aerodynamic characteristics of a small-sweep FWA were investigated.Then,flight tests were carried out to verify the control abilities,providing a novel technology for the design of a future rudderless FWA.Results show that synthetic jets could narrow the dead zone area,improve the flow velocity near the trailing edge,and then move the trailing-edge separation point and the leading-edge stagnation point downwards,which make the effective Attack of Angle(AOA)increase,thereby enhancing the pressure envelope area.Circulation control based on synthetic jets could improve the lift,drag and nose-down moment.The variations of lift and nosedown moment decrease with the growth of AOA caused by the improved reverse pressure gradient and the weakened circulation control efficiency.Finally,synthetic jet actuators were integrated into the trailing edge of a small-sweep FWA,which could realize the roll and pitch control without deflections of rudders during the cruise stage,and the maximum roll and pitch angular velocity are 12.64(°)/s and 8.51(°)/s,respectively.

陕西夏季旱涝与欧亚大气环流异常的关系

陕西处于青藏高原边坡地带,南北狭长,气候类型多样,地形复杂,生态条件脆弱,旱涝是夏季的主要气象灾害,因此分析其旱涝的成因对该地区防灾减灾具有重要意义。利用陕西78个气象站1961—2018年夏季(6—8月)降水资料、NCEP/NCAR高度场和风场再分析资料、西太平洋副高指数资料,通过相关、合成、多元回归分析方法,研究了陕西夏季旱涝与大气环流异常的关系。结果表明,500 hPa上乌拉尔山阻塞高压和西太平洋副高是影响陕西夏季旱涝的关键因素,当乌拉尔山阻高和西太副高偏强时,陕西夏季降水偏多,反之偏少。200 hPa西风急流位置与陕西夏季降水关系密切,急流偏南时陕西夏季降水偏多,反之偏少。西太平洋副高偏强、偏西时,陕西夏季降水偏多,反之偏少,副高脊线位置主要影响陕西夏季雨带的南北移动。

WINTERTIME MIDDLE EAST SUBTROPICAL WESTERLY JET STREAM INTERANNUAL VARIATION CHARACTERISTICS AND ITS POSSIBLE PHYSICAL FACTORS

Using National Centers for Environmental Prediction/Department of Energy(NCEP/DOE) monthly reanalysis data and an extended reconstruction of the sea surface temperature data provided by National Oceanic and Atmospheric Administration, the basic characteristics of the interannual variation in the wintertime Middle East subtropical westerly jet stream(MEJ) and its possible physical factors are studied. The results show that the climatological mean MEJ axis extends southwestward-northeastward and that its center lies in the northwest part of the Arabian Peninsula. The south-north shift of the MEJ axis and its intensity show obvious interannual variations that are closely related to the ElNio-Southern Oscillation(ENSO) and the mid-high latitude atmospheric circulation. The zonal symmetric response of the Asian jet to the ENSO-related tropical convective forcing causes the MEJ axis shift, and the Arctic Oscillation(AO)causes the middle-western MEJ axis shift. Due to the influences of both the zonal symmetric response of the Asian jet to the ENSO-related tropical convective forcing and the dynamical role of the AO, an east-west out-of-phase MEJ axis shift is observed. Furthermore, the zonal asymmetric response to the ENSO-related tropical convective forcing can lead to an anomalous Mediterranean convergence(MC) in the high troposphere. The MC anomaly excites a zonal wave train along the Afro-Asian jet, which causes the middle-western MEJ axis shift. Under the effects of both the zonal symmetric response to the ENSO-related tropical convective forcing and the wave train along the Afro-Asian jet excited by the MC anomaly, an east-west in-phase MEJ axis shift pattern is expressed. Finally, the AO affects the MEJ intensity, whereas the East Atlantic(EA) teleconnection influences the middle-western MEJ intensity. Under the dynamical roles of the AO and EA, the change in the MEJ intensity is demonstrated.

Different Configurations of Interannual Variability of the Western North Pacific Subtropical High and East Asian Westerly Jet in Summer

This study investigates the circulation and precipitation anomalies associated with different configurations of the western North Pacific subtropical high(WNPSH)and the East Asian westerly jet(EAJ)in summer on interannual timescales.The in-phase configuration of the WNPSH and EAJ is characterized by the westward(eastward)extension of the WNPSH and the southward(northward)shift of the EAJ,which is consistent with the general correspondence between their variations.The out-of-phase configuration includes the residual cases.We find that the in-phase configuration manifests itself as a typical meridional teleconnection.For instance,there is an anticyclonic(cyclonic)anomaly over the tropical western North Pacific and a cyclonic(anticyclonic)anomaly over the mid-latitudes of East Asia in the lower troposphere.These circulation anomalies are more conducive to rainfall anomalies over the Yangtze River basin and south Japan than are the individual WNPSH or EAJ.By contrast,for the out-of-phase configuration,the mid-latitude cyclonic(anticyclonic)anomaly is absent,and the lower-tropospheric circulation anomalies feature an anticyclonic(cyclonic)anomaly with a large meridional extension.Correspondingly,significant rainfall anomalies move northward to North China and the northern Korean Peninsula.Further results indicate that the out-of-phase configuration is associated with the developing phase of ENSO,with strong and significant sea surface temperature(SST)anomalies in the tropical central and eastern Pacific which occur simultaneously during summer and persist into the following winter.This is sharply different from the in-phase configuration,for which the tropical SSTs are not a necessity.

The Effect of the Subtropical Jet on the Rainfall over Southern China in January 2008

ABSTRACT The third precipitation episode of China＇s great snowstorms of 2008 was analyzed using station observations and ECMWF six-hourly data. The variation of the shape of the upper-level subtropical jet played an important role in the rainfall over south- ern China. With the eastward movement of the trough, the jet shape changed from two straight jets to a tilting jet over China and then it moved southward. With these variations, the south-north movement of ascending flow and precipitation area over southern China occurred.

Impact of the variation of westerly jets over East Asia on precipitation of eastern China in July

The impact of the northward jump and westward movement of the East Asian westerly jet core fi：om the westem Pacific Ocean to the Qinghai-Tibet Plateau on precipitation distribution of eastem China is studied. It is concluded that on the one hand, the northward jump of the jet causes the precipitation belt to move northward from the middle and lower reaches of the Yangtze River valley and withdraw during the Mei-yu season; on the other hand, the westward movement of the jet core has no correspondence with withdrawal of the Mei-yu season. However, the earlier or later occurrence of the westward movement of the jet has an influence on the process of the rain belt moving northward than the northward jump of the jet： the rain belt moves northward from the middle-lower Yangtze River valley to the Huaihe River and then to an area between the Yellow River and Huaihe River during years when the time of the westward movement of the jet core is later than that of the northward jump of the jet and from the middle-lower Yangtze River valley to an area between the Yellow River and Huaihe River in other years. Further analysis shows that： （1） The northward jump of the jet and the westward movement of the East Asian westerly jet core causes significant variation of the general atmospheric circulation in middle latitudes and water vapor transport from the western Pacific, but not from the Bay of Bengal. （2） Impact of the northward jump and the westward movement of the East Asian westerly jet core on circulation are different, therefore, water vapor transport from the western Pacific and its impact on the rain belt are different. The earlier or later occurrence of the westward movement of the jet core than the northward jump of the jet causes the process of circulation and water vapor transport to be different which produces a different process of the rain belt moving northward.

中国西部地区暴雨过程高、低空急流耦合影响机制的个例研究

高、低空急流对中国暴雨有重要影响,但是其对中国西部地区暴雨影响的深入研究缺乏,其耦合过程及机制的研究更少。本文利用常规观测、加密自动气象站降水资料以及NCEP/NCAR再分析资料,借助数值模拟,研究高、低空急流耦合效应对2018年7月8~11日中国西部一次特大暴雨过程的影响及其发生机制。结果表明:(1)此次暴雨过程是在中高纬东移冷涡低槽与副高西伸北抬的有利背景下产生的,高、低空急流耦合有利于暴雨的发展。(2)高、低空急流耦合主要通过次级环流和动量下传得以实现:高空急流加强高层辐散下沉,同时低空急流加强低层辐合上升,促使高、低空急流之间形成次级环流,其下沉支引导高层高值位涡向下层传播,形成动量下传,与中层高值位涡区相衔接,高、低空急流在中层耦合。(3)高、低空急流的耦合,加强了中层不稳定能量的聚集,促使低空急流加强发展;进而增强了辐合强度,促使上升运动加强,从而增强了降水强度。通过增减高、低空风速的敏感性试验发现,高低层风速的增减能够改变中低层最大位涡的增减,其基本对应了强降水时段,且位涡值越大降水强度越强。(4)高、低空急流强度共同对降水强度有重要影响:数值模式敏感试验表明,当同时增加高低空急流强度,降水强度将增强,而仅增加高空或低空急流,降水强度变化不大,但减弱高空或低空急流强度,降水强度均会减弱。

2021年黄河中游秋汛降水特点与环流特征分析

为了提高黄河中游秋汛降水预报能力,以便为该区农业生产乃至防灾减灾工作提供参考依据,利用水文站和气象站日降水资料、国家气候中心逐日副高脊线和西伸脊点资料、NCEP/NCAR再分析资料,对2021年黄河中游秋汛降水特点以及环流形势的逐日演变特征进行分析。结果发现:2021年黄河中游秋汛洪水由6次强降水过程造成,具有持续日数长、雨带稳定、雨势强、落区重叠度高的特点。秋汛期内,副高脊线相对稳定,副高季节性南落异常偏迟,同时西伸脊点偏西。欧亚中高纬地区盛行阻塞形势,黄河中游强降水过程主要发生在双阻形势下乌拉尔山阻高达到强盛期后的减弱崩溃期以及乌拉尔山形成阻高的单阻形势下。南亚高压偏强、偏东是200 hPa高空40°-45°N、110°-140°E形成急流的主要原因,低空急流前期不显著,位置偏南,9月下旬以后向北扩展,高、低空急流合适配置为黄河中游强降水发生时上升运动发展提供了有利的环流背景。秋汛期水汽主要来自西太平洋,依靠副高南侧异常强盛的偏东气流以及副高西北侧强盛的西南气流完成输送。

近60年青藏高原季风期降水的南北变化特征及机理研究

青藏高原(以下简称高原)对全球气候的影响一直是被研究的重点,国外的学者更多地关注的是青藏高原对全球气候系统的影响,但是其本身的气候变化也是全球气候系统变化中的重要分量。随着南亚夏季风的建立和副热带急流的北抬,高原降水呈现出多尺度变化和多因子影响的特征。本文基于1961-2020年的GPCC逐月降水资料和ERA5逐月再分析数据的环流场数据,分析了全球变暖背景下,青藏高原5-9月季风期降水的时空分布特征及其演变规律,分析了夏季风期高原降水时空演变特征的机制。结果表明:气候平均态下,高原降水自5月开始增强并向北推进,并于7月延伸至高原中部;9月份后高原降水开始南撤;季风期降水的经验正交函数分解(EOF)第二模态显示,以唐古拉山为界,高原南北部季风期降水异常呈南北反向的偶极性分布。在年代季尺度上,高原南部降水1961-1980年偏少,1981-2002年较多,2002-2019年又偏少的年代际变化特征。总体来看,1961-2020年的60年间,季风期高原南部降水呈略微减少的线性趋势,这可能和南亚夏季风的衰退有关。高原北部降水基本和南部呈相反变化,1961-2020年间,季风期高原北部降水则存在着28 mm·(10a)^(-1)增加的趋势,高原南部降水呈-3 mm·(10a)^(-1)略微减少趋势。对应高原南部和北部降水的大气环流结果表明,高原南部降水主要受南亚夏季风影响,南亚夏季风的推进及撤退直接影响着高原南部的降水的增加和减少,而高原北部降水则与中纬度西风急流中的Rossby波传播有关。

长江中下游冬季两类冷空气活动事件的环流差异及其与急流的关系

利用1981—2020年台站观测的降水和最低气温资料,从长江中下游地区冬季冷空气活动事件中分出“降温有降水”和“降温无降水”两类事件(简称为“冷湿”和“冷干”事件),结合再分析资料,分析两类事件的冷暖空气活动特征和大气环流差异,进而探讨其与急流的联系。结果发现,长江中下游冷空气活动事件发生频次逐年减少,其中冷干事件发生频次逐年减少,冷湿事件发生频次显著增加,且冷湿事件的降温幅度大于冷干事件。冷湿事件发生时,高层副热带急流北移、极锋急流偏弱,中层存在倾斜槽脊、副热带高压偏西,低层西伯利亚高压增强,有来自西南的暖湿气流在长江中下游地区辐合上升;冷干事件发生时,高层副热带急流偏弱、极锋急流偏强,中层槽脊倾斜程度偏弱、副热带高压偏东,低层西伯利亚高压南移,有来自北方的偏干气流在长江中下游地区辐散下沉。此外,与冷湿事件相比,冷干事件过程中急流强度指数和经向风位置指数的波动更加频繁,冷空气活动持续时间更短。

振荡射流控制方法在无舵面飞行控制中的应用

利用射流主动流动控制方法,飞行器无舵面飞行控制技术取消了传统的机械舵面,具有附加重量小、控制性能优异等优点,适合隐形设计。本文针对现有定常射流控制方法控制效率较低、耗气量大等问题,介绍了振荡射流在无舵面飞行控制中的应用,概述了2项无舵面飞行控制技术——环量控制技术和流体推力矢量技术——的研究现状,讨论了振荡射流在扩大控制区域、增强掺混和频率调节方面的机理和优势。从环量控制和流体推力矢量2个角度出发,详细介绍了振荡射流在无舵面飞行控制中的应用机理和优异表现。

华阳二矿选煤厂射流浮选柱分选试验研究

煤泥分选是影响精煤产率提高的主要瓶颈。华阳二矿选煤厂针对浮选环节中高灰细泥含量高、精煤产量低等问题,设计了新型射流浮选柱,并通过工艺试验,确定了新型射流浮选柱的最佳工艺参数。实践结果表明,新型射流浮选柱运行效果稳定,煤泥的分选效果好,浮选精煤灰分达标,有效解决细粒煤浮选灰分高、产率低的技术难题,体现出显著社会与经济效益。

Changes in Persistent Precipitation in Northwest China and Related Large-Scale Circulation Features

Based on China's daily precipitation data of 2415 stations and ERA5 hourly reanalysis data from 1961 to 2019, the station-based and regional precipitation events over Northwest China(NWC) are identified and sorted into persistent precipitation(PP, duration ≥ 2 days) events and non-persistent precipitation(NPP, duration = 1 day) events;and then changes in the persistence structure of the PP and NPP events over NWC and the long-term mean adjustment of the related large-scale circulation configuration are analyzed. The results show that PP and NPP both witness an increasing trend over most parts of NWC. In terms of the total precipitation at most stations and the regional mean, contributions from PP have been increasing, while those from NPP have been decreasing. This demonstrates that the wetting trend in NWC is mainly caused by the increase in PP. Through analyzing the large-scale circulation corresponding to regional PP events at several representative levels, we found that the westerly jet at 200 hPa, the ridge/trough systems at 500 hPa, and the Mongolian low at sea level are the key circulation systems responsible for regional PP events over NWC. As for long-term mean changes after and before 1990(a shifting point recognized by previous studies), it is found that the extent of the South Asian high becomes larger and the westerly jet shifts northward by approximately 1.5 degrees in the upper troposphere. The ridge near the Ural Mountains and the ridge downstream of NWC strengthen by approximately 10–30 hPa at 500 hPa. Furthermore, the difference between the Mongolian low trough and its surrounding high pressure increases by approximately 2 hPa at the sea level. The combinations of circulation changes from upper to lower levels facilitate the strengthening of ascending motions. These adjustments in circulations create more favorable conditions for PP to occur over NWC in the last three decades.

Lift enhancement method by synthetic jet circulation control

A novel circulation control technique is proposed to overcome the shortcomings of blowing jet circulation control,which uses the synthetic jet as the actuator and avoids the limitation about air supply requirement.The effectiveness of synthetic jet circulation control to enhance lift of NCCR1510-7067N airfoil is confirmed by solving the 2-D unsteady Reynolds-averaged Navier-Stokes equations.The aerodynamic characteristics and the flow structure(especially close to the trailing edge) of NCCR1510-7067N airfoil at zero angle of attack are also presented to discuss the mechanism of lift enhancement of the airfoil with synthetic jet circulation control.The results indicate that the synthetic jet can effectively delay the separation point on the airfoil trailing edge and increase the circulation and lift of the airfoil by Coanda effect.The numerical simulation results demonstrate that the lift augmentation efficiency with synthetic jet circulation control reaches △CL/Cμ=114 in the present study,which is much higher than the value 12.1 in the case with steady blowing jet circulation control.

Contrasting Regional Responses of Indian Summer Monsoon Rainfall to Exhausted Spring and Concurrently Emerging Summer El Nino Events

The inverse relationship between the warm phase of the El Nino Southern Oscillation(ENSO)and the Indian Summer Monsoon Rainfall(ISMR)is well established.Yet,some El Nino events that occur in the early months of the year(boreal spring)transform into a neutral phase before the start of summer,whereas others begin in the boreal summer and persist in a positive phase throughout the summer monsoon season.This study investigates the distinct influences of an exhausted spring El Nino(springtime)and emerging summer El Nino(summertime)on the regional variability of ISMR.The two ENSO categories were formulated based on the time of occurrence of positive SST anomalies over the Nino-3.4 region in the Pacific.The ISMR’s dynamical and thermodynamical responses to such events were investigated using standard metrics such as the Walker and Hadley circulations,vertically integrated moisture flux convergence(VIMFC),wind shear,and upper atmospheric circulation.The monsoon circulation features are remarkably different in response to the exhausted spring El Nino and emerging summer El Nino phases,which distinctly dictate regional rainfall variability.The dynamic and thermodynamic responses reveal that exhausted spring El Nino events favor excess monsoon rainfall over eastern peninsular India and deficit rainfall over the core monsoon regions of central India.In contrast,emerging summer El Nino events negatively impact the seasonal rainfall over the country,except for a few regions along the west coast and northeast India.

环量控制扑翼式获能器气动特性的数值研究

提出了一种采用环量控制的新型扑翼获能技术,首先对这种扑翼在不同折合频率下的获能效率进行了数值模拟,并与传统扑翼和表面施加协同射流控制扑翼的获能效率进行了对比,发现不同工况下对翼型尾缘部施加持续射流均能有效改善翼型的气动性能,使扑翼的能量转换效率显著提高,且提升幅度优于协同射流控制方法,表明该方法具有一定的开发应用潜力。此外,针对连续射流能耗较高的缺点进一步改进了射流施加策略,建立了四种不同射流喷射控制模式,对比研究了连续式、方波式、正弦式和三角波式射流模式下扣除射流能耗后采用环量控制扑翼的获能净效率,旨在以获取最高能量转换效率为目标的前提下尽可能降低射流所需能耗。不同射流模式下的能耗分析表明,连续式环量控制模式下所需能耗最高,方波式、正弦式和三角波式的能耗依次次之,因此扣除主动控制射流的能耗后,三角波式射流喷射模式下扑翼的获能净效率最高,比传统扑翼获能效率相比提升幅度最高可达22.2%,更具实际应用价值。