Climatology of the quasi two-day wave over Saskatoon (52°N, 107°W): 14 Years of MF radar observations

Oscillations in the wind field due to the “quasi two-day” wave (Q2DW) have been studied using 14 years of Medium Frequency (MF) radar data over Saskatoon (52°N). The results of analyses have shown that the Q2DW exhibits complex seasonal variability: in addition to the well-known strong summer activity the wave also has been found in winter months. In summer the amplitudes of the Q2DW in meridional (NS) and zonal (EW) winds have comparable values, while they tend to be larger in EW winds in winter. The heights of the maximum amplitude are lower in winter than in summer and there are indications of changes in the dominant period of oscillations throughout the year.     

Nonlinear Interactions between the Quasi 5-day Wave and Tides Based on Meteor Radar Observations at Maui

Nonlinear interactions between the quasi 5-day wave and tides based on meteor radar observation in the Mesosphere and Lower Thermosphere(MLT) at Maui are studied in this paper.Strong sum interaction between quasi 5-day wave and diurnal tide,and evident difference interaction between quasi 5-day wave and semidiurnal tide are observed during the time of attention.However,their difference and sum counterparts are clearly weaker.The secondary waves generated from those interactions beat with the tide and show intense modulation at the period of 5 days which confirms the existence of their interactions.Additionally,correlation coefficients among these waves are calculated to further explore their interactions and find that they can persist for several days although they are highly intermittent.The energy exchange among these waves can be reversible during the observational time.The periods when the significant difference interaction between the quasi 5-day wave and semidiurnal tide occur are much shorter than those when the significant sum interaction between the quasi 5-day wave and diurnal tide occur.Moreover,these two strong interactions can take place simultaneously.In generally,this study provides the proof of nonlinear interactions between quasi 5-day wave and tides which were seldom reported before.     

双射流环量控制翼型的控制力矩特性研究

为了探究环量控制技术在飞行控制性能方面的优势,在定常流场中对定常射流环量控制翼型的控制力矩作用机理展开了研究,采用数值仿真的方法,对比分析了单射流、双射流产生的虚拟舵面与传统舵面作用下的气动力系数的变化规律,并基于无舵面飞行器CCSCAOON对其气动力矩的控制特性进行了验证。验证结果表明:单射流作用下的虚拟舵面能够提供用于飞行器所需的滚转和俯仰力矩,且作用机理相似,控制性能优于传统舵面;无论是单射流还是双射流,在大迎角下虚拟舵面的气动控制特性较差,限制了环量控制的使用迎角;双射流较单射流而言,升阻比特性和控制力矩特性较好;双射流下的虚拟舵面通过调节下射流口动量系数,能够有效降低偏航力矩与滚转、俯仰力矩之间的耦合效应。      

粘性耗散对重力波波包共振相互作用的影响

采用数值方法考察了粘性耗散对重力波波包共振相互作用的影响．结果表明,粘性耗散不仅衰减相互作用波的能量,而且强烈地影响波包之间局地能量的传递,使波包的形状发生进一步的改变．粘性耗散减缓相互作用过程的发展,阻止高波数的次级波与主波进行相互作用．在低热层高度上,耗散过程占支配地位,三波能量演变的特征发生了相当大的变化．大尺度主波通过与小尺度次级波的相互作用,更快地实现对大气的加热．      

Long period wind oscillations in the 80–110 km altitudes observed by the Kyoto meteor radar in 1983–1985

During the MAP period, the Kyoto meteor radar has almost continuously monitored the wind fields in the 80–110 km altitudes. Wind oscillations with various periods ranging from 2 to 20 days are detected. The period of the quasi 2-day wave in 1983 was 2.2 days in summer months but became as short as about 2.0 days in autumn. Antisymmetry in phase profiles is detected by comparing the behavior of the quasi 2-day wave simultaneously observed at Adelaide and Kyoto.     

Circulation of the atmosphere from the surface to 100 km

A reference model of the atmospheric circulation on Venus based on available observations is presented. The reference atmosphere has the following main features: (i) the entire atmosphere below 85 km moves predominantly from east to west in the planet's reference system (in the same direction as the rotation of the solid planet itself) with the possible exception of the lowest 10 km where velocities are low, (ii) a jet is present near the cloud-top level at 45° latitude in both hemispheres, with a magnitude of approximately 100 ms^?1, (iii) a weak meridional (north-south component) flow directed towards either pole is superimposed on the zonal (east-west) motion at cloud-top level (about 68 km) altitudes, and, (iv) eddies or wave motions are present in the atmosphere, with amplitudes of less than 15 ms^?1 in the upper atmosphere.     

Helicity evolution during the life cycle of tropical cyclones formed over the north Indian Ocean

Tropical cyclones (TCs) are violent multiscale convections occurring in the atmosphere. The destructive impact of the TCs is commensurate to the helicity associated with their evolution. The evolution of helicity of three TCs viz. Fani, Luban, and Ockhi formed over the north Indian ocean have been analyzed in this study. The analysis of kinetic energy density of primary (EP), secondary (ES) circulation and total helicity has shown that TCs showed helical features when the secondary overturning circulation knotted with primary tangential circulation in a moist convective situation. This condition can be considered a starting of the self-sustained helical feedback process. At this time, the core region became a rotation-dominated region that suppressed strain-dominated surroundings. The Okubo-Weiss parameter demonstrates the similar qualitative behavior of deep convection as total helicity. The local maximas in helicity time series are related with the changes in tropical cyclones' stages (intensification/dissipation). Therefore, consideration of helicity analysis is essential to analyze the TC intensification and dissipation.     

Contraction of magnetized gas to the central gravitator and the production of magnetically accelerated jets

A magnetodynamic model proposed and worked on by Uchida and collaborators for the star formation jets (bipolar flows), by taking a genetic point of view into account, is reviewed. A large scale magnetic field, which is week in the primordial gas but intensified in the gravitational contraction of the gas, assists the continuous accretion of the gas to the central gravitator by extracting angular momentum from the rotating disk, and this process creates a large amplitude torsional Alfven wave that swirls up the gas into the direction of the axis. This torsional Alfven wave, as it propagates, pinches the large scale field into a slender strong field structure which we identify with the collimated jet. The rationale for extending this mechanism to the AGN jet cases is given, and some results of application to the AGN jet case are presented, with interpretation of some characteristic features like the wiggling of the jets, extended radio lobes and the hotspots at the end of the jets.     

损耗大气中惯性重力波的非线性相互作用方程及其初步讨论

根据弱相互作用理论,本文建立了损耗大气中极性重力波的非线性相互作用方程。这组方程在三个方面推广了前人的工作:考虑了波的空间传播;包含了粘滞产生的衰减;波谱可以是连续的。粘滞衰减率的大小与波的空间尺度以及传播方向有关。Coriolis力的引入使相互作用系数成为复量。根据这组方程,考察了惯性重力波的参量激发。结果表明:在共振条件满足时,主波存在一个阈值,阈值大小与次级波的损耗率成正比。当主波振幅大于这个阈值时,次级波将指数增长。在相互作用过程中,次级波的频率将发生变化,变化的大小与主波能量成正比。      

重力波波包在耗散大气中的非线性传播

本文对具有高斯分布的重力波波包在耗散大气中的非线性传播过程进行数据模拟和分析,并与重力波波包在无耗大气中非线性传播的数值计算结果进行了比较,以辨明耗散在重力波非线性传播过程中所起的作用。     

基于DFT的水射流红外热像频域时空分析

基于二维离散傅里叶变换及空间频谱分析,对水射流湍流脉动的空间尺度进行了研究,得到了由红外辐射温度表征的被动标量湍流场在对流区、耗散区、惯性子区的特征空间尺度及其时间演化规律.对射流不同区域的关心点重新采样,得到湍流场中关心点的时间序列,利用一维离散傅里叶变换,分析了对流区大尺度涡中心、惯性子区小尺度涡中心、耗散区及射流轴心线上各关心点的湍流波动特征.计算了时间序列频谱的分形维数,研究了自由湍流不同尺度区间上述各关心点湍流脉动的分形特征.      

急流与低层大气重力波能量的相关性研究

通过分析武汉(30.5oN, 114oE)上空2000至2004年的Radiosonde常规观测数据, 对当地对流层(1~10 km)与低平流层(18~25km)的某些惯性重力波特征进行了研究, 发现重力波能量与急流强度变化之间存在显著的相关. 同时分析了海口(20oN, 114oE)(2000至2004年)、北京(40oN, 116oE)(2001年12月至2003年2 月)的Radiosonde观测数据并进行了比较, 发现较高纬度地区的相关性明显大于低纬度地区. 通过对武汉地区2006年1月5天Radiosonde加密观测数据的分析, 讨论了重力波动能与势能的高度变化, 进一步发现纬向风的垂直剪切与急流中心的分布分别与重力波势能和动能的强弱分布相对应.      

星载电子器件用空气射流散热特性

在前期设计卫星大功率电子设备地面测试用通风散热系统的基础上,对系统散热性能进行了优化设计,对不同结构参数下电子器件的空气射流强化散热开展了数值仿真.研究结果表明系统中喷嘴出口直径、喷嘴出口至换热面距离、射流倾斜角以及喷嘴出口风速等参数对散热性能均有直接影响,并给出了定量的无量纲参数优化设计结果.该结论也可应用于表面热流密度为1 kW/m2级电子器件散热的优化设计,并为星载大功率电子设备对流式热控系统设计和地面测试提供技术参考.      

带喷流的超声速光学头罩流动显示

在马赫数3.8的超声速风洞中,以高时空分辨率的基于纳米示踪的平面激光散射(NPLS,Nano-tracer based Planar Laser Scattering)技术为实验手段,研究了有无喷流的超声速光学头罩流场的精细结构,清晰地再现了流场中的激波、膨胀波、剪切层和湍流边界层等复杂结构.通过分析时间相关的流场NPLS图像,可以发现流场结构随时间的演化特性.结果表明:无喷流情况下光学窗口上方的大部分流场处于层流状态;有喷流情况下剪切层的层流区域较短,在很短的距离内转捩至湍流状态;喷流出口压力高于外界压力情况下剪切层的转捩位置比压力匹配情况下较为靠前,光学窗口上方的涡结构也较为复杂.比较而言,后者对气动光学性能的影响更大.     

超音速喷流DPIV瞬时速度场实验测量

介绍了采用数字式互相关粒子图像测速系统(DPIV)在测量超音速喷流实验中的应用;实验给出了设计马赫数Ma=1.5的小型拉瓦尔喷管在不同总压和反压比条件下,喷流速度场、流线、涡量分布等定量信息.实验结果显示出流场中激波前后流体速度,涡量分布的明显变化,波系的结构和不同于一维管流的流动特性.     

气动弹爆破过程性能仿真分析

针对工业界对于安全有效的管道清洁装置的需求,设计了一种利用气动爆破的原理进行管道除垢的设备.该装置采用气动控制,利用压缩空气的瞬时释放产生的射流与冲击波的能量击碎管道内壁的附着物,实现管道除垢.通过分析装置工作的原理及运行过程,给出了重要参数的建模过程.通过仿真分析了气爆过程中压强、剪切力的分布特点以及传播过程,计算了其管道内气流速度场的分布变化,得出了气动弹爆破过程中对壁面产生的冲击主要来源于射流以及冲击波,并且在使用10MPa的工作压强下一次爆破可清理的管道范围超过160m.该设计可以高效的实现管道清污的作用.      

Secular variations of OH nightglow emission and of the OH intensity-weighted temperature induced by gravity–wave forcing in the MLT region

Secular variations of OH airglow (8,3) band and of the intensity-weighted temperature induced by a gravity wave packet at three latitudes in the northern hemisphere in the Mesosphere/Lower Thermosphere region are investigated using a 2-D, time-dependent, fully nonlinear OH chemistry–dynamics model. A net-cycled average survives due to wave transience and dissipation. The integrated OH (8,3) volume emission rates show a 20 percent increase induced by the wave packet. The corresponding intensity-weighted temperature shows an initial increase up to 2 percent then a gradual decrease for the remainder of the simulation time by the same wave packet. These secular variations could be mistaken as long-period or short-period waves in the airglow observations. Therefore, care must be taken when analyzing the data from observations.     

武汉上空惯性重力波活动

利用武汉中心气象台(30.5°N,114.4°E)无线电探空仪在2001年1月到2003年12月之间的观测数据,研究了武汉上空1-9km和14-25km高度范围内惯性重力波参数的变化特征.数据分析结果表明,重力波活动存在明显的季节变化,冬季较频繁,夏季活动较弱,与急流强度的季节变化一致,这意味着重力波的激发与背景风密切相关.矢端曲线分析显示1-9km范围内能量向上传播和向下传播的波的比例大致相同,而14-25km范围内绝大部分波能量向上传播,这与最大急流强度的高度相对应;进一步分析表明,夏天14-25km范围内波几乎全向上传播,而冬天则有相当一部分波向下传播,这可能是反射引起的.重力波的本征频率集中在1-3倍的惯性频率之间,水平波长约数百公里;1-9 km范围内垂直波长集中在3-3.5 km,14-25 km高度内则集中在4.5-5.5 km.      

脉冲射流对环量控制翼型气动性能的影响

定常射流在大迎角下气动性能较差,借助脉冲射流能够有效改善大迎角下的气动性能,并减少射流所需质量流量。采用非定常数值模拟的方法进行了脉冲射流作用下的环量控制翼型气动特性计算和流场分析。总结了占空比和频率分别对时均升力和升力脉动幅值的影响趋势;分析了不同迎角下的脉冲射流流动机理;进一步指出了射流动量系数的影响规律,并借助脉冲射流和定常射流的叠加效应有效缓解了升力脉动现象。结果表明:低占空比、同等升力系数下,脉冲射流可大幅度减小质量流量,但升力脉动幅值较大;小迎角下随频率增大,升力系数先增大后减小,但整体变化幅度不大,大迎角下随频率增大,升力系数持续性增大;脉冲射流能够推迟失速迎角,扩宽环量控制技术的可用迎角,并且随动量系数增大,这种优势更加明显;借助脉冲射流与定常射流的叠加效应,能够有效缓解脉冲射流作用下的升力脉动现象,达到飞行使用条件。