中纬度冬季低热层潮汐非线性相互作用的MF雷达观测

采用武汉(30°N,114°E)MF雷达在2001年冬季的风场观测数据研究中纬度低热层大气潮汐之间的二阶非线性相互作用.经向风场的Lomb-Scargle归一化振幅谱表明,周日、半日和8 h潮汐是中纬冬季中层顶区域占优势的大气扰动;此外6 h潮汐也清晰可见.双相干谱分析揭示大多数显著的双相干谱峰代表潮汐谐振分量之间的相位互相关或单个潮汐分量的自相关.对随时间变化的潮汐垂直波长的比较发现,实际观测的8h潮汐垂直波长与假定的由观测的24 h潮汐和12 h潮汐非线性相互作用产生的8 h潮汐的理论垂直波长具有明显的一致性.在94.0～98.0km高度范围,周日、半日和8h潮汐之间不仅存在明显的相位相关和垂直波数相关,且它们的振幅随时间变化也显示出振荡幅值相近、振荡相位同步或反相的相关性,表明它们之间已经发生了二阶非线性相互作用.但是在94.0 km以下,三个潮汐分量之间的各种相关性随高度的下降变得越来越弱,因此潮汐二阶相互作用更可能是一种局地和暂态的现象.      

中高层大气对低层大气脉冲扰动的响应

从基本的大气运动方程出发,采用二维全隐欧拉格式(FICE)建立极坐标下二维声重波传播的数值模式.对小振幅高斯形态声重波传播过程的模拟结果表明,该数值模式能够再现声重波波包向上的稳定传播过程.应用此数值模式模拟了在没有背景风场和存在背景风场条件下中高层大气对10km高空处近似脉冲点源扰动的响应过程,获得了中高层大气对低层大气脉冲扰动响应的图像.结果表明,电离层高度对重力波扰动的响应不但出现在激发源激发之后,还与激发源具有较大距离,扰动的幅度随高度的增大而增大;有背景风时,顺风情况下重力波波动传播路径较逆风情况下平缓,且传播的水平距离比逆风情况下远,波动的振幅较逆风情况下弱,逆向背景风场能够加速重力波向上传播.同时,模拟还表明脉冲扰动正上方可以激发产生一种以6 min为主要周期,具有声学分支特性的快速波动.本文模拟的扰动结果与2004年12月26日苏门答腊-安达曼地震引起的电离层TEC扰动具有类似的图像.      

波音737NG飞机前货舱后隔板下部支撑横梁腐蚀受损分析及改进

某航空公司波音737NG机队飞机前货舱后隔板下部支撑横梁腐蚀严重,受损率较高,如不及时更换将发生变形甚至断裂,影响周围其他重要结构部件甚至影响飞行安全,但更换该部件成本较高.统计表明,其受腐蚀损坏程度与机龄、密封、首次检查期限和重复检查间隔等因素相关.严格执行检查和提高维护标准可以降低维修成本,若进一步改进支撑梁底部密...     

适于低轨卫星IP网络的单核共享树组播算法(英文)

为了解决低轨卫星IP网络中现有典型源组播算法的信道资源浪费问题,本文提出了一套单核共享树组播算法,即核心群合并共享树(CCST)和加权核心群合并共享树(w-CCST)算法。CCST 算法包括动态近似中心(DAC)选核方法和核心群合并组播路径构建方法。DAC方法专为周期、规律运动的低轨卫星网络提出,不需要复杂的星上计算。在核心群合并方法中,以核节点作为初始核心群,通过核心群和剩余组成员的最短路径方法逐步扩展直至整棵组播树构建完成,从而使得组播树的树代价最小,大大提高了网络的带宽利用率和组播传输效率。w-CCST 算法中所提出的加权因子可以调整树代价和端到端传播时延之间的折衷程度,因此,可以通过调整加权因子来适度增大树代价、降低端到端传播时延以支持某些端到端时延要求苛刻的实时组播业务。最后,与低轨卫星 IP 网络中典型算法进行了性能比较,仿真结果说明,CCST 算法的平均树代价比其它算法显著降低,w-CCST 算法的平均端到端传播时延小于 CCST 算法。     

Stratospheric polar vortex as a possible reason for temporal variations of solar activity and galactic cosmic ray effects on the lower atmosphere circulation

Possible reasons for the temporal instability of long-term effects of solar activity (SA) and galactic cosmic ray (GCR) variations on the lower atmosphere circulation were studied. It was shown that the detected earlier ∼60-year oscillations of the amplitude and sign of SA/GCR effects on the troposphere pressure at high and middle latitudes (Veretenenko and Ogurtsov, Adv.Space Res., 2012) are closely related to the state of a cyclonic vortex forming in the polar stratosphere. The intensity of the vortex was found to reveal a roughly 60-year periodicity affecting the evolution of the large-scale atmospheric circulation and the character of SA/GCR effects. An intensification of both Arctic anticyclones and mid-latitudinal cyclones associated with an increase of GCR fluxes at minima of the 11-year solar cycles is observed in the epochs of a strong polar vortex. In the epochs of a weak polar vortex SA/GCR effects on the development of baric systems at middle and high latitudes were found to change the sign. The results obtained provide evidence that the mechanism of solar activity and cosmic ray influences on the lower atmosphere circulation involves changes in the evolution of the stratospheric polar vortex.     

Structure of the migrating diurnal tide in the Whole Atmosphere Community Climate Model (WACCM)

As part of an ongoing effort to understand the migrating diurnal tide generated by the NCAR Whole Atmosphere Community Climate Model, version 3 (WACCM3), we compare the WACCM3 migrating diurnal tide in the horizontal wind and temperature fields to similar results from the Global Scale Wave Model (GSWM). The WACCM3 diurnal tidal wind fields are also compared to tropical radar measurements at Kauai (22°N, 200.2°E) and Rarotonga (21.3°S, 199.7°E). The large-scale features of the WACCM3 results, such as the global spatial structure and the semiannual amplitude variation are in general agreement with past tidal studies; however, several differences do exist. WACCM3 exhibits a much higher degree of hemispheric asymmetry, lower overall amplitudes around the equinoxes, and peaks which are more confined in latitude when compared with the GSWM. Factors which may contribute to such differences between WACCM3 and GSWM are the solar heating profiles from ozone and water vapor, dissipation, and the zonal mean zonal winds. We find that the internally generated heating in WACCM3 and eddy dissipation values are both smaller than the values specified in the GSWM; the eddy dissipation fields and zonal mean zonal winds of the two models also display measurable differences in spatial structure. Comparisons with radar data show several differences in spatial and seasonal structure. In particular, the diurnal tide zonal winds in WACCM3 above Kauai are considerably larger in amplitude than those observed in the radar data, due to contributions from nonmigrating tidal components including wave numbers eastward 1 through 3, westward 2, and stationary components, which interfere constructively with the migrating component around equinox in WACCM3.     

数控慢走丝线切割机床锥度切割的方法

模具行业的迅速发展推动了电火花线切割技术的进步，数控慢走丝线切割机床以其自动化程度高、精度好、加工稳定、可靠的优点开辟了广阔的市场前景。本文主要介绍了FUNAC线切割机床锥度切割的方法，重点介绍了当锥度有误差时，应如何进行补偿。     

冲击噪声环境下基于任意阵列流形的空时二维DOA估计方法

 针对冲击噪声环境中信号源的高分辨二维波达方向(DOA)估计问题,提出了一种适合任意阵形的基于联合对角化分数低阶空时(ST)相关矩阵的二维DOA估计方法。该方法先对分数低阶空时矩进行采样构建伪快拍数据矩阵,然后对两个时延分数低阶空时矩阵进行联合对角化处理。其无需二维谱峰搜索和参数配对,在低信噪比下对强冲击噪声具有更好的抑制作用,适合存在一维角度兼并的情况。仿真结果证明了该方法的有效性。     

An intercomparison of meteor radar measurements at the South Pole using two different processing systems

A new meteor radar system was installed at the Amundsen–Scott station South Pole in 2001 to further the understanding of the dynamics of the Antarctic region. The antenna array consists of four yagis pointed along the 0°, 90°, 180°, and 270° meridians and five folded crossed dipoles arranged in a cross configuration and operating as an interferometer to provide position measurements for the detected radio meteors. The four yagis are time division multiplexed and used for both transmitting and receiving while the five folded crossed dipoles are only used for reception. The current arrangement of data acquisition (DAQ) systems at the South Pole allows the collection of meteors in a configuration similar to the previous meteor radar system that operated at the South Pole in the mid 1990s while also using an interferometer to accurately determine the meteor positions in the sky, which enables the determination of the vertical structure of the observed waves. This has been accomplished through the use of two DAQ and post-processing systems: COBRA (Colorado Obninsk radar) connected to the yagis and MEDAC (meteor echo detection and collection) connected to the folded crossed dipoles. With two separate DAQ systems operating in parallel we have the ability to directly compare the results and understand the inherent variability in the derived scientific results based on different system architectures and processing assumptions. The impact of operating a system without an interferometer on the amplitudes and phases of the observed wave components is considered. We find that the lack of altitude resolution of the COBRA DAQ system leads to an underestimation of the amplitude of the s = 1 component of the semidiurnal tide of ∼20% during the summer months.     

Long-period meteor radar temperature variations over Collm (51°N, 13°E) and Kazan (56°N, 49°E)

We have estimated temperatures from meteor radar measurements using the gradient method and the full width at half maximum method over Kazan (56°N 49°E) and Collm (51°N, 13°E). The time series cover the period 2016–2019. The temperature gradient model is constructed from SABER temperature observations. We demonstrate that annual mean, amplitudes and phases of the annual and semiannual oscillations of the radar temperatures are close to those of the MLS and SABER temperatures. The annual mean temperatures over Kazan and Collm differ non-significantly. The seasonal variability of the radar temperature is mostly due to the annual cycle which tends to grow with latitude. The gradient method produces temperatures which agree with the SABER temperatures better than with the MLS ones. The harmonics of the annual oscillations from periods of 73 days up to periods of about 40 days are the most significant day-to-day temperature oscillations and have zonal wavenumber zero. Their periods and phases are in good correspondence with those of the MLS and SABER ones. We also show some results which demonstrate that at 56°N the FWHM method is not as robust as the gradient method.