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.      

大气潮汐风场诱导中纬突发E层的观测证据及理论模拟分析

统计分析了中纬突发E层的测高仪数据,给出了潮汐风场诱导Es层的观测证据,证实了大气潮汐风场和突发E层的强烈相关性.另外,依据风剪切理论,从连续性方程出发,并结合运动方程,运用特征线方法求解,模拟了Es层在潮汐风场作用下的形成.模拟结果证实了风剪切理论的合理性及潮汐风场导致突发E层形成的可能性.      

利用二维核回归估计的大气密度模式修正

传统经验大气密度模式预测大气密度存在的较大误差会引起低轨卫星轨道预报误差,对卫星的再入轨、控制计划、碰撞规避及精密定轨造成不利影响.利用天宫一号卫星探测数据,针对大气NRLMSISE-00模式计算的误差特点,在地磁相对平静(Ap ≤ 30)的时间段内,对相近地方时和纬度的模式误差分布进行分析发现,相近地方时和纬度的模式误差分布基本相同.利用二维核回归估计方法,对与预测点相近地方时和纬度的样本误差进行加权,估计预测点处的模式误差,进而按距离预测日期天数的长短,采用加权修正法对模式预测结果进行修正,修正后大气模式误差的均方差(RMS)由14.09%降至4.05%.研究结果表明,该修正方法可以显著提高大气密度预报精度.      

地形产生的山地波及其传播过程模拟研究

气流经过地形产生的山地波是大气重力波研究的重要类别之一.从大气运动的控制方程组出发,建立模拟地形产生的山地波及其传播过程的二维数值模式.利用水平背景风场、地形和垂直速度之间的关系,在模式中引入垂直速度扰动作为地形产生山地波的激发源.通过模拟该激发源引起的扰动即山地波在大气中的传播过程,再现了山地波的产生、传播及充分发展过程.通过分析水平波长、垂直波长、位温扰动、流线,在空间尺度上描述了山地波的产生、传播及充分发展的过程.在气流经过地形产生的山地波的传播过程中,其水平波长λ_x的范围为2.5~5km,垂直波长λ_z约为2.5km.这些结果与利用山地波线性理论计算的垂直波长一致,从而验证了本模式能够模拟地形产生的山地波及其传播过程,为深入了解山地波的产生过程及其在中高层大气中的传播机制和效应奠定了基础.      

重力波波包在真实大气中传播特性的数值研究

采用二维全隐欧拉（FICE）格式，对重力波波包在真实大气中的非线性传播和演变过程进行了数值模拟，模拟结果表明，在中层大气下部激发的向上传播的重力波波包在传播到中层顶之前，波相关能量沿着射线路径传播，非线性效应和背景温场对波能量传播路径的影响很小，当波包传播到低热层大气后，波包饱和波相关能量几乎完全沿着水平方向传播，垂直方向的能量传播受到抑制，这与在无耗大气下，WKB近似条件下的线性重力波理论的预言相差很大，深入的分析表明抑制重力波波包向上传输能量的关键因素是大气分子粘性的垂直非均匀性。非线性和背景温场的影响不足以完全抑制波能量的向上传播，此外，在波包的整个传播过程中，由于非线性，背景温度和背景耗散的共同作用，重力波波包的垂直波长随时间明显减小，这些结果说明大气的分子粘性特别是分子粘性的垂直不均匀性对重力波波包在中、高层大气的非线性传播过程起着重要作用。     

中纬度冬季低热层潮汐水平风分量相位关系的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水平风分量之间的相位关系.统一用弧度定义的各潮汐经纬向分量的拟合初相位在三个连续的高度上分别显示出相同的时间变化倾向和相近的相位差,但是在绝大多数观测时间△ψ24和△ψ12准正交,而△ψ8出乎意料地准同相.周日、半日和8 h潮汐经纬向分量的二次相位耦合(QPC)方程被分别估计出来,利用它们相减还得到一个潮汐相位差相关方程.推测的8 h潮汐相位和相位差与相应的观测值很好地符合.在第14个时间窗内,三个潮汐一般表现为椭圆偏振而不是圆偏振或线偏振,但是△ψ24和△ψ12在三个连续的高度上准正交,而△ψ8在92.0和94.0 km上准同相.因此估计的潮汐QPC方程、推导的潮汐相位差相关方程、观测的8 h潮汐准同相相位差以及典型的潮汐偏振图都是观测的周日、半日和8 h潮汐之间真实QPC的反映.      

重力波非线性传播过程中的饱和与破碎

采用水平方向的显式算法与垂直方向的隐式算法相结合的时间分裂法,建立了二维可压缩大气中重力波非线性传播的数值模式.用本模式对小振幅重力波传播过程的模拟结果与线性重力波理论预测的结果吻合很好,从而验证了本模式的正确性.我们用此模式模拟了有限振幅重力波在非线性传播过程中的饱和与破碎,结果表明,(1)翻转出现在饱和之前,但向破碎演化仍需要一段时间,由于非线性波-波和波-流相互作用使得非线性数值模拟的饱和高度(出现时间)高(早)于线性饱和理论预测的结果;(2)重力波在不稳定之前已经有能量向背景场中转移,破碎直接导致非线性波-波相互作用,造成能量向小尺度短波上转移;(3)背景风场的加速方向,形成射流的方向与重力波的水平传播方向一致,表明重力波与背景流的非线性相互作用加剧了背景风剪切和不稳定性的发展.      

基于GNSS测量的天宫二号质心确定

由于轨道机动燃料消耗,科学载荷加载、分离,以及伴飞小卫星在轨释放等原因引起天宫二号空间站质心(COM)发生位移,从而影响天宫二号的动力学质心定轨精度。针对这一问题,提出了基于全球导航卫星系统(GNSS)测量数据的简化动力学质心估计方法。燃料消耗是引起天宫二号质心发生位移的主要原因,质心在本体坐标系X轴方向位移最为显著。利用GNSS测量数据对天宫二号进行质心估计和精密定轨,在三轴对地稳定姿态下,本体坐标系X轴方向与轨道切向重合,定轨结果对本体坐标系X轴方向的质心位移并不敏感。但在连续偏航模式下,本体坐标系X轴在轨道法向上有较大分量,X轴方向的质心位移对基于GNSS测量计算的精密定轨结果有较大影响。定性和定量分析结果表明:偏航姿态模式下天宫二号本体坐标系X轴方向质心位移估计具有可行性。天宫二号实测数据计算结果表明:与未做质心估计的定轨结果进行对比,质心估计后表征轨道动力学建模误差的经验加速度补偿水平在轨道径向、切向和法向上分别降低62%、50%和65%;载波相位后验残差标准差降低0.04 cm;精密轨道与全球激光测距数据比较精度提高0.86 cm。所提方法可以应用于大型低轨航天器在轨质心估计。      

内重力波传播的3维传输函数模式研究

在考虑背景风场及大气耗散的条件下,建立了3维内重力波传输函数数值模式.分析了300 km高度3维传输函数在频率波数域的特性,并以近地面单位脉冲点源为激发源,得到了内重力波在3维空间中的时空分布.讨论了不同时空尺度地面方波源激发的内重力波在电离层高度的能量分布特征.结果表明,(1)对内重力波而言,背景大气相当于一个带通滤波器,只有波动周期和波长分别在15～30 min和200～400 km之间的重力波扰动最容易上传到300km高度;(2)在背景风场的作用下水平面上以同心圆扩散的波阵面以及垂直方向上成漏斗状的波阵面发生了变形,并且逆风方向比顺风方向更有利于声重力波由对流层向电离层高度传播;(3)300km高度对时间尺度和空间尺度分别在20～30 min和150～250 km之间的地面方波源响应的总能量最强.      

损耗大气中随机重力波场的传输方程

从包含分子粘性的非线性相互作用方程出发, 采用随机相位近似, 推导了损耗大气中重力波场的非线性传输方程。由于分子损耗的引入, 谱演变的速率发生了改变, 在某些情况下, 还会得到与无耗条件下的传输规律相反的结论。损耗大气中重力波场的传输方程是研究中高层大气重力波能量收支平衡的出发点。      

Middle-atmosphere tides: Recent advances in theory and observation

Recent progress in the theoretical and observational investigation of middle atmosphere tides is reviewed. Theoretical advances include development of more realistic thermal excitation and numerical simulation models, investigation of seasonal — latitudinal and longitudinal variations in tidal structures, and the origin and effects of ‘unsteadiness’ in tidal oscillations over periods of days. Recent analyses of middle latitude radar data between 80 Km and 130 Km delineate consistent seasonal phase patterns in this region. Analyses of rocket data show stratosphere and lower mesosphere tides to be characterized by smaller amplitudes, shorter vertical scales, greater unsteadiness, and greater spatial variability than exhibited in the upper mesosphere and above. Results from the first two ATMAP (Atmospheric Tides Middle Atmosphere Program) campaigns are also discussed.     

Longitudinal MLT wind structure at higher mid-latitudes as seen by meteor radars at central and Eastern Europe (13°E/49°E)

The mid-latitude mesosphere and lower thermosphere (MLT) wind speeds measured by two SKiYMET meteor radars (MRs) at Collm (51°N, 13°E) and Kazan (56°N, 49°E) during 2016–2017 were analyzed to study longitudinal wind structures. The differences between monthly mean prevailing wind speeds and tidal amplitudes were compared with the corresponding differences obtained from TIMED/TIDI satellite winds and gradient wind speeds from the AURA/MLS instrument. It is shown that the MR wind difference between the two sites is statistically significant. The difference of the horizontal prevailing winds can be explained by a superposition of the background zonal flow, which is different at the two latitudes, with stationary planetary waves of different origin. Non-migrating tides contribute significantly to the difference of the semidiurnal tidal winds between the two sites.     

Temperature structure and dynamics of the middle atmosphere of Venus

The definitive data set for the mean thermal structure of the Venusian middle atmosphere is published for the first time. Some recent interim results on a modelling study to interpret the measured thermal field in terms of the global dynamics are also presented. These indicate that (a) the zonal winds on Venus fall to very low values above about 90 km, (b) there is a strong mid-latitude jet which circles the planet approximately every two days, (c) the observed solar tides are dominated by the semi-diurnal component, in agreement with theory.     

On the specification of TGCM tidal lower boundary conditions from radar wind measurements during the June 1984 GTMS period

Atmospheric tidal theory is applied to radar wind measurements of semidiurnal eastward and northward winds during June 1984 to specify the semidiurnal perturbation geopotential at lower thermosphere heights. Derived amplitudes for the longest-wavelength (2, 2) and (2, 3) tidal modes and their estimated vertical extensions are sufficiently large to modify the latitudinal structure of the thermosphere at levels of 150 km and above. These results can be used as the lower tidal boundary forcing in Thermospheric General Circulation Models (TGCM's) to incorporate the effects of upward propagating tides in simulations of the 26–28 June 1984 Global Thermosphere Mapping Study. (GTMS).     

Mesospheric doppler wind measurements from Aura Microwave Limb Sounder (MLS)

This paper describes a microwave limb technique for measuring Doppler wind in the Earth’s mesosphere. The research algorithm has been applied to Aura Microwave Limb Sounder (MLS) 118.75 GHz measurements where the O₂ Zeeman lines are resolved by a digital autocorrelation spectrometer. A precision of ∼17 m/s for the line-of-sight (LOS) wind is achieved at 80–92 km, which corresponds to radiometric noise during 1/6 s integration time. The LOS winds from Aura MLS are mostly in the meridional direction at low- and mid-latitudes with vertical resolution of ∼8 km. This microwave Doppler technique has potential to obtain useful winds down to ∼40 km of the Earth’s atmosphere if measurements from other MLS frequencies (near H₂O, O₃, and CO lines) are used. Initial analyses show that the MLS winds from the 118.75 GHz measurements agree well with the TIDI (Thermosphere Ionosphere Mesosphere Energetics and Dynamics Doppler Interferometer) winds for the perturbations induced by a strong quasi 2-day wave (QTDW) in January 2005. Time series of MLS winds reveal many interesting climatological and planetary wave features, including the diurnal, semidiurnal tides, and the QTDW. Interactions between the tides and the QTDW are clearly evident, indicating possible large tidal structural changes after the QTDW events dissipate.     

Atmospheric tides between 80 km and 120 km

The structure and variability of tides in the 80 – 120 km height region are reviewed. Particularly emphasised are seasonal-latitudinal variations in the vertical structure of diurnal and semidiurnal winds between 70 – 100 km as measured by meteor and partial reflection drift radars, and tidal temperatures determined by incoherent scatter radars between 100 and 140 km. Variations in tidal structures with longitude, from day to day, and during equinoctial transition periods are also addressed.     

Time variations of dynamical processes in the midlatitude upper mesosphere — lower thermosphere

Complex studies with the use of spectrum and harmonic analysis allow determination of wave disturbances in the prevailing and tidal wind, and also mesoscale short period oscillation intensity per unit mass. We particularly find enhanced periods of 4–6, 9–12, 15–20, 25–30 days, which are typical for planetary waves in the lower and middle atmosphere of the Earth. We also reveal the non-linear character of vertical amplitude and phase profiles for wave disturbances with planetary wave scales in the prevailing, tidal and short period oscillation intensity. This non-linearity is interpreted as a consequence of the non-linear interaction of waves such as internal gravity waves, tides and planetary waves among themselves and with background movements.     

大气中层顶区域波相互作用的一个观测个例

利用SOUSY VHF雷达的观测数据分析了极区中层顶83.4-91.2km范围内大气风场波动的非线性相互作用。大气风场的谱在不同高度上均有明显的潮汐分量峰值，纬向风分量中35h波、半日潮和8.9h惯必重力波构成共振相互作用对，经向风分量中33h波、半日潮和19h惯性重力波构成共振相互作用对。双谱分析表明，这些共振对在许多高度上都发生耦合，35h或33h波振幅的极小值与半日潮的极大值出现的高度几乎相同，呈现出明显的非线性相互作用在空间上不是局域的，而是存在于中层顶区域的几乎所有高度上，这种相互作用不仅导致半日潮振幅随时间的变化，也使半日潮的振幅随空间变化。35h和33h波动可能是在其他时段或其他位置通过行星波与周日潮相互作用产生的，然后传播到观测点并与半日潮发生相互作用。