地倾斜双轴垂直摆倾斜仪测量方法研究

介绍一种可同时测量两个正交方向(例如:东西向和南北向)地壳倾斜的双轴单摆体结构的垂直摆倾斜仪的基本原理,并给出其结构设计和初步的实验结果.实验结果表明,地倾斜双轴垂直摆倾斜仪能同时测量两个正交方向的倾斜信号,分辨率达到10-9 rad数量级,能够清晰记录地倾斜固体潮汐信号.     

Observations of semidiurnal internal tidal currents off central Chile (36.6°S)

Observations of semidiurnal internal tidal currents from three moorings deployed on the continental shelf off central Chile during summer and winter of 2005 are reported. The spectra of the baroclinic currents showed large peaks at the semidiurnal band with a dominant counterclockwise rotation, which was consistent with internal wave activity. The amplitude of the barotropic tidal currents varied according to the spring–neap cycle following the sea level fluctuations. In contrast, the amplitudes of the internal tide showed high spatial-temporal variability not directly related to the spring–neap modulation. Near the middle of the continental shelf and near the coast (San Vicente Bay) the variance of the semidiurnal baroclinic current is larger than the variance of its barotropic counterpart. The vertical structure of the baroclinic tidal current fluctuations was similar to the structure of the first baroclinic internal wave mode. In general, in the three study sites the variance of the baroclinic current was larger near the surface and bottom and tended to show a minimum value at mid depths. Kinetic energy related to semidiurnal internal waves was larger in winter when stratification of the water column was stronger. During summer, upwelling and the decrease of freshwater input from nearby rivers reduced the vertical density stratification. The amplitude of the semidiurnal internal tide showed a tendency to be enhanced with increasing stratification as observed in other upwelling areas. The continental shelf break and submarine canyons, which limit the continental shelf in the alongshore direction, represent near-critical slopes for the semidiurnal period and are suggested to be the main internal tide generation sites in the study region.     

The summertime 12-h wind oscillation with zonal wavenumber s = 1 in the lower thermosphere over the South Pole

Meteor radar measurements of winds near 95 km in four azimuth directions from the geographic South Pole are analyzed to reveal characteristics of the 12-h oscillation with zonal wavenumber one (s = 1). The wind measurements are confined to the periods from 19 January 1995 through 26 January 1996 and from 21 November 1996 through 27 January 1997. The 12-h s = 1 oscillation is found to be a predominantly summertime phenomenon, and is replaced in winter by a spectrum of oscillations with periods between 6 and 11.5 h. Both summers are characterized by minimum amplitudes (5–10 ms^–1) during early January and maxima (15–20 ms^–1) in November and late January. For 10-day means of the 12-h oscillation, smooth evolutions of phase of order 4–6 h occur during the course of the summer. In addition, there is considerable day-to-day variability (±5–10 ms^–1 in amplitude) with distinct periods (i.e., 5 days and 8 days) which suggests modulation by planetary-scale disturbances. A comparison of climatological data from Scott Base, Molodezhnaya, and Mawson stations suggests that the 12-h oscillation near 78°S is s = 1, but that at 68°S there is probably a mixture between s = 1 and other zonal wavenumber oscillations (most probably s = 2). The mechanism responsible for the existence of the 12-h s = 1 oscillation has not yet been identified. Possible origins discussed herein include in situ excitation, nonlinear interaction between the migrating semidiurnal tide and a stationary s = 1 feature, and thermal excitation in the troposphere.     

Transient eastward-propagating long-period waves observed over the South Pole

Observations of the horizontal wind field over the South Pole were made during 1995 using a meteor radar. These data have revealed the presence of a rich spectrum of waves over the South Pole with a distinct annual occurrence. Included in this spectrum are long-period waves, whose periods are greater than one solar day, which are propagating eastward. These waves exhibit a distinct seasonal occurrence where the envelope of wave periods decreases from a period of 10 days near the fall equinox to a minimum of 2 days near the winter solstice and then progresses towards a period near 10 days at the spring equinox. Computation of the meridional gradient of quasi-geostrophic potential vorticity has revealed a region in the high-latitude upper mesosphere which could support an instability and serve as a source for these waves. Estimation of the wave periods which would be generated from an instability in this region closely resembles the observed seasonal variation in wave periods over the South Pole. These results are consistent with the hypothesis that the observed eastward propagating long-period waves over the South Pole are generated by an instability in the polar upper mesosphere. However, given our limited data set we cannot rule out a stratospheric source. Embedded in this spectrum of eastward propagating waves during the austral winter are a number of distinct wave events. Eight such wave events have been identified and localized using a constant-Q filter bank. The periods of these wave events ranges from 1.7 to 9.8 days and all exist for at least 3 wave periods. Least squares analysis has revealed that a number of these events are inconsistent with a wave propagating zonally around the geographic pole and could be related to waves propagating around a dynamical pole which is offset from the geographic pole. Additionally, one event which was observed appears to be a standing oscillation.     

Inertia-gravity waves in the troposphere and lower stratosphere associated with a jet stream exit region

Radar measurements at Aberystwyth (52.4°N, 4.1°W) of winds at tropospheric and lower stratospheric heights are shown for 12–13 March 1994 in a region of highly curved flow, downstream of the jet maximum. The perturbations of horizontal velocity have comparable amplitudes in the troposphere and lower stratosphere with downward and upward phase propagation, respectively, in these two height regions. The sense of rotation with increasing height in hodographs of horizontal perturbation velocity derived for hourly intervals show downwards propagation of energy in the troposphere and upward propagation in the lower stratosphere with vertical wavelengths of 1.7 to 2.3 km. The results indicate inertia-gravity waves propagating in a direction similar to that of the jet stream but at smaller velocities. Some of the features observed contrast with those of previous observations of inertia-gravity waves propagating transverse to the jet stream. The interpretation of the hodographs to derive wave parameters has taken account of the vertical shear of the background wind transverse to the direction of wave propagation.     

Investigation of the time variability of diurnal tides and resonant FCN period

The time variability of diurnal tides was investigated by analyzing gravity observations from global superconducting gravimeter (SG) stations with running time intervals. Through least-square and Bayesian approaches, FCN resonance parameters were estimated for each data section after obtaining the tidal parameters of mainly diurnal tidal waves. The correlation of the time variation in diurnal tidal waves and FCN period was discussed. For comparison, a similar method was used to analyze VLBI observations to study the time variability of nutation terms and FCN period. The variation trend of the FCN period totally depends on the Ψ1 wave in tidal gravity and on the retrograde annual term in nutation. We observed a similar variation trend in the FCN periods obtained from different SG stations worldwide and VLBI observations. The relation between diurnal tides and LOD variations is discussed and the possible mechanisms of the decadal variation in FCN periods were discussed.     

固体潮调和分析的新算法

本文利用差分法对固体潮数据进行调和分析尝试。其结果表明该方法具有原理简单,对数据连续性要求低,解算精度高等优点。且对日波,半日波,1/3日波等三波段的潮汐导纳一次解出,同时得到唯一的比较切实的观测值中误差。     

体应变潮汐观测资料信息提取与映震效果

根据体应变观测资料的特点, 研究了体应变观测资料的处理方法, 提出了在时间域分析的数学模型。在数学模型中, 将潮汐因子、气压系数、非潮汐应变速率和加速度一并考虑, 在资料处理结果中, 这些参数可同时取得。分别用时间域分析方法和频率域分析方法对观测数据进行了处理, 发现潮汐因子、气压系数、应变速率和加速度等参数在大同地震前均有大小不同、持续时间不等的异常, 这些参数可作为物理意义明确的地震中短期预测的指标。     

全球Schwiderski海潮模型M_2分波在中国大陆产生的应变负荷潮

本文利用计算应变负荷潮的积分Green函数方法,计算了全球Schwiderski海潮模型M_2分波在中国大陆产生的应变负荷潮.根据负荷潮的分布特点,中国大陆大致可以分成以东经100°为界的东、西两个区域.在东区,负荷潮主要受太平洋海潮的控制;在西部内陆地区,除太平洋海潮外,它们还明显地受印度洋海潮的影响.根据本文计算结果绘制的M_2分波应变负荷潮在中国大陆的地理分布图,为如何正确考虑M_2分波负荷潮对应变固体潮观测结果的影响提供了重要的参考资料.