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61.
A 29-year time-series of four-times-daily atmospheric effective angular momentum (EAM) estimates is used to study the atmospheric
influence on nutation. The most important atmospheric contributions are found for the prograde annual (77 μas), retrograde
annual (53 as), prograde semiannual (45 as), and for the constant offset of the pole (δψsinɛ0=−86 as, δɛ=77 as). Among them only the prograde semiannual component is driven mostly by the wind term of the EAM function,
while in all other cases the pressure term is dominant. These are nonnegligible quantities which should be taken into account
in the new theory of nutation. Comparison with the VLBI corrections to the IAU 1980 nutation model taking into account the
ocean tide contribution yields good agreement for the prograde annual and semiannual nutations. We also investigated time
variability of the atmospheric contribution to the nutation amplitudes by performing the sliding-window least-squares analysis
of both the atmospheric excitation and VLBI nutation data. Almost all detected variations of atmospheric origin can be attributed
to the pressure term, the biggest being the in-phase annual prograde component (about 30 as) and the retrograde one (as much
as 100200 as). These variations, if physical, limit the precision of classical modeling of nutation to the level of 0.1 mas.
Comparison with the VLBI data shows significant correlation for the retrograde annual nutation after 1989, while for the prograde
annual term there is a high correlation in shape but the size of the atmospherically driven variations is about three times
less than deduced from the VLBI data. This discrepancy in size can be attributed either to inaccuracy of the theoretical transfer
function or the frequency-dependent ocean response to the pressure variations. Our comparison also yields a considerably better
agreement with the VLBI nutation data when using the EAM function without the IB correction for ocean response, which indicates
that this correction is not adequate for nearly diurnal variations.
Received: 10 September 1997 / Accepted: 5 March 1998 相似文献
62.
Observations of traveling ionospheric disturbances (TIDs) associated with atmospheric gravity waves (AGWs) generated by the moving solar terminator have been made with the Millstone Hill incoherent scatter radar. Three experiments near 1995 fall equinox measured the AGW/TID velocity and direction of motion. Spectral and cross-correlation analysis of the ionospheric density observations indicates that ST-generated AGWs/TIDs were observed during each experiment, with the more-pronounced effect occurring at sunrise. The strongest oscillations in the ionospheric parameters have periods of 1.5 to 2 hours. The group and phase velocities have been determined and show that the disturbances propagate in the horizontal plane perpendicular to the terminator with the group velocity of 300–400 m s–1 that corresponds to the ST speed at ionospheric heights. The high horizontal group velocity seems to contradict the accepted theory of AGW/TID propagation and indicates a need for additional investigation. 相似文献
63.
A series of enclosed ecosystem experiments were conducted in a land-based tank near the seaside of West Xiamen Harbor. The
results of experiments conducted in different seasons and years showed a repeatable phytoplankton succession. In this relatively
stable ecosystem with added nutrients and trace metals, diatoms dominated initially, dinoflagellates dominated in the later
stage, and dinoflagellate red tides eventually occurred. Vitamin B12 enrichment may speed up this succession process. Stirring the water column could stop this process. Soluble Mn at a level
of 3–4 μg/L in seawater, which also is the existing concentration of soluble Mn in Xiamen Harbor seawater, is sufficient for
the multiplication of algae and occurrence of red tide. The present study showed that excessive soluble Mn in Xiamen Harbor
cannot cause red tide, and that Fe was one of the important factors causing diatiom red tide in this present study.
Project 39570145 supported by NSFC. 相似文献
64.
The possibility that the Earth's tides are a triggering factor of Vrancea subcrustal earthquakes is investigated in the first part of this paper. A possible correlation between Vrancea subcrustal earthquakes and geomagnetic jerks is demonstrated in the second part. The last part of the paper presents a number of results concerning a possible relationship between the regularities of strong Vrancea subcrustal seismicity and the Chandler nutation parameters. An attempt is made to integrate all of these phenomena in a more general framework that takes into account physical processes in the Earth mantle and core. A long-term prediction of the next strong Vrancea earthquake is finally attempted. 相似文献
65.
Geophysical analysis of zonal tidal signals in length of day 总被引:5,自引:0,他引:5
Benjamin Fong Chao James B. Merriam Yoshiaki Tamura 《Geophysical Journal International》1995,122(3):765-775
66.
67.
C. Sozou 《Geophysical Journal International》1997,130(1):151-156
Laplace's tidal equations for the case of an ocean of constant depth bounded by meridians were considered by two authors at a specific frequency as an eigenvalue problem in the azimuthal wavenumber. A finite spectrum of eigenwavenumbers was found. That eigenvalue problem is re-examined by means of asymptotic techniques and numerical integration of the governing equation of the problem. At low frequencies a formula connecting the frequency and the number of eigensolutions is established. It is shown that at a given frequency the spectrum of eigenwavenumbers is wider than that reported, but (for this type of solution) the meridional boundary conditions are satisfied approximately only for the case of very low frequencies. 相似文献
68.
Previous studies devoted to the morphology and hydrodynamics of ridge and runnel beaches highlight characteristics that deviate from those initially postulated by King and Williams (Geographical Journal, 1949, vol. 113, 70–85) and King (Beaches and Coasts, 1972, Edward Arnold). Disagreements on the morphodynamics of these macrotidal beaches include the position of the ridges relative to the mean neap and spring tide levels, the variation in the height of the ridges across the intertidal profile and, most importantly, whether the ridges are formed by swash or surf zone processes. The morphological characteristics of ridge and runnel beaches from three locations with varying wave, tidal and geomorphic settings were investigated to address these disagreements. Beach profiles from each site were analysed together with water‐level data collected from neighbouring ports. It was found that the ridges occur over the entire intertidal zone. On one site (north Lincolnshire, east England), the ridges are uniformly distributed over the intertidal beach, whereas on the two other sites (Blackpool beach, northwest England, and Leffrinckoucke beach, north France) there is some indication that the ridges appear to occur at preferential locations. Most significantly, the locations of the ridge crests were found to be unrelated to the positions on the intertidal profile where the water level is stationary for the longest time. It was further found that the highest ridges generally occur just above mid‐tide level where tidal non‐stationarity is greatest. These findings argue against the hypothesis that the ridges are formed by swash processes acting at stationary tide levels. It is tentatively suggested that the ridges are the result of a combination of swash and surf zone processes acting across the intertidal zone. Elucidation of the morphodynamic roles of these two types of processes, and other processes such as strong current flows in the runnels, requires further comprehensive field measurements complemented by numerical modelling. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
69.
鉴于当前国际上关于自转微椭、非均匀地球(SREHI)的固体潮汐响应的结果之间存在明显分歧,特别是Love数k及重力潮汐因子δ对纬度的依赖情况截然不同,本文借助于摄动法与张量正则分量的广义球谐展开建立起来的侧向非均匀、自转微椭、粘弹地球的潮汐模拟理论,计算了SREHI地球的潮汐形变及相应的引力位变化.结果表明,描述径向位移的Love数的纬度依赖部分系数h_+与球对称部分h_0+δh_0之比不大于1.0‰;对O_1波为0.27‰;对M_2波为0.19‰;对M_3波为0.49‰;对M_4波为0.88‰.描述地球引力位变化的Love数的纬度依赖部分系数k_+与球对称部分k_0+δk_0之比小于3.0‰;对O_1波为2.67‰;对M_2波为1.89‰;对M_3波为2.24‰;对M_4波为2.70‰. 相似文献
70.
In this paper analytical expressions are derived for the temporal variations ofJ
2 andJ
22 due to the tides of the solid Earth, taking into account only the deformation of the mantle, and employing a procedure already used by the authors in their Hamiltonian theory of the Earth's rotation, which obtain the necessary parameters in a direct way by integration of those provided by a selected model of Earth interior.Numerical tables giving the periodic variation of coefficients are given, as well as a new prediction for UT1. For J
2 and J
22 the amplitudes reach such a magnitude that both two variations should not be ignored in studies involving the analysis of highly precise satellite tracking data. Moreover, the possibility of improving our knowledge of the value of those harmonic coefficients in only a more exact digit appears as to be strongly dependent on the limitations in the theoretical modeling of the variations of the inertia tensor due to solid tides. 相似文献