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Chen W.,Wuhan University | Chen W.,State Key Laboratory of Information Engineering in Surveying | Shen W.,Wuhan University | Shen W.,State Key Laboratory of Information Engineering in Surveying | Shen W.,Key Laboratory of Geospace Environment and Geodesy
Journal of Geophysical Research: Solid Earth

The Earth's rotation is perturbed by mass redistributions and relative motions within the Earth system, as well as by the torques from both the internal Earth and celestial bodies. The present study aims to establish a theory to incorporate all these factors perturbing the rotation state of the triaxial Earth, just like the traditional rotation theory of the axial-symmetric Earth. First of all, we reestimate the Earth's inertia tensor on the basis of two new gravity models, EIGEN-GL05C and EGM2008. Then we formulate the dynamic equations and obtain their normal modes for an Earth model with a triaxial anelastic mantle, a triaxial fluid core, and dissipative oceans. The periods of the Chandler wobble and the free core nutation are successfully recovered, being ∼433 and ∼430 mean solar days, respectively. Further, the Liouville equations and their general solutions for that triaxial nonrigid Earth are deduced. The Liouville equations are characterized by the complex frequency-dependent transfer functions, which incorporate the effects of triaxialities and deformations of both the mantle and the core, as well as the effects of the mantle anelasticity, the equilibrium, and dissipative ocean tides. Complex transfer functions just reflect the fact that decays and phase lags exist in the Earth's response to the periodic forcing. Our theory reduces to the traditional rotation theory of the axial-symmetric Earth when assuming rotational symmetry of the inertia tensor. Finally, the present theory is applied to the case of atmospheric-oceanic excitation. The effective atmospheric-oceanic angular momentum function (AMF) χeff = χeff1 + iχeff2 for the present theory is compared with the AMF χeff sym = χeff1 sym + iχeff2 sym for the traditional theory and the observed AMF χobs = χ1 obs + iχ2 obs; we find that the difference between χeff and χeff sym is of a few milliseconds of arc (mas) and can sometimes exceed 10 mas. In addition, spectrum analyses indicate that χeff is in good agreement with χeff sym and, further, show an increase of coherency with χobs especially in the low-frequency band. The obvious advantage of χeff in the low-frequency band with respect to χeff sym is the critical support of the present theory. However, still better performance of our theory can be expected if the models of the mantle anelasticity and oceanic dynamics were improved. Thus we conclude that the traditional Earth rotation theory should be revised and upgraded to include the effects of the Earth's triaxiality, the mantle anelasticity, and oceanic dynamics. The theory presented in this study might be more appropriate to describe the rotation of the triaxial Earth (or other triaxial celestial bodies such as Mars), though further studies are needed to incorporate the effects of the solid inner core and other possible influences. Copyright 2010 by the American Geophysical Union. Source

Ping P.,Wuhan University | Zhang Y.,Wuhan University | Zhang Y.,Key Laboratory of Geospace Environment and Geodesy | Xu Y.,Wuhan University
Journal of Applied Geophysics

In order to conquer the spurious reflections from the truncated edges and maintain the stability in the long-time simulation of elastic wave propagation, several perfectly matched layer (PML) methods have been proposed in the first-order (e.g., velocity-stress equations) and the second-order (e.g., energy equation with displacement unknown only) formulations. The multiaxial perfectly matched layer (M-PML) holds the excellent stability for the long-time simulation of wave propagation, even though it is not perfectly matched in the discretized M-PML equation system. This absorbing boundary approach can offer an alternative way to solve the problem of the late-time instability, especially for anisotropic media, which is also suffered by the convolutional perfectly matched layer (C-PML) that is supposed to be competent to handle most stable problems. The M-PML termination implementation in the first-order formulations is well proposed. The common drawback of the implementation of the first-order M-PML formulations is that it necessitates fundamental reconstruction of the existing codes of the second-order spectral element method (SEM) or finite element method (FEM). Therefore, we propose a nonconvolutional second-order M-PML absorbing boundary condition approach for the wave propagation simulation in elastic media that has not yet been developed before. Two-dimensional numerical simulation validations demonstrate that the proposed second-order M-PML has good performances: 1) superior efficiency and stability of absorbing the spurious elastic wavefields, both the surface waves and body waves, reflected on the boundaries; 2) superior stability in the long-time simulation even in the isotropic medium with a high Poisson's ratio; 3) superior efficiency and stability in the long-time simulation for anisotropic media. This method hence makes the SEM and FEM in the second-order wave equation formulation more efficient and stable for the long-time simulation. © 2013 Elsevier B.V. Source

Huang Y.Y.,Key Laboratory of Geospace Environment and Geodesy | Zhang S.D.,Hubei University | Yi F.,Key Laboratory of Geospace Environment and Geodesy | Huang C.M.,Key Laboratory of Geospace Environment and Geodesy | And 3 more authors.
Annales Geophysicae

This paper presents characteristics of quasi-two-day waves (QTDWs) in the mesosphere and lower thermosphere (MLT) between 52° S and 52° N from 2002 to 2011 using TIMED/SABER temperature data. Spectral analysis suggests that dominant QTDW components at mid-high latitudes of the Southern Hemisphere (SH) and the Northern Hemisphere (NH) are (2.13, W3) and (2.04, W4), respectively. The most remarkable QTDW is (2.13, W3), which happened in the southern summer of 2002-2003 at 32° S from 60 to 90 km in altitude. Its downward phase propagation indicates upward propagation of the wave energy and a potential source region below 60 km. Analysis of horizontal wind fields in the same period shows the westward and southward propagation of (2.13, W3) and a possible reflection region above 90 km. Fundamental parameters of QTDWs present significant interhemispheric differences and interannual variations in statistical analysis. Amplitudes in the SH are twice larger than that in the NH, and vertical wavelengths are a little longer in the SH. QTDWs may endure stronger dissipation in southern summer because of shorter durations of their attenuation stages. Impact of the equatorial quasi-biennial-oscillation (QBO) on QTDWs can extend to mid-high latitudes of both hemispheres. It seems easier for QTDWs to propagate upward in the equatorial QBO's westerly phase in the lower stratosphere and easterly phase in the middle stratosphere. Interannual variations of QTDW strength may be influenced by solar activity as well. Strengths of QTDWs appear to be stronger (weaker) in the solar maximum (minimum). © Author(s) 2013. Source

He Y.,Wuhan University | He Y.,Key Laboratory of Geospace Environment and Geodesy | Yi F.,Wuhan University | Yi F.,Key Laboratory of Geospace Environment and Geodesy
Advances in Meteorology

The vertical distribution, horizontal range, and optical properties of Asian dust were obtained using a ground-based depolarization lidar and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) over a two-year measurement period (2010-2012) in Wuhan (30.5°N, 114.4°E), China. The depolarization lidar registered 13 dust events, most of which occurred in the spring (5 events) and winter (6 events).Thedust layers occurred at heights of approximately 1.4-3.5 km.Thehorizontal ranges of the dust plumes were approximately 750-2400 km, based on the CALIPSO data. The average volume depolarization ratio (δ), particle depolarization ratio (δ p), extinction and optical depth (AOD) of the dust layers were 0.12, 0.22, 0.19 km-1, and 0.32, respectively. The dust layers observed in the winter occurred at a lower height and had larger mean extinction and AOD, and smaller mean δ and δ p than the spring dust layers. These wintertime features may result from a lower troposphere temperature inversion, the mixing of local aerosols, and hygroscopic growth under suitable relative humidity conditions. A dust event in April 2011 spanned 9 days. Compared with the observations at other sites, the dust layers over Wuhan exhibited more turbid along with suppressed nonspherical particle shape. Copyright © 2015 Y. He and F. Yi. Source

Zeng L.,Wuhan University | Zeng L.,Key Laboratory of Geospace Environment and Geodesy | Yi F.,Wuhan University | Yi F.,Key Laboratory of Geospace Environment and Geodesy
Journal of Atmospheric and Solar-Terrestrial Physics

Extensive lidar measurements of Fe and Na meteor trails were conducted with an integration period of 3.2s. A total of 155 Fe trails and 136 Na trails were registered, respectively, from the 260-h Fe and 320-h Na photon count profiles. They came from the observations that did not coincide with the major meteor showers and thus represent sporadic meteors. The mean input fluxes from the lidar meteor trail measurements are 1.5×10 5 atomcm -2s -1 for Fe and 1.4×10 4 atomcm -2s -1 for Na. The values might be temperate overestimates of the absolute lower bounds of the mean Na and Fe input fluxes when wind is advecting the metal vapor trails, because strong winds along with small-scale turbulence and shear could distort and dilute the trails, consequently shortening their lifetime. The trail altitude distribution for each metal species differs in details from the corresponding background layer, whereas the centroid height for each trail distribution approaches that of the relevant background layer (∼90.9km for Na trails and 89.1km for Fe trails). Only 8 two-element trails are detected from a total of 210-h simultaneous and common-volume Na and Fe lidar measurements. The observed two-element meteor trails yield the mean Fe/Na abundance ratio of ∼9.0. These trail features suggest a role of differential ablation. © 2011 Elsevier Ltd. Source

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