Experimental earth tidal models in considering nearly diurnal free wobble of the Earth＇s liquid core

Based on the 28 series of the high precision and high minute sampling tidal gravity observations at 20 stations in Global Geodynamics Project (GGP) network, the resonant parameters of the Earth‘s nearly diurnal free wobble (including the eigenperiods, resonant strengths and quality factots) are precisely determined. The discrepancy of the eigenperiod between observed and theoretical values is studied, the important conclusion that the real dynamic ellipticity of the liquid core is about 5% larger than the one under the static equilibrium assumption is approved by using our gravity technique. The experimental Earth‘s tidal gravity models with considering the nearly diurnal free wobble of the Earth‘s liquid core are constructed in this study. The numerical results show that the difference among three experimental models is less than 0.1%, and the largest discrepancy compared to those widely used nowdays given by Dehant (1999) and Mathews (2001) is only about 0.4%. It can provide with the most recent real experimental tidal gravity models for the global study of the Earth‘s tides, geodesy and space techniques and so on.     

Experimental earth tidal models in considering nearly diurnal free wobble of the Earth''''s liquid core

Based on the 28 series of the high precision and high minute sampling tidal gravity observations at 20 stations in Global Geodynamics Project (GGP) network, the resonant parameters of the Earth's nearly diurnal free wobble (including the eigenperiods, resonant strengths and quality factots) are precisely determined. The discrepancy of the eigenperiod between observed and theoretical values is studied, the important conclusion that the real dynamic ellipticity of the liquid core is about 5% larger than the one under the static equilibrium assumption is approved by using our gravity technique. The experimental Earth's tidal gravity models with considering the nearly diurnal free wobble of the Earth's liquid core are constructed in this study. The numerical results show that the difference among three experimental models is less than 0.1%, and the largest discrepancy compared to those widely used nowdays given by Dehant (1999) and Mathews (2001) is only about 0.4%. It can provide with the most recent real     

Characteristics of tidal gravity changes in Lhasa, Tibet, China

Tidal gravity changes arise from the response of the solid Earth to the tidal forces of the Sun,Moon and planets close to the Earth,and are a comprehensive reflection of the structure and distribution of physical properties of the Earth’s interior.As a result,observations of tidal gravity changes are the basis of studies on other global and/or regional dynamic processes.The characteristics of tidal gravity changes in the region of the Tibetan Plateau were investigated through continuous gravity measurements recorded with a superconducting gravimeter (SG) installed in Lhasa over a year.Through contrast measurements with a spring gravimeter LaCoste-Romberg ET20 at the same site,the gravity observations in Lhasa were scaled to the international tidal gravity reference in Wuhan.Meanwhile,the scale factor of the SG was determined accurately as-777.358 ± 0.136 nm s-2V-1,which is about 2.2% less than the value provided by the manufacturer.The results indicate that the precision of the tidal gravity observations made with the SG in Lhasa was very high.The standard deviation was 0.459 nm s-2,and the uncertainties of for the four main tidal waves (i.e.O 1,K 1,M 2 and S 2) were better than 0.006%.In addition,the observations of the diurnal gravity tides had an obvious pattern of nearly diurnal resonance.As a result,it is affirmed that the Lhasa station can provide a local tidal gravity reference for gravity measurements on the Tibetan Plateau and its surrounding regions.The loading effects of oceanic tides on tidal gravity observations in Lhasa are so weak that the resulting perturbations in the gravimetric factors are less than 0.6%.However,the loading effects of the local atmosphere on either the tidal or nontidal gravity observations are significant,although no seasonal variations were found.After removal of the atmospheric effects,the standard deviation of the SG observations in Lhasa decreased obviously from 2.009 to 0.459 nm s-2.Having removed the loading effects of oceanic tides and local atmosphere,it was found that the tidal gravity observations made with the SG in Lhasa significantly differed by about 1% from those expected theoretically,which may be related to active tectonic movement and the extremely thick crust in the region of the Tibetan Plateau.A more-certain conclusion requires longer accumulation of SG data and further associated theoretical studies.     

Method for removing interference in chaotic signals based on the Lyapunov exponent

A new method based on the phenomenon of synchronization and the properties of chaos is proposed to reduce interference in the transferred chaotic signals of synchronized systems. The interference is considered as a series of small deviations from the original clean trajectory in the phase space. By means of our special design, these small deviations can be estimated using positive Lyapunov exponents, and removed from interfered chaotic signals. Application is illustrated for the Lorenz attractor, and numerical computing demonstrates that the method is effective in removing typical external interference.     

Validating global hydrological models by ground and space gravimetry

The long-term continuous gravity observations obtained by the superconducting gravimeters (SG) at seven globally-distributed stations are comprehensively analyzed. After removing the signals related to the Earth’s tides and variations in the Earth’s rotation, the gravity residuals are used to describe the seasonal fluctuations in gravity field. Meanwhile, the gravity changes due to the air pressure loading are theoretically modeled from the measurements of the local air pressure, and those due to land water...     

Linear theory of the response of Na mixing ratio to gravity waves

The influence of gravity waves on the sodium layer is studied by using a linear photochemical-dynamical coupling gravity wave model. The model includes the back-ground photochemistry and the photochemical reactions in the sodium layer. The amplitude and phase difference of the response of sodium mixing ratio to gravity waves are calculated. The results indicate that the lower part of sodium layer is the most sensitive region responding to gravity waves. The perturbation of sodium mixing ratio is in phase with temperature in the lower part of the layer. However, it is out of phase with temperature fluctuation in the upper part.     

A local geopotential model for implementation of underwater passive navigation

A main aspect of underwater passive navigation is how to identify the vehicle location on an existing gravity map, and several matching algorithms as ICCP and SITAN are the most prevalent methods that many scholars are using. In this paper, a novel algorithm that is different from matching algorithms for passive navigation is developed. The algorithm implements underwater passive navigation by directly estimating the inertial errors through Kalman filter algorithm, and the key part of this implementation is a Fourier series-based local geopotential model. Firstly, the principle of local geopotential model based on Fourier series is introduced in this paper, thus the discrete gravity anomalies data can be expressed analytically with respect to geographic coordinates to establish the observation equation required in the application of Kalman filter. Whereafter, the indicated gravity anomalies can be gotten by substituting the inertial positions to existing gravity anomalies map. Finally, the classical extended Kalman filter is introduced with the differences between measured gravity and indicated gravity used as observations to optimally estimate the errors of the inertial navigation system （INS）. This navigation algorithm is tested on simulated data with encouraging results. Although this algorithm is developed for underwater navigation using gravity data, it is equally applicable to other domains, for example vehicle navigation on magnetic or terrain data.     

An element by element spectral element method for elastic wave modeling

The spectral element method which combines the advantages of spectral method with those of finite element method, provides an efficient tool in simulating elastic wave equation in complex medium. Based on weak form of elastodynamic equations, mathematical formulations for Legendre spectral element method are presented. The wave field on an element is discretized using high?order Lagrange interpolation, and integration over the element is accomplished based upon the Gauss?Lobatto?Legendre integration rule. This results in a diagonal mass matrix which leads to a greatly simplified algorithm. In addition, the element by element technique is introduced in our method to reduce the memory sizes and improve the computation efficiency. Finally, some numerical examples are presented to demonstrate the spectral accuracy and the efficiency. Because of combinations of the finite element scheme and spectral algorithms, this method can be used for complex models, including free surface boundaries and strong heterogeneity.     

Evaluation of the Photo-Protection of Eye-Patch Protectors Used in Phototherapy

An evaluation method for the practical photo-protection of eye-patch protectors (EPs) used in phototherapy for neonatal jaundice is developed.The protecting condition of neonatal eyes using EPs under typical phototherapy light is simulated.The simulation system consists of a neonatal head manikin,an International Light ILT 900 wideband rapid portable spectroradiometer,a standard Air Shields Isolette incubator,and a Medela fluorescent phototherapy unit.The results show that the practical protection of neonatal eyes,provided by EPs which are affected by the material characteristic,shape design,and wearing condition,is comprehensively illustrated using the indices of illuminance (Ev in lux unit) and the spectral irradiance (E in μW/(cm2·nm) unit).     

Influences of the surface wave-induced mixing and tidal mixing on the vertical temperature structure of the Yellow and East China Seas in summer

After a classification of the physical processes which affect the vertical mixing, diffusivity induced by the surface wave momentum and tidal currents and its influence on the vertical temperature structure are discussed. Based on three mixing schemes, the vertical temperature structure of the Yellow and East China Seas (YECS) is simulated. Results show that in summer, the surface wave-induced mixing plays a key role in forming the upper mixed layer in the YECS. The tidal mixing controls the lower layers within 30 m above the bottom, which is the main factor in forming the platform-shaped temperature structure in the southern Yellow Sea (YS). Together with the strong surface wave-induced mixing, the tidal mixing makes the thermocline ventilate near the east coast of the southern YS. The double cold cores in the deeper layers of the East China Sea have different causes. The western one is the maintenance of the winter cold water, while the eastern one is configured by circulation. The simulated vertical temperature structure of the YECS with the surface wave-induced mixing and tidal mixing has similar features to the observations, which indicates that these mixing processes are key factors in simulating the thermocline and pycnocline of the coastal oceans.     

Research progress in the inner surface modification of metal tubes by plasma processing

The recent progress in inner surface hardening of tubes by plasma processing is summerized. Several techniques of inner surface plasma source ion implantation and deposition are introduced, and their advantages and disadvantages are discussed. The basic principles, technical features and new progress of inner surface plasma source ion implantation methods for metal tubes, which were developed in our laboratory, are described in detail. And perspectives of the future technical development for inner surface ion implantation of tubes are presented.     

Combined adjustment project of national astronomical geodetic networks and 2000'' national GPS control network

The combined adjustment project of the nationwide astronomical geodetic networks and 2000' national GPS control network involve 48519 terrestrial observational stations and 2666 GPS observational stations. In the terrestrial network, 25107 stations are height fixed and 23412 stations are in three dimensions. 440793 terrestrial observations and 183668 unknowns are involved in the adjustment. The three-dimensional observational models for the adjustment have been established. The crustal deformation influences and corrections are researched. Fast methods of solving partitioned adjustment for super large-scale geodetic network have been studied. The standard deviations of three-dimensional coordinates for all stations are evaluated. As a result of the combined adjustment, a unified national geodetic network with nearly 50000 stations is established, the high accurate three-dimensional geocentric coordinates are obtained. The standard deviation for geoid is averagely 0.2 m, for vertical deflection is about 1.5″, for the horizontal position is about 0.12 m, for the geodetic height is about 0.14 m, and for the three-dimensional position is averagely 0.3 m.     

Decadal co-variability of the summer surface air temperature and soil moisture in China under global warming

The self-calibrating Palmer Drought Severity Index (PDSI) is calculated using newly updated ground observations of monthly surface air temperature (SAT) and precipitation in China. The co-variabilities of PDSI and SAT are examined for summer for the period 1961-2004. The results show that there exist decadal climate co-variabilities and strong nonlinear interactions between SAT and soil moisture in many regions of China. Some of the co-variabilities can be linked to global warming. In summer,sig-nificant decadal co-variabilities from cool-wet to warm-dry conditions are found in the east region of Northwest China,North China,and Northeast China. An important finding is that in the west region of Northwest China and Southeast China,pronounced decadal co-variabilities take place from warm-dry to cool-wet conditions. Because significant warming was observed over most areas of the global land surface during the past 20-30 years,the shift to cool-wet conditions is a unique phenomenon which may deserve much scientific attention. The nonlinear interactions between SAT and soil moisture may partly account for the observed decadal co-variabilities. It is shown that anomalies of SAT will greatly affect the climatic co-variabilities,and changes of SAT may bring notable influence on the PDSI in China. These results provide observational evidence for increasing risks of decadal drought and wet-ness as anthropogenic global warming progresses.     

Numerical simulation of tides and tidal currents in Liaoning Bay with POM

A three-dimensional ocean circulation model, called Princeton Ocean Model (POM), is employed to simulate tides and tidal currents in Liaodong Bay. The nested grid technique is adopted to improve the computation precision. Computed harmonic constants of m1, M2 tides at five tidal gauge stations and surface elevations at two oil platforms are compared with those observed, and show good agreements with them. Based on the calculated results, the co-amplitude and co-phase lag lines of m1 and M2 tidal constituents, the residual current field of M2 constituent, tidal form, tidal current ellipse and the moving style of tidal current are given. It is found that diurnal tidal constituents have no amphidromic point whereas semi-diurnal constituents have one in the region of interest. Meanwhile, some meaningful results are concluded and presented, which are conducive to a thorough knowledge of the characteristics of tides and tidal currents in the Liaodong Bay.     

A new method for detecting line spectrum of ship-radiated noise using Duffing oscillator

A detection scheme for line spectrum of ship-radiated noise is proposed using Duffing oscillator. The chaotic trajectory of Duffing oscillator is analyzed and the state equation of the system is improved to detect weak periodic signals in different frequencies. According to the simulation results, the phase transforms of Duffing oscillator are sensitive to periodic signals and immune to the random noise and the periodic interference signals which have larger angular frequency difference from the referential signal. By employing Lyapunov exponents in the field of detection as the criteria for chaos, the phase transforms of dynamic behaviors in quantity are successfully determined. Meanwhile, the threshold value in critical state has been evaluated more accurately. Based on the phase transforms of Duffing oscillator, a new method for detecting line spectrum of ship-radiated noise is given. Three types of ship-radiated noise signals are analyzed and the values of line spectrum are acquired successfully by this method. The experimental results show that this method has high sensitivity and high resolution.     

Effects of spectral sampling rate and range of CO2 absorption bands on XCO2 retrieval from TanSat hyperspectral spectrometer

The spectral sampling rate and range of CO2 absorption bands are critical for the optimal design of hyperspectral instrument for CO2 observation satellite. Undersampling of spectra in space-based spectrometer significantly contaminates signals measured in the CO2 1.61 ktm-band. The CO2 dry-air column （XCO2） error due to spectral undersampling can be up to ,1 ppm, which is the target precision of the Chinese Carbon Satellite （TanSat） for a single sounding. Undersampling error depends on surface albedo, solar zenith angle, and scattering properties in the atmosphere. The spectral sampling rate is recommended to be greater than 2.0 pixels per full width at half maximum to avoid undersampling. Reduction of spectral resolution and the use of narrower spectral regions can improve spectral sampling with little changes in CO2 retrieval sensitivity without losing much information. The full-band approach provides direct constraints on the wavelength-dependent surface albedo and particle scattering from the measurements. To keep a broader band, we recommend reduction of the spectral resolution by a factor of two.     

Global mean temperature changes during the last millennium

A synthetic study is made on the global or hemispheric mean temperature series for the last millennium worked out by Mann et al., Jones et al., Crowley and Lowery, and Briffa. The global mean temperature series reconstructed by using proxy data at 30 sites by Wang et al. and simulations from AD 1000 to 2000 by energy balance model are described and compared with the series of others. Wang's series gives greater variability and shows the highest correlation coefficient (0.83) with the simulation results. Uncertainties in the reconstructions and simulations are discussed. The errors in reconstructing a global mean temperature series according to 30 sites as used in the research are estimated. Wang's series indicate that temperature average for the 11th century is higher than the mean of the last millennium. It infers that the Medieval Warm Period predominated to some extent over the globe. However, the 20th century is no doubt the warmest century during the last millennium.     

Application of Wavelet Fractal Dimension Estimation Method on Flood Season Staged

Floodwater utilization is an important content in flood management. Controlling the limit water level of reservoir by stage is one of important contents in the management of multi-purpose reservoir＇s floodwater utilization for the sake of more benefits, and reasonable division of stage in flood season is precondition of controlling the limit water level by stage. On the background of Three Gorges Reservoir floodwater utilization management and on the foundation of self-similarity of hydrological series, determining the number of flood season staged in base of conventional statistical method, choosing the Db4 wavelet and Mallat algorithm, the computation mode of wavelet fractal dimension estimation method is proposed and each stage＇s fractal dimension is computed, then the final flood season staged is obtained. The results demonstrate the stages of Three Gorges Reservoir determined by using wavelet fractal dimension method are consistent with that from conventional method, but the fractal dimension results by former method are easier, more stable and objective which ensures the feasibility of the wavelet fractal dimension method applying in flood season staged. The obtained results are the base of deep coping with floodwater utilization management, also are the decision-making gist for the flood forecast, flood control and water allocation reasonably of Three Gorges Reservoir.     

Evaluation of earthquake-induced structural damages by wavelet transform

The dynamic behavior of inelastic structures during an earthquake is a complicated non-stationary process that is affected by the random characteristics of seismic ground motions. The conventional Fourier analysis describes the feature of a dynamic process by decomposing the signal into infinitely long sine and cosine series, which loses all time-located information. However, both time and frequency localizations are necessary for the analysis of an evolutionary spectrum of non-stationary processes. In this paper, an analytical approach for seismic ground motions is developed by applying the wavelet transform, which focuses on the energy input to the structure. The procedure of identification of the instantaneous modal parameters based on the continuous wavelet transform (CWT) is given in detail. And then, a novel method using the auto-regressive moving average (ARMA), called "prediction extension”, is presented to remedy the edge effect during the numerical computation of the CWT. The effectiveness of the method is verified by the use of the benchmark model developed by the American Society of Civil Engineers (ASCE). Finally, a scale model with three-storey reinforced concrete frame-share wall structure is made and tested on a shaking table to investigate the relation between the dynamic properties of structures and energy accumulation and its change rates during the earthquake. The results have shown that the wavelet transform is able to provide a deep insight into the identity of transient signals through time-frequency maps of the time variant spectral decomposition.     

Estimation to the turbulent kinetic energy dissipation rate and bottom shear stress in the tidal bottom boundary layer of the Yellow Sea

High frequency velocity fluctuations were measured by using an acoustic Doppler velocimeter (ADV) in the tidal bottom boundary layer (BBL) of the Yellow Sea (YS) for 25 h. The turbulent kinetic energy dissipation rate and the bottom shear stress were estimated and analyzed. Results show that: (1) in the tidal BBL of the YS, the variations of the dissipation rate and the bottom shear stress during 25 hare (1.8×10-8-3.4×10 -5) W·kg-1 and (6.6×10-4-7.5×10-1) N·m - 2 respectively, indicating that there are strong dissipations in the tidal BBL of the YS; (2) in the well-mixed tidal BBL, the turbulence is mainly shear-induced locally and the production and dissipation are generally in equilibrium; (3) for the seas where the semidiurnal tidal current is dominant, both the dissipation rate and the bottom shear stress exhibit a strong quarter-diurnal variation; (4) the mean bottom drag coefficient Cd (0.45) is 0.0017 (corresponding Cd( 1.00) = 0.0015), but it has significant variations (0.0005-0.0082). The mean bottom roughness length is 2.8×10-5 m.