Tidal effects on the thermosphere

Theoretical understanding of the earth's atmosphere is not possible without accounting for tidal waves and their interactions. In the thermosphere, tides represent the dominant motion system. Current observational efforts are aimed at providing tidal morphologies, i.e., maps of the vertical profiles of the tidal fields as a function of time for various locations. These are in hand for the mesosphere and have proved extraordinarily useful in deriving appropriate inputs for numerical models of the thermosphere. The basic latitudinal, seasonal, and solar cycle variation of the tides in the thermosphere is much less well known but the advent of coordinated global multi-day campaigns promises to ameliorate the situation. Progress would be facilitated by agreement on a standard data reduction procedure. Theoretical efforts are focused on simulating the observed morphologies and understanding the day to day variations while investigating mutual interactions and feedback between the mean atmosphere and the tidal, gravity, and planetary waves.     

Analytical solutions for tidal propagation in a rectangular basin

The tidal propagation in a rectangular basin of an estuary has been studied in this paper. The dynamic response of the tidal current and elevation inside the basin has been obtained using the concept of Kelvin waves and spectrum of Poincare waves. In this study, we have found that initial tidal elevations are amplified near the closed end of the basin or at the tidal barrier site.     

Lunar–solar tide effects in the Earth’s crust and atmosphere

The gravitational interaction in the Earth–Moon–Sun system is considered from the standpoint of influencing the formation of time variations in the geophysical fields and some natural processes. The analysis of the results of instrumental observations revealed the main periodicities and cycles in the time variations of subsoil radon volumetric activity with the same periods as the vertical component of the variations of the tidal force. The amplitude modulation of seismic noise by the lunar-solar tide is demonstrated. It is shown that the intensity of relaxation processes in the Earth’s crust has a near-diurnal periodicity, whereas the spectrum of groundwater level fluctuations includes clearly expressed tidal waves. Based on the data on the tilts of the Earth’s surface, the role of tidal deformation in the formation of the block motions in the Earth’s crust is analyzed. A new approach is suggested for identifying tidal waves in the atmosphere by analyzing micropulsations of the atmospheric pressure with the use of adaptive rejection filters.     

Signature of atmospheric oscillations in GPS-measured tropospheric delay

Ground-based GPS finds potential applications in many atmospheric studies such as spatial distribution of columnar water vapor as well as the tidal oscillations in the atmosphere. The zenith tropospheric delay (ZTD) derived from GPS data at two Indian IGS stations are used to establish its potential for studying the atmospheric tidal, intra-seasonal and planetary oscillations. The major tidal oscillations observed in ZTD data are diurnal, semi-diurnal and their harmonics. Prominent intra-seasonal oscillations observed in ZTD are reported for the first time in this context. These intra-seasonal oscillations are Madden–Julian Oscillation (30–70 days, 60–90 days, 100–120 days) and planetary waves (like 27, 16 and 5–10 days periodicities). Quantification of these periodicities will provide a useful handle to improve the empirical models employed in the estimation of tropospheric delay.     

Internal gravity waves in atmospheres with realistic dissipation and temperature part I. Mathematical development and propagation of waves into the thermosphere

Abstract

In this, the first part of a three part study, we develop a model for the theoretical analysis of 3‐dimensional internal gravity waves in atmospheres with arbitrary distributions of basic temperature, molecular weight, viscosity and conductivity (both eddy and molecular), Newtonian cooling, anisotropic hydromagnetic (ion) drag, and thermal excitation. Attention is given to the physical bases for our models, and a detailed outline is given of the numerical method used to solve the resulting system of equations.

As an application of the above development, we study the ability of five particular gravity waves (chosen for their observed importance in the neighborhood of 90–100 km—four of the waves are simulated tidal modes) to propagate from 90 km into the thermosphere. We choose to define the thermosphere as that portion of the atmosphere above the turbopause (ca. 110 km). Among the most significant results to emerge are the following: (i) the effects of molecular viscosity and conductivity appear to be more significant than the effects of hydromagnetic drag, and (ii) while most waves considered are significantly attenuated somewhere between 90 Ian and the thermosphere, the main semidiurnal tidal mode is not. In fact, semidiurnal temperature oscillations of only a few degrees amplitude at 90 km can give rise to oscillations of over a hundred degrees amplitude in the exosphere.     

The influence of time-dependent wind on gravity-wave propagation in the middle atmosphere

Ray-tracing techniques are used to computationally investigate the propagation of gravity waves through the middle atmosphere, as characterized by the vertically varying CIRA-86 wind and temperature models, plus a tidal wind model that varies temporally as well as vertically. For the wave parameters studied here, the background wind variation has a much stronger influence on the ray path and changes in wave characteristics than does the temperature variation. The temporal variation of the tidal component of the wind changes the observed frequency, sometimes substantially, while leaving the intrinsic frequency unaltered. It also renders temporary any critical levels that occur in the tidal region. Different starting times for the rays relative to the tidal phase provide different propagation environments, so that the temporary critical levels appear at different heights. The lateral component of the tidal wind is shown to advect propagating wave packets; the maximum lateral displacement of a packet varies inversely with its vertical group velocity. Time-dependent effects are more pronounced in local winter than in summer.     

远震前的地电场潮汐波异常

分析了5次远强震前河北省昌黎台、兴济台记录到的电场异常,发现该异常主要集中在震前2个月左右的时段内, 具有很好的短临预报意义. 震前电场呈现不同的异常特征,但与固体地球潮汐波变化关系密切,如半日、半月等潮汐波周期信号增强,引起电场变化幅度增大;或本该正常记录到的潮汐变化幅度突然减小或消失;以及高频信号增多并伴有跃变现象. 分析异常产生机理认为,强震前的这种异常现象是震源区临震孕育过程中岩石弱化产生的电场异常,经自由空间或地壳传播到达地电台站后,与台站记录的电场潮汐波相叠加产生潮汐波增强或减弱现象. 高频异常可能与台站下方岩石孔隙度、渗透率等介质性质的改变有关,反映了强震的远场动态效应.      

Tidal wave anomalies of geoelectrical field before remote earthquakes

Introduction Geoelectrical field is a kind of intrinsic geophysical field of the earth, affected by kinds of current systems in outer space and electric properties of media underground, so it carries abundant interior information of the earth. Since 1981 when the group of “VAN” in Greece carried out the study of electric field observation by multi-polar distances (Varotsos and Alexopoulous, 1984a, b), more and more scientists in the world paid extensive attention to it due to its better re…     

Impact of tidal power dams upon tides and environmental conditions in the Sea of Okhotsk

The transformation of natural tidal sea-level and currents is studied resulting from large-scale tidal power plant (TPP) dams in bays of the Sea of Okhotsk (SO). Some effects due to this transformation are estimated based on predictive modelling and a number of expected changes in amplitudes and phases, and spectral composition of tidal oscillations are described. Changes of morphometric properties of basins change the character of tidal motions even on significant distance from a dam. That is why, it is impossible to estimate this impact as usual boundary-value problems. The problem is solved based on “impedance” conditions on the open boundary of the model area, allowing to take into account the radiation of the additional perturbations induced by both waves reflected from the dam and nonlinear effects inside the area. In general, the transformation effects are proportional to the dam size and depend essentially on the dam location, the creation of which can change dissipative and resonance properties of the bays. The changes in tidal energetics of SO due to the dam construction are also considered to show noticeable reconstruction of horizontal energy fluxes and changes in the energy dissipation. Possible environmental consequences are related mainly to the transformation of tidal currents.     

Manifestation of gravitational tides and planetary waves in long-term variations in geophysical parameters

Long-term variations in the parameters of the Earth’s upper atmosphere and geophysical activity have been studied based on the current spectra. The main sources of quasiperiodic oscillations in the atmosphere (including variations in the solar radiation, geomagnetic activity, and gravity) have been considered. It was shown that the most stable quasiharmonic variations are related to tidal gravitational oscillations and Rossby planetary waves with stable spectra. These oscillatory processes substantially contribute to the dynamics of the middle and upper atmosphere and manifest themselves in ionospheric parameters.     

A 1D model for tides waves and fine sediment in short tidal basins—Application to the Wadden Sea

In order to simulate the dynamics of fine sediments in short tidal basins, like the Wadden Sea basins, a 1D cross-sectional averaged model is constructed to simulate tidal flow, depth-limited waves, and fine sediment transport. The key for this 1D model lies in the definition of the geometry (width and depth as function of the streamwise coordinate). The geometry is computed by implementing the water level and flow data, from a 2D flow simulation, and the hypsometric curve in the continuity equation. By means of a finite volume method, the shallow-water equations and sediment transport equations are solved. The bed shear stress consists of the sum of shear stresses by waves and flow, in which the waves are computed with a depth-limited growth equation for wave height and wave frequency. A new formulation for erosion of fines from a sandy bed is proposed in the transport equation for fine sediment. It is shown by comparison with 2D simulations and field measurements that a 1D schematization gives a proper representation of the dynamics in short tidal basins.     

精密引潮位展开的精度评定

文中介绍了一个新的引潮位展开,含有潮波3070项及一些新的信息;潮波振幅给至小数点后第6位.为了与精密引潮位比较,专门建立了一套标准数据,其精度为±0.001μGal.按照这一标准数据,我们评价了精密引潮位展开的精度,并给出了其余差及功率谱分析的结果.结果表明,对于潮汐重力,精密引潮位展开的精度,可达±0.005μGal.     

The influence of neutral atmospheric dynamics on MF differential absorption results

MF differential absorption data are fitted with a function which cannot exhibit a negative gradient with increasing scattering height. The fit error which results from such a fit is then interpreted to be an error in the reflection coefficient ratio of the magneto-ionic waves in the medium. It is shown that this error is caused by significant mean departures from the theoretical reflection coefficient ratio, and that the height profile of these departures recur on an annual and seasonal basis from 1983 to 1999. Also shown is that this error in the reflection coefficient ratio shows pronounced tidal characteristics, suggesting a link to dynamic processes in the neutral atmosphere.     

A 1D model for tides waves and fine sediment in short tidal basins—Application to the Wadden Sea

In order to simulate the dynamics of fine sediments in short tidal basins, like the Wadden Sea basins, a 1D cross-sectional averaged model is constructed to simulate tidal flow, depth-limited waves, and fine sediment transport. The key for this 1D model lies in the definition of the geometry (width and depth as function of the streamwise coordinate). The geometry is computed by implementing the water level and flow data, from a 2D flow simulation, and the hypsometric curve in the continuity equation. By means of a finite volume method, the shallow-water equations and sediment transport equations are solved. The bed shear stress consists of the sum of shear stresses by waves and flow, in which the waves are computed with a depth-limited growth equation for wave height and wave frequency. A new formulation for erosion of fines from a sandy bed is proposed in the transport equation for fine sediment. It is shown by comparison with 2D simulations and field measurements that a 1D schematization gives a proper representation of the dynamics in short tidal basins.

     

维尼迪科夫调和分析对大甸子井水位潮汐因子和相位的气象影响研究

利用维尼迪柯夫潮汐调和分析方法计算内蒙古大甸子井水位原始资料和剔除气压、降雨资料后的潮汐因子和相位。结果显示,两种情况下得到的潮汐因子和相位具有较好的一致性,说明采用维尼迪柯夫潮汐调和分析方法得到的结果基本不受降水、气压等因素的影响。这对于缺少气压和降水等辅助观测的水位观测资料,使用原始资料进行维尼迪科夫潮汐调和分析,可获取比较可靠的潮汐因子和相位参数。     

精密引潮位展开及某些诠释

作者再次改进了引潮位展开,潮波振幅给到小数后第六位,共3070个潮波.文中论述了引潮位展开的精度,同时给出为了保证潮汐计算的高精度而所需引入的各项改正及其说明.     

Observations of estuarine circulation and solitary internal waves in a highly energetic tidal channel

Despite vigorous tidal and wind mixing, observations in an estuarine tidal inlet in the Wadden Sea show that during part of the tidal cycle, vertical stratification and internal waves may still develop. Acoustic Doppler current profiler (ADCP) and conductivity, temperature, depth observations, collected over the past 6 years at 13 h anchor stations (ASs), reveal that these occur especially during slack tide, when there is little wind and large freshwater discharge from nearby Lake IJssel. Measurements with a moored ADCP show that in the same tidal phase, strong cross-channel circulation develops, which may suddenly reverse circulation sense due to passing density fronts. In the vertically stratified phase that follows after the front passage, propagating mode-one solitary internal waves are observed. These are resonantly generated during decelerating tidal ebb currents when the (shear) flow passes a transcritical regime (Froude number equal to 1). A combination of photographs (including one from the International Space Station), bathymetric data, and ASs data leads to the discovery of yet another source of internal waves in this area, produced during slackening tide by propagating lee waves that develop over a deep trench. We suggest that both the cross-channel circulation as well as the (solitary) internal waves may locally be of importance for the (re)distribution and transport of sediments and nutrients and may influence tidally averaged transports.     

Using the nonlinear geometrical acoustics method in the problem of moreton and EUV wave propagation in the solar corona

Propagation of shock related Moreton and EUV waves in the solar atmosphere is simulated by the nonlinear geometrical acoustics method. This method is based on the ray approximation and takes account of nonlinear wave features: dependence of the wave velocity on its amplitude, nonlinear dissipation of wave energy in the shock front, and the increase in its duration with time. The paper describes ways of applying this method to solve the propagation problem of a blast magnetohydrodynamic shock wave. Results of analytical modeling of EUV and Moreton waves in the spherically symmetric and isothermal solar corona are also presented. The calculations demonstrate deceleration of these waves and an increase in their duration. The calculation results of the kinematics of the EUV wave observed on the Sun on January 17, 2010 are presented as an example.     

云南曲靖井水位潮汐动态特征分析

以井-含水层系统潮汐理论为基础, 结合云南曲靖井水位观测资料实际情况, 利用Baytap-G提供的潮汐分析方法, 分别计算了曲靖井水位M2、 S2、 O1、 S1K1和M3共5个潮汐分波的振幅比、 相位和计算误差, 分析了井水位观测资料不同潮汐波振幅比和相位的动态变化特征, 认为能反映含水层参数的井水位潮汐振幅比和相位变化与附近的抽水和远距离大震引起的同震响应有关, 具体表现为, 2001年11月和2003年8月的振幅比和相位下降变化可能与抽水有关, 而几次大震后的井水位潮汐振幅比和相位小幅度上升和缓慢恢复过程, 则可能与中远场大震的地震波动力引起的含水层渗透系数增加有关．      

Magnetic effects of sea tides

The tidal motion of sea water across the earth's magnetic field is known to induce small electric currents to flow in the oceans and the surrounding land. There has been recently a great deal of interest in this phenomenon. Here we consider a model ocean in the form of an infinitely long channel with a tidal wave passing along it. It is shown that for the lunar tidal frequency of 12.45 hours the solution of this problem for typical ocean depths exhibits characteristics which are essentially due to the high frequency. The solution therefore differs appreciably from low-frequency solutions which are therefore only applicable as models of the shallow seas. In our model we observe concentrations of electric current near the coast and phase changes relative to the oceanic tide. A new “equivalent field exclusion principle” is presented and used to explain some of the results we have obtained. The method used is simple and applies readily to waves of any frequency, and results are given for waves of higher frequencies. The amplitude and phase lag of the magnetic field of a channel simulating the Atlantic Ocean are discussed.