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1.
Observation of stars from a spacecraft through the Earth’s atmosphere is a constituent part of remote sensing of the atmosphere. Recorded scintillation signals contain data on the structure of air-density irregularities induced by turbulence and internal waves. Currently, parameters of the structure in the stratosphere are determined using the procedures based on the weak-scintillation theory. However, during stellar occultation by the Earth’s atmosphere, scintillation becomes stronger as the line of sight plunges into denser air layers. This paper considers the problem of remote sensing of stratospheric irregularities under strong-scintillation conditions. The scintillation spectra are calculated in the phase-screen approximation under the assumption that the spectrum of the phase added by the screen corresponds to observations through the stratosphere. It is assumed that stratospheric irregularities of air density are generated by an ensemble of saturated internal waves whose three-dimensional spectrum contains two characteristic wave numbers corresponding to the outer and inner scales. In the calculation, no restrictions are imposed on the observed scintillation amplitude. It is shown that the effect of the scintillation amplitude on the observed scintillation spectra appears most prominent for large wave numbers corresponding to irregularities whose sizes are smaller than the inner scale. For these wave numbers, deviations from the weak-scintillation theory become appreciable if the rms relative fluctuation of light intensity exceeds 0.3. In contrast, for small wave numbers corresponding to scales exceeding the outer scale, the weak-scintillation theory remains valid to rms values as large as 2. Analysis of calculated spectra has shown that the parameters of the three-dimensional spectra of stratospheric irregularities can be retrieved under the conditions of relatively strong scintillation characterized by an rms value below 1.5–1.6.  相似文献   

2.
The first experimental studies of the spatial oblique and vertical spectra of temperature fluctuations in a stably stratified troposphere at heights of 2 to 8 km were conducted. The measurements were taken over northern European Russia. The spectra cover the wave number range from 5 10?4 to 3 10?2 rad/m. The estimates obtained for the spectral density are analyzed on the basis of a model developed previously for the three-dimensional (3D) spectrum of temperature fluctuations generated by a statistical ensemble of internal waves. This model made it possible to consider both oblique and horizontal spectra from a unified point of view and to use a unified set of parameters on the basis of the 3D spectrum concept. The quantitative estimates obtained for the parameters of the 3D spectrum have shown that large-scale temperature inhomogeneities with a vertical size of more than a hundred meters are strongly extended along the land surface. They have approximately the same form; their horizontal sizes are at least 20 times greater than their vertical sizes. The anisotropy of temperature inhomogeneities decreases with a decrease in their vertical sizes and reaches 1.5–2 for vertical sizes of 10–20 m or smaller.  相似文献   

3.
The climatology of the troposphere–stratosphere–mesosphere model of the Institute for Numerical Mathematics (INM) with the uppermost level at 0.003 hPa is presented. This model is vertically extended from the upper level of 10 hPa for the earlier version, and a drag parameterization due to internal gravity waves (GW) is included. The model describes the main features of the mesospheric circulation: decreasing and reversion of westerly and easterly winds, equatorward shift of the westerly wind maximum with height and reversal of the meridional temperature gradient in the upper mesosphere. The model underestimates to some extent the amplitude of wave number 1 for stationary waves in the winter hemisphere. The same holds for the internal low‐frequency variability in the winter stratosphere. The sensitivity of the model climate is studied with respect to the inclusion of orographic gravity wave drag and the variation of the source height of internal gravity waves.  相似文献   

4.
The frequency spectrum of surface elevations in the presence of wind waves is well known. On this basis, one can estimate the frequency spectrum of vertical velocities in sea-surface waves. Owing to liquid incompressibility, the spectrum of horizontal velocities should have the same frequency dependence. The use of the dispersion equation for waves on the surface of a heavy liquid allows one to obtain to the spatial spectrum of velocities. Therefore, one can estimate the spatial structure function of the velocity field. For short waves and large depths, the structure function increases as r 1/2, where r is the distance between the points of observations. For long waves and shallow depths h, this increase is proportional to r. The coefficient of turbulent mixing K(r) of pollution spots of size r on the sea surface is now estimated as the product of the spot size and the rms difference of velocities. As a result, depending on r and h, the exponent in the r n dependence of K(r) may vary between 1.25 and 1.5. This outcome provides an explanation for a scatter in the values of the exponent n, a phenomenon that has been observed by many experimentalists.  相似文献   

5.
A one-dimensional ionic-photochemical model of the gaseous composition of the atmosphere that describes the formation of the D layer of the ionosphere is presented. Based on this model, the vertical profiles of the concentration of electrons and ions in the D layer of the ionosphere were calculated, as were the vertical distributions of minor gaseous constituents in the atmosphere up to a height of 86 km for undisturbed conditions and after a powerful solar proton events (SPE) at the end of October 2003. The calculations showed that SPEs significantly increase NOx in the mesosphere of polar latitudes. In the lower mesosphere of polar caps, the NOx mixing ratio increases by 20–50 ppb; in the upper mesosphere it increases by 100 ppb and more. High NOx levels in zones of their formation can be retained for several weeks, producing a long-term but comparatively small ozone decrease in the lower mesosphere. The main ozone decrease is caused by a short-term HOx increase after SPEs and is also of a short-term character in the conditions of the illuminated mesosphere. After the SPE in October 2003, model calculations yield an ozone concentration decrease by 40% in the middle and upper mesosphere at 75 ° S and by 70% at the same heights at 70 ° N. The results of modeling NOx and O3 changes after the SPE in October 2003 agree well with the data of satellite measurements. The changes in minor gases of the mesosphere after the SPE obtained in the model with parameterized sources of HOx and NOx are compared with their changes obtained in the complete ionic-photochemical model. The changes in HOx, NOx, and O3 coincide rather well, whereas the changes in ClO noticeably differ, especially in the lower mesosphere. Thus, at a height of about 60 km, the parameterized photochemical model underestimated twofold the ClO formation after the SPE.  相似文献   

6.
The influence of the spatial heterogeneity of vegetation cover and topography on CO2 fluxes in the atmospheric surface layer is estimated using a two-dimensional (2D) hydrodynamic model of turbulent exchange. A ~4.5-km-long profile that crossed a hilly area with a mosaic vegetation cover in Tula region was selected for model experiments. During the first experiment, a wind field and vertical fluxes were calculated by the 2D model for the entire selected profile with respect to the horizontal heterogeneity of the vegetation cover and surface topography. In the second experiment, the profile was considered an assemblage of elementary independent homogeneous segments; for each of them, vertical fluxes were calculated by the 2D model with the assumption of ‘zero’ horizontal advection, i.e., the required functions are independent of the horizontal coordinates. The influences of any boundary effects that appear at the interface between the different vegetation communities and at topographical irregularities on the turbulent regime are ignored in this case. For the profile selected, ignoring the horizontal advection, disturbances in the wind field that appeared at surface topography irregularities, and boundaries between different vegetation communities can lead to a 26% underestimation of the total CО2 absorption by the ground surface on a clear sunny day under summer weather conditions.  相似文献   

7.
Recent numerical studies (Hibiya et al., 1996, 1998, 2002) showed that the energy cascade across the internal wave spectrum down to small dissipation scales was under strong control of parametric subharmonic instabilities (PSI) which transfer energy from low vertical mode double-inertial frequency internal waves to high vertical mode near-inertial internal waves. To see whether or not the numerically-predicted energy cascade process is actually dominant in the real deep ocean, we examine the temporal variability of vertical profiles of horizontal velocity observed by deploying a number of expendable current profilers (XCPs) at one location near the Izu-Ogasawara Ridge. By calculating EOFs, we find the observed velocity profiles are dominated by low mode semidiurnal (∼double-inertial frequency) internal tides and high mode near-inertial internal waves. Furthermore, we find that the WKB-stretched vertical scales of the near-inertial current shear are about 250 sm and 100 sm. The observed features are reasonably explained if the energy cascade down to small dissipation scales is dominated by PSI.  相似文献   

8.
Recent extensive and important studies have provided detailed information and compelling evidence on how the presence of waves influences the vertical diffusivity/dispersivity in the coastal environment, which can affect various water quality considerations such as the distribution of suspended sediments in the water column as well as the potential of eutrophication. Comparatively, how the presence of waves influences the horizontal diffusivity/dispersivity has received only scant attention in the literature. Our previous works investigated the role played by the Taylor mechanism due to the wave-induced drift profile which leads to the longitudinal dispersion of contaminants in the horizontal direction, under regular sinusoidal waves and random waves with single-peak spectra.Natural waves in the coastal environment, however, often possess dual-peak spectra, comprising both higher frequency wind waves and lower frequency swells. In this study, the Taylor dispersion of contaminants under random waves with dual-peak spectra is examined through analytical derivation and numerical calculations. The effects of various dual-peak spectral parameters on the horizontal dispersion, including the proportion of lower frequency energy, peak frequency ratio and spectral shape parameter, are investigated. The results show that the relative energy distribution between the dual peaks has the most significant effect. Compared with single-peak spectra with equivalent energy, the Taylor dispersion with dual-peak spectra is stronger when the lower frequency is close to the peak frequency of the single-peak spectrum, and weaker with the higher frequency instead. Thus, it can be concluded that with a dual-peak wave spectrum, wind-dominated seas with higher frequency lead to stronger dispersion in the horizontal direction than swell-dominated seas with lower frequency.  相似文献   

9.
An analysis of spectra of wave disturbances with zonal wave numbers 1 ≤ k ≤ 10 is carried out using winter (November to March) ERA-Interim reanalysis geopotential data in the troposphere and stratosphere for 1979–2016. Contributions of eastward-traveling (E), westward-traveling (W), and stationary (S) waves are estimated. The intensification of wave activity is observed in the tropical troposphere and stratosphere and in the upper stratosphere of the entire Northern Hemisphere. The intensification of wave activity in the tropics and subtropics is noted for waves of all types (E, W, and S), while in the middle and higher latitudes it is related mainly to stationary and eastward waves. Near the subtropical tropopause, the energy of stationary waves has increased in recent decades. In addition, in the tropical and subtropical troposphere and in the subtropical lower stratosphere, the energy of the eastward-traveling waves in El Niño years may be one and a half times or twice the energy in La Niña years. The spectrally weighted zonal wave numbers for waves of all types (E, W, and S) are the largest in the upper subtropical troposphere. The spectrally weighted zonal wave number for W and S waves is correlated with the Atlantic Multidecadal Oscillation index and varies by 15% in 1979–2016 (on an interdecadal time scale). The spectrally weighted wave period is larger in the stratosphere than in the troposphere. It is maximal in the middle extratropical stratosphere. The spectrally weighted wave periods correlate with the activity of sudden stratospheric warmings. The sign of this correlation depends on the latitude, atmospheric layer, and zonal wave number.  相似文献   

10.
A series of experimental studies about the force of internal solitary wave and internal periodic wave on vertical cylinders have been carried out in a two-dimensional layered internal wave flume. The internal solitary waves are produced by means of gravitational collapse at the layer thickness ratio of 0.2, and the internal periodic waves are produced with rocker-flap wave maker at the layer thickness ratio of 0.93. The wave parameters are obtained through dyeing photography. The vertical cylinders of the same size are arranged in different depths. The horizontal force on each cylinder is measured and the vertical distribution rules are researched. The internal wave heights are changed to study the impact of wave heights on the force. The results show that the horizontal force of concave type internal solitary wave on vertical cylinder in the upper-layer fluid has the same direction as the wave propagating, while it has an opposite direction in the lower-layer. The horizontal force is not evenly distributed in the lower fluid. And the force at different depths increases along with wave height. Internal solitary wave can produce an impact load on the entire pile. The horizontal force of internal periodic waves on the vertical cylinders is periodically changed at the frequency of waves. The direction of the force is opposite in the upper and lower layers, and the value is close. In the upper layer except the depth close to the interface, the force is evenly distributed; but it tends to decrease with the deeper depth in the lower layer. A periodic shear load can be produced on the entire pile by internal periodic waves, and it may cause fatigue damage to structures.  相似文献   

11.
《Ocean Modelling》2010,35(3-4):63-69
A numerical closure scheme has been developed to introduce dissipation processes in particular for the vertical movement of internal tides. This scheme is based on the assumption that a vertically oscillating water mass disturbs the pressure field and feels the viscosity from its neighborhood at the same time. The horizontal viscosity term, referred in this paper as the internal-tide viscosity (ITV) term, is retained in the vertical movement equation, which introduces a quasi-hydrostatic assumption. Therefore, a new expression of the total perturbation pressure has been derived. By applying this expression in a 5′ × 5′ z-coordinate regional ocean model, the results show great improvements. With consideration of the ITV-term, the numerically enhanced vertical movement locally near a ridge has been damped in a z-coordinate system, and the propagation of internal tides away from the ridge has been converted into a more reasonable dissipative mode. With the tunable parameter Cw equals to 0.2, the values of the simulated vertical velocity have been reduced to approximately 50%. And the simulated thermocline structure has been preserved, as well.  相似文献   

12.
Streaks of elevated concentrations of surface chlorophyll a (Chl_a) of various spacing were found to be associated with internal waves in their transmission zone and dissipation zone in the summertime in the deep open northern South China Sea. At an anchored station in the dissipation zone north of the Dongsha Atoll with a water depth of ca. 600?m, undulations of the mixed layer depth with an amplitude of ca. 30?m and a periodicity of ca. 12?h were observed, and they were accompanied by similar undulation in the isotherm and isopleth of the nutrients. These observations are consistent with the enhancement of vertical mixing by internal waves and the resulting transfer of cold, nutrient-rich subsurface water to the surface mixed layer to fuel biological productivity. In the transmission zone and dissipation zone, respectively, the summertime (May–October) average sea surface temperature was 0.5 and 0.8?°C lower and Chl_a was 19 and 43?% higher than those in a nearby subregion that was minimally affected by internal waves. The mean net primary productivity was elevated by 15 and 37?%. These results indicate that the enhancement of biological activity by internal waves is not confined to the shallow waters on the shelf. The effect can be detected in all phases of the internal waves although it may be especially prominent in the dissipation zone where mixing between subsurface and surface waters is more effective.  相似文献   

13.
ADCP measurements of the velocity structure in the permanent thermocline at two locations over the continental slope in the Bay of Biscay are presented. The vertical variation of the contribution of the inertia-gravity waveband to the kinetic energy, vertical motion, and current shear are analysed. The semi-diurnal tides together with near-inertial waves appear to provide over 70% of the high-frequency kinetic energy (>1/3 cpd). Over the vertical range of the ADCP observations the phase of the harmonic M2 tide changes up to 155°, while the kinetic energy varies in the vertical by a factor of 3.8, showing the importance of the contribution of internal waves to the observed tidal motion. Both semi-diurnal internal tidal waves and near-inertial waves have a vertically restricted distribution of the variance of the horizontal and vertical velocity, as in internal wave beams. The short-term 14-day averaged amplitude and phase lag of the M2 tide shows large temporal changes, with a characteristic 40–45 day time scale. These changes are probably related to variations in generation sites and propagation paths of the internal tide, because of changes in the temperature and salinity stratification due to the presence of meso-scale eddies. The relatively large shear in the inertia-gravity wave band, mainly at near-inertial frequencies, supports low-gradient Richardson numbers that are well below 1 for nearly half of the time. This implies that the large shear may support turbulent mixing for a large part of the time.  相似文献   

14.
Outer frequency spectrum of sea waves and its equilibrium range   总被引：3，自引：0，他引：3  
Ｔｈｅｐｒｅｓｅｎｔｐａｐｅｒｄｅｆｉｎｅｓｔｈｅｇｅｎｅｒａｌｉｚｅｄａｐｐａｒｅｎｔｅｎｅｒｇｙｄｉｓｔｒｉｂｕｔｉｏｎａｎｄｄｅｒｉｖｅｓｔｈｅａｎａｌｖｔｉｃａｌｆｏｒｍｏｆｔｈｅｓｏ－ｃａｌｌｅｄｇｅｎｅｒａｌｉｚｅｄｏｕｔｅｒｆｒｅｑｕｅｎｃｙｓｐｅｃｔｒｕｍｏｒｎｔｈｏｒｄｅｒａｐｐａｒｅｎｔｆｒｅｑｕｅｎｃｙｓｐｅｃｔｒｕｍ．Ｉｔｉｓｓｈｏｗｎｔｈａｔｔｈｅｇｅｎ－ｅｒａｌｉｚｅｄｏｕｔｅｒｆｒｅｑｕｅｎｃｙｓｐｅｃｔｒｕｍｈａｓａｎｅｑｕｉｌｉｂｒｉｕｍｒａｎｇｅｗｉｔｈａｎｅｘｐｏｎｅｎｔ（ｎ＋３）ａｎｄｔｈｅｕｐｐｅｒｌｉｍｉｔｏｆｔｈｅｅｘ－ｐｏｎｅｎｔｉｓ－３．ＴｈｅｒｅｓｕｌｔｓｏｆｔｈｉｓｐａｐｅｒａｒｅｕｎｉｖｅｒｓａｌａｎｄａｒｅａｐｐｌｉｃａｂｌｅｆｏｒａｎｙｏｔｈｅｒｗａｖｅｐｈｅｎｏｍｅｎａｉｆｔｈｅｒａｙｔｈｅｏｒｙｏｆｗａｖｅｓａｎｄｔｈｅＬｏｎｇｕｅｔ－Ｈｉｇｇｉｎｓ，ｌｉｎｅａｒｒａｎｄｏｍｗａｖｅｍｏｄｅｌａｒｅｅｘａｃｔｅｎｏｕｇｈｆｏｒｔｈｅｉｒｄｅｓｃｚｉｐｔｉｏｎ．  相似文献   

15.
A criterion for initiation of sediment movement on a horizontal bed under non-breaking waves is established. Bagnold's sediment transport model is used. The dissipation rate of energy has been related to the length and velocity scales of the large-scale turbulence. The proposed equation is compared with the available laboratory results for fine and coarse material 0.1 mm < D ? 45 mm over a wide range of particle sizes, density ratios and liquid viscosities and a reasonable agreement between the two is obtained. An incipient motion hypothesis based on the development of vorticity is proposed.  相似文献   

16.
The Resonant Triad Model (RTM) developed in (Ibragimov, 2007), is used to study the Thorpe’s problem (Thorpe, 1997) on the existence of self-resonant internal waves, i.e., the waves for which a resonant interaction occurs at second order between the incident and reflected internal waves off slopes. The RTM represents the extension of the McComas and Bretherton’s three wave hydrostatic model (McComas and Bretherton, 1977) which ignores the effects of the earth’s rotation to the case of the non-hydrostatic analytical model involving arbitrarily large number of rotating internal waves with frequencies spanning the range of possible frequencies, i.e., between the maximum of the buoyancy frequency (vertical motion) and a minimum of the inertial frequency (horizontal motion). The present analysis is based on classification of resonant interactions into the sum, middle and difference interaction classes. It is shown in this paper that there exists a certain value of latitude, which is classified as the singular latitude, at which the coalescence of the middle and difference interaction classes occurs. Such coalescence, which apparently had passed unnoticed before, can be used to study the Thorpe’s problem on the existence of self-resonant waves. In particular, it is shown that the value of the bottom slope at which the second-order frequency and wavenumber components of the incident and reflected waves satisfy the internal wave dispersion relation can be approximated by two latitude-dependent parameters in the limiting case when latitude approaches its singular value. Since the existence of a such singular latitude is generic for resonant triad interactions, a question on application of the RTM to the modeling of enhanced mixing in the vicinity of ridges in the ocean arises.  相似文献   

17.
The main sill of the Strait of Gibraltar (Camarinal Sill) is an area of very energetic internal wave activity. The highest amplitude internal wave is the well-known internal bore, generated at critical conditions over Camarinal Sill. A very energetic lee wave has recently been found and reported. This occurs in neap tides when favorable combination of the stratification, vertical profile of horizontal background velocity, and bottom topography determines its generation. When the lee wave is developed the manifestation of high-amplitude internal waves is observed at the sea surface as high-frequency chaotic oscillations, named boiling waters. We analyze the generation of the lee wave over the main sill of Gibraltar Strait on the basis of the data from a ship mounted ADCP, multi-probe CTD data taken during a survey carried out in November 1998, and the numerical solution of the Taylor–Goldstein equation for the prevailing hydraulic conditions previous to its generation. Stratification is computed from CTD data, and the tidal current prediction is made from the 2 years of ADCP hourly data at Camarinal Sill gathered during the Gibraltar Experiment 94-96. The main characteristic is that they happen during neap tides, and their magnitude is comparable to the internal bore generated during spring tides. The classical internal bore and the lee waves are different phenomena, and the presence of the latter is an indicator of minimum flow over Camarinal Sill. A prediction model for lee waves based on the tidal hydrodynamic conditions is also developed.  相似文献   

18.
Height-latitude distributions of the prevailing vertical wind for the mesosphere and lower thermosphere (70–110 km) are calculated on the basis of the empirical model of the monthly mean zonal mean prevailing horizontal wind. The presence of cellular structures is the main feature of the obtained vertical and meridional circulations. The ways such structures form and the problems of their modeling in global numerical models of the atmosphere are discussed.  相似文献   

19.
马汝建  赵锡平 《海洋科学》2002,26(11):38-43
应用非线性谱分析理论，对三阶Stokes型随机波浪载荷谱进行了分析，将波面方程及海水质点的水平速度用一阶波面的非线性组表示，导出了随机波浪谱的表达式。为了便于求解随机波浪的载荷谱，将阻力项展开为幂级数式，并应用非线性谱分析理论，确定了幂级数的系数，进而将波浪载荷表示为一阶波面及其导数的非线性组合，最后得出波浪载荷谱密度的表达式，并应用数值分析方法，得出单位桩柱波浪力及总波浪力谱密度。  相似文献   

20.
张力腿平台内孤立波作用特性数值模拟   总被引：1，自引：1，他引：0  
依据三类内孤立波理论KdV、eK dV和MCC的适用性条件,采用Navier-Stokes方程为流场控制方程,以内孤立波诱导上下层深度平均水平速度作为入口边界条件,建立了两层流体中内孤立波对张力腿平台强非线性作用的数值模拟方法。结果表明,数值模拟所得内孤立波波形及其振幅与相应理论和实验结果一致,并且在内孤立波作用下张力腿平台水平力、垂向力及力矩数值模拟结果与实验结果吻合。研究同时表明,张力腿平台内孤立波载荷由波浪压差力、粘性压差力和摩擦力构成,其中摩擦力很小,可以忽略;水平力的主要成分为波浪压差力和粘性压差力,粘性压差力与波浪压差力相比较小却不可忽略,流体粘性的影响较小;垂向力中粘性压差力很小,流体粘性影响可以忽略。  相似文献   

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