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1.
The results of a periodogramanalysis of the variations in the ionospheric parameters, measured using the vertical radio sounding method at midlatitude Irkutsk observatory (Eastern Siberia), are presented. The 1984–1986 period of observations was used. It has been indicated that the statistically significant oscillations with periods typical of planetary waves are present in the variations in f 0Es, f bEs, h′Es, f min, f 0F2, and h′F.  相似文献   

2.
We performed a statistical and spectral analysis of variations in two main parameters of the ionospheric F2 layer: critical frequency (f 0F2) and peak height (h m F2), recorded at an ionospheric station in Irkutsk (52.5°N, 104.0°E) in the period from December 1, 2006, to January 31, 2008, under low solar activity conditions. It was found that the f 0F2 and h m F2 variations contained quasi-harmonic oscillations with periods T n = 24/n h (n = 1−7). We studied the seasonal changes in the mean and median values of monthly f 0F2 and h m F2 time series, their spectra, as well as the amplitudes and phases of the diurnal (n = 1) and semidiurnal (n = 2) variations. It is shown that the amplitude of the diurnal f 0F2 variations was maximal in October–March 2007 and minimal in May–August 2007. The diurnal f 0F2 variations were maximal at noon in the winter months and at 1600 LT in the summer months. The semidiurnal f 0F2 variations had two maxima: a primary maximum in December and January and a secondary maximum in May–July. The maxima of semidiurnal f 0F2 variations were shifted from 0000 and 1200 LT in winter to 0900 and 2100 LT in summer.  相似文献   

3.
Summary The variations of the initialh E s height are investigated in the solar cycle 1957–1968, deriving the regressive dependency:h E s =121.4–6·10–2 R referring to the median monthly values at a solar zenith angle =75°. The similar variations ofh E s (R) during the day and night are interpreted as a domination of the sporadic layer formation from a redistribution of the day-time ionization and secondary participation of nightly ionizing sources. The analogous cyclich E s andh E variations confirm this conclusion while the seasonal variations in the state of the sporadic layer show outlined dynamical effects. The comparatively not big cyclic variation in the spatial state of theE-region are considered to confirm the predominating ionizing action of the ultraviolet range (933–1038 Å) in the lower part of theE-region, while the soft X-radiation influences mainly the near maximum part of this region.  相似文献   

4.
This paper presents some results on the following subjects obtained from in-situ forced vibration tests and earthquake observations. (1) The characteristics of the radiation damping of soil-foundation interaction systems vs. non-dimensional frequency a0 (=ωr/Vs) were experimentally estimated by the equivalent damping ratios hH ( = K′H/2KH) and hR ( = K′R/2KR), which were defined by complex stiffnesses 1KH (= KH + iKH) and 1KR (= KR + iK′R) of soil. The results for hH and hR of base rock were compared with those of soft soil. (2) A comparative study of experimental and theoretical results was made. The theoretical results were obtained from elastic half-space theory. (3) A semi-empirical equation to estimate the equivalent S-wave velocity for the elastic half-space model is proposed here, considering the effects of layered media. (4) Various comparisons of the results of 1 KH, 1 KR, hH and hR of forced vibration tests and earthquake observations were made.  相似文献   

5.
Determination of saturated hydraulic conductivity, Ks, and the van Genuchten water retention curve θ(h) parameters is crucial in evaluating unsaturated soil water flow. The aim of this work is to present a method to estimate Ks, α and n from numerical analysis of an upward infiltration process at saturation (Cap0), with (Cap0 + h) and without (Cap0) an overpressure step (h) at the end of the wetting phase, followed by an evaporation process (Evap). The HYDRUS model as well as a brute-force search method were used for theoretical loam soil parameter estimation. The uniqueness and the accuracy of solutions from the response surfaces, Ks–n, α–n and Ks–α, were evaluated for different scenarios. Numerical experiments showed that only the Cap0 + Evap and Cap0 + h + Evap scenarios were univocally able to estimate the hydraulic properties. The method gave reliable results in sand, loam and clay-loam soils.  相似文献   

6.
Partitioning resistance to overland flow on rough mobile beds   总被引：1，自引：0，他引：1  
For overland flows transporting predominantly bed load over rough mobile beds without rainfall, resistance to flow f may be divided into four components: surface resistance fs, form resistance ff, wave resistance fw, and bed‐mobility resistance fm. In this study it is assumed that f = fs + ff + fw + fm, and an equation is developed for each component. The equations for fs and ff are borrowed from the literature, while those for fw and fm are developed from two series of flume experiments in which the beds are covered with various concentrations of large‐scale roughness elements. The first series consists of 65 experiments on fixed beds, while the second series contains 194 experiments on mobile beds. All experiments were performed on the same slope (S = 0·114) and with the same size of sediment (D = 0·00074 m). The equations for fw and fm are derived by a combination of dimensional analysis and regression analysis. The analyses reveal that the major controls of fw and fm are the Froude number F and the concentration of the roughness elements Cr. When the equations for fw and fm are summed, the Cr terms cancel out, leaving fw+m = 0·63F?2. An equation is developed that predicts total f, and the contributions of fs, ff, fw and fm to f are computed from the series 1 and 2 experiments. An analysis of the first series reveals that in clear‐water flows over fixed beds, fw accounts for 52 per cent of f. A similar analysis of the second series indicates that in sediment‐laden flows over mobile beds fw comprises 37 per cent and fm 32 per cent of f, so that together fw and fm account for almost 70 per cent of f. Finally, regression analyses indicate that where F > 0·5, fw and fm each vary with F?2 and fw/fm = 1·18. The equation developed here for predicting total f applies only to the range of hydraulic, sediment, and bed roughness conditions represented by the experimental data. With additional data from a broader range of conditions the same methodology as employed here could be used to develop a more general equation. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

7.
Quantifying the timescales associated with moving freshwater–seawater interfaces is critical for effective management of coastal groundwater resources. In this study, timescales of interface movement in response to both inland and coastal water level variations are investigated. We first assume that seawater intrusion (SWI) and retreat (SWR) are driven by an instantaneous freshwater-level variation at the inland boundary. Numerical modelling results reveal that logarithmic timescales of SWI (lnTi) and SWR (lnTr) can be described respectively by various simple linear equations. For example, SWI timescales are described by lnTi = a + blnh′f–s, where a and b are linear regression coefficients and h′f–s is the boundary head difference after an instantaneous drop of inland freshwater head. For SWR cases with the same initial conditions, but with different increases in freshwater head, lnTr = c + dΔXT, where c and d are regression coefficients and ΔXT is the distance of toe response that can be estimated by a steady-state, sharp-interface analytical solution. For SWR cases with the same freshwater head increase, but with different initial conditions, in contrast, lnTr = e + flnΔXT, where e and f are regression coefficients. The timescale of toe response caused by an instantaneous variation of sea level is almost equivalent to that induced by an instantaneous inland head variation with the same magnitude of water level change, but opposite in direction. Accordingly, the empirical equations of this study are also applicable for sea-level variations in head-controlled systems or for simultaneous variations of both inland and coastal water levels. Despite the idealised conceptual models adopted in this study, the results imply that for a particular coastal aquifer, SWI timescales are controlled by the boundary water levels after variations, whereas SWR timescales are dominated by the distance of toe response.  相似文献   

8.
Summary A yearly variation of the virtual height of sporadicE, reaching a maximum in the spring and a minimum in the autumn, has been recently found. This variation ofh' E s is similar to the seasonal variation of the total amount of ozone. On the other hand, the seasonal variation of the virtual height of the lowest occurring sporadicE layer (l-type may be identified with the height variation of the boundary between homosphere and heterosphere. It may also be supposed that the latter is caused by the varying expansion of the homosphere. Since ozone strongly absorbs solar energy, the seasonal variation ofh' E s is attributed to the expansion of the homosphere depending on the total amount of ozone.
Zusammenfassung Eine jahreszeitliche Änderung der scheinbaren Höhe der sporadischenE Schicht (h' E s) konnte festgestellt werden, die ein Maximum im Frühling und ein Minimum im Herbst zeigt. Diese Änderung vonh' E s ist der Änderung des totalen Ozonbetrages ähnlich. Andererseits kann man die jahreszeitliche Änderung der untersten sporadischenE Schicht (Typl) mit der Höhenänderung der Grenzfläche zwischen Homosphäre und Heterosphäre identifizieren. Es kann auch angenommen werden, dass die letztere durch die Expansion der Homosphäre hervorgerufen wird. Da ozon bekanntlich die Sonnenstrahlung sehr stark absorbiert, wird die jahreszeitliche Änderung vonh E s auf die vom totalen Ozonbetrag abhängigen Expansion der Homosphäre zurückgeführt.
  相似文献   

9.
Dependence of the energy released during earthquake on ambient shear stress   总被引：1，自引：0，他引：1  
Starting with dislocation model, using the result of the fracture mechanics: the slip displacement at the crack tip is proportional to the length of the crack and the applied ambient shear stressτ 0 2 , we consider the dislocation in the earthquake to be the slip displacement at the crack tip and have obtained the analysis expresses of displacement and velocity pulse for the circular crack and have calculated the seismic wave energy radiated by earthquake. The seismic wave energyE ∞M 0 τ 0 2 f(v) r , i. e.E is proportional to the seismic momentM 0 and the square of the ambient shear stressτ 0 2 and increases with the rupture velocityv r . In frequency domain, integrating the square of source velocity spectrum derived from our the scaling law model, we have also obtained the seismic wave energyE released by earthquake and earthquake radiated effficiencyη.E ∞M 0 τ 0 2 also. If takingτ 0 = 10.0 MPa, E=4.79M 0. This result is consistent with the estimate by Vassiliou and Kanamori (1982). Theη=5.26%. The distribution of the seismic wave energy is that most of the energy contains in the frequency range between the first corner frequencyf c1 and thirdf c3, amount to 92.3% the energy in the rangef<f c1 is about 3.85% and 3.85% whenf>f c3. Thef c3 is about 8Hz forM ⩾ 6, thus most of radiated energy is below 2Hz. This phenomenon had been verified by Vassiliou Kanamori. Previous results show the energy radiated by earthquake to be strongly dependent on ambient shear stress. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,15, 146–152, 1993. This work was supported by the Deutsche Forschungsgemeinschaft, Bonn, F. R. Germany. The support is grateful acknowledged. The authors are also grateful to Professor Klussmann and Mr. Hasthoff for their lots of help.  相似文献   

10.
The vertical hydraulic conductivity (Kv) of a stream or lake sediment is often determined in the field using standpipe tests. Calculation of Kv is based on the assumption that the hydraulic head in the pipe is equal to that of the stream or lake stage. In this work, a modified equation for Kv is developed for the standpipe test which is applicable when this assumption is not valid. The equation involves not only the hydraulic head at different times but also the difference in the hydraulic head (a) between the groundwater level and river stage. The effects of certain factors on Kv, such as the ratio of the hydraulic head at different times (h1/h2), the difference a, and the initial water table height (h0), are also discussed. The results show that when h1/h2 is constant, the relative error (Er) in Kv increases with the ratio a/h2. Furthermore, if a/h2 < 0.05, then for any value of h1/h2, Er is less than 5% using the modified equation. Also, if a/h2 is large, hydraulic head readings with larger h1/h2 ratios must be used to avoid large Er values. The results of a field test also indicate that the error in Kv decreases as the value of h0 increases. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

11.
A non-hydrostatic model in cross-sectional form with an idealized sill is used to examine the influence of sill depth (h s) and aspect ratio upon internal motion. The model is forced with a barotropic tide and internal waves and mixing occurs at the sill. Calculations using a wide sill and quantifying the response using power spectra show that for a given tidal forcing namely Froude number F r as the sill depth (h s) increases the lee wave response and vertical mixing decrease. This is because of a reduction in across sill velocity U s due to increased depth. Calculations show that the sill Froude number F s based on sill depth and across sill velocity is one parameter that controls the response at the sill. At low F s (namely F s ≪ 1) in the wide sill case, there is little lee wave production, and the response is in terms of internal tides. At high F s, calculations with a narrow sill show that for a given F s value, the lee wave response and internal mixing increase with increasing aspect ratio. Calculations using a narrow sill with constant U s show that for small values of h s, a near surface mixed layer can occur on the downstream side of the sill. For large values of h s, a thick well-mixed bottom boundary layer occurs due to turbulence produced by the lee waves at the seabed. For intermediate values of h s, “internal mixing” dominates the solution and controls across thermocline mixing.  相似文献   

12.
The catalog of Kamchatka earthquakes is represented as a probability space of three objects {Ω, $ \tilde F $ \tilde F P}. Each earthquake is treated as an outcome ω i in the space of elementary events Ω whose cardinality for the period under consideration is given by the number of events. In turn, ω i is characterized by a system of random variables, viz., energy class ki, latitude φ i , longitude λ i , and depth h i . The time of an outcome has been eliminated from this system in this study. The random variables make up subsets in the set $ \tilde F $ \tilde F and are defined by multivariate distributions, either by the distribution function $ \tilde F $ \tilde F (φ, λ, h, k) or by the probability density f(φ, λ, h, k) based on the earthquake catalog in hand. The probabilities P are treated in the frequency interpretation. Taking the example of a recurrence relation (RR) written down in the form of a power law for probability density f(k), where the initial value of the distribution function f(k 0) is the basic data [Bogdanov, 2006] rather than the seismic activity A 0, we proceed to show that for different intervals of coordinates and time the distribution f elim(k) of an earthquake catalog with the aftershocks eliminated is identical to the distribution f full(k), which corresponds to the full catalog. It follows from our calculations that f 0(k) takes on nearly identical numeral values for different initial values of energy class k 0 (8 ≤ k 0 ≤ 12) f(k 0). The difference decreases with an increasing number of events. We put forward the hypothesis that the values of f(k 0) tend to cluster around the value 2/3 as the number of events increases. The Kolmogorov test is used to test the hypothesis that statistical recurrence laws are consistent with the analytical form of the probabilistic RR based on a distribution function with the initial value f(k 0) = 2/3. We discuss statistical distributions of earthquake hypocenters over depth and the epicenters over various areas for several periods  相似文献   

13.
Abstract

The flow of a rotating homogeneous, incompressible fluid past a long ridge is investigated. An analysis is presented for flows in which E ? 1, Ro ～ E½, H/D ～ E0, h/D ～ E½ and cosα ～ E0 where E is the Ekman number, Ro the Rossby number, H/D the fluid depth to ridge width ratio, h/D the ridge height to ridge width ratio and α the angle between the free stream flow and a line perpendicular to the ridge axis. The analysis includes effects of the nonlinear inertial terms. Particular examples of a ridge of triangular cross section and a sinusoidal topography are investigated in some detail. Experiments are presented for a triangular ridge which are in good agreement with the theory.  相似文献   

14.
The transient dynamic response of single piles in a layered half-space under a time-dependent vertical force is analyzed by an FEM-BEM coupling approach. The pile is modeled by FEM and the layered half-space is modeled by a general cylindrical coordinates time-domain BEM. Only one-dimensional discretization is necessary on the boundaries of the three-dimensional layered half-space by virtue of the Fourier theory, while the pile shaft can be discretized as a one-dimensional elastic beam. The compatibility and equilibrium conditions between pile shaft and soil layers are employed to assemble respective equations into one. Fairly good agreement between two unknown solutions and the current approach is found. Parametric studies reveal the influences of several dimensionless factors, such as Ep/Es, l/r0, p/s and νs. The effect of soil layering and the support condition of the pile tip is also reported by numerical examples.  相似文献   

15.
The presence and persistence of an 18-day quasi-periodic oscillation in the ionospheric electron density variations were studied. The data of lower ionosphere (radio-wave absorption at equivalent frequency near 1 MHz), middle and upper ionosphere (critical frequencies f0E and f0F2) for the period 1970–1990 have been used in the analysis. Also, solar and geomagnetic activity data (the sunspot numbers Rz and solar radio flux F10.7 cm, and aN index respectively) were used to compare the time variations of the ionospheric with the solar and geomagnetic activity data. Periodogram, complex demodulation, auto- and cross-correlation analysis have been used. It was found that 18-day quasi-periodic oscillation exists and persists in the temporal variations of the ionospheric parameters under study with high level of correlation and mean period of 18–19 days. The time variation of the amplitude of the 18-day quasi-periodic oscillation in the ionosphere seems to be modulated by the long-term solar cycle variations. Such oscillations exist in some solar and geomagnetic parameters and in the planetary wave activity of the middle atmosphere. The high similarities in the amplitude modulation, long-term amplitude variation, period range between the oscillation of investigated parameters and the global activity of oscillation suggests a possible solar influence on the 18-day quasi-periodic oscillation in the ionosphere.  相似文献   

16.
Abstract

The behavior of the flux Richardson number R f, as a function of the overall Richardson number Ri 0, was investigated for a stably stratified, grid-generated, turbulent flow evolving in a closed-loop water channel. The turbulent dissipation rate ε, the buoyancy or vertical mass flux p wbar; and the rms density fluctuation ρ′ were obtained from simultaneous single-point measurements of the horizontal and vertical velocity components and density fluctuations. From these, R f and Ri 0 were calculated at each point in the spatially evolving flow. The resulting curves of R f vs. Ri 0 exhibit the full range of behavior found in the very different case studied by Linden (1980). The length scale arguments of Gibson (1980) and Stillinger et al. (1983b) provide an underlying mechanism which successfully accounts for the shape of the R f vs. Ri 0 curve.  相似文献   

17.
We consider data obtained when the parameters of the ionospheric Es and F2 layers and the vertical gradient of the electric potential in the surface atmosphere were simultaneously measured during the preparatory period of crustal earthquakes with M = 5.0–6.2 in the Kamchatka region. The appearance of anomalously high Es, accompanied by an increase in frequency parameters of the sporadic layer and the regular F2 layer, was detected on days when possible earthquake precursors, as determined earlier, occurred in atmospheric electric fields. The presumed earthquake precursors in the ionosphere are divided into two groups with different earthquake lead times ranging from several hours to two weeks. Empirical dependences are presented that connect the lead time of an earthquake (from the moment of the appropriate anomaly’s occurrence in the ionosphere or in the atmospheric electric field to the moment of the shock) and the epicentral distance to the observation point with the earthquake magnitude. These dependences are different for the two groups of presumed earthquake precursors, but they are close inside each group of possible precursors selected on the basis of quasistatic electric field measurements and revealed in ionospheric parameter variations.  相似文献   

18.
This study was undertaken to evaluate the effects of climatic variability on inter‐annual variations in each component of evapotranspiration (ET) and the total ET in a temperate coniferous forest in Japan. We conducted eddy covariance flux and meteorological measurements for 7 years and parameterized a one‐dimensional multi‐layer biosphere‐atmosphere model (Kosugi et al., 2006 ) that partitions ET to transpiration (Tr), wet‐canopy evaporation (Ewet), and soil evaporation (Esoil). The model was validated with the observed flux data. Using the model, the components of ET were estimated for the 7 years. Annual precipitation, ET, Tr, Ewet, and Esoil over the 7 years were 1536 ± 334 mm, 752 ± 29 mm, 425 ± 37 mm, 219 ± 34 mm, and 108 ± 10 mm, respectively. The maximum inter‐annual fluctuation of observed ET was 64 mm with a coefficient of variance (CV) of 2.7%, in contrast to relatively large year‐to‐year variations in annual rainfall (CV = 20.1%). Tr was related to the vapour pressure deficit, incoming radiation, and air temperature with relatively small inter‐annual variations (CV = 8.2%). Esoil (CV = 8.6%) was related mainly to the vapour pressure deficit. Ewet was related to precipitation with large inter‐annual variations (CV = 14.3%) because of the variability in precipitation. The variations in Ewet were counterbalanced by the variations in Tr and Esoil, producing the small inter‐annual variations in total ET. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

19.
Measurements of saturated hydraulic conductivity (Ks) and diagnostic model simulations show that all types of logging road/trail in the 14·4 ha Bukit Tarek Experimental Catchment 3 (BTEC3) generate substantial Horton overland flow (HOF) during most storms, regardless of design and level of trafficking. Near‐surface Ks(0–0·05 m) on the main logging road, skid trails and newly constructed logging terraces was less than 1, 2 and 34 mm h?1, respectively. Near‐surface Ks on an abandoned skid trail in an adjacent basin was higher (62 mm h?1), owing to the development of a thin organic‐rich layer on the running surface over the past 40 years. Saturated hydraulic conductivity measured at 0·25 m below the surface of all roads was not different (all <6 mm h?1) and corresponded to the Ks of the adjacent hillslope subsoil, as most roads were excavated into the regolith more than 0·5–1 m. After 40 years, only limited recovery in near‐surface Ks occurred on the abandoned skid trail. This road generated HOF after the storage capacity of the upper near‐surface layer was exceeded during events larger than about 20 mm. Thus, excavation into low‐Ks substrate had a greater influence on the persistence of surface runoff production than did surface compaction by machinery during construction and subsequent use during logging operations. Overland flow on BTEC3 roads was also augmented by the interception of shallow subsurface flow traveling along the soil–saprolite/bedrock interface and return flow emerging from the cutbank through shallow biogenic pipes. The most feasible strategy for reducing long‐term road‐related impacts in BTEC3 is limiting the depth of excavation and designing a more efficient road network, including minimizing the length and connectivity of roads and skid trails. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

20.
Pan evaporation (Ep) is an important indicator of water and energy and the decline of Ep has been reported in many regions over the last decades. The climate and Ep are dependent on each other. In this study, the temporal trends of Ep and main Ep drivers, namely mean air temperature (Ta), wind speed (u), global solar radiation (Rs), net long‐wave radiation(Rnl) and vapour pressure deficit (D) from 1970 to 2012, were calculated on the basis of 26 meteorological stations on the Tibetan Plateau. The arithmetic average of Ep from 26 stations decreased with the rate of ?11.91 mm a?2; the trends of Rs, Rnl, Ta, u and D were ?1.434 w m?2 decade?1, 0.2511 w m?2 decade?1, 0.3590°C decade?1, ?0.2376 m s?1 decade?1 and 9.523 Pa decade?1, respectively. The diffuse irradiance is an essential parameter to model Ep and quantify the contribution of climatic factors to changing Ep. 60 724 observations of Rs and diffuse solar irradiance (Rd) from seven of the 26 stations were used to develop the correlation between the diffuse fraction (Rd/Rs), and the clearness index (Rs/Ro). On the basis of the estimation of the diffuse component of Rs and climatic data, we modified the PenPan model to estimate Chinese micro‐pan evaporation (Ep) and assess the attribution of Ep dynamics using partial derivatives. The results showed that there was a good agreement between the observed and calculated daily Ep values. The observed decrease in Ep was mostly due to declining wind speed (?13.7 mm a?2) with some contributions from decreasing solar irradiance (?3.1 mm a?2); and the increase of temperature had a large positive effect (4.55 mm a?2) in total whilst the increase of Rnl had insignificant effect (0.35 mm a?2) on Ep rates. The change of Ep is the net result of all the climatic variables. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

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