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1.
Frictional influence on sea level oscillations in Otago Harbour,New Zealand   总被引：1，自引：1，他引：0  
Oscillations in Otago Harbour, (45° 49’ S, 170° 38’ E) produced by the 1960 Chilean Tsunami are found by spectral analysis to have most of their energy at a period of about 80 min. By numerically integrating a one‐dimensional linear momentum equation and the continuity equation for various sections of the harbour, this period is found to correspond to the quarter wavelength oscillation in the main channel between the mouth of the harbour and the Halfway Islands. The large value of the linear frictional coefficient, calculated from the phase of the tide in the harbour, and the resulting excessive damping, indicates why long period non‐tidal oscillations are generally not found in the harbour.  相似文献   

2.
The paper considers zonal mean (65° S–65° N, with a step of 5°) monthly mean NCEP/DOE reanalysis data on zonal wind and temperature at levels of 20 to 100 mb and the TOMS data of version 8 on total ozone (TO) for the period 1979–2005. The results of calculating linear-trend coefficients, correlation coefficients, and characteristic decay times and the data of spectral analysis are presented. In recent decades, the decrease in TO and the cooling of the lower stratosphere were accompanied by a weakening of the westerly wind. For deseasonalized series, the significance of their linear trends are evaluated with the use of the Monte Carlo method and it is shown that TO trends are significant at a level of 0.99 in extratropical latitudinal zones and that temperature trends are significant everywhere except in a narrow equatorial zone and in latitudes south of 50° S, whereas wind trends are significant only at a 50-mb level in the latitudinal belt 30°–50° in both hemispheres. According to the results of spectral analysis, for the majority of latitudinal zones, a triplet in the range of quasibiennial oscillations and oscillations with periods of about 4–6 and 9–13 years manifest themselves most persistently in the series of temperature, wind, and TO. Maximum correlation coefficients of the series of TO, wind, and temperature are observed over the equator, and, depending on altitude and latitude, TO variations may lag or lead temperature and wind variations in phase. Latitudinal distributions of characteristic decay times show an increase in this parameter in tropical and equatorial zones and its opposite behavior with altitude for temperature and wind fields.  相似文献   

3.
The results of long-term (1980–2003) systematic measurements of the total ozone content at the Issyk Kul station (42.6° N, 77.0° E; 1650 m above sea level) are presented. The statistical characteristics and spectral structure of variations in the total ozone and the main tendencies of its temporal variability are determined. It is found that the total ozone content decreased in 1980–2003 at an average rate of (?1.29±0.08) DU/yr. The results of Fourier and wavelet analyses have shown that only oscillations with periods of 12, 27–29, and 102–105 months are rather stable and can be represented as harmonic oscillations. Oscillations with periods shorter than six months have the character of periodically arising pulsations. Among these, oscillations with periods of 27–29 and 34–37 days can be distinguished. It is noted that the spectral-temporal structure of variations in the total ozone content obtained from ground-based measurements at the Issyk Kul station is in good agreement with the corresponding structure obtained from TOMS satellite measurements.  相似文献   

4.
《Coastal Engineering》2002,46(2):109-126
A frequent problem with process-based coastal morphological models is the appearance of high wave number spatial oscillations in the simulated bed levels with time. After a sufficiently long time, these oscillations become dominant and mask the large-scale features of the bed level evolution.The equation for conservation of sediment mass is used to show that the spatial oscillations are generated by the dependence of the bed celerity (celerity of the bed level oscillations) with bed levels, which is due to the non-linear relationship between sediment transport and bed levels. This breeds higher spatial harmonics of the bed level oscillations with time. In this situation, using a Finite Difference (FD) scheme that does not damp oscillations with high wave numbers leads to the generated harmonics being kept in the solution. These generate further harmonics until the entire solution is dominated by high wave number oscillations.In this paper, a finite difference scheme, in combination with a filtering procedure, is used to dissipate high wave number oscillations. Analysis of the amplification portraits show that the filtering procedure in combination with a Lax–Wendroff scheme does not affect oscillations with lower wave numbers (larger scale features resolved with seven or more grid points). Some examples are also presented to illustrate these features.  相似文献   

5.
Long-term data from 23 tide gauges were used to analyze the spectrum of mesoscale sea level variability of the Black Sea. The tides have sharp spectral peaks, and they are detected at diurnal and semidiurnal frequencies for all stations. A local wide spectral peak associated with inertial oscillations is located between the diurnal and semidiurnal tidal peaks. This peak is well known in the spectra of the current velocity variations of the Black Sea, but in the sea level spectrum it has been identified for the first time. At frequencies of >3 cpd, sea level spectra of the Black Sea have (1) wide maxima in the continuous spectrum, which correspond to the main eigenmodes of the sea with periods of 5.6, 4.8, 4.1, and 3.1 h, and (2) sharp peaks of radiational harmonics S3, S4, S5, and S6. The periods of seiches calculated in this study are close to the periods of eigenmodes of the Black Sea, obtained by the numerical modeling of other authors. The main factors influencing the formation of radiational tides in the Black Sea are presumably breezes and runoff from large rivers. The significant predominance of a harmonic with frequency of 5 cpd (S5) over other radiational harmonics is caused by the influence of an eigenmode, with a frequency of about 5 cpd. The proximity of the periods of these oscillations leads to resonant amplification and to a corresponding increase in amplitude of the radiational harmonic S5.  相似文献   

6.
A field measurement was made at three stations near the head of Onagawa Bay to investigate the two-dimensional pattern of bay oscillations. Characteristics of the eigen oscillations are numerically calculated by finding the eigenvalues and eigenvectors of a matrix derived from a two-dimensional model. The observed oscillations can be explained, to a reasonable degree, by the calculated modes at the periods of 36, 18, 14, 12 and 10 min, where the modes at 18 and 12 min are of longitudinal oscillations and the ones at 14 and 10 min are of lateral oscillations.  相似文献   

7.
Large oscillations of water level in Nagasaki Bay are calledAbiki and are most frequently observed in winter. The largestAbiki recorded in the past 20 years at the tide station at Nagasaki occurred on March 31, 1979. Simultaneously, a distinct atmospheric pressure disturbance of solitary type with an amplitude of about 3 mb was recorded at several neighbouring stations in Kyûshû, which indicated the pressure disturbance probably travelled eastward with an average speed of about 110 km h–1.The quantitative relation between this pressure disturbance and notable seiches observed in Nagasaki Bay is examined by means of numerical simulation, and it is confirmed that the exceptionally large range of oscillations in the bay, which reached 278 cm at the tide station, was indeed produced by this travelling pressure disturbance.The leading part of shallow water waves induced by the atmospheric pressure disturbance was amplified up to about 10 cm in amplitude, over the broad continental shelf region off China, because of near resonant coupling to the pressure disturbance. After leaving this continental shelf region, the amplified water wave converged into the shelf region (Gotô Nada) surrounded by the north-western coast of Kyûshû and the Gotô Islands and excited eigenoscillations on the shelf. A train of waves thus formed with a period of about 35 min entered Nagasaki Bay and was resonantly amplified at periods of 36 min and 23 min which are the eigen periods of the bay. Besides resonance, the combined effects of shoaling and reflection inside Nagasaki Bay also enhanced the amplification.  相似文献   

8.
During the South China Sea monsoon experiment (SCSMEX),three autonomous temperature line acquisition system (ATLAS) buoys with acoustic Doppler current profiler (ADCP) were moored in the South China Sea to measure temperature,salinity and current velocity.Typhoon Faith passed through about 250 km south to one of the mooring buoys located at 12 58.5 N,114 24.5 E from December 11 to 14,1998.The data analysis indicates that the typhoon winds induce a great increase in the kinetic energy at near-inertial frequencies with two maxima in the mixed layer and thermocline.The near-inertial oscillations were observed at the upper 270 m in the wake of Typhoon Faith.The oscillations were originally excited in the sea surface layer and propagated downward.The amplitudes of the oscillations decrease with depth except in the thermocline.The near-inertial oscillation signals are also remarkable in temperature and salinity fields.  相似文献   

9.
Abstract

The techniques for computing the eigenfunctions of the velocity potential (Proudman functions) set out in Sanchez et al. (1986) in relation to the Atlantic‐Indian Ocean are here applied to the Pacific Ocean, using a 6° × 6° grid of 510 points (455 points for the associated stream functions). Normal modes are computed from the first 150 Proudman functions and have natural periods from 43.9 hours downwards. Tidal syntheses are derived from these modes by direct application of the (frictionless) dynamic equations and by least‐squares fitting of Proudman functions to the dynamically interpolated tide‐gauge data of Schwiderski (1983). The modes contributing most energy to the principal harmonic tidal constituents are different in the two computations; their natural periods are typically in the range of 9–16 hours for semidiurnal, 14–43 hours for diurnal tides. The RMS of fit for Proudman functions is in all cases better than the corresponding value for the same number of spherical harmonics.

Before fitting the Proudman functions to the altimetry from the 3‐day repeat cycle of Seasat, the data are processed by novel methods. The geoid component is eliminated by taking collinear differences at a fixed time‐lag of two repeat cycles. Orbit errors are reduced by extracting the 1 rev?1 component at every ascending node; this component varies slowly and nonlinearly in time. The spatial fitting process includes M2 and O1 frequencies, both of which emerge with significant and realistic tidal mapping, but residual noise in the data limits the number of Proudman functions to about 50–60 before showing signs of “over‐fitting.”; Fitting the same data by spherical harmonics gives marginally lower predicted variance for the same number of parameters.  相似文献   

10.
The process of hydrostatic adjustment to horizontally homogeneous heating in a stably stratified atmosphere of arbitrary thermal structure is investigated in the limit of small perturbations. A linear differential equation is derived for the vertical pressure distribution in the final balanced state. Solutions of this equation are compared with the time dependent solution which is found by numerically integrating the equations in time. During the process of hydrostatic adjustment acoustic‐buoyancy oscillations are generated. The amplitudes of these oscillations become so great that static instability is generated at heights above 100 km, depending on where and how abruptly the heat is added. As a crude representation of the unstable breakdown and damping of these waves, Rayleigh damping is introduced. If the associated damping coefficient in the upper atmosphere is sufficiently large (greater than the Brunt Väisälä frequency), the oscillations vanish. Below a height of about 50 km the steady state predicted by the above mentioned differential equation is reached approximately in 10 min.  相似文献   

11.
1IntroductionThe oceanic Rossby waves play an importantrole in the large-scale oceanic circulations.In the o-ceans baroclinic Rossby waves have surface manifes-tations of just a fewcentimeters,and wavelengths atmid-latitudes of hundreds to thousands of ki…  相似文献   

12.
The internal structure and composition of a 37-mm-thick Co-rich Mn crust from the Lamont Guyot in the Marcus-Wake Seamount cluster have been studied in detail by means of electron-probe microanalysis (EPMA). 184 point analyses for 16 elements were carried out at an average spacing of 0.20 mm and each point was dated using the Co-geochronometer method. Two types of variation in composition were observed in the crust: long-term trends and short-term erratic variations. The long-term trends were identified using the fifth order polynomial. Mn and Ni were shown to increase in concentration from 23.3 Ma to a maximum at about 20 Ma and then decline steadily to the Present, whereas Fe, P and Si showed the opposite trend. By contrast, Co displayed a double humped pattern with maxima at about 19 Ma and 3.5 Ma and minima at 23.3 Ma, about 11 Ma and at Present. The long-term trends in element concentrations in the crust lead us to suggest that much of the Fe in western Pacific Ocean ferromanganese crusts is aeolian in origin and derived from the deserts of central Asia. Cooling of the Asian mainland at about 20 Ma led to an increase in the flux of Fe to the oceans. This was supplemented by an additional input of Fe into the crusts as a consequence of the dissolution of biogenic CaCO3 tests at 4.5−10.5 Ma. For the short-term erratic variations, three periods of 0.61, 0.96 and 1.65 m.y. were identified by spectral analysis. The second harmonics of these periods are 1.22, 1.92 and 3.30 m.y., which may correspond to the highest-order periods for eccentricity of 1.31, 2.04 and 3.47 m.y. This suggests the possibility that the high-frequency oscillations of the time series data are linked to climatic changes controlled by the highest-order periods of the Milankovitch cycles.  相似文献   

13.
The effects of tropical instability waves (TIW) within the eastern equatorial Pacific during the boreal fall of 2005 were observed in multiple data sets. The TIW cause oscillations of the sea surface temperature (SST), meridional currents (V), and 20 °C isotherm (thermocline). A particularly strong 3-wave packet of ～15-day period TIW passed through the Galápagos Archipelago in Sep and Oct 2005 and their effects were recorded by moored near-surface sensors. Repeat Argo profiles in the archipelago showed that the large temperature (>5 °C) oscillations that occurred were associated with a vertical adjustment within the water column. Numerical simulations report strong oscillations and upwelling magnitudes of ～5.0 m d?1 near the Tropical Atmosphere Ocean (TAO) buoy at 0°, 95°W and in the Archipelago at 92°W and 90°W. A significant biological response to the TIW passage was observed within the archipelago. Chlorophyll a measured by the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) increased by >30% above 1998–2007 mean concentrations within the central archipelago. The increases coincide with coldest temperatures and the much larger increases within the archipelago as compared to those of 95°W indicate that TIW induced upwelling over the island platform itself brought more iron-enriched upwelling waters into the euphotic zone.  相似文献   

14.
To investigate the response characteristics of a bay to tsunamis, field measurements of long-period waves have been carried out at Onagawa and Okachi Bays, both of which face the Pacific Ocean in northern Japan. In Onagawa Bay, the observed transfer function is in good agreement with the prediction based on the one-dimensional numerical model, in the period range larger than about 15 minutes. The response of shorter periods seems to be influenced by the two-dimensionality of the bay. The oscillations within Onagawa Harbor are also discussed with respect to the relative amplitude and phase at two stations inside the harbor and it is estimated that the reflection coefficient at the waterfront is about 0.7. In Okachi Bay, the oscillations in the period range larger than about 10 minutes could be explained by a Y-shaped model of the bay. The dominant oscillations offshore of these two-bays are found to be the mode with the motion predominantly in the direction normal to the shelf orientation, and the estimated power spectral density of incoming waves in deep water varies asf –2,f being the frequency. The waves of lateral modes, such as edge waves on the shelf, are small and of minor importance to generate bay oscillations of longer periods.  相似文献   

15.
Natural and wave-induced oscillations in Nagasaki Bay, a coupled bay—river system, are numerically studied. Formulation of the problem is based on the mild slope wave equation with modeled dissipation. Computations are performed by the finite element method originated from the classical variational principle. The numerical results show that the bay at the mean tidal level has natural modes of periods of 30.60 minutes, 17.28 minutes, 10.08 minutes, 7.67 minutes, etc. The 30.60-minute mode of the bay is characterized by a monotonic increase of the amplitude of oscillation from the bay entrance to the Urakami River mouth, whereas the 17.28-minute mode and the 10.08-minute mode attain maximum near Fukahori. It is also demonstrated that the 30.60-minute mode, the 17.28-minute mode and the 10.08-minute mode can be most severely resonated when the bay is subjected to oscillations in the open sea with periods of about 33.2 minutes, 17.9 minutes, and 10.1 minutes, respectively. The existence of the Urakami River seems to have an effect on mitigating the resonant bay oscillations, particularly if the relevant mode is of relatively low frequency and maximizes near the river mouth.  相似文献   

16.
Long-term hourly data from 35 tide gauge stations, including 15 stations in the Gulf of Finland, were used to examine tidal sea level oscillations of the Baltic Sea. High-resolution spectral analysis revealed the well-defined fine structure of tidal peaks with diurnal peaks at most stations being higher than semidiurnal. At some stations (e.g., Narva, Daugava, and Wladyslawowo), high frequency radiational tidal peaks with periods multiple of the solar day (3, 4, 5, 6, and 8 cpd) were detected; the respective oscillations are supposed to be caused by seabreeze winds. Harmonic analysis of tides for individual yearly sea level series followed by vector averaging over the entire observational period was used to estimate the amplitudes and phases of 16 tidal constituents. The maximum tidal oscillations of 17–19 cm were found to be observed in the Gulf of Finland and, first of all, in Neva Bay (in the head of the gulf). Diurnal or mixed diurnal tides are predominant in almost the entire Baltic Sea. The comparison of the observed tides with those theoretically computed showed that the existing numerical models of the main tidal harmonics generally quite accurately reproduce the structure of the tides in the Baltic Sea except for some regions of the Gulf of Bothnia.  相似文献   

17.
Based on the satellite altimetry dataset of sea level anomalies, the climatic hydrological database World Ocean Atlas-2009, ocean reanalysis ECMWF ORA-S3, and wind velocity components from NCEP/NCAR reanalysis, the interannual variability of Antarctic Circumpolar Current (ACC) transport in the ocean upper layer is investigated for the period 1959–2008, and estimations of correlative connections between ACC transport and wind velocity components are performed. It has been revealed that the maximum (by absolute value) linear trends of ACC transport over the last 50 years are observed in the date-line region, in the Western and Eastern Atlantic and the western part of the Indian Ocean. The greatest increase in wind velocity for this period for the zonal component is observed in Drake Passage, at Greenwich meridian, in the Indian Ocean near 90° E, and in the date-line region; for the meridional component, it is in the Western and Eastern Pacific, in Drake Passage, and to the south of Africa. It has been shown that the basic energy-carrying frequencies of interannual variability of ACC transport and wind velocity components, as well as their correlative connections, correspond to the periods of basic large-scale modes of atmospheric circulation: multidecadal and interdecadal oscillations, Antarctic Circumpolar Wave, Southern Annual Mode, and Southern Oscillation. A significant influence of the wind field on the interannual variability of ACC transport is observed in the Western Pacific (140° E–160° W) and Eastern Pacific; Drake Passage and Western Atlantic (90°–30° W); in the Eastern Atlantic and Western Indian Ocean (10°–70° E). It has been shown in the Pacific Ocean that the ACC transport responds to changes of the meridional wind more promptly than to changes of the zonal wind.  相似文献   

18.
Sea surface temperature (SST) data derived from satellite and in situ measurements are used to study the thermal variability in the South China Sea (SCS). Time–frequency–energy distributions, periods of variability, and trends are computed by the Hilbert–Huang transform method. The SST trend from 1982 to 2005 is 0.276°C per decade in the SCS which is higher than 0.144°C per decade in the western Pacific warm pool (WPWP). The warm pool (SST ≥ 28°C) area in the SCS has increased by 0.20 × 106 km2 per decade. The SST and area of the warm pool in the SCS are strongly correlated, respectively, with the SST and area of the WPWP with a time lag of 1 month, suggestive of a strong connection between these two warm pools. Once the annual cycle is eliminated, decadal oscillations dominate the variability of SST and warm pool area in the SCS.  相似文献   

19.
Seasonal evolution of surface mixed layer in the Northern Arabian Sea (NAS) between 17° N–20.5° N and 59° E-69° E was observed by using Argo float daily data for about 9 months, from April 2002 through December 2002. Results showed that during April - May mixed layer shoaled due to light winds, clear sky and intense solar insolation. Sea surface temperature (SST) rose by 2.3 °C and ocean gained an average of 99.8 Wm−2. Mixed layer reached maximum depth of about 71 m during June - September owing to strong winds and cloudy skies. Ocean gained abnormally low ∼18 Wm−2 and SST dropped by 3.4 °C. During the inter monsoon period, October, mixed layer shoaled and maintained a depth of 20 to 30 m. November - December was accompanied by moderate winds, dropping of SST by 1.5 °C and ocean lost an average of 52.5 Wm−2. Mixed layer deepened gradually reaching a maximum of 62 m in December. Analysis of surface fluxes and winds suggested that winds and fluxes are the dominating factors causing deepening of mixed layer during summer and winter monsoon periods respectively. Relatively high correlation between MLD, net heat flux and wind speed revealed that short term variability of MLD coincided well with short term variability of surface forcing.  相似文献   

20.
A vertically integrated dynamic ice sheet model is coupled to the atmosphere-ocean-sea ice-land surface climate model recently developed by Wang and Mysak (2000). The background lateral (east-west) ice sheet discharge rate used by Gallee et al. (1992) is reduced and the planetary emissivity is increased (to parameterize the cooling effect of a decrease of the atmospheric CO2 concentration), in order to build up substantial ice sheets during a glacial period and hence set the stage for ice sheet-thermohaline circulation (THC) interactions. The following iceberg calving scheme is then introduced: when the maximum model height of the North American ice sheet reaches a critical value (2400 m), a prescribed lateral discharged rate is imposed on top of the background discharge rate for a finite time. Per a small prescribed discharge rate, repeated small iceberg calving events occur, which lead to millennial-scale climate cycles with small amplitudes. These are a crude representation of Dansgaard-Oeschger oscillations. Over one such cycle, the zonally averaged January surface air temperature (SAT) drops about 1.5°C at 72.5°N. However, a large prescribed lateral discharge rate leads to the shut down of the THC. In this case, the January SAT drops about 5°C at 72.5°N, the sea ice extent advances equatorward from 57.5° to 47.5°N and the net ice accumulation rate at the grid of maximum ice sheet height is reduced from 0.24 to 0.15 m/y. Since data strongly suggest that a collapsed THC was not a steady state during the last glacial, we restore the THC by increasing the vertical diffusivity in the North Atlantic Ocean for a finite time. The resulting climate cycles associated with conveyor-on and conveyor-off phases have much larger amplitudes; furthermore, the strong iceberg calving events lead to a larger loss of ice sheet mass and hence the period of the oscillations is longer (several thousand years). This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

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