共查询到20条相似文献，搜索用时 22 毫秒
1.
Averaged seasonal variations of wind perturbation intensities and vertical flux of horizontal momentum produced by internal gravity waves (IGWs) with periods 0.2/1 h and 1/6 h are studied at the altitudes 65/80 km using the MU radar measurement data from the middle and upper atmosphere during 1986/1997 at Shigaraki, Japan (35°N, 136°E). IGW intensity has maxima in winter and summer, winter values having substantial interannual variations. Mean wave momentum flux is directed to the west in winter and to the east in summer, opposite to the mean wind in the middle atmosphere. Major IGW momentum fluxes come to the mesosphere over Shigaraki from the Pacific direction in winter and continental Asia in summer. 相似文献
2.
The role of oceanic tide, wind stress, freshwater river inflows, and waves in the long-term circulation and residence time
in óbidos Lagoon is investigated using a sensitivity analysis carried out by means of a two-dimensional model. MOHID modeling
system coupled to Steady-State Spectral Wave model for simulate óbidos Lagoon circulation were implemented. For residence
time calculus, a Lagrangian transport model was used. Tidal forcing is shown to be the dominant forcing, although storm waves
must be considered to simulate accurately the long-term circulation. Tidal forcing enhances a spatial distribution in water
residence time. Renewal time scales varies from values of 2 days in the near-ocean areas and 3 weeks in the inner areas. Freshwater
river inflows decrease the residence time, while waves increase. In heavy rain periods, the water residence time decreases
by about 40% in the upper lagoon. When wave forcing is considered, the residence time increases between 10% and 50% depending
on lagoon area. The increase in residence time is explained by the sea level rise within lagoon (~1 m above average lagoon
sea level) during storm wave periods. Average residence time is 16 days for tidal forcing, 9 days when the rivers are included
(wet period), and 18 days when the waves are considered. 相似文献
3.
《Journal of Atmospheric and Solar》2002,64(8-11):1217-1228
Long period variations in the mesosphere wind have been observed for some time by ground-based radars. These planetary scale disturbances have reoccurring periods at or near 5–7, 10, and 16 days and at times dominate the wind field at mesospheric heights. Recently, due to the continuous operation of several of the MLT radars and the availability of measurements from the UARS satellite, it has been possible to compare observations during periods of large planetary wave activity. Wind measurements from four MLT radars; the meteor radars at Durham, NH (43°N,71°W) and Sheffield, UK (53°N,2°W) and MF radars at Urbana, IL (40°N,88°W) and Saskatoon, Canada (52°N,107°W) were compared with the HRDI measurements during intervals when 7-d planetary waves were present. Wind data from the HRDI instrument on UARS has been processed to show the latitudinal structure and the seasonal variation of the planetary scale wind variation. The phases and amplitudes of the waves as determined by both the satellite and the radars are in good agreement. The ground-based measurements show large modulation of tides by these long period components, and also show comparable responses of these low frequency components over thousands of kilometers. The satellite and the ground-based results both indicate a preponderance of wave occurrence during the equinoxes and at preferred latitudes. 相似文献
4.
Observations showed that the main engine water exhaust plumes from space shuttles released at ～110 km altitude from Florida could be transported over thousands of kilometers northward or southward, reaching the Arctic after a day or so, and in one case Antarctica after three days (Stevens et al., 2003, Stevens et al., 2005). In this work, we study the meridional transport associated with the quasi-two-day wave (QTDW) and migrating tides. Diagnostic calculations are performed to trace the particle trajectories using winds from the Thermosphere–Ionosphere–Mesosphere-Electrodynamics General Circulation Model (TIME-GCM) simulations for January, when the amplitude of the QTDW usually peaks. The calculations demonstrate that the mean meridional circulation, a QTDW or a migrating tide cannot individually sustain planetary-scale meridional transport for one to three days, but the combined effects of a QTDW and a tide can. In particular, when the QTDW and the tides are scaled according to the observed amplitudes, particles released at ～110 km and appropriate longitudes/local times can undergo transport fast enough to reach Antarctica within three days as observed. The magnitude and direction of the transport depend on the amplitudes and phases of the tides and the QTDW. These simulations thus suggest that the observed rapid planetary-scale meridional transport of the shuttle main engine plume can be driven by planetary waves and tides. 相似文献
5.
Anna Zacharioudaki Shunqi Pan Dave Simmonds Vanesa Magar Dominic E. Reeve 《Ocean Dynamics》2011,61(6):807-827
In this paper, we investigate changes in the wave climate of the west-European shelf seas under global warming scenarios.
In particular, climate change wind fields corresponding to the present (control) time-slice 1961–2000 and the future (scenario)
time-slice 2061–2100 are used to drive a wave generation model to produce equivalent control and scenario wave climate. Yearly
and seasonal statistics of the scenario wave climates are compared individually to the corresponding control wave climate
to identify relative changes of statistical significance between present and future extreme and prevailing wave heights. Using
global, regional and linked global–regional wind forcing over a set of nested computational domains, this paper further demonstrates
the sensitivity of the results to the resolution and coverage of the forcing. It suggests that the use of combined forcing
from linked global and regional climate models of typical resolution and coverage is a good option for the investigation of
relative wave changes in the region of interest of this study. Coarse resolution global forcing alone leads to very similar
results over regions that are highly exposed to the Atlantic Ocean. In contrast, fine resolution regional forcing alone is
shown to be insufficient for exploring wave climate changes over the western European waters because of its limited coverage.
Results obtained with the combined global–regional wind forcing showed some consistency between scenarios. In general, it
was shown that mean and extreme wave heights will increase in the future only in winter and only in the southwest of UK and
west of France, north of about 44–45° N. Otherwise, wave heights are projected to decrease, especially in summer. Nevertheless,
this decrease is dominated by local wind waves whilst swell is found to increase. Only in spring do both swell and local wind
waves decrease in average height. 相似文献
6.
E. Tragou V. Zervakis E. Papageorgiou S. Stavrakakis V.Lykousis 《Continental Shelf Research》2005,25(19-20):2315
This work constitutes an attempt to assess the relative importance of natural versus anthropogenic forcing for sediment resuspension on the shelf of the Thermaikos Gulf (NW Aegean) through a 2-year experiment in the framework of the E.U. project INTERPOL. Four periods of different hydrographic characteristics were identified, including two periods of stronger vertical homogenisation and two of stratified conditions. The former periods were characterized by stronger near-bed currents, while relatively weak internal wave motions dominated the periods of stratification. The near-bed currents showed strong coherence with the wind during the period of full homogenisation, whereas during stratification periods the wind provided indirect forcing evident mostly in the internal-wave bands. The site was too deep for the surface waves to cause any sediment resuspension. In conclusion, the observed near-bed currents at the site of interest did not appear to produce significant local resuspension of sediment; notably, the current-turbidity correlation suggested a shoreward transport of suspended material. The large-scale turbidity variability was rather related to the onset of the trawling period in mid-October 2001 and the increased riverine discharge in late summer/autumn 2002. 相似文献
7.
《Journal of Atmospheric and Solar》2008,70(1):123-137
Middle atmosphere temperatures have been measured by in situ and by remote sensing instruments for several decades. Extensive temperature measurements by rocket-borne falling spheres (FS) were performed from Andøya Rocket Range in northern Norway from the late 1980s onwards. About 90 rockets were successfully launched within eight measurement campaigns and compiled to an empirical temperature statistic. About half of these measurements were in July and August. Since 1997 the Bonn University Rayleigh/Mie/Raman lidar has been operated at Esrange in northern Sweden during winter as well as during summer. One hundred and eight night mean temperature profiles were obtained for July and August from this data set and have been compared to the FS-statistics. A systematic difference could be observed, i.e. the weekly average temperatures taken from the FS-based empirical temperature statistics are up to 10 K warmer than the temperatures measured by lidar, depending on altitude. In particular comparisons during August show larger differences than comparisons with July data. Temperatures were additionally derived from the Rayleigh-scattered light of the Bonn University Na-resonance lidar which was operated during the 1980s at Andøya. No systematic differences between these measurements and the FS-data were found. Gravity waves, tides, volcanic aerosol, and the solar cycle are not likely to cause the observed differences, since their influence is minimised either by data selection (gravity waves and tides) or by measurement times (volcanic aerosol, solar cycle). Additionally to the temperature difference a change in the gravity wave activity was observed, in particular during summer 2002 and 2006. During these years also noctilucent clouds occurred rather late in the season. The latest unambiguous observation of a noctilucent cloud by the U. Bonn lidar at Esrange was on 24 August 2006. All these observations are indications of a long-term temperature change in the polar summer middle atmosphere as predicted by model calculations. While similar changes have already been observed at middle and low latitudes, temperature trend analyses for the polar atmosphere did not reveal any variation up to now. 相似文献
8.
Heat waves (periods of extremely hot summer weather) in the region of south Moravia are in the focus of this study. The introduced definition consists of three requirements imposed on the period that is considered a heat wave: at least three days with T
MAX
30.0°C must be observed; the mean T
MAX
over the whole period is at least 30.0°C; and T
MAX
must not drop below 25.0°C. To compare the severity of the individual heat waves, various characteristics (duration, number of tropical days, peak temperature, cumulative temperature excess, precipitation amount) are examined. The heat wave index HWI is defined to express the severity of heat waves in the most comprehensive way.
An extraordinary heat wave occurred in July and August 1994; it lasted more than a month at several stations, while the duration of a typical heat wave is only 4 - 7 days. The extremely long unbroken period of tropical days, and even of days with T
MAX
32.0°C, represents the most distinct feature of the severe 1994 heat wave. With regard to heat wave characteristics, the summer temperature exceptionality of the early 1990s is indubitable. 相似文献
9.
In this short paper the exclusion circles and vertical phase locities for gravity waves launched from the ground into a time-varying wind are studied using a ray-tracing technique. It is shown that waves with initial observed phase speeds that should place them within the local temporally varying exclusion circle, are often Doppler shifted outside of the circle. This, and the finite lifetime of some critical levels, allow waves to survive the critical layer and reach higher altitudes. Also, for slower phase-speed waves, the temporally varying wind can shift the observed frequency to negative values, so that the observed phase motions will be opposite (i.e. horizontally reversed and vertically upward), even though the energy still propagates upward. This effect can also cause the phase velocity to move inside the local exclusion circle. Due to the directional filtering of wave sources by the stratospheric wind, the percentage of such reverse-propagating waves will change systematically with local time and height in our simplified but realistic model. These results are related to ground-based systems, optical and radar, which sample the wind field and gravity waves in the middle atmosphere. 相似文献
10.
N. M. Gavrilov 《Annales Geophysicae》1997,15(12):1570-1580
The mechanism of generation of internal gravity waves (IGW) by mesoscale turbulence in the troposphere is considered. The equations that describe the generation of waves by hydrodynamic sources of momentum, heat and mass are derived. Calculations of amplitudes, wave energy fluxes, turbulent viscosities, and accelerations of the mean flow caused by IGWs generated in the troposphere are made. A comparison of different mechanisms of turbulence production in the atmosphere by IGWs shows that the nonlinear destruction of a primary IGW into a spectrum of secondary waves may provide additional dissipation of nonsatu-rated stable waves. The mean wind increases both the effectiveness of generation and dissipation of IGWs propagating in the direction of the wind. Competition of both effects may lead to the dominance of IGWs propagating upstream at long distances from tropospheric wave sources, and to the formation of eastward wave accelerations in summer and westward accelerations in winter near the mesopause. 相似文献
11.
Suspended sediment fluxes at an intertidal flat: The shifting influence of wave,wind, tidal,and freshwater forcing 总被引：1，自引：0，他引：1
Using in situ, continuous, high frequency (8–16 Hz) measurements of velocity, suspended sediment concentration (SSC), and salinity, we investigate the factors affecting near-bed sediment flux during and after a meteorological event (cold front) on an intertidal flat in central San Francisco Bay. Hydrodynamic forcing occurs over many frequency bands including wind wave, ocean swell, seiching (500–1000 s), tidal, and infra-tidal frequencies, and varies greatly over the time scale of hours and days. Sediment fluxes occur primarily due to variations in flow and SSC at three different scales: residual (tidally averaged), tidal, and seiching. During the meteorological event, sediment fluxes are dominated by increases in tidally averaged SSC and flow. Runoff and wind-induced circulation contribute to an order of magnitude increase in tidally averaged offshore flow, while waves and seiching motions from wind forcing cause an order of magnitude increase in tidally averaged SSC. Sediment fluxes during calm periods are dominated by asymmetries in SSC over a tidal cycle. Freshwater forcing produces sharp salinity fronts which trap sediment and sweep by the sensors over short (∼30 min) time scales, and occur primarily during the flood. The resulting flood dominance in SSC is magnified or reversed by variations in wind forcing between the flood and ebb. Long-term records show that more than half of wind events (sustained speeds of greater than 5 m/s) occur for 3 h or less, suggesting that asymmetric wind forcing over a tidal cycle commonly occurs. Seiching associated with wind and its variation produces onshore sediment transport. Overall, the changing hydrodynamic and meteorological forcing influence sediment flux at both short (minutes) and long (days) time scales. 相似文献
12.
One of the main challenges of the Copernicus Marine Service is the implementation of coupled ocean/waves systems that accurately estimate the momentum and energy fluxes provided by the atmosphere to the ocean. This study aims to investigate the impact of forcing the Nucleus for European Modelling of the Ocean (NEMO) ocean model with forecasts from the wave model of Météo-France (MFWAM) to improve classical air-sea flux parametrizations, these latter being mostly driven by the 10-m wind. Three wave-related processes, namely, wave-state-dependent stress, Stokes drift-related effects (Stokes-Coriolis force, Stokes drift advection on tracers and on mass), and wave-state-dependent surface turbulence, are examined at a global scale with a horizontal resolution of 0.25°. Three years of sensitivity simulations (2014–2016) show positive feedback on sea surface temperature (SST) and currents when the wave model is used. A significant reduction in SST bias is observed in the tropical Atlantic Ocean. This is mainly due to the more realistic momentum flux provided by the wave model. In mid-latitudes, the most interesting impact occurs during the summer stratification, when the wind is low and the wave model produces a reduction in the turbulence linked with wave breaking. Magnitudes of the large-scale currents in the equatorial region are also improved by 10% compared to observations. In general, it is shown that using the wave model reduces on average the momentum and energy fluxes to the ocean in tropical regions, but increases them in mid-latitudes. These differences are in the order of 10 to 20% compared with the classical parametrizations found in stand-alone ocean models. 相似文献
13.
This study uses a series of scenarios of wave (boundary) and wind (local) forcing to examine the sensitivity and to quantify
the effects associated with nesting ProWAM and POLCOMS models for downscaling predictions of waves in the Irish Sea. The model
results show that the response of the modelling system to the wave and wind forcing during the downscaling varies widely depending
on wind conditions. Generally, the wave forcing has a greater effect on overall wave prediction in most of the Irish Sea,
except for the eastern Irish Sea/Liverpool Bay. The study also suggests detailed look-up tables at specific locations to quantify
the impacts of the different forcing scenarios over the Irish Sea, which can be readily extended to the location on any other
sites. 相似文献
14.
Sandy beaches typically have one or more shore-parallel bars with superimposed smaller-scale three-dimensional (3D) bars. Knowledge of their morphodynamic behaviour under more realistic wave conditions is limited. This study investigates the response of beaches with two shore-parallel bars to sinusoidally time-varying angles of incidence, using a non-linear morphodynamic model. Different periods and amplitudes of this sinusoidal variation are considered, as well as different time-mean wave angles. For time-invariant and normally incident waves, results show that alongshore rhythmic 3D bars form in the domains of inner and outer shore-parallel bars. The 3D bars in the inner domain are coupled at half the outer-bars wavelength. This phase coupling breaks up when the wave angle varies in time. Initially, regular 3D bars form in the inner domain (free behaviour), which become irregular when 3D bars develop in the outer domain (forced behaviour). The heights of the 3D bars oscillate with time, reaching maximum values when the forcing period is comparable to the system adjustment time scale (∼ 10–20 days). For a time-varying wave angle around an oblique mean, alongshore migrating 3D bars emerge in both inner and outer domains. In contrast, for an oblique (constant) wave angle, 3D bars only form in the inner domain and they hardly migrate alongshore. For any forcing period, the dominant response period of the oscillating bar heights is at half the forcing period when waves are (on average) normally incident, and it equals the forcing period when waves are on average obliquely incident. Compared with time-invariant angles, heights of inner and outer 3D bars are (on average) smaller and larger, respectively, when the angle varies with time, particularly for forcing periods in the order of the system adjustment time scale. Increasing the amplitude of the time-varying wave angle weakens bar growth. Explanations of these results are also provided. 相似文献
15.
16.
The linear theory predicts that Rossby waves are the large scale mechanism of adjustment to perturbations of the geophysical fluid. Satellite measurements of sea level anomaly (SLA) provided sturdy evidence of the existence of these waves. Recent studies suggest that the variability in the altimeter records is mostly due to mesoscale nonlinear eddies and challenges the original interpretation of westward propagating features as Rossby waves. The objective of this work is to test whether a classic linear dynamic model is a reasonable explanation for the observed SLA. A linear-reduced gravity non-dispersive Rossby wave model is used to estimate the SLA forced by direct and remote wind stress. Correlations between model results and observations are up to 0.88. The best agreement is in the tropical region of all ocean basins. These correlations decrease towards insignificance in mid-latitudes. The relative contributions of eastern boundary (remote) forcing and local wind forcing in the generation of Rossby waves are also estimated and suggest that the main wave forming mechanism is the remote forcing. Results suggest that linear long baroclinic Rossby wave dynamics explain a significant part of the SLA annual variability at least in the tropical oceans. 相似文献
17.
G. J. Fraser 《Pure and Applied Geophysics》1989,130(2-3):291-301
A medium frequency partial-reflection spaced-antenna wind radar was installed at Scott Base (78S) on Ross Island, Antarctica, in November 1982. Results from this radar for the period December 1982 to October 1984 inclusive are compared with simultaneous measurements made with a similar radar at Christchurch (44S), N. Z. Monthly mean zonal winds measured at 80 km are compared with recent models for the Southern Hemisphere middle atmosphere. There is a general agreement with the models but there is evidence that the Christchurch winter flow was atypical in 1983. 相似文献
18.
19.
S. E. Palo Y. I. Portnyagin J. M. Forbes N. A. Makarov E. G. Merzlyakov 《Annales Geophysicae》1998,16(11):1486-1500
Observations of the horizontal wind field over the South Pole were made during 1995 using a meteor radar. These data have revealed the presence of a rich spectrum of waves over the South Pole with a distinct annual occurrence. Included in this spectrum are long-period waves, whose periods are greater than one solar day, which are propagating eastward. These waves exhibit a distinct seasonal occurrence where the envelope of wave periods decreases from a period of 10 days near the fall equinox to a minimum of 2 days near the winter solstice and then progresses towards a period near 10 days at the spring equinox. Computation of the meridional gradient of quasi-geostrophic potential vorticity has revealed a region in the high-latitude upper mesosphere which could support an instability and serve as a source for these waves. Estimation of the wave periods which would be generated from an instability in this region closely resembles the observed seasonal variation in wave periods over the South Pole. These results are consistent with the hypothesis that the observed eastward propagating long-period waves over the South Pole are generated by an instability in the polar upper mesosphere. However, given our limited data set we cannot rule out a stratospheric source. Embedded in this spectrum of eastward propagating waves during the austral winter are a number of distinct wave events. Eight such wave events have been identified and localized using a constant-Q filter bank. The periods of these wave events ranges from 1.7 to 9.8 days and all exist for at least 3 wave periods. Least squares analysis has revealed that a number of these events are inconsistent with a wave propagating zonally around the geographic pole and could be related to waves propagating around a dynamical pole which is offset from the geographic pole. Additionally, one event which was observed appears to be a standing oscillation. 相似文献
20.
Elodie Charles Déborah Idier Pascale Delecluse Michel Déqué Gonéri Le Cozannet 《Ocean Dynamics》2012,62(6):831-848
The knowledge of offshore and coastal wave climate evolution towards the end of the twenty-first century is particularly important for human activities in a region such as the Bay of Biscay and the French Atlantic coast. Using dynamical downscaling, a high spatial resolution dataset of wave conditions in the Bay of Biscay is built for three future greenhouse gases emission scenarios. Projected wave heights, periods and directions are analysed at regional scale and more thoroughly at two buoys positions, offshore and along the coast. A general decrease of wave heights is identified (up to ?20?cm during summer within the Bay off Biscay), as well as a clockwise shift of summer waves and winter swell coming from direction. The relation between those changes and wind changes is investigated and highlights a complex association of processes at several spatial scales. For instance, the intensification and the northeastward shift of strong wind core in the North Atlantic Ocean explain the clockwise shift of winter swell directions. During summer, the decrease of the westerly winds in the Bay of Biscay explains the clockwise shift and the wave height decrease of wind sea and intermediate waves. Finally, the analysis reveals that the offshore changes in the wave height and the wave period as well as the clockwise shift in the wave direction continue toward the coast. This wave height decrease result is consistent with other regional projections and would impact the coastal dynamics by reducing the longshore sediment flux. 相似文献