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1.
In southwest Western Australia, strong and persistent sea breezes are common between September and February. We hypothesized
that on the inner continental shelf, in the absence of tidal forcing, the depth, magnitude, and lag times of the current speed
and direction responses to sea breezes would vary though the water column as a function of the sea breeze intensity. To test
this hypothesis, field data were used from four sites were that were in water depths of up to 13 m. Sites were located on
the inner continental shelf and were on the open coast and in a semi-enclosed coastal embayment. The dominant spectral peak
in currents at all sites indicated that the majority of the spectral energy contained in the currents was due to forcing by
sea breezes. Currents were aligned with the local orientation of the shoreline. On a daily basis, the sea breezes resulted
in increased current speeds and also changed the current directions through the water column. The correlation between wind–current
speeds and directions with depth, and the lag time between the onset of the sea breeze and the response of currents, were
dependent on the intensity of the sea breezes. A higher correlation between wind and current speeds occurred during strong
sea breezes and was associated with shorter lag times for the response of the bottom currents. The lag times were validated
with estimates of the vertical eddy viscosity. Solar heating caused the water column to stratify in summer and the sea breezes
overcame this stratification. Sea breezes caused the mixed layer to deepen and the intensity of the stratification was correlated
to the strength of the sea breezes. Weak sea breezes of <5 m s−1 were associated with the strongest thermal stratification of the water column, up to 1°C between the surface and bottom layers
(6 and 10 m below the surface). In comparison, strong sea breezes of >14 m s−1 caused only slight thermal stratification up to 0.5°C. Apart from these effects on the vertical structure of water column,
the sea breezes also influenced transport and mixing in the horizontal dimension. The sea breezes in southwest Western Australia
rotated in an anticlockwise direction each day and this rotation was translated into the currents. This current rotation was
more prominent in surface currents and in the coastal embayment compared to the open coast. 相似文献
2.
本文利用高分辨率WRF模式对2012年7月20日发生在海南地区的一次海风雷暴过程进行模拟,探讨了海南岛复杂地形下海风雷暴的结构、发展演变过程及其触发机制.结果表明,海南岛北部向内陆传播的海风与南部受地形阻挡的海风相遇后会形成海风辐合带,辐合带能影响当地的散度和涡旋特征,为雷暴的发生发展提供有利的动力和热力学条件.海南岛受热带海洋的影响较大,当地的水汽条件和对流潜势长期保持着有利于对流发展的状态,自由对流高度始终处于较低的位置,一旦海风辐合带来的抬升运动克服对流抑制到达自由对流高度后,对流就能自主地发展起来,所以单纯的海风辐合也常常能触发当地的强雷暴.雷暴发生发展过程中对流参数存在明显的变化,其演变曲线的突变位置对雷暴的发生有一定的指示作用.海南岛的海风雷暴过程与当地的复杂地形密切相关,地形的动力阻挡作用影响着低层海风的辐合以及对流的发展. 相似文献
3.
Prakash Mehra Michael N. Tsimplis R. G. Prabhudesai Antony Joseph Andrew G. P. Shaw Y. K. Somayajulu Paolo Cipollini 《Ocean Dynamics》2010,60(4):819-833
The contribution of atmospheric pressure and local wind to sea level variability at Goa (West coast of India) for the period
2007–2008 is investigated. Sea level data from a tide gauge are compared with measured local surface meteorological as well
as oceanographic data. Multilinear regression analysis is used to resolve the dependence of sea level on various forcing parameters.
The multilinear regression analysis performed over approx. 2-year data shows that the local surface meteorological data and
water temperature account for the sea level variability only up to 6%. The accounted sea level variability increases to 25%,
when the local wind and the surface currents obtained from satellite altimetry in the near vicinity of the study area are
incorporated in the regression analysis. The contribution of local wind increases substantially when the regression is performed
over a 2-month duration, and it is variable within the year. During the summer monsoon season (May–September), the sea level
variability attributable to wind is up to 47% and 75%, respectively, for 2007 and 2008; however, it reduces to <20% during
the winter monsoon (November–February) season. A significant part of the variability observed in sea level remains unaccounted
for and is attributed to remote forcing. 相似文献
4.
We address possibilities of minimising environmental risks using statistical features of current-driven propagation of adverse
impacts to the coast. The recently introduced method for finding the optimum locations of potentially dangerous activities
(Soomere et al. in Proc Estonian Acad Sci 59:156–165, 2010) is expanded towards accounting for the spatial distributions of probabilities and times for reaching the coast for passively
advecting particles released in different sea areas. These distributions are calculated using large sets of Lagrangian trajectories
found from Eulerian velocity fields provided by the Rossby Centre Ocean Model with a horizontal resolution of 2 nautical miles
for 1987–1991. The test area is the Gulf of Finland in the northeastern Baltic Sea. The potential gain using the optimum fairways
from the Baltic Proper to the eastern part of the gulf is an up to 44% decrease in the probability of coastal pollution and
a similar increase in the average time for reaching the coast. The optimum fairways are mostly located to the north of the
gulf axis (by 2–8 km on average) and meander substantially in some sections. The robustness of this approach is quantified
as the typical root mean square deviation (6–16 km) between the optimum fairways specified from different criteria. Drastic
variations in the width of the ‘corridors’ for almost optimal fairways (2–30 km for the average width of 15 km) signifies
that the sensitivity of the results with respect to small changes in the environmental criteria largely varies in different
parts of the gulf. 相似文献
5.
利用WRF模式探讨了两种近地层参数化方案(MM5方案和Eta方案)对2013年5月31日海南岛一次海风降水过程模拟的影响.结果表明,改变近地层方案可对当地的海风环流及相应的降水特征产生明显影响,两个试验最重要的差别主要体现在模拟的海风及降水的强度差异上,与MM5试验相比,Eta试验的低层海风及辐合程度更强,相应的降水也更强,表现为岛屿总格点降水量、大于10mm的降水区域、最大格点降水三个量化指标均比较大.通过分析两种方案在不同降水阶段的地表通量及近地层变量场,发现Eta试验模拟的降水前环境场更有利于对流的启动,随着午后热力湍流的不断增强,将MM5方案替换为Eta方案可使近地层感热通量、潜热通量分别增加约3.57%、5.65%,动量通量减小约10.79%,感热、潜热的增加使Eta试验中近地层大气的加热加湿作用更加明显,相应的低层大气不稳定度更高,再配合海风锋前较强的辐合上升运动,局地不稳定能量的释放变的更加容易,因此降水强度更大. 相似文献
6.
Orissa State, a meteorological subdivision of India, lies on the east coast of India close to north Bay of Bengal and to the
south of the normal position of the monsoon trough. The monsoon disturbances such as depressions and cyclonic storms mostly
develop to the north of 15° N over the Bay of Bengal and move along the monsoon trough. As Orissa lies in the southwest sector
of such disturbances, it experiences very heavy rainfall due to the interaction of these systems with mesoscale convection
sometimes leading to flood. The orography due to the Eastern Ghat and other hill peaks in Orissa and environs play a significant
role in this interaction. The objective of this study is to develop an objective statistical model to predict the occurrence
and quantity of precipitation during the next 24 hours over specific locations of Orissa, due to monsoon disturbances over
north Bay and adjoining west central Bay of Bengal based on observations to up 0300 UTC of the day. A probability of precipitation
(PoP) model has been developed by applying forward stepwise regression with available surface and upper air meteorological
parameters observed in and around Orissa in association with monsoon disturbances during the summer monsoon season (June-September).
The PoP forecast has been converted into the deterministic occurrence/non-occurrence of precipitation forecast using the critical
value of PoP. The parameters selected through stepwise regression have been considered to develop quantitative precipitation
forecast (QPF) model using multiple discriminant analysis (MDA) for categorical prediction of precipitation in different ranges
such as 0.1–10, 11–25, 26–50, 51–100 and >100 mm if the occurrence of precipitation is predicted by PoP model. All the above
models have been developed based on data of summer monsoon seasons of 1980–1994, and data during 1995–1998 have been used
for testing the skill of the models. Considering six representative stations for six homogeneous regions in Orissa, the PoP
model performs very well with percentages of correct forecast for occurrence/non-occurrence of precipitation being about 96%
and 88%, respectively for developmental and independent data. The skill of the QPF model, though relatively less, is reasonable
for lower ranges of precipitation. The skill of the model is limited for higher ranges of precipitation.
accepted September 2006 相似文献
7.
The Mediterranean Sea is a region of intense air–sea interactions, with in particular strong evaporation over sea which drives
the thermohaline circulation. The Mediterranean region is also prone to strong precipitation events characterized by low spatial
extent, short duration, and high temporal variability. The impacts of intense offshore precipitation over sea, in the Gulf
of Lions which is a spot for winter deep convection, are investigated using four sensitivity simulations performed at mesoscale
resolution with the eddy-resolving regional ocean model NEMO-MED12. We use various atmospheric fields to force NEMO-MED12,
downscaled from reanalyses with the non-hydrostatic mesoscale Weather Research and Forecasting model but differing in space
resolutions (20 and 6.7 km) or in time frequencies (daily and three-hourly). This numerical study evidences that immediate,
intense, and rapid freshening occurs under strong precipitation events. The strong salinity anomaly induced extends horizontally
(≃50 km) as vertically (down to 50 m) and persists several days after strong precipitation events. The change in the space
resolution of the atmospheric forcing modifies the precipitating patterns and intensity, as well as the shape and the dynamics
of the low-salinity layer formed are changed. With higher forcing frequency, shorter and heavier precipitation falls in the
ocean in the center of the Gulf of Lions, and due to a stronger vertical shear and mixing, the low-salinity anomaly propagates
deeper. 相似文献
8.
In this study an attempt has been made to examine the evolutionary features of the dynamic and thermodynamic characteristics
of the marine atmosphere over the South-East Arabian Sea near 9.22°N, 74.51°E just two to three days prior to the onset of
southwest monsoon over Kerala during 2003 and seek the linkages with the large-scale flow in the lower and middle troposphere
at that time over the region. The marine meteorological data collected onboard ORV Sagarkanya as part of the experiment ARMEX-2003
for 4–8 June, 2003 are used. The monsoon onset over Kerala occurred on 8 June, 2003. The observed changes in the marine atmospheric
boundary layer (MABL) characteristics just two days prior to the onset are discussed. It is observed that the MABL increased
in height up to 4 km on 6 June from an initial height 2.8 km on 5 June. The top of the MABL dried up (Relative Humidity RH
~ 30–40%) with weak and variable winds throughout the day on 6 June while the air at 850 hPa is relatively humid (RH ~ 50–80%)
but not saturated. A sequential increase in RH is associated with a change in the winds from southwesterly to westerly from
6 June onwards until the onset date. The changes in the lower and middle troposphere flow patterns over the Arabian Sea and
Indian region are highlighted. 相似文献
9.
Matthieu Kervyn Gerald G. J. Ernst Jörg Keller R. Greg Vaughan Jurgis Klaudius Evelyne Pradal Frederic Belton Hannes B. Mattsson Evelyne Mbede Patric Jacobs 《Bulletin of Volcanology》2010,72(8):913-931
On September 4, 2007, after 25 years of effusive natrocarbonatite eruptions, the eruptive activity of Oldoinyo Lengai (OL),
N Tanzania, changed abruptly to episodic explosive eruptions. This transition was preceded by a voluminous lava eruption in
March 2006, a year of quiescence, resumption of natrocarbonatite eruptions in June 2007, and a volcano-tectonic earthquake
swarm in July 2007. Despite the lack of ground-based monitoring, the evolution in OL eruption dynamics is documented based
on the available field observations, ASTER and MODIS satellite images, and almost-daily photos provided by local pilots. Satellite
data enabled identification of a phase of voluminous lava effusion in the 2 weeks prior to the onset of explosive eruptions.
After the onset, the activity varied from 100 m high ash jets to 2–15 km high violent, steady or unsteady, eruption columns
dispersing ash to 100 km distance. The explosive eruptions built up a ∼400 m wide, ∼75 m high intra-crater pyroclastic cone.
Time series data for eruption column height show distinct peaks at the end of September 2007 and February 2008, the latter
being associated with the first pyroclastic flows to be documented at OL. Chemical analyses of the erupted products, presented
in a companion paper (Keller et al. 2010), show that the 2007–2008 explosive eruptions are associated with an undersaturated carbonated silicate melt. This new phase
of explosive eruptions provides constraints on the factors causing the transition from natrocarbonatite effusive eruptions
to explosive eruptions of carbonated nephelinite magma, observed repetitively in the last 100 years at OL. 相似文献
10.
During the summer monsoon season over India a range of intraseasonal modulations of the monsoon rains occur due to genesis of weather disturbances over the Bay of Bengal (BOB) and the east Arabian Sea. The amplitudes of the fluctuations in the surface state of the ocean (sea-surface temperature and salinity) and atmosphere are quite large due to these monsoonal modulations on the intraseasonal scale as shown by the data collected during the field programs under Bay of Bengal Monsoon Experiment (BOBMEX) and Arabian Sea Monsoon Experiments (ARMEX). The focus of BOBMEX was to understand the role of ocean-atmospheric processes in organizing convection over the BOB on intra-seasonal scale. ARMEX-I was aimed at understanding the coupled processes in the development of deep convection off the West Coast of India. ARMEX-II was focused on the formation of the mini-warm pool across the southeast Arabian Sea in April-May and its role in the abrupt onset of the monsoon along the Southwest Coast of India and its further progress along the West Coast of India. The paper attempts to integrate the results of the observational studies and brings out an important finding that atmospheric instability is prominently responsible for convective organization whereas the upper ocean parameters regulate the episodes of the intraseasonal oscillations. 相似文献
11.
A first-order leveling survey across the northeast part of the Yellowstone caldera in September 1998 showed that the central
caldera floor near Le Hardy Rapids rose 24±5 mm relative to the caldera rim at Lake Butte since the previous survey in September
1995. Annual surveys along the same traverse from 1985 to 1995 tracked progressive subsidence near Le Hardy Rapids at an average
rate of –19±1 mm/year. Earlier, less frequent surveys measured net uplift in the same area during 1923–1976 (14±1 mm/year)
and 1976–1984 (22±1 mm/year). The resumption of uplift following a decade of subsidence was first detected by satellite synthetic
aperture radar interferometry, which revealed approximately 15 mm of uplift in the vicinity of Le Hardy Rapids from July 1995
to June 1997. Radar interferograms show that the center of subsidence shifted from the Sour Creek resurgent dome in the northeast
part of the caldera during August 1992 to June 1993 to the Mallard Lake resurgent dome in the southwest part during June 1993
to August 1995. Uplift began at the Sour Creek dome during August 1995 to September 1996 and spread to the Mallard Lake dome
by June 1997. The rapidity of these changes and the spatial pattern of surface deformation suggest that ground movements are
caused at least in part by accumulation and migration of fluids in two sill-like bodies at 5–10 km depth, near the interface
between Yellowstone's magmatic and deep hydrothermal systems.
Received: 30 November 1998 / Accepted: 16 April 1999 相似文献
12.
Ki Young Kim Jung Mo Lee Wooil Moon Chang-Eob Baag Heeok Jung Myung Ho Hong 《Pure and Applied Geophysics》2007,164(1):97-113
In order to investigate the velocity structure of the southern part of the Korean peninsula, seismic refraction profiles were
obtained along a 294-km WNW-ESE line and a 335-km NNW-SSE line in 2002 and 2004, respectively. Seismic waves were generated
by detonating 500–1000 kg explosives in drill holes at depths of 80–150 m. The seismic signals were recorded by portable seismometers
at nominal intervals of 1.5–1.7 km. Separate velocity tomograms were derived from first arrival times using a series expansion
method of travel-time inversion. The raypaths indicate several mid-crust interfaces including those at approximate depths
of 2–3, 15–17, and 22 km. The Moho discontinuity with refraction velocity of 7.8 to 8.4 km/s has a maximum depth of 37–39
km under the southern central portion of the peninsula. The Moho becomes shallower as the Yellow Sea and the East Sea are
approached on the west and east coasts of the peninsula, respectively. The depth of the 7.6 km/s velocity contour varies from
29.4 km to 36.5 km. The discrepancy in depth between the seismological Moho and the interpreted critically refracting interface
may result from the presence of a gradual transition between the crust and mantle. The velocity tomograms show particular
crustal structures including (1) the existence of an over 70-km wide low-velocity zone centered at 6–7 km depth under the
Okchon fold belt and Ryeongnam massif, (2) existence of high-velocity materials under the Gyeongsang basin, and (3) the downward
extension of the Yeongdong fault to depths greater than 10 km. 相似文献
13.
The rates of passive degassing from volcanoes are investigated by modelling the convective overturn of dense degassed and
less dense gas-rich magmas in a vertical conduit linking a shallow degassing zone with a deep magma chamber. Laboratory experiments
are used to constrain our theoretical model of the overturn rate and to elaborate on the model of this process presented by
Kazahaya et al. (1994). We also introduce the effects of a CO2–saturated deep chamber and adiabatic cooling of ascending magma. We find that overturn occurs by concentric flow of the magmas
along the conduit, although the details of the flow depend on the magmas' viscosity ratio. Where convective overturn limits
the supply of gas-rich magma, then the gas emission rate is proportional to the flow rate of the overturning magmas (proportional
to the density difference driving convection, the conduit radius to the fourth power, and inversely proportional to the degassed
magma viscosity) and the mass fraction of water that is degassed. Efficient degassing enhances the density difference but
increases the magma viscosity, and this dampens convection. Two degassing volcanoes were modelled. At Stromboli, assuming
a 2 km deep, 30% crystalline basaltic chamber, containing 0.5 wt.% dissolved water, the ∼700 kg s–1 magmatic water flux can be modelled with a 4–10 m radius conduit, degassing 20–100% of the available water and all of the
1 to 4 vol.% CO2 chamber gas. At Mount St. Helens in June 1980, assuming a 7 km deep, 39% crystalline dacitic chamber, containing 4.6 wt.%
dissolved water, the ∼500 kg s–1 magmatic water flux can be modelled with a 22–60 m radius conduit, degassing ∼2–90% of the available water and all of the
0.1 to 3 vol.% CO2 chamber gas. The range of these results is consistent with previous models and observations. Convection driven by degassing
provides a plausible mechanism for transferring volatiles from deep magma chambers to the atmosphere, and it can explain the
gas fluxes measured at many persistently active volcanoes.
Received: 26 September 1997 / Accepted: 11 July 1998 相似文献
14.
A temperature spike is reported in the haloclines of three Yucatan sinkholes along a 1 km NW-SE transect from 5 to 4 km inland from the Caribbean coast. The temperature spike decreases in magnitude from 3.5 degrees C to 0.2 degrees C, approaching the coast. The anomaly does not vary diurnally and does not extend down into the underlying sea water. These conditions are inconsistent with explanations such as radiation absorption within the halocline, in situ microbially mediated sulfate reduction within the halocline and the underlying sea water, and sulfide oxidation by photosynthetic purple and green bacteria within the halocline. One explanation consistent with the shape and halocline location of the temperature spike involves a localized sea water convection cell operating near the coast. Cold sea water from the Caribbean Sea enters the coastal limestone at depths of a few hundred meters and heats up because of the geothermal gradient, buoyantly rising in vertical fractures within the unconfined aquifer. Blocked by the less dense fresh water, the movement stops in the halocline where the warm sea water mixes with brackish water. The convection cycle would be completed by the coastward movement of cooling brackish water. The observed temperature anomalies could possibly be snapshots of this warm layer moving coastward. 相似文献
15.
Zonal propagation of kinetic energy and convection in the South China Sea and Indian monsoon regions in boreal summer 总被引：7，自引：0，他引：7
CHEN Longxun GAO Hui HE Jinhai TAO Shiyan & JIN Zuhui .Chinese Academy of Meteorological Sciences Beijing China .Nanjing Institute of Meteorology Nanjing China .Institute of Atmospheric Physics Chinese Academy of Sciences Beijing China 《中国科学D辑(英文版)》2004,47(12):1076-1084
As early as in the 1980s, Chinese scientists hadfirst proposed that there exits two summer monsoonsystems in Asia, namely the East Asian summer mon-soon (EASM) and the Indian summer monsoon(ISM)[1-4]. The two monsoon systems are quite dif-ferent in characteristics. Since then, such issue andconclusion had been documented and approved by alot of studies in the past two decades, and was appliedin the guideline of the South China Sea summer mon-soon experiment (SCSMEX), which was undertak… 相似文献
16.
Scales and structure of frontal adjustment and freshwater export in a region of freshwater influence
Sea surface temperature satellite imagery and a regional hydrodynamic model are used to investigate the variability and structure
of the Liverpool Bay thermohaline front. A statistically based water mass classification technique is used to locate the front
in both data sets. The front moves between 5 and 35 km in response to spring–neap changes in tidal mixing, an adjustment that
is much greater than at other shelf-sea fronts. Superimposed on top of this fortnightly cycle are semi-diurnal movements of
5–10 km driven by flood and ebb tidal currents. Seasonal variability in the freshwater discharge and the density difference
between buoyant inflow and more saline Irish Sea water give rise to two different dynamical regimes. During winter, when cold
inflow reduces the buoyancy of the plume, a bottom-advected front develops. Over the summer, when warm river water provides
additional buoyancy, a surface-advected plume detaches from the bottom and propagates much larger distances across the bay.
Decoupled from near-bed processes, the position of the surface front is more variable. Fortnightly stratification and re-mixing
over large areas of Liverpool Bay is a potentially important mechanism by which freshwater, and its nutrient and pollutant
loads, are exported from the coastal plume system. Based on length scales estimated from model and satellite data, the erosion
of post-neap stratification is estimated to be responsible for exporting approximately 19% of the fresh estuarine discharge
annually entering the system. Although the baroclinic residual circulation makes a more significant contribution to freshwater
fluxes, the episodic nature of the spring–neap cycle may have important implications for biogeochemical cycles within the
bay. 相似文献
17.
Coastal upwelling phenomenon along the China coast in the Yellow Sea during August 2007 is studied using ENVISAT Advanced
Synthetic Aperture Radar (ASAR) data, NOAA Advanced AVHRR series Sea Surface Temperature (SST) data, and NASA QuikSCAT Scatterometer
ocean surface wind data. A dark pattern in an ASAR image is interpreted as coastal upwelling. This is because the natural
biogenic slicks associated with coastal upwelling damp the Bragg waves on the sea surface and thus make the surface smoother.
Most of the incoming radar energy is reflected in the forward direction. As a result, the radar backscatter signal is very
weak. Analyzing the concurrent AVHRR SST image, we find that the dark pattern in the ASAR image is indeed corresponding to
the low SST area. The wind retrieval in the slicks dominant region is biased due to the low Normalised Radar Cross Section
(NRCS) associated with the coastal upwelling. We applied a SST correction to the NRCS values to improve the accuracy of wind
retrieval from ASAR data. 相似文献
18.
The storm surge period of 13–16 November 1977 when there was a major positive surge followed by a negative surge in the Irish
Sea is investigated using a two-dimensional unstructured mesh model of the west coast of Britain. The model accounts for tidal
and external surge forcing across its open boundaries which are situated in the Celtic Sea and off the west coast of Scotland.
Although this period has been examined previously using a uniform finite-difference model, and a finite element model, neither
of these could resolve the Mersey estuary which is the focus of the present study. By using a finite element model with very
high mesh resolution within the Mersey, the spatial variability of surge elevations and currents within the Mersey to rapidly
changing surge dynamics can be examined. The mesh in the model varies from about 7 km in deep water, to the order of 100 m
in the Mersey, with the largest mesh length reaching 17 km in deep offshore regions, and smallest of order 26 m occurring
in shallow coastal regions of the Mersey estuary. The model accounts for wetting/drying which occurs in shallow water coastal
areas. Calculations showed that during the positive surge period, the amplitude and speed of propagation of the surge was
largest in the deep water channels. This gave rise to significant spatial variability of surge elevations and currents within
the estuary. As wind stresses decreased over the Irish Sea, a negative surge occurred over Liverpool Bay and at the entrance
to the Mersey. However, within the Mersey there was a local positive surge which continued to propagate down the estuary.
This clearly showed that although the large scale response of the Irish Sea to changing wind fields occurred rapidly, the
response in the Mersey was much slower. These calculations with a west coast variable mesh model that included a high-resolution
representation of the Mersey revealed for the first time how elevations and currents within the Mersey responded to Irish
Sea surges that rapidly changed from positive to negative. 相似文献
19.
Based on wave equation a fundamental formula for plane wave propagaton is derived, the theoretical method of inverting wave
volocity structure of earth interior through the observational wave field is discussed in this paper. The observational wave
field can be decomposed into the surface plane wave field by using τ −p transform. The maximum amplitude curve in the plane wave field can show stably the change tendency of wave velocity with
depth in the Earth. This property can be used to restrict the solution space. By using the wave field continuation method
more useful information from the observational wave field can be extracted and the inverion solution not only can be obtained
simply and quickly, but also is stable and less influenced by the subjective factor. The wave field continuation is a fine
inversion method.
Theoretical analysis and numerical modelling are carried out in the study of wave field continuation. By applying homomorphic
decovolution the signal — to — noese ratio is improved.
Finaly a sonar refraction profile in the northern part of the South China Sea is interpreted and computed. It is found as
a result that there is a velocity interface from 1.76 km/s to 2.21 km/s at the depth of 1.4 km. The velocity gradients in
the upper and lower layers are 0.54 km · s−1/km and 0.63 km · s−1/km respectively. A discussion of the characteristics of shallow sea structure in the view of tectonic movements is geven.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,13. 41–52, 1991. 相似文献
20.
A set of two hundred shear-wave velocity models of the crust and uppermost mantle in southeast Europe is determined by application
of a sequence of methods for surface-waves analysis. Group velocities for about 350 paths have been obtained after analysis
of more than 600 broadband waveform records. Two-dimensional surface-wave tomography is applied to the group-velocity measurements
at selected periods and after regionalisation, two sets of local dispersion curves (for Rayleigh and Love waves) are constructed
in the period range 8–40 s. The shear-wave velocity models are derived by applying non-linear iterative inversion of local
dispersion curves for grid cells predetermined by the resolving power of data. The period range of observations limits the
velocity models to depths of 70 km in accordance to the penetration of the surface waves with a maximum period of 40 s. Maps
of the Moho boundary depth, velocity distribution above and below Moho boundary, as well as velocity distribution at different
depths are constructed. Well-known geomorphologic units (e.g. the Pannonian basin, southeastern Carpathians, Dinarides, Hellenides,
Rodophean massif, Aegean Sea, western Turkey) are delineated in the obtained models. Specific patterns in the velocity models
characterise the southeast Carpathians and adjacent areas, coast of Albania, Adriatic coast of southern Italy and the southern
coast of the Black Sea. The models obtained in this study for the western Black Sea basin shows the presence of layers with
shear-wave velocities of 3.5 km/s–3.7 km/s in the crust and thus do not support the hypothesis of existence of oceanic structure
in this region. 相似文献