共查询到20条相似文献，搜索用时 233 毫秒
1.
Sea level variations and extreme events are a major threat for coastal zones. This threat is expected to worsen with time because low-lying coastal areas are expected to become more vulnerable to flooding and land loss as sea level rises in response to climate change. Sea level variations in the coastal ocean result from a combination of different processes that act at different spatial and temporal scales. In this study, the relative importance of processes causing coastal sea level variability at different time-scales is evaluated. Contributions from the altimetry-derived sea-level (including the sea level rise due to the ocean warming and land ice loss in response to climate change), dynamical atmospheric forcing induced sea level (surges), wave-induced run-up and set-up, and astronomical tides are estimated from observational datasets and reanalyses. As these processes impact the coast differently, evaluating their importance is essential for assessment of the local coastline vulnerability. A case study is developed in the Gulf of Guinea over the 1993–2012 period. The leading contributors to sea level variability off Cotonou differ depending on the time-scales considered. The trend is largely dominated by processes included in altimetric data and to a lesser extent by swell-waves run-up. The latter dominates interannual variations. Swell-waves run-up and tides dominate subannual variability. Extreme events are due to the conjunction of high tides and large swell run-up, exhibiting a clear seasonal cycle with more events in boreal summer and a trend mostly related to the trend in altimetric-derived sea-level. 相似文献
2.
Aeromagnetic data collected in areas with severe diurnal magnetic variations (auroral zones) are difficult to level. This paper describes levelling of an aeromagnetic survey where such conditions prevail, and where sophisticated levelling techniques are needed. Corrections based on piecewise low‐order polynomial functions are often used to minimize mis‐ties in aeromagnetic data. We review this technique and describe similar mis‐tie fitting methods based on low‐pass filter levelling, tensioned B‐spline levelling and median levelling. It is demonstrated that polynomial levelling, low‐pass filter levelling and tensioned B‐spline levelling depend on the careful editing of outlying mis‐ties to avoid the introduction of false anomalies. These three techniques are equally efficient at removing level errors. Median levelling also removes level errors efficiently, but it is more robust in the sense that mis‐tie editing is not required. This is due to the inherent noise‐removal capabilities of the median filter. After mis‐tie editing, the total field anomalies of the other three techniques closely resemble the unedited median‐levelled total field anomaly. 相似文献
3.
Meltwater from the Greenland Ice Sheet (GIS) has been a major contributor to sea level change in the recent past. Global and regional sea level variations caused by melting of the GIS are investigated with the finite element sea-ice ocean model (FESOM). We consider changes of local density (steric effects), mass inflow into the ocean, redistribution of mass, and gravitational effects. Five melting scenarios are simulated, where mass losses of 100, 200, 500, and 1000 Gt/yr are converted to a continuous volume flux that is homogeneously distributed along the coast of Greenland south of 75°N. In addition, a scenario of regional melt rates is calculated from daily ice melt characteristics. The global mean sea level modeled with FESOM increases by about 0.3 mm/yr if 100 Gt/yr of ice melts, which includes eustatic and steric sea level change. In the global mean the steric contribution is one order of magnitude smaller than the eustatic contribution. Regionally, especially in the North Atlantic, the steric contribution leads to strong deviations from the global mean sea level change. The modeled pattern mainly reflects the structure of temperature and salinity change in the upper ocean. Additionally, small steric variations occur due to local variability in the heat exchange between the atmosphere and the ocean. The mass loss has also affects on the gravitational attraction by the ice sheet, causing spatially varying sea level change mainly near the GIS, but also at greater distances. This effect is accounted for by using Green's functions. 相似文献
4.
Sea level extremes and their temporal variability have been explored based on the hourly measurements at Marseille tide gauge for the period 1885–2008. A careful quality check has first been applied to the observations to ensure consistency of the record by eliminating outliers and datum shifts. Yearly percentiles have been used to investigate long-term trends of extremes revealing that secular variations in extremes are linked to mean sea level changes. The associated decadal changes show discrepancies between mean sea level trend and extreme fluctuations, due to the influence of the atmospheric forcing. A local regression model based on the generalized Pareto distribution has been applied to derive trends in return levels. The 50-years return levels reach values between 80 and 120 cm. The most significant changes in return levels are characterized by an increase since the 1970s. 相似文献
5.
新的全球冰川均衡调整(GIA)模型RF3L20(β=0.4)+ICE-4G考虑了地幔黏滞度沿横向的变化,其黏滞度参数得到大地测量、历史相对海平面变化观测和地震剪切波层析模型的较好约束.本文利用该模型预测了东亚现今重力变化和海平面变化,根据当前末次冰川时空变化和黏滞度参考模型中下地幔下部黏滞度认识的差异,评估了预测的不确定性.结果表明,GIA对东亚地区重力场和海平面长期变化有显著的影响:例如,在哈尔滨、长春、泰安、蓟县、郑州、武汉等测站,GIA重力影响达几十纳伽,可用超导重力仪和未来原子重力仪观测出来;在东亚大陆GIA对GRACE监测的等效水柱长期变化的影响为3%~10%,其中青藏高原西部、华北和三峡地区的影响较大.在东海-太平洋区,GIA的相对影响高达20%~40%;GIA使东亚海域绝对海平面以0.27~0.37 mm/a的速率在长期下降,在黄海、东海卫星测高监测的绝对海平面长期变化中,GIA的相对影响分别达6.9%和7.5%;在58个验潮站,平均相对海平面长期上升速率为2.22 mm/a,GIA影响为-0.17 mm/a,其中14个测站GIA的影响达-0.3~-0.4 mm/a.本文GIA预测的结果,对在东亚地区发现弱的地球动力学过程信号、监测水质量长期变化、监测海平面长期变化和分析其机制,提供精密的改正模型. 相似文献
6.
Bernhard Siemon 《Journal of Applied Geophysics》2009,67(3):206-218
For about three decades helicopter-borne electromagnetic (HEM) measurements have been used to reveal the resistivity distribution of the upper one hundred metres of the earth's subsurface. HEM systems record secondary fields, which are 3–6 orders of magnitude smaller than the transmitted primary fields. As both the primary fields and the secondary fields are present at the receivers, well-designed bucking coils are often used to reduce the primary fields at the receivers to a minimum. Remaining parts of the primary fields, the zero levels, are generally corrected by subtracting field values recorded at high altitudes (standard zero levelling) or estimated from resistivities of neighbouring lines or from resistivity maps (advanced zero levelling). These zero-levelling techniques enable the correction for long-term, quasi-linear instrumental drift. Short-term variations caused by temperature changes due to altitude variations, however, cannot be completely corrected by this procedure resulting in stripe patterns on thematic maps.Statistical methods and/or 2-D filter techniques called statistical levelling (tie-line levelling) and empirical levelling (microlevelling), respectively, used to correct stripe patterns in airborne geophysical data sets are, in general, not directly applicable to HEM data. Because HEM data levelling faces the problem that the parameter affected by zero-level errors, the secondary field, differs from the parameter generally levelled, the apparent resistivity. Furthermore, the dependency of the secondary field on both the resistivity of the subsurface and the sensor altitude is strongly nonlinear.A reasonable compromise is to microlevel both half-space parameters: apparent resistivity and apparent depth, followed by a recalculation of the secondary field components based on the half-space parameters levelled. Advantages and disadvantages of the diverse levelling techniques are discussed using a HEM data set obtained in a hilly region along the Saale River between the cities of Saalfeld and Jena in central Germany. It turns out from a comparison of apparent resistivity and apparent depth maps derived from levelled HEM data that manually advanced zero levelling of major level errors and automatic microlevelling of remaining minor level errors yield the best results. 相似文献
7.
Both coastal and global mean sea level rise by about 3.0 ± 0.5 mm/year from January 1993 to December 2004. Over shorter intervals the coastal sea level rises faster and over longer intervals slowly than the global mean, which trend is almost constant for each interval and is equal to 2.9 ± 0.5 mm/year in 1993–2008. The different trends are due to the higher interannual variability of coastal sea level, caused by the sea level regional variability, that is further averaged out when computing the global mean.Coastal sea level rise is well represented by a selected set of 267 stations of the Permanent Service for Mean Sea Level and by the corresponding co-located altimeter points. Its departure from coastal sea level computed from satellite altimetry in a 150 km distance from coast, dominated by a large rise in the Eastern Pacific, is due to the regional interannual variability.Regionally the trends of the coastal and open-ocean sea level variability are in good agreement and the main world basins have a positive averaged trend. The interannual variability is highly correlated with the El Nino Southern Oscillation (SO) and the North Atlantic Oscillation (NAO) climatic indices over both the altimeter period and the interval 1950–2001. Being the signal of large scale a small number of stations with good spatial coverage is needed. The reconstruction of the interannual variability using the spatial pattern from altimetry and the temporal patterns from tide gauges correlated to NAO and SOI restitutes about 50% of the observed interannual variability over 1993–2001. 相似文献
8.
The characteristics of air pollution in Tarragona (Spain) were investigated. Tarragona has an important petrochemical industry in a coastal region with a complex terrain. The numerical study was made in sea breeze conditions with a three-dimensional mesoscale model. Temporal and spatial variations of the wind fields have been used in the Eulerian equation for a non-reactive pollutant. The results of this study reveal the complexity of the dispersion patterns due to the combined effects of the sea breeze circulation and the orography. This work presents a comparison between the model output and the observed wind data by sodar and surface wind measurements. The evaluation shows that the model is capable of providing very realistic wind fields within this domain. 相似文献
9.
Yukio Hagiwara 《Surveys in Geophysics》1974,1(3):305-323
T. Inoh was the first who completed a nation-wide map of Japan, in the beginning of the 19th century. He determined geodetic positions by distance and angle measurements and by astronomical observations. When Japan entered into its modern era, about 100 years ago, the Military Land Survey was established and has conducted geodetic work in Japan ever since until the end of World War II. A German surveying system belonging to Helmert's school was adopted. The Ministry of Education organized later the Geodetic Commission which promoted the geodetic activities in cooperation with the Military Land Survey. Comparison between the first and second nation-wide triangulation results obtained by the Geographical Survey Institute (GSI), the successor of the Military Land Survey, brought out marked horizontal land-deformations associated with a large earthquake. Repetitions of levelling survey also make it clear that vertical land-movements, well consistent with tide-gauge observation data, take place in association with earthquakes. The extensive subsidence in the Northeast Japan may be explained by assuming a sinking lithosphere, as is argued by the theory of plate tectonics. On the other hand, most local movements are closely correlated to pre-, co- and post-seismic land-deformations. The nation-wide gravity survey carried out by the GSI disclosed a complicated gravity distribution in Japan. Ship-borne gravimeters have now been extensively working at sea. One of the recent highlights of gravimetric work is the detection of secular gravity changes which are in accordance with the secular changes of levelling data. A portable absolute-gravity measuring instrument was constructed by the Earthquake Research Institute although it is still in a testing stage. Much advance has been made in the astrogeodetic observation devices since 1950's. 相似文献
10.
The TOPEX/POSEIDON (T/P) satellite altimeter mission has provided estimates of global mean sea level since late 1992 with a precision of approximately 4 mm. Over the first 3.5 years of the mission, T/P has observed a mean sea level rise of +0.5 mm/year when on-board estimates of the instrument drift are employed (and after correcting for a recently discovered software error), and +2.8 mm/year when an additional external tide gauge-based calibration estimate is used. A preliminary estimate of the error in the latter estimate is 1.3 mm/year, however this issue requires more research. Characterization of the observed sea level variations using Empirical Orthogonal Functions (EOFs) indicates that most of the mean sea level rise can be described by a single mode of the EOF expansion. The spatial characteristics of this mode suggests it is related to the El Nino Southern Oscillation (ENSO) phenomena. EOF analysis of sea level variations from the Semtner/Chervin ocean circulation model reveal a nearly identical mode, although its effect on mean sea level is unknown due to a constant volume constraint used in the model. EOF analysis of measured sea surface temperature (SST) variations also show a mode with similar temporal and spatial structure. However, the concentration of the observed sea level rise in this mode does not preclude the possibility that multiple phenomena have contributed to this mode, thus a link between the observed sea level rise and the ENSO phenomena is only weakly suggested. The absolute value of the observed mean sea level rise will depend on refinements currently being made in the instrument calibration techniques. In addition, the possibility of interannual and decadal variations of global mean sea level requires that a much longer time series of satellite altimetry be collected before variations caused by climate change can be unambiguously detected. 相似文献
11.
Tal Ezer 《Ocean Dynamics》2017,67(5):651-664
Two aspects of the interactions between the Gulf Stream (GS) and the bottom topography are investigated: 1. the spatial variations associated with the north-south tilt of mean sea level along the US East Coast and 2. the high-frequency temporal variations of coastal sea level (CSL) that are related to Gulf Stream dynamics. A regional ocean circulation model is used to assess the role of topography; this is done by conducting numerical simulations of the GS with two different topographies–one case with a realistic topography and another case with an idealized smooth topography that neglects the details of the coastline and the very deep ocean. High-frequency oscillations (with a 5-day period) in the zonal wind and in the GS transport are imposed on the model; the source of the GS variability is either the Florida Current (FC) in the south or the Slope Current (SC) in the north. The results demonstrate that the abrupt change of topography at Cape Hatteras, near the point where the GS separates from the coast, amplifies the northward downward mean sea level tilt along the coast there. The results suggest that idealized or coarse resolution models that do not resolve the details of the coastline may underestimate the difference between the higher mean sea level in the South Atlantic Bight (SAB) and the lower mean sea level in the Mid-Atlantic Bight (MAB). Imposed variations in the model’s GS transport can generate coherent sea level variability along the coast, similar to the observations. However, when the bottom topography in the model is modified (or not well resolved), the shape of the coastline and the continental shelf influence the propagation of coastal-trapped waves and impact the CSL variability. The results can explain the different characteristics of sea level variability in the SAB and in the MAB and help understand unexpected water level anomalies and flooding related to remote influence of the GS. 相似文献
12.
LIU JiPing State Key Laboratory of Numerical Modeling for Atmospheric Sciences Geophysical Fluid Dynamics 《中国科学:地球科学(英文版)》2010,(6)
The impacts of the spatiotemporal variations of sea ice salinity on sea ice and ocean characteristics have not been studied in detail, as the existing climate models neglect or misrepresent this process. To address this issue, this paper formulated a parameterization with more realistic sea ice salinity budget, and examined the sensitivity of sea ice and ocean simulations to the ice salinity variations and associated salt flux into the ocean using a coupled global climate model. Results show that the inclus... 相似文献
13.
J.A. Donato C.D. Honebon W.G.V. Rosser 《Physics of the Earth and Planetary Interiors》1973,7(2):161-166
The M2 (12.42-h period) magnetic field variation present at night in the United Kingdom can be interpreted in terms of sea tides, the main contribution being from the Atlantic Ocean. Osgood et al. (1970) observed a difference between the M2-variations in the total magnetic field (F) variations at Sidmouth (0.8 km from the coast) and Exeter (16 km from the coast) of amplitude 0.8 γ, which must be due to local effects. Analysis of the phase of this difference between Exeter and Sidmouth has shown that it cannot be due entirely to tidally induced electric current systems confined to the English Channel. Measurements with two three-component magnetometers have shown that the night-time variations in the north-south (H) component of 12.42-h period are significantly different at Sidmouth and Exeter. The difference in H is in phase with the expected electric potential difference across Devon due to the difference in the phases of the sea tides in the English Channel and the Bristol Channel. The results of Donato and Rosser (1973) on micropulsations suggest the existence of a region of high conductivity under Exeter. If this connects the English Channel to the Bristol Channel, a current will flow beneath Exeter giving a difference in the M2-variations in H at Exeter and Sidmouth. This difference in H dominates the M2-variations in the total magnetic field (F) variations at Exeter and Sidmouth measured by Osgood et al. (1970). 相似文献
14.
Vertical movements in the Po plain (northern Italy) are controlled by natural and anthropogenic effects. Since Italy is located in the far–field of the former late Pleistocene ice sheets, isostatic deformations are primarily driven by melt water loading and represent a major component of long–term natural movements across the entire Mediterranean. In addition to far–field sources, here we consider the isostatic effects of melting of the nearby Würm Alpine ice–sheet, suggesting that it is possible to put bounds on its maximum thickness, extent and chronology by Holocene relative sea level observations from the northern Adriatic. Using various plausible ice models, and adopting a viscosity profile that matches Holocene relative sea level observations in the Mediterranean, we find that melting of the Alpine ice sheet is always responsible for upward movements in the Po plain, currently at rates of ~ 0.5 mm/yr. When both far– and near–field sources are considered, the rate of sea level change in the Venetian Lagoon for the most reasonable mantle rheology and melting chronology is negative, i.e., opposite to that attributed to human activity and recent climatic variations. However, its amplitude (fractions of mm/yr) is small compared to the secular signal observed by tide gauges (~2 mm/yr), which makes glacial isostasy a second–order mechanism of sea level variation in this region. 相似文献
15.
Sea level change is an important consequence of climate change due to its impact on society and ecosystems. Analyses of tide-gauge data have indicated that the global sea level has risen during the 20th century and several studies predict that the mean sea level will continue to rise during the 21st century, intensifying coastal hazards worldwide. In Portugal, the Ria de Aveiro is expected to be one of the regions most affected by sea level change.The main aim of this study is to evaluate the potential impacts of the mean sea level change on the hydrodynamics and morphodynamics of the Ria de Aveiro. With this purpose, local mean sea level change was projected for the period 2091-2100 relative to 1980-1999, for different Special Report on Emission Scenarios (SRES) scenarios developed by the Intergovernmental Panel on Climate Change (IPCC). These projections revealed an increase in the mean sea level between 0.28 m under scenario B1 and 0.42 m under scenario A2.The results obtained for sea level rise scenario A2 projection were used to force the morphodynamic model MORSYS2D, previously implemented for the Ria de Aveiro. The modelling results were compared with model forecasts for the present sea level. The residual sediment transport and its balance at the lagoon inlet were computed and analysed for both situations. While the residual sediment transport is generally seaward, sediments tend to deposit inside the inlet due to the weak sediment transport at its mouth. The direction of the residual flux will not change with the sea level rise, but sediment fluxes will intensify, and accretion inside the inlet will increase.The rise in mean sea level will also affect the lagoon hydrodynamics. The tidal prism at the lagoon mouth will increase by about 28% in spring tide. In the lower lagoon only a slight increase of the tidal asymmetry is predicted. 相似文献
16.
C. J. van der Veen 《Surveys in Geophysics》1987,9(3-4):389-418
Through the use of fossil fuels as an energy source, mankind is slowly changing the constitution of the atmosphere. The emission of CO2 and other greenhouse gases changes the radiative properties of the earth/atmosphere system, and as a result climate is expected to become warmer. As a starting point for the sea-level rise scenario discussed here it is assumed that the globally-averaged increase of surface air temperatures will amount to 2 to 4°C in the second half of the next century (i.e. around 2085 AD). One of the consequences of this warming is an accelerated rise in sea level, caused by thermal expansion of ocean water and further retreat of mountain glaciers. The Greenland Ice Sheet will also decrease in size, but on the other hand, Antarctica is expected to grow slightly due to increased snowfall. Taken together, the projection for future sea level presented here suggest that by 2085 AD, global sea-level stand will be 28–66 cm higher than the present level, which implies a rate of sea-level rise of about 2 to 4 times that observed during the last 100 yr. Our scenario does not include a contribution resulting from the possible collapse of the West Antarctic Ice Sheet. If this collapse is indeed likely to occur after the major peripheral ice shelves have thinned considerably, the effects on sea level will be small in the coming 100 yr. First, the oceans surrounding Antarctica must have warmed sufficiently to reduce the winter sea-ice extent to allow circumpolar deep water to penetrate into the sub-shelf cavities, thus increasing basal melt rates on the ice shelves. Of course, on longer time scales, West Antarctica could become the major contributor to rising sea level. 相似文献
17.
海平面变化是社会经济发展和科学研究的重要内容.利用1993年1月至2012年12月共20年的TOPEX/Poseidon、Jason-1和Jason-2卫星测高数据,研究中国海海平面的时空变化.首先通过三颗卫星伴飞阶段数据得到三颗卫星之间的逐点海面高系统偏差,进行逐点海面高改正,建立了20年的中国海海面高异常时间序列.分析了中国海海面高异常空间分布,给出了1月到12月月均平均海平面异常的空间变化规律.分析了中国海海面高异常的时变规律,分别给出了年、季度和月的海面上升速率.利用小波分析研究了中国海海面高异常周期变化规律,分别给出了渤海、黄海、东海和南海的海面高变化周期.讨论了ENSO对海面高异常的影响. 相似文献
18.
Alix Lombard Anny Cazenave Pierre Yves Le Traon Stephanie Guinehut Cécile Cabanes 《Ocean Dynamics》2006,56(5-6):445-451
In this paper, we first discuss the controversial result of the work by Cabanes et al. (Science 294:840–842, 2001), who suggested that the rate of past century sea level rise may have been overestimated, considering the limited and heterogeneous
location of historical tide gauges and the high regional variability of thermal expansion which was supposed to dominate the
observed sea level. If correct, this conclusion would have solved the problem raised by the IPCC third assessment report [Church
et al, Cambridge University Press, Cambridge, pp 881, 2001], namely, the factor two difference between the 20th century observed sea level rise and the computed climatic contributions.
However, recent investigations based on new ocean temperature data sets indicate that thermal expansion only explains part
(about 0.4 mm/year) of the 1.8 mm/year observed sea level rise of the past few decades. In fact, the Cabanes et al.’s conclusion
was incorrect due to a contamination of abnormally high ocean temperature data in the Gulf Stream area that led to an overestimate
of thermal expansion in this region. In this paper, we also estimate thermal expansion over the last decade (1993–2003), using
a new ocean temperature and salinity database. We compare our result with three other estimates, two being based on global
gridded data sets, and one based on an approach similar to that developed here. It is found that the mean rate of thermosteric
sea level rise over the past decade is 1.5±0.3 mm/year, i.e. 50% of the observed 3 mm/year by satellite altimetry. For both
time spans, past few decades and last decade, a contribution of 1.4 mm/year is not explained by thermal expansion, thus needs
to be of water mass origin. Direct estimates of land ice melt for the recent years account for about 1 mm/year sea level rise.
Thus, at least for the last decade, we have moved closer to explaining the observed rate of sea level rise than the IPCC third
assessment report. 相似文献
19.
Prediction and prevention of the impacts of sea level rise on the Yangtze River Delta and its adjacent areas 总被引：4，自引：0，他引：4
The Yangtze River Delta region is characterized by high density of population and rapidly developing economy. There are low lying coastal plain and deltaic plain in this region. Thus, the study area could be highly vulnerable to accelerated sea level rise caused by global warming. This paper deals with the scenarios of the relative sea level rise in the early half period of the 21st century in the study area. The authors suggested that relative sea level would rise 25 50 cm by the year 2050 in the study area, of which the magnitude of relative sea level rise in the Yangtze River Delta would double the perspective worldwide average. The impacts of sea level rise include: (i) exacerbation of coastline recession in several sections and vertical erosion of tidal flat, and increase in length of eroding coastline; (ii) decrease in area of tidal flat and coastal wetland due to erosion and inundation; (iii) increase in frequency and intensity of storm surge, which would threaten the coastal protection works; (iv) reduction of drainage capacity due to backwater effect in the Lixiahe lowland and the eastern lowland of Taihu Lake region, and exacerbation of flood and waterlogging disasters; and (v) increase in salt water intrusion into the Yangtze Estuary. Comprehensive evaluation of sea level rise impacts shows that the Yangtze River Delta and eastern lowland of Taihu Lake region, especially Shanghai Municipality, belong in the district in the extreme risk category and the next is the northern bank of Hangzhou Bay, the third is the abandoned Yellow River delta, and the district at low risk includes the central part of north Jiangsu coastal plain and Lixiahe lowland. 相似文献
20.
The problem of assessment of sea level rise impact on the hydrological regime and morphological structure of river deltas
is discussed. Studies of the response of river deltas, which are among the most vulnerable natural objects, to the sea level
rise has become urgent because of the global climate warming and the associated acceleration of the World Ocean level rise.
Methods are described that can be used for the analysis, calculation, and prediction of sea level rise impact on submergence
of deltas, propagation of backwater from the sea tides, surges, and salt seawater intrusion. Special emphasis is given to
channel processes in delta branches, which accompany sea level rise, as well as to delta coastline erosion and flow redistribution
among branches. In the course of research, due consideration was taken of the experience gained in studying the response of
river deltas on the Caspian Sea coasts to the recent considerable level rise in this water body. 相似文献