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1.
A recently extended and spatially rich English Channel sea level dataset has been used to evaluate changes in extreme still water levels throughout the 20th century. Sea level records from 18 tide gauges have been rigorously checked for errors and split into mean sea level, tidal and non-tidal components. These components and the interaction between surge and tide have been analysed separately for significant trends before determining changes in extreme sea level. Mean sea level is rising at 0.8–2.3 mm/year, depending on location. There is a small increase (0.1–0.3 mm/year) in the annual mean high water of astronomical tidal origin, relative to mean sea level, and an increase (0.2–0.6 mm/year) in annual mean tidal range. There is considerable intra- and inter-decadal variability in surge intensity with the strongest intensity in the late 1950s. Storm surges show a statistically significant weak negative correlation to the winter North Atlantic Oscillation index throughout the Channel and a stronger significant positive correlation at the boundary with the southern North Sea. Tide–surge interactions increase eastward along the English Channel, but no significant long-term changes in the distribution of tide–surge interaction are evident. In conclusion, extreme sea levels increased at all of the 18 sites, but at rates not statistically different from that observed in mean sea level.  相似文献   

2.
The vulnerability to short-term and long-term sea-level rises is particularly high in subsiding deltaic areas, especially in microtidal seas, when surges (the differences between the observed sea heights and the simultaneous astronomical tide) are frequent. At the Grau-de-la-Dent tide-gauge in the Camargue (Rhone delta, France), daily sea-level records are available since 1905. Hourly tide data spanning the period 1979–1995 were obtained through the digitisation of the original paper records: the local harmonic constants and the surges for the whole 20th century have been computed from these hourly observations. It appears that the annual maximum observed sea-level height increases by 4 mm/yr at a rate that is two times faster than the average observed relative sea level. The increasing trend of the annual maximum positive sea surges (+1.9 mm/yr), which is equal to the average relative sea-level rise, is thus responsible for this difference. The most important meteorological factor associated with local sea-surge occurrences is wind blowing from 100° to 120° sectors, which tends to push the water toward the coasts. Since 1961, the frequency and the speed of wind from this sector increased, although with some variability, thus contributing in part to the increase in the frequency and intensity of the surges. Due to the changing hydrodynamics phenomenon in the Camargue, a positive feedback mechanism between extreme marine events and shoreline regression is another factor to explain the sea-surge rise over the long term. The increase in sea-surge frequency and height during the last century is especially of concern in the deltaic area if the near-future global sea-level rise predicted by climate models is also taken into account.  相似文献   

3.
This paper is based on statistical analysis of hourly tide measurements for some 285 equivalent full years from the stations of Weymouth, Bournemouth, Portsmouth, Newhaven, Dover and Sheerness in the UK, and of Cherbourg, Le Havre, Dieppe, Boulogne, Calais and Dunkirk in France. For each tidal value, surge heights have been determined and correlated with hourly or three-hourly wind and air pressure data from nearby meteorological stations. Major surges in the area are generally produced by storms associated with wind from north-west or south-west that tend to push oceanic water into the Channel. Recent medium-term climate evolution does not seem to increase the flooding risk at French stations, where surge-related winds tend to decrease in frequency and speed (Cherbourg, Dieppe and Boulogne) or show little change (Le Havre). However, the long-term risk of flooding will increase through the loss in land elevation due to a continuation of the local relative sea-level rise, especially if this effect will be enhanced by an acceleration in the global sea-level rise predicted by climatic models. The northern side of the Channel (Weymouth, Bournemouth and Portsmouth) is mainly exposed to southerly winds that show variable trends. It is also apparently affected by strong subsidence trends during the last two decades. If lasting, such trends can only increase long-term flooding risk. The flooding risk has not increased near the eastern end of the Channel. The duration of significant cyclonic events tends to decrease near Cherbourg but tends to increase near Weymouth, with no conclusive trends in other stations (Portsmouth, Calais and Dunkirk), where extreme surges may occur also in relatively high-air-pressure situations. In conclusion, medium-term coastal flooding risk seems to increase especially at Weymouth, Bournemouth and Portsmouth, and also, but less so, at Le Havre and Sheerness. In addition, few extreme surges occurred during the last decades at the time of spring high tide, which would seem to be a fortunate coincidence or, in some cases, an effect of tide–surge interaction. The risk of occurrence of less favourable random events in the near future is therefore of concern, and flood potential would greatly increase if the global sea-level rise expected in the near future is also considered.  相似文献   

4.
Positive storm surges (PSS) lasting for several days can raise the water level producing significant differences between the observed level and the astronomical tide. These storm events can be more severe if they coincide with a high tide or if they bracket several tidal cycles, particularly in the case of the highest astronomical tide. Besides, the abnormal sea-level elevation near the coast can cause the highest waves generated to attack the upper beach. This combination of factors can produce severe erosion, threatening sectors located along the coastline. These effects would be more serious if the storm surge height and duration increase as a result of a climatic change. The Mar del Plata (Argentina) coastline and adjacent areas are exposed to such effects. A statistical characterization of PSS based on their intensity, duration and frequency, including a surge event classification, was performed utilizing tide-gauge records over the period 1956–2005. A storm erosion potential index (SEPI) was calculated from observed levels based on hourly water level measurements. The index was related to beach profile responses to storm events. Also, a return period for extreme SEPI values was calculated. Results show an increase in the average number of positive storm surge events per decade. Considering all the events, the last decade (1996–2005) exhibits an average 7% increase compared to each one of the previous decades. A similar behavior was found for the decadal average of the heights of maximum annual positive storm surges. In this case the average height of the last two decades exceeds that of the previous decades by approximately 8 cm. The decadal average of maximum annual duration of these meteorological events shows an increase of 2 h in the last three decades. A possible explanation of the changes in frequency, height and duration of positive storm surges at Mar del Plata would seem to lie in the relative mean sea-level rise.  相似文献   

5.
Planning and design of coastal protection rely on information about the probabilities of very severe storm tides and the possible changes that may occur in the course of climate change. So far, this information is mostly provided in the form of high percentiles obtained from frequency distributions or return values. More detailed information and assessments of events that may cause extreme damages or have extreme consequences at the coast are so far still unavailable. We describe and compare two different approaches that may be used to identify highly unlikely but still physically possible and plausible events from model simulations. Firstly, in the case when consistent wind and tide-surge data are available, different metrics such as the height of the storm surge can be derived directly from the simulated water levels. Secondly, in cases where only atmospheric data are available, the so called effective wind may be used. The latter is the projection of the horizontal wind vector on that direction which is most effective in producing surges at the coast. Comparison of events identified by both methods show that they can identify extreme events but that knowledge of the effective wind alone does not provide sufficient information to identify the highest storm surges. Tracks of the low-pressure systems over the North Sea need to be investigated to find those cases, where the duration of the high wind is too short to induce extreme storm tides. On the other hand, factors such as external surges or variability in mean sea level may enhance surge heights and are not accounted for in estimates based on effective winds only. Results from the analysis of an extended data set suggest that unprecedented storm surges at the German North Sea coast are possible even without taking effects from rising mean sea level into account. The work presented is part of the ongoing project “Extreme North Sea Storm Surges and Their Consequences” (EXTREMENESS) and represents the first step towards an impact assessment for very severe storm surges which will serve as a basis for development of adaptation options and evaluation criteria.  相似文献   

6.
Based on tide gauge observations spanning almost 200 years, homogeneous time series of the mean relative sea level were derived for nine sites at the southern coast of the Baltic Sea. Our regionally concentrated data were complemented by long-term relative sea-level records retrieved from the data base of the Permanent Service for Mean Sea Level (PSMSL). From these records relative sea-level change rates were derived at 51 tide gauge stations for the period between 1908 and 2007. A minimum observation time of 60 years is required for the determination of reliable sea-level rates. At present, no anthropogenic acceleration in sea-level rise is detected in the tide gauge observations in the southern Baltic. The spatial variation of the relative sea-level rates reflects the fingerprint of GIA-induced crustal uplift. Time series of extreme sea levels were also inferred from the tide gauge records. They were complemented by water level information from historic storm surge marks preserved along the German Baltic coast. Based on this combined dataset the incidence and spatial variation of extreme sea levels induced by storm surges were analysed yielding important information for hazard assessments. Permanent GPS observations were used to determine recent crustal deformation rates for 44 stations in the Baltic Sea region. The GPS derived height change rates were applied to reduce the relative sea-level changes observed by tide gauges yielding an estimate for the eustatic sea-level change. For 13 tide gauge-GPS colocation sites a mean eustatic sea-level trend of 1.3 mm/a was derived for the last 100 years.  相似文献   

7.
What dominates sea level at the coast: a case study for the Gulf of Guinea   总被引：1，自引：0，他引：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   

8.
Sea-level rise, as a result of global warming, may lead to more natural disasters in coastal regions where there are substantial aggregations of population and property. Thus, this paper focuses on the impact of sea-level rise on the recurrence periods of extreme water levels fitted using the Pearson type III (P-III) model. Current extreme water levels are calculated using observational data, including astronomical high tides and storm surges, while future extreme water levels are determined by superposing scenario data of sea-level rise onto current extreme water levels. On the basis of a case study using data from Shandong Province, China, results indicated that sea-level rise would significantly shorten the recurrence periods of extreme water levels, especially under higher representative concentration pathway (RCP) scenarios. Results showed that by the middle of the century, 100-year current extreme water levels for all stations would translate into once in 15–30 years under RCP 2.6, and once in ten to 25 years under RCP 8.5. Most seriously, the currently low probability event of a 1000-year recurrence would become common, occurring nearly every 10 years by 2100, based on projections under RCP 8.5. Therefore, according to this study, corresponding risk to coastlines could well be increase in future, as the recurrence periods of extreme water levels would be shortened with climate change.  相似文献   

9.
The study evaluates relationships between the North Atlantic Oscillation (NAO) index and winter temperatures (including indices of extremes) over Europe in an ensemble of transient simulations of current global climate models (GCMs). We focus on identification of areas in which the NAO index is linked to winter temperatures and temperature extremes in simulations of the recent climate (1961–2000), and evaluate how these relationships change in climate change scenarios for the late 21st century (2071–2100). Most GCMs are able to reproduce main features of the observed links. The NAO index is more important for cold than warm extremes, which is also reproduced by the GCMs. However, all GCMs underestimate the magnitude of the NAO influence on cold extremes when averaged over northern and western Europe. For future scenarios, the links between the NAO and temperatures are mostly analogous to those in the recent climate, except for one GCM (CM3) in which the influence of the NAO on temperature almost disappears over whole Europe. This suggests that future scenarios from this particular GCM should be evaluated with caution. The NAO index is found to represent a useful covariate that explains an important fraction of variability of cold extremes in winter, and its incorporation into extreme value models for daily temperatures (and their possible changes under climate change) may improve performance of these models and reliability of estimates of extremes and their uncertainty.  相似文献   

10.
The joint probability method (JPM) to estimate the probability of extreme sea levels (Pugh and Vassie, Extreme sea-levels from tide and surge probability. Proc. 16th Coastal Engineering Conference, 1978, Hamburg, American Society of Civil Engineers, New York, pp 911–930, 1979) has been applied to the hourly records of 13 tide-gauge stations of the tidally dominated Atlantic coast of France (including Brest, since 1860) and to three stations in the southwest of the UK (including Newlyn, since 1916). The cumulative total length of the available records (more than 426 years) is variable from 1 to 130 years when individual stations are considered. It appears that heights estimated with the JPM are almost systematically greater than the extreme heights recorded. Statistical analysis shows that this could be due: (1) to surge–tide interaction (that may tend to damp surge values that occur at the time of the highest tide levels), and (2) to the fact that major surges often occur in seasonal periods that may not correspond to those of extreme astronomical tides. We have determined at each station empirical ad hoc correction coefficients that take into account the above two factors separately, or together, and estimated return periods for extreme water levels also at stations where only short records are available. For seven long records, for which estimations with other computing methods (e.g. generalized extreme value [GEV] distribution and Gumbel) can be attempted, average estimations of extreme values appear slightly overestimated in relation to the actual maximum records by the uncorrected JPM (+16.7 ± 7.2 cm), and by the Gumbel method alone (+10.3 ± 6.3 cm), but appear closer to the reality with the GEV distribution (−2.0 ± 5.3 cm) and with the best-fitting correction to the JPM (+2.9 ± 4.4 cm). Because the GEV analysis can hardly be extended to short records, it is proposed to apply at each station, especially for short records, the JPM and the site-dependent ad hoc technique of correction that is able to give the closest estimation to the maximum height actually recorded. Extreme levels with estimated return times of 10, 50 and 100 years, respectively, are finally proposed at all stations. Because astronomical tide and surges have been computed (or corrected) in relation to the yearly mean sea level, possible changes in the relative sea level of the past, or foreseeable in the future, can be considered separately and easily added to (or deduced from) the extremes obtained. Changes in climate, on the other hand, may modify surge and tide distribution and hence return times of extreme sea levels, and should be considered separately. Parts of this paper have been presented orally at the session “Geophysical extremes: scaling aspects and modern statistical approaches” of the EGU General Assembly, Vienna, 2–6 April 2006.  相似文献   

11.
Drought is a slow‐onset, creeping natural hazard which is an inevitable part of normal climate fluctuation especially in arid and semiarid regions, and its variability can be explained in terms of large‐scale atmospheric circulation patterns. Standardized streamflow index (SSFI) was utilized to characterize hydrological drought in the west of Iran for the hydrological years of 1969–1970 to 2008–2009. The linkage of atmospheric circulation patterns (ENSO, NAO) to hydrological drought was also used to reveal relations of climate variability affecting hydrological drought. River discharges exhibited negative anomalies during the warm phase of ENSO (El Niño) which caused the extreme and severe droughts in the study area, being strongest during the hydrological years of 2007–2008 and 2008–2009. The analysis also indicated the teleconnection impact of ENSO on the hydrological drought severity in the first half of the hydrological year especially between November and March. Moreover, the concurrent and lag correlations revealed a weak relationship between the SSFI drought severity and the NAO index. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

12.
Extreme value analysis of sea levels is an essential component of risk analysis and protection strategy for many coastal regions. Since the tidal component of the sea level is deterministic, it is the stochastic variation in extreme surges that is the most important to model. Historically, this modelling has been accomplished by fitting classical extreme value models to series of annual maxima data. Recent developments in extreme value modelling have led to alternative procedures that make better use of available data, and this has led to much refined estimates of extreme surge levels. However, one aspect that has been routinely ignored is seasonality. In an earlier study we identified strong seasonal effects at one of the number of locations along the eastern coastline of the United Kingdom. In this article, we discuss the construction and inference of extreme value models for processes that include components of seasonality in greater detail. We use a point process representation of extreme value behaviour, and set our inference in a Bayesian framework, using simulation-based techniques to resolve the computational issues. Though contemporary, these techniques are now widely used for extreme value modelling. However, the issue of seasonality requires delicate consideration of model specification and parameterization, especially for efficient implementation via Markov chain Monte Carlo algorithms, and this issue seems not to have been much discussed in the literature. In the present paper we make some suggestions for model construction and apply the resultant model to study the characteristics of the surge process, especially in terms of its seasonal variation, on the eastern UK coastline. Furthermore, we illustrate how an estimated model for seasonal surge can be combined with tide records to produce return level estimates for extreme sea levels that accounts for seasonal variation in both the surge and tidal processes.
Jonathan Tawn (Corresponding author)Email:
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13.
The effect of the North Atlantic Oscillation (NAO) indices on climatic conditions and their subsequent influence on water temperature of two Basque estuaries (estuary of Bilbao and estuary of Urdaibai) were assessed by transfer function (TF) models for the period 1997–2006. Results showed that air temperature had an immediate (lag=0) and significant negative response to the NAO, whereas rainfall was not correlated with this climate index. The negative correlation between NAO and air temperature was found to be stronger with the seasonal indices derived from the differences in surface pressure between Iceland and Azores than with that derived from the principal component time-series of the leading eigenvector of the sea-level pressure in an Atlantic sector. The correlations between rainfall and river discharge, and between air temperature and water temperature were positive and highly significant in both estuaries. The response of water temperature to air temperature was immediate in both estuaries, whereas one-quarter lagged responses were also observed in the estuary of Bilbao, which is deeper and more stratified than the estuary of Urdaibai. Our study provides evidence that on the Basque coast the NAO plays an important role in climate variations, which in turn affect estuarine water temperature.  相似文献   

14.
Surge modelling in the eastern Irish Sea: present and future storm impact   总被引：1，自引：0，他引：1  
It is believed that, in the future, the intensity and frequency of extreme coastal flooding events may increase as a result of climate change. The Natural Environment Research Council (NERC) Flood Risk from Extreme Events (FREE) project, Coastal Flooding by Extreme Events and EU FP7 Morphological Impacts and Coastal Risks Induced by Extreme Storm Events project are investigating the flood risks in the eastern Irish Sea, an area that includes most of England’s coastal types. Using a previously modelled and validated historical extreme surge event, in November 1977, we now investigate the changes in peak surge as a result of possible future climate conditions. In order to simulate the surge, we have set up a one-way nested approach, using the Proudman Oceanographic Laboratory Coastal Ocean Modelling System 3D baroclinic model, from a domain covering the whole NW European continental shelf, through to a 1.85 km Irish Sea model; both areas are forced by tides, atmospheric pressure and winds. We use this modelling system to investigate the impact of enhanced wind velocities and increased sea levels on the peak surge elevation and residual current pattern. The results show that sea level rise has greater potential to increase surge levels than increased wind speeds.  相似文献   

15.
On the basis of General Circulation Model (GCM) experiments with increased CO2, many parts of the northern latitudes including western Europe, are expected to have enhanced hydrologic cycles. Using observations of precipitation and streamflow from Ireland, we test for climatic and hydrologic change in this maritime climate of the northeast Atlantic. Five decades of hourly precipitation (at eight sites) and daily streamflow at four rivers in Ireland were investigated for patterns of climate variability. An increase in annual precipitation was found to occur after 1975. This increase in precipitation is most noticeable on the West of the island. Precipitation increases are significant in March and October and are associated with increases in the frequency of wet hours with no change in the hourly intensities. Analysis of streamflow data shows the same trends. Furthermore, analysis of extreme rainfall events show that a much greater proportion of extremes have occurred in the period since 1975. A change also occurred in the North Atlantic Oscillation (NAO) index around 1975. The increased NAO since 1975 is associated with increased westerly airflow circulation in the Northeast Atlantic and is correlated with the wetter climate in Ireland. These climatic changes have implications for water resources management particularly flood analysis and protection.  相似文献   

16.
The Pearl River Delta (PRD) has one of the most complicated deltaic drainage systems with probably the highest density of crisscross-river network in the world. This article presents a regional flood frequency analysis and recognition of spatial patterns for flood-frequency variations in the PRD region using the well-known index flood L-moments approach together with some advanced statistical test and spatial analysis methods. Results indicate that: (1) the whole PRD region is definitely heterogeneous according to the heterogeneity test and can be divided into three homogeneous regions; (2) the spatial maps for annual maximum flood stage corresponding to different return periods in the PRD region suggest that the flood stage decreases gradually from the riverine system to the tide dominated costal areas; (3) from a regional perspective, the spatial patterns of flood-frequency variations demonstrate the most serious flood-risk in the coastal region because it is extremely prone to the emerging flood hazards, typhoons, storm surges and well-evidenced sea-level rising. Excessive rainfall in the upstream basins will lead to moderate floods in the upper and middle PRD region. The flood risks of rest parts are identified as the lowest in entire PRD. In order to obtain more reliable estimates, the stationarity and serial-independence are tested prior to frequency analysis. The characterization of the spatial patterns of flood-frequency variations is conducted to reveal the potential influences of climate change and intensified human activities. These findings will definitely contribute to formulating the regional development strategies for policymakers and stakeholders in water resource management against the menaces of frequently emerged floods and well-evidenced sea level rising.  相似文献   

17.
Twenty-four years of AVHRR-derived sea surface temperature (SST) data (1985–2008) and 35 years of NOCS (V.2) in situ-based SST data (1973–2008) were used to investigate the decadal scale variability of this parameter in the Mediterranean Sea in relation to local air–sea interaction and large-scale atmospheric variability. Satellite and in situ-derived data indicate a strong eastward increasing sea surface warming trend from the early 1990s onwards. The satellite-derived mean annual warming rate is about 0.037°C year–1 for the whole basin, about 0.026°C year–1 for the western sub-basin and about 0.042°C year–1 for the eastern sub-basin over 1985–2008. NOCS-derived data indicate similar variability but with lower warming trends for both sub-basins over the same period. The long-term Mediterranean SST spatiotemporal variability is mainly associated with horizontal heat advection variations and an increasing warming of the Atlantic inflow. Analysis of SST and net heat flux inter-annual variations indicates a negative correlation, with the long-term SST increase, driving a net air–sea heat flux decrease in the Mediterranean Sea through a large increase in the latent heat loss. Empirical orthogonal function (EOF) analysis of the monthly average anomaly satellite-derived time series showed that the first EOF mode is associated with a long-term warming trend throughout the whole Mediterranean surface and it is highly correlated with both the Eastern Atlantic (EA) pattern and the Atlantic Multidecadal Oscillation (AMO) index. On the other hand, SST basin-average yearly anomaly and NAO variations show low and not statistically significant correlations of opposite sign for the eastern (negative correlation) and western (positive correlation) sub-basins. However, there seems to be a link between NAO and SST decadal-scale variations that is particularly evidenced in the second EOF mode of SST anomalies. NOCS SST time series show a significant SST rise in the western basin from 1973 to the late 1980s following a large warming of the inflowing surface Atlantic waters and a long-term increase of the NAO index, whereas SST slowly increased in the eastern basin. In the early 1990s, there is an abrupt change from a very high positive to a low NAO phase which coincides with a large change in the SST spatiotemporal variability pattern. This pronounced variability shift is followed by an acceleration of the warming rate in the Mediterranean Sea and a change in the direction (from westward to eastward) of its spatial increasing tendency.  相似文献   

18.
Christian Onof 《水文研究》2013,27(11):1600-1614
Under future climate scenarios, possible changes of drought patterns pose new challenges for water resources management. For quantifying and qualifying drought characteristics in the UK, the drought severity indices of six catchments are investigated and modelled by two stochastic methods: autoregressive integrated moving average (ARIMA) models and the generalized linear model (GLM) approach. From the ARIMA models, autocorrelation structures are first identified for the drought index series, and the unexplained variance of the series is used to establish empirical relationships between drought and climate variables. Based on the ARIMA results, mean sea level pressure and possibly the North Atlantic Oscillation index are found to be significant climate variables for seasonal drought forecasting. Using the GLM approach, occurrences and amounts of rainfall are simulated with conditioning on climate variables. From the GLM‐simulated rainfall for the 1980s and 2080s, the probabilistic characteristics of the drought severity are derived and assessed. Results indicate that the drought pattern in the 2080s is less certain than for the 1961–1990 period, based on the Shannon entropy, but that droughts are expected to be more clustered and intermittent. The 10th and 50th quantiles of drought are likely higher in the 2080s scenarios, but there is no evidence showing the changes in the 90th quantile extreme droughts. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

19.
Results of the sea-level budget in the high latitudes (up to 80°N) and the Arctic Ocean during the satellite altimetry era. We investigate the closure of the sea-level budget since 2002 using two altimetry sea-level datasets based on the Envisat waveform retracking: temperature and salinity data from the ORAP5 reanalysis, and Gravity Recovery And Climate Experiment (GRACE) space gravimetry data to estimate the steric and mass components. Regional sea-level trends seen in the altimetry map, in particular over the Beaufort Gyre and along the eastern coast of Greenland, are of halosteric origin. However, in terms of regional average over the region ranging from 66°N to 80°N, the steric component contributes little to the observed sea-level trend, suggesting a dominant mass contribution in the Arctic region. This is confirmed by GRACE-based ocean mass time series that agree well with the altimetry-based sea-level time series. Direct estimate of the mass component is not possible prior to GRACE. Thus, we estimated the mass contribution from the difference between the altimetry-based sea level and the steric component. We also investigate the coastal sea level with tide gauge records. Twenty coupled climate models from the CMIP5 project are also used. The models lead us to the same conclusions concerning the halosteric origin of the trend patterns.  相似文献   

20.
Ezer  Tal 《Ocean Dynamics》2022,72(11):741-759

The long-term variability of sea level and surface flows in the Gulf of Mexico (GOM) is studied using global monthly sea level reconstruction (RecSL) for 1900–2015. The study explored the long-term relation between the dynamics of the GOM and inflows/outflows through the Yucatan Channel (YC) and the Florida Straits (FS). The results show a century-long trend of increased mean velocity and variability in the Loop Current (LC); however, no significant upward trend was found in the YC and FS flows, only increased variability. Empirical orthogonal function (EOF) analysis of sea surface height found spatial patterns dominated by variations in the LC and temporal variations on time scales ranging from a few months to multidecadal. The time evolution of each EOF mode of sea level is correlated with the velocity of either the LC, the YC, or the FS or some combination of the different flows. The mean sea level difference between the GOM and the northwestern Caribbean Sea was found to be influenced by the North Atlantic Oscillation (NAO), with unusually high differences during the 1970s when the NAO index was low and the Atlantic Ocean circulation was weak. Extreme peaks in SL difference coincide with the extension of the LC and the seasonal eddy shedding pattern. The observed seasonal cycle in the extension area of the LC as obtained from 20 years of altimeter data is significantly correlated (R = 0.63; confidence level = 98%) with the seasonal YC flow obtained from 116 years of the RecSL data. However, the same LC extension record had lower correlation (R = 0.45; confidence level = 90%) with the observed YC transport obtained from direct moored measurements over ~ 5 years, indicating the need for much longer measurements, since the LC extension and the YC flow are strongly affected by interannual and decadal variations. The study demonstrates the usefulness of even a coarse-resolution reconstruction for studies of regional ocean variability and climate change over longer time scales than current direct observations allow.

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