Low-frequency Sea Level Variations Research Articles

Gulf Stream Effects on Sea Level Oscillations: Enhancing Performance of a Coastal and Estuarine Model Nested into Global Model through Modified Boundary Conditions

This study investigates the effects of the gulf stream (GS) on sea-level oscillations across various time scales and assesses the performance of a coastal and estuarine model nested within a global model in simulating these variations. It aims to improve boundary conditions to simulate sea-level oscillations more accurately by considering the influence of GS flow. An inverse correlation is observed between observed sea-level oscillation and GS flow, which becomes more pronounced over longer time scales. Using Delft3D, a high-resolution coastal and estuarine model is developed to simulate circulation dynamics in the central Indian River Lagoon (IRL), FL, and adjacent coastal areas on the Florida east coast. The model is nested into the HYCOM (Hybrid Coordinate Ocean Model), and meteorological forcings are derived from the NARR (North American Regional Reanalysis) model. The model demonstrates satisfactory performance across key parameters, including tide, salinity, water temperature, and currents. However, there remains a noticeable difference between the modeled and observed data. To address this, the model is executed with modified flow boundary conditions at eastern boundary nodes, integrating HYCOM tide, and observing low-frequency sea-level variations. The implementation of the new boundary conditions results in an improved simulation of sea-level oscillations. This study presents the conceptual framework and detailed methodologies employed in the creation of a high-resolution model tailored for estuarine and coastal areas nested into global models capable of satisfactorily simulating sea-level oscillations even when the global model does not represent GS effects.

Sea level acceleration under the magnifier

Abstract Detection and quantification of sea level accelerations at tide gauge stations are needed for assessing anthropogenic contributions to the climate change. Nonetheless, uniform or non-uniform sea level accelerations/decelerations are particularly di˚cult to discern partly because of their small magnitudes and partly because of the low frequency sea level variations as confounders. Moreover, noisy excursions in the observed sea level variations also exacerbate reliability of estimated sea level accelerations. This study explores the uniformity of a sea level acceleration graphically that is left unmodeled in the residuals of a least squares solution using cumulative sum charts. Key West, USA tide gauge station’s record is studied for a demonstration. The cumulative sum charts of the residuals of a rigorous kinematic model solution without the acceleration parameter revealed its crisp and uniform signature experienced at this station since 1913.

Low-frequency sea level variability and impact of recent sea ice decline on the sea level trend in the Arctic Ocean from a high-resolution simulation

The Arctic Ocean is undergoing significant changes, with rapid sea ice decline, unprecedented freshwater accumulation, and pronounced regional sea level rise. In this paper, we analyzed the sea level variation in the Arctic Ocean based on a global simulation with 4.5-km resolution in the Arctic Ocean using the multi-resolution Finite Element Sea Ice-Ocean Model (FESOM). The simulation reasonably reproduces both the main spatial features of the sea surface height (SSH) and its temporal evolution in the Arctic Ocean in comparison with tide gauge and satellite data. Using the model results, we investigated the low-frequency variability of the Arctic SSH. Both the first two dominant modes of the annual-mean SSH evolution in the Arctic Ocean present decadal variability and can be mainly attributed to the variability of the halosteric height, thus the freshwater content. The first mode can be explained by the Arctic Oscillation (AO). The AO-related atmospheric circulation drives the accumulation and release of freshwater in the Arctic deep basin and the consequent ocean mass change over the continental shelf, leading to the antiphase changes in SSH between the shelf seas and the deep basin. The second mode shows an antiphase oscillation between the two Arctic deep basins, the Amerasian and Eurasian Basins, which is driven by the Arctic dipole anomaly (DA). The DA-related wind anomaly causes a spatial redistribution of freshwater between the two basins, leading to the antiphase SSH changes. By using a dedicated sensitivity simulation in which the recent sea ice decline is eliminated, we find that the sea ice decline contributed considerably to the observed sea level rise in the Amerasian Basin in the recent decades. Although the sea ice decline did not change the mean SSH averaged over the Arctic Ocean, it significantly changed the spatial pattern of the SSH trend. Our finding indicates that both the wind regime and ongoing sea ice decline should be considered to better understand and predict the changes in regional sea level in the Arctic Ocean.

Conflation of satellite altimetry and tide gauge records at coast

Abstract This study demonstrates that absolute (geocentric) and relative sea level trends, sea level acceleration, low frequency sea level variations and linear trends in vertical crustal movements experienced at a tide gauge station can be estimated simultaneously using conflated satellite altimetry and tide gauge measurements without the aid of GPS measurements. The formulation is the first of its kind in sea level studies and its effectiveness is exemplified using tide gauge, and satellite altimetry measurements carried out in the vicinity of a tide gauge station.

Satellite Altimetry and Tide Gauge Observed Teleconnections between Long-Term Sea Level Variability in the U.S. East Coast and the North Atlantic Ocean

Rising sea levels amplify the threat and magnitude of storm surges in coastal areas. The U.S. east coast region north of Cape Hatteras has shown a significant sea level rise acceleration and is believed to be a “hot-spot” for accelerating tidal flooding. To better understand the forcing mechanism of long-term regional sea level change, in order to more efficiently implement local sea level rise adaptation and mitigation measures, this work investigated the teleconnections between low-frequency sea level variability in the coastal region north of Cape Hatteras and the subpolar/tropical North Atlantic Ocean by using tide gauge measurements, satellite altimetry data and a sea level reconstruction dataset. The correlation analysis demonstrates that the tide-gauge measured sea level variability in the area north of Cape Hatteras is highly and positively correlated with that observed by satellite altimetry in the subpolar and tropical North Atlantic between 1993 and 2002. Over the following decade (2003–2012), the phase of the teleconnection in the subpolar region was reversed and the spatio-temporal correlation in the tropical North Atlantic was enhanced. Furthermore, the positive correlation in the region north of Cape Hatteras’s near shore area is strengthened, while the negative correlation in the Gulf Stream front region is weakened. The North Atlantic Oscillation and Atlantic Multidecadal Oscillation, which affect variations of the Atlantic Meridional Overturning Circulation and Gulf Stream, were shown to have significant impacts on the decadal changes of the teleconnections. Coherent with satellite altimetry data, the reconstructed sea level dataset in the 20th century exhibits similar spatial correlation patterns with the Atlantic Meridional Overturning Circulation, North Atlantic Oscillation and Atlantic Multidecadal Oscillation indices.

Sea level variability in the Swedish Exclusive Economic Zone and adjacent seawaters: influence on a point absorbing wave energy converter

Abstract. Low-frequency sea level variability can be a critical factor for several wave energy converter (WEC) systems, for instance, linear systems with a limited stroke length. Consequently, when investigating suitable areas for deployment of those WEC systems, sea level variability should be taken into account. In order to facilitate wave energy developers finding the most suitable areas for wave energy park installations, this paper describes a study that gives them additional information by exploring the annual and monthly variability of the sea level in the Baltic Sea and adjacent seawaters, with a focus on the Swedish Exclusive Economic Zone. Overall, 10 years of reanalysis data from the Copernicus project have been used to conduct this investigation. The results are presented by means of maps showing the maximum range and the standard deviation of the sea level with a horizontal spatial resolution of about 1 km. A case study illustrates how the results can be used by the WEC developers to limit the energy absorption loss of their devices due to sea level variation. Depending on the WEC technology one wants to examine, the results lead to different conclusions. For the Uppsala point absorber L12 and the sea state considered in the case study, the most suitable sites where to deploy WEC parks from a sea level variation viewpoint are found in the Gotland basins and in the Bothnian Sea, where the energy loss due to sea level variations is negligible.

Low-Frequency Baltic Sea Level Spectrum

This study examines the Baltic sea level spectrum in the interval of periods from a few months to decades. Effective statistical methods of time series analysis have been applied to the long-term data from 36 tide gauges in the Baltic Sea, the Danish straits, and southeastern part of the North Sea to examine the character of low-frequency sea level variability. Using the spectral and wavelet analyses, we obtained estimates of the magnitudes of the main long period components of the sea level oscillations with periods of 8.4, 7.76, 6.16, 2.5, 1.7, 1.2 yr and discussed their possible origin. The peak with a period of 255 days is revealed in both the sea level spectra of the Baltic Sea and in the spectra of atmospheric processes. It is more pronounced in the air pressure variations from atmospheric reanalyses, especially ERA-Interim and NCEP/CFSR. Wavelet analysis revealed high coherence between the sea level oscillations at different stations and also with the zonal wind component. The result of the study shows that the low-frequency sea level variability in the Baltic Sea is highly correlated with the zonal wind variations over the extensive shallow-water areas of the sea.

Effect of coastal-trapped waves on the synoptic variations of the Yellow Sea Warm Current during winter

Significant short-term fluctuations of the Yellow Sea Warm Current (YSWC) at several days' time scale were observed in the Yellow Sea (YS) during winter of 2006–2007. Observations indicated that the synoptic fluctuations of the YSWC appear to be associated with low-frequency sea level variations. By analyzing direct current measurements, sea level elevations and results from a regional ocean model, this study characterizes the variation of the YSWC at synoptic time scale and examines its connection with propagation of coastal-trapped waves during winter. The model captures the observed short-term fluctuations of the YSWC at several days’ periods and suggests a close relation between coastal-trapped waves and the YSWC variability. The YSWC is intensified (weakened) when the westward sea level-related barotropic pressure gradient is enhanced (diminished) due to the propagation of coastal-trapped waves. Model experiments with idealized periodic surface forcing further identify the important role of the coastal-trapped waves on adjusting the strength of the YSWC. The model results also suggest that the propagation of coastal-trapped waves contribute to the intermittent northwestward intrusion of Cheju Warm Current (CWC) in the frontal region northwest of Cheju. Generation and propagation of the coastal-trapped waves give rise to the westward barotropic pressure gradient in the YS entrance, which periodically pumps the CWC water into the YS interior west of Cheju.

Sea level oscillations in Japan and China since the start of the 20th century and consequences for coastal management - Part 2: China pearl river delta region

This study examines low-frequency (>10 years) sea level variations in the Pearl River Delta (PRD) Region. The low-frequency sea level variability is relevant to regional sea level forecasting and flood risk management. Linear and parabolic fittings are applied to the monthly average mean sea levels (MSL) measured by tide gauges. A spectral analysis is performed of the time series of the MSL and the time series of the monthly climate indices of Pacific Decadal Oscillation (PDO) and El Niño–Southern Oscillation (ENSO)/NINO. Based on the analysis of a composite record of different tide gauges, the PRD Region sea levels, despite being complicated by the river discharge, have reduced similarity with either ENSO, NINO or PDO indices. The PRD Region sea levels have low frequency similarities with the sea level pattern in the Western North Pacific (e.g. Hosojima, Japan) and Western South Pacific (e.g. Sydney, Australia), while at higher frequencies the similarities reduce. One strong low frequency fluctuation of periodicity quasi-20 years is very clear and another of a longer periodicity of quasi-60 years is clear. There is then a relevant fluctuation of about 12 years of periodicity, of reduced amplitude compared to the quasi-20 years fluctuation. In the medium frequency range (<10 years), there are several components detected, but the intensity of the fluctuations is largely reduced compared to the fluctuation of 12 years periodicity. Regionally, the sea levels in the PRD region and Japan show no significant acceleration from 1900 to present, but only oscillations. This result is consistent with the other coastal area of the world where long-term tide gauges are located. Policy making, and management, should therefore focus on adaptive measures linked to the monitoring by tide gauges and Global Navigation Satellite System (GNSS) of relative sea level rise and land subsidence. Extreme sea level rise warnings based on predictions by never validated models, or speculations, that are defocusing coastal management from every other relevant situation, should be discharged.

Distinguishing the Quasi-Decadal and Multidecadal Sea Level and Climate Variations in the Pacific: Implications for the ENSO-Like Low-Frequency Variability

Low-frequency sea level variations with periods longer than interannual time scales have been receiving much attention recently, with the aim of distinguishing the anthropogenic regional sea level change signal from the natural fluctuations. Based on the available sea level products, this study finds that the dominant low-frequency sea level mode in the Pacific basin has both quasi-decadal variations and a multidecadal trend reversal in the early 1990s. The dominant sea level modes on these two time scales have different tropical structures: a west–east seesaw in the tropical Pacific on the multidecadal time scale and a dipole between the western and central tropical Pacific on the quasi-decadal time scale. These two sea level modes in the Pacific basin are closely related to the ENSO-like low-frequency climate variability on respective time scales but feature distinct surface wind forcing patterns and subbasin climate processes. The multidecadal sea level mode is associated with the Pacific decadal oscillation (PDO) and Aleutian low variations in the North Pacific and tropical Pacific sea surface temperature anomalies toward the eastern basin, while the quasi-decadal sea level mode is accompanied by tropical Pacific sea surface temperature anomalies centered in the central basin along with the North Pacific part, which resembles the North Pacific Oscillation (NPO) and its oceanic expressions [i.e., the North Pacific Gyre Oscillation (NPGO) and the Victoria mode]. The authors further conclude that the ENSO-like low-frequency variability, which has dominant influences on the Pacific sea level and climate, comprises at least two distinct modes with different spatial structures on quasi-decadal and multidecadal time scales, respectively.

On the Drivers and Predictability of Seasonal-to-Interannual Variations in Regional Sea Level

Abstract Observations and eddy-permitting ocean model simulations are used to evaluate the drivers of sea level variability associated with 15 modes of climate variability covering the Atlantic, Pacific, Indian, and Southern Oceans. Sea level signals are decomposed into barotropic, steric, and inverted barometer contributions. Forcings are decomposed into surface winds, buoyancy fluxes, and Ekman pumping. Seasonal-to-interannual sea level variability in the low latitudes is governed almost entirely by the thermosteric response to wind forcing associated with tropical modes of climate variability. In the extratropics, changes to dynamic sea level associated with atmospheric modes of variability include a substantial barotropic response to wind forcing, particularly over the continental shelf seas. However, wind-driven steric changes are also important in some locations. On interannual time scales, wind-forced steric changes dominate, although heat and freshwater fluxes are important in the northwest Atlantic, where low-frequency sea level variations are associated with changes in the Atlantic meridional overturning circulation. Using the version 3 of the Met Office Decadal Prediction System (DePreSys3), the predictability of large-scale dynamic sea level anomalies on seasonal-to-interannual time scales is evaluated. For the first year of the hindcast simulations, DePreSys3 exhibits skill exceeding persistence over large regions of the Pacific, Atlantic, and Indian Oceans. Skill is particularly high in the tropical Indo-Pacific because of the accurate initialization and propagation of thermocline depth anomalies associated with baroclinic adjustments to remote wind forcing. Skill in the extratropics is hindered by the limited predictability of wind anomalies associated with modes of atmospheric variability that dominate local and/or barotropic responses.

Tidal and sub-tidal sea level variability at the northern shelf of the Brazilian Northeast Region.

A characterization of the sea level variability at tidal and sub-tidal frequencies at the northern shore of the Brazilian Northeast shelf for the period 2009-2011 is presented. The sea level data used was obtained from the Permanent Geodetic Tide Network from the Brazilian Institute of Geography and Statistics for the Fortaleza gauge station. Local wind data was also used to assess its effects on the low-frequency sea level variability. The variability of the sea level was investigated by classical harmonic analysis and by morphology assessment over the tidal signal. The low frequencies were obtained by low-pass filtering. The tidal range oscillated with the highest value of 3.3 m during the equinox and the lowest value of 0.7 m during the solstice. Differences between the spring and neap tides were as high as 1 m. A total of 59 tidal constituents were obtained from harmonic analysis, and the regional tide was classified as semi-diurnal pure with a form number of 0.11. An assessment of the monthly variability of the main tidal constituents (M2, S2, N2, O1, and K1) indicated that the main semi-diurnal solar S2 presented the highest variability, ranging from 0.21 to 0.41 m; it was the main element altering the form number through the years. The low frequency sea-level variability is negligible, although there is a persistent signal with an energy peak in the 10-15 day period, and it cannot be explained by the effects of local winds.

Role of the barotropic water exchange in the formation of the Baltic Sea level spectrum

The spectrum of low-frequency sea level variations was analyzed on the basis of long-term (15–124 years) time series of sea-level data from three tide gauge stations in the Baltic Sea and two stations in the North Sea. The principal periodicities revealed in the spectrum are seasonal as well as the tidal oscillations including the pole tide with a period of about 14 months. The response function of the Baltic Sea level to variations in the North Sea level is calculated using a cross spectral analysis. It is shown that the barotropic water exchange through the Danish Straits is a basic factor in the formation of the low-frequency sea level spectrum in the Baltic Sea. The limited throughput of these straits plays the role of a natural low-pass filter for the sea level variations: high frequency sea level variations from the North Sea are effectively damped, while the low frequency signal can pass through into the Baltic Sea almost undisturbed. The simple model of the barotropic water exchange used in the study enables us to estimate the parameters of this filter. It is shown that the cutoff frequency is about 0.014 cpd (a period of 74 days): the energy of the sea level oscillations at this frequency is reduced by one half after their penetration into the Baltic Sea.

Sea-level rise in the Mediterranean Sea by 2050: Roles of terrestrial ice melt, steric effects and glacial isostatic adjustment

To assess the regional pattern of future low-frequency sea-level variations in the Mediterranean Sea, we combine the terrestrial ice melt, the glacio-isostatic and the steric sea-level components. The first is obtained from global scenarios for the future mass balance of the Greenland and Antarctica ice sheets, glaciers and ice caps. The second is based on modeling, using different assumptions about the Earth's rheology and the chronology of deglaciation since the Last Glacial Maximum. The third is obtained from published simulations based on regional atmosphere–ocean coupled models. From a minimum and a maximum scenario by 2040–2050, we find that the total, basin averaged sea-level rise will be 9.8 and 25.6cm. The terrestrial ice melt component will exceed the steric contribution, which however will show the strongest regional imprint. Glacial isostatic adjustment will have comparatively minor effects. According to our estimates, at the Mediterranean Sea tide gauges, the rate of sea-level change will increase, by 2050, by a factor of ~1–6 relative to the observed long-term rates.

Decadal and long-term sea level variability in the tropical Indo-Pacific Ocean

In this study, we analysed decadal and long-term steric sea level variations over 1966–2007 period in the Indo-Pacific sector, using an ocean general circulation model forced by reanalysis winds. The simulated steric sea level compares favourably with sea level from satellite altimetry and tide gauges at interannual and decadal timescales. The amplitude of decadal sea level variability (up to ~5 cm standard deviation) is typically nearly half of the interannual variations (up to ~10 cm) and two to three times larger than long-term sea level variations (up to 2 cm). Zonal wind stress varies at decadal timescales in the western Pacific and in the southern Indian Ocean, with coherent signals in ERA-40 (from which the model forcing is derived), NCEP, twentieth century and WASWind products. Contrary to the variability at interannual timescale, for which there is a tendency of El Nino and Indian Ocean Dipole events to co-occur, decadal wind stress variations are relatively independent in the two basins. In the Pacific, those wind stress variations drive Ekman pumping on either side of the equator, and induce low frequency sea level variations in the western Pacific through planetary wave propagation. The equatorial signal from the western Pacific travels southward to the west Australian coast through equatorial and coastal wave guides. In the Indian Ocean, decadal zonal wind stress variations induce sea level fluctuations in the eastern equatorial Indian Ocean and the Bay of Bengal, through equatorial and coastal wave-guides. Wind stress curl in the southern Indian Ocean drives decadal variability in the south-western Indian Ocean through planetary waves. Decadal sea level variations in the south–western Indian Ocean, in the eastern equatorial Indian Ocean and in the Bay of Bengal are weakly correlated to variability in the Pacific Ocean. Even though the wind variability is coherent among various wind products at decadal timescales, they show a large contrast in long-term wind stress changes, suggesting that long-term sea level changes from forced ocean models need to be interpreted with caution.

Inter-annual and decadal sea level variations in the north-western Pacific marginal seas

Long term sea level changes in the Okhotsk, Japan/East, East China and Yellow Seas have been explored based on mean monthly values of sea level from tide gauge and altimetry measurements. The analysis of low frequency sea level variability reveals clearly differentiated areas: the Okhotsk Sea and the northern sector of the Japan/East Sea display lower sea level variances and no sea level rise. The southern Japan/East Sea presents larger sea level variability associated with the circulation regime of the warm current entering through the Tsushima Strait and inter-annual sea level variations that are driven by steric and atmospheric changes. The largest sea level variances are found in the Yellow Sea due to the effect of atmospheric forcing over the continental shelf. Inter-annual variability is spatially varying within the Yellow Sea and the East China Sea and is mainly related to the steric sea level changes. Regional mean sea level indices have been synthesized for each area using the longest tide gauge records and have revealed correlations between the southern Japan/East and Yellow Seas with PDO and NP climatic indices. Linear trends at coastal sites in the Japan/East, East China and Yellow Seas show a rather heterogeneous pattern, with values between −1.5 and 5.5mm/yr for the period 1960–2000. During the period 1993–2008 linear trends derived from coastal tide gauges and from altimetry observations are coherent and reveal a southwards increasing pattern with maximum averaged values reached at the Yellow Sea (4.9±1.9mm/yr) followed by the Japan/East Sea (3.8±0.9mm/yr). Decadal rates of sea level change show distinct behaviour among basins as well as with the global average. The southern Japan/East Sea, the East China Sea and the Yellow Sea display decadal variability which is out of phase with respect to the global values.

Low-frequency variability of sea level along the Mid-Atlantic Coast of South America, in 1983

Meteorological events cause pronounced low-frequency sea level variations along the Mid-Atlantic coast of South America. Spectral analysis of hourlysea level data during 1983 from tide gauges at Puerto Madryn and Mar del Plata, Argentina, and Cananeia and Ilha Fiscal, Brazil, yielded energetic variance peaks withperiods between 2 and 28 days, with good coherence among the four gauges. These results suggest that coherent low-frequency sea level disturbances may propagatealong the Mid-Atlantic coast of South America towards the northeast, mostly as barotropic shelf waves. The principal long waves were identified with heights up to 1 m,periods of 7.8 and 9.0 days, with variances of 2.5-5.4 m2 and coherences in the order of 0.88 to 0.98. These long waves recur every 5-16 days, propagate towards theequator with an average phase speed of 11 m/s, and require 77 hours to travel the 3,010 km distance from Puerto Madryn to Ilha Fiscal.

Sea level variability and trends in the Adriatic Sea in 1993–2008 from tide gauges and satellite altimetry

The scope of this paper is to give a consistent view of the low frequency sea level variability in the Adriatic Sea from both satellite altimetry and tide gauge records. We analyze 16years of sea level observations from multi-satellite altimetry and tide gauge records in the time interval 1993–2008. First, the impact of the corrections applied to the altimetry-derived sea level variations and the consistency of the altimetric and the tide gauge sea level observations are evaluated. Both observations are then used to characterize sea level trends, interannual variability and land vertical motion in the Adriatic region.Eight tide gauges along the coast show very coherent interannual sea level variations, with an increase in sea level before 2001 and decrease afterwards. The average of the eight de-seasoned time-series agrees with the basin average of the altimeter data, with correlation coefficient 0.84 and root mean square difference 12mm. The linear change is higher for altimetry than for tide gauges and strongly depends on the length of the time-interval, being 3.2±0.3mm/yr and 1.9±0.3mm/yr in the interval 1993–2008. The steric contribution to sea level change correlates well with the sea level suggesting that the low frequency variability is likely related to oceanic and climatic processes and mainly due to temperature and salinity variations. The decadal sea level variability is correlated in Adriatic and Eastern Mediterranean, anti-correlated in Adriatic and Ionian Sea.At a given location, the trend of the differences of sea level observations by tide gauges and co-located satellite altimetry gives the vertical land motion, if we assume that the sea level signals are truly common. We find trends statistically significant at the 90% confidence level at two locations, that indicate land uplift along the eastern coast in Rovinj (3.0±1.2mm/yr) and land subsidence in Marina di Ravenna (−1.5±1.1mm/yr), while at other locations, e.g. in Trieste (1.3±1.1mm/yr) the significance is lower. The results agree in general in sign with GPS derived rates, but not in magnitude, like in Marina di Ravenna, where the strong subsidence measured by GPS is related to the local anthropogenic subsidence. The differences are partly explained by the spatial distance between the tide gauge and the co-located altimeter locations.

Low-frequency sea-level variability in the South China Sea and its relationship with ENSO

Sea-level variability in the South China Sea was investigated based on satellite altimetry, tide-gauge data, and temperature and salinity climatology. The altimetric sea-level results clearly reveal three distinct amphidromes associated with the annual cycle. The annual sea level is higher in fall/winter in the coast and shelf region and lower in summer/fall in the central sea, agreeing well with independent tide-gauge data. Averaged over the deep basin (bottom depth > 2,000 m), the annual cycle can be approximately accounted for by the steric height relative to 700 db. Significant interannual sea-level change is observed from altimetry and tide-gauge data. The interannual and longer-term sea-level variability in the altimetric data is negatively correlated (significant at the 95% confidence level) with the El Nino - Southern Oscillation (ENSO), attributed in part to the steric height change. The altimetric sea-level rise rate is 1.0 cm/year for the period from 1993 to 2001, which is consistent with the rate derived from coastal tide-gauge data and approximately accountable for by the steric height calculated relative to 700 db. The tide-gauge sea-level (steric height) rise rate of 1.05 (0.9) cm/year from 1993 to 2001 is much larger than that of 0.22 (0.12) cm/year for the period from 1979 to 2001, implying the sensitivity to the length of data as a result of the decadal variability. Potential roles of the ENSO in the interannual and longer-term sea-level variability are discussed in terms of regional manifestations such as the ocean temperature and salinity.

Low-frequency sea-level variability in the South China Sea and its relationship to ENSO

Low-frequency sea-level variability in the South China Sea and its relationship to ENSO