Changing seasonality in North Atlantic coastal sea level from the analysis of long tide gauge records

Abstract Understanding the relationship between coastal sea level and the variable ocean circulation is crucial for interpreting tide gauge records and projecting sea level rise. In this study, annual sea level records (adjusted for the inverted barometer effect) from tide gauges along the North American northeast coast over 1980–2010 are compared to a set of data-assimilating ocean reanalysis products as well as a global barotropic model solution forced with wind stress and barometric pressure. Correspondence between models and data depends strongly on model and location. At sites north of Cape Hatteras, the barotropic model shows as much (if not more) skill than ocean reanalyses, explaining about 50% of the variance in the adjusted annual tide gauge sea level records. Additional numerical experiments show that annual sea level changes along this coast from the barotropic model are driven by local wind stress over the continental shelf and slope. This result is interpreted in the light of a simple dynamic framework, wherein bottom friction balances surface wind stress in the alongshore direction and geostrophy holds in the across-shore direction. Results highlight the importance of barotropic dynamics on coastal sea level changes on interannual and decadal time scales; they also have implications for diagnosing the uncertainties in current ocean reanalyses, using tide gauge records to infer past changes in ocean circulation, and identifying the physical mechanisms responsible for projected future regional sea level rise.

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Linear and non-linear sea-level variations in the Adriatic Sea from tide gauge records (1872-2012)

Annals of Geophysics ◽

10.4401/ag-6536 ◽

2015 ◽

Vol 57 (6) ◽

Author(s):

Gaia Galassi ◽

Giorgio Spada

Keyword(s):

Sea Level ◽

North Atlantic ◽

Adriatic Sea ◽

Tide Gauge ◽

Ensemble Empirical Mode Decomposition ◽

Tide Gauges ◽

Tide Gauge Records ◽

Mode Decomposition ◽

Sea Level Variations ◽

Global Values

We have analyzed tide gauge data from the Adriatic Sea in order to assess the secular sea-level trend, its acceleration and the existence of possible cyclic variation. Analyzing the sea-level stack of all Adriatic tide gauges, we have obtained a trend of (1.25±0.04) mm yr-1, in agreement with that observed for the last century in the Mediterranean Sea, and an acceleration that is negligibile compared to the average global values. By means of the Ensemble Empirical Mode Decomposition technique, we have evidenced an energetic oscillation with a period of ∼20 years that we relate with the recurrence of opposite phases in the Atlantic Multi–decadal Oscillation and North Atlantic Oscillation indices. We suggest that anomalously high sea-level values observed at all the Adriatic tide gauges during 2010 and 2011 can be explained by the rising phase of this 20 years cycle.

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Atmospheric and Climatic Drivers of Tide Gauge Sea Level Variability along the East and South Coast of South Africa

Journal of Marine Science and Engineering ◽

10.3390/jmse9090924 ◽

2021 ◽

Vol 9 (9) ◽

pp. 924

Author(s):

Bernardino J. Nhantumbo ◽

Björn C. Backeberg ◽

Jan Even Øie Nilsen ◽

Chris J. C. Reason

Keyword(s):

Sea Level ◽

Tide Gauge ◽

Southern Annular Mode ◽

South Coast ◽

Tide Gauge Records ◽

Sea Level Variability ◽

Sea Levels ◽

Modes Of Variability ◽

Mode Decomposition ◽

Coastal Sea

Atmospheric forcing and climate modes of variability on various timescales are important drivers of sea level variability. However, the influence of such drivers on sea level variability along the South African east and south coast has not yet been adequately investigated. Here, we determine the timescales of sea level variability and their relationships with various drivers. Empirical Mode Decomposition (EMD) was applied to seven tide gauge records and potential forcing data for this purpose. The oscillatory modes identified by the EMD were summed to obtain physically more meaningful timescales—specifically, the sub-annual (less than 18 months) and interannual (greater than two years) scales. On the sub-annual scale, sea level responds to regional zonal and meridional winds associated with mesoscale and synoptic weather disturbances. Ekman dynamics resulting from variability in sea level pressure and alongshore winds are important for the coastal sea level on this timescale. On interannual timescales, there were connections with ENSO, the Indian Ocean Dipole (IOD) and the Southern Annular Mode (SAM), although the results are not consistent across all the tide gauge stations and are not particularly strong. In general, El Niño and positive IOD events are coincident with high coastal sea levels and vice versa, whereas there appears to be an inverse relationship between SAM phase and sea level.

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Mechanisms of variability of decadal sea-level trends in the Baltic Sea over the 20th century

10.5194/esd-2017-30 ◽

2017 ◽

Author(s):

Sitar Karabil ◽

Eduardo Zorita ◽

Birgit Hünicke

Keyword(s):

Baltic Sea ◽

Sea Level ◽

Atmospheric Circulation ◽

Tide Gauge ◽

The Baltic Sea ◽

Tide Gauge Records ◽

Underlying Factor ◽

The North ◽

Coastal Sea ◽

The Baltic

Abstract. Coastal sea-level trends in the Baltic Sea display decadal-scale variations around a centennial trend. These long-term centennial trends are likely determined by climate change and centennial vertical land movements. In this study, we analyse the spatial and temporal characteristics of the decadal trend variations and investigate the links between coastal sea-level trends and atmospheric forcing on decadal time scale. This investigation mainly focuses on the identification of the possible impact of an underlying factor, apart from the effect of atmospheric circulation, on decadal sea-level trend anomalies. For this analysis, we use monthly means of long tide gauge records and gridded sea-surface-height (SSH) reconstructions. The SSH time series are constructed over the past 64 years and based on tide-gauge records and satellite altimetry. Climatic data sets are composed of the North Atlantic Oscillation (NAO) index, the Atlantic Multidecadal Oscillation (AMO) index, gridded sea-level-pressure (SLP), gridded near-surface air temperature and gridded precipitation fields. The analysis indicates that atmospheric forcing is a driving factor of decadal sea-level trends. However, its effect is geographically heterogeneous. The Baltic Sea can be classified into two parts according to atmospheric impacts on decadal sea-level trends: one part consists of the northern and eastern regions of the Baltic Sea, where this impact is large. The other one covers the southern Baltic Sea area, with a smaller impact of the atmospheric circulation. To identify the influence of the large-scale factors other than the simultaneous effect of atmospheric circulation on the Baltic Sea level trends, we filter out the direct signature of atmospheric circulation on the Baltic Sea level by a multivariate linear regression model and analysed the residuals of this regression model. These residuals hint at a common underlying factor that coherently drives the decadal sea-level trends into the similar direction in the whole Baltic Sea region. We found that this underlying effect is partly a consequence of precipitation contribution to the Baltic Sea basin in the previous season. The investigation on the relation between the AMO-index and sea-level trends implies that this detected underlying factor is not connected to oceanic forcing driven from the North Atlantic region.

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Evaluation of ocean circulation models in the computation of the mean dynamic topography for geodetic applications. Case study in the Greek seas

Journal of Geodetic Science ◽

10.1515/jogs-2019-0015 ◽

2019 ◽

Vol 9 (1) ◽

pp. 154-173

Author(s):

I. Mintourakis ◽

G. Panou ◽

D. Paradissis

Keyword(s):

Sea Level ◽

Ocean Circulation ◽

Tide Gauge ◽

Dynamic Topography ◽

Tide Gauge Records ◽

Mean Dynamic Topography ◽

Case Study Area ◽

Extensive Evaluation ◽

Precise Knowledge

Abstract Precise knowledge of the oceanic Mean Dynamic Topography (MDT) is crucial for a number of geodetic applications, such as vertical datum unification and marine geoid modelling. The lack of gravity surveys over many regions of the Greek seas and the incapacity of the space borne gradiometry/gravity missions to resolve the small and medium wavelengths of the geoid led to the investigation of the oceanographic approach for computing the MDT. We compute two new regional MDT surfaces after averaging, for given epochs, the periodic gridded solutions of the Dynamic Ocean Topography (DOT) provided by two ocean circulation models. These newly developed regional MDT surfaces are compared to three state-of-theart models, which represent the oceanographic, the geodetic and the mixed oceanographic/geodetic approaches in the implementation of the MDT, respectively. Based on these comparisons, we discuss the differences between the three approaches for the case study area and we present some valuable findings regarding the computation of the regional MDT. Furthermore, in order to have an estimate of the precision of the oceanographic approach, we apply extensive evaluation tests on the ability of the two regional ocean circulation models to track the sea level variations by comparing their solutions to tide gauge records and satellite altimetry Sea Level Anomalies (SLA) data. The overall findings support the claim that, for the computation of the MDT surface due to the lack of geodetic data and to limitations of the Global Geopotential Models (GGMs) in the case study area, the oceanographic approach is preferable over the geodetic or the mixed oceano-graphic/geodetic approaches.

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The sea level changes in Hong Kong from tide-gauge records and remote sensing observations over the last seven decades

IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing ◽

10.1109/jstars.2021.3087263 ◽

2021 ◽

pp. 1-1

Author(s):

Fang Zou ◽

Robert Tenzer ◽

Hok Sum Fok ◽

Guojie Meng ◽

Qian Zhao

Keyword(s):

Remote Sensing ◽

Hong Kong ◽

Sea Level ◽

Tide Gauge ◽

Sea Level Changes ◽

Tide Gauge Records

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Inferring regional vertical crustal velocities from averaged relative sea level trends: A proof of concept

Journal of Geodetic Science ◽

10.1515/jogs-2017-0007 ◽

2017 ◽

Vol 7 (1) ◽

Author(s):

H. Bâki Iz ◽

C. K. Shum ◽

C. Zhang ◽

C. Y. Kuo

Keyword(s):

Sea Level ◽

Tide Gauge ◽

Eastern Coast ◽

Adjustment Process ◽

Tide Gauge Records ◽

Relative Sea Level ◽

Isostatic Adjustment ◽

Vertical Crustal Motion ◽

Gps Time Series

AbstractThis study demonstrates that relative sea level trends calculated from long-term tide gauge records can be used to estimate relative vertical crustal velocities in a region with high accuracy. A comparison of the weighted averages of the relative sea level trends estimated at six tide gauge stations in two clusters along the Eastern coast of United States, in Florida and in Maryland, reveals a statistically significant regional vertical crustal motion of Maryland with respect to Florida with a subsidence rate of −1.15±0.15 mm/yr identified predominantly due to the ongoing glacial isostatic adjustment process. The estimate is a consilience value to validate vertical crustal velocities calculated from GPS time series as well as towards constraining predictive GIA models in these regions.

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Performance Assessment of GNSS-R Polarimetric Observations for Sea Level Monitoring

10.5194/egusphere-egu21-12709 ◽

2021 ◽

Author(s):

Mahmoud Rajabi ◽

Mstafa Hoseini ◽

Hossein Nahavandchi ◽

Maximilian Semmling ◽

Markus Ramatschi ◽

...

Keyword(s):

Time Series ◽

Circular Polarization ◽

Sea Level ◽

Tide Gauge ◽

Satellite System ◽

Sea Surface ◽

Analysis Tool ◽

Lower Accuracy ◽

Coastal Sea ◽

Global Navigation Satellite

Determination and monitoring of the mean sea level especially in the coastal areas are essential, environmentally, and as a vertical datum. Ground-based Global Navigation Satellite System Reflectometry (GNSS-R) is an innovative way which is becoming a reliable alternative for coastal sea-level altimetry. Comparing to traditional tide gauges, GNSS-R can offer different parameters of sea surface, one of which is the sea level. The measurements derived from this technique can cover wider areas of the sea surface in contrast to point-wise observations of a tide gauge. &#160;We use long-term ground-based GNSS-R observations to estimate sea level. The dataset includes one-year data from January to December 2016. The data was collected by a coastal GNSS-R experiment at the Onsala space observatory in Sweden. The experiment utilizes three antennas with different polarization designs and orientations. The setup has one up-looking, and two sea-looking antennas at about 3 meters above the sea surface level. The up-looking antenna is Right-Handed Circular Polarization (RHCP). The sea-looking antennas with RHCP and Left-Handed Circular Polarization (LHCP) are used for capturing sea reflected Global Positioning System (GPS) signals. A dedicated reflectometry receiver (GORS type) provides In-phase and Quadrature (I/Q) correlation sums for each antenna based on the captured interferometric signal. The generated time series of I/Q samples from different satellites are analyzed using the Least Squares Harmonic Estimation (LSHE) method. This method is a multivariate analysis tool which can flexibly retrieve the frequencies of a time series regardless of possible gaps or unevenly spaced sampling. The interferometric frequency, which is related to the reflection geometry and sea level, is obtained by LSHE with a temporal resolution of 15&#160;minutes. The sea level is calculated based on this frequency in six modes from the three antennas in GPS L1 and L2 signals.Our investigation shows that the sea-looking antennas perform better compared to the up-looking antenna. The highest accuracy is achieved using the sea-looking LHCP antenna and GPS L1 signal. The annual Root Mean Square Error (RMSE) of 15-min GNSS-R water level time series compared to tide gauge observations is 3.7 (L1) and 5.2 (L2) cm for sea-looking LHCP, 5.8 (L1) and 9.1 (L2) cm for sea-looking RHCP, 6.2 (L1) and 8.5 (L2) cm for up-looking RHCP. It is worth noting that the GPS IIR block satellites show lower accuracy due to the lack of L2C code. Therefore, the L2 observations from this block are eliminated.

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Synthetically generated low-pressure systems to support studies of sea level extremes

10.5194/ems2021-132 ◽

2021 ◽

Author(s):

Mika Rantanen ◽

Jani Särkkä ◽

Jani Räihä ◽

Matti Kämäräinen ◽

Kirsti Jylhä

Keyword(s):

Sea Level ◽

Power Plants ◽

Tide Gauge ◽

Gaussian Function ◽

Low Pressure ◽

Tide Gauge Records ◽

Pressure System ◽

Sea Levels ◽

Input Parameters ◽

Low Pressure Systems

Extremely high sea levels on the Finnish coast are typically caused by close passages of extratropical cyclones (ETCs), which raise the sea level with their associated extreme winds and lower air pressure. For coastal infrastructure, such as nuclear power plants, it is crucial to study physically possible sea level heights associated with ETCs. Such sea levels are not straightforward to determine from observational datasets only, because tide gauge records&#160; cover about 100 years and do not necessarily capture the most extreme cases having return periods longer than 100 years.In this study, a method for generating an ensemble of synthetic low-pressure systems is being developed to investigate the extreme sea level heights on the Finnish coast of Baltic sea. As input parameters for the method, the point of origin, velocity of the center of the cyclone and depth of the pressure anomaly need to be given. Based on the input parameters, the method forms an idealized low-pressure system using a two-dimensional Gaussian function. In order to find extreme, but still reasonable values for the input parameters, cyclone tracks from ERA5 reanalysis data will be analysed.The ensemble of synthetic low pressure systems (i.e. the wind and pressure data) is used as an input to a numerical sea level model. As a result, we have an ensemble of simulated sea levels, from which we can determine the properties of the ETCs that induce the highest sea levels on a given location on the coast. The preliminary simulation results show that this method works well, forming a basis for studies on extreme sea levels.&#160;&#160;

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