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

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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Timescales of emergence of chronic flooding in the major economic center of Guadeloupe

Natural Hazards and Earth System Science ◽

10.5194/nhess-21-703-2021 ◽

2021 ◽

Vol 21 (2) ◽

pp. 703-722

Author(s):

Gonéri Le Cozannet ◽

Déborah Idier ◽

Marcello de Michele ◽

Yoann Legendre ◽

Manuel Moisan ◽

...

Keyword(s):

Sea Level ◽

Tide Gauge ◽

Ground Motions ◽

Weather Conditions ◽

Coastal Zones ◽

Tide Gauge Records ◽

Sea Levels ◽

Vertical Ground Motions ◽

Vertical Ground ◽

Flooding Events

Abstract. Sea-level rise due to anthropogenic climate change is projected not only to exacerbate extreme events such as cyclones and storms but also to cause more frequent chronic flooding occurring at high tides under calm weather conditions. Chronic flooding occasionally takes place today in the low-lying areas of the Petit Cul-de-sac marin (Guadeloupe, West Indies, French Antilles). This area includes critical industrial and harbor and major economic infrastructures for the islands. As sea level rises, concerns are growing regarding the possibility of repeated chronic flooding events, which would alter the operations at these critical coastal infrastructures without appropriate adaptation. Here, we use information on past and future sea levels, vertical ground motion, and tides to assess times of emergence of chronic flooding in the Petit Cul-de-sac marin. For RCP8.5 (Representative Concentration Pathway 8.5; i.e., continued growth of greenhouse gas emissions), the number of flood days is projected to increase rapidly after the emergence of the process so that coastal sites will be flooded 180 d a year within 2 decades of the onset of chronic flooding. For coastal locations with the lowest altitude, we show that the reconstructed number of floods is consistent with observations known from a previous survey. Vertical ground motions are a key source of uncertainty in our projections. Yet, our satellite interferometric synthetic-aperture radar results show that the local variability in this subsidence is smaller than the uncertainties in the technique, which we estimate to be between 1 (standard deviation of measurements) and 5 mm/yr (upper theoretical bound). Despite these uncertainties, our results imply that adaptation pathways considering a rapid increase in recurrent chronic flooding are required for the critical port and industrial and commercial center of Guadeloupe. Similar processes are expected to take place in many low-elevation coastal zones worldwide, including on other tropical islands. The method used in this study can be applied to other locations, provided tide gauge records and local knowledge of vertical ground motions are available. We argue that identifying times of emergence of chronic flooding events is urgently needed in most low-lying coastal areas, because adaptation requires decades to be implemented, whereas chronic flooding hazards can worsen drastically within years of the first event being observed.

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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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Extreme sea levels at the Finnish coast due to large-scale wind storms

10.5194/egusphere-egu21-8839 ◽

2021 ◽

Author(s):

Jani Särkkä ◽

Jani Räihä ◽

Mika Rantanen ◽

Kirsti Jylhä

Keyword(s):

Baltic Sea ◽

Sea Level ◽

Large Scale ◽

Low Pressure ◽

The Baltic Sea ◽

Sea Levels ◽

Sea Level Variation ◽

Level Model ◽

The Baltic ◽

Low Pressure Systems

In the Baltic Sea, the short-term sea level variation might be several meters, even if the tides in the Baltic Sea are negligible. The short-term sea level fluctuations are caused by passing wind storms, inducing sea level variation through wind-induced currents, inverse barometric effect and seiches. Due to the shape of the Baltic Sea with several bays, the highest sea levels are found in the ends of bays like the Gulf of Finland and the Bothnian Bay. The sea level extremes caused by the large-scale windstorms depend strongly on the storm tracks. Within the natural climatic variability during the past centuries, there have most likely been higher sea level extremes than the extreme values found in the tide gauge records.To study this variability of sea levels, induced by varying tracks of the passing windstorms, we construct an ensemble of synthetic low-pressure systems. In this ensemble, the parameters of the low-pressure systems (e.g. point of origin, velocity of the center of the system and depth of the pressure anomaly) are varied. The ensemble of low pressure systems is used as an input to a numerical sea level model based on shallow-water hydrodynamic equations. The sea level model is fast to calculate, enabling a study of a large set of varying storm tracks. As a result we have an ensemble of simulated sea levels. From the simulation results we can determine the low-pressure system that induces the highest sea level on a given location on the coast. We concentrate our studies on the Finnish coast, but the method can be applied to the entire Baltic coast.&#160;

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Measuring Coastal Absolute Sea-Level Changes Using GNSS Interferometric Reflectometry

Remote Sensing ◽

10.3390/rs13214319 ◽

2021 ◽

Vol 13 (21) ◽

pp. 4319

Author(s):

Dongju Peng ◽

Lujia Feng ◽

Kristine M. Larson ◽

Emma M. Hill

Keyword(s):

Sea Level ◽

Satellite Altimetry ◽

Tide Gauge ◽

Global Navigation Satellite Systems ◽

Coastal Zones ◽

Sea Level Changes ◽

Tide Gauge Records ◽

Sea Levels ◽

Satellite Systems ◽

Linear Trends

Rising sea levels pose one of the greatest threats to coastal zones. However, sea-level changes near the coast, particularly absolute sea-level changes, have been less well monitored than those in the open ocean. In this study, we aim to investigate the potential of Global Navigation Satellite Systems Interferometric Reflectometry (GNSS-IR) to measure coastal absolute sea-level changes and tie on-land (coastal GNSS) and offshore (satellite altimetry) observations into the same framework. We choose three coastal GNSS stations, one each in regions of subsidence, uplift and stable vertical land motions, to derive both relative sea levels and sea surface heights (SSH) above the satellite altimetry reference ellipsoid from 2008 to 2020. Our results show that the accuracy of daily mean sea levels from GNSS-IR is <1.5 cm compared with co-located tide-gauge records, and amplitudes of annual cycle and linear trends estimated from GNSS-IR measurements and tide-gauge data agree within uncertainty. We also find that the de-seasoned and de-trended SSH time series from GNSS-IR and collocated satellite altimetry are highly correlated and the estimated annual amplitudes and linear trends statistically agree well, indicating that GNSS-IR has the potential to monitor coastal absolute sea-level changes and provide valuable information for coastal sea-level and climate studies.

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Regional Trends of Sea Level Rise along the Coast of Bangladesh

International Journal of Engineering Sciences ◽

10.36224/ijes.130102 ◽

2020 ◽

Vol 13 (1) ◽

Author(s):

Naila Matin ◽

G. M. Jahid Hasan ◽

Myisha Ahmad

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Tide Gauge ◽

Water Levels ◽

Linear Regression Method ◽

Tide Gauge Records ◽

Efficient Manner ◽

Sea Levels ◽

Regional Trends ◽

Changing Trend

Bangladesh is becoming increasingly vulnerable to the growing threat of climate change induced sea level rise. Considering the potential severe impacts that sea level rise will have on the coastal population and the country’s economy, it has become very important to know about the regional trends of changing sea levels along the coastlands of Bangladesh. The present study attempted to portray a representative scenario of sea level rise in the coastal regions of Bangladesh. Historic tide gauge records, ranging from 20 to 45 years, were used to determine reliable trends at multiple locations along the coast. Linear regression method was applied to derive the changing trend of annual high, mean and low tidal water levels. The location-specific trends of sea level rise determined in this study can be helpful to planners and policy makers to combat the emerging threat of SLR in a more efficient manner.

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Effects of the basin dynamics on sea level rise in the Black Sea

10.5194/os-2016-69 ◽

2016 ◽

Author(s):

A. A. Kubryakov ◽

S. V. Stanichny ◽

D. L. Volkov

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Black Sea ◽

Tide Gauge ◽

The Black Sea ◽

Tide Gauges ◽

Tide Gauge Records ◽

Sea Levels ◽

The Difference

Abstract. Satellite altimetry measurements show that magnitude of the Black Sea level trends is spatially uneven. While the basin-averaged sea level was increasing at a rate of 3.15 mm/year from 1993 to 2014, the sea level rise varied from 0.15–2.5 mm/year in the central part to 3.5–3.8 mm/year in coastal areas and 5 mm/year in the southwestern part of the sea. These differences are caused by changes in the large- and mesoscale circulation of the Black Sea. A long-term increase of the cyclonic wind curl over the basin from 1979 to 2014 strengthened divergence in the center of the Black Sea that led to an increase of sea level near the coast and a decrease in the center of the basin. Changes in the distribution and intensity of mesoscale eddies caused the formation of the local extremes of sea level trend. The variability of the dynamic sea level (DSL) – the difference between the local and the basin-averaged sea levels – contributes significantly (up to ~ 50 % of the total variance) to the seasonal and interannual variability of sea level in the basin. The DSL variability in the Black Sea depends strongly on the basin-averaged wind curl and is well reconstructed using the ERA-Interim winds from 1979 to present, including the time when altimetry data was unavailable. The reconstruction can be used to correct historical tide gauges data for dynamic effects, which are usually neglected in the analysis of the Black Sea tide gauge records.

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Rescuing historical sea level data using a citizen science platform

10.5194/egusphere-egu21-3211 ◽

2021 ◽

Author(s):

Andrew Matthews ◽

Elizabeth Bradshaw ◽

Joanne Williams

Keyword(s):

Sea Level ◽

Citizen Science ◽

Character Recognition ◽

Optical Character Recognition ◽

Tide Gauge ◽

Digital Data ◽

Tide Gauge Records ◽

Sea Levels ◽

North West ◽

The Uk

Tide gauge records provide the main source of data behind the study of sea level change over the past 200 years. However, our understanding of changes in mean sea levels, tides and extremes is limited by the length of the records available. A large amount of potential data exists in libraries and archives across the world in the form of historical tidal ledgers and charts that have never been converted into digital data suitable for use in scientific studies. The Intergovernmental Oceanographic Commission&#8217;s Global Sea Level Observing System (GLOSS) has been encouraging organisations to locate, catalogue and digitise such material.Unfortunately, the processes required to extract usable data from charts and ledgers is slow, laborious work. Promising attempts have been made to automate this using optical character recognition, but these are often hindered by changes in document formats, and hard to decipher handwriting, particularly in older records.A possible solution is to use online citizen science platforms such as Zooniverse that bring together scientists and volunteers in projects as diverse as searching for supernovae, identifying whale sounds, transcribing manuscripts from the archives of natural history museums, and helping train algorithms that analyse images of cancer cells. Last year, 5.25 million rainfall observations from the UK were digitised in a few weeks by about 16,000 volunteers.Here we present a citizen science project to digitise 16,000 images of ledgers recording 15-minute observations of sea level from North West England that is currently in progress. We describe the process the volunteers undertake, the lessons learnt from early testing, and an overview of the results obtained so far. Finally, we discuss some potential extensions of the project, including the possibility of using the platform to digitise tidal charts.

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Status of Mean Sea Level Rise around the USA (2020)

GeoHazards ◽

10.3390/geohazards2020005 ◽

2021 ◽

Vol 2 (2) ◽

pp. 80-100

Author(s):

Phil J. Watson

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Satellite Altimetry ◽

Gulf Coast ◽

Tide Gauge ◽

Tide Gauge Records ◽

Mean Sea Level ◽

Sea Levels ◽

Vertical Land Motion ◽

The Usa

The potential threats to the USA from current and projected sea level rise are significant, with profound environmental, social and economic consequences. This current study continues the refinement and improvement in analysis techniques for sea level research beyond the Fourth US National Climate Assessment (NCA4) report by incorporating further advancements in the time series analysis of long tide gauge records integrated with an improved vertical land motion (VLM) assessment. This analysis has also been synthesised with an updated regional assessment of satellite altimetry trends in the sea margins fringing the USA. Coastal margins more vulnerable to the threats posed by rising sea levels are those in which subsidence is prevalent, higher satellite altimetry trends are evident and higher ‘geocentric’ velocities in mean sea level are being observed. The evidence from this study highlights key spatial features emerging in 2020, which highlight the northern foreshore of the Gulf Coast and along the east coast of the USA south of the Chesapeake Bay region being more exposed to the range of factors exacerbating threats from sea level rise than other coastlines at present. The findings in this study complement and extend sea level research beyond NCA4 to 2020.

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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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