Sea Level Trends Research Articles

General pattern of sea level in Safaga and Qusseir Harbours on the Egyptian Red Sea coast

Safaga and Qusseir are two important harbours on the Egyptian Proper Red Sea coast. To the best of the authors’ knowledge, this is the first work to describe the sea level characteristics at these two ports. The study is based on hourly sea level records over 3 years (2012–2014). There are no missed data at Qusseir site, but Safaga dataset missed 25% of records (April–December 2014). The hourly water level ranged between 0.02 m and 1.70 m at Safaga and between 0.04 m and 1.03 m at Qusseir, with a mean sea level (MSL) of 0.56 m and 0.50 m at the two Harbours, respectively. The T_TIDE package was used to produce astronomical and residual elevations at the two Harbours. Results revealed that the two Harbours examine explicit semidiurnal tidal cycle, with a bit higher astronomical amplitudes in Safaga. Moreover, the two sites exhibit almost the same seasonal sea level trend with very slight differences. The monthly mean levels at the two Harbours are always below their averages except during the summer months. The principal features of the semidiurnal tides indicated a ratio of 1.3 and 1.5 between spring and neap ranges at Safaga and Qusseir, respectively. The most pronounced sea level range at Safaga Harbour was 0.50 m, while it was 0.60 m at Qusseir Harbour. The astronomical elevations fluctuated between − 0.55 m and + 0.71 m and between − 0.47 m and + 0.53 m in Safaga and Qusseir Harbours, respectively.

Sea-level inundation and risk assessment along the south and southwest coasts of Sri Lanka

Global sea-level changes have been a major topic among scientists. Sea-level changes are not globally uniform. Reconstruction of paleo sea-level changes and monitoring of variations in regional sea-level are important to (i) evaluate future sea-level changes, and (ii) predict risk assessment. In this study, we examined sea-level inundation during the middle Holocene highstands based on paleo sea-level indicators along the south and southwest coasts of Sri Lanka. Besides, future sea-level inundation was predicted considering the calculated sea-level trends based on tidal gauge data and high-resolution surface elevation data. Light Detection and Ranging (LiDAR) is one of the most accurate optical remote sensing methods currently available to obtain high-resolution land surface elevation data. Therefore, in this study, Digital Elevation Models (DEMs) were prepared using LiDAR data for estimating the risk assessment in coastal lowlands. Tide gauge data of Colombo in Sri Lanka (from 2006 to 2017), Gan in the Maldives (from 1995 to 2017), and Hulhule in the Maldives (from 1995 to 2017) showed that sea-level has increased with a rate of 0.288 ± 0.118, 0.234 ± 0.025, and 0.368 ± 0.027 mm/month, respectively. DEMs based on LiDAR data suggested that south and southwest coasts are a risk of future sea-level inundation (height = 0.1–0.2 m during next 50 years and about 0.7 m in height during next 200 years, and distance = about 3.5–15.0 m from the present sea-level towards the inland). Consequently, it is important to consider future sea-level changes in disaster management and mitigation activities along the south and southwest coasts of Sri Lanka.

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.

Vulnerability of Venice's coastland to relative sea-level rise

Abstract. Relative sea-level rise (RSLR), i.e. sea-level rise due to climate changes combined with land subsidence, is one of the processes that is most severely threatening the coastal systems around the world. The Venice coastland forms the major low-lying area in Italy and encompasses a variety of environments, such as farmlands, estuaries, deltas, lagoons and urbanized areas. Valuable ecosystems, historical heritages and economic activities are located in this area. Since most of the territory lies at a ground elevation below or slightly above the mean sea-level, also a few mm yr−1 of land subsidence can seriously impacts on the Venice coastal system. In this study, we present an analysis of the vulnerability to RSLR considering an uneven land subsidence distribution, with an application on the Venice coastland. The analysis is delineated at the regional scale by an index-based model and a proper coupling of various thematic layers, such as high spatial resolution land subsidence data retrieved by satellite SAR interferometry, ongoing and projected sea-level rise trends, and morpho-physiographic setting of the coastland.

Improved and extended tide gauge records for the British Isles leading to more consistent estimates of sea level rise and acceleration since 1958

This paper describes methods of obtaining improved estimates of long-term sea level trends for the British Isles. This is achieved by lengthening the sea level records where possible, then removing known sources of variability, and then further adjusting for datum errors that are revealed by the previous processes after verification using metadata from archived sources. Local sea level variability is accounted for using a tide and surge model. Far field variability is accounted for using a “common mode”. This combination reduces the residual variability seen at tide gauges around the coast of the British Isles to the point that a number of previously unrecognised steps in individual records become apparent, permitting a higher level of quality control to be applied. A comprehensive data archaeology exercise was carried out which showed that these step-like errors are mostly coincident with recorded site-specific changes in instrumentation, and that in many cases the periodic tide gauge calibration records can be used to quantify these steps. A smaller number of steps are confirmed by “buddy-checking” against neighbouring tide gauges. After accounting for the observed steps, using levelling information where possible and an empirical fit otherwise, the records become significantly more consistent. The steps are not found to make a large difference to the trend and acceleration observed in UK sea level overall, but their correction results in much more consistent estimates of first order (Sea Level Rise) and second order (Sea Level Acceleration) trends over this 60-year period. We find a mean rate of sea level rise of 2.39 ± 0.27 mm yr−1, and an acceleration of 0.058 ± 0.030 mm yr−2 between Jan. 1958 and Dec. 2018. The cleaner dataset also permits us to show more clearly that the variability other than that derived from local meteorology is indeed consistent around the UK, and relates to sea level changes along the eastern boundary of the North Atlantic.

The rigorous adjustment of the global mean sea level budget during 2005–2015

Global mean sea level budget is rigorously adjusted during the period 2005–2015. The emphasis is to provide the best estimates for the linear rates of changes (trends) of the global mean sea level budget components during this period subject to the constraint: Earth's hydrosphere conserves water. The newly simultaneously adjusted trends of the budget components suggest a larger correction for the global mean sea level trend implicated by the other budget components' trends under the budget constraint. The simultaneous estimation of the linear trends of the budget components subject to the constraint for closure improves their uncertainties and enables a holistic assessment of the global mean sea budget, which has implications for future sea level science studies, including the future Intergovernmental Panel on Climate Change (IPCC) Assessment Reports, and the US Climate Assessment Reports.

Sea Level, Tidal, and River Flow Trends in the Lower Columbia River Estuary, 1853–present

AbstractFew tidal records are available pre‐1900 for the Pacific Ocean. We improve data coverage by recovering historical tabulations and digitizing analog tide rolls from Astoria, Oregon, for 1853–1876. Nearly 13,500 overlapping images of tides from 1855–1870 were digitized at a 6 min resolution using a line‐finding algorithm. Available hourly and high/low tabulations were also digitized, as were nearby hourly records from 1933 to 1943. Uncertainty was assessed by evaluating manual staff measurements, historical documents, and leveling surveys. Results suggest that uncertainty in mean sea level varies from ±0.07 m (early 1850s) to ±0.03 m (1867–1876) and is driven primarily by datum and benchmark uncertainty, rather than measurement precision, data reduction procedures, or hydrodynamic changes. We also corrected an up‐to 0.05 m error in the 1925–1960 tidal datum at Astoria. Harmonic analysis shows that major tidal constituents increased by up to 7% between 1855 and 2018. Mean tidal range increased by 0.1 m (5%), with more change occurring in July (0.17 m larger) than winter (0.07 m larger). By contrast, sea level increased most in winter and least in spring/summer. Tidally based estimates of river discharge suggest that these observations are caused by a ~50% reduction in peak spring discharge and a 30–60% increase in winter discharge. No evidence of altered upwelling is found. Overall, Astoria relative sea level (RSL) increased by 0.06 m ± 0.04 m since the 1858–1876 epoch or, after accounting for vertical land motion, 0.11 ± 0.09 m. Consistent with GNSS measurements, RSL has dropped near the estuary mouth since 1905, indicating a strong tectonic influence.

Estimating sea level rise around Australia using a new approach to account for low frequency climate signals

Regional sea level studies help to identify the vulnerable areas to the sea level rise. This study investigates the impact of climate modes on sea level variations and trends around Australia using altimetry data, climate indices, and sea level records from tide gauge stations. Here, we show that the sea level variations are negatively correlated with climate indices to the north and west of Australia. The spectral analyses of the climate indices and tide gauge data suggest that a low frequency signal with a period of 11 years emerges during the mid 1980s. Since the 25-year length of the satellite altimetry record is yet too short to detect low frequency signals, their effect on the estimation of regional sea level trend is unknown. Therefore, we estimate the sea level trend with consideration of this signal and using a two-step method. All signals with periods shorter than 7.5 years are first removed from sea level time series and then the trend is estimated using the parametric model that includes the 11-year signal. The skill of the parametric model in explaining the variations in sea level anomaly validates the presence of the 11-year signal detected in the spectrograms of the tide gauge data and climate indices. The average sea level trend for the study area is estimated as 3.85 ± 0.15 mm/year.

Sensitivity of Iberian estuaries to changes in sea water temperature, salinity, river flow, mean sea level, and tidal amplitudes

This study evaluated how multiyear changes in sea water temperature, salinity, river flow, sea level, and tidal amplitudes influenced the exchange mass flow, tidal energy propagation, water column stratification, and saline intrusion in 93 Iberian estuaries. To do this, trends estimated between 2000 and 2015 in four vulnerability indices that characterize these properties were evaluated. The analysis of the indices suggested that most of the estuaries reduced both exchange mass flow and tidal energy during the analysis period mainly due to the overall decreasing trends in the M2 tidal amplitude from 2000 to 2015, which are more significantly in the southwestern estuaries of the Atlantic façade. The bulk Richardson number for most of the Spanish estuaries, particularly those in Mediterranean waters, decreased due to the strong reduction of river flows in recent years. This fact, along with the increasing trends in mean sea level, produced a saline intrusion increase at all locations, being more pronounced in the Mediterranean and the South Atlantic estuaries of the Iberian Peninsula. With a view to identify the most sensitive estuaries to environmental changes, the four indices were merged into a single net sensitivity index. Overall, the most vulnerable estuaries were those located along the Mediterranean coast, especially Júcar and Segura inlets. In Atlantic waters, the Guadalquivir and Guadiana River estuaries showed the highest relative variations of the four indices. This study indicates that the reduction of river flows is the most influential factor that affects most Spanish Iberian estuaries.

Incorporating natural habitats into coastal risk assessment frameworks

The coastal risk assessment (CRA) has important implications for policy development, resilience enhancement, and risk reduction to reduce the magnitude and likelihood of future losses to coastal hazards. However, few if any existing in-practice CRA approaches account for the effects of coastal natural habitats (CNHs), which shield communities from natural hazards and support resilience enhancement in coastal regions. Here, we use a coupled human-nature system-based CRA framework to provide evidence on the influence of CNHs on coastal storm-risk levels and spatial distributions. We calculate a risk index for each coastal county along the U.S. Atlantic coast and employ different spatial assessment approaches to systematically analyse the risk. This index incorporates several bio-geo-physical variables (e.g., geomorphology, natural habitats, coastal relief, and historical data on sea level trends, wind, and wave) and data on socio-ecological systems. The index is calculated under two CNH scenarios (i.e., without- and with-habitat) and is further used for mapping the at-risk population. We find that the without-habitat scenario overestimates the population in the highest risk category by 10 % and the number of counties by as much as 40 % as compared to the with-habitat scenario—mostly in the Gulf region. Also, the without-habitat scenario miscalculates the spatial distribution of the risk (e.g., over/under-estimate the relative risk for Florida/New York). These findings highlight the role of CNHs to provide defensive services and the importance of incorporating CNHs into the risk assessment process. While the CNHs inclusive risk results are important for coastal risk-reduction through prioritization and smart resource allocation, the well evident influence of CNHs on risk level and its distribution is also supportive for conservationists to stress the policies relevant to the protection and restoration of coastal natural systems owing to their multiple services.

Contributions to Arctic sea level from 2003 to 2015

As one of the most remote and inaccessible regions in the world, the sea level in the Arctic is still today in large parts uncertain. Sea level estimates from GRACE and satellite altimetry show disagreements in areas of the Arctic while only few in-situ measurements are present to validate satellite products. By using an independent in-situ based dataset of hydrographic data (DTUSteric), this study compares different available datasets from GRACE and altimetry. The best agreement (R = 0.76) is reached between the combination of DTUSteric and the JPL Mascon solution and the altimetry product from Centre of Polar Observation and Modelling (CPOM). A large residual signal is found in the East Siberian Sea, an area with no in-situ observations and in general uncertain satellite observations. The spatial correlation coefficients ranging from 0.32 to 0.76 reflects a large number of unknowns and uncertainties, with coarse GRACE resolution, extensive interpolation and lack of in-situ data in parts of the Arctic Ocean and uncertainty of the altimetric products being the largest sources of error. In general, we recommended that satellite observations are used carefully in the Arctic. Even this study shows that steric estimates from in-situ observations to some extent can explain the gap between GRACE and altimetry, the observed sea level trend in significant regions of the Arctic cannot be validated with in-situ hydrographic data.

Trends of significant wave height and sea level in the southern water of the Special Region of Yogyakarta

Coastal zone is very vulnerable to the impacts of climate change. The increase of sea wave and sea level rise threaten coastal zone. The purpose of this study is to determine trends of significant wave height and sea level in the southern waters of the special region of Yogyakarta. The data used consists of daily significant wave height from 2010-2018, weekly absolute dynamics topography from 2005-2018 and daily surface wind from 2010-2018. Trends of significant wave height and sea level were analyzed by using linear regression. The results showed that significant wave height during the east season until the second transition season was higher than the west season and the first transition season. Vice versa, sea level during the east season until the second transition season was lower than the west season and the first transition season. Trends of significant wave height has increased of 0.63 cm/year, meanwhile sea level rise reached 0.82 cm/years.

Can We Resolve the Basin‐Scale Sea Level Trend Budget From GRACE Ocean Mass?

AbstractUnderstanding sea level changes at a regional scale is important for improving local sea level projections and coastal management planning. Sea level budget (SLB) estimates derived from the sum of observation of each component close for the global mean. The sum of steric and Gravity Recovery and Climate Experiment (GRACE) ocean mass contributions to sea level calculated from measurements does not match the spatial patterns of sea surface height trends from satellite altimetry at 1° grid resolution over the period 2005–2015. We investigate potential drivers of this mismatch aggregating to subbasin regions and find that the steric plus GRACE ocean mass observations do not represent the small‐scale features seen in the satellite altimetry. In addition, there are discrepancies with large variance apparent at the global and hemispheric scale. Thus, the SLB closure on the global scale to some extent represents a cancelation of errors. The SLB is also sensitive to the glacial isostatic adjustment correction for GRACE and to altimery orbital altitude. Discrepancies in the SLB are largest for the Indian‐South Pacific Ocean region. Taking the spread of plausible sea level trends, the SLB closes at the ocean‐basin scale ( ) but with large spread of magnitude, one third or more of the trend signal. Using the most up‐to‐date observation products, our ocean‐region SLB does not close everywhere, and consideration of systematic uncertainties diminishes what information can be gained from the SLB about sea level processes, quantifying contributions, and validating Earth observation systems.

Microfossil assemblages as key to reconstruct sea-level fluctuations, cooling episodes and palaeogeography: The Albian to Maastrichtian of Boreal and Peri-Tethyan Russia

Abstract The main palaeogeographic features of the Late Cretaceous Eastern European Platform and its southern framework are reconstructed mainly based on micropalaeontological data. An integrated foraminiferal–radiolarian zonation for the Upper Albian–Maastrichtian serves as a basis for palaeogeographic reconstructions and as a framework for the interpretation of palaeoclimate and sea-level trends. The study focuses on time slices of late Albian–Cenomanian, Turonian–Coniacian and Santonian–Campanian intervals. The late Albian was characterized by the gradual disappearance of a meridional seaway and the opening of connections into the Tethys Ocean and parts of the Peri-Tethys seas during the Cenomanian. As a result, mainly carbonate sedimentation prevailed during middle Turonian–Santonian times, characterized by high global sea-level. A cold Boreal water influence can be discerned not only along the northern margin of the Eastern European Platform, but as far south as the Northern Caucasus during certain time intervals, particularly during the Campanian. The Western Siberia Boreal Basin also influenced the study area, giving evidence of cooler-water episodes through the Palaeo-Ural territory and the Turgai Seaway.

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.

Mediterranean Sea level trends from long-period tide gauge time series

The main purpose of this study is to highlight, on the basis of statistical tests, the significant long-term changes of the Mediterranean Sea level, through the analysis of historical tide gauge records. In this framework, 14 tide gauge monthly series selected from the Permanent Service of the Mean Sea Level (PSMSL) database were used. The search for the presence or not of trends within these series, that have a temporal coverage from 59 to 142 years, was carried out using the Mann-Kendall test and the Sen’s slope estimator. The obtained results show that the Split Rt Marjana series are the only ones which does not exhibit a significant trend. The other 13 series show significant increasing trends. This result seems sufficient to suppose the presence, in the past century, of a new climatic phase on the scale of the Mediterranean basin, where the rising sea level is one of the consequences.

Global Trends of Sea Surface Gravity Wave, Wind, and Coastal Wave Setup

AbstractAssessing trends of sea surface wave, wind, and coastal wave setup is of considerable scientific and practical importance in view of recent and projected long-term sea level rise due to global warming. Here we analyze global significant wave height (SWH) and wind data from 1993 to 2015 and a wave model to (i) calculate wave age and explain the causal, or the lack thereof, relationship between wave and wind trends; and (ii) estimate trends of coastal wave setup and its contributions to secular trends of relative sea level at coastal locations around the world. We show in-phase, increasing SWH and wind trends in regions dominated by younger waves, and decreasing SWH trends where older waves dominate and are unrelated to the local wind trends. In the central North Pacific where wave age is transitional, in-phase decreasing wave and wind trends are found over the west-northwestern region, but wave and wind trends are insignificantly correlated in the south-southeastern region; here, a reversed, upward momentum flux from wave to wind is postulated. We show that coastal wave setup depends primarily on open-ocean SWH but only weakly on wind, varying approximately like SWH/(wind speed)1/5. The wave-setup trends are shown to be increasing along many coastlines where the local relative sea level trends are also increasing: the North and Irish Seas, Mediterranean Sea, East and South Asian seas, and eastern United States, exacerbating the potential for increased floods along these populated coastlines.

Long-term variations of the sea level on the western coast of the Antarctic Peninsula

The aim of the study is to analyze seasonal and interannual changes in sea level on the western coast of the Antarctic Peninsula. Objects of study are seasonal and interannual variability of sea level, air temperature, pressure at sea level, precipitation in the period 1960–2018 at the Faraday/Akademik Vernadsky station, which was considered as representative site for the Antarctic Peninsula. Statistical methods of study were used, including estimates of linear trends of time series using the nonparametric Sen’s estimator of slope. The Mann-Kendall test was used to assess the significance of the slope of the trend. Time variability analysis was performed using wavelet analysis. Using the MATrix LABoratory (MATLAB) software package, squared of wavelet coefficients were calculated depending on the scale and shift or scalograms that characterize the local energy spectrum, and scalegrams calculated by averaging the scalograms by time shifts. The Morlet wavelet transformations were used. The results of the calculations showed that the trend of sea level at the Faraday/ Akademik Vernadsky station in the period 1960—2018, according to observations and correction on glacial isostatic adjustment of the crust is in the range from 3.05 to 3.45 mm/year, which is significantly higher than the global trend of 2.1 mm/year. Sea level scalograms allow estimating time-averaged periods and amplitudes of the coefficients for each season. In the austral winter and spring characteristic periods were 4—6 years, whereas the summer and autumn periods are characterized by 6–8 years, as well as by the highest amplitudes of the coefficients. All seasons are characterized by the appearance of a weakly pronounced period of about 4 years. The presence of peaks in the scalegrams at 6–8 and 3–4 years confirms the relationship of atmospheric and oceanic processes in West Antarctica to the natural variations of the ocean-atmosphere system, such as the Southern Annular Mode and El Nino-Southern Oscillation, which varies with typical 3–4 and 6–8 year periods. It was concluded that, unlike air temperature, the sea level trend is relatively weakly depends on the season, with the exception of autumn, when sea level trend is three times smaller than the average value. At the same time, the air temperature trend is the largest in the austral winter and the lowest in the summer.

Characterization of Sea-level Variations Along the Metropolitan Coasts of France: Waves, Tides, Storm Surges and Long-term Changes

Dodet, G.; Bertin, X.; Bouchette, F.; Gravelle, M.; Testut, L., and Wöppelmann, G., 2019. Characterization of sea-level variations along the metropolitan coasts of France: Waves, tides, storm surges and long-term changes. In: Castelle, B. and Chaumillon, E. (eds.), Coastal Evolution under Climate Change along the Tropical Overseas and Temperate Metropolitan France. Journal of Coastal Research, Special Issue No. 88, pp. 10–24. Coconut Creek (Florida), ISSN 0749-0208.With 5853 km of coastlines facing the North Sea, the English Channel, the Atlantic Ocean and the Mediterranean Sea, France displays littoral zones exposed to a wide spectrum of wave climates, tidal ranges and storm surges. This study aims at characterizing in a systematic way sea level variations along the coasts of France. Wave climates are first characterized using state-of-the-art high resolution hindcasts validated against available observations from the national network CANDHIS. This analysis reveals a contrasting situation between coastal zones located along the Bay of Biscay, exposed to energetic and moderate-to-long period swells, and coastal zones located in the English Channel and the Mediterranean Sea, exposed mostly to wind seas and shorter period swells. Tides are characterized using available tide gauge measurements retrieved from the national REFMAR database and display large contrasts, between microtidal regimes along the Mediterranean Sea and macrotidal regimes along the English Channel. The analysis of storm surges computed from the same data reveals that they are controlled not only by storm tracks but also by the width of the continental shelf. Thus, during the studied period 1998-2018, storm surges derived from tide gauges measurements hardly reach 1.0 m along the coastlines of the southern Bay of Biscay and the eastern Mediterranean Sea but can exceed 2.0 m in the English Channel. The analysis of long-term sea level trends reveals significant variabilities, with an accelerated sea level rise on average from 1.2 mm/yr over the 20th century to 2.4 mm/yr over the two last decades, and ranging locally from 1.23 mm/yr (Roscoff) to 4.25 mm/yr (Nice). Finally, these values are compared against vertical land motions, computed from a state-of-the-art GPS reanalysis. A moderate land subsidence (<1 mm/year) is found for the majority of the stations.

P.224 BAD activation is involved in survival-promoting effect of NGF and BDNF dipeptide mimetics

Global sea level rise due to an increasingly warmer climate has begun to induce hazards, adversely affecting the lives and properties of people residing in low-lying coastal regions and islands. Therefore, it is important to monitor and understand variations in coastal sea level covering offshore regions. Signal-to-noise ratio (SNR) data of Global Navigation Satellite System (GNSS) have been successfully used to robustly derive sea level heights (SLHs). In Taiwan, there are a number of continuously operating GNSS stations, not originally installed for sea level monitoring. They were established in harbors or near coastal regions for monitoring land motion. This study utilizes existing SNR data from three GNSS stations (Kaohsiung, Suao, and TaiCOAST) in Taiwan to compute SLHs with two methods, namely, Lomb–Scargle Periodogram (LSP)-only, and LSP aided with tidal harmonic analysis developed in this study. The results of both methods are compared with co-located or nearby tide gauge records. Due to the poor quality of SNR data, the worst accuracy of SLHs derived from traditional LSP-only method exceeds 1 m at the TaiCOAST station. With our procedure, the standard deviations (STDs) of difference between GNSS-derived SLHs and tide gauge records in Kaohsiung and Suao stations decreased to 10 cm and the results show excellent agreement with tide gauge derived relative sea level records, with STD of differences of 7 cm and correlation coefficient of 0.96. In addition, the absolute GNSS-R sea level trend in Kaohsiung during 2006–2011 agrees well with that derived from satellite altimetry. We conclude that the coastal GNSS stations in Taiwan have the potential of monitoring absolute coastal sea level change accurately when our proposed methodology is used.