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T. Verhoelst, J. Granville, F. Hendrick, U. Köhler, C. Lerot, J.-P. Pommereau, A. Redondas, M. Van Roozendael, J.-C. Lambert. (2015). Metrology of ground-based satellite validation: co-location mismatch and smoothing issues of total ozone comparisons (Vol. 8).
Abstract: Abstract. Comparisons with ground-based correlative measurements constitute a key component in the validation of satellite data on atmospheric composition. The error budget of these comparisons contains not only the measurement errors but also several terms related to differences in sampling and smoothing of the inhomogeneous and variable atmospheric field. A versatile system for Observing System Simulation Experiments (OSSEs), named OSSSMOSE, is used here to quantify these terms. Based on the application of pragmatic observation operators onto high-resolution atmospheric fields, it allows a simulation of each individual measurement, and consequently, also of the differences to be expected from spatial and temporal field variations between both measurements making up a comparison pair. As a topical case study, the system is used to evaluate the error budget of total ozone column (TOC) comparisons between GOME-type direct fitting (GODFITv3) satellite retrievals from GOME/ERS2, SCIAMACHY/Envisat, and GOME-2/MetOp-A, and ground-based direct-sun and zenith–sky reference measurements such as those from Dobsons, Brewers, and zenith-scattered light (ZSL-)DOAS instruments, respectively. In particular, the focus is placed on the GODFITv3 reprocessed GOME-2A data record vs. the ground-based instruments contributing to the Network for the Detection of Atmospheric Composition Change (NDACC). The simulations are found to reproduce the actual measurements almost to within the measurement uncertainties, confirming that the OSSE approach and its technical implementation are appropriate. This work reveals that many features of the comparison spread and median difference can be understood as due to metrological differences, even when using strict co-location criteria. In particular, sampling difference errors exceed measurement uncertainties regularly at most mid- and high-latitude stations, with values up to 10 % and more in extreme cases. Smoothing difference errors only play a role in the comparisons with ZSL-DOAS instruments at high latitudes, especially in the presence of a polar vortex due to the strong TOC gradient it induces. At tropical latitudes, where TOC variability is lower, both types of errors remain below about 1 % and consequently do not contribute significantly to the comparison error budget. The detailed analysis of the comparison results, including the metrological errors, suggests that the published random measurement uncertainties for GODFITv3 reprocessed satellite data are potentially overestimated, and adjustments are proposed here. This successful application of the OSSSMOSE system to close for the first time the error budget of TOC comparisons, bodes well for potential future applications, which are briefly touched upon.
Programme: 209
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Anne Boynard, Daniel Hurtmans, Mariliza E. Koukouli, Florence Goutail, Jérôme Bureau, Sarah Safieddine, Christophe Lerot, Juliette Hadji-Lazaro, Catherine Wespes, Jean-Pierre Pommereau, Andrea Pazmino, Irene Zyrichidou, Dimitris Balis, Alain Barbe, Semen N. Mikhailenko, Diego Loyola, Pieter Valks, Michel Van Roozendael, Pierre-François Coheur, Cathy Clerbaux. (2016). Seven years of IASI ozone retrievals from FORLI: validation with independent total column and vertical profile measurements (Vol. 9).
Abstract: Abstract. This paper presents an extensive intercomparison and validation for the ozone (O3) product measured by the two Infrared Atmospheric Sounding Interferometers (IASIs) launched on board the MetOp-A and MetOp-B satellites in 2006 and in 2012 respectively. IASI O3 total columns and vertical profiles obtained from Fast Optimal Retrievals on Layers for IASI (FORLI) v20140922 software (running up until recently) are validated against independent observations during the period 2008–2014 on a global scale. On average for the period 2013–2014, IASI-A and IASI-B total ozone columns (TOCs) retrieved using FORLI are consistent, with IASI-B providing slightly lower values with a global difference of only 0.2±0.8%. The comparison between IASI-A and IASI-B O3 vertical profiles shows differences within ±2% over the entire altitude range. Global validation results for 7 years of IASI TOCs from FORLI against the Global Ozone Monitoring Experiment-2 (GOME-2) launched on board MetOp-A and Brewer–Dobson data show that, on average, IASI overestimates the ultraviolet (UV) data by 5–6% with the largest differences found in the southern high latitudes. The comparison with UV–visible SAOZ (Système d'Analyse par Observation Zénithale) measurements shows a mean bias between IASI and SAOZ TOCs of 2–4% in the midlatitudes and tropics and 7% at the polar circle. Part of the discrepancies found at high latitudes can be attributed to the limited information content in the observations due to low brightness temperatures. The comparison with ozonesonde vertical profiles (limited to 30km) shows that on average IASI with FORLI processing underestimates O3 by ∼ 5–15% in the troposphere while it overestimates O3 by ∼ 10–40% in the stratosphere, depending on the latitude. The largest relative differences are found in the tropical tropopause region; this can be explained by the low O3 amounts leading to large relative errors. In this study, we also evaluate an updated version of FORLI-O3 retrieval software (v20151001), using look-up tables recalculated to cover a larger spectral range using the latest HITRAN spectroscopic database (HITRAN 2012) and implementing numerical corrections. The assessment of the new O3 product with the same set of observations as that used for the validation exercise shows a correction of ∼ 4% for the TOC positive bias when compared to the UV ground-based and satellite observations, bringing the overall global comparison to ∼ 1–2% on average. This improvement is mainly associated with a decrease in the retrieved O3 concentration in the middle stratosphere (above 30hPa/25km) as shown by the comparison with ozonesonde data.
Programme: 209
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Anne Boynard, Daniel Hurtmans, Katerina Garane, Florence Goutail, Juliette Hadji-Lazaro, Maria Elissavet Koukouli, Catherine Wespes, Corinne Vigouroux, Arno Keppens, Jean-Pierre Pommereau, Andrea Pazmino, Dimitris Balis, Diego Loyola, Pieter Valks, Ralf Sussmann, Dan Smale, Pierre-François Coheur, Cathy Clerbaux. (2018). Validation of the IASI FORLI/EUMETSAT ozone products using satellite (GOME-2), ground-based (Brewer–Dobson, SAOZ, FTIR) and ozonesonde measurements (Vol. 11). Bachelor's thesis, , .
Abstract: This Paper Assesses The Quality Of Iasi (Infrared Atmospheric Sounding Interferometer)/metop-a (Iasi-a) And Iasi/metop-b (Iasi-b) Ozone (O3) Products (Total And Partial O3 Columns) Retrieved With The Fast Optimal Retrievals On Layers For Iasi Ozone (Forli-o3; V20151001) Software For 9 Years (2008–july 2017) Through An Extensive Intercomparison And Validation Exercise Using Independent Observations (Satellite, Ground-based And Ozonesonde). Compared With The Previous Version Of Forli-o3 (V20140922), Several Improvements Have Been Introduced In Forli-o3 V20151001, Including Absorbance Look-up Tables Recalculated To Cover A Larger Spectral Range, With Additional Numerical Corrections. This Leads To A Change Of ∼4% In The Total Ozone Column (Toc) Product, Which Is Mainly Associated With A Decrease In The Retrieved O3 Concentration In The Middle Stratosphere (Above 30hpa/25km). Iasi-a And Iasi-b Tocs Are Consistent, With A Global Mean Difference Of Less Than 0.3% For Both Daytime And Nighttime Measurements; Iasi-a Is Slightly Higher Than Iasi-b. A Global Difference Of Less Than 2.4% Is Found For The Tropospheric (Tropo) O3 Column Product (Iasi-a Is Lower Than Iasi-b), Which Is Partly Due To A Temporary Issue Related To The Iasi-a Viewing Angle In 2015. Our Validation Shows That Iasi-a And Iasi-b Tocs Are Consistent With Gome-2 (Global Ozone Monitoring Experiment-2), Dobson, Brewer, Saoz (Système D'analyse Par Observation Zénithale) And Ftir (Fourier Transform Infrared) Tocs, With Global Mean Differences In The Range Of 0.1%–2% Depending On The Instruments Compared. The Worst Agreement With Uv–vis Retrieved Toc (Satellite And Ground) Is Found At The Southern High Latitudes. The Iasi-a And Ground-based Toc Comparison For The Period From 2008 To July 2017 Shows The Long-term Stability Of Iasi-a, With Insignificant Or Small Negative Drifts Of 1%–3%decade−1. The Comparison Results Of Iasi-a And Iasi-b Against Smoothed Ftir And Ozonesonde Partial O3 Columns Vary With Altitude And Latitude, With The Maximum Standard Deviation Being Seen For The 300–150hpa Column (20%–40%) Due To Strong Ozone Variability And Large Total Retrievals Errors. Compared With Ozonesonde Data, The Iasi-a And Iasi-b O3 Tropo Column (Defined As The Column Between The Surface And 300hpa) Is Positively Biased In The High Latitudes (4%–5%) And Negatively Biased In The Midlatitudes And Tropics (11%–13% And 16%–19%, Respectively). The Iasi-a-to-ozonesonde Tropo Comparison For The Period From 2008 To 2016 Shows A Significant Negative Drift In The Northern Hemisphere Of -8.6±3.4%decade−1, Which Is Also Found In The Iasi-a-to-ftir Tropo Comparison. When Considering The Period From 2011 To 2016, The Drift Value For The Tropo Column Decreases And Becomes Statistically Insignificant. The Observed Negative Drifts Of The Iasi-a Tropo O3 Product (8%–16%decade−1) Over The 2008–2017 Period Might Be Taken Into Consideration When Deriving Trends From This Product And This Time Period.
Programme: 209
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Katerina Garane, Christophe Lerot, Melanie Coldewey-Egbers, Tijl Verhoelst, Maria Elissavet Koukouli, Irene Zyrichidou, Dimitris S. Balis, Thomas Danckaert, Florence Goutail, Jose Granville, Daan Hubert, Arno Keppens, Jean-Christopher Lambert, Diego Loyola, Jean-Pierre Pommereau, Michel Van Roozendael, Claus Zehner. (2018). Quality assessment of the Ozone_cci Climate Research Data Package (release 2017) – Part 1: Ground-based validation of total ozone column data products (Vol. 11).
Abstract: The Gome-type Total Ozone Essential Climate Variable (Gto-ecv) Is A Level-3 Data Record, Which Combines Individual Sensor Products Into One Single Cohesive Record Covering The 22-year Period From 1995 To 2016, Generated In The Frame Of The European Space Agency's Climate Change Initiative Phase Ii. It Is Based On Level-2 Total Ozone Data Produced By The Godfit (Gome-type Direct Fitting) V4 Algorithm As Applied To The Gome/ers-2, Omi/aura, Sciamachy/envisat And Gome-2/metop-a And Metop-b Observations. In This Paper We Examine Whether Gto-ecv Meets The Specific Requirements Set By The International Climate–chemistry Modelling Community For Decadal Stability Long-term And Short-term Accuracy. In The Following, We Present The Validation Of The 2017 Release Of The Climate Research Data Package Total Ozone Column (Crdp Toc) At Both Level 2 And Level 3. The Inter-sensor Consistency Of The Individual Level-2 Data Sets Has Mean Differences Generally Within 0.5% At Moderate Latitudes (±50°), Whereas The Level-3 Data Sets Show Mean Differences With Respect To The Omi Reference Data Record That Span Between −0.2±0.9% (For Gome-2b) And 1.0±1.4% (For Sciamachy). Very Similar Findings Are Reported For The Level-2 Validation Against Independent Ground-based Toc Observations Reported By Brewer, Dobson And Saoz Instruments: The Mean Bias Between Godfit V4 Satellite Toc And The Ground Instrument Is Well Within 1.0±1.0% For All Sensors, The Drift Per Decade Spans Between −0.5% And 1.0±1.0% Depending On The Sensor, And The Peak-to-peak Seasonality Of The Differences Ranges From ∼ 1% For Gome And Omi To ∼ 2% For Sciamachy. For The Level-3 Validation, Our First Goal Was To Show That The Level-3 Crdp Produces Findings Consistent With The Level-2 Individual Sensor Comparisons. We Show A Very Good Agreement With 0.5 To 2% Peak-to-peak Amplitude For The Monthly Mean Difference Time Series And A Negligible Drift Per Decade Of The Differences In The Northern Hemisphere Of −0.11±0.10%decade−1 For Dobson And +0.22±0.08%decade−1 For Brewer Collocations. The Exceptional Quality Of The Level-3 Gto-ecv V3 Toc Record Temporal Stability Satisfies Well The Requirements For The Total Ozone Measurement Decadal Stability Of 1–3% And The Short-term And Long-term Accuracy Requirements Of 2 And 3%, Respectively, Showing A Remarkable Inter-sensor Consistency, Both In The Level-2 Godfit V4 And In The Level-3 Gto-ecv V3 Datasets, And Thus Can Be Used For Longer-term Analysis Of The Ozone Layer, Such As Decadal Trend Studies, Chemistry–climate Model Evaluation And Data Assimilation Applications.
Programme: 209
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Abdelhadi El Yazidi, Michel Ramonet, Philippe Ciais, Gregoire Broquet, Isabelle Pison, Amara Abbaris, Dominik Brunner, Sebastien Conil, Marc Delmotte, Francois Gheusi, Frederic Guerin, Lynn Hazan, Nesrine Kachroudi, Giorgos Kouvarakis, Nikolaos Mihalopoulos, Leonard Rivier, Dominique Serça. (2018). Identification of spikes associated with local sources in continuous time series of atmospheric CO, CO2 and CH4 (Vol. 11). Bachelor's thesis, , .
Abstract: This Study Deals With The Problem Of Identifying Atmospheric Data Influenced By Local Emissions That Can Result In Spikes In Time Series Of Greenhouse Gases And Long-lived Tracer Measurements. We Considered Three Spike Detection Methods Known As Coefficient Of Variation (Cov), Robust Extraction Of Baseline Signal (Rebs) And Standard Deviation Of The Background (Sd) To Detect And Filter Positive Spikes In Continuous Greenhouse Gas Time Series From Four Monitoring Stations Representative Of The European Icos (Integrated Carbon Observation System) Research Infrastructure Network. The Results Of The Different Methods Are Compared To Each Other And Against A Manual Detection Performed By Station Managers. Four Stations Were Selected As Test Cases To Apply The Spike Detection Methods: A Continental Rural Tower Of 100m Height In Eastern France (Ope), A High-mountain Observatory In The South-west Of France (Pdm), A Regional Marine Background Site In Crete (Fkl) And A Marine Clean-air Background Site In The Southern Hemisphere On Amsterdam Island (Ams). This Selection Allows Us To Address Spike Detection Problems In Time Series With Different Variability. Two Years Of Continuous Measurements Of Co2, Ch4 And Co Were Analysed. All Methods Were Found To Be Able To Detect Short-term Spikes (Lasting From A Few Seconds To A Few Minutes) In The Time Series. Analysis Of The Results Of Each Method Leads Us To Exclude The Cov Method Due To The Requirement To Arbitrarily Specify An A Priori Percentage Of Rejected Data In The Time Series, Which May Over- Or Underestimate The Actual Number Of Spikes. The Two Other Methods Freely Determine The Number Of Spikes For A Given Set Of Parameters, And The Values Of These Parameters Were Calibrated To Provide The Best Match With Spikes Known To Reflect Local Emissions Episodes That Are Well Documented By The Station Managers. More Than 96% Of The Spikes Manually Identified By Station Managers Were Successfully Detected Both In The Sd And The Rebs Methods After The Best Adjustment Of Parameter Values. At Pdm, Measurements Made By Two Analyzers Located 200m From Each Other Allow Us To Confirm That The Ch4 Spikes Identified In One Of The Time Series But Not In The Other Correspond To A Local Source From A Sewage Treatment Facility In One Of The Observatory Buildings. From This Experiment, We Also Found That The Rebs Method Underestimates The Number Of Positive Anomalies In The Ch4 Data Caused By Local Sewage Emissions. As A Conclusion, We Recommend The Use Of The Sd Method, Which Also Appears To Be The Easiest One To Implement In Automatic Data Processing, Used For The Operational Filtering Of Spikes In Greenhouse Gases Time Series At Global And Regional Monitoring Stations Of Networks Like That Of The Icos Atmosphere Network.
Programme: 416
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Sentia Goursaud, Valérie Masson-Delmotte, Vincent Favier, Anaïs Orsi, Martin Werner. (2018). Water stable isotope spatio-temporal variability in Antarctica in 1960–2013: observations and simulations from the ECHAM5-wiso atmospheric general circulation model (Vol. 14).
Abstract: Abstract. Polar ice core water isotope records are commonly used to infer past changes in Antarctic temperature, motivating an improved understanding and quantification of the temporal relationship between δ18O and temperature. This can be achieved using simulations performed by atmospheric general circulation models equipped with water stable isotopes. Here, we evaluate the skills of the high-resolution water-isotope-enabled atmospheric general circulation model ECHAM5-wiso (the European Centre Hamburg Model) nudged to European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis using simulations covering the period 1960–2013 over the Antarctic continent.
We compare model outputs with field data, first with a focus on regional climate variables and second on water stable isotopes, using our updated dataset of water stable isotope measurements from precipitation, snow, and firn–ice core samples. ECHAM5-wiso simulates a large increase in temperature from 1978 to 1979, possibly caused by a discontinuity in the European Reanalyses (ERA) linked to the assimilation of remote sensing data starting in 1979.
Although some model–data mismatches are observed, the (precipitation minus evaporation) outputs are found to be realistic products for surface mass balance. A warm model bias over central East Antarctica and a cold model bias over coastal regions explain first-order δ18O model biases by too-strong isotopic depletion on coastal areas and underestimated depletion inland. At the second order, despite these biases, ECHAM5-wiso correctly captures the observed spatial patterns of deuterium excess. The results of model–data comparisons for the inter-annual δ18O standard deviation differ when using precipitation or ice core data. Further studies should explore the importance of deposition and post-deposition processes affecting ice core signals and not resolved in the model.
These results build trust in the use of ECHAM5-wiso outputs to investigate the spatial, seasonal, and inter-annual δ18O–temperature relationships. We thus make the first Antarctica-wide synthesis of prior results. First, we show that local spatial or seasonal slopes are not a correct surrogate for inter-annual temporal slopes, leading to the conclusion that the same isotope–temperature slope cannot be applied for the climatic interpretation of Antarctic ice core for all timescales. Finally, we explore the phasing between the seasonal cycles of deuterium excess and δ18O as a source of information on changes in moisture sources affecting the δ18O–temperature relationship. The few available records and ECHAM5-wiso show different phase relationships in coastal, intermediate, and central regions.
This work evaluates the use of the ECHAM5-wiso model as a tool for the investigation of water stable isotopes in Antarctic precipitation and calls for extended studies to improve our understanding of such proxies.
Programme: 411
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Bart Van de Vijver, Carlos E. Wetzel, Luc Ector. (2018). Analysis of the type material of Planothidium delicatulum (Bacillariophyta) with the description of two new Planothidium species from the sub-Antarctic Region (Vol. 18).
Abstract: During a survey of the freshwater diatom flora on the sub-Antarctic islands of the southern Indian Ocean, two new Planothidium species were observed, showing some resemblance to Planothidium delicatulum. Therefore, the type material of Achnanthidium delicatulum Kützing was analysed, a common species in northern hemisphere waterbodies that was later transferred to the genus Planothidium. Additionally the material of Types du Synopsis des Diatomées de Belgique n° 234, designated in 1980 as neotype for Achnanthes delicatula was investigated. This analysis showed that the population in Types n° 234 is not conspecific with Achnanthidium delicatulum but in fact is a population of Planothidium galaicum. Both Planothidium species in the investigated Antarctic material are described as new to science: P. lilianeanum Van de Vijver sp. nov. and P. australodelicatulum Van de Vijver, C.E.Wetzel et Ector sp. nov. The new species can be differentiated based on differences in valve outline, presence of ridges and silica outgrowths on the rapheless valve, the structure of the raphe and the shape and size of the central area. Notes on the ecology and distribution of the new Antarctic species are added. Achnanthidium delicatulum is formally lectotypified.
Programme: 136
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Julie M. Jones, Sarah T. Gille, Hugues Goosse, Nerilie J. Abram, Pablo O. Canziani, Dan J. Charman, Kyle R. Clem, Xavier Crosta, Casimir de Lavergne, Ian Eisenman, Matthew H. England, Ryan L. Fogt, Leela M. Frankcombe, Gareth J. Marshall, Valérie Masson-Delmotte, Adele K. Morrison, Anaïs J. Orsi, Marilyn N. Raphael, James A. Renwick, David P. Schneider, Graham R. Simpkins, Eric J. Steig, Barbara Stenni, Didier Swingedouw, Tessa R. Vance. (2016). Assessing recent trends in high-latitude Southern Hemisphere surface climate (Vol. 6).
Abstract: Understanding the causes of recent climatic trends and variability in the high-latitude Southern Hemisphere is hampered by a short instrumental record. Here, we analyse recent atmosphere, surface ocean and sea-ice observations in this region and assess their trends in the context of palaeoclimate records and climate model simulations. Over the 36-year satellite era, significant linear trends in annual mean sea-ice extent, surface temperature and sea-level pressure are superimposed on large interannual to decadal variability. Most observed trends, however, are not unusual when compared with Antarctic palaeoclimate records of the past two centuries. With the exception of the positive trend in the Southern Annular Mode, climate model simulations that include anthropogenic forcing are not compatible with the observed trends. This suggests that natural variability overwhelms the forced response in the observations, but the models may not fully represent this natural variability or may overestimate the magnitude of the forced response.
Programme: 1154
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Christopher S. Watson, Neil J. White, John A. Church, Matt A. King, Reed J. Burgette, Benoit Legresy. (2015). Unabated global mean sea-level rise over the satellite altimeter era (Vol. 5).
Abstract: The rate of global mean sea-level (GMSL) rise has been suggested to be lower for the past decade compared with the preceding decade as a result of natural variability1, with an average rate of rise since 1993 of +3.2 ± 0.4 mm yr−1 (refs 2, 3). However, satellite-based GMSL estimates do not include an allowance for potential instrumental drifts (bias drift4,5). Here, we report improved bias drift estimates for individual altimeter missions from a refined estimation approach that incorporates new Global Positioning System (GPS) estimates of vertical land movement (VLM). In contrast to previous results (for example, refs 6, 7), we identify significant non-zero systematic drifts that are satellite-specific, most notably affecting the first 6 years of the GMSL record. Applying the bias drift corrections has two implications. First, the GMSL rate (1993 to mid-2014) is systematically reduced to between +2.6 ± 0.4 mm yr−1 and +2.9 ± 0.4 mm yr−1, depending on the choice of VLM applied. These rates are in closer agreement with the rate derived from the sum of the observed contributions2, GMSL estimated from a comprehensive network of tide gauges with GPS-based VLM applied (updated from ref. 8) and reprocessed ERS-2/Envisat altimetry9. Second, in contrast to the previously reported slowing in the rate during the past two decades1, our corrected GMSL data set indicates an acceleration in sea-level rise (independent of the VLM used), which is of opposite sign to previous estimates and comparable to the accelerated loss of ice from Greenland and to recent projections2,10, and larger than the twentieth-century acceleration2,8,10.
Programme: 688
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Angélique Melet, Benoit Meyssignac, Rafael Almar, Gonéri Le Cozannet. (2018). Under-estimated wave contribution to coastal sea-level rise (Vol. 8). Bachelor's thesis, , .
Abstract: Coastal communities are threatened by sea-level changes operating at various spatial scales; global to regional variations are associated with glacier and ice sheet loss and ocean thermal expansion, while smaller coastal-scale variations are also related to atmospheric surges, tides and waves. Here, using 23 years (1993–2015) of global coastal sea-level observations, we examine the contribution of these latter processes to long-term sea-level rise, which, to date, have been relatively less explored. It is found that wave contributions can strongly dampen or enhance the effects of thermal expansion and land ice loss on coastal water-level changes at interannual-to-multidecadal timescales. Along the US West Coast, for example, negative wave-induced trends dominate, leading to negative net water-level trends. Accurate estimates of past, present and future coastal sea-level rise therefore need to consider low-frequency contributions of wave set-up and swash.
Programme: 688
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