An improved and homogeneous altimeter sea level record from the ESA Climate Change Initiative

Abstract. Sea level is a very sensitive index of climate change since it integrates the impacts of ocean warming and ice mass loss from glaciers and the ice sheets. Sea level has been listed as an essential climate variable (ECV) by the Global Climate Observing System (GCOS). During the past 25 years, the sea level ECV has been measured from space by different altimetry missions that have provided global and regional observations of sea level variations. As part of the Climate Change Initiative (CCI) program of the European Space Agency (ESA) (established in 2010), the Sea Level project (SL_cci) aimed to provide an accurate and homogeneous long-term satellite-based sea level record. At the end of the first phase of the project (2010–2013), an initial version (v1.1) of the sea level ECV was made available to users (Ablain et al., 2015). During the second phase of the project (2014–2017), improved altimeter standards were selected to produce new sea level products (called SL_cci v2.0) based on nine altimeter missions for the period 1993–2015 ( https://doi.org/10.5270/esa-sea_level_cci-1993_2015-v_2.0-201612 ; Legeais and the ESA SL_cci team, 2016c). Corresponding orbit solutions, geophysical corrections and altimeter standards used in this v2.0 dataset are described in detail in Quartly et al. (2017). The present paper focuses on the description of the SL_cci v2.0 ECV and associated uncertainty and discusses how it has been validated. Various approaches have been used for the quality assessment such as internal validation, comparisons with sea level records from other groups and with in situ measurements, sea level budget closure analyses and comparisons with model outputs. Compared with the previous version of the sea level ECV, we show that use of improved geophysical corrections, careful bias reduction between missions and inclusion of new altimeter missions lead to improved sea level products with reduced uncertainties on different spatial and temporal scales. However, there is still room for improvement since the uncertainties remain larger than the GCOS requirements (GCOS, 2011). Perspectives on subsequent evolution are also discussed.

[1]  J. Kusche,et al.  Water mass variation in the Mediterranean and Black Seas , 2012 .

[2]  F. Mercier,et al.  Satellite Radar Altimetry : Principle, Accuracy, and Precision , 2017 .

[3]  A. Cazenave,et al.  Satellite Altimetry-Based Sea Level at Global and Regional Scales , 2016, Surveys in Geophysics.

[4]  S. Sathyendranath,et al.  Causes of the Regional Variability in Observed Sea Level, Sea Surface Temperature and Ocean Colour Over the Period 1993–2011 , 2016, Surveys in Geophysics.

[5]  Andrey A. Kurekin,et al.  Development of an ENVISAT Altimetry Processor Providing Sea Level Continuity Between Open Ocean and Arctic Leads , 2018, IEEE Transactions on Geoscience and Remote Sensing.

[6]  P. Prandi,et al.  Analyses of altimetry errors using Argo and GRACE data , 2016 .

[7]  Matt A. King,et al.  Unabated global mean sea-level rise over the satellite altimeter era , 2015 .

[8]  J. Benveniste,et al.  Satellite Altimetry in Coastal Regions , 2017 .

[9]  George L. Mellor,et al.  Sea level variations induced by heating and cooling: An evaluation of the Boussinesq approximation in ocean models , 1995 .

[10]  Clara Lázaro,et al.  Improved wet path delays for all ESA and reference altimetric missions , 2015 .

[11]  S. Somot,et al.  A fully coupled Mediterranean regional climate system model: design and evaluation of the ocean component for the 1980–2012 period , 2014 .

[12]  Kristian Mogensen,et al.  Arctic sea ice in the global eddy-permitting ocean reanalysis ORAP5 , 2017, Climate Dynamics.

[13]  M. Ablain,et al.  Accuracy of the mean sea level continuous record with future altimetric missions: Jason-3 vs. Sentinel-3a , 2015 .

[14]  Sergei Rudenko,et al.  A new phase in the production of quality-controlled sea level data , 2017 .

[15]  Matt A. King,et al.  The increasing rate of global mean sea-level rise during 1993–2014 , 2017 .

[16]  Frank J. Wentz,et al.  SSM/I Version-7 Calibration Report , 2012 .

[17]  Ron Kwok,et al.  Changing Arctic Ocean freshwater pathways , 2012, Nature.

[18]  S. Esselborn,et al.  Impact of Atmospheric and Oceanic De-aliasing Level-1B (AOD1B) products on precise orbits of altimetry satellites and altimetry results , 2016 .

[19]  Anny Cazenave,et al.  Causes for contemporary regional sea level changes. , 2013, Annual review of marine science.

[20]  David W. Hancock,et al.  On the "Cal-Mode" Correction to TOPEX Satellite Altimetry and Its Effect on the Global Mean Sea Level Time Series , 2017 .

[21]  Yannice Faugère,et al.  DUACS DT2014: the new multi-mission altimeter data set reprocessed over 20years , 2016 .

[22]  Armin Köhl,et al.  Evaluation of the GECCO2 ocean synthesis: transports of volume, heat and freshwater in the Atlantic , 2015 .

[23]  A. Simmons,et al.  The Concept of Essential Climate Variables in Support of Climate Research, Applications, and Policy , 2014 .

[24]  Nicolas Picot,et al.  Comparing Altimetry with Tide Gauges and Argo Profiling Floats for Data Quality Assessment and Mean Sea Level Studies , 2012 .

[25]  M. Ablain,et al.  Evaluation of wet troposphere path delays from atmospheric reanalyses and radiometers and their impact on the altimeter sea level , 2014 .

[26]  Andrea Pisano,et al.  The Copernicus Marine Environment Monitoring Service Ocean State Report , 2016 .

[27]  G. Meehl,et al.  Spatial Patterns of Sea Level Variability Associated with Natural Internal Climate Modes , 2016, Surveys in Geophysics.

[28]  M. Joana Fernandes,et al.  GPD+ Wet Tropospheric Corrections for CryoSat-2 and GFO Altimetry Missions , 2016, Remote. Sens..

[29]  Testing the Quality of Sea-Level Data Using the GECCO Adjoint Assimilation Approach , 2016, Surveys in Geophysics.

[30]  Sergei Rudenko,et al.  Improvements in Precise Orbits of Altimetry Satellites and Their Impact on Mean Sea Level Monitoring , 2017, IEEE Transactions on Geoscience and Remote Sensing.

[31]  H. Dieng,et al.  New estimate of the current rate of sea level rise from a sea level budget approach , 2017 .

[32]  Byron D. Tapley,et al.  Seasonal global water mass budget and mean sea level variations , 1998 .

[33]  M. Lander,et al.  Multidecadal sea level anomalies and trends in the western tropical Pacific , 2012 .

[34]  Anny Cazenave,et al.  Tropical Pacific spatial trend patterns in observed sea level: internal variability and/or anthropogenic signature? , 2012 .

[35]  Anny Cazenave,et al.  The rate of sea-level rise , 2014 .

[36]  Ole Baltazar Andersen,et al.  ALES+: Adapting a homogenous ocean retracker for satellite altimetry to sea ice leads, coastal and inland waters , 2018, Remote Sensing of Environment.

[37]  Jens Schröter,et al.  Revisiting the contemporary sea-level budget on global and regional scales , 2016, Proceedings of the National Academy of Sciences.

[38]  J. Johannessen,et al.  Arctic Sea Level During the Satellite Altimetry Era , 2016, Surveys in Geophysics.

[39]  Anny Cazenave,et al.  Satellite Altimetry over Oceans and Land Surfaces , 2017 .

[40]  H. Drange,et al.  Influence of the Atlantic Subpolar Gyre on the Thermohaline Circulation , 2005, Science.

[41]  Sergei Rudenko,et al.  Influence of time variable geopotential models on precise orbits of altimetry satellites, global and regional mean sea level trends , 2014 .

[42]  Sergei Rudenko,et al.  Improved Sea Level record over the satellite altimetry era (1993-2010) from the Climate Change Initiative project , 2015 .

[43]  A. Cazenave,et al.  Spatial trend patterns in the Pacific Ocean sea level during the altimetry era: the contribution of thermocline depth change and internal climate variability , 2015, Ocean Dynamics.

[44]  Shannon T. Brown.  A Novel Near-Land Radiometer Wet Path-Delay Retrieval Algorithm: Application to the Jason-2/OSTM Advanced Microwave Radiometer , 2010, IEEE Transactions on Geoscience and Remote Sensing.

[45]  H. Palanisamy.  Is anthropogenic sea level fingerprint already detectable in the Pacific Ocean? , 2015 .

[46]  S. Griffies,et al.  Ocean Modeling and Data Assimilation in the Context of Satellite Altimetry , 2017 .

[47]  John M. Wahr,et al.  Deformation induced by polar motion , 1985 .

[48]  S. Desai,et al.  Revisiting the pole tide for and from satellite altimetry , 2015, Journal of Geodesy.

[49]  Ge Chen,et al.  Annual amphidromes: a common feature in the ocean? , 2005, IEEE Geoscience and Remote Sensing Letters.

[50]  P. Ruti,et al.  Effects of seasonal cycle fluctuations in an A1B scenario over the Euro-Mediterranean region , 2012 .

[51]  M. Balmaseda,et al.  The new eddy-permitting ORAP5 ocean reanalysis: description, evaluation and uncertainties in climate signals , 2017, Climate Dynamics.

[52]  Thierry Penduff,et al.  Impact of partial steps and momentum advection schemes in a global ocean circulation model at eddy-permitting resolution , 2006 .

[53]  Yannice Faugère,et al.  Major improvement of altimetry sea level estimations using pressure-derived corrections based on ERA-Interim atmospheric reanalysis , 2016 .

[54]  Bruce J. Haines,et al.  Towards the 1 mm/y Stability of the Radial Orbit Error at Regional Scales , 2014 .

[55]  Duncan J. Wingham,et al.  Western Arctic Ocean freshwater storage increased by wind-driven spin-up of the Beaufort Gyre , 2012 .

[56]  K. Taylor.  Summarizing multiple aspects of model performance in a single diagram , 2001 .