Improved Sea Level record over the satellite altimetry era (1993-2010) from the Climate Change Initiative project

Abstract. Sea level is one of the 50 Essential Climate Variables (ECVs) listed by the Global Climate Observing System (GCOS) in climate change monitoring. In the past two decades, sea level has been routinely measured from space using satellite altimetry techniques. In order to address a number of important scientific questions such as "Is sea level rise accelerating?", "Can we close the sea level budget?", "What are the causes of the regional and interannual variability?", "Can we already detect the anthropogenic forcing signature and separate it from the internal/natural climate variability?", and "What are the coastal impacts of sea level rise?", the accuracy of altimetry-based sea level records at global and regional scales needs to be significantly improved. For example, the global mean and regional sea level trend uncertainty should become better than 0.3 and 0.5 mm year−1, respectively (currently 0.6 and 1–2 mm year−1). Similarly, interannual global mean sea level variations (currently uncertain to 2–3 mm) need to be monitored with better accuracy. In this paper, we present various data improvements achieved within the European Space Agency (ESA) Climate Change Initiative (ESA CCI) project on "Sea Level" during its first phase (2010–2013), using multi-mission satellite altimetry data over the 1993–2010 time span. In a first step, using a new processing system with dedicated algorithms and adapted data processing strategies, an improved set of sea level products has been produced. The main improvements include: reduction of orbit errors and wet/dry atmospheric correction errors, reduction of instrumental drifts and bias, intercalibration biases, intercalibration between missions and combination of the different sea level data sets, and an improvement of the reference mean sea surface. We also present preliminary independent validations of the SL_cci products, based on tide gauges comparison and a sea level budget closure approach, as well as comparisons with ocean reanalyses and climate model outputs.

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

[2]  Tong Lee,et al.  The Ocean Reanalyses Intercomparison Project (ORA-IP) , 2015 .

[3]  Ann M. Fridlind,et al.  Intercomparison of cloud model simulations of Arctic mixed‐phase boundary layer clouds observed during SHEBA/FIRE‐ACE , 2011 .

[4]  K. Schuckmann,et al.  How well can we derive Global Ocean Indicators from Argo data , 2011 .

[5]  P. Féménias,et al.  Envisat Ocean Altimeter Becoming Relevant for Mean Sea Level Trend Studies , 2012 .

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

[7]  R. Ray,et al.  Precise comparisons of bottom‐pressure and altimetric ocean tides , 2013 .

[8]  Don P. Chambers,et al.  Evaluation of Release-05 GRACE time-variable gravity coefficients over the ocean , 2012 .

[9]  Remko Scharroo,et al.  A global positioning system–based climatology for the total electron content in the ionosphere , 2010 .

[10]  Z. Altamimi,et al.  ITRF2008: an improved solution of the international terrestrial reference frame , 2011 .

[11]  M. Joana Fernandes,et al.  GNSS-Derived Path Delay: An Approach to Compute the Wet Tropospheric Correction for Coastal Altimetry , 2010, IEEE Geoscience and Remote Sensing Letters.

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

[13]  Gilles Larnicol,et al.  Jason-2 in DUACS: Updated System Description, First Tandem Results and Impact on Processing and Products , 2011 .

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

[15]  Shannon T. Brown,et al.  Microwave radiometer calibration on decadal time scales using on-earth brightness temperature references: application to the TOPEX Microwave Radiometer. , 2009 .

[16]  M. Kimoto,et al.  Reevaluation of historical ocean heat content variations with time-varying XBT and MBT depth bias corrections , 2009 .

[17]  M. Ablain,et al.  Detection of Long-Term Instabilities on Altimeter Backscatter Coefficient Thanks to Wind Speed Data Comparisons from Altimeters and Models , 2012 .

[18]  L. Eymard,et al.  Trend and Variability of the Atmospheric Water Vapor: A Mean Sea Level Issue , 2014 .

[19]  Fabrice Hernandez,et al.  Can We Merge GEOSAT Follow-On with TOPEX/Poseidon and ERS-2 for an Improved Description of the Ocean Circulation? , 2003 .

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

[21]  M. Balmaseda,et al.  Evaluation of the ECMWF ocean reanalysis system ORAS4 , 2013 .

[22]  A. Cazenave,et al.  A new assessment of the error budget of global mean sea level rate estimated by satellite altimetry over 1993–2008 , 2009 .

[23]  Sergei Rudenko,et al.  New improved orbit solutions for the ERS-1 and ERS-2 satellites , 2012 .

[24]  Malcolm Davidson,et al.  CryoSat‐2 estimates of Arctic sea ice thickness and volume , 2013 .

[25]  Gilles Reverdin,et al.  Global high-resolution mapping of ocean circulation from TOPEX/Poseidon and ERS-1 and -2 , 2000 .

[26]  J. Thepaut,et al.  The ERA‐Interim reanalysis: configuration and performance of the data assimilation system , 2011 .

[27]  A. Cazenave,et al.  Effect of the processing methodology on satellite altimetry-based global mean sea level rise over the Jason-1 operating period , 2014, Journal of Geodesy.

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

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