Climate Change Initiative ESA’s Sea Level Climate Change Initiative An accurate Mean Sea Level record for climate studies: Progress status of the ESA Sea Level CCI project Phase II JF. Legeais1, J. Benveniste2, A. Cazenave3, M. Ablain1, G. Larnicol1, B. Meyssignac3, J. Johannessen13, M. Scharffenberg4, G. Timms5, P. Knudsen6, O. Andersen6, P. Cipollini7, M. Roca8, S. Rudenko9, J. Fernandes10, M. Balmaseda11, G. Quartly12, L. Fenoglio14-15, A. Ambrozio2 1CLS, 2ESA, 3LEGOS, 4University of Hamburg, 5 CGI,6 DTU, 7 NOCS, 8IsardSAT, 9GFZ, 10 University of Porto, 11 ECMWF, 12 PML, 13NERSC, 14TUD, 15University of Bonn

Outlines Context: phase I output Progress of phase II activities: Production of the ECV temporal extension Preparation of an improved reprocessed ECV Focus on Arctic and coastal areas ECV quality assessment Error characterization 3. Conclusion

Context: Phase I output SL_cci phase I (2010-2013): 7 altimeter missions (re)processed: T/P, Jason1/2, ERS-1/2, ENVISAT & GFO Period: [1993-2010] 70 cumulated years of data (re)processed Based on SSALTO/DUACS infra-structure . Mapping along track data...

Context: Phase I output SL_cci phase I (2010-2013): 7 altimeter missions (re)processed: T/P, Jason1/2, ERS-1/2, ENVISAT & GFO Period: [1993-2010] 70 cumulated years of data (re)processed Based on SSALTO/DUACS infra-structure Mapping along track data... ... to gridded maps This has led to an accurate, stable, long-term, satellite-based sea level record at global and regional scales, designed to answer the users needs, for climate applications

2013 delivery: end of phase I Phase II activities: ECV temporal extension Preparation of ECV reprocessing Arctic and coasts Quality assessment Error characterization Yearly extensions of the ECV time series: Database preparation: update of all level 2 altimeter standards Production of the ECV extension Update ocean indicators over the updated total period Extension validation Dissemination 2013 delivery: end of phase I V1.1 SL ECV Delivery [1993-2010] 2014 delivery V1.1 SL ECV Extension [2011-2013] 2015 delivery V1.1 SL ECV Extension [2014] 1993 2000 2005 2010 2013 2014

Phase II activities: ¼° Gridded Monthly mean SLCCI ECV release : V1.1 ECV temporal extension Preparation of ECV reprocessing Arctic and coasts Quality assessment Error characterization SLCCI ECV release : V1.1 available via: http://www.esa-sealevel-cci.org/ Please contact us: info-sealevel@esa-sealevel-cci.org ¼° Gridded Monthly mean

SL_cci Algorithm Selection Meeting, 25-27th Nov. 2015 Phase II activities: ECV temporal extension Preparation of ECV reprocessing Arctic and coasts Quality assessment Error characterization Since the beginning of phase II, a significant work has focused on improving the altimeter standards that should contribute to increase the ECV homogeneity and reduce the errors. A full reprocessing of the ECV is planned in summer 2016 (V2.0). New algorithms/altimeter standards have been developed, validated and selected. SL_cci Algorithm Selection Meeting, 25-27th Nov. 2015

Phase II activities: ECV reprocessing: ECV temporal extension Preparation of ECV reprocessing Arctic and coasts Quality assessment Error characterization ECV reprocessing: 9 altimeter missions involved (2 new missions) About 10 altimeter standards to be selected per mission New tides (model) corrections: GOT4.10 and FES2014 was evaluated New orbit solutions New GFZ and CNES orbit solutions New atmospheric fields Model forced by atmospheric reanalysis Enhanced radiometer correction (GPD+, Univ. of Porto) A new instrumental correction (IsardSAT) of the Envisat altimeter mission has been developed in order to provide a new version of the altimeter ionospheric correction for this mission. New instrumental correction (IsardSAT) New altimeter missions included CryoSat-2, SARAL/AltiKa

Phase II activities: ECV temporal extension Preparation of ECV reprocessing Arctic and coasts Quality assessment Error characterization New Sea-Level Arctic products significantly improved over the frozen Arctic Ocean Continuity between open and ice covered ocean (thanks to new retracking) Very good coverage over leads and SLA quality seems good Monthly sea level maps from 20 Hz Envisat Data Paper in preparation The same retracking has been applied to the 20Hz waveforms over the open ocean and over leads (ice covered ocean) which significantly improves the SLA quality at the transition between these two different kinds of areas. This also contributes to the regional homogeneity of the product.

Phase II activities: ECV temporal extension Preparation of ECV reprocessing Arctic and coasts Quality assessment Error characterization Regional in-situ validation against geodetic data (tide gauges + GPS) Improved retracking of the altimeter radar echo in coastal areas: Implementation and evaluation of a 2D waveform retracker 3. Validation of the sea level ECV in coastal zones: Comparison with tide gauge Estimation of the total relative sea level at the coast

All analyses show that the SL_ECV_V1.1 Phase II activities: ECV temporal extension Preparation of ECV reprocessing Arctic and coasts Quality assessment Error characterization Validation of the SL_ECV (Climate Research Group): Two approaches : 1- Evaluation using a ‘Sea Level Closure Budget’ approach Differences with other GMSL products from international groups have been analyzed Better agreement found between GMSL and the sum of mass and steric components when using the SL_cci 2- Evaluation by comparison with ocean and/or coupled models outputs: Impact on the performances of ocean models assimilating these new products Good agreement of SL_cci with other data sets in 2 regions of the North Atlantic and Arctic ocean All analyses show that the SL_ECV_V1.1 product provide better results compared to previous versions and other existing products

Regional Mean Sea Level Phase II activities: ECV temporal extension Preparation of ECV reprocessing Arctic and coasts Quality assessment Error characterization Altimetry measurement errors at climate scales have been characterized (Ablain et al., 2015) Spatial Scales Temporal Scales User Requirements Altimetry errors CCI products Global Mean Sea Level (10-day averaging) Long-term evolution (> 10 years ) 0.3 mm/yr < 0.5 mm/yr Inter annual signals (< 5 years) 0.5 mm over 1 year < 2 mm over 1 year Periodic signals (Annual, 60-days,…) Not defined Annual < 1 mm 60-day < 5 mm Regional Mean Sea Level (2x2 deg boxes and 10-day averaging) (trend) 1 mm/yr < 3 mm/yr (> 1 year) Not Defined Not evaluated Annual < 1mm Regarding the inter annual signals of the regional mean sea level, it is very difficult to estimate the associated errors which have not been evaluated yet. No specific diagnosis has been defined yet to allow their characterization and their evaluation will be the aim of a dedicated task within phase II of the project (work planned in 2016). Ablain and SL_cci team, Improved sea level record over the satellite altimetry era (1993–2010) from the Climate Change Initiative project, Ocean Sci., 11, 67-82, doi:10.5194/os-11-67-2015.

Phase II activities: ECV temporal extension Preparation of ECV reprocessing Arctic and coasts Quality assessment Error characterization Additional information requested by users or climate modellers : 1. Refine the error budget at interannual time scale Distinguish error estimation over the two different altimetry decades Work in progress in 2016 3. Provide regional sea level trend error maps 2. Define the envelop error of the Global MSL evolution 1) Message super important et intéressant ! => message : super important de travailler sur les nouvelles missions. Regarding the inter annual and periodic signals of the regional mean sea level, it is very difficult to estimate the associated errors separating the two altimetry decades. No specific diagnosis has been defined yet to allow their characterization and their evaluation will be the aim of a dedicated task within phase II of the project (work planned in 2016). 2) The linking error is associated with the process which aims at calibrating Jason-2 mission compared with Jason-1 mission thanks to the data acquired during the calibration phase that have lasted a few months when both satellites have measured the ocean almost at the the time and same location. When no overlap / calibration phase is available, the data are calibrated thanks to multi mission cross comparison (via crossovers analyses,…) or in-situ measurements… 3) The regional sea level trend error is not known and we would correct it from the trends if we would know it! This map is half the width of the confidence interval at 95%. This means that for a given pixel of the map, the sea level trend (not shown here) is in the interval « +/- the confidence interval » (this map) with a 95% probability. The histogram below is associated with the colorbar used on the map and provides the associated « statistical » distribution of the confidence intervals.

Conclusions (1) Sea-Level CCI Products: Work in progress: V1.1 release available over the [1993-2014] period Description of errors available (error budget table, envelop error) Improvements of inter-annual signals and long-term trends for global and regional scales An accurate product for MSL closure budget studies Work in progress: A whole reprocessing is planned in 2016 Improvements of sea level with new altimeter corrections and new missions Improvement of the sea level error description Improvement of sea level estimation in coastal areas and in the Arctic Ocean Interactions with SEWG, Open Data Portal, Obs4MIPs submission, Visualization tool…

Conclusions (2) For more information: Project website : http://www.esa-sealevel-cci.org/ Ablain et al., 2015. Improved sea level record over the satellite altimetry era (1993–2010) from the Climate Change Initiative project, Ocean Sci., 11, 67-82, doi:10.5194/os-11-67-2015. Newsletters regularly published (available on the website): Access to the products: info-sealevel@esa-sealevel-cci.org 7500 views and downloads!

After the end of CCI phase II Perspectives After the end of CCI phase II what happens ? The Sea Level ECV production will be taken over in C3S Further developments are needed to improve the SL_cci ECV : Better Sea Level estimation in Arctic ocean Improved Sea Level retrieval in Coastal areas Better characterization of errors and uncertainties Improvement of all altimeter standards (e.g. orbits, ocean tides,…) Improvement of the ocean indicators (MSL trend) through a better processing / mapping of large scale signals Supported by CCI+ ?