1. Dry Troposphere Correction comparison for Jason-2 mission between the JRA55-based and the ERA-Interim-based corrections The JRA55-based correction is referred to as JRA55 in the following study The EAR-Interim-based correction is referred to as ERA Lionel Zawadzki, Michael Ablain (CLS)

2. Introduction: We will observe and analyse the impact of the Dry Troposphere Correction (DTC) computed from JRA55 atmospheric reanalysis for climate applications. It will be referred to as “JRA55”. We will compare this correction with the reference DTC in SL_cci products, computed from ERA- Interim atmospheric reanalysis. It will be referred to as “ERA”. In order to determine the impact of the JRA55 correction in terms of climate applications and temporal scales, we will try in this study to indicate for each impact detected if it’s a positive (+) or a negative (-) impact : Dry Troposphere correction comparison for Jason-2 mission No impact detected Low impact Significant impact

3. Jason-2 Climate Applications Temporal Scales Round Robin Data Package (RRDP) JRA55 Versus ERA Global Mean Sea Level Long-term evolution (trend) Inter annual signals (> 1 year) Annual and semi-annual Signals Regional Mean Sea Level Long-term evolution (trend) Annual and semi-annual Signals Mesoscale Signals < 2 months Global Mean Sea Level No impact detected on Global Mean Sea Level trend  0.02 mm/yr on the Global MSL is not significant. Temporal evolution of SLA mean calculated globally.

4. Jason-2 Climate Applications Temporal Scales Round Robin Data Package (RRDP) JRA55 Versus ERA Global Mean Sea Level Long-term evolution (trend) Inter annual signals (> 1 year) Annual and semi-annual Signals Regional Mean Sea Level Long-term evolution (trend) Annual and semi-annual Signals Mesoscale Signals < 2 months Global Mean Sea Level No impact detected on Inter annual Signals  The figure below shows the mean difference between the two corrections calculated globally by cycle.

5. Jason-2 Climate Applications Temporal Scales Round Robin Data Package (RRDP) JRA55 Versus ERA Global Mean Sea Level Long-term evolution (trend) Inter annual signals (> 1 year) Annual and semi-annual Signals Regional Mean Sea Level Long-term evolution (trend) Annual and semi-annual Signals Mesoscale Signals < 2 months Global Mean Sea Level No impact detected on Annual and Semi-annual Signals

6. Jason-2 Climate Applications Temporal Scales Round Robin Data Package (RRDP) JRA55 Versus ERA Global Mean Sea Level Long-term evolution (trend) Inter annual signals (> 1 year) Annual and semi-annual Signals Regional Mean Sea Level Long-term evolution (trend) Annual and semi-annual Signals Mesoscale Signals < 2 months No impact detected on a short temporal scale (signals < 2 months): No impact detected on a short temporal scale (signals < 2 months):  Crossovers Variance Differences are generally positive (see figures on next slide) near + 2 mm² : This means that the new JRA55 correction shows a very low (non significant) degradation by comparison to the reference correction.  No impact is detected on the map of SSH crossovers Variance Differences. Mesoscale

7.  Map of Variance differences of Sea Surface Height at crossovers between the JRA55 and ERA corrections (over all the period): - No impact detected  Temporal evolution of Variance differences of Sea Surface Height at crossovers between two DTCs : - Very low degradation (~ 2mm²) with JRA55

8. Jason-2 Climate Applications Temporal Scales Round Robin Data Package (RRDP) JRA55 Versus ERA Global Mean Sea Level Long-term evolution (trend) Inter annual signals (> 1 year) Annual and semi-annual Signals Regional Mean Sea Level Long-term evolution (trend) Annual and semi-annual Signals Mesoscale Signals < 2 months Low impact detected on Regional Mean Sea Level  We observe a low impact (<0.2 mm/yr) on the regional trends. It is positive in the ACC, west Pacific and North Atlantic. These differences are however small. Regional Mean Sea Level

9.  Map of Sea Level Anomaly differences between two Dry Troposphere Corrections (over all the period)

10. Jason-2 Climate Applications Temporal Scales Round Robin Data Package (RRDP) JRA55 Versus ERA Global Mean Sea Level Long-term evolution (trend) Inter annual signals (> 1 year) Annual and semi-annual Signals Regional Mean Sea Level Long-term evolution (trend) Annual and semi-annual Signals Mesoscale Signals < 2 months  At low latitudes, amplitude differences reach 0.5mm or -0.5mm for annual and semi-annual signal (see figures on next slide).  These differences are small and it is not possible to determine which correction is the best one for theses scales. Regional Mean Sea Level Low impact detected on Annual and Semi-Annual Signals

11. Regional Mean Sea Level  Map of Sea Level Anomaly differences amplitude for annual signal  Map of Sea Level Anomaly differences amplitude for semi-annual signal SLA with JRA55 amplitude – SLA with ERA amplitude : semi-annual signal SLA with JRA55 amplitude – SLA with ERA amplitude : annual signal

12. Regional Mean Sea Level  Map of Sea Level Anomaly differences phase for annual signal.  Map of Sea Level Anomaly differences phase for semi-annual signal. To be noted a phase value equal to 30° corresponds to a period of one month SLA with JRA55 phase – SLA with ERA phase : semi-annual signal SLA with JRA55 phase – SLA with ERA phase: annual signal

13.  Map of Mean differences between JRA55 and ERA (whole Jason-2 period) On this map we observe a differences of 1cm near coasts between the two dry troposphere corrections  Map of Standard deviation of the differences between JRA55 and ERA (whole Jason-2period) On this map we observe low differences (>5mm) near coasts Regional statistics between corrections

14. To conclude: The Dry Troposphere Correction based on JRA-55 shows performances close to ERA-Interim. The main impacts are on the long-term evolutions at regional scale and periodic signals. Jason-2 Climate Applications Temporal Scales Round Robin Data Package (RRDP) JRA55 Versus ERA Global Mean Sea Level Long-term evolution (trend) Inter annual signals (> 1 year) Annual and semi-annual Signals Regional Mean Sea Level Long-term evolution (trend) Annual and semi-annual Signals Mesoscale Signals < 2 months Dry Troposphere correction comparison for Jason-2 mission