Assimilating Satellite Sea-Surface Salinity in NOAA Eric Bayler, NESDIS/STAR Dave Behringer, NWS/NCEP/EMC Avichal Mehra, NWS/NCEP/EMC Sudhir Nadiga, NWS/NCEP/EMC 5/21/ th JCSDA Science Workshop

Sea-Surface Salinity (SSS) Data Satellite: ESA Soil Moisture – Ocean Salinity (SMOS) mission – Barcelona Expert Centre (SMOS-BEC) Level-3 gridded SSS fields for 2012 – 2013 Uses ECMWF modeled winds for the retrieval – 0.25-degree resolution – 3-day average (global coverage), updated every 3 days – Interpolated to model grid NASA Aquarius mission (AQRS) – Jet Propulsion Lab (JPL) Physical Oceanography Distributed Active Archive Center (PO.DAAC) – Version 2 (V2) Level-3 gridded SSS fields for 2012 – 2013 Uses NOAA modeled winds for the retrieval – 1.0-degree resolution – 7-day average (global coverage), updated every 7 days – Interpolated to model grid In Situ : World Ocean Atlas (WOA) 2009 climatology – NOAA’s National Oceanographic Data Center (NODC) – 1.0-degree resolution – Interpolated to model grid Argo profiling floats – Near-surface observations (~ 5m depth) – Monthly-mean SSS – 1.0-degree resolution – Interpolated to model grid 5/21/201412th JCSDA Science Workshop2

3 SSS Data: RMS difference of monthly means 5/21/2014 Salinity RMS difference (psu) SMOS - WOA AQRS - WOA SMOS - AQRS

5/21/201412th JCSDA Science Workshop4 Equatorial Pacific (2°S – 2°N) SSS: Mean WOA2009ArgoAQRSSMOS Salinity (psu)

5/21/201412th JCSDA Science Workshop5 Equatorial Pacific (2°S – 2°N) SSS Mean: Differences AQRS -WOASMOS-WOASMOS -AQRS Salinity Difference (psu)

Model Modular Ocean Model v.4 (MOM4) – NOAA National Weather Service / Environmental Modeling Center (EMC) Operational Global Ocean Data Assimilation System (GODAS) Ocean component of NOAA’s operational Coupled Forecast System (CFS) – Near-global 1.0-degree resolution Increased resolution (1/3-degree) between 10°S – 10°N – Forcing: NCEP Climate Forecast System Reanalysis (CFSR) Saha et al., 2010 Daily fluxes – Model runs are for only Period of overlapping Aquarius and SMOS data All runs were initiated from the same initial conditions Relaxed to daily satellite sea-surface temperature (SST) fields. 5/21/201412th JCSDA Science Workshop6

Modeled Cases CONTROL – CTRL30 : NODC World Ocean Atlas (WOA) monthly climatological SSS, relaxation = 30 days Current operational configuration – CTRL10 : NODC World Ocean Atlas (WOA) monthly climatological SSS, relaxation = 10 days SMOS – SMOS30 : SMOS SSS, 1/4° resolution, 3-day averages (SMOS-BEC), relaxation = 30 days – SMOS10 : SMOS SSS, 1/4° resolution, 3-day averages (SMOS-BEC), relaxation = 10 days Aquarius – AQ30 : Aquarius V.2 daily SSS, 1° resolution (NASA/JPL PO.DAAC), relaxation = 30 days – AQ10 : Aquarius V.2 daily SSS, 1° resolution (NASA/JPL PO.DAAC), relaxation = 10 days Satellite data gaps, e.g., radio frequency interference (RFI) areas, are filled with World Ocean Atlas (WOA) 2009 monthly mean values. All runs began from the same initial conditions. Model forcing: CFSR daily fluxes 5/21/201412th JCSDA Science Workshop7

Definitions 5/21/201412th JCSDA Science Workshop8

Validation Reference = Satellite Salinity Observations 5/21/201412th JCSDA Science Workshop9 Salinity RMSE (psu) (a) AQ10 RMSE; reference = AQRS (b) SMOS10 RMSE; reference = SMOS Model seems to better assimilate the Aquarius data.

Improvement Near-real-time Observations versus Climatology 5/21/201412th JCSDA Science Workshop10 AQ10 – CTRL10; ref = AQRS obsSMOS10 – CTRL10; ref = SMOS obs Salinity RMSE (psu) (a)(b) Blue = Reduction in RMS errors

Validation: Altimetry 12th JCSDA Science Workshop115/21/2014 Normalized RMSE difference (%); reference = satellite sea-surface height anomalies RMSE difference (cm); reference = satellite sea-surface height anomalies SMOS10 – CTRL10AQRS10 – CTRL10AQRS10 – SMOS10 SMOS10 – CTRL10AQRS10 – CTRL10AQRS10 – SMOS10

Satellite SSS vs Climatology: 30-day Relaxation Average and RMS Temperature Differences 5/21/201412th JCSDA Science Workshop12 Temperature Difference (°C) AQ30 – CTRL30SMOS30 – CTRL30 Average Difference RMS Difference Red line indicates the average depth of the 20C isotherm

Satellite SSS vs Climatology: 30-day Relaxation Average and RMS Salinity Differences 5/21/201412th JCSDA Science Workshop13 Salinity Difference (psu) AQ30 – CTRL30SMOS30 – CTRL30 Average Difference RMS Difference Red line indicates the average depth of the 20C isotherm

SSS Constraint: 10-day vs 30-day Relaxation Average and RMS Temperature Differences 5/21/201412th JCSDA Science Workshop14 Temperature Difference (°C) AQ10 – CTRL30SMOS10 – CTRL30 Average Difference RMS Difference Red line indicates the average depth of the 20C isotherm

SSS Constraint: 10-day vs 30-day Relaxation Average and RMS Salinity Difference 5/21/201412th JCSDA Science Workshop15 Salinity Difference (psu) AQ10 – CTRL30SMOS10 – CTRL30 Average Difference RMS Difference Red line indicates the average depth of the 20C isotherm

SSS Data vs Relaxation Period Average and RMS Temperature Differences 5/21/201412th JCSDA Science Workshop16 Temperature Difference (°C) AQ10 – CTRL10SMOS10 – CTRL10 Average Difference RMS Difference Red line indicates the average depth of the 20C isotherm

SSS Data vs Relaxation Period Average and RMS Salinity Differences 5/21/201412th JCSDA Science Workshop17 Salinity Difference (psu) AQ10 – CTRL10SMOS10 – CTRL10 Average Difference RMS Difference Red line indicates the average depth of the 20C isotherm

Aquarius SSS vs SMOS SSS (AQ10 – SMOS10) 5/21/201412th JCSDA Science Workshop18 Temperature DifferenceSalinity Difference Average Difference RMS Difference Red line indicates the average depth of the 20C isotherm

Latitudinal Differences 5-degree-wide Longitudinal Slice at 120° W: Temperature 5/21/201412th JCSDA Science Workshop19 AQ10 – CTRL10: Avg Difference AQ10 – CTRL10: RMS Difference SMOS10 – CTRL10: RMS Difference SMOS10 – CTRL10: Avg Difference Temperature Difference (°C) Red line indicates the average depth of the 20C isotherm

Latitudinal Differences 5-degree-wide Longitudinal Slice at 120° W: Salinity 5/21/201412th JCSDA Science Workshop20 AQ10 – CTRL10: Avg Difference AQ10 – CTRL10: RMS Difference SMOS10 – CTRL10: RMS Difference SMOS10 – CTRL10: Avg Difference Salinity Difference (psu) Red line indicates the average depth of the 20C isotherm

Summary Assimilating satellite SSS fields improve the simulated ocean state, thus will provide better initialization of coupled seasonal and tropical cyclone forecast systems. – Significant commonalities in results when using two independent satellite SSS data sets demonstrate the robustness of the results – Improvements accrue from using satellite SSS data, as well as shortening the salinity relaxation period Most temperature and salinity differences at or above the 20° isotherm Generally more intense impact with respect to the current operational configuration (SSS monthly climatology) when using Aquarius data. Results indicate largest differences/improvements in the tropical Pacific Ocean. – Possible improvement in countering the model’s tendency toward mirroring the ITCZ in the Southern Hemisphere. Validation – Sea-surface height error reduction indicates some improvement in this region – No obvious impact on ocean heat content other than a very faint indication of improvement in the tropical Pacific (figure not shown) Next: – Examination of model response in the Atlantic and Indian Oceans – Assimilation of SSS Level-2 data 5/21/201412th JCSDA Science Workshop21