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Assimilating Satellite Sea-Surface Salinity in NOAA

Eric Bayler, NESDIS/STARDave Behringer, NWS/NCEP/EMCAvichal Mehra, NWS/NCEP/EMC

Sudhir Nadiga, IMSG @ NWS/NCEP/EMC

5/21/2014 12th JCSDA Science Workshop

12th JCSDA Science Workshop 2

Sea-Surface Salinity (SSS) DataSatellite:• 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

5/21/2014

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SSS Data: RMS difference of monthly means

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Salinity RMS difference (psu)

SMOS - WOA AQRS - WOA

SMOS - AQRS

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Equatorial Pacific (2°S – 2°N) SSS: MeanWOA2009 Argo AQRS SMOS

Salinity (psu)

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Equatorial Pacific (2°S – 2°N) SSS Mean: DifferencesAQRS -WOA SMOS-WOA SMOS -AQRS

Salinity Difference (psu)

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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 2012-2013 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.

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Modeled CasesCONTROL

– 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

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ValidationReference = Satellite Salinity Observations

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Salinity RMSE (psu)(a)

AQ10 RMSE; reference = AQRS

(b)

SMOS10 RMSE; reference = SMOS

Model seems to better assimilate the Aquarius data.

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ImprovementNear-real-time Observations versus Climatology

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AQ10 – CTRL10; ref = AQRS obs SMOS10 – CTRL10; ref = SMOS obs

Salinity RMSE (psu)(a) (b)

Blue = Reduction in RMS errors

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Validation: Altimetry

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Normalized RMSE difference (%); reference = satellite sea-surface height anomalies

RMSE difference (cm); reference = satellite sea-surface height anomalies

SMOS10 – CTRL10 AQRS10 – CTRL10 AQRS10 – SMOS10

SMOS10 – CTRL10 AQRS10 – CTRL10 AQRS10 – SMOS10

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Satellite SSS vs Climatology: 30-day RelaxationAverage and RMS Temperature Differences

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Temperature Difference

(°C)

AQ30 – CTRL30 SMOS30 – CTRL30Average Difference Average Difference

RMS Difference RMS Difference

Red line indicates the average depth of the 20C isotherm

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Satellite SSS vs Climatology: 30-day RelaxationAverage and RMS Salinity Differences

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Salinity Difference

(psu)

AQ30 – CTRL30 SMOS30 – CTRL30Average Difference Average Difference

RMS Difference RMS Difference

Red line indicates the average depth of the 20C isotherm

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SSS Constraint: 10-day vs 30-day RelaxationAverage and RMS Temperature Differences

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Temperature Difference

(°C)

AQ10 – CTRL30 SMOS10 – CTRL30Average Difference Average Difference

RMS Difference RMS Difference

Red line indicates the average depth of the 20C isotherm

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SSS Constraint: 10-day vs 30-day Relaxation Average and RMS Salinity Difference

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Salinity Difference

(psu)

AQ10 – CTRL30 SMOS10 – CTRL30Average Difference Average Difference

RMS Difference RMS Difference

Red line indicates the average depth of the 20C isotherm

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SSS Data vs Relaxation PeriodAverage and RMS Temperature Differences

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Temperature Difference

(°C)

AQ10 – CTRL10 SMOS10 – CTRL10Average Difference Average Difference

RMS Difference RMS Difference

Red line indicates the average depth of the 20C isotherm

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SSS Data vs Relaxation Period Average and RMS Salinity Differences

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Salinity Difference

(psu)

AQ10 – CTRL10 SMOS10 – CTRL10Average Difference Average Difference

RMS Difference RMS Difference

Red line indicates the average depth of the 20C isotherm

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Aquarius SSS vs SMOS SSS(AQ10 – SMOS10)

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Temperature Difference Salinity DifferenceAverage Difference Average Difference

RMS Difference RMS Difference

Red line indicates the average depth of the 20C isotherm

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Latitudinal Differences 5-degree-wide Longitudinal Slice at 120° W: Temperature

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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

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Latitudinal Differences5-degree-wide Longitudinal Slice at 120° W: Salinity

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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

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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

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