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The Physical Basis of SST MeasurementsOne (biased) look at progress
Gary A. WickNOAA ESRL/PSD
October 29, 2013
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Physical Basis – Priority Topics
• Diurnal Variability• Spatial/Temporal Variability• Skin effect
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Physical Basis – Priority Topics
• Diurnal Variability• Spatial/Temporal Variability• Skin effect• SST / Sea Surface Salinity Interactions
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SST/SSS Interactions
• Talks today
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Skin Effect
• Undertake additional research into the physics and modeling of the skin effect
• Improve our understanding of how errors in model forcing parameters impact skin model errors
• Relevant measurements continue– MAERI and other radiometric time series
• Marginal Ice Zone Processes Experiment - MIZOPEX– Radiometric and in situ SST measurements near melting
ice
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Spatial/Temporal Variability
• Develop methods to integrate an improved understanding of the SST variability into the SST retrievals error
• Expand the library of sub-pixel scale SST data sets– Improve understanding of sub-pixel scale variability to better characterize the
contribution of point-to-pixel errors to overall retrieval uncertainty estimates– Explore methodologies to validate representation of spatial variability in SST
products
• Investigate development of a high-resolution μ-wave sensor
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Spatial Variability - Activities
• MIZOPEX– UAS-based infrared imagery collocated with
surface observations– Satellite-buoy comparisons
• Frontal Work
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L4 SST Analysis Evaluation in the Beaufort Sea
• Castro et al., in preparation
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Diurnal Variability
• Continue/expand research into development of diurnal warming models and analysis of satellite observed diurnal warming
• Improve specification of diurnal model uncertainty• Continue and expand research into the role of penetrating
radiation and its relationship to available optical properties in the water column
• Perform additional field observations of diurnal warming events• Develop/enhance links with other communities with interests in
diurnal warming such as the ocean color and the meteorological communities
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Diurnal Variability - Progress
• Measurements– Satellite-based
• Diurnal warming matchup database• TWP+• Climatology work
– In situ• Argo• SPURS
• Models
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GHRSST XIV, Woodshole, 17-21June 2013
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A DW dedicated Matchup database
Overview - DW dedicated MDB based on SEVIRI data. - 20 S to 80 N and 80 W to 80 N - June to September 2012.- daily files in ~1 GB netCDF4 format.
Content- Continuous drifting and moored buoy measurements-“sst” and “flx” data in a 5-pixel square box in satellite coordinates-box is centred at the nearest pixel to the buoy position-Model outputs:
- air temperature at 2m, air humidity at 2m, - surface pressure and integrated water vapour- wind speed at 10m
Sonia Péré, Anne Marsouin, Gérard Legendre, Pierre Le BorgneMétéo-France/Centre de Météorologie Spatiale, Lannion, France
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GHRSST XIV, Woodshole, 17-21June 2013
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Conclusion (still many mysteries…)
Anyone interested please contact
AATSR, METOP,… Local time
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Aims• Assess multiple satellite SST products
over TWP• Quantify diurnal warm-layer events
using satellite data• Assess ≥ 8 diurnal warming models
run using common inputsPeriod
Jan–Apr 2010Location
25°S to 15°N, 90°E to 170°ECollaborators
Bureau of Meteorology, NOAA, Meteo- France, Met Office, WHOI, Uni of Colorado, Uni of Edinburgh, Uni of Arizona, Uni of Miami, JMA
Tropical Warm Pool Diurnal Variability Project (TWP+)
Wick Modified Kantha-Clayson DW
MTSAT-1R Observed DW
Castro Look-Up Table DW
26 Apr 2010Helen Beggs, Bureau of Meteorology
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TWP+ Data Set• Satellite SST
• IR: AVHRR (METOP-A, NOAA-17,18 & 19)
• IR dual-view: AATSR (Envisat)• MW: AMSR-E (AQUA)• MW: WindSat (Coriolis)• Geo: JAMI (MTSAT-1R)
• Bureau Regional foundation SST Analysis (RAMSSA)
• In Situ SST (buoys, ships)• Bureau Numerical Weather Prediction
surface flux fields (ACCESS-R)• Bureau Sea State Forecasts
(AUSWAM)• 7 DV Model outputs
Tropical Warm Pool Diurnal Variability Project (TWP+)
MTSAT-1R Observed DW
Castro Look-Up Table DW
26 Apr 2010
ACCESS-R 10m Wind
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Diurnal Warming Climatology
• NASA funded project• How large is DW throughout the globe and
how do magnitudes vary with season?• How does frequency vary with magnitude?• What are the spatial scales of DW?• Influences on air-sea fluxes and climate
variability
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Diurnal Variability - Progress
• Measurements– Satellite-based
• Diurnal warming matchup database• TWP+• Climatology work
– In situ• Argo• SPURS
• Models
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Comparison of Subskin and Foundation Estimates (Argo – SEVIRI)
Warm Count Bias Stdev Bias Stdev
Yes 223 -0.04 0.39 0.23 0.44
No 405 -0.10 0.37 -0.09 0.35
All 628 -0.08 0.38 0.03 0.42
Warm Count Bias Stdev Bias Stdev
Yes 211 -0.02 0.36 -0.16 0.36
No 495 -0.11 0.39 -0.10 0.38
All 706 -0.09 0.38 -0.12 0.39
Subskin SST
Foundation SST
Castro et al., RSE, doi:10.1016/J.RSE.2013.08.042
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Comparison of Derived Diurnal Warming
Warm Counts
Bias Stdev
Yes 192 0.00 0.25
No 317 0.02 0.17
All 509 0.01 0.21
Castro et al., RSE, doi:10.1016/J.RSE.2013.08.042
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Dedicated ARGO Diurnal Warming Experiment
• Discussed at GHRSST 2013 Science Team Meeting• Dedicated experiment “perfectly doable”
– Majority of new floats use iridium communications– Float could repeatedly sample near-surface ocean for
period of 3-5 days– Willing to explore sampling closer to surface
• Group to develop plans for experiment of opportunity– Explore forecasting capability
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Diurnal Variability - Progress
• Measurements• Models
– Clayson and Bogdanoff– Weihs and Bourassa– Karagali and Høyer– Coupled modeling– Scanlon et al.– Wick– …
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GHRSST DVWG Focus
• Desired approaches/requirements for diurnally resolved SST– Provision of diurnal warming estimates
• Temporal frequency• Representative depth• Representative spatial scale
– Direct provision of models/parameterizations– Provision of error characteristics for existing models
and predictions– Increasing available validation data– Understanding of basic physics
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Scanlon et al., Ocean Science, in press
• Compared simulated near-surface temperature profiles from the Kantha-Clayson model with observations from SkinDeep
• Individual profile comparison difficult, but reasonable agreement in average sense
• Base scheme performed well• Provides some estimate of
errors with depth
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Real-Time Diurnal Warming Estimates Forced with GFS Model Inputs
Gary A. WickNOAA ESRL/PSD
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Motivation
• Compensation for presence of diurnal warming in SST analyses
• Facilitation of further comparison and validation of models
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Components
• Model Inputs– GFS analysis fields, 6 hourly, 0.5 degree
• Wind stress• Radiative and turbulent fluxes
– Wave Watch III Wave Model• Wave period, direction, and significant wave height
• Models initially evaluated– Kantha Clayson with wave effects– COARE– Parameterizations
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Sample Forcing Fields
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Logistics
• Models initialized based on SST• Fluxes interpolated to model time step• Model run globally for 2 days with output
taken from the second day• Warming taken as Tsubskin - Tdepth
• Warming compared against SEVIRI observations
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Kantha Clayson Stokes Drift ModelDiurnal Warming Evolution, 00-23 UTC, 21 March 2013
SAMPLE MODEL RESULTS
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Comparison of Warming with SEVIRI Observations
• SEVIRI warming computed as SSThour – SSTFoundation
• SSTFoundation computed as nighttime average
• Initial comparison in terms of warming distribution– Tests models ability to reproduce
range of diurnal warming– Less sensitive to errors in model
wind stress• Supplementary absolute
comparisons to follow
SEVIRI-Derived Diurnal Warming1400 UTC, 21 March 2013
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Comparison of Observed and Modeled Diurnal WarmingSEVIRI Domain – 21 March 2013, 1400 UTC
K-C Stokes Drift K-C Stokes Enh (2) K-C Stokes Enhanced
COAREWick K-C Blended Gentemann
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Comparison of Observed and Modeled Diurnal WarmingSEVIRI Domain – 21 March 2013, 2200 UTC
K-C Stokes Drift K-C Stokes Enh (2) K-C Stokes Enhanced
COAREWick K-C Blended Gentemann
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TIME EVOLUTION OF WARMING DISTRIBUTIONS FOR MODELS
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Comparison of Observed and Modeled Diurnal WarmingSEVIRI Domain – 21 March 2013
Kantha Clayson Model with Stokes Drift
0200 UTC 0600 UTC 1000 UTC
1800 UTC1400 UTC 2200 UTC
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Comparison of Observed and Modeled Diurnal WarmingSEVIRI Domain – 22 March 2013
Kantha Clayson Model with Stokes Drift
0200 UTC 0600 UTC 1000 UTC
1800 UTC1400 UTC 2200 UTC
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Summary
• Automated daily computation of global diurnal warming from NWP forcing coming on line for application to SST analyses
• Distribution of diurnal warming reasonably well reproduced
• Some instances of persistent warming, but not entirely without support
• Display, distribution, and further evaluation of products to follow
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Extra Slides
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Gentemann ParameterizationDiurnal Warming Evolution, 00-23 UTC, 21 March 2013
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COARE ModelDiurnal Warming Evolution, 00-23 UTC, 21 March 2013
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Scanlon et al., Ocean Science, in press
• Compared simulated near-surface temperature profiles from the Kantha-Clayson model with observations from SkinDeep
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Comparison of Warming with SEVIRI Observations
• SEVIRI warming computed as SSThour – SSTFoundation
• SSTFoundation computed as nighttime average• Initial comparison in terms of warming distribution
– Tests models ability to reproduce range of diurnal warming
– Less sensitive to errors in model wind stress• Supplementary absolute comparisons to follow
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Conclusions: The potential utility of Argo data for diurnal warming applications has been a key question for the DVWG
Results demonstrate remarkable consistency between the estimates of the subskin and foundation temperatures and corresponding diurnal warming from SEVIRI and unpumped Argo. This lends support to both products and associated methodologies.
Unpumped Argo floats provide accurate estimates of diurnal warming. They constitute a very valuable independent data set for L4 SST validation and diurnal warming studies, suggesting we advocate for more unpumped Argo floats.
Castro et al., RSE, in press