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  • Assimilation of gridded terrestrial water storage observations from GRACE into a land surface model.

    Author(s) : Girotto, M.Lannoy, G. J. M. deReichle, R. H.Rodell, M.

    Author Affiliation : NASA Goddard Space Flight Center, Greenbelt, Maryland, USA.

    Author Email : manuela.girotto@nasa.gov

    Journal article : Water Resources Research 2016 Vol.52 No.5 pp.4164-4183 ref.many

    Abstract : Observations of terrestrial water storagewater storageSubject Category: Miscellaneous
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    (TWS) from the Gravity Recovery and ClimateclimateSubject Category: Climate Related
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    Experiment (GRACE) satellite mission have a coarse resolution in time (monthly) and space (roughly 150,000 km2 at midlatitudes) and vertically integrate all water storage components over land, including soil moisturemoistureSubject Category: Miscellaneous
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    and groundwatergroundwaterSubject Category: Miscellaneous
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    . Data assimilationassimilationSubject Category: Natural Processes
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    can be used to horizontally downscale and vertically partition GRACE-TWS observations. This work proposes a variant of existing ensemble-based GRACE-TWS data assimilation schemes. The new algorithm differs in how the analysis increments are computed and applied. Existing schemes correlate the uncertainty in the modeled monthly TWS estimates with errors in the soil moisture profile state variables at a single instant in the month and then apply the increment either at the end of the month or gradually throughout the month. The proposed new scheme first computes increments for each day of the month and then applies the average of those increments at the beginning of the month. The new scheme therefore better reflects submonthly variations in TWS errors. The new and existing schemes are investigated here using gridded GRACE-TWS observations. The assimilation results are validated at the monthly time scale, using in situ measurements of groundwater depth and soil moisture across the U.S. The new assimilation scheme yieldsyieldsSubject Category: Properties
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    improved (although not in a statistically significant sense) skill metrics for groundwater compared to the open-loop (no assimilation) simulations and compared to the existing assimilation schemes. A smaller impact is seen for surface and root-zone soil moisture, which have a shorter memory and receive smaller increments from TWS assimilation than groundwater. These results motivate future efforts to combine GRACE-TWS observations with observations that are more sensitive to surface soil moisture, such as L-band brightness temperature observations from Soil Moisture Ocean SalinitysalinitySubject Category: Properties
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    (SMOS) or Soil Moisture Active Passive (SMAP). Finally, we demonstrate that the scaling parameters that are applied to the GRACE observations prior to assimilation should be consistent with the land surface model that is used within the assimilation system.

    ISSN : 0043-1397

    DOI : 10.1002/2015WR018417

    Record Number : 20163233488

    Publisher : Wiley-Blackwell

    Location of publication : Hoboken

    Country of publication : USA

    Language of text : English

    Indexing terms for this abstract:

    Descriptor(s) : analysisanalysisSubject Category: Techniques, Methodologies and Equipment
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    , assimilationassimilationSubject Category: Natural Processes
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    , climateclimateSubject Category: Climate Related
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    , data analysisdata analysisSubject Category: Techniques, Methodologies and Equipment
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    , data processingdata processingSubject Category: Techniques, Methodologies and Equipment
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    , groundwatergroundwaterSubject Category: Miscellaneous
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    , measurementmeasurementSubject Category: Techniques, Methodologies and Equipment
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    , moisturemoistureSubject Category: Miscellaneous
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    , salinitysalinitySubject Category: Properties
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    , soil watersoil waterSubject Category: Miscellaneous
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    , time seriestime seriesSubject Category: Miscellaneous
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    , water resourceswater resourcesSubject Category: Miscellaneous
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    , water storagewater storageSubject Category: Miscellaneous
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    , yieldsyieldsSubject Category: Properties
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    Identifier(s) : metrology, soil moisture