GRACE Mascons and Hydrological Data for the Continents: GRACE

ACCESSD. Rowlands(1) , F. Lemoine(1), S. Luthcke(1), S. Klosko(2),

D. Chinn(2), K. Akoumany(2), A. Griffin(2), M. Rodell(3)

(1) Plantary Geodynamics Laboratory, Code 698, NASA/GSFC, Greenbelt MD USA 20771

(2) SGT Inc., 7701 Greenbelt Rd, Greenbelt MD USA 20770(3) Hydrological Sciences Branch, NASA/GSFC, Greenbelt MD USA 20771

GRACE Science Team MeetingPotsdam, October 2007

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Overview of Project Goals

• GOAL: Make available through www access, high resolution estimates of mass flux/change from GRACE that provide important measures of the entire hydrological signal

• Employ a standard 4x4 degree grid over continental regions and provide mass flux estimates (in units of cm of water) as a surface mass anomaly. These values are obtained every 10 days over a significant portion of the GRACE mission

• Provide auxiliary estimates of the hydrological signal as available from state-of-the-art assimilative hydrological models (e.g. GLDAS)

http://grace.sgt-inc.com

Groundwater Flux is a Major Societal Concern

Aquifers are being depleted in scores of countries which collectively account for half of the world grain harvest. Overpumping has largely depleted the shallow aquifers, so the amount of water that can be pumped from it each year is restricted to the annual recharge from precipitation. This is forcing well drillers to go down to the region's deep aquifer, which, unfortunately, is not replenishable

http://grace.sgt-inc.com

MASCON Approach

• We directly estimate mass change in 4°x4° blocks – as geographically specific mascons (as opposed to global coefficients that are used to reconstruct mass change locally)

• We directly estimate mass change every 10 days (as opposed to every 30 days)

• We smooth our solutions by combining spatial and temporal constraint equations together with the GRACE tracking data in a simultaneous solution (as opposed to Gaussian smoothing gravity solution products a posteriori)

• Only the precise KBRR tracking data is utilized in the our mascon solutions (as opposed to using both GPS and KBRR data)

http://grace.sgt-inc.com

GRACE Data Processing: Standards for Current Products

• Gravity model: GGM02C (vs. GGM01C).• Atmospheric Gravity Series:• Based on NCEP Reanalysis by L. Petrov.• 2.5° x 2.5° and 6 hour resolution (0.25°x 0.25° land mask).• Consistent series from 1976------> Present (few days latency).• 50x50 spherical harmonic expansion @ 6 hours.

• Ocean tide modelling (e.g. M2 to 70x70; Other major constituents to 50x50), (GOT00.2)

• Improved processing of GRACE accelerometry.

• Reprocessing underway with updated background models (e.g. ECMWF 3-hr; GOT4.7b…..)

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Water Storage Variations

GLDAS model average soil moisture + snow

Ground water from well observations

Observed ground water + GLDAS average soil moisture + snow

Matt RodellMatt RodellHydrological Sciences Branch, NASA GSFCHydrological Sciences Branch, NASA GSFC

Mississippi Basin: GRACE mascon vs hydrology cross correlation

ρ=+o.85

RMS = 2.9cm

http://grace.sgt-inc.com

GRACE Hydrology ACCESS Site:

4°x4° Mascon Solutionsfor all Continental Regions

http://grace.sgt-inc.com/

India / South Asia

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Eastern Australia

Australia: Lat -28, Long 146GRACE Hydrology

Linear = -0.85 cm/y Linear = -1.40 cm/y

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rms 1.83 cm rms 1.86 cm

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North Central Australia

GRACE Hydrology

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Australia: Lat -16, Long 134

rms 4.2 cmAnnual amp 5.7 cm phase 1 daySemi-annual amp 1.7 cm phase -12 day

rms 5.1 cmAnnual amp 11.3 cm phase 0 daySemi-annual amp 2.7 cm phase -14 day

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Sahara

40 cm

Amazon Basin

NASA ACCESS Program: Generation of Gridded Hydrological Mass Anomalies: Cross Correlation

with GLDAS

Coherence Spectrum Between GRACE 4o Mascons and Coincident NOAH Hydrology

Stacked Coherence Spectrum for North America

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Time Shift for Optimal Cross Correlation of GRACE and Hydrology: North America

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Optimal Phase Shift Between Hydrology and GRACE

(239 N. American 4o Cells)

Australia Lat -20 Long 122 GRACE Mascons

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4 Year Time Series is Now Available

Summary◙ GRACE KBRR tracking has provided the means to monitor global changes in the hydrological column

◙ 10-day estimates of 4 x 4 degree mass anomalies having accuracy assessments of 1-2 cm (equivalent water height) are available for both GRACE and coincident hydrological model –GLDAS

◙ The GRACE ACCESS site is at HTTP://GRACE.SGT-INC.com.

◙ Data are provided for a four year time period allowing comparison of the annual and semi-annual cycles repeatedly over each region.

◙ These data are easily downloadable and a toolkit is provided to perform various analysis functions on-line.

◙ Future upgrades to the GRACE solutions, extended times series, and enhanced toolkit are planned