Facilitating Joint Analysis of Data From Several Systems Using Geophysical Models Hans-Peter Plag, William C. Hammond, Geoffrey Blewitt Nevada Bureau of Mines and Geology and Seismological Laboratory University of Nevada, Reno Reno, NV, USA

Motivation Many different observational techniques are used to observe Earth's shape, gravity field, and rotation in situ, airborne, and spaceborne. The 'three pillars of geodesy': - Earth's Shape (Geokinematics)‏ - Earth's Gravity Field - Earth Rotation (Fourth pillar: - remote sensing of the atmosphere ) Output: - Reference Frame - Observations of the Shape - Gravitational Field and - Rotation of the Earth

Motivation

Science questions potentially benefiting from geodetic observations: Convection: chemical anomalies or temperature anomalies? whole mantle convection or layered convection? Plate tectonics: location of and processes at plate boundaries? extent of deformation zones? Ice sheets/glaciers and sea level: ice load history? present-day mass changes? Ocean circulation; mass and energy balance: variations and changes? separation of steric and non-steric component? Hydrological cycle: quantifying the fluxes? variations in continental water storage? Atmospheric circulation: past and present air pressure and wind fields? Tides: validation of ocean tide models? Seismic waves and free oscillations: structure and mechanical parameter of the solid Earth? e.g., Rummel et al., 2009 Societal challenges potentially benefiting from geodetic observations: Disasters: knowing the locations, nature, and probability of hazards; particularly geohazards; Water: Monitoring the global water cycle and land water storage changes; Climate change: detecting climate change signals in the dynamics; Sea level rise: detecting rapid sea level rise in a timely many

Are we as a community exploiting the full potential of the rich, accurate, comprehensive, and complementary geodetic observations in the three pillars?

State-of-the-Art Current approach to geodetic data interpretation: - many studies within one pillar: - surface displacements; - in situ or spaceborne gravity; - Earth rotation; - often only one type of observations, e.g.: - GNSS - InSAR - recently significant progress with joint inversions for mass loads (e.g., Gross et al., 2004; Wu et al., 2006,..., 2011) - forward models/studies often focused on one phenomenon (e.g., partial loads: atmosphere, land water storage, ocean) - recent progress towards more integrated models (e.g., Juettner and Plag, 1998, Thomas et al., 2005) - combination of techniques: e.g. InSAR and GPS; Lui et al., 2011; Hammond et al., 2011

Combination of Techniques Example: Combination of GPS and InSAR using models Hammond et al., 2011

Integrated Models Example: Earth Rotation Models Models with different level of complexity can be combined A system composed of physically defined subsystems Modules interact through boundary conditions and far-field interactions Couplings between different subsystems defined as meaningful physical quantities independent of structure and dynamics of the subsystems External excitations may be acting on several subsystems (such as tidal potential, magnetic field)

Dynamical Integrate Modular Earth Rotation System (DIMERS) Modules of DIMERS: (i) a quasi rigidly rotating core, (ii) a quasi rigidly rotating mantle including crust, (iii) a non-global equilibrium ocean, (iv) an autonomous atmosphere, (v) a deformation system which represents the deformation of core, mantle and crust disregarded in (i) and (ii) Coordinate system for all subsystem: dynamical Tisserand system of the mantle (DTM) with origin placed in the CoM of the mantle Integrated Models Emerging system characteristics: Chandler wobble period and Q Nearly diurnal free wobble period and Q...

Results of joint analyses, joint inversions, and model studies indicate that there is a considerable potential of geodetic observations to constrain Earth system models.

Geodesy and Earth System Models Solid Earth mainly is a rigid, static boundary condition

Model Comparison Geodetic models:"Earth System models": - no dynamic feedback from the solid Earth to atmosphere, ocean, and cryosphere; - no feedbacks between climate system and solid Earth; - focused on the solid Earth; - focused on the climate system; - solid Earth is a rigid boundary; - forces from atmosphere, ocean, cryosphere are inputs; What about geodetic data assimilation in a Earth system framework? - geodetic observations are not assimilated in models - Earth observations are assimilated to constrain the past

Geodetic Data Assimilation Assimilation of geodetic observations in models: - tropospheric water contents in numerical weather forecast models - satellite altimetry-derived sea surface variations in ocean circulation models Direct assimilation of geodetic observations in system models virtually not done. - GRACE-derived water equivalents in models of terrestrial water storage (e.g. (G)LDAS)

Community Modeling Frameworks

Should we create a community modeling framework that would facilitate the joint analysis and interpretation of geodetic observations?

Geodetic Data Assimilating System (GDAS) Analysis of geodetic observations in an Earth system model concept: - parameterizing the Earth system: - surface mass loads (land, ocean, atmosphere) - modeling of processes: - solid Earth processes (tectonics, strain, rotation,...) - known contributions (tides, tidal loading, …)

+ Point measurements: S i (x) = ∫σ(x') G s (x,x') ds i Filtered, averaged observations: S ij = F(S i (x)) Local models for: - tectonics, - post-seismic strain, -... Global models for: - earth tides; - rotational effects; - tidal loading; - post-glacial rebound; -... Analysis of geodetic observations in an Earth system model concept: + Geodetic Data Assimilating System (GDAS)

Challenge: Different spatial and temporal resolution of geodetic observations GRACE GPS/GNSS Superconducting gravimeters

Analysis of geodetic observations in an Earth system model concept: - parameterizing the Earth system: - surface mass loads (land, ocean, atmosphere) - modeling of processes: - solid Earth processes (tectonics, strain, rotation,...) - known contributions (tides, tidal loading, …) Fingerprint approach for loads: - compute fingerprints for unit mass load on grid elements; - determine loads for each grid element; - global grid, 1 degree spatial resolution: - 64,800 elements; - ~4*10 9 fingerprints for each parameter; - possible to include lateral heterogeneities - nested approach: high spatial resolution in vicinity, low resolution in the far-field. Geodetic Data Assimilating System (GDAS)

Analysis of geodetic observations in an Earth system model concept: - propagating the system state constrained by all available geodetic observations: - surface displacements (> 10,000 points) - gravity (GRACE, in situ) - Earth rotation - altimetry system propagation in time: Kalman filter approach - parameterizing the Earth system: - surface mass loads (land, ocean, atmosphere) - modeling of processes: - solid Earth processes (tectonics, strain, rotation,...) - known contributions (tides, tidal loading, …) Geodetic Data Assimilating System (GDAS)

A community-based Geodetic Data Assimilation System (GDAS) with: - parametrized surface loads, - local geophyscial models - global geophyscial models would: - allow for assimilation of geodetic observations in an Earth system context; - facilitate joint analyses of multi-technique observations; - support local and regional studies with regional and global contributions; - provide a framework to develop community products for use in other disciplines; - have a significant impact on eductation. Facilitating Joint Analysis of Data From Several Systems Using Geophysical Models