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COSMIC and Land Data Assimilation. Rafael Rosolem. W. J. Shuttleworth 1 , M. Zreda 1 , A. Arellano 1 , X. Zeng 1 , T. Hoar 2 , J. Anderson 2 , T . Franz 1 , S . A. K. Papuga 1 , Z. M. S. Mejia 1 , M. Barlage 2 , J. S. Halasz 1. 1 University of Arizona
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COSMIC and Land Data Assimilation Rafael Rosolem W. J. Shuttleworth1, M. Zreda1, A. Arellano1, X. Zeng1, T. Hoar2, J. Anderson2, T. Franz1, S. A. K. Papuga1, Z. M. S. Mejia1, M. Barlage2, J. S. Halasz1 1 University of Arizona 2 National Center for Atmospheric Research COSMOS 3rd Workshop December 11, 2012
Why do we need a forward operator for COSMOS? • “Effective” measurement depth depends on soil moisture • Can reach several individual layers of a typical land surface model Therefore, direct assimilation of neutron intensity is more desirable!!!
Data Assimilation of Neutron Counts GOAL to update LSM soil moisture profiles by assimilating the cosmic-ray fast neutron count Land Surface Model (LSM) Requires an accurate model to interpret modeled soil moisture profiles in terms of the above-ground fast neutron count Modeled Soil Moisture Profile Monte Carlo Neutron Particle model (MCNPx) does that but it is too slow for use in data assimilation
COsmic-ray Soil Moisture Interaction Code (COSMIC) • COSMIC is a simple analytic model which: • captures the essential below-ground physics that MCNPX represents • can be calibrated by optimization against MCNPX so that the nuclear collision physics is re-captured in parametric form Ne z z Exponential reduction in the number of high energy neutrons with depth Isotropic creation of fast neutrons from high energy neutrons at level “z” Exponential reduction in the number of the fast neutrons created at level “z” before their surface measurement high energy neutrons fast neutrons
COsmic-ray Soil Moisture Interaction Code (COSMIC) The resulting analytic function that describes the total number of fast neutrons reaching measurement point is: A few meters will do! Exponential reduction in the number of the fast neutrons created at level “z” before their surface measurement Exponential reduction in the number of high energy neutrons with depth Isotropic creation of fast neutrons from high energy neutrons at “z” • Two parameters measured in situ (soil bulk density and lattice water) and six to be defined: • L1 , L2 and L4are site-independent and are easily determined from MCNPX • L1= 162.0 g cm-2 • L2= 129.1 g cm-2 • L4= 3.16 g cm-2 • N , and L3 require multi-parameter optimization against site specific-specific runs of MCNPX for a range of hypothetical soil moisture profiles
Calibrating COSMIC Fort Peck Hypothetical soil water profiles Bondville Chestnut Ridge Santa Rita Coastal Sage
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COSMIC Performance at Santa Rita (AZ) Using COSMIC to estimate COSMOS counts from measured soil moisture profiles (TDT sensors) Running time for a single soil moisture profile MCNPx ~ 30-60 minutes COSMIC ~ 0.5 seconds
Data Assimilation Framework COSMIC COSMOS http://www.ral.ucar.edu/research/land/technology/lsm.php http://www.image.ucar.edu/DAReS/DART/
Soil Moisture Dynamics • 40 ensembles with perturbed forcing data (Santa Rita, AZ): 2010-07-28_00Z through 2010-08-23_23Z (x-axis hour timesteps) • No assimilation!!! member runs are unconstrained!!! • “Damped” process driven by (rainfall) pulses
Data Assimilation Results: Santa Rita (AZ) • 40 ensembles: 2011-07-03_00Z through 2011-09-14_23Z • With and without assimilation of observed COSMOS neutron counts R2 = 0.97, RMSE = 48 cph, BIAS = -26 cph R2 = 0.84, RMSE = 840 cph, BIAS = -832 cph
Updated Soil Moisture Profiles NOAH Δz1 NOAH Δz2 No Assimilation NOAH Δz1 NOAH Δz2 Assimilated TDT (independent) measurements
Problems to be solved • Reduced ensemble spread at lower soil moisture • test other filter types • test different inflation parameters • log-transform: initial tests = simulation crashes • assimilation of multiple observations (e.g., SMOS) • adopt a minimum soil moisture threshold in DART but add small noise when updating variables (to ensure individual ensemble members won’t converge to minimum allowed) • Calibrate key soil moisture/surface flux parameters in Noah (currently working on that) DART