A Lagrangian Assimilation System for North American Carbon Flux Estimates
Abstract:Understanding biospheric CO2 fluxes is paramount for climate studies to be able to analyze the responses of terrestrial ecosystems to climate change. To improve North American carbon flux estimates, we have built a new data assimilation system that couples the contemporary global carbon cycle model CarbonTracker with the Weather Research and Forecasting/Stochastic Time-Inverted Lagrangian Transport (WRF-STILT) model (referred as CarbonTracker-WRF-STILT).
The current CarbonTracker-WRF-STILT system assimilates atmospheric observations of CO2 mole fractions at eight tower sites in North America and optimizes the a priori carbon fluxes from the simple biosphere (SiB) model. The system employs a two-lag Ensemble Kalman smoother to optimize scaling factors for both biospheric fluxes and the boundary conditions every 10 days. We will present the optimized carbon fluxes for North America for 2010, and compare them with the results from the CT2013B and CTE2014. To estimate the transport uncertainties, we also plan to test an alternative Lagrangian transport model Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT) driven by the NAM12 meteorological fields.
In the following step, the CarbonTracker-WRF-STILT system will be adapted to assimilate multiple tracers, e.g. CO2 and carbonyl sulfide (COS) to simultaneously optimize photosynthesis (Gross Primary Production, GPP) and respiration.