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(Jan. 5) Spatial Statistical Downscaling for Constructing High-Resolution Nature Runs in Global

Last updated :2018-01-02

Topic: Spatial Statistical Downscaling for Constructing High-Resolution Nature Runs in Global Observing System Simulation Experiments
Speaker: Associate Professor Emily Kang
(University of Cincinnati)
Time: 3:00-5:30 om, Friday, January 5, 2018
Venue: Room 415, New Mathematics Building, Guangzhou South Campus, SYSU

Abstract:
Observing system simulation experiments (OSSEs) have been widely used as a rigorous and cost-effective way to guide development of new observing systems, and to evaluate the performance of new data assimilation algorithms. Nature runs (NRs), which are outputs from deterministic models, play an essential role in building OSSE systems for global atmospheric processes because they are used both to create synthetic observations at high spatial resolution, and to represent the “true” atmosphere against which the forecasts are verified. However, most NRs are generated at resolutions coarser than actual observations. Here, we propose a principled statistical downscaling framework to construct high-resolution NRs via conditional simulation from coarse-resolution numerical model output. We use nonstationary spatial covariance function models that have basis function representations. This approach not only explicitly addresses the change-of-support problem, but also allows fast computation with large volumes of numerical model output. We also propose a data-driven algorithm to select the required basis functions adaptively, in order to increase the flexibility of our nonstationary covariance function models. We demonstrate these techniques by downscaling a coarse-resolution physical NR at a native resolution of 1 degree latitude by 1.25 degrees longitude of global surface CO2 concentrations to 655,362 equal-area hexagons. This is joint work with Pulong Ma (University of Cincinnati), Amy J. Braverman (Jet Propulsion Laboratory), and Hai M. Nguyen (Jet Propulsion Laboratory).