Data assimilation

The NCAR Data Assimilation Program includes a postdoctoral program that provides an opportunity to postdoctoral researchers to advance their careers while working collaboratively at NCAR on data assimilation topics of importance to the community.

Schematic diagram for methodology of the assimilation system
Schematic diagram for methodology of the assimilation system. Sequential Kalman filter was run from 1 March 2000 to 31 December 2015 to produce the optimized initial conditions (monthly) and boundary conditions (hourly). Monthly 4D-Var inversions were performed with the optimized initial conditions. Only MOPITT data over land (white grids) were assimilated in the 4DVar inversions, while the CO abundances over ocean (red grids) were defined as boundaries and rewritten using the optimized hourly CO fields from the Kalman filter. The Kalman filter run is completely independent of the 4D-Var inversions. There is no feedback of the 4D-Var inversion results to the boundary conditions.

An example of the research being carried out under this program is the recently published paper of postdoc Zhe Jiang, in collaboration with NCAR/ACOM scientists and researchers at the University of Toronto, University of Arizona, and University of Colorado.  The objective of this work is to investigate the dominant reasons for the observed variation of global tropospheric CO over the past 15 years. 

Long-term measurements from satellites and surface stations have demonstrated a decreasing trend of tropospheric carbon monoxide (CO) in the Northern Hemisphere over the past decade. Likely explanations for this decrease include changes in anthropogenic, fires, and/or biogenic emissions or changes in the primary chemical sink hydroxyl radical (OH). Using remotely sensed CO measurements from the Measurement of Pollution in the Troposphere (MOPITT) satellite instrument, in situ methyl chloroform (MCF) measurements from theWorld Data Centre for Greenhouse Gases (WDCGG) and the adjoint of the GEOS-Chem model, we estimate the change in global CO emissions from 2001 to 2015.

We show that the loss rate of MCF varied by 0.2% in the past 15 years, indicating that changes in global OH distributions do not explain the recent decrease in CO.

Our analysis highlights the importance of space-based instruments for monitoring changes in global pollutant emissions. Our results demonstrate successful emission controls in the US and China over the past 15 years and suggest that emission controls in Europe may need re-evaluation. We also recommend more efforts in the future to better understand the regional and global effects of increasing pollutant emissions from India and southeast Asia.

Jiang, Z., Worden, J. R., Worden, H., Deeter, M., Jones, D. B. A., Arellano, A. F., and Henze, D. K., 2017: A 15-year record of CO emissions constrained by MOPITT CO observations, Atmos. Chem. Phys., 17, 4565-4583, doi:10.5194/acp-17-4565-2017.