5B.2 Spatial and Temporal Representativeness of ATom Transects Using GEOS-5 and GMI–CTM Simulations

Tuesday, 9 January 2018: 10:45 AM
Room 9 C (ACC) (Austin, Texas)
Junhua Liu, NASA USRA, Greenbelt, MD; and S. A. Strode, M. J. Prather, L. Lait, A. Conaty, M. R. Damon, S. D. Steenrod, P. A. Newman, R. Commane, B. C. Daube, S. C. Wofsy, T. B. Ryerson, J. Peischl, C. Thompson, H. Bian, and S. E. Strahan

ATom provides a contiguous, global-scale dataset of the remote troposphere using transects through the middle of the Pacific and Atlantic Ocean basins. The GEOS-5 global model reproduces the observed background CO levels very well, including the timing and topography of CO enhancements during the ATom mission. In this study, we use these GEOS-5 CO simulations to investigate the spatial and temporal representativeness of the specific ATom flights during ATom-1 and -2. Our model analysis shows that probability distribution (PD) of simulated CO over regional Pacific latitudinal bands (e.g., 20˚N-40˚N, 20˚S-20˚N, 20˚S-80˚S) is similar to the ATom transects, demonstrating that ATom-sampled CO is likely representative of typical regional concentrations in August. Over the North Pacific (40˚N-80˚N), the CO distribution on the ATom-1 path peaks around 85 ppb, which is about 10 ppb less than that over the larger region. A second peak in the PDs low tail indicates a possible perturbation from stratospheric very-low CO air. Over the tropical and subtropical south Atlantic, CO is mainly driven by southern African biomass burning during ATom-1 period. CO along ATom transects over tropical Atlantic shows “skewed right" distribution with a higher peak compared to the broader region, indicating a stronger contribution from Africa to the transect than to the mean Atlantic basin. PDs for simulated CO along ATom flights are compared with the monthly-accumulated PDs to test the sensitivity of ATom results to episodic transport events. In addition to the GESO-5 CO statistics, we also take a quick look at the NASA Global Modeling Initiative – Chemistry transport model (GMI-CTM) results, which are driven by assimilated MERRA-2 meteorological fields for the ATom-1 and -2 flight periods. This full-chemistry simulation allows us to include similar statistical analyses of PDs for the ATom ozone, which is reproduced well by the GMI-CTM in magnitude and variability as suggested by the initial model-data comparison.
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