[A-AS08] Weather, Climate, and Environmental Science Studies using High-Performance Computing

[AAS08-P08] A Study of Influence of Atmospheric Transport on Interhemispheric Gradient of Carbon Dioxide Based on Observations and Model Simulations

*Guangyu LIU¹, Hisashi Yashiro¹, Yosuke Niwa¹ (1.National Institute for Environmental Studies)

Keywords:carbon dioxide, model simulation

The interhemispheric gradient (IHG) of carbon dioxide (CO₂) has been used as an important constraint on sources and sinks of carbon. IHG is maintained because anthropogenic CO₂ emissions from fossil-fuel consumption are concentrated mainly in the Northern Hemisphere. However, previous studies have reported that the observed IHG variability cannot be reproduced without considering the recent increase in CO₂ uptake by vegetation in midlatitudes of the Northern Hemisphere (Ciais et al., 2019). IHG also reflects the variation in interhemispheric CO₂ transport. In this study, we used National Centers for Environmental Prediction (NCEP) reanalyses dataset and numerical simulation by Nonhydrostatic Icosahedral Atmospheric Model (NICAM), to make a detailed investigation on the interannual IHG variability focusing on the influence of atmospheric transport on the IHG. Using long-term CO₂ observation record of ground stations (compiled by WDCGG), we compared the observed IHG with simulated IHG. Following the previous studies (e.g. Francey and Frederiksen, 2016), we focused on the zonal wind in upper-tropospheric equatorial region (140W-170W, 5N-5S) in boreal winter, called the “duct”. We found that the reproducibility of the duct region was strongly affected by model bias and that interhemispheric transport of CO₂ through the duct region was enhanced in the absence of data assimilation (nudging), underestimating the IHG.