Qingyu Wang-November 9 BUL Seminar

Atmospheric Variations in Column Integrated CO₂ on Synoptic and Seasonal Time Scale over the U.S.

Qingyu Wang¹, Sean Crowell¹, Xiao-Ming Hu^1,2

Past studies have demonstrated that synoptic events play an important role in the spatial and temporal variations of carbon dioxide (CO2). Total column measurements should help constrain CO2 emissions with greater precision because total column CO2 is less sensitive to convective transport errors and the exact boundary layer height than in-situ measurements, though this lack of sensitivity is balanced with smaller dynamic range and poorer measurement accuracy. In this study, in order to find whether Orbiting Carbon Observatory-2 (OCO-2) is precise enough on mesoscale and synoptic variations, we investigate whether gradients in XCO2 across cold fronts are detectable by OCO-2 We calculate the XCO2 gradient for 83 cold frontal cases over the United States, East Pacific Ocean and West Atlantic Ocean from 2015 to 2017 and assess the statistical significance for these gradients relative to climatology in each season to assess whether the satellite based measurements can distinguish between frontal and non-frontal CO2 gradients. The results show that OCO-2 XCO2 frontal gradients in different seasons match past studies on in situ CO2 frontal contrasts in boundary layer, indicating OCO-2 can see mesoscale and synoptic features.

Seeing that OCO-2 measures well on mesoscale and synoptic scale, we examine whether simulations from WRF-VRPM are simulating XCO2 well over the contiguous United States (CONUS). The model agrees well with OCO-2 for some land cover types and seasons, like forests in the winter, while still relative high bias in summer for grassland, shrubland and savannah.

These results suggest that OCO-2 data contain information not only on synoptic scale transport mechanisms, but also on the surface CO2 flux processes that drive the gradients seen in the atmosphere.