Frontal Gradients in CO2 as Seen from OCO-2

Day to day weather events play an important role in the spatial and temporal gradients of carbon dioxide (, with previous studies noting sharp gradients in surface observations across frontal boundaries. In this study, we analyze the behavior in column average dry air mole fraction (XCO2) in the vicinity of cold fronts to determine the visibility of these features from space. We use data from the Orbiting Carbon Observatory-2 (OCO-2) for 83 cold frontal cases over the United Sates and neighboring oceans from 2015 to 2017 and examine difference anomalies across the fronts to establish that the gradient anomalies are significant relative to instrument noise. In order to deduce potential surface flux influence on these frontal gradients, we separate gradient anomalies based on 7 land cover types with different biological surface flux parameterizations that are derived from EVI, LSWI, and modeled radiation and temperature. The results show cold fronts in the summer in these three years exhibit strong gradients in CO2 over and above instrument noise, but XCO2 gradients across fronts in the rest of the year are not statistically significant.

OCO-2 soundings are not retrieved in cloudy frontal regions, and so the observations alone cannot be used to analyze XCO2 variations at the frontal boundaries. WRF-VPRM is used to explore XCO2 variations in order to understand both horizontal and vertical structures and variations of CO2 near the leading edge of cold air advection.