The Role of Deep Convection in Assessing the Vertical Transport of CO2 in Mesoscale Models

Modeling of CO₂ in the atmosphere on a domain encompassing the entire contiguous United States does not currently combine any convection parameterization with vertical mass flux explicitly. This is remedied by combining CO₂ vertical transport with Kain-Fritsch convective mass flux within the Weather Research and Forecasting (WRF) model. This study assesses this new parameterization within WRF-Chem through analysis of model output of various grid spacing as well as observations from DISCOVER-AQ’s July 2011 campaign. Model outputs utilized in this study include 27km resolution with and without the new parameterization, as well a 1km resolution, which explicitly solves for convection. Different visualization methods are employed, such as horizontal maps at given model levels, vertical transects, and point vertical profiles. Plots of the difference between the coupled and uncoupled 27km output show slight variation over the entire domain, with much higher differences in locations of convection. A transect of 1km model output has strong agreement with observations; the mean errors of the modeled CO₂ is about 0.5 ppm with local maximum errors of 4 ppm. 27km CO₂ transects match nearly identically and agree well with the observations for the selected cases, with the coupled 27km output an improvement of up to 1 ppm. Vertical profiles of model output and observations show all models fail to capture near-surface CO₂ variability, which can be attributed to the complexity of the CO₂ surface flux. This work shows the ability to combine the Kain-Fritsch convective scheme with CO₂ mass flux, while showing that it is also necessary to further improve CO₂ modeling.