Development and application of the WRFPLUS-Chem online chemistry adjoint and WRFDA-Chem assimilation system

Abstract

Abstract.Here we present the online meteorology and chemistry adjoint and tangent linear model, WRFPLUSChem (Weather Research and Forecasting plus chemistry), which incorporates modules to treat boundary layer mixing, emission, aging, dry deposition, and advection of black carbon aerosol. We also develop land surface and surface layer adjoints to account for coupling between radiation and vertical mixing. Model performance is verified against finite difference derivative approximations. A second-order checkpointing scheme is created to reduce computational costs and enable simulations longer than 6 h. The adjoint is coupled to WRFDA-Chem, in order to conduct a sensitivity study of anthropogenic and biomass burning sources throughout California during the 2008 Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) field campaign. A cost-function weighting scheme was devised to reduce the impact of statistically insignificant residual errors in future inverse modeling studies. Results of the sensitivity study show that, for this domain and time period, anthropogenic emissions are overpredicted, while wildfire emission error signs vary spatially. We consider the diurnal variation in emission sensitivities to determine at what time sources should be scaled up or down. Also, adjoint sensitivities for two choices of land surface model (LSM) indicate that emission inversion results would be sensitive to forward model configuration. The tools described here are the first step in conducting four-dimensional variational data assimilation in a coupled meteorology-chemistry model, which will potentially provide new constraints on aerosol precursor emissions and their distributions. Such analyses will be invaluable to assessments of particulate matter health and climate impacts.

Four-dimensional variational inversion of black carbon emissions during ARCTAS-CARB with WRFDA-Chem

“…The model domain is similar to that used by Guerrette and Henze (2015). The spatial extent encompasses California and other southwestern US states.…”

“…While we use GO-CART, the results presented are limited to BC. The model configuration is the same as was used in Guerrette and Henze (2015), and is summarized as follows: ACM2 PBL mixing (Pleim, 2007a, b), the Pleim-Xiu land surface model (Xiu and Pleim, 2001;Pleim and Xiu, 2003;Pleim and Gilliam, 2009) and surface layer (Pleim, 2006) mechanisms without soil moisture and temperature nudging, Wesely dry deposition velocities (Wesely, 1989), GSFC shortwave and Goddard longwave radiation, and microphysics turned off. Microphysical and radiative responses to online aerosols are not taken into account for GOCART aerosols in WRF-Chem.…”

“…Second-order checkpointing reduces the memory footprint to a feasible level for ADM and TLM simulations over longer durations (>∼ 6 h) and/or that use many chemical tracers (>∼ 10). Guerrette and Henze (2015) applied the ADM in calculating sensitivities relevant to the emission inversion carried out here. Section 3.5 includes a comparison of the results of that study with the posterior emissions here.…”

“…We utilize the recently developed WRFPLUS-Chem (Guerrette and Henze, 2015), which contains ADM and TLM code extending the original WRFPLUS software . WRFPLUS-Chem describes chemical tracers in the context of planetary boundary layer (PBL) mixing, emissions, dry deposition, and GOCART aerosols.…”

“…The modifications to that system that are required for this work are described in Sect. 2 as well as in Guerrette and Henze (2015) (GH15). These include new linearized model descriptions (GH15), memory and I/O trajectory management (GH15), a log-normal emission control variable (Sect.…”