Beijing Climate Center Earth System Model version 1 (BCC-ESM1): Model Description and Evaluation of Aerosol Simulations
The performance of BCC-ESM1 in simulating aerosols and their optical properties is comprehensively evaluated as required by the Aerosol Chemistry Model Intercomparison Project (AerChemMIP), covering the preindustrial mean state and time evolution from 1850 to 2014. The simulated aerosols from BCC-ESM1 are quite coherent with Coupled Model Intercomparison Project Phase 5 (CMIP5)-recommended data, in situ measurements from surface networks (such as IMPROVE in the US and EMEP in Europe), and aircraft observations. A comparison of modeled aerosol optical depth (AOD) at 550 nm with satellite observations retrieved from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Multi-angle Imaging SpectroRadiometer (MISR) and surface AOD observations from the AErosol RObotic NETwork (AERONET) shows reasonable agreement between simulated and observed AOD. However, BCC-ESM1 shows weaker upward transport of aerosols from the surface to the middle and upper troposphere, likely reflecting the deficiency of representing deep convective transport of chemical species in BCC-ESM1. With an overall good agreement between BCC-ESM1 simulated and observed aerosol properties, it demonstrates a success of the implementation of interactive aerosol and atmospheric chemistry in BCC-ESM1.
This paper presents a primary evaluation of aerosols simulated in version 1 of the BCC-ESM1 with the implementation of the interactive atmospheric chemistry and aerosol based on the newly developed BCC-CSM2. Global aerosols (including sulfate, organic carbon, black carbon, dust, and sea salt) and major greenhouse gases (e.g., O3, CH4, N2O) in the atmosphere can be interactively simulated when anthropogenic emissions are provided to the model. Concentrations of all aerosols in BCC-ESM1 are determined by the processes of advective transport, emission, gas-phase chemical reactions, dry deposition, gravitational settling, and wet scavenging by clouds and precipitation. The nucleation and coagulation of aerosols are ignored in the present version of BCC-ESM1. The effects of aerosols on radiation, cloud, and precipitation are fully included.
We evaluate the performance of BCC-ESM1 in simulating aerosols and their optical properties in the 20th century following CMIP6 historical simulation according to the requirement of the AerChemMIP. It is forced with anthropogenic emissions evolving from 1850 to 2014, but some WMGHGs such as CH4, N2O, CO2, CFC11, and CFC12 are prescribed using CMIP6 prescribed concentrations (to replace prognostic values of CH4 and N2O from the chemistry scheme). Both direct and indirect effects of aerosols are considered in BCC-ESM1. Initial conditions of the CMIP6 historical simulation are obtained from a 600-year piControl simulation in the absence of anthropogenic emissions, which captures the preindustrial concentrations of SO2−4, organic carbon (OC), black carbon (BC), dust, and sea salt aerosols well and is consistent with the CMIP5 recommended concentrations for the year 1850. With the CMIP6 anthropogenic emissions of SO2, OC, and BC from 1850 to 2014 and their natural emissions implemented in BCC-ESM1, the model-simulated SO2−4, BC, and OC aerosols in the atmosphere are highly correlated with the CMIP5-recommended data. The long-term trends in CMIP5 aerosols from 1850 to 2000 are also well simulated by BCC-ESM1. Global budgets of aerosols were evaluated through comparisons of BCC-ESM1 results for 1990–2000 with reports in various contributions to the literature for sulfate, BC, OC, sea salt, and dust. Their annual total emissions, atmospheric mass loading, and mean lifetimes are all within the range of values reported in the relevant literature. Evaluations of the spatial and vertical distributions of BCC-ESM1 simulated present-day SO2−4, OC, BC, dust, and sea salt aerosol concentrations against the CMIP5 datasets and in situ measurements of surface networks (IMPROVE in the US and EMEP in Europe), and HIPPO aircraft observations indicate good agreement among them. The BCC-ESM1 simulates weaker upward transport of aerosols from the surface to the middle and upper troposphere (with reference to CMIP5-recommended data), likely reflecting a lack of deep convection transport of chemical species in the present version of BCC-ESM1. The AOD at 550 nm for all aerosols including sulfate, BC, OC, sea salt, and dust aerosols was further compared with the satellite AOD observations retrieved from MODIS and MISR and surface AOD observations from AERONET. The BCC-ESM1 model results are overall in good agreement with these observations within a factor of 2. All these comparisons demonstrate the success of the implementation of interactive aerosol and atmospheric chemistry in BCC-ESM1.