Current State of the global operational aerosol multi-model ensemble: an update from the International Cooperative for Aerosol Prediction (ICAP)

Since the first International Cooperative for Aerosol Prediction (ICAP) multi-model ensemble (MME) study, the number of ICAP global operational aerosol models has increased from five to nine. An update of the current ICAP status is provided, along with an evaluation of the performance of the ICAP-MME over 2012-2017, with a focus on the June 2016-May 2017 time period. Evaluated with ground based Aerosol Robotic Network (AERONET) aerosol optical depth (AOD) and data assimilation quality Moderate Resolution Imaging Spectroradiometer (MODIS) retrieval products, the ICAP-MME AOD consensus remains the overall top scoring and most consistent performer among all models in terms of root mean square error (RMSE), bias and correlation for total, fine and coarse mode AODs as well as dust AOD; this is similar to the first ICAP-MME study. Further, over the years, the performance of ICAP-MME is relatively stable and reliable compared to more variability in the individual models. The extent to which the AOD forecast error of the ICAP-MME can be predicted is also examined. Leading predictors are found to be the consensus mean and spread. Regression models of absolute forecast errors were built for AOD forecasts of different lengths for potential applications. Evolution of the ICAP-MME performance over 2012-2017 is also investigated and the performance in terms of AOD RMSE is shown.