Abstract 157

Abstract ID: 157

The Second Phase of the WGNE Aerosol Project: Evaluating the impact of aerosols on the Subseasonal Prediction

Lead Author: Ariane Frassoni
INPE, Brazil

Keywords: Atmospheric composition, Aerosols, Subseasonal prediction, Coupled modelling, Aerosol-climate feedbacks

Abstract: Despite the unprecedented opportunity to advance in the provision of relevant information on key climate characteristics in the Subseasonal (S2S) timescale, there is still an avenue to improve the predictive skill of S2S forecasts. For example, the operational models contributing to the S2S Project database represent atmospheric composition by climatology, which translates into a limitation for the skill of S2S models. Atmospheric composition plays important role in the climate system. For example, atmospheric aerosols act as a climate forcing due to their interaction with radiation (direct effect) and changes in cloud lifecycle and precipitation (indirect effect). Model design and development studies have explored the role of aerosols in the predictive skill of global circulation models. The studies evolved from the climatological aerosol state representation to the fully-coupled treatment of the atmospheric composition in the models. When considering the second, it is important to highlight that there are many feedbacks related to the climate-chemistry-aerosol-cloud-radiation coupling that should be accurately represented in climate models. There is an important limitation: a fully-coupled climate-chemistry-aerosol-cloud-radiation model requires a large computational cost that needs to be weighed against prediction skill benefits. Therefore, the level of sophistication of such a coupled system is dependent on the computational infrastructure, making it difficult for meteorological centres to operate a fully-coupled climate-chemistry-aerosol-cloud-radiation system for any timescale, but especially for longer time scales, such as (S2S) scales.
As the atmospheric composition is fundamental to improving weather and climate prediction capability given its importance for the global climate system, the WGNE, the WWRP-S2S Steering Group and the GAW-SAG-APP have been co-leading the second phase of the WGNE Aerosol Project that aims to better understand the role of aerosols on the predictive skill of models in the S2S timescale. The Project considers the participation of operational meteorological centres around the world that contribute with their state-of-the-art climate-chemistry-aerosol-cloud-radiation coupled modelling systems. The project has been fed with S2S retrospective predictions (hindcasts) based on the ensemble approach. The hindcasts were provided for at least two experiments: 1) aerosols’ direct (and indirect, optionally) effect and 2) predictions either with no-aerosol loading or with climatological aerosols.
The performance assessment of the contributions focuses on the intercomparison of the different experiments (direct/indirect x climatological/no-loading) and among different models. In this work, we will present the results of the assessment of S2S 2-meter temperature, precipitation, solar radiation and aerosol optical depth hindcasts from both the deterministic and probabilistic perspectives considering common statistical metrics. Each metric is computed considering the four weekly average lead times counting from the hindcast start dates of each model.
The WGNE Aerosol Project provides an opportunity to better understand the feedbacks represented in current climate-chemistry-aerosol-cloud-radiation coupled systems, and their impact on the prediction of climate variability, air quality forecasting and extreme meteorological events in the S2S timescale. It is also expected to identify the uncertainties associated with model predictions of feedbacks that should be addressed in future developments and provide information on how the complexity of the coupled modelling system can impact the predictive skill of models in the S2S timescale.

Ariane Frassoni (Brazilian National Institute for Space Research, Center for Weather Forecasting and Climate Studies, Cachoeira Paulista, SP, Brazil)
Angela Benedetti (European Centre for Medium-range Weather Forecasts, Reading, UK)
Andrea Molod (National Aeronautics and Space Administration/Goddard Global Modeling and Assimilation Office, Greenbelt, USA)
Frederic Vitart (European Centre for Medium-range Weather Forecasts, Reading, UK)
Georg Grell (National Oceanic and Atmospheric Administration/Earth System Research Laboratories/Global Systems Laboratory, Earth Prediction Advancement Division, Boulder, USA)
Paul Makar (Environment and Climate Change Canada)
Francois Engelbrecht (Global Change Institute University of the Witwatersrand, South Africa)