PNNL

Abstract

Evaluating Earth System Models (ESMs) with observations reveals shortcomings in these models and provides directions for future model improvements. However, most well-established diagnostics packages focus on large-scale features and climatology, while a comprehensive evaluation of aerosols, clouds, and aerosol-cloud interactions is needed to increase the confidence of process representations in the models. We developed an ESM aerosol-cloud diagnostics package (ESMAC Diags) to facilitate routine evaluation of aerosols, clouds and aerosol-cloud interactions simulated by the Department of Energy’s (DOE) Energy Exascale Earth System Model (E3SM), and this paper documents its version 2 functionality, which has substantial differences from ESMAC Diags version 1 (Tang et al., 2022a). ESMAC Diags v2 produces comparisons of simulated aerosol and cloud properties with in-situ and remote-sensing measurements from aircraft, ship, surface and satellite platforms. It currently includes six field campaigns and two permanent sites covering four geographical regions: Eastern North Atlantic, Central U.S., Northeastern Pacific and Southern Ocean, where frequent liquid or mixed-phase clouds are present and extensive measurements are available from the DOE Atmospheric Radiation Measurement (ARM) user facility and other agencies. ESMAC Diags v2 includes various types of single-variable and multi-variable diagnostics, such as percentiles, histograms, joint histograms and heatmaps, to assess aerosols, clouds, and aerosol-cloud interactions. A few examples are shown when evaluating E3SM version 2 (E3SMv2) using ESMAC Diags. Overall E3SMv2 qualitatively reproduces the observed aerosol and cloud properties, with quantitative biases in some variables such as aerosol particle and cloud droplet numbers and sizes. The coupling of aerosol and cloud number concentrations may be too strong in E3SMv2, possibly indicating a bias in processes that control aerosol activation. In addition, the liquid water path adjustment to perturbed cloud droplet number concentration behaves differently in E3SMv2 and observations, indicating a need for further improvements to cloud microphysics parameterization in E3SMv2.