ARM Ground-Based Cloud Simulators and Their Applications to E3SM

Clouds play an important role in Earth’s radiation budget and hydrological cycle. However, current global climate models (GCMs) have difficulties in accurately simulating clouds and precipitation. To improve the representation of clouds in climate models, it is crucial to identify where simulated clouds differ from real-world observations of them. This can be difficult, since significant differences exist between how a climate model represents clouds and what instruments observe, both in terms of spatial scale and the properties of the hydrometeors that are either modeled or observed. To address these issues and minimize impacts of instrument limitations, the concept of instrument “simulators,” which convert model variables into pseudo-instrument observations, has evolved with the goal to facilitate and improve the comparison of modeled clouds with observations.

In this study, we introduce our work for the ground-based cloud radar/lidar simulators developed by the U.S. Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) program for comparing climate model clouds with ARM observations from its radars and Lidars. The Earth Model Column Collaboratory (EMC²) is a newly developed open-source subcolumn generator and ground-based lidar and radar instrument simulator (Silber et al. 2022). The current EMC² efforts are focused on detailed process studies on selected ARM field campaigns cases. To make EMC² more suitable for use in evaluating global climate model (GCM) simulated clouds, We enhanced the EMC2 for statistical evaluation of GCMs with ARM cloud observations by adding a statistical module to the package and creating the observational data product to compare with simulator output. The statistical aggregation module provides grid-box statistical diagnostics (e.g., vertical cloud fraction and signal-height joint histograms). The statistical module is based on what is currently used in the CFMIP Observation Simulator Package (COSP). Examples for application to the U.S. DOE Earth System Model (E3SM) cloud evaluations are given. The plan to customize EMC² for the E3SM as well as generate long-term ARM simulator-oriented data products over ARM fixed and mobile facility sites will be discussed.