Evaluation of a general circulation model by the CERES Flux-by-cloud type simulator

Area of Science:

• Climate modeling
• Atmospheric science
• Radiative transfer

Background:

• Accurate representation of clouds is crucial for climate models.
• The Clouds and the Earth's Radiant Energy System (CERES) provides valuable data for evaluating cloud properties and radiative fluxes.
• The HadGEM2-A model is a key component in climate change research.

Purpose of the Study:

• To evaluate the performance of the HadGEM2-A climate model using the CERES Flux-by-cloud type simulator.
• To assess the model's ability to simulate cloud properties and their impact on top-of-atmosphere (TOA) radiative fluxes.
• To identify discrepancies between simulated and observed cloud characteristics and radiative budgets.

Main Methods:

• Utilized the CERES Flux-by-cloud type data product.
• Employed a simulator comprising a cloud generator, cloud property simulator, and radiative transfer model.
• Applied the simulator to specific regions (Southern Great Plains, Southeast Pacific) and globally (60° N - 60° S).
• Optimized calculations by identifying and reducing duplicate atmospheric profiles.

Main Results:

• In the Southern Great Plains, simulated cloud tops were higher, and outgoing longwave radiation (OLR) was greater than observed, resulting in a compensating error for OLR.
• In the Southeast Pacific, simulated clouds were lower, less numerous, and had higher optical depths than observed, leading to higher albedo.
• Globally, the model simulated fewer clouds but with higher albedos for most cloud types, indicating a compensating error in the shortwave radiative budget.

Conclusions:

• The HadGEM2-A model exhibits compensating errors in simulating cloud properties and radiative fluxes in different regions.
• Discrepancies in cloud altitude, frequency, and optical depth contribute to inaccurate albedo and radiative budget simulations.
• Further model development is necessary to improve the representation of cloud processes and their radiative impacts for more reliable climate projections.