Warm Clouds Biases in CMIP6 Models Linked to Indirect Effects of Falling Ice‐Radiation Interactions Over the Tropical and Subtropical Pacific

We examine the spatial distributions of CMIP6‐simulated cloud liquid water path (CLWP) and content (CLWC) against MODIS and CloudSat synthesized data over the tropical and subtropical Pacific. Three subsets of models are categorized based on their treatments of frozen ice‐radiative interactions. CLWP/CLWC are generally well simulated in subset with separately‐calculated radiative effects of cloud ice and falling ice (SON2). Too much warm clouds above 750 hPa are produced in either subset with total frozen ice radiative effects (SON1) or subset without radiative effects of falling ice (NOS) and thus CLWP/CLWC are overestimated over the open ocean including the trade‐wind regions. Stratocumulus clouds off the coasts of North and South America are severely underestimated in NOS models. We attribute the overestimates of clouds above the trade‐wind boundary layers to anomalous ascending motion associated with warmer sea surface temperature and weaker surface wind stress linked to indirect effects of falling ice‐radiation interactions. Plain Language Summary We explore how different formulations of frozen particle radiative effects in global climate models have effects on the simulation of warm clouds in the subtropical and tropical Pacific. Coupled Model Intercomparison Project Phase 6 (CMIP6) models are divided into three subsets for this study. We find that models with a separated treatment of floating ice and falling ice radiative effects (SON2) perform better than models with floating ice radiative effects only (NOS) or combined frozen ice radiative effects (SON1) in terms of biases of cloud liquid water content and cloud liquid water path against satellite measurements. This study suggests that biases in broad‐scale meteorological environments such as anomalous ascending motion, warmer sea surface temperature and weaker surface wind stress may cause excessive amounts of warm clouds above the trade‐wind boundary layers in NOS and SON1, thereby leading to excessive cloud liquid water. Key Points CloudSat‐MODIS synthesized estimates of warm cloud liquid water path/content (CLWP/CLWC) are used to evaluate three CMIP6 model subsets CLWP/CLWC are simulated well with separately‐calculated radiative effects of cloud ice and falling ice over subtropical and tropical Pacific Produce too much liquid water above 750 hPa over the trade‐wind regions in subsets with cloud ice only or total frozen ice radiative effects