Mechanisms of Rainfall Biases in Two CORDEX-CORE Regional Climate Models at Rainfall Peaks over Central Equatorial Africa

Abstract Two regional climate models (RCMs) participating in the CORDEX–Coordinated Output for Regional Evaluations (CORDEX-CORE) project feature a dipole-type rainfall bias during March–May (MAM) and September–November (SON) over central equatorial Africa (CEA), consisting of positive west (WCEA) negative east (ECEA). One is Model version 2015 (REMO2015) other fourth Climate (RegCM4-v7). RCMs are nested three Earth system (ESMs) from phase 5 Coupled Intercomparison Project (CMIP5), reanalysis ERA-Interim, at ?25-km spacing grid resolution. This study highlights misrepresented underlying physical processes associated with these biases through process-based evaluation. Both produce weaker Congo basin cell, land–ocean zonal surface pressure gradient. Consequently, less water vapor enters region, little transported WCEA to ECEA, resulting higher moisture availability than east. leads an unevenly distributed across favoring stronger atmospheric instability where moist static energy (MSE) anomalously increases enhanced latent (LSE). Moisture arrives slower pace weak cell’s strength. The intensity ascent motions response orographic constraint destabilize stability lower layers, necessary initiating deep convection. Therefore, convection shallow ECEA related underestimating MSE due reduced LSE.