Diurnal cycles of deep convective processes: Biases of ERA5 and DYAMOND km-scale models revealed by satellite observations of frozen water path and precipitation

Abstract. Tropical convective processes show pronounced diurnal variability with strong land and ocean contrasts. Here, we compare their diurnal cycles from satellite observations, ERA5 and km-scale models. As observational base, we use the Chalmers Cloud Ice Climatology (CCIC), a machine-learning satellite product, for frozen water path (FWP) and high cloud cover, and IMERG for precipitation. CCIC captures the full diurnal cycle of FWP in contrast to older satellite FWP products. The satellite observations show late-night or early-morning peaks over the oceans, and afternoon peaks over tropical land areas for FWP and precipitation. The diurnal cycle of tropical FWP and precipitation has a general synchronicity in satellite observations. High cloud cover over tropical land lags behind FWP and precipitation by several hours and peaks during the night in the warm, wet season. ERA5 shows a smaller diurnal amplitude of FWP over tropical land with local phase shifts of more than ± 6 hours compared to CCIC. In contrast, the diurnal amplitude of ERA5 precipitation exceeds that of IMERG over land areas and lacks night-time peaks related to mesoscale convective systems and topography. Km-scale models have smaller diurnal phase shifts; however, regional biases exist over the South Pacific Convergence Zone, as well as systematic differences in diurnal amplitudes over tropical land areas, which can be quantified with satellite observations like CCIC. Our analysis illustrates the power of combining different satellite products to better understand the diurnal cycles of tropical convective processes when evaluating reanalyses or models.