The paper by Gui-Ying Yang and Julia Slingo from the University of Reading's Centre for Global Atmospheric Modelling examines the diurnal cycle in the tropics using high-resolution brightness temperature (Tb) data from multiple satellites. The data, part of the CLAUS project, covers all regions of the tropics and is used to construct a climatology of convection, cloudiness, and surface temperature. The study finds that the characteristics of the diurnal cycle are consistent with previous observational studies, showing that land and ocean, as well as clear sky and convective regimes, have distinct diurnal patterns. Oceanic deep convection peaks in the early morning, while continental convection generally peaks in the evening, with regional variations influenced by land-sea and mountain-valley breezes. A notable finding is the spread of the diurnal signal over adjacent oceans, likely through gravity waves, which can lead to significant diurnal variations in convection and precipitation. The analysis also highlights the importance of orographic influences and mesoscale convective systems in modulating the diurnal cycle. The study concludes that the CLAUS data provide a powerful tool for evaluating the physical parameterizations in climate models, as demonstrated by the comparison with the Met Office Unified Model (UM). The UM struggles to capture the observed phase of the diurnal cycle, particularly in convective regions, suggesting areas for improvement in model physics.The paper by Gui-Ying Yang and Julia Slingo from the University of Reading's Centre for Global Atmospheric Modelling examines the diurnal cycle in the tropics using high-resolution brightness temperature (Tb) data from multiple satellites. The data, part of the CLAUS project, covers all regions of the tropics and is used to construct a climatology of convection, cloudiness, and surface temperature. The study finds that the characteristics of the diurnal cycle are consistent with previous observational studies, showing that land and ocean, as well as clear sky and convective regimes, have distinct diurnal patterns. Oceanic deep convection peaks in the early morning, while continental convection generally peaks in the evening, with regional variations influenced by land-sea and mountain-valley breezes. A notable finding is the spread of the diurnal signal over adjacent oceans, likely through gravity waves, which can lead to significant diurnal variations in convection and precipitation. The analysis also highlights the importance of orographic influences and mesoscale convective systems in modulating the diurnal cycle. The study concludes that the CLAUS data provide a powerful tool for evaluating the physical parameterizations in climate models, as demonstrated by the comparison with the Met Office Unified Model (UM). The UM struggles to capture the observed phase of the diurnal cycle, particularly in convective regions, suggesting areas for improvement in model physics.