Changes in Daytime Cirrus Properties From the ISCCP‐H Data Set and Their Impacts on the Radiation Energy Budget.

The change in clouds during the day is critical to the Earth's energy balance and climatic evolution. However, there have been relatively few studies on cloud variations at daily timescales, owing to limitations of ground‐ and satellite‐observations, especially for cirrus clouds. In this study, we examined the daytime cirrus variation (DCV) at the global scales and its associated effects on radiation budgets based on the International Satellite Cloud Climatology Project H data set. The changes in continental cirrus cover are more significant than that over the ocean, reaching a maximum of 17.3% in the afternoon. Over the tropical deep convection regions, cirrus cloud cover and optical depth exhibit large amplitudes during the daytime, closely linked to average properties of cirrus clouds. Using a process‐based radiative transfer model, we calculated the variations in daytime cirrus cloud radiative forcing (CRF). After noon, cirrus clouds over both land and ocean generate the strongest shortwave (SW) cooling and longwave (LW) warming effects at the top of the atmosphere (TOA). At the global scale, daytime cirrus clouds cause an average net CRF of 3.6 W/m2 at the TOA. If the DCV is neglected in the model, the SW cooling and LW warming effects are overestimated by 2.5 and 1.8 W/m2 at the TOA, leading to a net radiation bias of 0.7 W/m2. The findings provide key information for targeting specific aspects of the cirrus parameterization scheme in climate models. Plain Language Summary: Cirrus clouds comprise large amounts of ice crystals, and frequently appear over tropical and mid‐latitude storm track areas. They play a crucial role in Earth's energy balance through interactions with shortwave and thermal radiation. These processes are closely related to the diurnal changes in cirrus clouds. However, accurately representing the daily changes in cirrus clouds in climate models remains challenging due to observational limitations, which affects the simulation of cloud radiation processes. We investigated the daytime cirrus variation (DCV) and its impacts on radiation budgets using the International Satellite Cloud Climatology Project‐H data set, combined with a radiative transfer model, and found that DCV contributes considerably to the radiation budget. This work may help improve the cirrus parameterization scheme in climate models. Key Points: The changes in daytime cirrus clouds and their impacts on the Earth's energy budget were investigated using the International Satellite Cloud Climatology Project‐H observationsThe changes in daytime cirrus clouds exhibit an obvious difference between land and oceanThe changes in daytime cirrus clouds have a considerable contribution to radiation calculation [ABSTRACT FROM AUTHOR]