The diurnal cycle of cloud ice water path

Abstract

Ice clouds play a critical role in Earth’s climate system through their impact on radiation and precipitation. Their diurnal variation, although vital for their net impact, remains poorly observed and simulated in models. This study presents the first global characterisation of the diurnal cycle of total ice water path (TIWP). This was done using the Chalmers Cloud Ice Climatology (CCIC), a novel satellite derived dataset that combines CloudSat-based training with geostationary infrared observations. Diurnal patterns in CCIC are compared with those from ERA5 reanalysis and GCRMs (Global Storm-Resolving Models) from DYAMOND project (DYnamics of the Atmospheric general circulation Modeled On Non-hydrostatic Domains). Re sults show that CCIC captures regional diurnal cycle contrasts: a strong diurnal cycle over land with an afternoon peak and a weaker diurnal cycle over oceans. ERA5 shows a dampened diurnal cycle with shifted peak times. The DYAMOND models offer an improved diurnal cycle representation. These findings show that CCIC can be used as a tool for validating model repre sentation of cloud processes. Validation at the diurnal level remains an important metric for model performance, both for reanalyses and emerging global models.