Global Ice Clouds and Their Radiative Effects

The ability of current GCM models in simulating cloud ice is particularly poor, compared to their ability in simulating other cloud-related variables. Recent climate model validation studies showed that GCM models couldn’t agree with each other even in the order of magnitude of the climatological mean cloud ice water path. Global measurements of cloud ice from satellites have been advanced in recent years due to the combined observations from lidar and cloud radar, which can hopefully provide guidance to GCM models as to the magnitude and spatial distribution of cloud ice. We have analyzed multiyear cloud ice data retrieved from combined CloudSat/CALIPSO observations with the goal of understanding the global ice cloud climatology. In this talk, the mean state of ice cloud properties based on the data analysis will be presented first, including spatial distributions of ice water content, effective radius and optical depth, as well as their seasonal variations. In particular, we’ll present the ice water properties as a function of optical depth as thin and thick ice clouds have different effects (warm or cool the Earth) on Earth’s radiation budget. Then, results from radiative modeling of ice cloud forcing will be presented with the intention to answer the question: Within the broad spectrum of ice clouds, which part of them warms and which part cools the Earth?