Using A-Train Observations to Evaluate Ice Water Path and Ice Cloud Radiative Effects in the Community Atmosphere Model

Abstract:

In this study we first use A-Train satellite data to investigate the distribution of clouds, along with their radiative and microphysical properties, in Southeast Asia during the summer monsoon. The distribution of ice water path (IWP) in this region is highly skewed, such that the mean value is not representative of the typical ice cloud. In examining how cirrus cloud radiative effects at the TOA vary as a function of IWP, we find that cirrus with an IWP less than 200 g m^-2 produce a net warming. And weighting the radiative effect by the frequency of occurrence of IWP, reveals that cirrus with an IWP around 20 g m^-2contribute most to the heating at the TOA.

Next, we use the A-Train results to address the issues of IWP occurrence and high cloud forcing in the Community Atmosphere Model version 5. Our goal is to determine if the clouds that heat the upper troposphere in the model are the same genre of clouds that heat the upper troposphere in the real atmosphere. First, we assess the distribution of ice cloud fraction in the model. Then we define a cloud radiative kernel that’s a function of cloud top pressure and IWP, to determine whether the modeled ice clouds produce similar shortwave and longwave radiative effects at the TOA. Lastly, we use the cloud radiative kernel and cloud fraction histogram to evaluate how the ice cloud forcing in the model compares to the ice cloud forcing derived from A-Train.