The Impacts of Cloud Snow Radiative Effects on Pacific Oceans Surface Heat Fluxes, Surface Wind Stress, and Ocean Temperatures in Coupled GCM Simulations

Abstract:

An accurate representation of the climatology of the coupled ocean-atmosphere system in global climate models (GCMs) has strong implications to the reliability of projected climate change inferred by these models. Our previous efforts have identified substantial biases of ocean surface wind stress that are fairly common in two generations of the CMIP models, relative to QuikSCAT climatology. One of the potential causes of the CMIP model biases is the missing representation of large frozen precipitating hydrometeors (i.e., cloud snow) in all CMIP3 and most CMIP5 models, which has not been investigated. We examine the impacts of cloud snow on the radiation and atmospheric circulation, air-sea fluxes, and explore the implications to common biases in CMIP models using the National Center for Atmospheric Research (NCAR)-coupled Community Earth System Model (CESM) to perform sensitivity experiments with and without cloud snow radiation effects. This study focuses on the impacts of cloud snow in CESM on ocean surface wind stress and air-sea heat fluxes, as well as their relationship with sea surface temperatures (SSTs) and ocean potential temperatures in the Pacific sector. It is found that inclusion of the cloud snow parameterization in CESM reduces the surface wind stress and ocean temperatures including SSTs biases in the tropical and mid-latitude Pacific. These differences in SSTs and wind stress with and without the cloud snow parameterization can be partly attributed to the wind stress differences and the related influence on vertical mixing in the ocean, but cannot be explained by the differences in net air-sea heat fluxes.