Mixed-Phase Clouds and Climate

Mixed-phase clouds (MPCs), which are composed of both ice and supercooled water, play an important role in modulating Earth’s weather and climate. The majority of land falling precipitation originates from MPCs, and the way cloud phase changes under global warming has emerged as a critically important climate feedback. Atmospheric aerosols may also have affected climate via MPCs, but the magnitude and even sign of this effect is currently unknown. Recently, satellite observations have revealed that cloud phase is misrepresented in global climate models (GCMs), suggesting systematic GCM biases in both precipitation formation and cloud-climate feedbacks. Such biases give reason to question GCM projections of the climate response to increasing CO₂ concentrations or changing atmospheric aerosol loadings.

Through a synergistic combination of tools, the Mixed-phase Clouds and Climate (MC²) project aims to improve the process-level understanding of MPCs at small scales, to ultimately aid in constraining climate change predictions on the global scale. The MC² project consists of: (1) Airborne in situ observations of Arctic, sub-Arctic, and mid-latitude MPCs to address the small-scale heterogeneity of cloud phase within MPCs, (2) satellite remote sensing to determine the large-scale variability of MPCs and to what extent variations in cloud phase can be explained by variations in the presence of ice nucleating particles, and (3) Large Eddy Simulations to identify the underlying physical processes responsible for the observed structures in MPCs.

The information obtained from these three sub projects will be incorporated into GCMs to re-evaluate the aerosol effects on MPCs and to provide improved estimates of the cloud phase feedback in a changing climate. Here we present an overview of the project as well as our initial results.