Nonturbulent Liquid-Bearing Polar Clouds: Observed Frequency of Occurrence and Simulated Sensitivity to Gravity Waves

A common feature of polar liquid-bearing clouds (LBCs) is radiatively driven turbulence, which may variously alter cloud lifecycle via vertical mixing, droplet activation, and subsequent feedbacks. However, polar LBCs are commonly initiated under stable, nonturbulent conditions. Using long-term data from the North Slope of Alaska and McMurdo, Antarctica, we show that nonturbulent conditions prevail in ~25% of detected LBCs, surmised to be preferentially early in their lifecycle. We conclude that nonturbulent LBCs are likely common over the polar regions owing primarily to atmospheric temperature and stability. Such stable environments are known to support gravity wave activity. Using large-eddy simulations, we find that short to intermediate period gravity waves may catalyze turbulence formation when aerosol particles available for activation are sufficiently small. We posit that the frequent occurrence of nonturbulent LBCs over the polar regions has implications for polar aerosol-cloud interactions and their parameterization in large-scale models.