The Koren Lab

Accurately assessing cloud feedback on global warming is essential for producing reliable climate projections. Linear regression analysis is a widely used method for this purpose, offering a straightforward approach for examining the relationship between cloud radiative effects and global-mean surface temperature. However, the El Ni & ntilde;o-Southern Oscillation (ENSO) can significantly contribute to these estimates, which is often overlooked due to ENSO's relatively short periodicity (2-7 years). Using 72 years of reanalysis data and 150 years of simulations by 11 global climate models, this study demonstrates that, over a large portion of the low- to mid-latitude oceans, ENSO can contribute up to a few W m-2 K-1 to the regression-based cloud feedback estimates over decades and even centuries. Through a detailed spatial and temporal analysis, our findings underscore the importance of accounting for and removing ENSO's influence to improve the accuracy of cloud feedback assessments in the context of global warming.

Köhler theory predicts the supersaturation required for an aerosol particle to activate into a cloud droplet by considering curvature and solute effects. However, in a saturated environment containing numerous aerosols, the competition for water vapor and the subsequent droplet activation process become highly complex. This complexity is further amplified by the presence of turbulence, which introduces significant variability in the local supersaturation experienced by each particle. This study employs Brownian models to investigate the activation of polydisperse aerosols in a turbulent environment. Turbulence is represented by temporally correlated stochastic disturbances, resulting in diverse supersaturation histories for individual particles. Our findings demonstrate that turbulence can enhance aerosol activation, but this effect exhibits nonlinear dependence on aerosol number concentration and size distribution breadth. Furthermore, our simulations reveal a counterintuitive phenomenon: Smaller aerosols can activate at the expense of larger ones due to the influence of turbulent fluctuations. This effect becomes more pronounced with increasing turbulence intensity. SIGNIFICANCE STATEMENT: This study investigates how turbulence impacts cloud droplet activation beyond traditional Köhler theory. By incorporating stochastic supersaturation fluctuations, we demonstrate a complex interplay between turbulence, aerosol number concentration, and size distribution breadth. Our findings reveal that turbulence can enhance activation, but with nonlinear and sometimes counterintuitive effects. Notably, smaller aerosols can gain an activation advantage over larger ones in turbulent conditions. These results have significant implications for understanding cloud microphysics and precipitation formation, emphasizing the critical role of turbulence in shaping cloud droplet distributions and ultimately influencing climate.

Warm cumulus clouds are key components of Earth's weather and climate systems, yet mixing processes within them and their interaction with their environment remain a major source of uncertainty in climate predictions. Based on adiabatic fraction (AF), such clouds can be divided into three regions: the adiabatic core, the skin (the diluted cloud edge), and the periphery, which lies between them, in terms of AF values. Despite its large volume and mass, the periphery is still poorly understood. This study shows that the periphery is equally supplied by air coming from the core and skin. However, periphery air flows mainly toward the skin, with limited transport into the core. The skin contributes to the periphery primarily through transport associated with the toroidal vortex. Each zone also exhibits distinct microphysical properties, including differences in droplet mean radius, variance, and relative dispersion.