Impact of wind shear and radiatively-driven convection on tropical tropopause layer cirrus structure, microphysical properties, and evolution

Thin cirrus that form at very low temperatures in the Tropical Tropopause Layer (TTL) are important for climate inasmuch as they regulate the humidity of air entering the stratosphere and directly affect the radiation budget. Recent studies have also shown that these clouds can also affect vertical transport through the TTL: thin cirrus radiative heating is an important component of the TTL thermal budget. In addition recent modeling studies have shown that cloud radiative heating can help maintain TTL thin cirrus via upward motion and convergence of water vapor. Using three-dimensional cloud resolving model simulations with bin microphysics, we investigate the impacts of interactions between radiation, dynamics, and microphysics on cloud structure, cloud microphysical properties, and cloud evolution. We extend previous studies by including realistic wind shear. Results are constrained by recent high-altitude aircraft in situ measurements of TTL thin cirrus microphysical properties, and simulated cloud structures are compared in detail with ground-based and airborne lidar observations.