TY  - JOUR
A1  - Schulz, Bernhard
A1  - Mellado, Juan Pedro
T1  - Competing Effects of Droplet Sedimentation and Wind Shear on Entrainment in Stratocumulus
Y1  - 2019
VL  - 11
IS  - 6
SP  - 1830
EP  - 1846
JF  - Journal of Advances in Modeling Earth Systems
DO  - 10.1029/2019MS001617
DO  - 10.23689/fidgeo-4946
N2  - The joint effect of droplet sedimentation and wind shear on cloud top entrainment in stratocumulus is investigated with direct numerical simulations. Although it is well understood that droplet sedimentation weakens entrainment while wind shear enhances entrainment, there is no consensus on the magnitude of each process. We find that the entrainment reduction by droplet sedimentation is sufficiently strong to completely compensate the entrainment enhancement by wind shear, and thus, droplet sedimentation and wind shear effects can be equally important for cloud top entrainment. For instance, for the subtropical conditions considered here, droplet sedimentation weakens entrainment by up to 40% while wind shear enhances entrainment by up to 40%. This result implies that the droplet size distribution can substantially affect cloud lifetimes not only because of its effect on rain formation but also because of its effect on cloud top entrainment, which emphasizes the need for a better characterization of droplet size distributions in stratocumulus. A second implication is that entrainment velocity parametrizations should pay equal attention to droplet sedimentation and to wind shear effects.
UR  - http://resolver.sub.uni-goettingen.de/purl?gldocs-11858/9292
ER  -