Turbulence and cloud microphysical characteristic of decoupled marine stratocumulus-topped boundary layer
This study investigates turbulence and cloud microphysical characteristics within the decoupled bound-ary layer,focusing on selected decoupling cases.High-frequency meteorological data and cloud microphysics data from stratocumulus-topped boundary layers,obtained during the POST(Physics of Stratocumulus Top)observa-tion campaign,form the basis of our analysis.Results reveal that atmospheric static stability strengthens in the tran-sition layer,inhibiting upward buoyancy work and rapidly depleting turbulent kinetic energy,leading to boundary layer decoupling.Maximum turbulent kinetic energy occurs within the cloud,driven primarily by cooling at the cloud top,enhanced downdraft from falling and sinking large cloud droplets,and latent heat release from conden-sation above the cloud base.Buoyancy and shear contributions augment turbulent kinetic energy in the near-surface layer,with shear playing a more prominent role,while within-cloud turbulent kinetic energy is mainly buoyancy-driven.Downward heat flux near the transition layer hinders upward heat transport and buoyancy en-hancement,further promoting decoupling.Upward sensible heat flux within the cloud correlates with cloud top cooling and latent heat release from condensation in the lower cloud region.Increased moisture at the cloud top fa-cilitates downward latent heat flux transport,amplifying water vapor content within the cloud,fostering positive feedback role in decoupled boundary layer cloud development.Cloud-top buoyancy reversal induces inhomoge-neous mixing,leading to the appearance of adiabatic or super-adiabatic droplets and promoting condensation and coalescence growth.Additionally,enhanced moisture at the cloud top drives microphysical growth within the cloud.The cloud base exhibits homogeneous mixing characteristics due to entrainment.
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