Comprehensive quantification of height dependence of entrainment mixing between stratiform cloud top and environment

Different entrainment-mixing processes of turbulence are crucial to processes related to clouds; however, only a few qualitative studies have been concentrated on the vertical distributions of entrainment-mixing mechanisms with low vertical resolutions. To quantitatively study vertical profiles of entrainment-mixing mechanisms with a high resolution, the stratiform clouds observed in the Physics of Stratocumulus Top (POST) project are examined. The unique sawtooth flight pattern allows for an examination of the vertical distributions of entrainment-mixing mechanisms with a 5 m vertical resolution. Relative standard deviation of volume mean radius divided by relative standard deviation of liquid water content is introduced to be a new estimation of microphysical homogeneous mixing degree, to overcome difficulties of determining the adiabatic microphysical properties required in existing measures. The vertical profile of this new measure indicates that entrainmentmixing mechanisms become more homogeneous with decreasing altitudes and are consistent with the dynamical measures of Damkohler number and transition scale number. Further analysis shows that the vertical variation of entrainmentmixing mechanisms with decreasing altitudes is due to the increases of turbulent dissipation rate in cloud and relative humidity in droplet-free air and the decrease of size of droplet-free air. The results offer insights into the theoretical understanding and parameterizations of vertical variation of entrainment-mixing mechanisms.

Automated summary

The study quantitatively analyzed the vertical profiles of entrainment-mixing mechanisms in stratiform clouds observed in the POST project, revealing that the mechanisms become more homogeneous with decreasing altitudes. The results show that the vertical variation of these mechanisms with decreasing altitudes is influenced by increases in turbulent dissipation rate in cloud and relative humidity in droplet-free air.