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

Abstract

Abstract. 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 entrainment-mixing mechanisms become more homogeneous with decreasing altitudes and are consistent with the dynamical measures of Damköhler number and transition scale number. Further analysis shows that the vertical variation of entrainment-mixing 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.

Impacts of Drop Clustering and Entrainment‐Mixing on Mixed Phase Shallow Cloud Properties Over the Southern Ocean: Results From SOCRATES

“…This is analogous to clustering being positively correlated with mixing strength (i.e., low Da), which is expected as drop clustering is shown as strongly correlated to entrainment‐mixing further in this section. Additionally, all samples having Da > 1 is consistent with most prior studies commonly observing inhomogeneous rather than homogeneous mixing (e.g., Andrejczuk et al., 2009; Beals et al., 2015; Burnet & Brenguier, 2007; S. Gao et al., 2021; Jia et al., 2019), especially at the relatively large mixing length scales used here (Burnet & Brenguier, 2007; Kumar et al., 2018; Lehmann et al., 2009). This finding is also consistent with Sanchez et al.…”

“…To calculate τ m , ε is determined using equations 11 and 12 from Meischner et al (2001), which utilizes work from Paluch and Baumgardner (1989) and Panofsky and Dutton (1984). The calculation of L follows S. Gao et al (2021), namely…”

“…where TAS is true air speed of the aircraft, f is the sampling frequency and F is the fraction of clear-sky observations within each 1 Hz sample, determined using 10 Hz observations. Clear-sky samples in S. Gao et al (2021) were defined as droplet free, whereas a less stringent definition of derived mass content less than 10 −3 g m −3 is applied here (D'Alessandro et al, 2021). The calculations of τ r for the liquid and mixed phase follow Pinsky et al (2018), where both expressions are phase relaxation times expressing the time for reaching equilibrium conditions between the condensate and vapor content (Appendix A).…”

“…Clear‐sky samples in S. Gao et al. (2021) were defined as droplet free, whereas a less stringent definition of derived mass content less than 10 −3 g m −3 is applied here (D’Alessandro et al., 2021). The calculations of τ r for the liquid and mixed phase follow Pinsky et al.…”

“…The calculation of L follows S. Gao et al. (2021), namely $$$\mathrm{L}=\mathrm{F}\times \mathrm{T}\mathrm{A}\mathrm{S}/f$$$ where TAS is true air speed of the aircraft, f is the sampling frequency and F is the fraction of clear‐sky observations within each 1 Hz sample, determined using 10 Hz observations. Clear‐sky samples in S. Gao et al.…”