Convective and Turbulent Motions in Nonprecipitating Cu. Part III: Characteristics of Turbulence Motions

Mark Pinsky, Alexander Khain*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

3 Scopus citations

Abstract

Velocity field in a nonprecipitating Cu under BOMEX conditions, simulated by SAM with 10-m resolution and spectral bin microphysics is separated into the convective part and the turbulent part, using a wavelet filtering. In Part II of the study properties of convective motions of this Cu were investigated. Here in Part III of the study, the parameters of cloud turbulence are calculated in the cloud updraft zone at different stages of cloud development. The main points of this study are (i) application of a fine-scale LES model of a single convective cloud allowed a direct estimation of turbulence parameters using the resolved flow in the cloud and (ii) the separation of the resolved flow into the turbulence flow and the nonturbulence flow allowed us to estimate different turbulent parameters with sufficient statistical accuracy. We calculated height and time dependences of the main turbulent parameters such as turbulence kinetic energy (TKE), spectra of TKE, dissipation rate, and the turbulent coefficient. It was found that the main source of turbulence in the cloud is buoyancy whose contribution is described by the buoyancy production term (BPT). The shear production term (SPT) increases with height and reaches its maximum near cloud top, and so does BPT. In agreement with the behavior of BPT and SPT, turbulence in the lower cloud part (below the inversion level) is weak and hardly affects the processes of mixing and entrainment. The fact that BPT is larger than SPT determines many properties of cloud turbulence. For instance, the turbulence is nonisotropic, so the vertical component of TKE is substantially larger than the horizontal components. Another consequence of the fact that BPT is larger than STP manifests itself in the finding that the turbulence spectrum largely obeys the 211/5 Bolgiano–Obukhov scaling. The classical Kolmogorov 25/3 scaling dominates for the low part of a cloud largely at the dissolving stage of cloud evolution. Using the spectra obtained we evaluated an “effective” dissipation rate which increases with height from nearly zero at cloud base up to 20 cm2 s23 near cloud top. The coefficient of turbulent diffusion was found to increase with height and ranged from 5 m2 s21 near cloud base to 25 m2 s21 near cloud top. The possible role of turbulence in the process of lateral entrainment and mixing is discussed.

Original languageAmerican English
Pages (from-to)457-471
Number of pages15
JournalJournals of the Atmospheric Sciences
Volume80
Issue number2
DOIs
StatePublished - Feb 2023

Bibliographical note

Publisher Copyright:
© 2023 American Meteorological Society.

Keywords

  • Cumulus clouds
  • Filtering techniques
  • Large eddy simulations
  • Turbulence

Fingerprint

Dive into the research topics of 'Convective and Turbulent Motions in Nonprecipitating Cu. Part III: Characteristics of Turbulence Motions'. Together they form a unique fingerprint.

Cite this