The role of air turbulence in warm rain initiation

Quantitative parameterization of turbulent collision of cloud droplets represents a major unsolved problem in cloud physics. Here a hybrid direct simulation tool is used specifically to quantify the turbulent enhancement of the gravitational collision-coalescence. Simulation results show that air turbulence can enhance the collision kernel by an average factor of about 2, and the observed trends are supported by scaling arguments. An impact study using the most realistic collection kernel suggests that cloud turbulence can significantly reduce the time for warm rain initiation. Areas for further development of the hybrid simulation and the impact study are indicated. Copyright © 2009 Royal Meteorological Society

[1]  Ka-Ming Lau,et al.  Warm rain processes over tropical oceans and climate implications , 2003 .

[2]  J. Klett,et al.  Microphysics of Clouds and Precipitation , 1978, Nature.

[3]  Efstathios E Michaelides,et al.  Effects of turbulence , 2006 .

[4]  Alexander Khain,et al.  Effects of in‐cloud nucleation and turbulence on droplet spectrum formation in cumulus clouds , 2002 .

[5]  R. C. Srivastava.  Growth Of Cloud Drops by Condensation: A Criticism of Currently Accepted Theory and a New Approach , 1989 .

[6]  G. Falkovich,et al.  Acceleration of rain initiation by cloud turbulence , 2002, Nature.

[7]  Jennifer Prestigiacomo,et al.  A Hybrid Approach , 2018, How High the Sky?.

[8]  Wojciech W. Grabowski,et al.  Comments on “Preferential Concentration of Cloud Droplets by Turbulence:Effects on the Early Evolution of Cumulus Cloud Droplet Spectra” , 1999 .

[9]  W. Hall,et al.  A Detailed Microphysical Model Within a Two-Dimensional Dynamic Framework: Model Description and Preliminary Results , 1980 .

[10]  Krishnan Mahesh,et al.  Direct numerical simulation , 1998 .

[11]  C. Franklin.  A Warm Rain Microphysics Parameterization that Includes the Effect of Turbulence , 2008 .

[12]  J. Brenguier,et al.  Cumulus Entrainment and Cloud Droplet Spectra: A Numerical Model within a Two-Dimensional Dynamical Framework , 1993 .

[13]  Ben C. Bernstein,et al.  Meteorological Conditions Associated with the ATR72 Aircraft Accident near Roselawn, Indiana, on 31 October 1994 , 1997 .

[14]  Bogdan Rosa,et al.  Effects of turbulence on the geometric collision rate of sedimenting droplets. Part 1. Results from direct numerical simulation , 2008 .

[15]  Wojciech W. Grabowski,et al.  Diffusional and accretional growth of water drops in a rising adiabatic parcel: effects of the turbulent collision kernel , 2008 .

[16]  Bogdan Rosa,et al.  Effects of turbulence on the geometric collision rate of sedimenting droplets. Part 2. Theory and parameterization , 2008 .

[17]  Lance R. Collins,et al.  Clustering of aerosol particles in isotropic turbulence , 2005, Journal of Fluid Mechanics.

[18]  C. Knight,et al.  The Role of Giant and Ultragiant Nuclei in the Formation of Early Radar Echoes in Warm Cumulus Clouds , 2003 .

[19]  Edwin X. Berry,et al.  An Analysis of Cloud Drop Growth by Collection: Part I. Double Distributions , 1974 .

[20]  Paul A. Vaillancourt,et al.  Microscopic approach to cloud droplet growth by condensation , 1998 .

[21]  Olivier Simonin,et al.  Two statistical models for predicting collision rates of inertial particles in homogeneous isotropic turbulence , 2003 .

[22]  Lian-Ping Wang,et al.  A bin integral method for solving the kinetic collection equation , 2007, J. Comput. Phys..

[23]  Alexander Khain,et al.  Collisions of small drops in a turbulent flow , 1999 .

[24]  L. Finch.  A hybrid approach , 1998 .

[25]  B. Grits,et al.  Collisions of Small Drops in a Turbulent Flow. Part III: Relative Droplet Fluxes and Swept Volumes , 2006 .

[26]  J. Brenguier,et al.  Droplet Spectra Broadening in Cumulus Clouds. Part II: Microscale Droplet Concentration Heterogeneities , 2001 .

[27]  Wojciech W. Grabowski,et al.  Observations of the width of cloud droplet spectra in stratocumulus , 2006 .

[28]  Edwin X. Berry,et al.  An Analysis of Cloud Drop Growth by Collection: Part IV. A New Parameterization , 1974 .

[29]  Lian-Ping Wang,et al.  A hybrid approach for simulating turbulent collisions of hydrodynamically-interacting particles , 2007, J. Comput. Phys..

[30]  Jean-Louis Brenguier,et al.  Droplet Spectra Broadening in Cumulus Clouds. Part I: Broadening in Adiabatic Cores , 2001 .

[31]  Alexander Khain,et al.  Collisions of Small Drops in a Turbulent Flow. Part I: Collision Efficiency. Problem Formulation and Preliminary Results , 1999 .

[32]  L. Collins,et al.  Collision statistics in an isotropic particle-laden turbulent suspension. Part 1. Direct numerical simulations , 1997, Journal of Fluid Mechanics.

[33]  M. Baker,et al.  Cloud Microphysics and Climate , 1997 .

[34]  Armann Gylfason,et al.  Inertial clustering of particles in high-Reynolds-number turbulence. , 2008, Physical review letters.

[35]  Bogdan Rosa,et al.  Turbulent collision efficiency of heavy particles relevant to cloud droplets , 2008 .

[36]  G. Huffman,et al.  The Supercooled Warm Rain Process and the Specification of Freezing Precipitation , 1988 .

[37]  Wojciech W. Grabowski,et al.  Effects of stochastic coalescence and air turbulence on the size distribution of cloud droplets , 2006 .

[38]  Wojciech W. Grabowski,et al.  Theoretical Formulation of Collision Rate and Collision Efficiency of Hydrodynamically Interacting Cloud Droplets in Turbulent Atmosphere , 2005 .

[39]  H. Fernando,et al.  How turbulence enhances coalescence of settling particles with applications to rain in clouds , 2005, Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences.

[40]  Wojciech W. Grabowski,et al.  Growth of Cloud Droplets by Turbulent Collision–Coalescence , 2006 .

[41]  Wojciech W. Grabowski,et al.  Effects of aerodynamic interactions on the motion of heavy particles in a bidisperse suspension , 2007 .

[42]  D. Arenberg.  Turbulence As The Major Factor in the Growth of Cloud Drops , 1939 .

[43]  Paul A. Vaillancourt,et al.  Statistics and Parameterizations of the Effect of Turbulence on the Geometric Collision Kernel of Cloud Droplets , 2007 .

[44]  M. Maxey,et al.  Settling velocity and concentration distribution of heavy particles in homogeneous isotropic turbulence , 1993, Journal of Fluid Mechanics.