Objective:
This is a workshop to understand how cloud microphysics are influenced by the atmospheric turbulence. Relatively a long time is assigned to each speakers. This is intended to enhance active discussions and to help the audience learn each topic deeper.
Date:
Thu, 24 Nov, 2016. 13:00-17:00.
Venue: 兵庫県立大学神戸情報科学キャンパス313号室(セミナー室)
(http://www.simulation-studies.org/access)
Timetable:
13:00-13:05 Opening remark
13:05-13:50 “Understanding turbulent collision rate of cloud droplets through direct numerical simulation”,
Lian-Ping Wang (Delaware University)
14:00-14:45 “Bulk, Bin and Lagrangian cloud microphysics simulations”,
Ryo Onishi (JAMSTEC)
Coffee break
15:15-16:00 “Numerical study on turbulent enhancement of radar reflectivity factor of cumuli”,
Keigo Matsuda (JAMSTEC)
16:10-16:55 “Growth of cloud droplets in turbulent clouds”,
Wojciech W. Grabowski (NCAR).
16:55-17:00 Closing remark
18:00 After Party at Sannomiya area
Contact: Shin-ichiro Shima / 島伸一郎 (兵庫県立大学大学院シミュレーション学研究科)
e-mail: s_shima@sim.u-hyogo.ac.jp, tel/fax: 078-303-1995
Sponsor: JSPS KAKENHI Grant-in-Aid for Scientific Research(B): (Proposal number: 26286089).
Abstracts
“Understanding turbulent collision rate of cloud droplets through direct numerical simulation”
Lian-Ping Wang
Department of Mechanical Engineering, University of Delaware, USA
In this talk, I will provide a historical background of the attempts to understand how air turbulence affects the collision rate of cloud droplets, and why a quantitative understanding was difficult. Then I move to discuss what we have learned about various mechanisms through which air turbulence could alter or enhance the collision rate relative to the gravitational collision rate. Most recent advances have been derived from direct numerical simulations of small-scale turbulence along with Lagrangian tracking of inertial particles. Several physical processes affecting the collision rate are illustrated: enhanced sedimentation, turbulent acceleration, and preferential concentration. We then illustrate how direct numerical simulations have helped us to develop the theoretical framework for quantifying the collision rate, and to obtain the pair statistics, such as the radial relative velocity and radial distribution function. A particular challenging aspect is the turbulent collision efficiency when local hydrodynamic interactions are considered. Attempts to formulate theoretical parameterizations of turbulent collision kernel will be reviewed, along with open questions. I will also briefly comment on recent experimental efforts to measure the collision rate of cloud droplets.
“Bulk, Bin and Lagrangian cloud microphysics simulations”
Ryo Onishi
Center for Earth Information Science and Technology (CEIST), Japan Agency for Marine-Earth Science and Technology (JAMSTEC)
Our research on cloud microphysics simulations is overviewed. We have been working on research and development of various cloud microphysics simulations; such as bulk and spectral-bin simulations, on the Euler framework, and Lagrangian tracking simulations. For example, we have developed a turbulent collision kernel model, which is used in spectral-bin simulations, based on the dataset obtained by Lagrangian tracking simulations in the so-called Euler-Lagrangian framework, where flow motion is computed with the Euler method and particle motion with the Lagrangian method. Developed turbulent kernel model, which can consider the turbulence enhancement, has been further utilized to develop a bulk parameterization on conversion rate of cloud to rain due to collision growth. Point-particle assumption has been used for the Lagrangian tracking simulations. We are currently working on developing a size-resolving version of the Lagrangian tracking simulations. My talk will include these recent research activities on cloud microphysics processes, together with an introduction of our multiscale weather model –the Multi-Scale Simulator for the Geoenvironment (MSSG) –.
“Numerical study on turbulent enhancement of radar reflectivity factor of cumuli”
Keigo Matsuda
Center for Earth Information Science and Technology (CEIST), Japan Agency for Marine-Earth Science and Technology (JAMSTEC)
The influence of turbulent droplet clustering on radar cloud observations is investigated by using the direct numerical simulation (DNS) of particle-laden isotropic turbulence. The increment of the radar reflectivity factor is evaluated based on the mechanism of particulate Bragg scattering, in which the increment of radar reflectivity factor is proportional to the power spectrum of droplet number density fluctuations. The results show that the power spectrum calculated from the DNS data is strongly dependent on the Stokes number of droplets, and turbulent clustering enhances the radar reflectivity factor significantly under a monodispersed ideal cloud condition. For evaluating the influence for polydispersed droplets cases, the cross spectrum of number density fluctuations is calculated. The result show that the cross spectrum is dependent on the combination of the Stokes numbers. This study propose a simple model for the cross spectrum based on the DNS data and the model is applied to the results of a high-resolution cloud-simulation, in which a spectral-bin cloud microphysics scheme is used. The result show the influence of turbulent clustering can be also significant in the radar observation of cumulus clouds.
“Growth of cloud droplets in turbulent clouds”,
Wojciech W. Grabowski (NCAR)
Observed cloud droplet spectra are wide and often multimodal. This presentation will provide a review of processes affecting the spectrum with the emphasis on the effects of cloud turbulence and entrainment. Cloud turbulence involves a wide range of spatial scales, from those characterizing energy-containing eddies, of the order of 100 meters in small cumulus clouds, down to the Kolmogorov microscale, about 1 millimeter or so in typical cloud conditions. I will review previous studies that emphasize processes at either end of the range. This review will leave one wondering what spatial scales are indeed most important for the overall impact. Although I will not provide the answer to this question, I will suggest a research strategy that will eventually do.