NITech Lectures on Turbulence and Cloud
ProgramMarch 8-9, 2018, Room 110, Building No. 4, Nagoya Institute of Technology
URL: http://comphys.web.nitech.ac.jp/cloudlec.html

March 89:00

9:25

Reception

9:25

9:30

Opening

9:30 10:30

Pumir

10:30 10:40
10:40 11:40

Break
Pumir

11:40 13:30
13:30 14:30(continue)
Lunch

Shaw

14:30 14:40
14:40 15:40

Collisions and aggregation of particles by turbulence in clouds

Cloud droplet growth by vapor condensation in a turbulent flow
BreakShaw

15:40 16:00(continue)
Break16:00 16:40

Ishihara

Motion of inertial particles in high-Reynolds-number turbulence

16:40 17:20

SatoA grid refinement study on shallow cumuli using a large eddy simulation model

17:20 18:00

Watanabe

Large-scale simulation of monodispersed small solid particles in isotropic turbulence

18:30 20:30

BanquetMarch 99:00 9:30
9:30 10:30

ReceptionYum

10:30 10:40
10:40 11:40

Cloud condensation nuclei distribution in East Asia
Aircraft measurement of cloud microphysical relationships
BreakYum(continue)

11:40 12:00

Photo Session

12:00 13:30

Lunch

13:30 14:10

SuzukiLinkage of cloud microphysics to climate: Satellite observations and global modeling

14:10 14:50

MatsudaNumerical study on cloud radar reflectivity enhancement
due to turbulent droplet clustering

14:50 15:30

Saito

Turbulence and cloud droplets in cloud micro-physics simulator

15:30 16:00

Round Table Discussion

Abstracts

March 8Collisions and aggregation of particles by turbulence in clouds
Alain Pumir (Laboratoire de Physique, Ecole Normale Superieure de Lyon)
In clouds, aggregation of droplets and/of ice crystals plays an important role in the growth of particles
to form rain drops or ice-graupels that eventually lead to precipitation. Turbulence creates relative
motions between particles, which result in an enhancement of the collision rate between particles.
I will first review our current understanding of the role of turbulence in collisions of small droplets,
viewed as small inertial particles. In particular, two main eﬀects will been discussed. Droplets muchheavier than ambient air, tend to accumulate in special regions of the flow; this eﬀect is known as
preferential concentration. If the inertia of the particles is large enough, particles may collide with avery large relative velocity; this is known as the sling eﬀect . Both eﬀects play an important role tounderstand collisions of droplets.
I will also discuss the problem of collisions involving small ice-crystals, focusing on crystals shaped
approximately as oblate ellipsoids. I will first discuss collisions between these crystals, which is relevantto the formation of graupels/hail particles. In mixed phase clouds, ice-crystals, which coexist with small
water droplets, can grow as a result of collisions with droplets. I will present new results on this process,known as riming .

Cloud droplet growth by vapor condensation in a turbulent flow
Raymond Shaw (Michigan Technological University)
Turbulence and mixing influence cloud droplet growth by vapor condensation, which in turn leads
to implications for precipitation formation and cloud optical properties. Recent laboratory experiments
and field observations support the view that the response time of water vapor resulting from droplet
growth defines two growth regimes: fast response yielding relatively uniform cloud properties, versus
slow response yielding broad droplet size distributions.

Motion of inertial particles in high-Reynolds-number turbulence
Takashi Ishihara (Okayama University)
Turbulence plays a key role in collision and coagulation process of droplets in cloud. Since turbulencein realistic cloud is at very high Reynolds number, our understanding of such processes in high-Reynoldsnumber turbulence is necessary. In this presentation, firstly vortical structures observed in high-resolution
direct numerical simulations (DNSs) are reviewed. Next, the motions of inertial particles numericallytracked in the DNSs of high-Reynolds-number turbulence (the Reynolds number based on the Taylor
micro-scale up to 730) are discussed.

A grid refinement study on shallow cumuli using a large eddy simulation modelYousuke Sato (Nagoya University)
The eﬀects of grid resolution on the simulated shallow cumuli was investigated using a large eddy
simulation (LES) model coupled with an Eulerian cloud microphysical model (ECM) and a particlebased Lagrangian cloud microphysical model (LCM). We swept he horizontal/vertical grid resolution
from 100 m/80 m to 6.25 m/5 m. Cloud cover was increased with fining the grid resolution, and it wasnumerically converged with a horizontal/vertical grid resolution of 12.5 m/10 m. The turbulent structurein the subcloud layer was critical to the cloud cover. Using the fine grid resolution, the roll convection
was clearly simulated in the sub-cloud layer, but it became obscure with coarsening the grid resolution.
The dependency of the grid resolution was commonly seen in both LCM and ECM.

Large-scale simulation of monodispersed small solid particles in isotropic turbulenceTakeshi Watanabe (Nagoya Institute of Technology)
We investigate modifications of isotropic turbulence due to the monodispersed small solid particles
using the large-scale direct numerical simulation. Although the particle diameter is comparable to theKolmogorov length lK , the flow around each particles is accurately resolved by computing the incompressible Navier-Stokes equations with volume penalization. It is found that the far dissipation range ofkinetic energy spectrum is strongly modified by particles, and the eﬀect of particles becomes stronger
when increasing the volume fraction of particles. However the body of spectrum in klK < 1 is not aﬀectedby particles as far as the particle concentration is not so large. Turbulence modulation is also examinedby changing the mass density of particle, where it is found that the kinetic energy spectrum is strongly
modified over whole wavenumber range when the mass density of particle is larger. These properties arealso discussed by examining the behavior of transfer function originated from the interaction between
particles and turbulence.

March 9
Cloud condensation nuclei distribution in East AsiaSeong Soo Yum (Yonsei University)
Cloud condensation nuclei (CCN) are a subset of atmospheric particles that can serve as nucleus of clouddroplet. It means that cloud microphysics (number concentration and sizes of cloud droplets) is largely
determined by CCN, which in turn determine radiative properties of clouds. Therefore, an important
climatic implication is that change of CCN distribution can alter earth radiation budget. Nevertheless,information on CCN is still lacking in many parts of the world and especially in East Asia. Shown in thislecture are the results of CCN measurements in and around the Korean Peninsula on various platforms,ground, ship and aircraft, which may represent the CCN distribution in East Asia.

Aircraft measurement of cloud microphysical relationships
Seong Soo Yum (Yonsei University)
Cloud microphysical relationships are initially determined by adiabatic condensational growth of embryonic droplets formed on CCN but are being modulated by entrainment and mixing of clear air fromthe surrounding that lead to evaporation and/or new cloud droplet activation on CCN from the entrained
air. Importantly, depending on how entrained air is mixed with cloudy air, further development of cloud
droplets is aﬀected. To estimate what type of mixing process is dominant in clouds of diﬀerent thermodynamic and dynamic conditions, cloud microphysical relationships are examined for stratocumulus andcumulus clouds measured in several aircraft field projects. Some important results are highlighted in thislecture.

Linkage of cloud microphysics to climate: Satellite observations and global
modeling
Kentaroh Suzuki (University of Tokyo)
This presentation highlights our recent studies that combine satellite observations and global modeling to explore how cloud microphysics is linked to climate and to expose a fundamental gap in ourunderstanding of the linkage.

Numerical study on cloud radar reflectivity enhancement due to turbulent
droplet clustering
Keigo Matsuda (Japan Agency for Marine-Earth Science and Technology)
Cloud droplets form a nonuniform spatial distribution in turbulence, which is referred to as turbulent
clustering. The cloud radar reflectivity factor can be enhanced by turbulent clustering of cloud droplets.
The quantitative influence of turbulent clustering on radar reflectivity factor is investigated by using a
direct numerical simulation of particle-laden homogeneous isotropic turbulence.

Turbulence and cloud droplets in cloud micro-physics simulator
Izumi Saito (Nagoya Institute of Technology)
Cloud micro-physics simulator is a DNS model developed for the seamless simulation of turbulence
and the evolution of cloud droplets to rain drops in a turbulent cloud environment from a first principle.
In this talk, I provide an overview of the recent progress and result of cloud micro-physics simulator,including the eﬀect of turbulence on condensation and collision growth of cloud droplets and the eﬀectof droplets on turbulent fluctuations.