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Aerosols effects on turbulence in mixed-phase deep convective clouds investigated with a 2D cloud model with spectral bin microphysics The 26th Annual Meeting of the Israeli Association of Aerosol Research. Nir Benmoshe, Alexander Khain Atmospheric science department

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nir benmoshe alexander khain atmospheric science department the hebrew university in jerusalem

Aerosols effects on turbulence in mixed-phase deep convective clouds investigated with a 2D cloud model with spectral bin microphysicsThe 26th Annual Meeting of the Israeli Association of Aerosol Research

Nir Benmoshe, Alexander Khain

Atmospheric science department

The Hebrew University in Jerusalem

slide2
HUCM
  • A 2D cloud model with 43 bins spectral bins
  • 7 different hydrometeors type
  • Aerosols
  • Diffusional growth, collision, freezing, melting, advection
  • Model resolution of 50 m x 50 m was used.
slide4

Formation of eddies

Relative velocities

Absolute velocities

slide5

Physical mechanisms of effects of turbulence on collisions

Formation of concentration inhomogeneity

(droplet clustering)

Formation of relative velocity

between particles and environment

slide6

How does turbulence influence droplet collisions?

is the collision kernel

Swept volume

Collision efficiency

Fluctuations of concentration

References:

Saffman and Turner (1956);

Khain and Pinsky, 1995;

Pinsky and Khain, 1996,1997a,b;

Pinsky et el, 2000, 2001;

Zhou et al, 1998;

Wang et al, 1998, 2000;

Elperin and Dodin, 2012

References:

Pinsky et al, 1999, 2000; 2001; 2004; 2008

Khain et al, 2000;

Pigeonneau and Feuillebois, 2002

Wang et al, 2004; Ayala et al 2010

References:

Maxey, 1987,

Wang and Maxey, 1993;

Pinsky et al. 1997; 1999, Pinsky and Khain 2001, 2003.

Shaw et al, 1998;

Shaw and Kostinsky 2003; Elperin et. al 1996; 1998, 2002

Falkovich et al, 2001, 2002;

Benmoshe et al. (2012)combined effect of all factors

slide7

Collision kernel enhancement factors for different dissipation rates and Reynolds numbers

Cumulonimbus

Cumulus

Stratocumulus

Collision rate enhancement is determined by two parameters : eps and Re

Mean normalized collision kernel in turbulent flow for three cases: stratiform clouds (left panel), cumulus clouds (middle) and cumulonimbus (right panel). Pressure is equal to 1000mb. (After Pinsky et al, 2008)

slide8

Novel approach for calculation of collisions:

  • Calculation of dissipation rate in each grid point at each time step
  • Calculation of Reynolds number in each grid point at each time step;
  • Calculation of collision enhancement factor in each grid point at each time step
  • This method makes it possible to investigate effects of turbulence on precipitation formation.
turbulence kinetic energy equation

Calculation of dissipation rate

Turbulence kinetic energy equation

Dissipation rate cm^2/sec^3

Benmoshe et al. (2012)

calculating
Calculating

L is the external turbulent scale

Characteristic velocity

fluctuation

Taylor microscale

Reynolds lambda

Benmoshe et al. (2012)

slide11

CASE STUDIES: LBA-SMOC FIELD EXPERIMENT

Andreae et al, 2004

  • Blue ocean - CCN concentration 200 cm-3
  • Green ocean – CCN concentration 700-900 cm-3
  • Smoky clouds - CCN concentration 5000-10000 cm-3
slide13

Turbulence properties

Benmoshe et al. (2012)

the turbulence effect on ice particles collision is larger than on water droplets
The turbulence effect on ice particles collision is larger than on water droplets

Nowell 2010

von Blohn et.al. 2005

Effects of turbulence on ice collisions should be larger because of lower sedimentation velocity at the same mass (inertia)

slide19

Increase in the collision kernel

Pinsky, M.B., A.P. Khain, D. Rosenfeld and A. Pokrovsky, 1998

slide20

CONTROL

EFFECTSWITH ENHANCED RIMING

graupel

graupel

CWC

CWC

slide21

CONTROL

EFFECTSWITH ENHANCED RIMING

Graupel, turb

Graupel, grav

Snow, turb

Snow, grav

slide23

Conclusions – turbulence structure

  • High resolution of the model gives us real fractal cloud structures.
  • This is the first time that time and spatial depended turbulence characteristics were calculated for cumulus clouds
  • Turbulence in clouds is highly inhomogeneous: mean values do not reflect effects of turbulence on collisions
  • Turbulent intensity in clouds increase in the presence of higher aerosols concentration
  • Turbulence substantially accelerates formation of warm rain, especially in polluted clouds.
  • Increase in the collision rate between droplets reduces the total amount of precipitation since it eventually weakens cold precipitation processes
  • Turbulence in mixed phase clouds increases the rate of riming, mass and size of graupel and accelerates formation of cold rain
questions
Questions ?

Next time you are in an air pocket think about its good side….

slide26

IMPORTANCE OF THE STUDY

  • increasing the collision rate in highly turbulent clouds by order of the magnitude.
  • cloud turbulence determines processes of entrainment of dry air into the cloud and affects the cloud height.
  • The knowledge of the cloud turbulence intensity is important for purposes of flights safety.
  • why the shape of DSD is wider than it is supposed to be according to the equation for the diffusion droplet growth (e.g., Brenguier and Chaumat, 2001)
  • and why warm rain formation, as shown by Jonas (1996), occurs significantly faster than it is supposed to in accordance with the classical theory of gravitational coagulation.
  • Pinsky et al 2008 tell how turbulence kernel effect a DSD
  • Falkovich et al (2002); Pinsky et al (1997a,b; 2008); Xue et al (2008); Wang and Grabowsky (2009), the authors presented solutions of the stochastic collision equation in which turbulent effects on the evolution of the initially given DSD were simulated.
so what are we talking about
So, what are we talking about

סרטון של ענן מצולם

previous work
Previous work
  • The mean kinetic energy dissipation rate in stratocumulus clouds (Sc) is estimated as (Siebert et al. 2006) and in small cumuli as (MacPherson and Isaac, 1977; Mazin et al 1989; Pinsky and Khain 2003).
  • According to Panchev (1971) and Weil et al (1993), the values of measured in deep cumulus clouds range from several hundreds to .
  • The recent measurements of the turbulent structure of the boundary layer using a helicopter (Siebert et al 2006) indicated dramatic spatial inhomogeneity of: while the typical mean values of are , in some zones of Sc clouds (possibly in zones of imbedded convection) the values of can increase up to .
  • the typical values of were estimated by Pinsky et al (2007, 2008) as ranging from ~ in stratiform clouds to ~in strong deep convective clouds (Cb).
  • According to Siebert et al (2006), turbulent intensity varies dramatically within stratocumulus clouds. One can expect a high variability of and in cumulus and Cb clouds as well.
  • To our knowledge, there have been no regular measurements of the fine spatial distribution of and in deep cumulus clouds.
  • Turbulence determines small scale spatial fluctuations of the liquid water content (e.g., Spyksma and Bartello, 2008).
  • turbulence affects droplet size distributions (DSD) thus having an impact on diffusion growth/evaporation of drops (e.g., Jensen and Baker, 1989; Khvorostyanov and Curry 1999a,b).
where are the first drops forms

3

3

3

RAIN DROP mass,1500sec,g/m

RAIN DROP mass,1500sec,g/m

RAIN DROP mass,1800sec,g/m

0.7

1.6

1.6

0.6

1.4

1.4

10.35

10.35

10.35

1.2

1.2

0.5

7.85

7.85

7.85

1

1

Height, km

Height, km

0.4

Height, km

0.8

0.8

5.35

5.35

5.35

0.3

0.6

0.6

0.2

0.4

0.4

2.85

2.85

2.85

0.1

0.2

0.2

0.35

0.35

0.35

0

0

0

2.5

2.5

5

5

7.5

7.5

10

10

12.5

12.5

2.5

5

7.5

10

12.5

X, km

X, km

X, km

2

2

3

3

eps,1500sec,M

eps,1500sec,M

/S

/S

2

2

3

3

eps,1800sec,M

eps,1800sec,M

/S

/S

0.22

0.22

0.22

0.22

0.13

0.13

0.13

0.13

10.35

10.35

10.35

10.35

0.08

0.08

0.08

0.08

0.05

0.05

0.05

0.05

7.85

7.85

7.85

7.85

Height, km

Height, km

0.03

0.03

Height, km

Height, km

0.03

0.03

0.02

0.02

0.02

0.02

5.35

5.35

5.35

5.35

0.01

0.01

0.01

0.01

2.85

2.85

0.00

0.00

2.85

2.85

0.00

0.00

0.00

0.00

0.00

0.00

0.35

0.35

0.35

0.35

0.00

0.00

2.5

2.5

5

5

7.5

7.5

10

10

12.5

12.5

2.5

2.5

5

5

7.5

7.5

10

10

12.5

12.5

X, km

X, km

X, km

X, km

Where are the first drops forms?

E200T

E2000T

Rain water content, gm

Rain water content, gm

, t=1500s

, t=1500s

-

-

3

3

Rain water content, gm

Rain water content, gm

, t=1800s

, t=1800s

-

-

3

3

Dissipation rate, m

Dissipation rate, m

s

s

, t=1500s

, t=1500s

2

2

-

-

3

3

Dissipation rate, m

Dissipation rate, m

s

s

, t=1800s

, t=1800s

2

2

-

-

3

3

slide31

How is the first precipitation influenced by turbulence ?

GO-turb

Strange notations

GO-grav

S-grav

S-turb