How large is large enough? Large-eddy simulation of clear and cloudy - - PowerPoint PPT Presentation

How large is large enough? Large-eddy simulation of clear and cloudy convective boundary layers

Stephan R. de Roode Peter G. Duynkerke Harm J. J. Jonker (1) Institute for Marine and Atmospheric Research Utrecht (IMAU), Utrecht, The Netherlands

(1)Thermofluids Section, Department of Applied Physics, Delft University of Technology, Delft, The

Netherlands

The investigations were supported by the Netherlands Organization for Scientific Research (NWO). This work was sponsored by the National Computing Facilities Foundation (NCF) for the use of supercomputer facilities.

Simulation of the clear convective boundary layer

4 different horizontal domain sizes L L = 3200 m L = 6400 m L = 12800 m L = 25600 m

0.125 0.25 0.375 0.5 200 400 600 800 1000 1200

L = 3200 m L = 6400 m L = 12800 m L = 25600 m

w'w' [mK/s] height [m]

• 0.02

0.02 0.04 0.06 200 400 600 800 1000 1200

L = 3200 m L = 6400 m L =12800 m L = 25600 m

w'

v' [mK/s]

height [m]

Variance spectra in the middle of the boundary layer at t=8h

0.1 0.2 0.3 0.4 10

• 5

0.0001 0.001 0.01

L = 3200 m L = 6400 m L = 12800 m L = 25600 m

kS [m

2s

• 2]

0.1 km 1 km 10 km 100 km 0 10 2 10

• 4

4 10

• 4

6 10

• 4

8 10

• 4

1 10

• 3

10

• 5

0.0001 0.001 0.01 kS [K

2]

wavenumber k [m

• 1]

L=3.2 km BL height

vertical velocity virtual potential temperature

(Co)-variance spectra in the middle of the boundary layer

0 10 2 10

• 5

4 10

• 5

6 10

• 5

8 10

• 5

1 10

• 4

10

• 5

0.0001 0.001 0.01

L = 3200 m L = 6400 m L = 12800 m L = 25600 m

kS [(g kg

• 1)ms
• 1]

0.1 km 1 km 10 km 100 km 0 10 5 10

• 8

1 10

• 7

1.5 10

• 7

2 10

• 7

10

• 5

0.0001 0.001 0.01 kS [(g kg

• 1)

2]

wavenumber k [m

• 1]

L=3.2 km BL height

moisture flux moisture variance

Structures in the middle of the clear convective BL

Liquid water path evolution in stratocumulus simulation during the night

(kg/m2 )

(Co)-variance spectra in the middle of the stratocumulus layer

0.02 0.04 0.06 0.08 10

• 5

10

• 4

10

• 3

10

• 2

L = 3200 m L = 6400 m L = 12800 m L = 25600 m

k S

ww [m 2s

• 2]

0.1 km 1 km 10 km 100 km

L=3.2 km BL height

0 10 2 10

• 9

4 10

• 9

6 10

• 9

8 10

• 9

10

• 5

10

• 4

10

• 3

10

• 2

kS [(g kg

• 1)

2]

wavenumber k [m

• 1]

vertical velocity variance moisture variance

(Co)-variance spectra in the middle of the stratocumulus layer

L=3.2 km BL height

0.02 0.04 0.06 0.08 0.1 0.12 10

• 5

0.0001 0.001 0.01

L = 3200 m L = 6400 m L = 12800 m L = 25600 m

0.1 km 1 km 10 km 100 km kS [m

2s

• 2]

0.02 0.04 0.06 0.08 0.1 0.12 10

• 5

0.0001 0.001 0.01 kS [m

2s

• 2]

wavenumber k [m

• 1]

uu-variance vv-variance

Production of variance in the clear CBL Žw'w' Žt

P

= Pw2 = 2 g 0 w'v' Žv'v' Žt

P

= Pv

2 = - 2 w'v' Žv

Žz

• 0.02

0.02 0.04 0.06 0.2 0.4 0.6 0.8 1 w'

v' (mKs

• 1)

scaled height 304.6 304.8 305 0.2 0.4 0.6 0.8 1

• v (K)

scaled height

Pw2 > 0 , Pv

2 > 0

Pw2 > 0 , Pv

2 < 0

Pw2 < 0 , Pv

2 > 0

Length scale in stratocumulus A = 1 , B = 0.61 ≈ 180 (subcloud) A ≈ 0.6 , B ≈ 1200 (cloud)

w'v' = A w'l' + B w'qt'

• 0.04
• 0.02

0.02 0.2 0.4 0.6 0.8 1 1.2 w'

v'

w'

l'

(Kms

• 1)

z/z

i

How large is large enough? Conclusions

• larger w-fluctuations at mesoscales, more production of

mesoscale scalar variance

• Scalar variance at mesoscales may grow with time -> longer

duration of simulation requires larger horizontal domain

This talk: http://www.phys.uu.nl/~roode/presentations.html Paper: http://www.phys.uu.nl/~roode/publications.html

• S. R. de Roode, P. G. Duynkerke and H. J. J. Jonker, 2002: Large Eddy Simulation:

How large is large enough? Submitted to the J. Atmos. Sci.