Dynamical downscaling of wind fields in stratified flow: a high

resolution mesoscale approachPedro Miranda, R Tomé, A Rodrigues, J Palma,

F Castro, J Pinto, E Dutra

University of Lisbon, CGUL, IDL, PortugalUniversity of Porto, CEsA, Portugal

Issues

Merging meteorology and mechanical engineering approaches to wind simulation

What resolution is needed/possible to get the most from mesoscale meteorological models?

Is it worth using even higher resolution nested CFD codes?

Forecast and mapping: how different are they?

What is in a weather prediction model?

• Resolved scales: full dynamic equations (hydrostatic or non-hydrostatic)Problems

• initial state, boundary conditions• interaction with unresolved scales (higher-resolution?)• misrepresentation of non-dynamical processes

• Unresolved scales and processes• Orography (small and some mesoscale)> local wind• Clouds• Turbulence• ...

D1 [ 81 km x 81 km ]

D2

D2 [ 27 km x 27 km ]

D3

D3 [ 9 km x 9 km ]

D4

D4 [ 3km x 3 km ]

D5

D5 [ 1 km x 1 km ]

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

1300

1400

1500

1600

1700

1800

1900

2000

m

ECMWF (T511L60~40km) 3km

Models

MeteorologicalBoundary conditions from ECMWF analysis

MM5 (nested, down to 33, 22 or 11 km), full physics, 5 years54x54km18x18 6x6 (3x3 or 2x2 or 1x1)

WRF (nested domains, down to 22 km), full physics, 1 month

MesoNH (nested domains, down to 22 km), full physics, 1 month

NH3D (single domain, 1.51.5km), simple physics

CFD codeBoundary Conditions from NH3D

VENTOS, dry, unrotating, adiabatic, ~300300 m, 1 week

-17.3 -17.2 -17.1 -17 -16.9 -16.8 -16.7

M esoN H 2x2

32.6

32.7

32.8

32.9

20

100

200

300

400

500

600

700

800

900

1000

1100

1200

1300

1400

1500

-17.3 -17.2 -17.1 -17 -16.9 -16.8 -16.7

M esoN H 2x2

32.6

32.7

32.8

32.9 “Real”100x100m

Model2x2km

Dec 2002

Linear model

OBSLinearNH3D

ResolutionP 1

P 2

P 3

5 7 9 11 13 15

x (km )

12

14

16

18

20

y (k

m)

303429342834

29332833

2832 2932

3033

3032

1316

-10 -5 0 5 10

x (km )

5

10

15

20

y (k

m) P 1

P 3

P 2

3km1.5km

10 15 20 25 30

-6

-4

-2

0

2

4

6

8

10

u (

m/s

)

dia

P1 P3034 nh3d

10 15 20 25 30

-14

-12

-10

-8

-6

-4

-2

0

2

4

v (m

/s)

dia

P1 P3034 nh3d

u

v

December 2002

2001-2005

0 2 4 6 8 10 12 14 16 18 200

2

4

6

8

10

12

14

16

18

20

Mod

el

Observation

3km: r=0.40, y=0.77x2km: r=0.66, Y=1.15x1km: r=0.58, y=1.10x

Resolution (MM5)

0 5 10 15 20 25 30

0

5

10

15

20

25

30

win

d P32

2

November 2005

OBS30 MesoNH30 WRF27 MM5a36

Best mast (Nov 2005)

Nov 2005 Models (MM5, WRF, MesoNH) @2km

0 2 4 6 8 10 12 14 16 18 200

2

4

6

8

10

12

14

16

18

20

Mod

el

Observation (P322)

MM5: r=0.66, y=1.15xWRF: r=0.68, y=1.00xMesoNH: r=0.78, y=0.88x

Coupling NH3D (1.5km) with VENTOS (300m)

0 5 10 15 20 25 300

5

10

15 obs30 MM5x36 Ventos NH3d

win

d P

1

June 2001

-17.4 -17.3 -17.2 -17.1 -17 -16.9 -16.8 -16.7 -16.6

W RF

32.5

32.6

32.7

32.8

32.9

33

-17.4 -17.3 -17.2 -17.1 -17 -16.9 -16.8 -16.7 -16.6

M M 5

32.5

32.6

32.7

32.8

32.9

33

-17.5 -17.4 -17.3 -17.2 -17.1 -17 -16.9 -16.8 -16.7 -16.6 -16.5

M esoNH

32.5

32.6

32.7

32.8

32.9

33

33.1

Nov 2005Mean wind2x2km

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

8.0

8.5

9.0

9.5

10.0

Final thoughts

Results are model dependent and resolution dependent (same analysed boundary conditions)

“High” mesoscale resolution is needed (e.g. 2km)

There may be gains in higher resolution (100m) if the microscale model is good

There is a clear need for improvement!

Remember: this is a very rough case in terms of topography. Results in mainland Portugal are often better