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Verification of the dynamical downscaling of ERA40 by ALADIN. Nedjeljka Žagar 1 , M. Žagar 2 , J. Cedilnik 2 , G. Gregorič 2 and J. Rakovec 1. 1 Chair of Meteorology, University of Ljubljana 2 Meteorological office, Environmental Agency of Slovenia. Motivation.

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Verification of the dynamical downscaling of ERA40 by ALADIN

Nedjeljka Žagar1,

M. Žagar2, J. Cedilnik2, G. Gregorič2 and J. Rakovec1

1Chair of Meteorology, University of Ljubljana

2Meteorological office, Environmental Agency of Slovenia


Motivation ALADIN

Modelling the wind climatology for Slovenia at scales around 10 km

This is an intermediate step towards a higher-resolution climatology for the wind energy estimates

This talk:

 optimal modelling setup for the dynamical downscaling of ERA40

 comparison with observations during MAP-SOP (autumn 1999) and with the ECMWF reanalyses of the MAP-SOP period (Keil&Cardinali, QJRMS, 2004)

27th EWGLAM meeting 4 October 2005


M ALADINethodology

Dynamical downscaling of ERA40 (10-year period)

Mesoscale model: a 10-km ALADIN model

10-km ALADIN

120-km ERA40

27th EWGLAM meeting 4 October 2005


Direct vs. two-step nesting ALADIN

ERA40  30-km ALADIN  10-km ALADIN

ERA40  10-km ALADIN

27th EWGLAM meeting 4 October 2005


Increasing spatial variability ALADIN

An example: building-up of the kinetic energy spectrum during the first hours of the forecast

Model level 20, time +12

Model level 20, time 0

Model level 10, time +12

100 km

Model level 10, time 0

27th EWGLAM meeting 4 October 2005


Average spectra shape ALADIN

Average kinetic energy

Average vorticity

Average divergence

Lowest model level

100 km

Average over 70 days of MAP-SOP and for model levels 8-18 (4-9 km)

27th EWGLAM meeting 4 October 2005


Below 10 km ALADIN

Dynamical downscaling of ERA40

Mesoscale model: a 10-km ALADIN model

Pure dynamical downscaling (Žagar&Rakovec, 1999) to 2.5 km

2.5-km ALADIN

10-km ALADIN

27th EWGLAM meeting 4 October 2005


M ALADINethodology

Define the optimal model setup by

comparison against observations, and

comparison against MAP-SOP reanalyses

10-km ALADIN

40-km MAP-SOP reanalyses

27th EWGLAM meeting 4 October 2005


Observations ALADIN

exposed mountaintops

3-4 m/s

valleys, basins and lowlands

Adriatic coast

2-3 m/s

1-2 m/s

27th EWGLAM meeting 4 October 2005


Observations ALADIN

LI windrose

exposed mountaintops

3-4 m/s

valleys, basins and lowlands

Adriatic coast

2-3 m/s

1-2 m/s

27th EWGLAM meeting 4 October 2005


Diurnal periods (26-22 hrs) ALADIN

Longer than diurnal periods (<26 hrs)

Subdiurnal periods (6-22 hrs)

Observed temporal variability

Frequency (cycles/day)

96

48

12

8

6

24

Period (hours)

Based on the time serie of the zonal wind during MAP-SOP, data every three hours, totally 560 data points

27th EWGLAM meeting 4 October 2005


Diurnal periods (26-22 hrs) ALADIN

Longer than diurnal periods (<26 hrs)

Subdiurnal periods (6-22 hrs)

Observed temporal variability

Frequency (cycles/day)

LTD D SD

86 12 2%

exposed mountaintop station RO

27th EWGLAM meeting 4 October 2005


Diurnal periods (26-22 hrs) ALADIN

Longer than diurnal periods (<26 hrs)

Subdiurnal periods (6-22 hrs)

Observed temporal variability

Frequency (cycles/day)

LTD D SD

86 12 2%

exposed mountaintop station RO

38 26 36%

coastal station PO

27th EWGLAM meeting 4 October 2005


Observed temporal variability ALADIN

Diurnal periods (26-22 hrs)

Longer than diurnal periods (<26 hrs)

Subdiurnal periods (6-22 hrs)

Frequency (cycles/day)

LTD D SD

86 2 12%

exposed mountaintop station RO

38 26 36%

coastal station PO

valley station SG

52 7 41%

27th EWGLAM meeting 4 October 2005


Specific questions ALADIN

How well are these spectra reproduced by an operational LAM?

Can we relate modelled spectra with traditional verification scores (mae, rmse)?

How dependent are model-produced spectra on the nesting method and the horizontal domain size?

How much better is the wind field from the 10-km ALADIN than from the ECMWF model (40-km MAP-SOP reanalyses) ?

27th EWGLAM meeting 4 October 2005


MAP-SOP reanalyses ALADIN

Observations

ALADIN-10

ALADIN-2.5

ERA40 reanalyses

Modelled spectra

Exposed mountaintop station RO

27th EWGLAM meeting 4 October 2005


MAP-SOP reanalyses ALADIN

Observations

ALADIN-10

ALADIN-2.5

ERA40 reanalyses

Modelled spectra

Coastal station PO

27th EWGLAM meeting 4 October 2005


MAP-SOP reanalyses ALADIN

Observations

ALADIN-10

ALADIN-2.5

ERA40 reanalyses

Modelled spectra

Valley station SG

27th EWGLAM meeting 4 October 2005


Subdiurnal power range ALADIN

mountain stations

coastal station

valley stations

27th EWGLAM meeting 4 October 2005


Longer than diurnal power range ALADIN

mountain stations

valley stations

coastal station

27th EWGLAM meeting 4 October 2005


Traditional score comparison ALADIN

3 ALADIN domains

Mean absolute error for various ALADIN-10 horizontal domains

24-h persistence

subdiurnal range

27th EWGLAM meeting 4 October 2005


Subdiurnal varibility: a 12-h filter ALADIN

Mean absolute error

Filtering improved scores for MAP-SOP

27th EWGLAM meeting 4 October 2005


Wind roses: impact of a 12-h filter ALADIN

OBS

ALADIN

MAP-SOP

After filtering

27th EWGLAM meeting 4 October 2005


Conclusions ALADIN

  • Downscaling of ERA40 by the ALADIN model - ok

  • Conventional verification scores: a 10-km ALADIN superior to the MAP-SOP reanalysis data – expected

    However,

  • More energy in the sub-diurnal (SD) range in the MAP-SOP data than in the ALADIN – less expected, peculiar

  • Spatial spectra slope does not follow – 5/3 law

  • Direct nesting (resolution jump 12010 km) produced best conventional scores – !?

  • Smoothing MAP-SOP dataset improves its conventional scores

    Consequences:

  • The mesoscale model wind field displays significant senstivity with respect to the horizontal domain definition – basin stations contain 30-50% of energy in the SD range

27th EWGLAM meeting 4 October 2005


Question ALADINs

  • In dynamical downscaling, spatial variability increase is much more important than the increase of the temporal variabiliy?

  • What shift from low frequency to high-frequency variability can/should be expected?

  • -5/3 slope: how strong constraint should it be?

27th EWGLAM meeting 4 October 2005


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