Verification of the dynamical Verification of the dynamical downscaling of ERA40 by ALADINdownscaling of ERA40 by ALADIN

Nedjeljka ŽagarNedjeljka Žagar11, ,

M. ŽagarM. Žagar22, J. Cedilnik, J. Cedilnik22, G. Gregorič, G. Gregorič22 and J. Rakovec and J. Rakovec11

11Chair of Meteorology, University of LjubljanaChair of Meteorology, University of Ljubljana22Meteorological office, Environmental Agency of SloveniaMeteorological office, Environmental Agency of Slovenia

MotivationMotivation

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

2277th th EWGLAM meeting EWGLAM meeting 4 October 2005 4 October 2005

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)

MMethodologyethodology

Dynamical downscaling of ERA40 (10-year period)

Mesoscale model: a 10-km ALADIN model

120-km ERA40 10-km ALADIN

2277th th EWGLAM meeting EWGLAM meeting 4 October 2005 4 October 2005

Direct vs. two-step nestingDirect vs. two-step nesting

ERA40 30-km ALADIN 10-km ALADIN

2277th th EWGLAM meeting EWGLAM meeting 4 October 2005 4 October 2005

ERA40 10-km ALADIN

Increasing spatial variabilityIncreasing spatial variability

2277th th EWGLAM meeting EWGLAM meeting 4 October 2005 4 October 2005

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

Model level 10, time +12100 km

Model level 10, time 0

Model level 20, time 0

Model level 20, time +12

Average spectra shapeAverage spectra shape

2277th th EWGLAM meeting EWGLAM meeting 4 October 2005 4 October 2005

Average kinetic energy

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

Lowest model level

Average vorticity

Average divergence

100 km

Below 10 kmBelow 10 km

Dynamical downscaling of ERA40

Mesoscale model: a 10-km ALADIN model

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

10-km ALADIN 2.5-km ALADIN

2277th th EWGLAM meeting EWGLAM meeting 4 October 2005 4 October 2005

MMethodologyethodology

Define the optimal model setup by comparison against observations, and comparison against MAP-SOP reanalyses

40-km MAP-SOP reanalyses10-km ALADIN

2277th th EWGLAM meeting EWGLAM meeting 4 October 2005 4 October 2005

ObservationsObservations

exposed mountaintops

Adriatic coastvalleys, basins and lowlands

3-4 m/s

1-2 m/s2-3 m/s

2277th th EWGLAM meeting EWGLAM meeting 4 October 2005 4 October 2005

ObservationsObservations

exposed mountaintops

Adriatic coastvalleys, basins and lowlands

LI windrose

3-4 m/s

1-2 m/s2-3 m/s

2277th th EWGLAM meeting EWGLAM meeting 4 October 2005 4 October 2005

Frequency (cycles/day)

Subdiurnal periods (6-22 hrs)

Diurnal periods (26-22 hrs)

Longer than diurnal periods

(<26 hrs)

2277th th EWGLAM meeting EWGLAM meeting 4 October 2005 4 October 2005

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

24 68124896Period (hours)

Observed temporal variabilityObserved temporal variability

Frequency (cycles/day)

exposed mountaintop station RO

Subdiurnal periods (6-22 hrs)

Diurnal periods (26-22 hrs)

Longer than diurnal periods

(<26 hrs)

LTD D SD86 12 2%

2277th th EWGLAM meeting EWGLAM meeting 4 October 2005 4 October 2005

Observed temporal variabilityObserved temporal variability

Frequency (cycles/day)

exposed mountaintop station RO

Subdiurnal periods (6-22 hrs)

Diurnal periods (26-22 hrs)

Longer than diurnal periods

(<26 hrs)

LTD D SD86 12 2%

coastal station PO 38 26 36%

2277th th EWGLAM meeting EWGLAM meeting 4 October 2005 4 October 2005

Observed temporal variabilityObserved temporal variability

Frequency (cycles/day)

exposed mountaintop station RO

Subdiurnal periods (6-22 hrs)

Diurnal periods (26-22 hrs)

Longer than diurnal periods

(<26 hrs)

LTD D SD86 2 12%

coastal station PO 38 26 36%valley station SG 52 7 41%

2277th th EWGLAM meeting EWGLAM meeting 4 October 2005 4 October 2005

Observed temporal variabilityObserved temporal variability

Specific questionsSpecific questions

2277th th EWGLAM meeting EWGLAM meeting 4 October 2005 4 October 2005

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) ?

Modelled spectraModelled spectra

Exposed mountaintop station RO

Observations

MAP-SOP reanalyses

ALADIN-10

ALADIN-2.5

ERA40 reanalyses

2277th th EWGLAM meeting EWGLAM meeting 4 October 2005 4 October 2005

Modelled spectraModelled spectra

Coastal station PO

ObservationsMAP-SOP

reanalyses

ALADIN-10

ALADIN-2.5

ERA40 reanalyses

2277th th EWGLAM meeting EWGLAM meeting 4 October 2005 4 October 2005

Modelled spectraModelled spectra

Valley station SG

Observations

MAP-SOP reanalyses

ALADIN-10

ALADIN-2.5

ERA40 reanalyses

2277th th EWGLAM meeting EWGLAM meeting 4 October 2005 4 October 2005

Subdiurnal power rangeSubdiurnal power range

valley stations

coastal station

mountain stations

2277th th EWGLAM meeting EWGLAM meeting 4 October 2005 4 October 2005

Longer than diurnal power rangeLonger than diurnal power range

mountain stations valley stations

coastal station

2277th th EWGLAM meeting EWGLAM meeting 4 October 2005 4 October 2005

2277th th EWGLAM meeting EWGLAM meeting 4 October 2005 4 October 2005

Traditional score comparison Traditional score comparison

Mean absolute error for various

ALADIN-10 horizontal domains

24-h persistence

subdiurnal range

3 ALADIN domains

2277th th EWGLAM meeting EWGLAM meeting 4 October 2005 4 October 2005

Subdiurnal varibility: a 12-h filterSubdiurnal varibility: a 12-h filter

Filtering improved scores for MAP-SOP

Mean absolute error

2277th th EWGLAM meeting EWGLAM meeting 4 October 2005 4 October 2005

Wind roses: impact of a 12-h filterWind roses: impact of a 12-h filter

OBS ALADIN MAP-SOP

Afte

r filte

ring

Conclusions Conclusions

2277th th EWGLAM meeting EWGLAM meeting 4 October 2005 4 October 2005

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 12010 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

QuestionQuestions s

2277th th EWGLAM meeting EWGLAM meeting 4 October 2005 4 October 2005

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?