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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. - PowerPoint PPT Presentation
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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?