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Grid scale parameterization of topographic effects on radiation. Matteo Buzzi, Mathias W. Rotach and Marco Arpagaus MeteoS wiss. Overview. Introduction The topographic problem General aspects Topographic parameters Parameterization scheme Corrections factors - PowerPoint PPT Presentation
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aLMo
Grid scale parameterization of topographic effects on radiation
Matteo Buzzi, Mathias W. Rotach and Marco Arpagaus
MeteoSwiss
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aLMoOverview
Introduction The topographic problemGeneral aspects
Topographic parametersParameterization scheme
Corrections factorsCorrected surface radiation components
Case studiesSummary, conclusions and outlook
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aLMoThe problem: shortwave radiation
.
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aLMoThe problem: thermal downward radiation
T 4eff
T 4slopeT 4
slope
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aLMoIntroduction
NWP mesoscale models resolution tends to the order of magnitude of 1 km: topographic effects become important
Topographic shadowing (horizon, sun elevation)Slope angleSlope aspectSky view (horizon)
aLMo radiation scheme (Ritter and Geleyn,1992): surface radiation is computed on horizontal surfaces, topographic effects are not consideredIdea: try a simple approach with correction factors for surface radiation components Müller and Scherrer (2005)
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aLMoOverview
The topographic problem IntroductionTopographic parametersParameterization scheme
Corrections factorsCorrected surface radiation components
Case studiesSummary, conclusions and outlook
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aLMoTopographic parameters: slope aspect (7 km)
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aLMoTopographic parameters: slope aspect (2 km)
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aLMoTopographic parameters: slope angle (7 km)
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0
aLMoTopographic parameters: slope angle (2 km)
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1
aLMoOverview
The topographic problemIntroductionTopographic parametersParameterization scheme
Correction factorsCorrected surface radiation components
Case studiesSummary, conclusions and outlook
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2
aLMoSky view factor: 7 km
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3
aLMoSky view factor: 2 km
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4
aLMoCorrection factor for direct radiation
2004-12-11 08 UTC (7 km)
radiation on horizontal surface radiation on inclined and oriented surface
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aLMoCorrection factor for direct radiation
2004-12-11 08 UTC (2 km)
Shadowing NW slope
SE slope increased radiation
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aLMoCorrection factor for direct radiation
2004-12-11 12 UTC (7 km)
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aLMoCorrection factor for direct radiation
2004-12-11 12 UTC (2 km)
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aLMoCorrection factor for direct radiation
2004-12-11 15 UTC (7 km)
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aLMoCorrection factor for direct radiation
2004-12-11 15 UTC (2 km)
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0
aLMoDirect solar radiation
angleazimuthsun
aspectslope
angleelevationsun
angleslope
maskfcor
S
N
S
N
NSS
Nshadow
:
:
:
:
)cos(tantan
1
φφθθ
φφθθ
⎟⎠
⎞⎜⎝
⎛−⋅+=
Müller and Scherrer (2005)
dirdir SWfcorSW ↓↓ ⋅=*
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1
aLMoDiffuse downwelling solar radiation
factorviewskyf
fSWfSWSW
sky
skydiffskydiffdiff
:
)1(* −⋅+⋅= ↑↓↓
Müller and Scherrer (2005)
factorviewskyf
anglehorizon
f
sky
h
jjhsky
:
:
)sin(1241 23
015,
θ
θ ⎟⎟⎠
⎞⎜⎜⎝
⎛−= ∑
=°⋅
Assumptions: Diffuse downwelling radiation considered isotropic Adjacent areas have the same upwelling diffuse radiation
Reduced sky view
Reflections by adjacent areas
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2
aLMoThermal downwelling radiation
factorviewskyf
facfLWfLWLW
sky
skysky
:
)1(* ⋅−⋅+⋅= ↑↓↓
Modified from Müller and Scherrer (2005)
factorviewskyf
anglehorizon
f
sky
h
jjhsky
:
:
)sin(1241 23
015,
θ
θ ⎟⎟⎠
⎞⎜⎜⎝
⎛−= ∑
=°⋅
Assumptions: fac = ratio of the upwelling thermal radiation of a grid-point
and its adjacent points (at higher elevation): considers a horizontal length scale (7 or 4 km), a mean slope angle (sky view) and a mean vertical temperature lapse rate (6.5°C/1000m)
Reduced sky view
Radiation from adjacent areas
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aLMoOverview
IntroductionTopographic parametersParameterization scheme
Correction factorsCorrected surface radiation components
Case studies2004-12-11: aLMo 3.15, 7 km and 2 km2003-06-22: aLMo 3.15, 7 km and 2 km
Summary, conclusions and outlook
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aLMoResults: 7 km, 2004-12-11 00 UTC +09
Surface temperature difference
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aLMoResults: 7 km, 2004-12-11 00 UTC +12
Surface temperature difference
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aLMoResults: 7 km, 2004-12-11, grid-point
controlcorrected
Correction factor NET solar radiation
Surface temperature Sensible heat flux at the surface
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aLMoResults: 7 km, 2004-12-11, grid-point
controlcorrected
Correction factor NET solar radiation
Surface temperature Snow amount
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aLMoResults: 2 km, 2004-12-11 00 UTC +09
Surface temperature difference
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aLMoResults: 2 km, 2004-12-11 00 UTC +12
Surface temperature difference
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aLMoResults: 2 km, 2004-12-11 00 UTC +14
Total cloud cover difference
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aLMoResults: 2 km, 2004-12-11 00 UTC +12
10 m wind vectors difference
controlcorrected
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aLMoResults: 7 km, 2003-06-22 00 UTC +08
Surface temperature difference
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aLMoResults: 7 km, 2003-06-22 00 UTC +12
Surface temperature difference
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aLMoResults: 2 km, 2003-06-22 00 UTC +08
Surface temperature difference
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aLMoResults: 2 km, 2003-06-22 00 UTC +12
Surface temperature difference
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aLMoResults: 2 km, 2003-06-22 00 UTC +12
Total cloud cover difference
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aLMoResults: 2 km, 2003-06-22 00 UTC +14
Total cloud cover difference
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aLMoOverview
IntroductionTopographic parametersParameterization scheme
Correction factorsCorrected surface radiation components
Case studiesSummary, conclusions and outlook
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aLMoSummary and conclusions
The Müller and Scherrer (2005) scheme for topographic effects on radiation has been implemented into the aLMoSome sensitivity case studies have been carried outThe impact of the topographic effects (shadowing, slope angle, slope aspect and sky view) is substantial at high resolution Some significant indirect impacts (feedbacks) even at 7km: related to snow melt, stability (turbulence) and low cloudsHigher impact during the winter time due to sun elevation and snow conditionsSignificant secondary effects on clouds cover at 2kmSurface thermal changes at high resolution have also secondary effects on thermal circulation
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aLMoOutlook
Next step: systematic validation with observationsExtension of the domain to the entire aLMo operational domain (7 km and 2 km) and start test suiteCompare implementation results with the sub-grid-scale version of the Müller and Scherrer (2005) scheme (differences in preprocessor)Indirect effects (feedbacks) on clouds and stability (turbulence) have to be further investigatedHow to solve the problem of clouds at high resolution?
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aLMoImplementation into the LM
Preprocessor: prior to model integrationComputes corrections factors (time dipendent) + sky view factor (time indipendent) and save results in binary file
LM reads the correction factors (parallelized)Corrections take place in the fesft.incf radiation subroutine
In spectral loop for solar radiation (direct and diffuse)After the spectral loop for thermal radiation: the two components (up and down) have to be recomputed from the thermal radiation balance, corrected and added to a new radiation balance
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aLMoTopography: 7 km
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aLMoTopography: 2 km
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aLMoThe problem: clouds at high resolution
Reality: cloud cover
Model: no cloud cover
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aLMoResults: 2 km, 2003-06-22 00 UTC +12
10 m wind vectors difference
controlcorrected
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aLMoResults: 2 km, 2004-12-11 00 UTC +12
Total cloud cover difference
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aLMoResults: 7 km, 2003-06-22 00 UTC +14
Surface temperature difference
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aLMoResults: 7 km, 2004-12-11 00 UTC +15
Surface temperature difference
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aLMoResults: 7 km, 2003-08-07 00 UTC +15
Surface temperature difference
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aLMoResults: 2 km, 2004-12-11 00 UTC +14
Surface temperature difference
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aLMoResults: 7 km, 2003-08-07 00 UTC +08
Surface temperature difference
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aLMoResults: 7 km, 2003-08-07 00 UTC +12
Surface temperature difference
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aLMoResults: 7 km, 2003-08-07 00 UTC +12
Total cloud cover
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aLMoResults: 2 km, 2004-12-11 00 UTC +12 Wind speed difference ctrlcorr
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aLMoThe problem: shortwave radiation (1)
.