Upload
alexandre-dale
View
213
Download
1
Tags:
Embed Size (px)
Citation preview
28th EWGLAM meeting, Zurich, October 2006
ALARO Physics developments at LACE
Neva Pristov
LACE Working group for physisc
28th EWGLAM meeting, Zurich, October 2006
ALARO physics package - introduction
• continous transition from ARPEGE/ALADIN to AROME (continuity + improvements)
• to treat ‘grey-zone’ 3-7 km mesh size • economical computation, numerical efficiency• algorithmic flexibility good basis for
further developments
28th EWGLAM meeting, Zurich, October 2006
Main developments topics
• Radiation
• Orographic forcing
• Large scale precipitation
• Prognostic turbulent scheme
• Precipitating convectionLuc GerardLuc Gerard, J-M Piriou, D. Banciu, , J-M Piriou, D. Banciu, I.Stiperski, R. BrožkovaI.Stiperski, R. Brožkova, , J-F GeleynJ-F Geleyn
J-F Geleyn, G. Hello, J-F Geleyn, G. Hello, N. PristovN. Pristov, Y. Bouteloup, , Y. Bouteloup, M. DerkovaM. Derkova, J. Mašek, A.Trojakova, J. Mašek, A.Trojakova, R. Fournier, R. Fournier
B. Carty, F. Bouyssel, B. Carty, F. Bouyssel, R. BrožkovaR. Brožkova, J-F Geleyn, , J-F Geleyn, M. Derkova, R. Mladek, J. Cedilnik, D. DrvarM. Derkova, R. Mladek, J. Cedilnik, D. Drvar, I. Beau, I. Beau
B. Carty, J-F Geleyn, B. Carty, J-F Geleyn, R. Brožkova, R. Brožkova, J. Cedilnik, D. DrvarJ. Cedilnik, D. Drvar
F. Vana,F. Vana, J. Cedilnik, J. Cedilnik, MM. . TudorTudor, , J-F GeleynJ-F Geleyn, , A.SimonA.Simon
28th EWGLAM meeting, Zurich, October 2006
Radiation
Aim:• using the current delta-two stream approximation of
radiative transfer equation for solar and thermal bands• economical computation (a good quality cost ratio)• better consideration of clouds
New features:• new technique for thermal radiative fluxes computation on
the basis of Net Exchanged Rate (NER) formalism• gaseous transmition functions for computation of optical
depth closer to RRTM scheme • introduction of the complete aerosol model • updating of the cloud optical properties
28th EWGLAM meeting, Zurich, October 2006
Cloud optical properties
• availability of prognostic cloud water calls for more sophisticated treatment of clouds in radiative transfer
• static treatment of saturation effect in old scheme (clouds are too opaque in some circumstances)
• new scheme: coefficients k_abs, k_scat dependent on cloud water content dynamic treatment of saturation, taking into account cloud
depth and geometry
• remain cheap, only two bands: solar and thermal
28th EWGLAM meeting, Zurich, October 2006
Cloud optical properties – strategy
• Dependency of coefficients k_abs, k_scat on cloud water content was fitted using experimental sample of 7 liquid and 16 ice cloud types
• Evaluation of saturation effect in idealized framework: multi-layer delta-two stream system only clouds taken into account, gases and aerosols ignored cloud geometry with random or maximum overlaps between
adjacent layers atmosphere illuminated from one side by direct flux (solar) or
diffuse flux (thermal), reflected and transmitted fluxes evaluated broadband fluxes diagnosed by summing up monochromatic
results computed for several hundred separate wavelengths
28th EWGLAM meeting, Zurich, October 2006
Cloud optical properties
red – liquid clouds, blue – ice clouds, black – mixed clouds
Saturation factor versus optical depth for homogeneous clouds, solar band
k_absorbtion k_scatter
28th EWGLAM meeting, Zurich, October 2006
Cloud optical properties
parameterized versus reference solar reflectance, sample of non-homogeneous 3 layer clouds
old new
28th EWGLAM meeting, Zurich, October 2006
Cloud optical properties
Solar absorbtion new (blue) versus old (red) scheme
Problematic peak around model level 20
28th EWGLAM meeting, Zurich, October 2006
Statistical method for the weighting function in NER
parameterized versus computed thermal flux
28th EWGLAM meeting, Zurich, October 2006
Pseudo-prognostic turbulent scheme pTKE
• the turbulent memory of the previous timesteps is kept
• the advection and diffusion of TKE are added to the current scheme
• more general computation of mixing length • prognostic variable TKE
28th EWGLAM meeting, Zurich, October 2006
TKE vs pseudoTKE
= advection
+ diffusion
+ mechanical or shear production/destruction
+ buoyancy production/consumption
+ viscous dissipation
t
TKE
full
= advection + diffusion + Newtonian relaxation towards stationary
solution
pseudo
t
TKE
28th EWGLAM meeting, Zurich, October 2006
Academic test with 1D model: GABLS II experiment
28th EWGLAM meeting, Zurich, October 2006
Mixing length computation - current formulation
• Empirical formula dependent on the height of the PBL (Ayotte, et al. 1996)
= f (z, hPBL) -exponential function
Increase of the mixing lengthwith the PBL height (hPBL)
Modifications: 1 , 2 = f (hPBL)
1
1 0
0
zz
zzlGC
28th EWGLAM meeting, Zurich, October 2006
Tests with the BL89 parameterization
• Bougeault-Lacarrère (1989) : “non-local” mixing length dependent on TKE and integral buoyancy (used e.g. in ARPEGE and Mèso-NH)
• Direct application of BL89 in the pseudo-TKE scheme: numerically stable but not consistent with the original K-theory part (too large mixing length – increase of exchange coefficients and turbulent fluxes)
• Consequences: systematic increase of TKE and winds at surface, too big diffusion in the upper troposphere, danger of
tropopause erosion
28th EWGLAM meeting, Zurich, October 2006
Merger with BL89 or TKE/N schemes
• current mixing length (GC) taken as a first guess• additional information about TKE and buoyancy from the
BL89 scheme, modulation with k-parameter• more suitable for computation of K-coefficients
• Merger with TKE/N scheme (only extensively tested, 1-D evolution too noisy, not so good properties)
2max ,minN
TKEklll GC
GCBLGC llkll 89 1,0k
28th EWGLAM meeting, Zurich, October 2006
Academic test with 1D model: GABLS II experiment
• Vertical profile and time course of mixing length
Modified GC GC +BL89
PBL top
28th EWGLAM meeting, Zurich, October 2006
3-D case: strong jet stream
15 December 2005, Northern GermanyTKE and cross-sections
Modified GC BL89
A B
only small TKE (no CAT)
BA
impact injet-stream area
higher TKEin the PBL
28th EWGLAM meeting, Zurich, October 2006
3-D case: strong jet stream
• GC+BL89: more feasible for PBL, TKE signals in jet region (CAT) but not too violent
• TKE/N: Too much TKE in upper troposphere
GC +BL89 GC +TKE/N
28th EWGLAM meeting, Zurich, October 2006
Large scale precipitation
• a simple micro-physics scheme with 5 water species included into precipitation scheme cloud water, cloud ice, rain, snow - new
prognostic variables fluxes statistical approach for sedimentation of rain
and snow
28th EWGLAM meeting, Zurich, October 2006
ALARO-0 minus 3MT
better space distribution of precipitation
oper alaro
6h precipitation6h precipitation
28th EWGLAM meeting, Zurich, October 2006
ALARO-0 minus 3MT
Vertical profiles of horizontal averaged values
cloud water cloud ice
28th EWGLAM meeting, Zurich, October 2006
Plans
• Evaluation of parameterization developments Technical and scientific validation Case studies, verification
• Training
• Continuation of work Convection (3MT) More complex options