28th ewglam meeting, zurich, october 2006 alaro physics developments at lace neva pristov lace...

28th EWGLAM meeting, Zurich, October 2006

ALARO Physics developments at LACE

Neva Pristov

LACE Working group for physisc


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


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


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


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


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



red – liquid clouds, blue – ice clouds, black – mixed clouds

Saturation factor versus optical depth for homogeneous clouds, solar band

k_absorbtion k_scatter



parameterized versus reference solar reflectance, sample of non-homogeneous 3 layer clouds

old new



Solar absorbtion new (blue) versus old (red) scheme

Problematic peak around model level 20


Statistical method for the weighting function in NER

parameterized versus computed thermal flux


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


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


Academic test with 1D model: GABLS II experiment


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


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


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


Academic test with 1D model: GABLS II experiment

• Vertical profile and time course of mixing length

Modified GC GC +BL89

PBL top


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


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


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


ALARO-0 minus 3MT

better space distribution of precipitation

oper alaro

6h precipitation6h precipitation


ALARO-0 minus 3MT

Vertical profiles of horizontal averaged values

cloud water cloud ice


Plans

• Evaluation of parameterization developments Technical and scientific validation Case studies, verification

• Training

• Continuation of work Convection (3MT) More complex options

28th ewglam meeting, zurich, october 2006 alaro physics developments at lace neva pristov lace...

Documents

ewglam meeting

thermal slide

developments slide

physisc slide

experiment slide

scatter slide

simon slide

f h pbl slide