ALARO Physics developments at LACE

1
ALARO Physics developments at LACE

• Neva Pristov
• LACE Working group for physisc

2
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

3
Main developments topics

• Radiation
• Orographic forcing
• Large scale precipitation
• Prognostic turbulent scheme
• Precipitating convection

J-F Geleyn, G. Hello, N. Pristov, Y. Bouteloup,
M. Derkova, J. Mašek, A.Trojakova, R. Fournier
B. Carty, F. Bouyssel, R. Brožkova, J-F Geleyn,
M. Derkova, R. Mladek, J. Cedilnik, D. Drvar, I.
Beau
B. Carty, J-F Geleyn, R. Brožkova, J. Cedilnik,
D. Drvar
F. Vana, J. Cedilnik, M. Tudor, J-F Geleyn,
A.Simon
Luc Gerard, J-M Piriou, D. Banciu, I.Stiperski,
R. Brožkova, J-F Geleyn
4
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

5
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

6
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

7
Cloud optical properties
Saturation factor versus optical depth for
homogeneous clouds, solar band
k_absorbtion
k_scatter
red liquid clouds, blue ice clouds, black
mixed clouds
8
Cloud optical properties
parameterized versus reference solar reflectance,
sample of non-homogeneous 3 layer clouds
new
old
9
Cloud optical properties
Solar absorbtion new (blue) versus old (red)
scheme
Problematic peak around model level 20
10
Statistical method for the weighting function in
NER
parameterized versus computed thermal flux
11
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

12
TKE vs pseudoTKE
full

• advection
• diffusion
• mechanical or shear
  production/destruction
• buoyancy production/consumption
• viscous dissipation

pseudo
advection
diffusion Newtonian relaxation
towards stationary solution
13
Academic test with 1D model GABLS II experiment
14
Mixing length computation - current formulation

• Empirical formula dependent on the height of the
  PBL (Ayotte, et al. 1996)

Increase of the mixing length with the PBL height
(hPBL)
? f (z, hPBL) -exponential function
Modifications ? ? ?1 , ?2 ?
f (hPBL)
15
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

16
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)

17
Academic test with 1D model GABLS II experiment

• Vertical profile and time course of mixing length

PBL top
Modified GC
GC BL89
18
3-D case strong jet stream

• 15 December 2005, Northern Germany
• TKE and ? cross-sections

only small TKE (no CAT)
Modified GC
BL89
19
3-D case strong jet stream

• GCBL89 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
20
Mixing length - conclusion

• GCBL89 reasonable solution for both PBL and
  upper troposphere
• rather neutral results for surface parameters
  (wind, MSL pressure)
• tuning, more case studies in 3-D, verification
  (scores)

21
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

22
ALARO-0 minus 3MT
6h precipitation
6h precipitation
alaro
oper
better space distribution of precipitation
23
ALARO-0 minus 3MT
Vertical profiles of horizontal averaged values
cloud water
cloud ice
24
Plans

• Evaluation of parameterization developments
• Technical and scientific validation
• Case studies, verification
• Training
• Continuation of work
• Convection (3MT)
• More complex options