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LM Physics Overview and Outlook

Marco Arpagaus

28 th EWGLAM and 13 th SRNWP Meeting Zurich, 9-12 October 2006

Radiation

Scheme: • δ-two stream radiation scheme after

Ritter and Geleyn

(1992) for short- and long-wave fluxes; full cloud radiation feedback.

Recent Extensions: • Quasi-3d: Inclusion of 3d

orographic effects

on radiation (shadowing, slope angle, slope aspect, sky view).

• Upscaling: Use of

coarser horizontal mesh

to run the 1d radiation scheme in favour of running the scheme more often (aim: use 2*2 grid-points and reduce update frequency from hourly to every 15 min).

LM Physics

| Overview and Outlook Marco Arpagaus ( [email protected]

), Consortium for Small-Scale Modelling (COSMO) 3

Radiation: Quasi-3d and upscaling

Average solar surface radiation budget

since forecast start (4 April 2005 00 UTC + 8 hrs) original LM grid ( 2.8 km mesh-size ) difference plot: version with topographic corrections

minus

version without topographic corrections coarser (2x2) grid W/m 2

LM Physics

| Overview and Outlook Marco Arpagaus ( [email protected]

), Consortium for Small-Scale Modelling (COSMO) 4

Grid-scale clouds and precipitation

• • Operational schemes:

Cloud-ice

scheme:

5-class

(vapour, cloud-water, ice , rain, and snow ) single-moment scheme.

cloud-

Graupel

scheme:

6-class

(vapour, cloud-water, cloud-ice , rain, snow , and graupel ) single-moment scheme

for convection-resolving scales

.

Additional schemes: • Seifert-Beheng (2006): 6 class

two-moment scheme

• Reisner-Thompson (2004): 6 class single-moment scheme

LM Physics

| Overview and Outlook Marco Arpagaus ( [email protected]

), Consortium for Small-Scale Modelling (COSMO) 5

Grid-scale clouds and precipitation: Graupel scheme

Problem:

underestimation of precipitation amounts for convection-resolving LM.

Cure:

Use hail instead of graupel

of idealised strong convection)?

(as suggested by studies  No!

r g N 0  0.2 g/cm 3 = 4*10 6 m -4 LM ( 2.8 km mesh-size ), 7 August 2004 r g N 0  0.9 g/cm 3 = 4*10 4 m -4 radar

LM Physics

| Overview and Outlook Marco Arpagaus ( [email protected]

), Consortium for Small-Scale Modelling (COSMO) 6

Grid-scale clouds and precipitation: Prognostic precipitation

Problem:

Orographic luv/lee pattern of precipitation.

(Partial) solution:

full

prognostic treatment

hydrometeors (e.g., rain, snow, and graupel).

of precipitating LM – radar; north-westerly flow only ( 7 km mesh-size ) 2004 2005

LM Physics

| Overview and Outlook Marco Arpagaus ( [email protected]

), Consortium for Small-Scale Modelling (COSMO) 7

Convection: For 7 km mesh size or larger …

• Operational:

Tiedtke

mass-flux scheme (1989); closure based on moisture convergence.

• Options: • • Tiedtke scheme with CAPE closure.

Kain-Fritsch

mass-flux scheme (1993) by Kain.

• Recently tested:

Kain-Fritsch

mass-flux scheme by Bechtold (2001), with closure based on CAPE. •  Results: •

Improved diurnal cycle

• •

Spin-up problem

.

(over flat terrain).

(Stronger)

overestimation of precipitation amounts

, especially for light precipitation.

Code no longer maintained (???). – Test of IFS scheme instead?

LM Physics

| Overview and Outlook Marco Arpagaus ( [email protected]

), Consortium for Small-Scale Modelling (COSMO) 8

Convection: For convection resolving scales …

No

parameterisation scheme for (deep) convection.

This however generates a serious problem:

• Boundary layer too moist.

• Low cloud cover too high.

 Insufficient transport of moisture through top of the boundary layer!

Quick solution:

Use of

Tiedtke

scheme for

shallow convection

only.

Envisaged long-term solution:

Unification of turbulence and shallow convection scheme.



UTCS project.

LM Physics

| Overview and Outlook Marco Arpagaus ( [email protected]

), Consortium for Small-Scale Modelling (COSMO) 9

Turbulence

•

2 nd -order one-equation closure

scheme:

prognostic TKE

, algebraic relations for other 2 nd -order moments. Included are: • subgrid-scale condensation and evaporation (moist conservative variables); • effect of subgrid-scale horizontal inhomogeneity of the underlying surface (additional source of TKE, most notably in the stably stratified PBL).

• Surface-layer transfer scheme with a laminar-turbulent roughness sub-layer.

• Extensions: 

UTCS project.

LM Physics

| Overview and Outlook Marco Arpagaus ( [email protected]

), Consortium for Small-Scale Modelling (COSMO) 10

Lower boundary condition: Known surface types in LM

A grid box is covered

completely

either by

sea / sea ice:

externally prescribed surface temperature; constant during integration

land:

soil temperature and water content predicted by soil and vegetation model

TERRA rock or ice:

impermeable for water; temperature profile simulated by

TERRA lake:

prognostic surface temperature (water or ice) forecasted by lake model

Flake LM Physics

| Overview and Outlook Marco Arpagaus ( [email protected]

), Consortium for Small-Scale Modelling (COSMO) 11

Multi-layer soil and vegetation model

Two-layer TERRA (old) Multi-layer TERRA (new) Interception Interception Snow Snow 0.01 m 0.1 m 1.0 m no water flux prescribed T

* * * *

free drainage 0.81 m 2.43 m Modification for thermal part: 7.29 m solution of

heat conduction equation

instead of extended force restore method constant T 

arbitrary number (and thickness) of soil layers



freezing/melting of soil water

included (improved T2m in Winter)  simpler lower boundary condition

LM Physics

| Overview and Outlook Marco Arpagaus ( [email protected]

), Consortium for Small-Scale Modelling (COSMO) 12

Multi-layer soil and vegetation model

Further modifications: • thermal part: • simplified treatment of melting snow •

time-dependent snow density

(  [50, 400] kg/m 3 ; to reduce negative T2m bias over snow) •

dependence of snow albedo on time and forest cover

(  [0.7, 0.2]; to reduce negative T2m bias over snow) • hydrological part: •

new lower boundary condition

(no water flux  gravitational drainage) • Problems:

soil dries out

(especially lower layers)

LM Physics

| Overview and Outlook Marco Arpagaus ( [email protected]

), Consortium for Small-Scale Modelling (COSMO) 13

New: Lake Model ‚ FLake ‘

(D. Mironov et al., see http://nwpi.krc.karelia.ru/flake)

A computationally-efficient

lake parameterisation scheme

based on the idea of self-similarity (assumed shape, similar to the mixed-layer idea) of the evolving temperature profile.

Prognostic variables are … • the surface temperature, • the mean temperature of the water column, • the bottom temperature, • the mixed-layer depth, • the depth within bottom sediments penetrated by the thermal wave, and the temperature at that depth (bottom sediment module may be switched off).



S (t)

Snow Ice Water 

I (t)



s (t)



b (t) -H I (t)-H S (t) -H I (t) h(t)



H (t) D

… plus in case of ice-covered lake • the ice thickness, • the temperature at the ice upper surface, • the snow thickness, and the temperature at the snow upper surface (in the present pre-operational configuration, snow is treated in a simplified way). Sediment (b)

LM Physics

| Overview and Outlook Marco Arpagaus ( [email protected]

), Consortium for Small-Scale Modelling (COSMO) 

L H(t) L

15

New: Lake Model ‚FLake‘

Single column test: LM test suite: Lake Balaton, 2006 26 25 24 23 22 21 20 FLake 19 18 0 observations 48 96 144 192

time, h

lake surface temperature 240 288 336 test operational (SST analysis) ice thickness FLake is able to simulate diurnal as well as seasonal variations of lake surface temperature (T of water surface or of ice surface) realistically!

LM Physics

| Overview and Outlook Marco Arpagaus ( [email protected]

), Consortium for Small-Scale Modelling (COSMO) 16

Lower boundary condition: New developments

•

Urban model

• development within the FUMAPEX project •

Mosaic & tile approach

• is currently being implemented •

Measurement derived soil moisture analysis

• • based on a standalone version of TERRA driven by observations

LM Physics

| Overview and Outlook Marco Arpagaus ( [email protected]

), Consortium for Small-Scale Modelling (COSMO) 17

COSMO Priority Projects

•

UTCS

: Towards a Unified Turbulence Shallow Convection Parameterisation  talk by Dmitrii Mironov •

QPF

: Tackle deficiencies in Quantitative Precipitation Forecasts

LM Physics

| Overview and Outlook Marco Arpagaus ( [email protected]

), Consortium for Small-Scale Modelling (COSMO) 18

Quantitative Precipitation Forecasts

Aim: Study LM ( 7 km mesh-size )

deficiencies concerning QPF

by running

sensitivity experiments

on a series of

well chosen cases with poor model performance.

 Results expected by September 2007.

18 March 2005

LM Physics

| Overview and Outlook Marco Arpagaus ( [email protected]

), Consortium for Small-Scale Modelling (COSMO) 19

To conclude …

• More information: Scientific documentation available on COSMO web-site at http://www.cosmo-model.org/public/documentation.htm

.

• Acknowledgements: All COSMO members, especially colleagues of Working Group 3 ‘Physical Aspects’.

•

Thank you for your attention!

LM Physics

| Overview and Outlook Marco Arpagaus ( [email protected]

), Consortium for Small-Scale Modelling (COSMO) 20