LM Physics Overview and Outlook

Federal Department of Home Affairs FDHAFederal Office of Meteorology and Climatology MeteoSwiss

LM PhysicsOverview and Outlook

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

Marco Arpagaus

3 LM Physics | Overview and OutlookMarco Arpagaus ([email protected]), Consortium for Small-Scale Modelling (COSMO)

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).


Radiation:Quasi-3d and upscalingAverage solar surface radiation budget since forecast start (4 April 2005 00 UTC + 8 hrs)

difference plot: version with topographic corrections minusversion without topographic corrections

original LM grid (2.8 km mesh-size)

coarser (2x2) grid

W/m2


Grid-scale clouds and precipitation

Operational schemes:

• Cloud-ice scheme: 5-class (vapour, cloud-water, cloud-ice, rain, and snow) single-moment scheme.

• Graupel scheme: 6-class(vapour, cloud-water,

cloud-ice, rain, snow, and graupel) single-moment schemefor convection-resolving scales.

Additional schemes:• Seifert-Beheng (2006): 6 class two-moment scheme• Reisner-Thompson (2004): 6 class single-moment scheme


g 0.9 g/cm3

N0 = 4*104 m-4

radarg 0.2 g/cm3

N0 = 4*106 m-4

Grid-scale clouds and precipitation: Graupel schemeProblem: underestimation of precipitation amounts for convection-resolving LM.

Cure: Use hail instead of graupel (as suggested by studies of idealised strong convection)?

No!

LM (2.8 km mesh-size), 7 August 2004


Grid-scale clouds and precipitation:Prognostic precipitation

LM – radar; north-westerly flow only (7 km mesh-size)

2004 2005

Problem: Orographic luv/lee pattern of precipitation.

(Partial) solution: full prognostic treatment of precipitating hydrometeors (e.g., rain, snow, and graupel).


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 (over flat terrain).• Spin-up problem.• (Stronger) overestimation of precipitation amounts,

especially for light precipitation.

Code no longer maintained (???).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


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.


Turbulence

• 2nd-order one-equation closure scheme: prognostic TKE, algebraic relations for other 2nd-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.


Lower boundary condition: Known surface types in LM

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

A grid box is covered completely by either


Multi-layer soil and vegetation model

Modification for thermal part: solution of heat conduction equation instead of extended force restore method arbitrary number (and thickness) of soil layers

freezing/melting of soil water included (improved T2m in Winter)

simpler lower boundary condition

InterceptionSnow

no water flux

prescribed T

Two-layer TERRA (old)

1.0 m

0.1 m

Snow

constant T

free drainage

***

*

Multi-layer TERRA (new)

*

*

Interception

2.43 m

7.29 m

0.01 m

0.81 m


Multi-layer soil and vegetation model

Further modifications:

• thermal part:• simplified treatment of melting snow• time-dependent snow density

( [50, 400] kg/m3; 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)


New: Lake Model ‚FLake‘ (D. Mironov et al., see http://nwpi.krc.karelia.ru/flake)

s(t)

b(t)

I(t)

S(t)

(b)

L

H

(t)

h(t)

D

L

H(t)

-HI(t)

-HI(t)-H

S(t)

Snow

Ice

Water

Sediment

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).

… 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).


New: Lake Model ‚FLake‘

0 48 96 144 192 240 288 33618

19

20

21

22

23

24

25

26

time, h

s-

f , K

Single column test:Kossenblatter See, June 1998

FLakeobservations

ice thickness

LM test suite:Lake Balaton, 2006

testoperational (SST analysis)

lake surface temperature

FLake is able to simulate diurnal as well as seasonal variations of lake surface temperature (T of water surface or of ice surface) realistically!


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


COSMO Priority Projects

• UTCS: Towards a Unified Turbulence Shallow Convection Parameterisation

talk by Dmitrii Mironov

• QPF: Tackle deficiencies in Quantitative Precipitation Forecasts


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


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!

Documents

LM Physics Overview and Outlook