Treatment of Small Scale Land Surface Heterogeneity for Atmospheric Modelling

(SSSAM)

Günther Heinemann (1) and Michael Kerschgens (2)

1 Meteorologisches Institut der Universität Bonn, Auf dem Hügel 20, 53121 Bonn2 Institut für Geophysik und Meteorologie der Universität zu Köln, Kerperner Str. 13, 50923 Köln

Regional Evaporation at Grid / Pixel Scale over Heterogeneous Land Surfaces

Effects of land surface heterogeneity on atmospheric transports

Landsat TM 50m (Statistisches Bundesamt, 1997)

False colours0.63-0.690.76-0.901.55-1.75μm

20 km

Measurement areaLindenberg experimentsLITFASS 1998-2003

°C

Scha

rmüt

zels

ee

FOOT 250m (20km, 80x80)

Isamp=2

F=FalkenbergL=LindenbergW=WulfersdorfH=HerzbergK=Forst Kehrigk

idealizedFOOT simulationLITFASS 199817 June, 11 UTC

Mesoscale and convective organized transports (dynamical transports) Feedback processes between dynamical transports and subgrid turbulence

Dynamical effect

Effects of land surface heterogeneity on atmospheric transports

Investigation of the dynamical effect and its role in the vertical energy- and momentum transport

Goals SSSAM

Development of averaging strategies for vertical transports on the scale of weather forecast and regional climate models (Grid / Pixel Scale)

Non-hydrostatic numerical model FOOT3DKparameterizations:Vegetation and soil moisture: ISBA, Noilhan and Planton (1989)turbulent fluxes: SL: Louis (1979)PBL: prognostic TKE closuresubsurface heat flux: 2 layer modelradiation (two-stream)moist convection (Tiedke, 1989, modified Sogalla and Kerschgens, 2001)

grid:Arakawa-C40x40, 80x800.25-48 km21-31 -levelsnon-hydrostatic

input data:initial fields: LM (7km)synthetic data

Idealized simulations for idealized inhomogeneities and for the Lindenberg area: T/q profiles for 17 June 1998, idealized geostrophic forcing

Realistic simulations for the Lindenberg area

LM 7km FOOT 1km FOOT 0.25km

u, v, w, T, q, p, ug, vg

CLW, RRSoil: type, T, W

u, v, w, T, q, p, ug, vg

CLW, RRSoil: type, T, W

Treatment of heterogeneity effects for surface energy fluxes

w a k T V q za a

zL Sa eff' ' , , ,

( )

,,

00

0

Mahrt (1996) w a C V w V a a za e ff fc sg' ' ( ) ( ),

0

2 2 2

1 / 2

0

u v V sg

* *2 2 2 subgrid velocity scalewfc=w*= convection velocity scale

Ca,eff = effective exchange coefficient (e.g. from effective z0)

Mosaic method w aN

k T T V q q za a

zm o s aF x

' ' , , ,,0 0 0 0

01

w a k T V w q za a

zL S wa eff' ' , , ,

( )

, , ** ,

0

22

1 / 2

0

0

Standard mosaic method: T0, q0, a0 from 1D-SVAT model

‘Optimal‘ mosaic method: T0, q0, a0 from sub-grid model

Aggregation method

Aggregation methodmodified with w*

250m, LC = 4 km, Vg = 2 m/s, Fx = 12km

3 6 9 12 15 18 21

U TC

0

100

200

300

H0

,E0

in W

/m²

H0

H0,LS

H0,LS,w*

H0,LS m os

E0

E0,LS

E0,LS,w*

E0,LS m os

Idealized simulations meadow/bare soil

3 6 9 12 15 18 21

U TC

0

100

200

300

H0

,E0

in W

/m²

H0

H0,LS

H0,LS,w*

H0,LS m os

E0

E0,LS

E0,LS,w*

E0,LS m os

250m, LC = 4 km, Vg = 8 m/s, Fx = 12km

3 6 9 12 15 18 21

U TC

0

100

200

300

H0

,E0

in W

/m²

H0

H0,LS

H0,LS,w*

H0,LS m os

E0

E0,LS

E0,LS,w*

E0,LS m os

1 km, LC = 16 km, Vg = 2 m/s, Fx = 48km

3 6 9 12 15 18 21

U TC

0.8

1

1.2

1.4

Ra

tio

1km vg2 ratio sim /mosaic

LC1LC2LC4LC8LC16

3 6 9 12 15 18 21

U TC

0

100

200

300

H0

,E0

in W

/m²

H0

H0,LS

H0,LS,w*

H0,LS m os

E0

E0,LS

E0,LS,w*

E0,LS m os

250 m, LITFASS, Vg = 2 m/s, Fx = 12km, W = 60%

Idealized simulations LITFASS area

Realistic simulations LITFASS area 17 June 1998, nesting LM7

250 m, LITFASS, vg(LM)≈14 m/s , Fx = 12km, W = W(LM)

3 6 9 12 15 18 21

U TC

0

100

200

300

H0

,E0

in W

/m²

H0

H0,LS

H0,LS,w*

H0,LS m os

E0

E0,LS

E0,LS,w*

E0,LS m os

3 6 9 12 15 18 21

U TC

0

1

2

3

TK

E in

m²/

s²

250m_vg2_nes1km_12.km*12.km(48*48)

SKE

TKE

Idealized simulations LITFASS area

a a a a * ' T K E u i 1

22' S K E u i

1

2

2*

Subgrid and mesoscale TKE

3 6 9 12 15 18 21

U TC

0

1

2

3T

KE

in m

²/s

²

250m_n1km_litfass98_12.km*12.km(48*48)

SKE

TKE

Realistic simulations LITFASS area 17 June 1998, nesting LM7

TKE/SKE at 30m

vg(LM)≈14 m/s , Fx = 12 kmVg = 2 m/s, Fx = 12km

Non-linear effects for area-averaged surface fluxes

Q H E Bo 0 0 0

Energy balance

Q0H0

Q: net radiationE: latent heat fluxH: sensible heat fluxB: soil heat flux

E0

B0

Q H E Bo 0 0 0

w a ka

za' '0

B k WT

zSS

0 ( )

Q T q z N z0 0 , ( ( )), ( ), ...

1D Area average

Dependence on averaging scale

0 4 8 12

A veraging scale km

100

150

200

250

300

H0

,E0

in W

/m²

H0

H0,LS

H0,LS,w*

H0,mos

E0

E0,LS

E0,LS,w*

E0,mos

250m_n1km_litfass98

Realistic simulations LITFASS area 17 June 1998, nesting LM7

Average 9-17 UTC

250 m, LITFASS, vg(LM)≈14 m/s, W = W(LM)

0 4 8 12

A veraging scale km

100

150

200

250

300

H0

,E0

in W

/m²

H0

H0,LS

H0,LS,w*

H0,mos

E0

E0,LS

E0,LS,w*

E0,mos

250m_vg2_nes1km

Idealized simulations LITFASS area

Average 9-17 UTC

250 m, LITFASS, Vg = 2 m/s, W = 60%

H in W/m² H in W/m²

Idealized simulations LITFASS area

250 m, Fx = 2 km, vg=2 m/s250 m, Fx = 250 m, vg=2 m/s

250 m, Fx = 2 km, vg=2 m/s250 m, Fx = 2 km, vg=2 m/s

H0-H0,mosa in W/m²E0-E0,mosa in W/m²

Variance ff(30m) in m²/s²Variance T(0m) in K²

Summary

Method: FOOT3DK simulations (resolution down to 250m)idealized and realistic surfaces and synoptic forcings (LITFASS98)

Assessment of the dynamic effect for averaging methods (mosaic and aggregation) for scales of 10-20 km- dependence on the scale/structure of the heterogeneity- mosaic method yields good results for wind speeds exceeding 4 m/s

Scale dependence of area-averaged surface fluxes caused by non-linear effects- sub-grid TKE (SKE)- radiation and clouds- surface temperature and soil moisture

Outlook

LindenbergexperimentLITFASS 2003

EC

Profiles

Precip.

Precip./G

Scintillometer