Slide 1 PA Surface II of IV - training course 2006 Slide 1 Introduction General remarks Model development and validation The surface energy budget Soil

PA Surface II of IV - training course 2006

Slide 1

Slide 1

Introduction

General remarks

Model development and validation

The surface energy budget

Soil heat transfer

Soil water transfer

Surface water fluxes

Initial conditions

Snow

Conclusions and a look ahead

Layout


Slide 2

Slide 2

Thermal budget of a ground layer at the surface

G

SR

SR

D

TgR

4Tg

H

LE

G nR H LE

Day

Night

( ) sg n

TC D R H LE G

t


Slide 3

Slide 3

Energy budget: Summer examplesDry

Barley field

Fir canopy

Arya, 1988

n N

G

L

R R

G H

H H

LE H


Slide 4

Slide 4

The surface radiation

In some cases (snow, sea ice, dense canopies) the impinging solar radiations penetrates the “ground” layer and is absorbed at a variable depth. In those cases, an extinction coefficient is needed.

sks

sk

g

skgTgSn

TT

T

TRRR

4)1(

Surface albedo

Surface emissivity

Skin temperature

Arya, 1988


Slide 5

Slide 5

The other terms

,

( , )

( , ,state and nature of the soil,soil cover)h L L h L L L s sat sk s

L s L s

sE C u q C u a q a q T p

a f q T

q

Evaporation

omoh

omohBh

skpLpLh

zz

zzRifC

TCgzTCuCH

,

),,(

)(

Sensible heat flux

specify the surface

)(f,Cz

T

zz

G

t

TC

Tg

Ts

g

sticscharacteri soilother type, soil

Ground heat flux


Slide 6

Slide 6

Recap: The surface energy equation

Equation for

For:

- a thin soil layer at the top

- G (Ts,Tsk) is known, or parameterized or G << Rn

we have a non-linear equation defining the skin temperature

t

TDC)T,T(G)p,T(qaqauC

)TCgzTC(uCTRR)1(

sgsksssksatsLLLh

skpLpLh4skgTgS

sks TT ,

0t

TDC s

g


Slide 7

Slide 7

Skin layer at the interface between soil (snow) and atmosphere; no thermal inertia, instantaneous energy balance

At the interface soil/atmosphere, each grid-box is divided into fractions (tiles), each fraction with a different functional behaviour. The different tiles see the same atmospheric column above and the same soil column below.

If there are N tiles, there will be N fluxes, N skin temperatures per grid-box

There are currently up to 6 tiles over land (N=6)

TESSEL

N,...,1i

i

TTG i,sksi,ski

for tileindex


Slide 8

Slide 8

TESSEL skin temperature equation

Grid-box quantities

4,

,

,

,

, , ,

, ,

(1 )

( )

( , )

( ) 0

i S g T g

h i L

sk i

skp L p

h i L L i L s i sat s

sk i s

i

sk i

sk i

R R

C u C T gz C

C

T

T

u a q a q pT

TT

fraction Tile

,

i

iiskisk

iii

iii

C

TCT

ECE

HCH


Slide 9

Slide 9

Tiles

Interception layer

Bare ground

Snow on low vegetation

High vegetation with snow beneath

Sea ice / frozen lakesLow vegetation

Open sea / unfrozen lakesHigh vegetation

Sea and iceLand


Slide 10

Slide 10

TESSEL geographic characteristics

Annual, Dependent on vegetation type

1 m

Global constant

Root depth

Root profile


Global constantsLAI

rsmin

MonthlyAnnualAlbedo

Dominant low type

Dominant high type

Global constant (grass)

Vegetation type

Fraction of low

Fraction of high

FractionVegetation

TESSELERA15Fields


Slide 11

Slide 11

High vegetation fraction at T511 (now at T799)

Aggregated from GLCC 1km


Slide 12

Slide 12

Low vegetation fraction at T511 (now at T799)



Slide 13

Slide 13

High vegetation type at T511 (now at T799)



Slide 14

Slide 14

Low vegetation type at T511 (now at T799)



Slide 15

Slide 15

Introduction

General remarks



Soil heat transfer

Soil water transfer


Initial conditions

Snow


Layout


Slide 16

Slide 16

Soil science miscellany (1)

The soil is a 3-phase system, consisting of

- minerals and organic matter soil matrix

- water condensate (liquid/solid) phase

- moist air trapped gaseous phase

Texture - the size distribution of soil particles

Hillel 1982, 1998


Slide 17

Slide 17

Soil science miscellany (2)

Structure - The spatial organization of the soil particles

Porosity - (volume of maximum air trapped)/(total volume)

Composition

Water content

Hillel 1982,1998

Reference:Hillel 1998 Environmental Soil Physics, Academic Press Ed.


Slide 18

Slide 18

Soil properties

Rosenberg et al 1983

Arya 1988


Slide 19

Slide 19

Ground heat flux

2

2s

g

T

T

g

Ts

g

z

Tk

t

T

k

Cz

T

zz

G

t

TC

soil, shomogeneou anFor

ydiffusivit Thermal C

tyconductivi Thermal

capacityheat volumetric Soil

In the absence of phase changes, heat conduction in the soil obeys a Fourier law

Boundary conditions:•Top Net surface heat flux•BottomNo heat flux OR prescribed climate


Slide 20

Slide 20

Diurnal cycle of soil temperature

summer

winter

bare sod

Rosenberg et al 1983

50 cm depth

surface

summer


Slide 21

Slide 21

TESSEL

Solution of heat transfer equation with the soil discretized in 4 layers, depths 7, 21, 72, and 189 cm.

No-flux bottom boundary condition

Heat conductivity dependent on soil water

Thermal effects of soil water phase change

↓ 10.6 ~ 55.8 d

↓0.1~0.6 d

↓ 1.1~5.8 d

Time-scale for downward heat transfers in wet/dry soil


Slide 22

Slide 22

TESSEL soil energy equations

0G

TTG

DD5.0

TTG

D

GGTT

t

C

2/41

i1i,ski,sk2/1

1jj

1nj

1n1j

2/1j,T1n2/1j

j

1n2/1j

1n2/1jn

j1n

jj

conditions Boundary

1,...,4j

DjTj

j-1

j+1

Gj+1/2

Gj-1/2


Slide 23

Slide 23

Case study: winter (1)

Model vs observations, Cabauw, The Netherlands, 2nd half of November 1994

Soil

140 m

2 m


Slide 24

Slide 24

Case study: winter (2)Soil Temperature, North Germany, Feb 1996: Model (28-100 cm) vs OBS 50 cm

Observations: Numbers

Model: Contour


Slide 25

Slide 25

Model bias:- Net radiation (Rnet) too large

- Sensible heat (H) too small

But (Tair-Tsk) too large (too large diurnal cycle)

Therefore f(Ri) problem

- Soil does not freeze (soil temperature drops too quickly seasonally)


T air

T skin

Rnet H LE

G

))(( skairHnairp TTRifCUCH

Stability functions

Soil water freezing

Viterbo, Beljaars, Mahfouf, and Teixeira, 1999: Q.J. Roy. Met. Soc., 125,2401-2426.


Slide 26

Slide 26

Winter: Soil water freezing

water frozen Soil

T

I

Iwfs t

Lz

T

zt

T)C(

Soil heat transfer equation in soil freezing condition

)T(f)T(II

z

T

zt

T

T

fL)C( Twfs

Apparent heat capacity


Slide 27

Slide 27


1 Oct 1 Jan1 Dec

1 Nov 1 Feb

Germany soil temperature: Observations vs Long model relaxation integrations

Observations

Control

Stability

Stab+Freezing


Slide 28

Slide 28

Northern Hemisphere


Soil water freezing acts as a thermal regulator in winter, creating a large thermal inertia around 0 C.

Simulations with soil water freezing have a near-surface air temperature 5 to 8 K larger than control.

In winter, stable, situations the atmosphere is decoupled from the surface: large variations in surface temperature affect only the lowest hundred metres and do NOT have a significant impact on the atmosphere.

Europe

850 hPa T RMS forecast errors

Stab+freezing

Control


Slide 29

Slide 29

Introduction

General remarks



Soil heat transfer

Soil water transfer


Initial conditions

Snow


Layout


Slide 30

Slide 30

More soil science miscellany

3 numbers defining soil water properties

- Saturation (soil porosity) Maximum amount of water that the soil can hold when all pores are filled 0.472 m3m-3

- Field capacity “Maximum amount of water an entire column of soil can hold against gravity” 0.323 m3m-3

- Permanent wilting point Limiting value below which the plant system cannot extract any water 0.171 m3m-3

Hillel 1982Jacquemin and Noilhan 1990


Slide 31

Slide 31

Schematics

extractionroot ie k,source/sin water Soil

flux water Soil

water soil 12

33

S

skgmF

mm

Sz

F

t ww

Hillel 1982

Root extraction The amount of water transportedfrom the root system up to the stomata(due to the difference in the osmoticpressure) and then available fortranspiration

Boundary conditions:Top See laterBottom Free drainage or bed rock


Slide 32

Slide 32

Soil water flux

1

12

ty conductivi hydraulic

y diffusivit hydraulic

)(

ms

sm

zF w

Darcy’s law

> 3 orders of

magnitude> 6 orders of

magnitude

Mahrt and Pan 1984


Slide 33

Slide 33

TESSEL: soil water budget

Solution of Richards equation on the same grid as for energy

Clapp and Hornberger (1978) diffusivity and conductivity dependent on soil liquid water

Free drainage bottom boundary condition

Surface runoff, but no subgrid-scale variability; It is based on infiltration limit at the top

One soil type for the whole globe: “loam”


Slide 34

Slide 34

TESSEL soil water equations (1)

2/412/412/12/1

2/11

111

2/11

2/1

,

12/1

12/1

1

conditionsBoundary

5.0

ws

jjj

nj

nj

jwnj

jwj

nj

nj

nj

nj

w

FEYTF

DDF

SD

FF

t

Dj

j-1

j+1

Fj+1/2

Fj-1/2

j ↓ 11.7 ~ >> d

↓0.1~19.7 d

↓ 1.2~195.9 d

Time-scale for downward water transfers in wet/dry soil


Slide 35

Slide 35

TESSEL soil water equations (2)

2

32

,/,

,/,//,

tscoefficien Hydraulic

1,...,4j

n vegetatio(H/L) high/lowfor separate j,layer at extractionRoot

b

satsat

satsat

b

satsat

jjliqjLHj

jliqjLHjLHLHjw

b

DR

DRCS


Slide 36

Slide 36

TESSEL geographic characteristics


1 m

Global constant

Root depth

Root profile


Global constantsLAI

rsmin

MonthlyAnnualAlbedo

Dominant low type

Dominant high type

Global constant (grass)

Vegetation type

Fraction of low

Fraction of high

FractionVegetation

TESSELERA15Fields


Slide 37

Slide 37

FIFE: Time evolution of soil moisture

Viterbo and Beljaars 1995

pwp cap

Tim

e

pwp cap

156

167

184

177

217

213

191

226

231

247

257

268

276

285

June

July

August

September

October

z

Documents

Slide 1 PA Surface II of IV - training course 2006 Slide 1 Introduction General remarks Model development and validation The surface energy budget Soil