kit – die kooperation von forschungszentrum karlsruhe gmbh und universität karlsruhe (th) the...

KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH)

The dependence of convection-related parameters on surface and boundary layer conditions

over complex terrain: results from the COPS experiment

N. Kalthoff, M. Kohler, Ch. Barthlott, L. Krauss, U. Corsmeier,

T. Foken, R. Eigenmann, S. Khodayar, P. Di Girolamo


The surface - atmosphere feedback loop consists of:

The impact of soil moisture on the surface fluxes

The influence of surface fluxes on the PBL conditions and convection-related parameters

The triggering and modification of convection by surface and PBL inhomo-geneities

The impact of convection on the condi-tions of the surface and atmosphere

Here we focus on part and :

CAPE, CIN

H E

PBL

Soil moisture

1

2

3

4

1

2

3

4

How strong is the impact of soil moisture > surface fluxes > PBL conditions >

convection-related parameters during COPS (i.e. over complex terrain)

1 2


1 COPS experimental setup

COPS domain (left) and measurement sites in the northern part of the COPS domain (right).

• Soil moisture network

• Energy balance and surface flux network

• Radiosonde network

Rhine valley: FZK, Achern/Baden Airpark

Black Forest: Hornisgrinde, Heselbach

We used data from the:


2.1 Impact of soil moisture on the surface characteristics

10

15

20

25

30

35

40

45

50

TS in

°C

15 20 25 30 35

vol,5 in %

FZK

Baden Airpark

10

15

20

25

30

35

40

45

50

TS in

°C

30 35 40 45 50 55 60 65 70

vol,5 in %

Heselbach

Hornisgrinde

a)

b)• Soil moisture increases with the elevation

• No dependence of the albedo on θvol

• Only in the Rhine valley: A dependence of the surface temperature, Ts, on θvol

=> Only in the Rhine valley a weak dependence of net radiation (available energy) on θvol was

observed

H E

1

Soil moisture

0.10

0.12

0.14

0.16

0.18

0.20

0.22

0.24

0.26

0.28

0.30

15 20 25 30 35 40 45 50 55 60 65 70

vol,5 in %

FZK

Baden Airpark

Heselbach

Hornisgrinde

alb

ed

o


0.0

0.2

0.4

0.6

0.8

1.0

H0/

Q0,

E0/

Q0

15 20 25 30 35

vol,5 in %

H0/Q0 E0/Q0

0.0

0.2

0.4

0.6

0.8

1.0

H0/

Q0,

E0/

Q0

15 20 25 30 35

vol,5 in %

H0/Q0 E0/Q0

a) b)

0.0

0.2

0.4

0.6

0.8

1.0

H0/

Q0,

E0/

Q0

25 30 35 40 45

vol,5 in %

H0/Q0 E0/Q0

c)

0.0

0.2

0.4

0.6

0.8

1.0

H0/

Q0,

E0/

Q0

55 60 65 70 75

vol,5 in %

H0/Q0 E0/Q0

d)

2.2 Impact of soil moisture on the surface fluxes

Rhine valley

•Ho/Qo is slightly lower for higher soil moisture

•Eo/Qo is slightly higher for higher soil moisture

Black Forest

•No dependence of Ho/Qo and Eo/Qo on soil moisture

=> During the COPS period the impact of soil moisture on the surface

characteristics and on the surface fluxes was weak – probably due to the high

vegetation coverage!


3.1 The dependence of zi on the sensible heat flux

0

500

1 000

1 500

2 000

2 500

zi i

n m

ag

l

0 20 40 60 80 100 120 140 160

H0 in W m-2

0

500

1 000

1 500

2 000

2 500

z i in

m a

gl

0 20 40 60 80 100 120 140 160

H0 in W m-2

FZK

Achern

Heselbach

0

500

1 000

1 500

2 000

2 500

z i in

m a

gl

0 20 40 60 80 100 120 140 160

H0 in W m-2

Hornisgrinde

a)

b)

c)

• In the Rhine valley (FZK, Achern) and at Heselbach a weak correlation between zi and Ho was found

• Over the mountain crest (Hornisgrinde) zi is independent of Ho

2

3

H E

PBL

Soil moisture

1

2


3.2 The impact of the surface fluxes on Θe in the PBL

-3

-2

-1

0

1

2

3

4

5

et

-1 in

K h

-1

0 100 200 300 400 500 600

H0 + E0 in W m-2

-3

-2

-1

0

1

2

3

4

5

e t

-1 in

K h

-1

0 100 200 300 400 500 600

H0 + E0 in W m-2

Baden Airpark

FZK

Heselbach

Hornisgrinde

a)

b)

• The dependence of the diurnal increase of moist static energy / Θe in the Rhine valley (FZK, Baden Airpark) and at Heselbach is weak

• There is nearly no dependence of the evolution of the moist static energy / Θe at the mountain crest (Hornisgrinde)

=> Especially in the Black Forest the impact of the surface fluxes on the PBL conditions (zi, Θe ) is weak, i.e. advection processes must be important for the evolution of the PBL


4.1 Dependence of convection indices on PBL conditions

0

200

400

600

800

1 000

1 200

1 400

CA

PE

in J

kg

-1

300 310 320 330 340 350

e in K

a) b)

-20

-15

-10

-5

0

5

10

15

20

KO

in K

300 310 320 330 340 350

e in K

c)

-20

-15

-10

-5

0

5

10

15

20

KO

in K

300 310 320 330 340 350

e in K

d)

0

200

400

600

800

1 000

1 200

1 400

CA

PE

in J

kg

-1

300 310 320 330 340 350

e in K

Achern

FZK

Heselbach

Hornisgrinde

Heselbach

Hornisgrinde

Achern

FZK

-10

-5

0

5

10

15

20

25

30

LI i

n K

300 310 320 330 340 350

e in K

e)

-10

-5

0

5

10

15

20

25

30

LI i

n K

300 310 320 330 340 350

e in K

f)

Heselbach

Hornisgrinde

Achern

FZK

• The convection indices CAPE, LI (conditional instability)

and

KO (potential instability) are highly correlated with Θe in the PBL

• This finding is valid for the Rhine valley and the Black Forest!

H E

PBL

Soil moisture

1

2CAPE, CIN


4.1 Dependence of evolution of the convection indices on the PBL evolution

• The diurnal increase of CAPE, LI and KO was caused by the PBL evolution on most of the days

Original CAPE, LI and KO values at Heselbach

Modified CAPE, LI and KO values:

initial nocturnal profile but in PBL the data are replaced by the conditions at noontime

Strong changes in the mid- and upper troposphere


0

50

100

150

200

250

300

350

400C

IN i

n J

kg

-1

0 500 1 000 1 500 2 000 2 500

zi in m agl

0

50

100

150

200

250

300

350

400

CIN

in

J k

g-1

0 500 1 000 1 500 2 000 2 500

zi in m agl

a) b)

c) d)

Achern

FZK

Heselbach

Hornisgrinde

0

2

4

6

8

10

CA

P in

K

0 500 1 000 1 500 2 000 2 500

zi in m agl

0

2

4

6

8

10

CA

P in

K

0 500 1 000 1 500 2 000 2 500

zi in m agl

Heselbach

Hornisgrinde

Achern

FZK

4.2 Dependence of convection inhibition on PBL conditions

• The higher zi the lower the upper threshold for CIN and CAP strength

This was observed at all sites!

• CIN and CAP strength were independent of Θe in the PBL

CAP=max(Te-Tp)


0

100

200

300

400

500

600

CIN

in J

kg

-1

0 2 4 6 8 10

CAP in K

Achern

FZK

Heselbach

Hornisgrinde

a)

b)

0

100

200

300

400

500

600

CIN

in J

kg

-1

0 200 400 600 800 1 000 1 200 1 400

CAPE in J kg-1

Achern

FZK

Heselbach

Hornisgrinde

0

10

20

30

40

50

60

70

freq

uen

cy in

%

0 50 100 150 200 250 300 350 400 450 500

CIN in J kg-1

Rhine valley

Black Forest

• A good correlation between CIN and CAP strength existed at all sites

• The occurrence of low CIN values was higher over the Black Forest than over the Rhine valley

=> Lower CIN values are favourable for convection initiation over the mountains

4.3 Characteristics of convection inhibition


5 Conclusions

Soil > surface

The impact of soil moisture on the surface parameters (α, Ts, Qo) and on the energy transformation at the Earth‘s surface (β) is weak

Surface > PBL

Rhine valley: The dependence of the PBL characteristics like Θe and zi on the surface fluxes is weak

Black Forest: Nearly no dependence of the PBL characteristics like Θe and zi on the surface fluxes

=>Consequently, advection processes must be important for the evolution of the PBL - especially over the mountains

PBL > Convection-related parameters

CAPE, LI and KO depend on Θe in the PBL (observed at all site)The impact of PBL conditions on CIN and CAP is weak (except: max CIN and max CAP depend on zi) CAP and CIN are highly correlatedThe frequency of occurrence of low CIN values is higher over the Black Forest than over the Rhine valley => Favours CI over the mountains


Outline

1 Introduction

2 Experimental setup

3 Impact of soil moisture on the surface characteristics and

the turbulent fluxes

4 The dependence of CBL conditions on the turbulent fluxes

5 The dependence of convection-related parameters on

boundary-layer conditions

6 Conclusions


3 Impact of the surface fluxes on the CBL conditions

For homogeneous terrain:

• zi is higher for higher Ho and for higher

Bowen ratio

• CIN and CAPE depend the surface and PBL conditions in the PBL (β => q, Θ, Θe, zi)

• What about the dependences over complex terrain?

2

3

H E

PBL

Soil moisture

1

2


2 Impact of soil moisture on the surface characteristics and the turbulent fluxes

• Precipitation increases with elevation

• Soil moisture, θvol, increases with elevation

H E1

Soil moisture


4

H E

1

Soil moisture

CAPE, CIN

2

H E

PBL

Soil moisture

1

2

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