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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. CAPE, CIN. PBL. H. E.

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The dependence of convection-related parameters on surface and boundary layer conditions over complex terrain: results from the COPS experimentN. Kalthoff, M. Kohler, Ch. Barthlott, L. Krauss, U. Corsmeier, T. Foken, R. Eigenmann, S. Khodayar, P. Di Girolamo

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

the surface atmosphere feedback loop consists of

CAPE, CIN

PBL

H

E

Soil moisture

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The surface - atmosphere feedback loop consists of:

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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 :

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How strong is the impact of soil moisture > surface fluxes > PBL conditions > convection-related parameters during COPS (i.e. over complex terrain)

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

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1 COPS experimental setup

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

We used data from the:

  • Soil moisture network
  • Energy balance and surface flux network
  • Radiosonde network

Rhine valley: FZK, Achern/Baden Airpark

Black Forest: Hornisgrinde, Heselbach

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

2 1 impact of soil moisture on the surface characteristics

albedo

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Soil moisture

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2.1 Impact of soil moisture on the surface characteristics
  • 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

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

2 2 impact of soil moisture on the surface fluxes
2.2 Impact of soil moisture on the surface fluxes
  • Rhine valley
  • Ho/Qois slightly lower for higher soil moisture
  • Eo/Qo is slightly higher for higher soil moisture
  • Black Forest
  • No dependence of Ho/QoandEo/Qoon 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!

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

3 1 the dependence of z i on the sensible heat flux

PBL

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Soil moisture

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3.1 The dependence of zi on the sensible heat flux
  • 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

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

3 2 the impact of the surface fluxes on e in the pbl
3.2 The impact of the surface fluxes on Θe in the PBL
  • 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

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

4 1 dependence of convection indices on pbl conditions

CAPE, CIN

Soil moisture

PBL

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4.1 Dependence of convection indices on PBL conditions
  • 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!

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

4 1 dependence of evolution of the convection indices on the pbl evolution
4.1 Dependence of evolution of the convection indices on the PBL evolution

Strong changes in the mid- and upper troposphere

Modified CAPE, LI and KO values:

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

Original CAPE, LI and KO values at Heselbach

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

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

4 2 dependence of convection inhibition on pbl conditions
4.2 Dependence of convection inhibition on PBL conditions

CAP=max(Te-Tp)

  • The higherzithe lower the upper threshold for CIN and CAP strength
  • This was observed at all sites!
  • CIN and CAP strength were independent of Θein thePBL

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

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4.3 Characteristics of convection inhibition

  • A good correlation betweenCIN 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

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

5 conclusions
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 correlated
  • The frequency of occurrence of low CIN values is higher over the Black Forest than over the Rhine valley => Favours CI over the mountains

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

outline
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

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

3 impact of the surface fluxes on the cbl conditions

PBL

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Soil moisture

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3 Impact of the surface fluxes on the CBL conditions
  • For homogeneous terrain:
  • zi is higher for higher Ho andforhigherBowen 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?

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

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

Soil moisture

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2 Impact of soil moisture on the surface characteristics and the turbulent fluxes
  • Precipitation increases with elevation
  • Soil moisture, θvol, increases with elevation

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

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CAPE, CIN

PBL

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Soil moisture

Soil moisture

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