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

KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH) 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 HE PBL Soil moisture How strong is the impact of soil moisture > surface fluxes > PBL conditions > convection-related parameters during COPS (i.e. over complex terrain) 12

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

KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH) 2.1 Impact of soil moisture on the surface characteristics Soil moisture increases with the elevation No dependence of the albedo on θ vol Only in the Rhine valley: A dependence of the surface temperature, T s, on θ vol => Only in the Rhine valley a weak dependence of net radiation (available energy) on θ vol was observed HE 1 Soil moisture albedo

KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH) 2.2 Impact of soil moisture on the surface fluxes Rhine valley H o /Q o is slightly lower for higher soil moisture E o /Q o is slightly higher for higher soil moisture Black Forest No dependence of H o /Q o and E o /Q o 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!

KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH) 3.1 The dependence of z i on the sensible heat flux In the Rhine valley (FZK, Achern) and at Heselbach a weak correlation between z i and H o was found Over the mountain crest (Hornisgrinde) z i is independent of H o 2 3 H E PBL Soil moisture 1 2

KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH) 3.2 The impact of the surface fluxes on Θ e in the PBL The dependence of the diurnal increase of moist static energy / Θ e 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 / Θ e at the mountain crest (Hornisgrinde) => Especially in the Black Forest the impact of the surface fluxes on the PBL conditions (z i, Θ e ) 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 The convection indices CAPE, LI (conditional instability) and KO (potential instability) are highly correlated with Θ e in the PBL This finding is valid for the Rhine valley and the Black Forest! H E PBL Soil moisture 1 2 CAPE, CIN

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

KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH) 4.2 Dependence of convection inhibition on PBL conditions The higher z i the lower the upper threshold for CIN and CAP strength This was observed at all sites! CIN and CAP strength were independent of Θ e in the PBL CAP=max(T e -T p )

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

KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH) 5 Conclusions Soil > surface The impact of soil moisture on the surface parameters (α, T s, Q o ) and on the energy transformation at the Earth‘s surface (β) is weak Surface > PBL Rhine valley: The dependence of the PBL characteristics like Θ e and z i on the surface fluxes is weak Black Forest: Nearly no dependence of the PBL characteristics like Θ e and z i 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 Θ e 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 z i ) 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 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 For homogeneous terrain: z i is higher for higher H o and for higher Bowen ratio CIN and CAPE depend the surface and PBL conditions in the PBL (β => q, Θ, Θ e, z i ) What about the dependences over complex terrain? 2 3 HE PBL Soil moisture 1 2

KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH) 2 Impact of soil moisture on the surface characteristics and the turbulent fluxes Precipitation increases with elevation Soil moisture, θ vol, increases with elevation H E 1 Soil moisture

KIT – die Kooperation von Forschungszentrum Karlsruhe GmbH und Universität Karlsruhe (TH) 4 HE 1 Soil moisture CAPE, CIN 2 HE PBL Soil moisture 1 2