A new convective cloud field model based on principles of self-organisation

International audienceA new cumulus convection parameterisation is presented in this paper. The parameterisation uses an explicit spectral approach and determines, unlike other convection schemes, for each convection event a new cloud distribution function regarding to the given vertical temperature and humidity profiles. This is done by using a one dimensional cloud model to create a spectrum of different clouds. The interaction between all non convective physical processes in the AGCM and all different clouds is taken into account to calculate a selfconsistent cloud spectrum. The model has been implemented in the ECHAM5 AGCM and tested against a large eddy simulation model. The representation of a shallow cumulus cloud field by the AGCM could be much improved. Diurnal cycle, cloud cover, liquid water path and the vertical structure of the mass flux, determined by the new convection scheme are close to the large eddy simulation, whereas the standard convection scheme failed in simulating this convection episode

Sensitivity of the global circulation to the suppression of precipitation by anthropogenic aerosols

From recent satellite observations, it is evident that an increase in cloud condensation nuclei-for instance, due to biomass burning-can substantially reduce rain efficiency of convective clouds. This is potentially important for the global climate since the release of latent heat due to condensation of water vapour and fallout of rain from cumulus convection is the most important source for available potential energy in the free troposphere. Beyond this, cumulus convection is a key process in controlling the water vapour content of the atmosphere. The sensitivity of the global climate to modification in rain efficiency of convective clouds due to the suppression of drop coalescence by anthropogenic aerosols is studied by using the atmospheric general circulation model (A-GCM), ECHAM4. This paper presents results from a 15-year sensitivity study, which considers the aerosol effect on warm precipitation formation. Effects on ice processes are not included yet, and therefore the results likely underestimate the magnitude of the full effects due to suppression of precipitation. Instantaneous forcing is large locally (up to 100% reduction of precipitation and the related latent heat release) but confined to small areas, leading to small large-scale mean anomalies in the convective heating and therefore the vertical temperature gradient. We found a definite perturbation of the global circulation, showing distinct sensitivity to the impact of aerosols on suppressing rainfall. (C) 2003 Elsevier Science B.V. All rights reserved

A new convective cloud field model based on principles of self-organisation

A new cumulus convection parameterisation is presented in this paper. The parameterisation uses an explicit spectral approach and determines, unlike other convection schemes, for each convection event a new cloud distribution function regarding to the given vertical temperature and humidity profiles. This is done by using a one dimensional cloud model to create a spectrum of different clouds. The interaction between all non convective physical processes in the AGCM and all different clouds is taken into account to calculate a selfconsistent cloud spectrum. The model has been implemented in the ECHAM5 AGCM and tested against a large eddy simulation model. The representation of a shallow cumulus cloud field by the AGCM could be much improved. Diurnal cycle, cloud cover, liquid water path and the vertical structure of the mass flux, determined by the new convection scheme are close to the large eddy simulation, whereas the standard convection scheme failed in simulating this convection episode

Sensitivity of the global circulation to the suppression of precipitation by anthropogenic aerosols

From recent satellite observations, it is evident that an increase in cloud condensation nuclei-for instance, due to biomass burning-can substantially reduce rain efficiency of convective clouds. This is potentially important for the global climate since the release of latent heat due to condensation of water vapour and fallout of rain from cumulus convection is the most important source for available potential energy in the free troposphere. Beyond this, cumulus convection is a key process in controlling the water vapour content of the atmosphere. The sensitivity of the global climate to modification in rain efficiency of convective clouds due to the suppression of drop coalescence by anthropogenic aerosols is studied by using the atmospheric general circulation model (A-GCM), ECHAM4. This paper presents results from a 15-year sensitivity study, which considers the aerosol effect on warm precipitation formation. Effects on ice processes are not included yet, and therefore the results likely underestimate the magnitude of the full effects due to suppression of precipitation. Instantaneous forcing is large locally (up to 100% reduction of precipitation and the related latent heat release) but confined to small areas, leading to small large-scale mean anomalies in the convective heating and therefore the vertical temperature gradient. We found a definite perturbation of the global circulation, showing distinct sensitivity to the impact of aerosols on suppressing rainfall. (C) 2003 Elsevier Science B.V. All rights reserved

Anwendung, Validierung und Weiterentwicklung eines komplexen nichthydrostatischen Plumemodells fuer Fragen der Biomasseverbrennung Abschlussbericht

Ziel dieses Projektes war die Untersuchung des Einflusses von Biomasseverbrennung auf die Zusammensetzung der Atmosphaere und moeglicher Auswirkungen auf die globale Zirkulation. Fuer die Untersuchung lokaler Auswirkungen in der Naehe von Vegetationsfeuern wurde das active tracer high resolution model (ATHAM) verwendet und anhand von Beobachtungsdaten evaluiert. Das general circulation model ECHAM wurde verwendet, um globale Auswirkungen zu untersuchen. Generell wurde gezeigt, und in den Modellsimulationen nachgebildet, dass lokale Prozesse in jungen Biomasse-Verbrennungsrauchwolken zu einer signifikanten Bildung von Ozon fuehren. Diese und weitere Simulationen werden unser Verstaendnis der Prozesse, die in Biomasseverbrennungsrauchwolken ablaufen, sowie ihre Wiedergabe in grossskaligen Modellen erhoehen. Der Einfluss von Rauchauswirkungen auf die Niederschlagleistung tiefer, konvektiver Wolken fuehrte zu grossen Anomalien im lokalen Bereich (Niederschlag, Strahlung und Wolkendecke), der sich ueber die gesamte Erdkugel verteilt. Ausserdem wurden signifikante Veraenderungen der globalen Zirkulation simuliert. Der Grund ist, dass die Hauptantriebskraft globaler Zirkulation, d.h. Freigabe latenter Waerme in die Atmosphaere durch das Zusammenwirken von Rauch und Wolken in einigen neuralgischen Gebieten beeinflusst wird. (orig.)The goal of this project was to explore the impact of biomass burning on the composition of the atmosphere and potential effects on the global circulation. For the investigation of local effects near vegetation fires, the active tracer high-resolution atmospheric model (ATHAM) was used and evaluated with observations. The general circulation model ECHAM was used to study global effects. Overall it was shown that local processes in young biomass burning plumes lead to significant formation of ozone which is reproduced in the model simulations. These and further simulations will increase our understanding of the processes in biomass burning plumes and their representation in larger scale models. Introduction of smoke effects on the precipitation efficiency of deep convective clouds led to large anomalies at the local scale (precipitation, radiation and cloud cover) distributed over the whole globe. In addition, significant changes of global circulation were simulated. The reason is that the main driving force of global circulation, i.e., the deliberation of latent heat to the atmosphere is being influenced by the smoke-cloud interaction at some neuralgic regions. (orig.)Available from TIB Hannover: DtF QN1(99,60) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Bildung und Forschung, Berlin (Germany)DEGerman

Impact of vegetation fires on composition and circulation of the atmosphere (EFEU)

The project addresses the contribution of vegetation fires to the local trace gas and particle budgets of the troposphere and the lower stratosphere, their direct and indirect radiative impact, their impact on cloud formation and chemical and microphysical processes in cloud