Numerische Simulation von Cumulus-Konvektion und Skalenwechselwirkungen mit einem eineinhalbdimensionalen Modell

Available from TIB Hannover: MA 8085 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Should we use a simple or complex model for moisture recycling and atmospherix moisture tracking?

This paper compares state-of-the-art atmospheric moisture tracking models. Such models are typically used to study the water component of coupled land and atmosphere models, in particular quantifying moisture recycling and the source-sink relations between evaporation and precipitation. There are several atmospheric moisture tracking methods in use. However, depending on the level of aggregation, the assumptions made and the level of detail, the performance of these methods may differ substantially. In this paper, we compare three methods. The RCM-tag method uses highly accurate 3-D water tracking (including phase transitions) directly within a regional climate model (online), while the other two methods (WAM and 3D-T) use a posteriori (offline) water vapour tracking. The original version ofWAM is a single-layer model, while 3D-T is a multi-layer model, but both make use the “well-mixed” assumption for evaporation and precipitation. The a posteriori models are faster and more flexible, but less accurate than online moisture tracking with RCM-tag. In order to evaluate the accuracy of the a posteriori models, we tagged evaporated water from Lake Volta inWest Africa and traced it to where it precipitates. It is found that the strong wind shear in West Africa is the main cause of errors in the a posteriori models. The number of vertical layers and the initial release height of tagged water in the model are found to have the most significant influences on the results. With this knowledge small improvements have been made to the a posteriori models. It appeared that expanding WAM to a 2-layer model, or a lower release height in 3D-T, led to significantly better results. Finally, we introduced a simple metric to assess wind shear globally and give recommendations about when to use which model. The “best” method, however, very much depends on the research question, the spatial extent under investigation, as well as the available computational power.Water ManagementCivil Engineering and Geoscience

Localized charged-neutral fluctuations in 158A GeV Pb+Pb collisions

First results on the measurement of localized fluctuations in the multiplicity of charged particles and photons produced in central 158 A GeV Pb+Pb collisions are presented. The charged versus neutral correlations in common phase space regions of varying azimuthal size are analyzed by two different methods. The measured results are compared to those from simulations and to those from different types of mixed events. The comparison indicates the presence of non-statistical fluctuations in both charged particle and photon multiplicities in limited azimuthal regions. However, no correlated charge-neutral fluctuations are observed.First results on the measurement of localized fluctuations in the multiplicity of charged particles and photons produced in central 158 A GeV Pb+Pb collisions are presented. The charged versus neutral correlations in common phase space regions of varying azimuthal size are analyzed by two different methods. The measured results are compared to those from simulations and to those from different types of mixed events. The comparison indicates the presence of non-statistical fluctuations in both charged particle and photon multiplicities in limited azimuthal regions. However, no correlated charge-neutral fluctuations are observed