An intercomparison experiment involving 15 commonly used detection and tracking algorithms for extratropical cyclones reveals those cyclone characteristics that are robust between different schemes and those that differ markedly.

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For Northern Hemisphere extra-tropical cyclone activity, the dependency of a potential anthropogenic climate change signal on the identification method applied is analysed. This study investigates the impact of the used algorithm on the changing signal, not the robustness of the climate change signal itself. Using one single transient AOGCM simulation as standard input for eleven state-of-the-art identification methods, the patterns of model simulated present day climatologies are found to be close to those computed from re-analysis, independent of the method applied. Although differences in the total number of cyclones identified exist, the climate change signals (IPCC SRES A1B) in the model run considered are largely similar between methods for all cyclones. Taking into account all tracks, decreasing numbers are found in the Mediterranean, the Arctic in the Barents and Greenland Seas, the mid-latitude Pacific and North America. Changing patterns are even more similar, if only the most severe systems are considered: the methods reveal a coherent statistically significant increase in frequency over the eastern North Atlantic and North Pacific. We found that the differences between the methods considered are largely due to the different role of weaker systems in the specific methods.

This article investigates extratropical winter cyclone activity in the Southern Hemisphere (SH) in a multimodel ensemble (MME) of coupled atmosphere-ocean general circulation model (AOGCM) simulations of recent and potential future climate conditions. Most individual models and also the ensemble mean yield good reproductions of the typical cyclone characteristics found in reanalysis data, although some individual models show peculiarities, and a large inter-model spread in terms of quantity of identified cyclone tracks is found. We use a scaling approach to combine the cyclone statistics from different models into a MME. In the future climate simulations, the total number of SH cyclones is reduced, whereas an increased number of strong cyclones is found in most models and in the ensemble mean. The long term trend with respect to all cyclones is a robust feature throughout the simulations. It is associated with a general poleward shift, shown to be related to both tropical upper tropospheric warming and shifting meridional sea surface temperature gradients in the Southern Ocean. The magnitude of increased strong cyclone activity has a focus on the Eastern Hemisphere. It is clearly influenced by natural variability and thus depends on specific time periods considered.

SummaryA 3-D finite-difference elastic wave propagation code that incorporates a number of advanced computational and physics-bawd enhancements has been dcvdoped. These enhancements include full 3-D elastic, viscoelastic, and topographic modeling (anisotropic capabilities arc being added), low-level optimization, propagating and variable density grids, hybridization, and parallclization. This code takes advantage of high perfonnancc computing and massively parallel processing to make 3-D full-physics simulations of seismic problems feasible. This computational tool will be used to generate an elastic subset of the SEGiEAEG acoustic data set. The acoustic and elastic data will be compared to examine pitfalls with traditional processing, and to test the effectiveness of using elastic data as an aid to seismic imaging.