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- ItemLong-term trends in the ionospheric E and F1 regions(Göttingen : Copernicus, 2008) Bremer, J.Ground based ionosonde measurements are the most essential source of information about long-term variations in the ionospheric E and F1 regions. Data of such observations have been derived at many different ionospheric stations all over the world some for more than 50 years. The standard parameters foE, h'E, and foF1 are used for trend analyses in this paper. Two main problems have to be considered in these analyses. Firstly, the data series have to be homogeneous, i.e. the observations should not be disturbed by artificial steps due to technical reasons or changes in the evaluation algorithm. Secondly, the strong solar and geomagnetic influences upon the ionospheric data have carefully to be removed by an appropriate regression analysis. Otherwise the small trends in the different ionospheric parameters cannot be detected. The trends derived at individual stations differ markedly, however their dependence on geographic or geomagnetic latitude is only small. Nevertheless, the mean global trends estimated from the trends at the different stations show some general behaviour (positive trends in foE and foF1, negative trend in h'E) which can at least qualitatively be explained by an increasing atmospheric greenhouse effect (increase of CO2 content and other greenhouse gases) and decreasing ozone values. The positive foE trend is also in qualitative agreement with rocket mass spectrometer observations of ion densities in the E region. First indications could be found that the changing ozone trend at mid-latitudes (before about 1979, between 1979 until 1995, and after about 1995) modifies the estimated mean foE trend.
- ItemClassification and clustering: models, software and applications(Berlin : Weierstraß-Institut für Angewandte Analysis und Stochastik, 2009) Mucha, Hans-Joachim; Ritter, GunterWe are pleased to present the report on the 30th Fall Meeting of the working group ``Data Analysis and Numerical Classification'' (AG-DANK) of the German Classification Society. The meeting took place at the Weierstrass Institute for Applied Analysis and Stochastics (WIAS), Berlin, from Friday Nov. 14 till Saturday Nov. 15, 2008. Already 12 years ago, WIAS had hosted a traditional Fall Meeting with special focus on classification and multivariate graphics (Mucha and Bock, 1996). This time, the special topics were stability of clustering and classification, mixture decomposition, visualization, and statistical software.
- ItemSimilarities and differences in polar mesosphere summer echoes observed in the Arctic and Antarctica(München : European Geopyhsical Union, 2008) Latteck, R.; Singer, W.; Morris, R.J.; Hocking, W.K.; Murphy, D.J.; Holdsworth, D.A.; Swarnalingam, N.Polar Mesosphere Summer Echoes (PMSE) have been observed in the high latitudes of the Northern and Southern Hemisphere for several years using VHF radars located at Andenes/Norway (69° N, 16° E), Resolute Bay/Canada (75° N, 95° W), and Davis/Antarctica (69° S, 78° E). The VHF radars at the three sites were calibrated using the same methods (noise source and delayed transmitting signal) and identical equipment. Volume reflectivity was derived from the calibrated echo power and the characteristics of the seasonal variation of PMSE were estimated at the sites for the years 2004 to 2007. The largest peak volume reflectivity of about 2×10−9 m−1 was observed at Andenes compared with their counterparts at Davis (~4×10−11 m−1) and Resolute Bay (~6×10−12 m−1). The peak of the PMSE height distribution is 85.6 km at Davis which is about 1 km higher than at Andenes. At Resolute Bay the height distribution peaks at about 85 km but only a few layers were found below 84 km. The mean PMSE occurrence rate is 83% at Andenes, 38% at Davis with larger variability and only 18% at Resolute Bay (in late summer). The duration of the PMSE season varies at Andenes from 104 to 113 days and at Davis from 88 to 93 days. In general the PMSE seasons starts about 5 days later at Davis and ends about 10 days earlier compared to Andenes. In all three seasons the PMSE occurrence suddenly drops to a much lower level at Davis about 32 days after solstice whereas the PMSE season decays smoothly at Andenes. The duration of the PMSE season at Andenes and Davis is highly correlated with the presence of equatorward directed winds, the observed differences in PMSE occurrence are related to the mesospheric temperatures at both sites.
- ItemEmerging pattern of global change in the upper atmosphere and ionosphere(München : European Geopyhsical Union, 2008) Laštovička, J.; Akmaev, R.A.; Beig, G.; Bremer, J.; Emmert, J.T.; Jacobi, C.; Jarvis, M.J.; Nedoluha, G.; Portnyagin, Yu. I.In the upper atmosphere, greenhouse gases produce a cooling effect, instead of a warming effect. Increases in greenhouse gas concentrations are expected to induce substantial changes in the mesosphere, thermosphere, and ionosphere, including a thermal contraction of these layers. In this article we construct for the first time a pattern of the observed long-term global change in the upper atmosphere, based on trend studies of various parameters. The picture we obtain is qualitative, and contains several gaps and a few discrepancies, but the overall pattern of observed long-term changes throughout the upper atmosphere is consistent with model predictions of the effect of greenhouse gas increases. Together with the large body of lower atmospheric trend research, our synthesis indicates that anthropogenic emissions of greenhouse gases are affecting the atmosphere at nearly all altitudes between ground and space.
- ItemReactive Flow and Transport Through Complex Systems(Zürich : EMS Publ. House, 2005) Mikelic, Andro; Schwab, ChristophThe meeting focused on mathematical aspects of reactive flow, diffusion and transport through complex systems. The research interest of the participants varied from physical modeling using PDEs, mathematical modeling using upscaling and homogenization, numerical analysis of PDEs describing reactive transport, PDEs from fluid mechanics, computational methods for random media and computational multiscale methods.
- ItemAlgebraic K-Theory(Zürich : EMS Publ. House, 2006) Huber-Klawitter, Annette; Jannsen, Uwe; Levine, MarcThis is the report on the Oberwolfach workshop Algebraic KTheory, held in July 2006. The talks covered mainly topics from Algebraic Geometry and Number Theory in connection with K-Theory. Special emphasis was placed on motivic cohomology and motivic homotopy of general schemes.
- ItemWavelet and Multiscale Methods(Zürich : EMS Publ. House, 2007) Dahmen, Wolfgang; DeVore, Ronald A.; Kunoth, AngelaVarious scientific models demand finer and finer resolutions of relevant features. Paradoxically, increasing computational power serves to even heighten this demand. Namely, the wealth of available data itself becomes a major obstruction. Extracting essential information from complex structures and developing rigorous models to quantify the quality of information leads to tasks that are not tractable by standard numerical techniques. The last decade has seen the emergence of several new computational methodologies to address this situation. Their common features are the nonlinearity of the solution methods as well as the ability of separating solution characteristics living on different length scales. Perhaps the most prominent examples lie in multigrid methods and adaptive grid solvers for partial differential equations. These have substantially advanced the frontiers of computability for certain problem classes in numerical analysis. Other highly visible examples are: regression techniques in nonparametric statistical estimation, the design of universal estimators in the context of mathematical learning theory and machine learning; the investigation of greedy algorithms in complexity theory, compression techniques and encoding in signal and image processing; the solution of global operator equations through the compression of fully populated matrices arising from boundary integral equations with the aid of multipole expansions and hierarchical matrices; attacking problems in high spatial dimensions by sparse grid or hyperbolic wavelet concepts. This workshop proposed to deepen the understanding of the underlying mathematical concepts that drive this new evolution of computation and to promote the exchange of ideas emerging in various disciplines.
- ItemAlgebraic K-Theory and Motivic Cohomology(Zürich : EMS Publ. House, 2009) Huber-Klawitter, Annette; Jannsen, Uwe; Levine, MarcAlgebraic K-theory and the related motivic cohomology are a systematic way of producing invariants for algebraic or geometric structures. Its definition and methods are taken from algebraic topology, but it has also proved particularly fruitful for problems of algebraic geometry, number theory or quadratic forms. 19 one-hour talks presented a wide range of results on K-theory itself and applications. We had a lively evening session trading questions and discussing open problems.
- ItemAlgebraic Groups(Zürich : EMS Publ. House, 2007) Jantzen, Jens Carsten; Rouquier, RaphaelThe workshop dealt with a broad range of topics from the structure theory and the representation theory of algebraic groups (in the widest sense). There was emphasis on the following areas: structure and classification of wonderful varieties, finite reductive groups and character sheaves, quantum cohomology of homogeneous varieties, representation categories and their connections to orbits and flag varieties.
- ItemArbeitsgemeinschaft: Percolation(Zürich : EMS Publ. House, 2007) van den Berg, Jacob; Camia, FedericoAbstract. Percolation as a mathematical theory is more than fifty years old. During its life, it has attracted the attention of both physicists and mathematicians. This is due in large part to the fact that it represents one of the simplest examples of a statistical mechanical model undergoing a phase transition, and that several interesting results can be obtained rigorously. In recent years the interest in percolation has spread even further, following the introduction by Oded Schramm of the Schramm-Loewner Evolution (SLE) and a theorem by Stanislav Smirnov showing the conformal invariance of the continuum scaling limit of two-dimensional critical percolation. These results establish a new, powerful and mathematically rigorous, link between lattice-based statistical mechanical models and conformally invariant models in the plane, studied by physicists under the name of Conformal Field Theory (CFT). The Arbeitsgemeinschaft on percolation has attracted more than thirty participants, most of them young researchers, from several countries in Europe, North America, and Brazil. The main focus has been on recent developments, but several classical results have also been presented.