Reconstructions of spring/summer precipitation for the Eastern Mediterranean from tree-ring widths and its connection to large-scale atmospheric circulation

This study represents the first large-scale systematic dendroclimatic sampling focused on developing chronologies from different species in the eastern Mediterranean region. Six reconstructions were developed from chronologies ranging in length from 115 years to 600 years. The first reconstruction (1885–2000) was derived from principal components (PCs) of 36 combined chronologies. The remaining five, 1800–2000, 1700–2000, 1600–2000, 1500–2000 and 1400–2000 were developed from PCs of 32, 18, 14, 9, and 7 chronologies, respectively. Calibration and verification statistics for the period 1931–2000 show good levels of skill for all reconstructions. The longest period of consecutive dry years, defined as those with less than 90% of the mean of the observed May–August precipitation, was 5 years (1591–1595) and occurred only once during the last 600 years. The longest reconstructed wet period was 5 years (1601–1605 and 1751–1755). No long term trends were found in May–August precipitation during the last few centuries. Regression maps are used to identify the influence of large-scale atmospheric circulation on regional precipitation. In general, tree-ring indices are influenced by May–August precipitation, which is driven by anomalous below (above) normal pressure at all atmospheric levels and by convection (subsidence) and small pressure gradients at sea level. These atmospheric conditions also control the anomaly surface air temperature distribution which indicates below (above) normal values in the southern regions and warmer (cooler) conditions north of around 40°N. A compositing technique is used to extract information on large-scale climate signals from extreme wet and dry summers for the second half of the twentieth century and an independent reconstruction over the last 237 years. Similar main modes of atmospheric patterns and surface air temperature distribution related to extreme dry and wet summers were identified both for the most recent 50 years and the last 237 years. Except for the last few decades, running correlation analyses between the major European-scale circulation patterns and eastern Mediteranean spring/summer precipitation over the last 237 years are non-stationary and insignificant, suggesting that local and/or sub-regional geographic factors and processes are important influences on tree-ring variability over the last few centuries.     

Response of littoral chironomid communities and organic matter to late glacial lake—level,vegetation and climate changes at Lago dell’Accesa (Tuscany,Italy)

This study focuses on the response of lacustrine littoral chironomid communities to late glacial changes in limnological, environmental and climate conditions in the Mediterranean context. Late glacial chironomid (Diptera: Chironomidae) assemblages, organic petrography and geochemistry were analysed in a sediment core from the littoral zone of Lago dell’Accesa (Tuscany, Italy), where the lake-level fluctuations and the vegetation history have been previously reconstructed. Comparison of the chironomid stratigraphy to other proxies (pollen assemblages, organic petrography and geochemistry, lake-level) and regional climate reconstruction suggested the predominant influence of lake-level changes on the littoral chironomid fauna. The main lowering events that occurred during the Oldest and the Younger Dryas were followed by higher proportions of taxa typical of littoral habitats. A complementary study of organic matter suggested the indirect impact of lake-level on the chironomids through changes in humic status and habitat characteristics, such as the type of substrate and aquatic macrophyte development. Several chironomid taxa, such as Glyptotendipes, Microtendipes and Cricotopus type patens, were identified as possible indicators of low lake-level in the late glacial records. Nevertheless, this study suggested that parallel analyses of organic matter and chironomid assemblages may be needed to circumvent misinterpretation of littoral chironomid assemblage stratigraphy. There was a weak response of the chironomid assemblages to small lake-level lowerings that corresponded to the Older Dryas and Preboreal oscillations. A higher level of determination, e.g. to the species group level, may be necessary to increase the sensibility of the indicators to lake-level changes.     

Paleolithic archeology and the paleogeographical study of loess-paleosol sequences in Eastern Europe

The paper is concerned with problems of the study of Paleolithic sites in the loess regions of the Russian Plain. It is of great significance to correlate prehistorical settlement with Upper Pleistocene cycles of loess and soil formation — not solely in the reconstruction of paleoenvironments. From the cultural layers at various sites paleontological finds and objects were collected for radiocarbon dating. A complex analysis of archeological objects embedded in the loess-paleosol sequence helps us date Upper Pleistocene loess formation cycles. The data acquired from the investigation of the lithological properties of loess and their modification through time and their dependence on relief characteristics permitted a correlation between the various paleoenvironments and the dust accumulation cycles, which played a decisive role in the selection of the most habitable sites.     

On very-low-frequency atmospherics at Roburent,Northern Italy

Summary The diurnal and seasonal variation of the VLF sferics pulse rate recorded at Roburent, Northern Italy, on 27 kHz since 1966 is derived. By analyzing the sunrise effect, the minimum distance of the thunderstorm centers providing at that time an unperturbed behaviour of the sferics pulse rate is obtained: this distance varies in azimuth and with the seasons and lies between 600 and 1300 km. In the time of the equinoxes, however, it is more stable between 700 and 900 km. The role of the groundwave propagation, generated by thunderstorm center within a radius of less than 500 km, is emphasized.

---

Zusammenfassung Der Tagesgang und der Jahresgang der Sferics-Impulshäufigkeit werden abgeleitet. Diese Sferics-Häufigkeit ist seit 1966 auf 27 kHz in Roburent, in Nord-Italien, registriert worden. Der Mindestabstand der Gewitterherde, welche zur Zeit des Sonnenaufgangs ein ungestörte Bild der Impulshäufigkeit geben, wird mit Hilfe des Sonnenaufgangseffekts abgeleitet: der Abstand liegt — abhängig von der Jahreszeit und der Einfallsrichtung — zwischen 600 und 1300 km; jedoch bewegt er sich in dem engeren Rahmen zwischen 700 und 900 km zur Zeit der Tag-und Nachtgleichen. Betont wird die Rolle der Bodenwelle, welche von Gewitterherden in einem Abstand von weniger als 500 km erzeugt wird.

---

---

Contribution No. 241 of the Istituto Geofisico e Geodetico, Università di Genova,Genoa, Italy. This work has been supported by a grant from the Consiglio Nazionale delle Ricerche (Comitato Nazionale per le Scienze Fisiche), Roma.     

Public policy and the changing landscape

The paper illustrates how spatially explicit forecasting of residential development can be undertaken and how it can be made sensitive to policy instruments available to local and state governments. Predicted values in residential use based on a hedonic analysis of residential property prices is found to have a significant effect on the hazard of development in a survival model used to explain the likelihood that a farm or forest will be converted to residential use. Policy instruments are imbedded in both the hedonic model of residential property values and a hazard model of parcel conversion, so as to test how effective changes in policies can be at changing the pattern of land-use change. Some of the statistical and modeling obstacles that impede progress on this spatially explicit modeling are also discussed.     

On the Structure of Symplectic Mappings. The Fast Lyapunov Indicator: a Very Sensitive Tool

It is already known (Froeschlé, Lega and Gonczi, 1997) that the Fast Lyapunov Indicator (FLI), that is the computation on a relatively short time of the largest Lyapunov indicator, allows to discriminate between ordered and weak chaotic motion. We have found that, under certain conditions, the FLI also discriminates between resonant and non-resonant orbits, not only for two-dimensional symplectic mappings but also for higher dimensional ones. Using this indicator, we present an example of the Arnold web detection for four and six-dimensional symplectic maps. We show that this method allows to detect the global transition of the system from an exponentially stable Nekhoroshevs like regime to the diffusive Chirikovs one.     

3D structure of the Earth's crust beneath the northern part of the Bohemian Massif

The SUDETES 2003 wide-angle refraction/reflection experiment covered the area of the south-western Poland and the northern Bohemian Massif. The good quality data that were gathered combined with the data from previous experiments (POLONAISE'97, CELEBRATION 2000) allowed us to prepare a 3D seismic model of the crust and uppermost mantle for this area. We inverted travel times of both refracted and reflected P waves using the JIVE3D package. This allowed us to obtain a model of P-wave velocity distribution as well as the shape of major boundaries in the crust. We also present a detailed uncertainty analysis for both the boundary depths and the velocity field. In doing the uncertainty analysis we found an interesting, strong dependence between uncertainty and inversion scheme (order of used phases). We also compared the model with surface geology and found good correlation between velocity inhomogeneities in the uppermost crust (down to 2 km) and major geological units. The higher velocity lower crust (6.9–7.2 km/s) could result from remelting of the lower crust or magmatic underplating.     

Comparison of convergence towards invariant distributions for rotation angles, twist angles and local Lyapunov characteristic numbers

Using the standard map as a model problem and in the spirit of cluster analysis we have studied the invariance of the distributions of different indicators introduced to detect and measure weak chaos. We show that the problem is less straightforward than expected and that, except for very strong chaotic dynamical systems, all the complexities (islands, sticking phenomena, cantori) of mixed Hamiltonian systems are reflected into the indicators of convergence towards invariant distributions.