Simulated Urban Climate Response to Historical Land Use Modification in the Basin of Mexico

Numerical simulations of thermal field variation due to land use changes, such as the reduction of the lacustrine system and the growth of the urban area, in the Basin of Mexico are presented. It is shown that the historically recorded warming in the basin could be attributed, not only to the growth of the urban area, but more importantly to the drastic reduction in the lacustrine system that existed in the basin.     

The Cretaceous–Palaeogene boundary at Gorgonilla Island,Colombia, South America

The discovery of a new Cretaceous/Palaeogene (K/Pg) bathyal marine sequence on Gorgonilla Island, SW Colombia, extends the presence of Chicxulub impact spherule deposits to the Pacific region of northern South America and to the Eastern Pacific Ocean. The Gorgonilla spherule layer is approximately 20 mm thick and consists of extraordinarily well‐preserved glass spherules up to 1.1 mm in diameter. About 70–90% of the spherules are vitrified, and their chemical composition is consistent with Haiti (Beloc) impact glass spherules. Normal size‐grading, delicate spherule textures, welded melt components and an absence of bioturbation or traction transport suggest that the Gorgonilla spherule layer represents an almost undisturbed settling deposit.     

Exploring the relationships between perceived neighborhood boundaries and street network orientation

The neighborhood is a core unit of analysis in urban research, planning, and policy-making. However, perceptual and historical processes oftentimes result in neighborhoods that are not tied to sub-urban jurisdictions. For instance, historic neighborhoods might lack official spatial definitions, hampering neighborhood-based tasks in local offices. In this case, urban practitioners can benefit from readily available spatial proxies, such as the local street network. In this study, we conducted an exploratory analysis that combines neighborhood mapping and street network modeling. By retrieving participants' sketched boundaries and quantifying spatial orientations of sketched polygons and local network patterns, we were able to measure and compare the relationships between the urban fabric and the perceived extents of two historic neighborhoods in Lisbon, Portugal. The results provided insights for enhancing existing definitions of non-official neighborhoods, outlining new urban districts as well as for discussions about the role of the urban form in shaping people's perceptions.     

Evolution of vegetation activity on vegetated,eroded, and erosion risk areas in the central Spanish Pyrenees,using multitemporal Landsat imagery

The temporal evolution of vegetation activity on various land cover classes in the Spanish Pyrenees was analyzed. Two time series of the normalized difference vegetation index (NDVI) were used, corresponding to March (early spring) and August (the end of summer). The series were generated from Landsat TM and Landsat ETM+ images for the period 1984–2007. An increase in the NDVI in March was found for vegetated areas, and the opposite trend was found in both March and August for degraded areas (badlands and erosion risk areas). The rise in minimum temperature and the time variation of the cloud cover during the study period appears to be the most important factors explaining increased NDVI in the vegetated areas. In degraded areas, no climatic or topographic variable was associated with the negative NDVI trend, which may be related to erosion processes taking place in these regions. Copyright © 2010 John Wiley & Sons, Ltd.     

FIRST RESULTS FROM VIRGO,THE EXPERIMENT FOR HELIOSEISMOLOGY AND SOLAR IRRADIANCE MONITORING ON SOHO

First results from the VIRGO experiment (Variability of solar IRradiance and Gravity Oscillations) on the ESA/NASA Mission SOHO (Solar and Heliospheric Observatory) are reported. The observations started mid-January 1996 for the radiometers and sunphotometers and near the end of March for the luminosity oscillation imager. The performance of all the instruments is very good, and the time series of the first 4–6 months are evaluated in terms of solar irradiance variability, solar background noise characteristics and p-mode oscillations. The solar irradiance is modulated by the passage of active regions across the disk, but not all of the modulation is straightforwardly explained in terms of sunspot flux blocking and facular enhancement. Helioseismic inversions of the observed p-mode frequencies are more-or-less in agreement with the latest standard solar models. The comparison of VIRGO results with earlier ones shows evidence that magnetic activity plays a significant role in the dynamics of the oscillations beyond its modulation of the resonant frequencies. Moreover, by comparing the amplitudes of different components ofp -mode multiplets, each of which are influenced differently by spatial inhomogeneity, we have found that activity enhances excitation.     

Ancient Forests in European drylands: Holocene palaeoecological record of Mazarrón,south-eastern Spain

This paper presents a new Holocene palaeoecological record from coastal south-eastern Spain, a region characterised by high plant species diversity, varied physiography, high risk of desertification, and a history of human pressure on the landscape that stretches to antiquity. The pollen sequence shows four main vegetation phases: the first characterised by mixed forests of Pinus and evergreen Quercus accompanied by broad-leaved mesophilous trees, and a diversity of Mediterranean scrub; the second phase is characterised by mesophytic decline and expansion of Artemisia; a third, mid-Holocene phase of thermo-mesophytic maxima with prevalence of forested landscapes; and, finally, the progressive opening of the landscape with sparse pines, halo-xerophytic grasslands and sclerophyllous brushwood. The current treeless situation of south-eastern Spain is a relatively recent feature resulting from a dramatic change in the ecological structure of the regional landscapes. This paper stresses the continued vulnerability of these arid systems in the face of a changing climate. This sequence adds to previous palaeobotanical records (pollen and charcoal) and archaeological reports to suggest that deforestation started earlier in low-elevation areas and river basins than in the inland mountains and platforms, a factor that appears in connection to human exploitation of the natural environment.