Impact of climate change and urban development on extreme flows in the Grote Nete watershed,Belgium

This study investigates how extreme flows in the Grote Nete watershed located in the Flanders region of Belgium will respond to climate change and urban growth using the hydrological model WetSpa. Three climate change scenarios (low, mean and high), three urban development scenarios (low, medium and high) and the nine combined climate–urban change scenarios are considered. The results indicate that extreme low flows would decrease noticeably by climate change, while they would be less sensitive to urban development. On the other hand, extreme peak flows are predicted to increase considerably due to both climate change and urban growth. It is concluded that coupling the effects of land use change with climate change may lead to severe increase in the frequency river floods in winter as well as the frequency of extreme river low flows in summer.     

Persian Gulf response to a wintertime shamal wind event

The results from a～1 km resolution HYbrid Coordinate Ocean Model (HYCOM), forced by 1/2° Navy Operational Global Atmospheric Prediction System (NOGAPS) atmospheric data, were used in order to study the dynamic response of the Persian Gulf to wintertime shamal forcing. Shamal winds are strong northwesterly winds that occur in the Persian Gulf area behind southeast moving cold fronts. The period from 20 November to 5 December 2004 included a well defined shamal event that lasted 4–5 days. In addition to strong winds (16 m s^?1) the winter shamal also brought cold dry air (T_a=20 °C, q_a=10 g kg^?1) which led to a net heat loss in excess of 1000 W m^?2 by increasing the latent heat flux. This resulted in SST cooling of up to 10 °C most notably in the northern and shallower shelf regions. A sensitivity experiment with a constant specific humidity of q_a=15 g kg^?1 confirmed that about 38% of net heat loss was due to the air–sea humidity differences. The time integral of SST cooling closely followed the air–sea heat loss, indicating an approximate one-dimensional vertical heat balance. It was found that the shamal induced convective vertical mixing provided a direct mechanism for the erosion of stratification and deepening of the mixed layer by 30 m. The strong wind not only strengthened the circulation in the entire Persian Gulf but also established a northwestward flowing Iranian Coastal Current (ICC, 25–30 cm s^?1) from the Strait of Hormuz to about 52°E, where it veered offshore. The strongest negative sea level of 25–40 cm was generated in the northernmost portion of the Gulf while the wind setup against the coast of the United Arab Emirates established a positive sea level of 15–30 cm. The transport through the Strait of Hormuz at 56.2°E indicated an enhanced outflow of 0.25 Sv (Sv≡10⁶ m³ s^?1) during 24 November followed by an equivalent inflow on the next day.     

Changes to sediment sources following wildfire in a forested upland catchment,southeastern Australia

Few investigations link post‐fire changes to sediment sources and erosion processes with sediment yield response at the catchment scale. This linkage is essential if downstream impacts on sediment transport after fire are to be understood in the context of fire effects across different forest environments. In this study, we quantify changing source contributions to fine sediment (<63 µm) exported from a eucalypt forest catchment (136 ha) burnt by wildfire. The study catchment is one of a pair of research catchments located in the East Kiewa River valley in southeastern Australia that have been the subject of a research program investigating wildfire effects on runoff, erosion, and catchment sediment/nutrient exports. This previous research provided the opportunity to couple insights gained from a range of measurement techniques with the application of fallout radionuclides ¹³⁷Cs and ²¹⁰Pb_ex to trace sediment sources. It was found that hillslope surface erosion dominated exports throughout the 3·5‐year post‐fire measurement period. During this time there was a pronounced decline in the proportional surface contribution from close to 100% in the first six months to 58% in the fourth year after fire. Over the study period, hillslope surface sources accounted for 93% of the fine sediment yield from the burnt catchment. The largest decline in the hillslope contribution occurred between the first and second years after fire, which corresponded with the previously reported large decline in sediment yield, breakdown of water repellency in burnt soils, substantial reduction in hillslope erodibility, and rapid surface vegetation recovery. Coupling the information on sediment sources with hillslope process measurements indicated that only a small proportion of slopes contributed sediment to the catchment outlet, with material derived from near‐channel areas dominating the post‐fire catchment sediment yield response. Copyright © 2011 John Wiley & Sons, Ltd.     

Finite element implementation of a homogenized constitutive law for stone column-reinforced foundation soils,with application to the design of structures

Making use of the homogenization method for periodic media, developed in the context of elastoplasticity, a simplified constitutive law is proposed for a stone column-reinforced soil, regarded as a homogeneous but anisotropic medium. The closed-form expressions derived for such a constitutive law allow for its implementation into a f.e.m-based numerical procedure. The computational code so obtained is then applied to simulating the response of a foundation soil reinforced by a group of floating columns, expressed in terms of load–settlement curves drawn up to the ultimate bearing capacity.     

Oort Cloud Comet Perihelion Asymmetries: Galactic Tide, Shower or Observational Bias?

We investigate the distribution of Oort cloud comet perihelia. The data considered includes comets having orbital elements of the two highest quality classes with original energies designated as new or young. Perihelion directions are determined in galactic, ecliptic and geocentric equatorial coordinates. Asymmetries are detected in the scatter and are studied statistically for evidence of adiabatic galactic tidal dynamics, an impulse-induced shower and observational bias. The only bias detected is the well-known deficiency of observations with perihelion distances q > 2.5 AU. There is no significant evidence of a seasonal dependence. Nor is there a substantive hemispherical bias in either ecliptic or equatorial coordinates. There is evidence for a weak stellar shower previously detected by Biermann which accounts for ≈ 10% of the total observations. Both the q bias and the Biermann star track serve to weaken the evidence for a galactic tidal imprint. Nevertheless, statistically significant asymmetries in galactic latitude and longitude of perihelia remain. A latitude asymmetry is produced by a dominant tidal component perpendicular to the galactic disk. The longitude signal implies that ≈ 20% of new comets need an additional dynamical mechanism. Known disk non-uniformities and an hypothetical bound perturber are discussed as potential explanations. We conclude that the detected dynamical signature of the galactic tide is real and is not an artifact of observational bias, impulsive showers or poor data. This revised version was published online in July 2006 with corrections to the Cover Date.     

EROS-II Variable Stars: Eclipsing Binaries in the EROS Microlensing Surveys

More than 10 years of microlensing survey observations by the EROS Collaboration have monitored several million stars, amongst them several thousand eclipsing binary stars. In this poster we present some of the difficulties and rewards of the study of this immense database.Based on observations made at ESO by the EROS collaboration     

Mid-infrared, spatially resolved spectroscopy of the nucleus of the Circinus galaxy

High spatial resolution spectroscopy at 8–13 μm with T-ReCS on Gemini-S has revealed striking variations in the mid-infrared emission and absorption in the nucleus of the Circinus galaxy (hereafter Circinus) on subarcsecond scales. The core of Circinus is compact and obscured by a substantial column of cool silicate dust. Weak extended emission to the east and west coincides with the coronal line region and arises from featureless dust grains which are probably heated by line emission in the coronal emission zone. The extended emission on the east side of the nucleus displays a much deeper silicate absorption than that on the west, indicating significant columns of cool material along the line of sight and corresponding to an additional extinction of   A_V ∼ 25 mag  . Emission bands from aromatic hydrocarbons are not subject to this additional extinction, are relatively weak in the core and in the coronal line region, and are much more spatially extended than the continuum dust emission; they presumably arise in the circumnuclear star-forming regions. These data are interpreted in terms of an inclined disc-like structure around the nucleus extending over tens of parsecs and possibly related to the inner disc found from observations of water masers by Greenhill et al..