Analysis of the length scale characterized by the yield stress fluids porosimetry method for consolidated media: comparison with pore network models and mercury intrusion porosimetry

Substantial progress has been recently achieved in the development of a clean alternative to mercury intrusion porosimetry (MIP) based on single-phase flow measurements in porous samples using yield stress fluids. However, no study to date has examined the scale of the pore length actually provided by the yield stress fluids porosimetry method (YSM) in consolidated porous media. Indeed, while the results of YSM were compared to those provided by MIP in the past, the relationships between the characterized pore size distribution (PSD) and the actual pore geometry have still not been addressed for this type of porous media. This issue is of special interest to geoscientists involved in seeking relevant information from core characterization operations. With this aim in mind, the objective of the present paper is to evaluate the agreement between the PSDs characterized by YSM, the pore-opening size distributions provided by MIP tests, and the pore-throat and pore-body size distributions obtained from X-ray computed microtomography. For this purpose, a set of artificial and natural porous samples with permeability values extending over two magnitudes were characterized by using both YSM and MIP laboratory tests. Then, the results were matched to the model pore geometries extracted from digital images of the real microstructure. This analysis led to the main conclusion that YSM can be reliably used as an adequate substitute for MIP in the case of the investigated consolidated media, given the general agreement observed between these methods.

     

Biological and chemical consequences of the 1997–1998 El Niño in central California waters

The physical, chemical and biological perturbations in central California waters associated with the strong 1997–1998 El Niño are described and explained on the basis of time series collected from ships, moorings, tide gauges and satellites. The evolution of El Niño off California closely followed the pattern observed in the tropical Pacific. In June 1997 an anomalous influx of warm southerly waters, with weak signatures on coastal sea level and thermocline depth, marked the onset of El Niño in central California. The timing was consistent with propagation from the tropics via the equatorial and coastal wave-guide. By late 1997, the classical stratified ocean condition with a deep thermocline, high sea level, and warm sea surface temperature (SST) commonly associated with El Niño dominated the coastal zone. During the first half of 1998 the core of the California Current, which is normally detected several hundred kilometers from shore as a river of low salinity, low nutrient water, was hugging the coast. High nutrient, productive waters that occur in a north–south band from the coast to approximately 200 km offshore during cool years disappeared during El Niño. The nitrate in surface waters was less than 20% of normal and new production was reduced by close to 70%. The La Niña recovery phase began in the fall of 1998 when SSTs dropped below normal, and ocean productivity rebounded to higher than normal levels. The reduction in coastal California primary productivity associated with El Niño was estimated to be 50 million metric tons of carbon (5×10¹³ g C). This reduction certainly had deleterious effects on zooplankton, fish, and marine mammals. The 1992–1993 El Niño was more moderate than the 1997–1998 event, but because its duration was longer, its overall chemical and biological impact may have been comparable. How strongly the ecosystem responds to El Niño appears related to the longer-term background climatic state of the Pacific Ocean. The 1982–1983 and 1992–1993 El Niños occurred during the warm phase of the Pacific Decadal Oscillation (PDO). The PDO may have changed sign during the 1997–1998 El Niño, resulting in weaker ecological effects than would otherwise have been predicted based on the strength of the temperature anomaly.     

Pollution — a French perspective

A summary of the various forms of pollution control discussed at an international Anti-Pollution Course held at the French Merchant Marine School in Marseilles on 13–25 June 1977.     

Synoptic-scale physical mechanisms associated with the Mei-yu front: A numerical case study in 1999

The Mei-yu front system occurring from 23 to 27 June 1999 consists of the Mei-yu front and the dewpoint front, which confine a warm core extending from the eastern flank of the Tibetan Plateau to the west of 145°E. To further understand the synopticscale physical mechanisms associated with the Mei-yu front system, the present study proposes another insight into the physical significance of the x-component relative vorticity (XRV) whose vertical circulation is expected to tilt isentropic surfaces. The XRV equation diagnoses exhibit that the twisting effect of the planetary vorticity (TEPV) is positive along the Mei-yu front and negative in the dewpoint front region, and tilts isentropic surfaces from south to north in the Mei-yu frontal zone. Conversely, the meridional gradient of the atmospheric buoyancy (MGAB) tilts isentropic surfaces in the opposite direction and maintains negative in the regions where the TEPV is positive and vice versa. Thus, the TEPV plays the role of the Mei-yu frontogenesis, whereas the MGAB demonstrates the Meiyu frontolysis factor. Both terms control the evolution of the cross-front circulation. The other terms show much minor contributions in this case study. The present simulations also indicate that the weakening of the upper-level jet evidently induces the weakening of the Mei-yu front and reduces the amplitude of the East Asia cold trough. Furthermore, the impact can also penetrate into the lower troposphere in terms of mesoscale disturbances and precipitation, proving that the upper-level jet imposes a noticeable top-down influence on the Mei-yu front system.     

Fine-scale vertical distribution of coastal and offshore copepods in the Golfo de Arauco, central Chile, during the upwelling season

In order to understand the mechanism by which zooplankters from different origins co-occur during the upwelling season within Golfo de Arauco, one of the most productive areas in central Chile, we assessed short term variations in the vertical distribution of the most abundant copepod species. Fine-scale, day and night vertical zooplankton sampling was done with a pump over 12 days in summer. The water column in the gulf consisted of three layers: Equatorial Subsurface Water of low dissolved oxygen content in the deeper part of the water column, strong temperature and oxygen gradients at mid-depth (15-25 m), and a layer of warmer, more oxygenated, less saline water at the surface. Copepods within the gulf originated from offshore, from the continental shelf, and from the coastal area. Most taxa showed distinctive vertical distributions. Three copepod groups were identified by their mean weighted depths of residence. One group included shallow residents found above the thermocline/oxycline (Acartia tonsa, Centropages brachiatus, Corycaeus sp., Paracalanus parvus, Oncaea sp.). A second group was comprised by species distributed at or below the thermocline/oxycline (Oithona sp., Oncaea conifera, Lucicutia sp., Metridia sp., Heterorhabdus papilliger). The third group was composed of vertical migrators that crossed the thermocline/oxycline (Calanus chilensis, Calanoides patagoniensis, Aetideus armatus, Pleuromamma piseki). In spite of their different vertical distribution ranges, the most abundant and frequent copepod species (P. parvus, C. chilensis, C. patagoniensis, C. brachiatus) share a common capacity to withstand wide ranges of oxygen concentration and temperature. This characteristic, along with the capacity to vary their life strategies under different environmental conditions, seems to facilitate the maintenance of large numbers of copepods in coastal waters along the Humboldt Current.     

Turbulence Over Urban-type Roughness: Deductions from Wind-tunnel Measurements

Turbulence data from experiments conducted over a staggered cube array, modelling a neutrally stable atmospheric boundary layer in an urban environment, are presented. The results support the contention that organised eddy structures in the near-wall region differ significantly from those in regular smooth-wall flows or in rough-wall boundary layers with much smaller h/δ ratios (where δ and h are the boundary-layer thickness and the height of the roughness elements, respectively). Attention is concentrated on spatial correlations, spectra (and thus the dominant length and time scales), maps of anisotropy invariants and quadrant analyses of the stress tensor. Results are obtained within both the roughness sublayer (i.e. the region above the roughness but within which the flow is spatially inhomogeneous) and the canopy region (i.e. below the height of the roughness elements) and discussion includes consideration of the turbulence kinetic energy balance at various heights.     

POlarization Emission of Millimeter Activity at the Sun (POEMAS): New Circular Polarization Solar Telescopes at Two Millimeter Wavelength Ranges

We present a new system of two circular polarization solar radio telescopes, POEMAS, for observations of the Sun at 45 and 90 GHz. The novel characteristic of these instruments is the capability to measure circular right- and left-hand polarizations at these high frequencies. The two frequencies were chosen so as to bridge the gap at radio frequencies between 20 and 200 GHz of solar flare spectra. The telescopes, installed at CASLEO Observatory (Argentina), observe the full disk of the Sun with a half power beam width of 1.4^°, a time resolution of 10 ms at both frequencies, a sensitivity of 2?–?4 K that corresponds to 4 and 20 solar flux unit (=10⁴ Jy), considering aperture efficiencies of 50±5 % and 75±8 % at 45 and 90 GHz, respectively. The telescope system saw first light in November 2011 and is satisfactorily operating daily since then. A few flares were observed and are presented here. The millimeter spectra of some flares are seen to rise toward higher frequencies, indicating the presence of a new spectral component distinct from the microwave one.