Modeling Forest Emissivity at L-Band and a Comparison With Multitemporal Measurements

This letter describes recent advances in modeling forest emissivity at L-band. The formulation is based on a previously developed discrete model and includes a new representation of forest litter. Comparisons with multitemporal radiometric data collected in the framework of the ldquoBray 2004rdquo experiment, which was carried out within Les Landes forest, are shown and discussed. Input variables are given by using detailed ground measurements. In general, the model reproduces both absolute values and temporal variations of measured brightness temperature. The contribution of the litter to overall emission was found to be important.     

Climatology of extratropical cyclones over the South American–southern oceans sector

A climatology of extratropical cyclones is presented. Extratropical cyclones, their main characteristics and their predominant tracks, as well as their interannual variability, affect weather in South America. For that purpose, a storm track database has been compiled by applying a cyclone tracking scheme to six-hourly sea level pressure fields, available from the National Center for Environmental Prediction–National Center for Atmospheric Research reanalyses II for the 1979–2003 period. The spatial distribution of the cyclogenesis frequency shows two main centers: one around Northern Argentina, Uruguay, and Southern Brazil in all seasons and the other near to the North Antarctic Peninsula. The lifetime of extratropical cyclones in the South American sector exhibits small seasonality, being typically of the order of 3.0 days during most of the year and slightly higher (3.5 days) in austral summer. The distance travelled by the cyclones formed in the South American sector tends to be smaller than the total paths found in other areas of the Southern Hemisphere. A k-mean clustering technique is used to summarize the analysis of the 25-year climatology of cyclone tracks. Three clusters were found: one storm-track cluster in Northeast Argentina; a second one west of the Andes Cordillera; and a third cluster located to the north of the Antarctic Peninsula (around the Weddell Sea). The influence of the Antarctic Oscillation (AAO) in the variability of extratropical cyclones is explored, and some signals of the impacts of the variability of the AAO can be observed in the position of the extratropical cyclones around 40°S, while the impacts on the intensity is detected around 55°S.     

RESURGENT MEXICAN PHOENIX*

ABSTRACT. Popular impressions of Phoenix, Arizona perpetuate the notion that this metropolitan area is an overwhelmingly Anglo place. We challenge this assertion and demonstrate that the city has substantial Mexican roots and is presently being shaped by a vibrant, resurgent Mexican population. Employing historical records, surveys, and landscape data, we articulate the Mexican character of early Phoenix and highlight how the revival of Mexican Phoenix has transformed the urban landscape. We then relate how Phoenix's Mexican population is a more nuanced regional subculture formed through both historical and contemporary connections with specific Mexican states. We conclude with a call for greater understanding of the internal heterogeneity of Mexicans in the United States and how this can inform our geographical interpretations of the growing Latinization of American cities.     

The development and the projective methods of geodesy and their effect on large triangulation and trilateration networks

The projective methods of Helmert and Pizzetti enable the measured elements of a geodetic network to be reduced rigorously to the surface of a reference ellipsoid. However, in most existing triangulation networks, the routine development method has been used for this purpose. Some of the differences between the development and projective methods are investigated by interpreting the results of two numerical examples. It is concluded that use of the development method may cause appreciable discrepancies to occur within geodetic networks, depending primarily upon the extent of the networks, the orientation of the ellipsoid used, and the magnitude of the geoid undulations. Geophysical Studies Section Aeronautical Chart and Information Center     

Arsenite sequestration at the surface of nano-Fe(OH)2, ferrous-carbonate hydroxide, and green-rust after bioreduction of arsenic-sorbed lepidocrocite by Shewanella putrefaciens

X-ray Absorption Fine Structure (XAFS) spectroscopy was used in combination with high resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS), X-ray energy dispersive spectroscopy (XEDS), X-ray powder diffraction, and Mössbauer spectroscopy to obtain detailed information on arsenic and iron speciation in the products of anaerobic reduction of pure and As(V)- or As(III)-adsorbed lepidocrocite (γ-FeOOH) by Shewanella putrefaciens ATCC 12099. We found that this strain of S. putrefaciens is capable of using Fe(III) in lepidocrocite and As(V) in solution or adsorbed on lepidocrocite surfaces as electron acceptors. Bioreduction of lepidocrocite in the absence of arsenic resulted in the formation of hydroxycarbonate green rust 1 [Fe^II₄Fe^III₂(OH)₁₂CO₃: GR1(CO₃)], which completely converted into ferrous-carbonate hydroxide (Fe^II₂(OH)₂CO₃: FCH) over nine months. This study thus provides the first evidence of bacterial reduction of stoichiometric GR1(CO₃) into FCH. Bioreduction of As(III)-adsorbed lepidocrocite also led to the formation of GR1(CO₃) prior to formation of FCH, but the presence of As(III) slows down this transformation, leading to the co-occurrence of both phases after 22-month of aging. At the end of this experiment, As(III) was found to be adsorbed on the surfaces of GR1(CO₃) and FCH. After five months, bioreduction of As(V)-bearing lepidocrocite led directly to the formation of FCH in association with nanometer-sized particles of a minor As-rich Fe(OH)₂ phase, with no evidence for green rust formation. In this five-month experiment, As(V) was fully converted to As(III), which was dominantly sorbed at the surface of the Fe(OH)₂ nanoparticles as oligomers binding to the edges of Fe(OH)₆ octahedra at the edges of the octahedral layers of Fe(OH)₂. These multinuclear As(III) surface complexes are characterized by As-As pairs at a distance of 3.32 ± 0.02 Å and by As-Fe pairs at a distance of 3.50 ± 0.02 Å and represent a new type of As(III) surface complex. Chemical analyses show that the majority of As(III) produced in the experiments with As present is associated with iron-bearing hydroxycarbonate or hydroxide solids, reinforcing the idea that, at least under some circumstances, bacterial reduction can promote As(III) sequestration instead of mobilizing it into solution.     

Use of Roche coordinates in the problems of small oscillations of tidally distorted stellar models

The system of Roche coordinates developed by Kopal to study the problems of stars in close binary systems has been used to study the problems of small oscillations of tidally distorted stars.     

THE INFLUENCE OF SLOPE AND RAIN INTENSITY ON RUNOFF AND INFILTRATION / L'influence de l'inclinaison de terrain et de l'intensité de pluie sur l'écoulement et l'infiltration

Abstract

The design and construction of a special-purpose laboratory catchment and rainfall simulator is described. The equipment consists of a soil catchment area that can be inclined at various angles. Additional instrumentation then measures the flow of water across the surface of, and through, the soil bed. Precipitation is provided by a unit that simulates rainfall at particular rates with uniform distribution.

The equipment was used to examine infiltration, runoff and other hydrological properties of a number of soils under different rainfall intensities and with different catchment slopes. Correlations were obtained for these variables.     

Evaluation of site effects on ground motions based on equivalent linear site response analysis and liquefaction potential in Chennai,south India

We study local site effects with detailed geotechnical and geophysical site characterization to evaluate the site-specific seismic hazard for the seismic microzonation of the Chennai city in South India. A Maximum Credible Earthquake (MCE) of magnitude 6.0 is considered based on the available seismotectonic and geological information of the study area. We synthesized strong ground motion records for this target event using stochastic finite-fault technique, based on a dynamic corner frequency approach, at different sites in the city, with the model parameters for the source, site, and path (attenuation) most appropriately selected for this region. We tested the influence of several model parameters on the characteristics of ground motion through simulations and found that stress drop largely influences both the amplitude and frequency of ground motion. To minimize its influence, we estimated stress drop after finite bandwidth correction, as expected from an M6 earthquake in Indian peninsula shield for accurately predicting the level of ground motion. Estimates of shear wave velocity averaged over the top 30 m of soil (V_S30) are obtained from multichannel analysis of surface wave (MASW) at 210 sites at depths of 30 to 60 m below the ground surface. Using these V_S30 values, along with the available geotechnical information and synthetic ground motion database obtained, equivalent linear one-dimensional site response analysis that approximates the nonlinear soil behavior within the linear analysis framework was performed using the computer program SHAKE2000. Fundamental natural frequency, Peak Ground Acceleration (PGA) at surface and rock levels, response spectrum at surface level for different damping coefficients, and amplification factors are presented at different sites of the city. Liquefaction study was done based on the V_S30 and PGA values obtained. The major findings suggest show that the northeast part of the city is characterized by (i) low V_S30 values (<?200 m/s) associated with alluvial deposits, (ii) relatively high PGA value, at the surface, of about 0.24 g, and (iii) factor of safety and liquefaction below unity at three sites (no. 12, no. 37, and no. 70). Thus, this part of the city is expected to experience damage for the expected M6 target event.