An Observation Operator for Radar Refractivity Change: Comparison of Observations and Convective-Scale Simulations

Weather radar refractivity depends on low-level moisture, temperature, and pressure and is available at high space–time resolutions over large areas. It is of definite meteorological interest for assimilation, verification, and process-study purposes. In this study, the path-averaged refractivity change is simulated from the Arome cloud-resolving atmospheric system analyses and compared with corresponding radar observations over a 35-day period with various meteorological conditions. For that, a novel post-processing procedure is applied to radar data to improve its quality. Also, an observation operator is developed that ingests Arome analyses and simulates a 3-h path-averaged refractivity change. A sensitivity study shows that simulated path-averaged refractivity change is immune to the modelling of the beam height as long as it remains below approximately 60 m above the ground. Comparisons show overall consistency between observed and simulated path-averaged refractivity change, with discrepancies at times that suggest an improvement in analyses once radar refractivity change observations are assimilated. Finally, errors introduced when retrieving local refractivity from path-averaged refractivity are estimated and it is found for our dataset that such retrievals halve the range of usable observations.     

Suspended sediment dynamics associated with snowmelt runoff in a small mountain stream of Lake Tahoe (Nevada)

The Lake Tahoe basin is experiencing an environmental decline that is partly due to sediment intakes from its tributaries. Many studies have estimated suspended sediment loads in these streams with a discrete sampling programme by collecting water samples and using a rating technique. However, the relationship between stream discharge and suspended sediment concentration (SSC) in these tributaries is known to differ during the rising and falling limbs of the snowmelt‐dominated hydrograph. Because of this hysteresis effect, sediment rating curves are poor predictors of suspended sediment dynamics in the stream. In this study, suspended sediment transport was investigated using a turbidity meter to provide a continuous record of sediment concentration during the snowmelt period. Hysteresis in suspended sediment transport was also investigated and is quantified with an H index, which is the ratio of the areas under the curve at different stages of the hydrograph. The temporal lag between the peak of SSC and the peak of stream discharge was quantified using cross‐correlation analysis. For almost all events, SSCs were higher during the rising limb of the hydrograph for a given discharge, with SSC peaks occurring before discharge peaks, resulting in clockwise hysteresis (H > 1). The H indices increased (looser hysteresis loop) as the availability of sediments increased and as the lag between peaks in SSC and discharge was larger. A restriction of the proposed H index was that it could only be computed when stream discharge increased by more than 30% during a melt event. Copyright © 2005 John Wiley & Sons, Ltd.     

Land cover effects on soil infiltration capacity measured using plot scale rainfall simulation in steep tropical lowlands of Central Panama

Understanding land use/land cover (LULC) effects on tropical soil infiltration is crucial for maximizing watershed scale hydro-ecosystem services and informing land managers. This paper reports results from a multiyear investigation of LULC effects on soil bulk infiltration in steep, humid tropical, and lowland catchments. A rainfall simulator applied water at measured rates on 2 × 6 m plots producing infiltration through structured, granulated, and macroporous Ferralsols in Panama's central lowlands. Time-lapse electrical resistivity tomography (ERT) helped to visualize infiltration depth and bulk velocity. A space-for-time substitution methodology allowed a land-use history investigation by considering the following: (a) a continuously heavy-grazed cattle pasture, (b) a rotationally grazed traditional cattle pasture, (c) a 4-year-old (y.o.) silvopastoral system with nonnative improved pasture grasses and managed intensive rotational grazing, (d) a 7 y.o. teak (Tectona grandis) plantation, (e) an approximately 10 y.o. secondary succession forest, (f) a 12 y.o. coffee plantation (Coffea canephora), (g) an approximately 30 y.o. secondary succession forest, and (h) a >100 y.o. secondary succession forest. Within a land cover, unique plot sites totalled two at (a), (c), (d), (e), and (g); three at (b); and one at (f) and (h). Our observations confirmed measured infiltration scale dependency by comparing our 12 m² plot-scale measurements against 8.9 cm diameter core-scale measurements collected by others from nearby sites. Preferential flow pathways (PFPs) significantly increased soil infiltration capacity, particularly in forests greater than or equal to 10 y.o. Time-lapse ERT observations revealed shallower rapid bulk infiltration and increased rapid lateral subsurface flow in pasture land covers when compared with forest land covers and highlighted how much subsurface flow pathways can vary within the Ferralsol soil class. Results suggest that LULC effects on PFPs are the dominant mechanism by which LULC affects throughfall partitioning, runoff generation, and flow pathways.     

Comparison of simulated longitudinal profiles of hadronic air showers with MASS2 balloon data

The KASKADE and CORSIKA air shower generators are compared to the data collected by MASS2 balloon experiment in 1991. The test of longitudinal profile for proton, helium and muon flux production provide good constraints on these air shower generators. KASKADE and CORSIKA especially with the new simulator UrQMD for low energies are found to fit these data well. This study is limited to a comparison of longitudinal profiles and therefore does not provide constraints on the overall shower development.     

Interferometry: The tool to study giant, supergiant and Mira stars

Late-type giant stars have been traditional targets for infrared interferometers. They are bright and big and are therefore easy targets to resolve and to detect. Considerable progress has been and is being made on the spatial structure of these objects thanks to existing interferometers. Beyond the classical measurement of their diameters, pulsations have been directly detected, spatial intensity distributions are more and more understood and more important, consistent scenarios for both spectroscopic and interferometric measurements are on the verge to be validated. All this has been possible with prototype instruments having a small number of baselines and very limited spectral capabilities. AMBER and MIDI will surely open a new era with high spectral resolution, high efficiency and imaging capabilities. This is not an exhaustive review of all the work done in the field but rather a presentation of the context. A recent review of Mira star observations with interferometers was recently written (Scholz, 2003).A brief science case is first introduced in this paper. Achievements with high angular resolution single-telescope techniques are presented. The contributions of optical and infrared interferometers are then explained. Eventually, some hints about the possible progress with VLTI are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

GEOLOGICAL DATING PRINCIPLES QUESTIONED Paleohydraulics:a new approach

1　Situation1 .1　ThebasicassumptionNicolasStenonwasthefounderofstratigraphy .Itwasin 1 667,inhisworkCanisCalchariaethatheintroducedthepostulatethat:layersofsub soilare‘strata’(Fig .1 )ofancientsuccessive‘sediments’.Tobemoreprecise ,astratumisalayerofhomoge neousorsegregatedlithologicalcontent (e .g .sand stone ,limestone ,clay)betweentwosurfacelimitsofsuperposedadjacentstrata.Thesesurfacessometimescorrespondtoanerosion ,aninterruptionofsedi men tation ,characterisedbyabeddingplane,orali…     

PAMPRE: A dusty plasma experiment for Titan's tholins production and study

Organic aerosols play a significant role in the properties and evolution of Titan's atmosphere. But our knowledge of them and their physico-chemical mechanisms of formation and evolution are currently limited to a few data obtained by Titan observations from the Earth or from space probes. For this reason, laboratory experiments are developed to simulate the atmospheric chemistry and produce analogues of these aerosols in order to understand better their properties and how they are formed. The plasma discharges are the most efficient devices for the production of such analogues. However, the existing plasmas simulations introduce experimental biases compared with the conditions of aerosols production in Titan's atmosphere: chemistry is induced by electrons instead of photons; the solid analogues are produced and deposited on solid surfaces; direct analysis of the particles inside the reactive chamber is not easy. In order to avoid some of these experimental problems, we have developed another method of production of Titan's aerosols analogues. It is based on a capacitively coupled radio-frequency (RF) cold plasma system at low pressure in a N₂-CH₄ gaseous mixture. In this plasma, solid particles produced from the gas phase are in levitation, thus preventing any wall effect on their production, and allowing the study of the formation and growth of the particles directly in the plasma. Moreover, the electron energy distribution of this plasma can be compared with the solar spectrum. This article describes the RF plasma experiment and presents the first results obtained with an initial N₂-CH₄ (90:10) gaseous mixture which produced our first studied analogues of Titan's aerosols.     

TM/ETM+/LDCM Images for Studying Land Surface Temperature (LST) Interplay with Impervious Surfaces Changes over Time Within the Douala Metropolis,Cameroon

Douala, the most important metropolis of Cameroon, is a sub-Saharan wet coastal environment of which the anarchic urbanization is a socio-economic and environmental problem, significantly influencing the local climate. In this study, three Landsat images from 1986 (TM), 2007 (ETM+) and 2016 (LDCM), were utilized to investigate the effect of this urbanization on the increasing land surface temperature (LST) between these dates. Thus, the urban indices (UI), determined from the Landsat Visible and NIR channels were used to identify impervious areas (Urban Fabric and bare soil) of urban area. It has been shown from the UI images that, impervious areas have been increased from 1986 to 2016. The LST images derived have a continual expansion of zones and points of heat throughout these dates. The correlation analysis of LST and UI, at the pixel-scale, indicated the positive relationship between these parameters, which could show a real impact of urbanization on the increasing temperature in the area. These correlations are fairly low in 1986 (maximum R-square value is about 0.35) and in 2007 (maximum R-square value is about 0.44. In 2016, a high positive correlation (maximum R-square value is about 0.77) confirm that, the impervious areas strengthen the temperature and the Urban Heat Island effect in Douala urban zone. Overall, the earth observation images and the geographic information system techniques were effective approaches for aiming at environment monitoring and analyzing urban growth patterns and evaluating their impacts on urban climates.     

Physical properties of the stone meteorites: Implications for the properties of their parent bodies

The physical properties of the stone meteorites provide important clues to understanding the formation and physical evolution of material in the Solar protoplanetary disk as well providing indications of the properties of their asteroidal parent bodies. Knowledge of these properties is essential for modeling a number of Solar System processes, such as bolides in planetary atmospheres, the thermal inertia of atmosphereless solid body surfaces, and the internal physical and thermal evolution of asteroids and rock-rich icy bodies. In addition, insight into the physical properties of the asteroids is important for the design of robotic and crewed reconnaissance, lander, and sample return spacecraft missions to the asteroids. One key property is meteorite porosity, which ranges from 0% to more than 40%, similar to the range of porosities seen in asteroids. Porosity affects many of the other physical properties including thermal conductivity, speed of sound, deformation under stress, strength, and response to impact. As a result of the porosity, the properties of most stone meteorites differ significantly from those of compact terrestrial rocks, whose physical properties have been used in many models of asteroid behavior. A few physical properties, such as grain density, magnetic susceptibility, and heat capacity are not functions of porosity. Taken together, the grain density and the magnetic susceptibility can be used to classify unweathered or minimally weathered ordinary chondrites. This provides a rapid screening technique to identify heterogeneous samples, classify new samples, and identify misclassified meteorites or interlopers in strewn fields.     

Constraint on foreland basin migration in the Zagros mountain belt using Sr isotope stratigraphy

We have constrained the time‐space migration of the Zagros foredeep basin by performing Sr isotope stratigraphy on 31 samples of marine macrofossils from Neogene sediments now exposed in the Zagros mountain belt in southwest Iran. Our results show that these deposits (represented mainly by the Mishan Formation) are strongly diachronous, with ages ranging between 17.2 ± 0.2 and 1.1 ± 0.1 Ma. These deposits are older in the west (Dezful region) and become progressively younger towards the south and the south‐east (Fars region). Our results show that the marine foredeep was replaced by a fluvial sedimentary environment between ca. 14 and 12 Ma in the western sector, while this occurred between ca. 8 and 1 Ma in the eastern sector, becoming younger towards the south. These results enable us to show that the foreland basin migrated perpendicular to the orogen at rates of between 17.5 and 50 mm year^?1 throughout the Neogene, exceeding migration rates in the Alps, Pyrenees, Apennines and Himalayan foreland basins. The sporadically elevated rates in the Zagros appear to be related to times when major widely spaced pre‐existing basement faults became reactivated. Finally, our results, when combined with published data, have enabled us to establish a new chronostratigraphic diagram for the Neogene portion of the Zagros foreland basin. Our study highlights that foreland basins are extremely dynamic settings where depocentres and palaeoenvironments may change rapidly in both time and space in relation to migrating deformation.