Surface moisture area during rainfall–run‐off events to understand the hydrological dynamics of a basin in a plain region

The understanding of the hydrology of plain basins may be improved by the combined analysis of rainfall–run‐off records and remote sensed surface moisture data. Our work evaluates the surface moisture area (SMA) produced during rainfall–run‐off events in a plain watershed of the Argentine Pampas Region, and studies which hydrological variables are related to the generated SMA. The study area is located in the upper and middle basins of the Del Azul stream, characterized by the presence of small gently hilly areas surrounded by flat landscapes. Data from 9 rainfall–run‐off events were analysed. MODIS surface reflectance data were processed to calculate SMA subsequent to the peak discharge (post‐SMA), and previous to the rainfall events (prev‐SMA), to consider the antecedent wetness. Rainfall–run‐off data included total precipitation depth (P), maximum intensity of rainfall over 6 hr (I6max), surface run‐off registered between the beginning of the event and the day previous to the analysed MODIS scene (R), peak flow (Qp), and flood intensity (IF). In contrast with other works, post‐SMA showed a negative relationship with the R. Three groups of cases were identified: (a) Events of low I6max, high prev‐SMA, and low R were associated with slow and weakly channelized flow over plain areas, leading to saturated overland flow (SOF), with large SMA; (b) events of high I6max, low prev‐SMA, and medium to high R were rapidly transported along the gentle slopes of the basin, related to Hortonian overland flow (HOF) and low post‐SMA; and (c) events of medium to high I6max and prev‐SMA with medium R were related to heterogeneous input‐antecedent‐run‐off conditions combined: Local spatial conditions may have produced HOF or SOF, leading to an averaged response with medium SMA. The interactions between the geomorphology of the basin, the characteristics of the events, and the antecedent conditions may explain the obtained results. This analysis is relevant for the general knowledge of the hydrology of large plains, whose functioning studies are still in their early stages.     

Eutrophication and retention time affecting spatial heterogeneity in a tropical reservoir

Longitudinal heterogeneity in reservoirs is especially related to increase in sedimentation and water transparency along the river/dam axis. Consequently, primary production tends to reach higher values in intermediate regions where there is a balance between the availability of the main resources (light and nutrients) suitable for phytoplankton growth. Many factors such as reservoir morphometry, retention time, thermal stratification and geographical location can affect the boundaries between these regions. The tropical Funil Reservoir (Brazil), despite a low retention time, has experienced severe eutrophication in recent decades, with persistent cyanobacteria blooms. During the course of 1 year, samples were collected at four stations along the reservoir (fluvial, intermediate and lentic compartments) to evaluate if spatial heterogeneity could affect the occurrence and distribution of these blooms along the reservoir. Although the reservoir has a short annual retention time (mean 41.5 days), the typical zonation pattern was observed for the main abiotic variables and phytoplankton abundance. However, higher biomass occurred in the lentic compartment rather than in the intermediate zone. Despite the peculiar heterogeneity in total biomass, the phytoplankton composition and seasonal variability were very similar along the entire reservoir, with a few marked differences only in the fluvial zone. Phytoplankton total biomass in Funil Reservoir was high, even in periods of lower seasonal retention time (around 15 days), and was especially related to high input of nutrients. Moreover, retention time directly affects the spatial heterogeneity of phytoplankton biomass, since strong variability was only observed during the cold-dry season, corresponding to periods of longer retention time (around 80 days). While high availability of nutrients promoted high cyanobacterial biomass in the entire system, the few periods of heterogeneous spatiality seemed to be related to changes in retention time.     

A low cosmic microwave background variance in the Wilkinson Microwave Anisotropy Probe data

We have estimated the cosmic microwave background (CMB) variance from the three-year Wilkinson Microwave Anisotropy Probe ( WMAP ) data, finding a value which is significantly lower than the one expected from Gaussian simulations using the WMAP best-fitting cosmological model, at a significance level of 98.7 per cent. This result is even more prominent if we consider only the North ecliptic hemisphere (99.8 per cent). Different analyses have been performed in order to identify a possible origin for this anomaly. In particular, we have studied the behaviour of single-radiometer and single-year data as well as the effect of residual foregrounds and 1/f noise, finding that none of these possibilities can explain the low value of the variance. We have also tested the effect of varying the cosmological parameters, finding that the estimated CMB variance tends to favour higher values of n _s than the one of the WMAP best-fitting model. In addition, we have also tested the consistency between the estimated CMB variance and the actual measured CMB power spectrum of the WMAP data, finding a strong discrepancy. A possible interpretation of this result could be a deviation from Gaussianity and/or isotropy of the CMB.     

Understanding Amazonian fluvial rias based on a Late Pleistocene–Holocene analog

Fluvial rias are elongated lakes at tributary mouths that can reach dozens of kilometers in length, constituting one of the most remarkable features in the Amazonian landscape. Thus far, definitive data which documents the genesis of fluvial rias have not been published. The main goal of this work was to integrate morphological, sedimentological and chronological information in order to characterize fluvial paleorias in the interfluve of the Purus and Madeira Rivers and discuss the most likely hypothesis for their genesis. These paleorias were first observed through remote sensing imagery as several elongated and interconnecting belts of open vegetation that are in sharp contact with the surrounding dense forest. The belts are branched and form a dendritic pattern similar to many modern drainage networks. The sedimentary record of these belts revealed the prevalence of sharp‐based sandstones and mudstones arranged into fining‐upward successions, which are compatible with deposition within channels. Active channel and abandoned channel deposits were recognized. These are topped by continuous mudstones related to rapid channel abandonment and formation of a low energy basin or ria environment. Radiocarbon dating of these deposits recorded only Late Pleistocene and Holocene ages ranging from 21 547–22 285 cal yr bp to 5928–6124 cal yr bp . This chronology for sediment deposition is not compatible with the hypothesis of Amazonian rias being formed by fluvial erosion during the Last Glaciation Maximum low sea level, with sediment accumulation during the subsequent Holocene transgression. Instead, the studied paleorias record previous tributaries of the Madeira River that became abandoned as the position of this river shifted southeastward and its interfluve tilted northward, inverting the drainage systems. Therefore, a neotectonic origin of some Amazonian paleorias seems most likely. This hypothesis should be considered in further investigations aiming at understanding the origin of numerous modern fluvial rias that typify the Amazonian landscape. Copyright © 2014 John Wiley & Sons, Ltd.     

Synoptic patterns associated with landslide events in the Serra do Mar, Brazil

Heavy rains frequently occur over the Serra do Mar, in the southeast coastal mountain region in Brazil, particularly during the summer season. These rains can cause landslides and loss of life. The objective of this work is to produce a synoptic climatology of heavy rainfall episodes of the period from November to April using 10-year reanalyses data. The identification of the synoptic pattern of these events should provide guidance to forecasters. The landslide events were mostly related to cold front passages and the South Atlantic Convergence Zone (SACZ). These systems differed from the climatology by exhibiting more intense characteristics for the frontal situations and a blocking circulation configuration for the SACZ situations. In both cases, the composite fields showed that the 250-hPa mass divergence was strikingly more intense than the climatology and had a preferred location in the 24 h prior to landslide events. Anomalies of this ten-year event climatology showed above-normal moisture anomalies, which are more evident in the SACZ than in the frontal cases.     

Estimating the Random Error in Eddy-Covariance Based Fluxes and Other Turbulence Statistics: The Filtering Method

A spatially local decomposition of turbulent fluxes based on properties of spatial filters is used to develop a new method of estimating random error in turbulent moments of any order. The proposed error estimation method does not require an estimate of the integral time scale, which can be highly sensitive to the method used to calculate it. The error estimation method is validated using synthetic flux data with a known ensemble mean and intercompared with existing methods using data from the Advection Horizontal Array Turbulence Study (AHATS). Typical errors for a 27.3-min block of data collected at a height of 8 m are found to be approximately 10% for the heat flux and 7–15% for variances. The error in the momentum flux increases rapidly with increasing atmospheric instability, reaching values of 40% or greater for unstable conditions. A new method based on filtering is also proposed to estimate integral time scales of turbulent quantities.     

A unified mechanical and retention model for saturated and unsaturated soil behaviour

The coupled mechanical and water retention elasto-plastic constitutive model of Wheeler, Sharma and Buisson (the Glasgow coupled model, GCM) predicts unique unsaturated isotropic normal compression and unsaturated critical state planar surfaces for specific volume and degree of saturation when soil states are at the intersection of mechanical (M) and wetting retention (WR) yield surfaces. Experimental results from tests performed by Sivakumar on unsaturated samples of compacted speswhite kaolin confirm the existence and form of these unique surfaces. The GCM provides consistent representation of transitions between saturated and unsaturated conditions, including the influence of retention hysteresis and the effect of plastic volumetric strains on retention behaviour, and it gives unique expressions to predict saturation and de-saturation conditions (air-exclusion and air-entry points, respectively). Mechanical behaviour is modelled consistently across these transitions, including appropriate variation of mechanical yield stress under both saturated and unsaturated conditions. The expressions defining the unsaturated isotropic normal compression planar surfaces for specific volume and degree of saturation are central to the development of a relatively straightforward methodology for determining values of all GCM parameters (soil constants and initial state) from a limited number of laboratory tests. This methodology is demonstrated by application to the experimental data of Sivakumar. Comparison of model simulations with experimental results for the full set of Sivakumar’s isotropic loading stages demonstrates that the model is able to predict accurately the variation of both specific volume and degree of saturation during isotropic stress paths under saturated and unsaturated conditions.     

On the Machian origin of inertia

We examine Sciama’s inertia theory: we generalise it, by combining rotation and expansion in one unique model, we find the angular speed of the Universe, and we stress that the theory is zero-total-energy valued. We compare with other theories of the same null energy background. We determine the numerical value of a constant which appears in the Machian inertial force expression devised by Graneau and Graneau (In the Grip of the Distant Universe—the Science of Inertia, World Scientific, Singapore, 2006), by introducing the above angular speed. We point out that this last theory is not restricted to Newtonian physics as those authors stated but is, in fact, compatible with other cosmological and gravitational theories. An argument by Berry (Principles of Cosmology and Gravitation, Adam Hilger, Bristol, 1989) is shown in order to “derive” Brans-Dicke relation in the present context.     

An elastoplastic mechanical constitutive model for microbially mediated cemented soils

Microbially induced calcite precipitation (MICP) is an innovative bio-mediated soil improvement technique that develops cementation within originally loose and potentially collapsible soils. This method utilizes biogeochemical processes with microbes. It has the advantage of being friendly to the environment and sustainable. In spite of the current interest in the MICP technique, the mechanical modeling of MICP-treated soils is still limited. In this paper, a constitutive model for MICP-treated sands is presented. The core components of the proposed approach include: a critical state yield surface, sub-loading concepts, a mechanism to account for the MICP-induced cementation enhancement, and an evolution law to consider bonding degradation effects during shearing. The mathematical framework is presented in detail. The model is then applied to analyze recently published experiments involving MICP-treated samples, with different calcite contents, and tested under different conditions (i.e., various confining pressure and loading paths). The model was able to properly capture the main features of MICP-treated sands behavior observed in the tests. It also assisted to interpret the response of this type of soil under different loading conditions.