Terrain trapped airflows and precipitation variability during an atmospheric river event

We examine thermodynamic and kinematic structures of terrain trapped airflows (TTAs) during an atmospheric river (AR) event impacting Northern California 10–11 March 2016 using Alpha Jet Atmospheric eXperiment (AJAX) aircraft data, in situ observations, and Weather and Research Forecasting (WRF) Model simulations. TTAs are identified by locally intensified low-level winds flowing parallel to the coastal ranges and having maxima over the near-coastal waters. Multiple mechanisms can produce TTAs, including terrain blocking and gap flows. The changes in winds can significantly alter the distribution, timing, and intensity of precipitation. We show here how different mechanisms producing TTAs evolve during this event and influence local precipitation variations. Three different periods are identified from the time-varying wind fields. During period 1 (P1), a TTA develops during synoptic-scale onshore flow that backs to southerly flow near the coast. This TTA occurs when the Froude number (Fr) is less than 1, suggesting low-level terrain blocking is the primary mechanism. During period 2 (P2), a Petaluma offshore gap flow develops, with flows turning parallel to the coast offshore and with Fr \u3e 1. Periods P1 and P2 are associated with slightly more coastal than mountain precipitation. In period 3 (P3), the gap flow initiated during P2 merges with a pre-cold-frontal low-level jet (LLJ) and enhanced precipitation shifts to higher mountain regions. Dynamical mixing also becomes more important as the TTA becomes confluent with the approaching LLJ. The different mechanisms producing TTAs and their effects on precipitation pose challenges to observational and modeling systems needed to improve forecasts and early warnings of AR events

Structure of the AlgKX modification and secretion complex required for alginate production and biofilm attachment in Pseudomonas aeruginosa

Synthase-dependent secretion systems are a conserved mechanism for producing exopolysaccharides in Gram-negative bacteria. Although widely studied, it is not well understood how these systems are organized to coordinate polymer biosynthesis, modification, and export across both membranes and the peptidoglycan. To investigate how synthase-dependent secretion systems produce polymer at a molecular level, we determined the crystal structure of the AlgK-AlgX (AlgKX) complex involved in Pseudomonas aeruginosa alginate exopolysaccharide acetylation and export. We demonstrate that AlgKX directly binds alginate oligosaccharides and that formation of the complex is vital for polymer production and biofilm attachment. Finally, we propose a structural model for the AlgEKX outer membrane modification and secretion complex. Together, our study provides insight into how alginate biosynthesis proteins coordinate production of a key exopolysaccharide involved in establishing persistent Pseudomonas lung infections.Bio-organic Synthesi

Magnetic susceptibility to identify landscape segments on a detailed scale in the region of Jaboticabal, São Paulo, Brazil

The agricultural potential is generally assessed and managed based on a one-dimensional vision of the soil profile, however, the increased appreciation of sustainable production has stimulated studies on faster and more accurate evaluation techniques and methods of the agricultural potential on detailed scales. The objective of this study was to investigate the possibility of using soil magnetic susceptibility for the identification of landscape segments on a detailed scale in the region of Jaboticabal, São Paulo State. The studied area has two slope curvatures: linear and concave, subdivided into three landscape segments: upper slope (US, concave), middle slope (MS, linear) and lower slope (LS, linear). In each of these segments, 20 points were randomly sampled from a database with 207 samples forming a regular grid installed in each landscape segment. The soil physical and chemical properties, CO2 emissions (FCO2) and magnetic susceptibility (MS) of the samples were evaluated represented by: magnetic susceptibility of air-dried fine earth (MS ADFE), magnetic susceptibility of the total sand fraction (MS TS) and magnetic susceptibility of the clay fraction (MS Cl) in the 0.00 - 0.15 m layer. The principal component analysis showed that MS is an important property that can be used to identify landscape segments, because the correlation of this property within the first principal component was high. The hierarchical cluster analysis method identified two groups based on the variables selected by principal component analysis; of the six selected variables, three were related to magnetic susceptibility. The landscape segments were differentiated similarly by the principal component analysis and by the cluster analysis using only the properties with higher discriminatory power. The cluster analysis of MS ADFE, MS TS and MS Cl allowed the formation of three groups that agree with the segment division established in the field. The grouping by cluster analysis indicated MS as a tool that could facilitate the identification of landscape segments and enable the mapping of more homogeneous areas at similar locations

Knowledge discovery from models of soil properties developed through data mining

We modelled the distribution of soil properties across the agricultural zone on the Australian continent using data mining and knowledge discovery from databases (DM&KDD) tools. Piecewise linear tree models were built choosing from 19 climate variables, digital elevation model (DEM) and derived terrain attributes, four Landsat multi-spectral scanner (MSS) bands, land use and lithology maps as predictors of topsoil and subsoil pH, organic C, % clay, and total N and P. The actual geographic location of the sampled soil data points was not used as a predictor. Classification trees were used to estimate topsoil and subsoil horizon thickness and texture class using similar predictors. That maps could be made using the decision tree models attests to the occurrence of knowledge discovery from the soil point databases used as training data. The decision tree models were evaluated and interpreted in a spatial context by: (1) tabulation of variables selected by the tree models; (2) mapping of the extent over which individual predictors were used and their thresholds; and (3) mapping of the extent over which combinations of predictors were used. The evaluation and interpretation process indicates that the models are consistent with general principles of soil genesis and that detailed investigation of the models¿ structure in a spatial context may have other uses in biogeographical studies and geo-ecological process modelling

Linked fluvial and aeolian processes fertilize Australian bioregions

The pattern of 137Cs-derived net (1950s–1990) soil redistribution over Australia, together with back-trajectory modeling of major dust storms, shows extensive areas of contemporary aeolian deposition. While the Cobar Peneplain and Gawler bioregions are the largest, the Wet Tropics is also a locus of deposition, consistent with the theory that dust is a source of nutrients for tropical rainforests growing on ancient weathered soils. Here we describe a new dust transport pathway over northeastern Australia and substantiate the link between fluvial and aeolian processes, and biogeochemical cycling between Australia’s arid interior and its coastal forest

Use of soil survey information to assess regional salinization risk using geographical information systems

Previous experience in southern and western Australia has shown that tree clearing alters the water balance in a landscape, leading to increased deep drainage and consequent rises in phreatic water tables. Assessment of the risk of regional salinization involves integration of hydrology, hydrogeology, soil and land management issues. An example of the use of soil survey data, integrated with water resources and digital elevation data in a GIS, to estimate the risk of salinization after tree clearing is illustrated for the upper Burdekin river basin in the wet/dry tropics of North Queensland. Soft map unit descriptions include information on soil-landform relations, parent material, soil thickness, depth to bedrock and dominant and subdominant soil types. Such information can be used to qualitatively estimate permeability and drainage classes (high, medium, or low) and to determine likely recharge and discharge areas in the landscape. Analysis of the spatial association between surveyed electrical conductivity measurements and estimated recharge and discharge areas was used to cross-check this qualitative classification. The distributions of saline soils and shallow water tables are used to assess the salinity hazard of the region. Where % total soluble salts (TSS) are >0.25% and water table 0.25%, recharge areas should not be cleared