A technique for the determination of areal average rainfall / Une méthode pour la détermination de précipitation moyenne pour une zone donnée

Abstract

A method was developed for allocating an area likely to be shared by a raingauge station. Average areal precipitation was found by weighting the rainfall at the gauging station in terms of the product of distances enclosing it or radiating from it. The method was applied to two real and two hypothetical basins and the results were compared with those obtained by existing techniques.     

A GENERALIZED METHOD OF COMPUTING SECOND DERIVATIVE OF GRAVITY FIELD*

The unsuitability of a particular method of computation of second derivative to varying types of field problems evinces the need of a method by which it may be possible to obtain a wide range of filters. This requirement is achieved by incorporating a mathematical smoothing operator, e^-λρ2, λ and ρ being the smoothing parameter and radial frequency respectively, in the theoretical frequency response of second derivative operation. A few sets of weights for various smoothing parameters, are presented. The analysis of Bouguer gravity anomaly map of Los Angeles Basin, California, U.S.A., is carried out by Elkins's (1951) and Rosenbach's (1953) methods and the sets of weights given in this paper which clearly establishes their filtering equivalence.     

Assessing spatial variability in soil characteristics with geographically weighted principal components analysis

Dimensionality reduction methods such as principal components analysis (PCA) provide a means of identifying trends in soil characteristics which may be represented by a wide range of variables. However, these characteristics may be highly spatially variable and so the results from PCA represent, in some sense, an “average” of locally distinct characteristics. One approach to account for these local differences is to introduce a geographical weighting scheme into the PCA process. In this paper, such an approach is assessed in the exploration of soil characteristics in the state of Pennsylvania, USA. Data from 878 georeferenced soil profiles which include different soil parameters (n = 12) were extracted from the National Soil Survey Center database. Where data are parts of compositions (e.g., percentages of sand, silt, and clay), analysis using raw data is not appropriate and such data were transformed using log ratios (specifically, balances). Single variables (i.e., those which are not parts of compositions) were logged. The first two principal components explain over 50% of the variance. The mapped values suggest marked spatial variation in soil characteristics, but it is not possible to assess which of these variables explain most variation in particular regions from the simple maps of raw variables. Geographically weighted PCA (GWPCA) provides additional information which is obscured by PCA, and it also provides a set of component scores and loadings at all data locations. The soil variable with the largest loading at most locations of Pennsylvania is the logged base saturation (BSln), and this supports the findings of the conventional PCA analysis. While BSln loads most highly in most of the eastern third, the middle and the south west of the state, the northwest is less spatially consistent in terms of the variables which explain most variation. For GWPC 1, the variable with the second largest loading at most locations (i.e., primarily the south and west) is CEC.B1 (the log ratio of Ca, Mg, and Na to K and EXACID), while CEC.B2 (the log ratio of Ca and Mg to Na), pHln (logged pH) and BSln dominate in other areas. The GWPCA results suggest that there is marked spatial variation in multivariate soil characteristics across Pennsylvania state and that results from standard PCA obscure this considerable variation.     

Erosional effects on terrestrial resources over the last millennium in Reykjanes, southwest Iceland

The study presents the effect of soil erosion on vegetation, soil accumulation (SA), SA rate (SAR), soil quality, soil mass, and the soil organic carbon (SOC) pool in Brown Andosols and Histosols in a 24-km² area in southwest Iceland. Undisturbed prehistoric soils were distinguished from disturbed historic soils using tephrochronology. Soil erosion has been severe during historic time (last 1135 yr), resulting in the increase of the soil mass deposited in soils covered by vegetation by a factor of 7.3-9.2 and net loss of soil in unvegetated areas. The SAR correlated positively with SOC sequestration. SOC is easily transported and, given the extensive accumulation of soil, the net effect of burial and subsequent reduction in decomposition is to increase SOC storage. Nevertheless, the increased accumulation and soil depletion has decreased soil quality, including the SOC, and reduced soil resistance to erosion with the depleted SOC contributing to enrichment of atmospheric CO₂. The initial terrestrial disturbance was triggered by anthropogenic land use during the Medieval Warm Period, followed by volcanic activity approximately three centuries later. The combination of harsh climate during the Little Ice Age and drastic anthropogenic perturbations has led to land degradation at a catastrophic scale.     

美国俄亥俄州土壤有机碳密度空间分布(英文)

Historical database of National Soil Survey Center containing 1424 geo-referenced soil profiles was used in this study for estimating the organic carbon(SOC) for the soils of Ohio,USA.Specific objective of the study was to estimate the spatial distribution of SOC density(C stock per unit area) to 1.0-m depth for soils of Ohio using geographically weighted regression(GWR),and compare the results with that obtained from multiple linear regression(MLR).About 80% of the analytical data were used for calibration and 20% for validation.A total of 20 variables including terrain attributes,climate data,bedrock geology,and land use data were used for mapping the SOC density.Results showed that the GWR provided better estimations with the lowest(3.81 kg m 2) root mean square error(RMSE) than MLR approach.Total estimated SOC pool for soils in Ohio ranged from 727 to 742 Tg.This study demonstrates that,the local spatial statistical technique,the GWR can perform better in capturing the spatial distribution of SOC across the study region as compared to other global spatial statistical techniques such as MLR.Thus,GWR enhances the accuracy for mapping SOC density.     

P-T-X Relationships Deduced from Corona Textures in Sapphirine--Spinel--Quartz Assemblages from Paderu, Southern India

The sapphirine (Sa)-spinel (Sp)-quartz (Qz)-bearing rocks fromPaderu occur as lenticular enclaves within the Precambrian khondalite-charnockiteterrane of southern India. In addition these rocks contain orthopyroxene(Opx), sillimanite (Sill), garnet (Gt), cordierite (Cd), biotite,potash feldspar (Kf), plagioclase, and symplectites of Cd-Kf-Qz-Opx.The symplectites may have formed from the breakdown of osumilite.Grain contacts of sapphirine and spinel with quartz are rarelyobserved and the incompatibility with quartz during later stagesis displayed by the development of several types of polymineralicreaction coronas. The coronas in the different rock types A,B, etc. are (minerals listed from core to rim of corona): (A-1) sapphirine-bearing rock type without spinel: Sa-Sill-Opx,Sa-Sill-Cd, Sa-Cd-Opx (A-2) sapphirine and spinel-bearing: Sp-Sa-Sill-Opx-Qz, Sp-Sa-Sill,Sp-Sa-Opx, Sp-Sill-Opx, Sp-Sa-Sill-Gt-Qz, Sa-Sill-Opx, Sp-Sa-Sill-Opx,Sa-Sill-Opx-Gt, Sp-Sa-Opx-Gt, Sp-Sa-Sill-Gt; and (B) spinel-bearingbut sapphirine free: Sp-Sill-Opx, Sp-Sill-Gt, Sp-Cd. Commonlythe coronas in the rock type A 2 and B also contain ilmeno-hematite?corundumin the core in association with spinel. These rock types alsoprovide textural evidence for later crystallization of Cd, Cd+ Sa, and Gt + Qz from Opx+Sill?Qz and Gt+Sill+Qz. Sapphirine is aluminous (near 7(Mg, Fe²⁺)O?9(Al, Fe³⁺)₂O₃?3SiO₂)and contains up to 12?2 wt. per cent iron as FeO. Orthopyroxeneis also aluminous, containing up to 10?4 wt. per cent Al₂O₃.Sapphirine and spinel have relatively high contents of Fe₂O₃.X_Mg in the Fe-Mg minerals increases from rock type B to A2 toA1. A sequence of reactions has been deduced from coronas and otherreaction textures, and from the phase compatibility relationsin the FeO-MgO-Al₂O₃-SiO₂-H₂O system. The P-T-X relationshipsfrom geothermobarometry and petrogenetic grids, viz. µ_Fe2O3vs. µ_FeO and µ_H2O vs. µ_Fe2O3, suggest: (1)a retrograde, mildly decompressive trajectory from 900?60?C/65?0?7kb (core) to 760?50?C/5 ? 0?6 kb (rim); and (2) the observedmineralogy of the coronas and reactions deduced from them aredependent on the relative FeO, Fe₂O₃, and H₂O contents of therocks (µ_FeO3, µ_Fe2O3), and µ_H2O).     

Soil evidence for historical human-induced land degradation in West Iceland

Human impacts have been severe on Icelandic soils and vegetation. In order to assess human impact on soils soil quality, soil organic C (SOC), soil bulk density (BD), soil moisture content (SMC), soil mass, and SOC sequestration were measured from two Histosol cores in West Iceland. The cores cover a period from around 665 BC to present, capturing the initial human settlement of Iceland in AD 871. Tephrochronology allowed for a reliable correlation and comparison between the two cores. The initial settlement had profound impacts on the soil quality, causing decreased SOC concentration and SMC, and increased vegetation degradation, soil exposure, eolian deposition, and BD. The total SOC pool was 34.6 kg C m² at one of the sites, of which 60.1% was formed during historic times, driven by increased soil mass deposition from surrounding eroded areas. The SOC pool was 43.7 kg C m² at the other site, of which 31.4% was formed during historic time, constrained by water cycling and decomposition.