Identification of the Ca-sulfate bassanite in Mawrth Vallis, Mars

The region surrounding the Mawrth Vallis outflow channel on Mars hosts thick layered deposits containing diverse phyllosilicate minerals. Here we report detection of the Ca-sulfate bassanite on the outflow channel floor, requiring a more complex aqueous chemistry than previously inferred for this region. The sulfate-bearing materials underlie phyllosilicate-bearing strata, and provide an opportunity for testing proposed models of martian geochemical evolution with a future landed mission.     

L’analyse des surfaces enveloppes appliquée à l’étude morpho-structurale de l’est de la France

Résumén

Dans certaines régions où les sédiments récents (plio-quaternaires) sont rares ou inutilisables comme enregistreurs de déformations, seule l’analyse morpho-strcturale peut mettre en évidence des indices de néotectonique. Deux types d’objets morphologiques se révèlent particulièrement utiles : les surfaces (d’érosion et de comblement) et le réseau hydrographique. Leur prise en compte et leur analyse s’effectuent essentiellement à partir des cartes topographiques à différentes échelles (de 1/50 000 à 1/500 000).

* La démarche est la suivante: 1 – Des traitements appropriés sont développés, mettant en évidence des discontinuités et des anomalies au sein des surfaces enveloppes et du réseau hydrographiques;

2 – Ces discontinuités sont analysées puis interprétées afin de déterminer les causes de leur existence dans le cadre d’un modèle d’évolution du relief qui tient compte de facteurs internes (la lithologie, la structure), et de facteurs externes (le climat, la végétation et les actions humaines);

3 – Des travaux de terrain confirment et précisent les caractéristiques de ces facteurs (nature et quantification de la déformation : âge. amplitude, sens des mouvements).

* Les principaux résultats de cette démarche appliquée à l’Kst du Bassin parisien sont les suivants: 1 – Les cuestas orientales du Bassin parisien apparaissent structurées par des accidents NK-SW (prolongement du fossé de Sarre Nahe) et NNW-SSK ( Argonne-Bar-le-Due);

2 – Les discontinuités morpho-structurales sont localisées et caractérisées par des mouvements récents.

     

Modeling the effects of historical vegetation change on near-surface atmosphere in the northern Chihuahuan Desert

Our goal was to evaluate effects of broad-scale changes in vegetation from grasslands to shrublands over the past 150 years on near-surface atmosphere over the Jornada Experimental Range in the northern Chihuahuan Desert, using a regional climate model. Simulations were conducted using 1858 and 1998 vegetation maps, and data collected in the field. Overall, the vegetation shift led to small changes in sensible heat (SH) and an increase in latent heat (LH). The impacts of shrub encroachment depended on shrubland type: conversion from grass to mesquite cools the near-surface atmosphere and from grass to creosotebush warms it. Higher albedo of mesquite relative to grasses reduced available energy, which was dissipated mainly as LH due to the deeper root system in mesquite. In creosotebush-dominated areas, a decrease in albedo, an increase in roughness length and displacement height contributed to the SH increase and warmer temperatures. Sensitivity simulations showed that an increase in soil moisture content enhanced shrub LH and a reduction in mesquite cover enhanced the temperature differences. The observed shift in vegetation led to complex interactions between land and surface fluxes, demonstrating that vegetation itself is a weather and climate variable as it significantly influences temperature and humidity.     

一种以能量平衡为基础的干旱指数

本文以能量平衡公式为基础,根据实际蒸发与潜在蒸发的关系依赖于土壤水分含量的事实,导出一种表达干湿状况的指标——土壤水分干旱指数。     

Interactions between groundwater and surface water in a virginia coastal plain watershed. 1. Hydrological flowpaths

A field study of surface water and groundwater interactions during baseflow and stormflow conditions was performed at the Reedy Creek watershed in the Virginia Coastal Plain. Three estimates of the average saturated hydraulic conductivity (K_s) of the unconfined aquifer were in reasonable agreement (ranging from 0.0033 to 0.010 cm/s), indicating that baseflow in the creek is entirely from the drainage of shallow groundwater from the relatively thin (1–6 m thick) unconfined aquifer. This relatively permeable surficial aquifer was found to be underlain by dark, olive grey, clay-silt and diatomaceous Miocene deposits of low permeability known as the Calvert Formation, which is believed to function as a confining bed in the area. A chemical hydrograph separation technique was used to resolve the contributions of [old] (pre-event) and [new] (event) water to stormflow. Results from a major rainstorm indicated that old water dominated the stormflow response of the watershed, although the new water contribution approached 40% at the hydrograph peak. Stormflow at Reedy Creek appears to result from saturation overland flow from variable source areas which include the stream channels and a significant part of the riparian wetland area. This response appears to be attributable to the transient dynamics of the shallow groundwater flow system and to the formation of localized groundwater mounds which raise the water-table to the wetland surface.     

利用SIR-C极化数据提取地面参数

本文根据简化的积分公式模型（ＩＥＭ）,分析了面散射过程中后向散射系数与地面参数之间的关系。利用航天飞机成像雷达（ＳＩＲ－Ｃ）获取极化的雷达图像,提取新疆北部地区冲扇的散射系数以及介电常数（湿度）与粗糙度。由图像获得的地面参数数据,可以用于分布冲积扇成因、时代以及其次的关系。     

AIEM模型在积雪散射模拟中的应用

 介绍一种基于一阶辐射传输的积雪散射模型。该模型考虑了积雪覆盖地表微波散射的3种回波分量： 雪层表面散射、下垫面散射以及雪层体散射。对于其中2个面散射分量，文章中应用一种新的面散射模型——AIEM取代原有的IEM模型进行处理。最后，使用Michigan大学的实测数据对改进后模型的模拟结果进行验证，并与改进前的模拟结果进行了对比。     

高分散性、粒度高正态分布氢氧化镁的制备研究进展

近年来Mg(OH)2的改性研究受到广泛重视;对水热处理技术和表面改性手段处理Mg(OH)2的研究现状进行概述,并讨论制备超细粉体改性Mg(OH)2的影响因素。     

南极瑞穗高原1987—1988年度表面物质平衡及其变化

根据1987/1988年度表面物质积累资料,对Mizuho(瑞穗)高原该年度物质平衡的分布规律及其变化进行了讨论,同时还对年内短期天气过程及地形变化对物质平衡的影响进行了分析。研究发现1987/1988年度物质平衡的空间分布与多年平均状况存在较大区别:海拔550m以下的沿海地带表现为负物质平衡状态。从S_16点向内陆80km范围内为高值物质平衡区。年平均净物质平衡量达0.84m雪层深;80km到瑞穗高原内陆的瑞穗站之间为低值物质平衡区,年平均物质平衡量仅0.14m雪层深。在瑞穗高原,表面物质平衡水平表现为低积累,低支出的特征。此外,年内短期气候和地形变化对物质平衡的影响均大于多年平均状态,在高值物质平衡区,气候变化对物质平衡的影响大于地形变化的影响;而在低值物质平衡区,地形变化对物质平衡的影响则大于气候变化对物质平衡的影响。