Differential absorption measurements of mesospheric and lower thermospheric electron densities using the Buckland Park MF radar

The differential absorption experiment (DAE) was first proposed in the 1950s for the estimation of mesospheric and lower thermospheric electron density using MF/HF radars. The technique was used extensively until the late 1970s, when interest in the technique declined, due to experimental limitations and questions regarding the assumptions of the technique. This paper describes the application of the DAE within the online observations of the Buckland Park MF (BPMF) radar. The experimental limitations of the technique for the BPMF radar are discussed, with particular attention paid to effects of complex gain differences between receiving channels used to decompose the linearly received signals into circular components. Hourly and monthly averaged midday DAE electron densities are presented, revealing good agreement with IRI model estimates. Monthly averaged midnight DAE electron densities are also presented, revealing good qualitative agreement with the IRI model estimates.     

科尔沁沙地土壤水分动态分析及其概率密度函数模拟

基于Laio土壤水分动态随机模型(Laio模型),利用2006-2010年5~9月土壤水分连续监测数据及日降水资料,分析科尔沁沙地固定沙丘和沙质草地生长季根系层土壤水分动态及其与降水格局的关系,研究点尺度土壤水分概率密度函数,并对Laio模型涉及的13个参数进行了敏感性分析。结果表明:① 研究区年降水的季节分配极不均匀,主要集中在4~10月的生长季,占全年降水量的93%;0~5 mm降水事件占全年降水事件的73%,但其降水量只占全年降水量的25%;降水间隔期以0~10 d为主,占全年无降水期的38%,其频数最高,占全年间隔期频数的87%。② 固定沙丘和沙质草地根系层厚度分别为0~100 cm和0~70 cm,沙质草地根系层土壤水分显著高于固定沙丘;两类沙地7月份的土壤水分都显著高于生长季其他月份。③ 两类沙地生长季根系层土壤水分均服从正态分布;通过Laio模型得到了两类沙地生长季根系层土壤水分概率密度函数p(s),其峰值及峰值出现的位置和峰的阔度均与观测结果很接近,说明Laio模型能对科尔沁沙地土壤水分概率密度函数进行较好的模拟。④ Laio模型涉及的13个参数中,对p(s)最为敏感的参数是降水频率λ、平均降水量α、最大蒸散量E_max、水分胁迫点s*和凋萎系数s_w,主要影响p(s)曲线的峰值。     

Systematic Methodology for Velocity-dependent Gravity Modelling of Density Crustal Cross-Sections, using an Optimization Procedure

The paper describes a new method of gravity modelling of the density cross section along a DSS profile. We propose a systematic procedure of gravity interpretation using structural information contained both in the velocity distribution of the seismic model and the geometry of its layers. The procedure is based on the optimisation of the density parameters of the model. The values of the parameters are limited by relationships between the seismic velocity and the density (optimisation with inequalities). The formulation of the method allows for discussion of the presence of isostasy and the distribution of compensating masses. The discussion is very important for the considered crust-lithosphere system. The presented calculations are done for one Carpathian profile (CEL01). The analysis of the properties of the fitting procedure provides the characteristic depth of subcrustal compensating density structures, the position of crucial tectonic boundaries along the profiles, locations of the crustal areas having exceptional lithology, the regional density differences of subcrustal matter and the estimation of regional deviations from the isostatic equilibrium.     

Effect of particle density and inflow concentration of suspended sediment on bedload transport in rill flow

Laboratory flume experiments were carried out to evaluate the effect of particle density on bedload transport of sand‐sized particles and the effect of a suspended load of clay particles (kaolinite) on bedload transport of sand‐sized particles in rill flow conditions. Three materials in the range 400–600 µm were selected to simulate bedload transport of primary particles and aggregates: sand (2650 kg/m³), crushed brick (2450 kg/m³) and anthracite (1300–1700 kg/m³). In the two first experiments, two different methods were applied to determine bedload transport capacity of coarse particles for various conditions of flow discharge (from 2 to 15 L/min) and slope (2.2, 3 and 4%). In the third experiment, clear water was replaced with kaolinite–water mixture and bedload transport capacity of crushed brick particles was determined for a 4% slope and different concentrations of kaolinite (0, 7, 41 and 84 g/L). The results showed that bedload transport increased significantly with the decrease in particle density but the effect of particle density on transport rates was much less important than flow discharge. Velocity measurements of clear flow, flow mixed with coarse particles and coarse particles confirmed the existence of a differentiation between suspended load and bedload. In these experimental conditions, suspended load of kaolinite did not affect bedload rates of crushed brick particles. Three transport capacity formulae were tested against observed bedload rates. A calibration of the Foster formula revealed that the shear stress exponent should be greater than 1.5. The Low and the Govers unit stream power (USP) equations were then evaluated. The Low equation was preferred for the prediction of bedload rates of primary particles but it was not recommended in the case of aggregates of low density because of the limited experimental conditions applied to derive this equation. Copyright © 2008 John Wiley & Sons, Ltd.     

裂缝性储层的电各向异性响应特征研究

以水平裂缝分布的孔隙介质模型为基础,建立了水平裂缝面的平行裂缝分布和带粗糙表面的点接触裂缝模型,导出了两类裂缝模型的水平和垂直电阻率响应关系,分析了两类裂缝模型在没有围压和存在围压条件下的水平电阻率、垂直电阻率变化规律和电各向异性系数的变化特征.讨论了裂缝开度、裂缝密度和裂缝粗糙度等裂缝特征参数对裂缝性储层电各向异性的影响.为简化讨论,所有电性响应特征的分析都忽略了裂缝和孔隙表面的导电性和极化的影响.利用平行分布水平裂缝面模型和带粗糙面的裂缝模型,考察了围压条件下的裂缝性岩石的电各向异性响应特征,得到了对实际应用有意义的结果.     

Spectral features of geomagnetic low point displacement and its mechanism

In this paper,Changli station in Hebei Province was taken as an example,in which the minute data of geomagnetic Z component was used to analyze the spectral values of its main frequencies during normal time,geomagnetic storm time and low point displacement time interval respectively. After fitting of ten high spectral values to loga-rithmic functions,it is found that,by using same length of data,the spectral values at geomagnetic storm time in-crease apparently compared with those at normal time,especially at the high frequency segment. While low point displacement occurred,the spectral values at high frequency are approximate to those at normal time,but at period above 4 hours they are mostly lower than those at normal time. Comparison of accumulating of some FFT results at low point displacement and normal time shows that,spectral values at periods of 8.5 and 13.7 hours increase at low point displacement time relative to those at normal time. Compared with the images of Ne observed at DE-METER satellite,it is illustrated that the occurrence of geomagnetic low point displacement is well corresponding with the increase of Ne in ionosphere. Finally it was discussed about those spectral features and the occurrence mechanism of geomagnetic low point displacement.     

The influence of variable topography on the depositional behaviour of pyroclastic density currents: The examples of the Upper Pollara eruption (Salina Island,southern Italy)

Stratigraphic reconstruction of the Upper Pollara eruption has allowed for the inference of eruptive mechanisms and the distillation of a sedimentological model for pyroclastic density currents (PDCs) moving across variable topography. The pre-eruptive topography in the study area was characterised by a tuff ring-like morphology, with both inward and outward dipping slopes. Highly viscous, moderately porphyritic, dacitic to rhyolitic magmas fed the eruption, which was characterised by a Vulcanian eruptive style. The stratigraphic succession was divided into five eruption units (EUs), which result from different phases of the eruption separated by stases. Sustained columns occurred only during EU1, while PDC generation dominates EU2–5. Lithofacies analysis of the PDC deposits indicates the prevalence of massive coarse-grained deposits on the inner slopes of the Pollara crater, which are interpreted as the deposits of a flow-boundary zone dominated by granular flow or fluid escape regimes. Dune-bedded, massive to stratified lithofacies dominate the outer slopes of the Pollara crater, and are interpreted as the deposits of PDCs with flow-boundary zones in which traction played a major role. Thin, massive PDC deposits are exposed on the sub-horizontal Malfa terrace, and are interpreted as representative of flow-boundary zones dominated by a granular flow regime. The occurrence of stacked deposits indicates that most of the PDCs were characterised by unsteady pulsatory behaviour, with development of trains of pulses during their transport. The downcurrent lithofacies transitions observed for the Upper Pollara deposits have finally been compared with other similar lithofacies associations which have been described for short-lived PDCs at tuff rings, in order to discuss the influence of pre-eruptive topography on lithofacies association.     

Rainfall‐induced consolidation and sealing effects on soil erodibility during concentrated runoff for loess‐derived topsoils

Flume experiments simulating concentrated runoff were carried out on remolded silt loam soil samples (0·36 × 0·09 × 0·09 m³) to measure the effect of rainfall‐induced soil consolidation and soil surface sealing on soil erosion by concentrated flow for loess‐derived soils and to establish a relationship between soil erodibility and soil bulk density. Soil consolidation and sealing were simulated by successive simulated rainfall events (0–600 mm of cumulative rainfall) alternated by periods of drying. Soil detachment measurements were repeated for four different soil moisture contents (0·04, 0·14, 0·20 and 0·31 g g^?1). Whereas no effect of soil consolidation and sealing is observed for critical flow shear stress (τ_cr), soil erodibility (Kc) decreases exponentially with increasing cumulative rainfall depth. The erosion‐reducing effect of soil consolidation and sealing decreases with a decreasing soil moisture content prior to erosion due to slaking effects occurring during rapid wetting of the dry topsoil. After about 100 mm of rainfall, Kc attains its minimum value for all moisture conditions, corresponding to a reduction of about 70% compared with the initial Kc value for the moist soil samples and only a 10% reduction for the driest soil samples. The relationship estimating relative Kc values from soil moisture content and cumulative rainfall depth predicts Kc values measured on a gradually consolidating cropland field in the Belgian Loess Belt reasonably well (MEF = 0·54). Kc is also shown to decrease linearly with increasing soil bulk density for all moisture treatments, suggesting that the compaction of thalwegs where concentrated flow erosion often occurs might be an alternative soil erosion control measure in addition to grassed waterways and double drilling. Copyright © 2007 John Wiley & Sons, Ltd.     

The Holocene Secche di Lazzaro phreatomagmatic succession (Stromboli,Italy): evidence of pyroclastic density current origin deduced by facies analysis and AMS flow directions

The edifice of Stromboli volcano gravitationally collapsed several times during its volcanic history (>100 ka–present). The largest Holocene event occurred during the final stage of the Neostromboli activity (∼13–5 ka), and was accompanied by the emplacement of phreatomagmatic and lahar deposits, known as the Secche di Lazzaro succession. A stratigraphic and paleomagnetic study of the Secche di Lazzaro deposits allows the interpretation of the emplacement and the eruptive processes. We identify three main units within the succession that correspond to changing eruption conditions. The lower unit (UA) consists of accretionary lapilli-rich, thinly bedded, parallel- to cross-stratified ash deposits, interpreted to indicate the early stages of the eruption and emplacement of dilute pyroclastic density currents. Upward, the second unit (UB) of the deposit is more massive and the beds thicker, indicating an increase in the sedimentation rate from pyroclastic density currents. The upper unit (UC) caps the succession with thick, immediately post-eruptive lahars, which reworked ash deposited on the volcano’s slope. Flow directions obtained by Anisotropy of Magnetic Susceptibility (AMS) analysis of the basal bed of UA at the type locality suggest a provenance of pyroclastic currents from the sea. This is interpreted to be related to the initial base-surges associated with water–magma interaction that occurred immediately after the lateral collapse, which wrapped around the shoulder of the sector collapse scar. Upward in the stratigraphy (upper beds of UA and UB) paleoflow directions change and show a provenance from the summit vent, probably related to the multiple collapses of a vertical, pulsatory eruptive column.