Fhe application of electromagnetic-induction on the measurement of sea ice thickness in the Antarctic

As an important component of the cryosphere, sea ice is very sensitive to climate change. The study of sea ice physics needs accurate sea ice thickness. This paper presents an electromagnetic induction （EM） technique which can be used to measure the sea ice thickness distribution efficiently and its successful application in the Antarctic Neila Fjord. Based on the electrical properties of sea ice and seawater and the application of electromagnetic field theory, this technique can accurately detect the distance between the EM instrument and the ice/water interface to measure the sea ice thickness. Analyzing the apparent conductivity data obtained by the electromagnetic induction technique and drill-hole measurements at same location allows the construction of a transform equation for the apparent conductivity and sea ice thickness. The verification of the calculated sea ice thickness using this equation indicates that the electromagnetic induction technique is able to determine reliable sea ice thickness with an average relative error of only 5.5%. The ice thickness profiles show the sea ice distribution in Neila Fjord is basically level with a thickness of 0.8 - 1.4 m.     

Ionospheric effetcs of an intense geomagnetic storm

An investigation of the response of the mid-high, mid and low latitude critical frequency foF2 to the geomagnetic storm of 15 July 2000 is made. Ground-based hourly foF2 values (proportional to square root of peak electron density of F2-layer) from four chains of ionospheric stations located in the geographic longitude ranges 10°W–35°E, 60°E–120°E, 130°E–170°E, 250°E–295°E are used. Relative deviations of foF2 are considered. The main ionospheric effects for the considered storm are: long-duration negative disturbances at mid-high latitudes in summer hemisphere in sectors where the storm onset occurred in the afternoon/night-time hours; short-duration positive disturbances in the summer hemisphere at mid-high latitudes in the pre-sunset hours during the end of main phase-first stage of the recovery; small and irregular negative disturbances in the low latitude winter hemisphere which predominate during the main phase and first part of the recovery, and positive disturbances in both hemispheres at mid-high and mid latitudes prior to the storm onset irrespective of the local time. In addition, the validity of some physical mechanisms proposed to explain the F2 region behaviour during disturbed conditions is considered. gus-mansilla@hotmail.com     

The structure of the mid- and high-latitude ionosphere during the November 2004 storm event obtained from GPS observations

GPS data from the International GNSS Service (IGS) network were used to study the development of the severe geomagnetic storm of November 7–12, 2004, in the total electron content (TEC) on a global scale. The TEC maps were produced for analyzing the storm. For producing the maps over European and North American sectors, GPS measurements from more than 100 stations were used. The dense network of GPS stations provided TEC measurements with a high temporal and spatial resolution. To present the temporal and spatial variation of TEC during the storm, differential TEC maps relative to a quiet day (November 6, 2004) were created. The features of geomagnetic storm attributed to the complex development of ionospheric storm depend on latitude, longitude and local time. The positive, as well as negative effects were detected in TEC variations as a consequence of the evolution of the geomagnetic storm. The maximal effect was registered in the subauroral/auroral ionosphere during substorm activity in the evening and night period. The latitudinal profiles obtained from TEC maps for Europe gave rise to the storm-time dynamic of the ionospheric trough, which was detected on November 7 and 9 at latitudes below 50°N. In the report, features of the response of TEC to the storm for European and North American sectors are analyzed.     

Climatically relevant periodicities in the thickness of biogenic carbonate varves in Spooensee, Switzerland (9740-6870 calendar yr BP)

Accurate determination of the thicknesses of 2717 biogenic carbonate varves from a Swiss lake (Soppensee), spanning the period from about 9740 to 6870 calendar yr BP, allowed the computation of a power spectrum using classical FFT methods. The presence of pronounced peaks at 40-50 and 20-25 yr agrees with the results of other studies on varve thickness and D¹⁴C which have been interpreted as indicating an association between solar forcing and varve thickness. The presence in the Soppensee varve series of an additional peak at 10.9 yr, corresponding to the Schwabe sunspot cycle, lends further support to this hypothesis. Because the Soppensee varves are of biogenic rather than clastic origin, any influence fluctuations in solar irradiance may have had on sedimentation rates is likely to have been exerted via primary production.     

电离层诸参量对大气重力波的响应与重力波参数反演

本文利用欧洲非相干散射雷达数据,分析研究了电离层不同等离子体参量对大气重力波的响应之间的关系.应用这种关系,发展了一种在垂直于地磁场的电场可以忽略等简化假设下,由电子密度和离子沿场速度的同时测量数据,反演求解较高（约250km以上）F区中引起TID的重力波传播参数的方法.用此法对一典型TID事件进行分析计算,所得结果与全波解数值研究结果很好符合.     

Strain segmentation and lateral membrane deformation rate of the subducted Ryukyu slab

Abstract Focal mechanisms of intermediate-depth earthquakes within the subducted Ryukyu slab indicate a systematic pattern of down-dip extension in the northern part under Kyushu. These mechanisms switch rapidly around the Tokara channel to down-dip compression in the southern part toward Taiwan. This intriguing pattern of strain segmentation, together with the differences between the slab geometry of the northern and southern parts, has raised the question of whether stress segmentation, as defined possibly by a tear fault, might exist in the slab. However the Ryukyu trench has a concave oceanward shape in the northern segment while it is convex in the southern oceanward part toward Taiwan. The inflection zone is located around the Tokara channel. The concept of Gaussian curvature of a curved surface suggests that the along-arc variation of the geometric configuration of a subducted slab is related to the shape of the trench. This is in order to accommodate the lateral membrane deformation of the slab as the oceanic lithosphere subducts from a spherical shell to the geometry delineated by the Wadati-Benioff zone. The membrane deformation regime of the subducted Ryukyu slab and its relation with the trench geometry was examined by assuming that the subduction be modelled by the flow field of a thin viscous sheet. A projection operator was utilized to compute the membrane strain-rate tensor of an arbitrary non-Euclidean surface. Numerical experiments indicated that the northern segment of the slab was dominated by lateral compression and down-dip extension and the southern part by lateral extension and down-dip compression. This transition is sharply located near the Tokara channel. These patterns were compatible with what had been observed from studies of focal mechanisms, suggesting that the strain segmentation might be controlled, at least in part, by the lateral membrane deformation within the slab due to the trench shape in this subduction zone. The slab geometry was predicted by minimizing the integrated total dissipation power; this revealed distinct features that were consistent with observations. This implies that the slab geometry may also be affected by the membrane deformation in a systematic fashion.     

基于Swarm卫星GPS/TEC观测的顶部电离层三维电子密度分布的层析法研究

利用两颗伴飞的Swarm A/C卫星搭载的双频GPS接收机获取的TEC数据,在两个卫星轨道平面同时对顶部电离层电子密度进行层析成像,实现对顶部电离层电子密度的三维观测.为了能够重现扰动期间电离层电子密度的空间变化特征,在正则化求解过程中,我们引入了水平矩阵H和垂直矩阵V刻画电子密度的空间变化特征,引入整体约束矩阵C以调节不同空间对电子密度相对变化的权重.数值验证结果表明我们的算法对常见的观测误差具有较强的包容性,反演计算出的电子密度平均偏差优于10%.在不同地磁活动条件下,与第三方观测数据的对比,验证了本文反演算法的可靠性.实测数据反演结果表明我们的算法不仅能够较好地重现顶部电离层子午向百公里级别的不规则结构,还能有效分辨纬向相隔~150 km的两个卫星轨道平面的电子密度差异.     

The response of the azimuthal component of the ionospheric electric field to auroral arc brightening

We have analyzed the response of azimuthal component of the ionospheric electric field to auroral arc activity. We have chosen for analysis three intervals of coordinated EISCAT and TV observations on 18 February, 1993. These intervals include three kinds of arc activity: the appearance of a new auroral arc, the gradual brightening of the existing arc and variations of the arc luminosity. The arcs were mostly east-west aligned. In all cases, the enhancement of arc luminosity is accompanied by a decrease in the westward component of the ionospheric electric field. In contrast, an increase of that component seems to be connected with arc fading. The observed response is assumed to have the same nature as the short circuit of an external electric field by the conductor. The possible consequence of this phenomenon is discussed.     

The relationship between formation structure and thickness in the Permo-Triassic succession of the Southern Coalfield, Sydney Basin, New South Wales, Australia

Using trend-surface analysis, the patterns of formation structure and thickness variation in the Permo-Triassic succession of the Southern Coalfield, Sydney Basin, are resolved into geologically meaningful large- and small-scale features. The structural trends correspond to the regional syncline of the southern Sydney Basin and the negative and positive residual domains to smaller-scale structures including the South Bulli and Douglas Park Synclines and the Bulli and Kemira Anticlines. The results of trend-surface analysis and simple linear regression reveal an inverse relationship between structural elevation (relative to sea level) and formation thickness on both a regional and a local scale. This relationship is strongest for the Bulli Coal and the Bald Hill Claystone. In the case of the Bulli Coal, the present-day structural trends and formation thickness trends show a strong inverse correlation and the residuals show a moderate inverse correlation; the correlations between the inferred Middle Triassic structure of the Bulli Coal and formation thickness are even stronger than those involving the present-day structure. These results indicate that structures which were active during the Permo-Triassic and which influenced sedimentation have been preserved in the present-day structure. The persistence of the patterns of structure and thickness variation upward through the Permo-Triassic sequence suggests that sedimentation was controlled by contemporaneous basement subsidence, rather than by short-lived compaction-induced subsidence patterns.