Photometry and Imaging of Comet C/2000 Wm1 (Linear)

Earth, Moon, and Planets -     

The impact of meridional circulation on stellar butterfly diagrams and polar caps

Observations of rapidly rotating solar-like stars show a significant mixture of opposite-polarity magnetic fields within their polar regions. To explain these observations, models describing the surface transport of magnetic flux demand the presence of fast meridional flows. Here, we link subsurface and surface magnetic flux transport simulations to investigate (i) the impact of meridional circulations with peak velocities of  ≤125 m s⁻¹  on the latitudinal eruption pattern of magnetic flux tubes and (ii) the influence of the resulting butterfly diagrams on polar magnetic field properties. Prior to their eruption, magnetic flux tubes with low field strengths and initial cross-sections below  ∼300 km  experience an enhanced poleward deflection through meridional flows (assumed to be polewards at the top of the convection zone and equatorwards at the bottom). In particular, flux tubes which originate between low and intermediate latitudes within the convective overshoot region are strongly affected. This latitude-dependent poleward deflection of erupting magnetic flux renders the wings of stellar butterfly diagrams distinctively convex. The subsequent evolution of the surface magnetic field shows that the increased number of newly emerging bipoles at higher latitudes promotes the intermingling of opposite polarities of polar magnetic fields. The associated magnetic flux densities are about 20 per cent higher than in the case disregarding the pre-eruptive deflection, which eases the necessity for fast meridional flows predicted by previous investigations. In order to reproduce the observed polar field properties, the rate of the meridional circulation has to be of the order of 100 m s⁻¹, and the latitudinal range from which magnetic flux tubes originate at the base of the convective zone (≲50°) must be larger than in the solar case (≲35°).     

Cometary Rotation: an Overview

I discuss our current understanding of the spin states of cometary nuclei. Cometary spin influences the temporal and spatial patterns of outgassing from the nucleus (through diurnal and seasonal effects) and is in turn influenced by outgassing-driven torques. The current challenge to cometary astronomers is to quantify the interactions between the spin, the outgassing, and the resultant torques on the nucleus, and to understand the role of rotation in determining the basic physical properties of the nucleus. This revised version was published online in July 2006 with corrections to the Cover Date.     

VLBI技术测月的数学模型探讨

近年各国已纷纷制定测月计划,采用何种技术对月球进行定位,变得尤为重要。本文通过对VLBI技术特点进行分析,VLBI是目前大地测量中精度最高的技术手段,但只适用于深空探测,因为深空射电信号到达地面时,可看作平行信号。本文针对VLBI技术特点及数学模型,对存在不可忽略视差的VLBI测月模型,通过级数展开,解决月面射电信号到达地球时的视差问题,并顾及地球自转得出最终数学模型,通过站间一次差分消除钟差等影响,得出VLBI对近轨天体(月球)表面射电源定位的数学模型。     

京杭大运河镇江段近岸土壤重金属含量与空间分布特征

通过多目标区域地球化学调查方法,研究了京杭大运河镇江段流域近岸土壤中重金属元素的含量、来源及空间分布特征。结果表明：重金属含量总体较低,仅局部地区存在重金属污染,其中Cr、Ni、As未见明显污染,Cu、Pb、Zn、Hg、Cd在局部地区存在不同程度的污染,尤其是Cd污染最严重;污染区域主要位于辛丰镇和丹阳城区附近,污染源主要为附近的金属制品业和钢铁厂。     

风云四号静止轨道气象卫星成像仪典型观测区域设计

风云四号气象卫星是我国新一代静止轨道气象卫星,采用三轴稳定姿态控制方式,极大地提高对地观测精度及观测频次,同时也对有效载荷观测模式的灵活设计提出了更高要求。星上装载的静止轨道辐射成像仪是我国静止轨道气象卫星携带的同类仪器中最为先进的。利用最先进的观测仪器,提高观测效率,在气象服务中发挥更大的作用是气象卫星应用的根本。深入探讨了风云四号静止轨道气象卫星成像仪的工作模式,首次针对不同的观测需求提出了灵活的成像仪观测区域设计方案,有效满足典型区域的不同观测需求,在成像仪在轨测试中发挥了重要作用,为开展业务运行奠定了坚实的基础。     

Potash–Forming Regularity of the Ordovician Marine Northern Shaanxi Salt Basin: Insight from Review and Prospect of the Deep Geology of the Ordos Basin

The Ordovician Northern Shaanxi Salt Basin(ONSSB), located in the east–central Ordos Basin, western North China Craton(NCC), is one of the largest marine salt basins yet discovered in China. A huge amount of halite deposited in the Mid-Ordovician Majiagou Formation, and potashcontaining indication and local thin layer of potash seam were discovered in O2 m65(6 th submember, 5 th member of the Majiagou Formation). This makes ONSSB a rare Ordovician potash-containing basin in the world, and brings new hope for prospecting marine solid potash in this basin. However, several primary scientific problems, such as the coupling relationship between ONSSB and the continent nucleus, how the high-precision basement fold controls the ONSSB, and how the basement faults and relief control ONSSB, are still unclear due to the limitations of the knowledge about the basement of the Ordos Basin. This has become a barrier for understanding the potash-forming regularity in the continental nucleus(CN) area in marine salt basin in China. Up to now, the material accumulation has provided ripe conditions for the answers to these questions. Latest zircon U-Pb ages for the basement samples beneath the Ordos Basin reveal that there exists a continental nucleus(Yi-Meng CN) beneath the northern Ordos Basin. And this brings light into the fact that the ONSSB lies not overlying on the YiMeng CN but to south Yi-Meng CN. Both do not have superimposed relationship in space. And borehole penetrating into the basement reached Palaeoproterozoic meta-sedimentary rocks, which suggests the ONSSB is situated in the accretion belt of Yi-Meng CN during geological history. Basement relief beneath the ONSSB area revealed by seismic tomography and aeromagnetic anomaly confirms the existence of basement uplift and faults, which provides tectonic setting for sedimentary center migration of the ONSSB. Comparative research with various data sources indicates that the expanding strata in the ONSSB adopted the shape of the basement folds. We found that the orientations of the potash sags showed high correlation with those of several basement and sedimentary cover faults in the ONSSB. The secondary depressions are also controlled by the faults. Comparative research between all the global salt basins and continental nuclei distribution suggests that distribution of the former is controlled by the latter, and almost all the salt basins developed in or at the margin of the continental nucleus area. The nature of the tectonic basement exerts a key controlling effect on potash basin formation. And on this basis we analyzed in detail the geological conditions of salt-forming and potash-forming in the ONSSB.     

从地壳密度结构看中国大陆深层油气盆地的分布

面对21世纪的中国能源问题,要研究深埋在5km以下的古生代沉积盆地和潜在油气储层。由于结晶基底密度大、磁性较强,盆地沉积岩密度低而磁性弱,可用密度成像及磁性体顶面深度反演来确定深埋沉积盆地和潜在储层的分布范围。应用重力异常多尺度分析和密度成像方法,可以计算出反映中国深埋沉积盆地和潜在储层分布的密度扰动图,预测中国深埋盆地的分布。密度成像的低密度扰动区与磁性结晶基底顶面深度大的区域吻合,与反射地震剖面探测结果一致。通过密度扰动成像预测深埋沉积盆地主要分布在中国西部的塔里木、柴达木、四川、准噶尔和鄂尔多斯等盆地深层。东部岩石圈裂谷带也可形成深埋结晶基底裂隙型储层, 分布在华北和东北下方。中国深埋沉积盆地和潜在储层的总面积可达地面沉积盆地面积的45%左右,估计陆上面积1600000km2左右,海域面积600000km2左右,具有广阔的天然气勘探前景。     

Calpionellid zones of the Tithonian–Berriasian exotic limestone clasts from the Outer Carpathians,Poland

Calpionellids and chitinoidellids were identified from exotic limestone clasts occurring in flysch deposits of the Early Cretaceous to Oligocene age from the Silesian and Subsilesian nappes of the Polish Outer Carpathians. They represent the remnants of carbonate sedimentation along the northern and southern margin of the Severin-Moldavidic Basin, areas which are no longer preserved on the surface. Chitinoidellid and calpionellid assemblages characterize the Chitinoidella, Crassicollaria and Calpionella zones (latest early Tithonian–early Berriasian). The calpionellid zonation for the Western Carpathians was used for the present study, but some difficulties were encountered resulting from the application of this zonation. Cathodoluminescence imaging (CL) was useful for the identification of these microfossils in samples containing sparse and poorly preserved specimens, especially in the studied shallow-water limestone (the so-called Štramberk-type limestones).