共查询到17条相似文献，搜索用时 921 毫秒
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极盖区等离子体云块是电子密度比背景高出2倍及以上的高密度不均匀体,极向边界点亮是夜侧极光卵极向边界亮度显著增强的极光结构。探究极盖区等离子体云块与极向边界点亮现象的形成和演化以及二者之间的关系对理解极区电离层-磁层耦合具有重要意义。本文基于北极黄河站全天空极光成像仪、欧洲非相干散射雷达(EISCAT)、SuperDARN雷达和GPSTEC等多手段观测数据,揭示极盖区等离子体云块运动到夜侧极光卵极向边界,进而触发极向边界点亮的完整过程。研究结果表明,(1)高密度等离子体云块从极盖区运动到夜侧极光卵极向边界时,极向边界附近的极光强度明显增加,即出现了极向边界点亮现象。(2)极光亚暴发生后,极光卵极向膨胀,极向边界到达EISCAT Svalbard 42 m雷达观测视野。该雷达观测到了高密度、高电子和离子温度的结构,并伴随着电子密度峰值高度下降和离子上行等现象,这与高密度等离子体云块的输运和当地的极光粒子沉降密切相关。(3)从日侧向夜侧输运的等离子体云块到达夜侧极光卵极向边界附近时可能触发极向边界点亮,并且影响等离子体云块和极光粒子沉降接触区域的等离子体特征,这有助于加深我们对夜侧极区电离层... 相似文献
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本文从ＥＩＳＣＡＴ探测资料分析确认，沉降粒子对极光区电离层的电离生成率有极重要的作用，但高能和低能粒子的有效电离高度范围完全不同，另一方面，磁层对流的增强却常使Ｆ层电子密度Ｎ下降，１９８５年１月２８～２９日期间出现Ｎ（Ｅ层）Ｎ（Ｆ层），且１４７ｋｍ以上Ｎ随高度增加而下降的典型扰动剖面。这是高能粒子和强磁层对流共同作用的结果。１９９３年２月１６～１７日期间，中午前后ＮｍＦ异常地增大，而Ｎ（Ｅ层）却无明显变化。这是与前者特征不同的另一类典型剖面。磁层内低能粒子（能量小于１ｋｅＶ）从极隙区沉降直抵电离层是使Ｆ层电子密度剧增的物理机制 相似文献
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太阳风动压的显著变化能导致沉降进入极区电离层的能量粒子通量以及磁层-电离层电流系发生扰动。磁层高能粒子沉降到极区上层大气并与中性气体碰撞所激发的弥散极光,能够对这种扰动做出相应的响应。基于斯瓦尔巴特（Svalbard）群岛新奥尔松（Ny-?lesund）地区北极黄河站优越的地理优势,我们利用安装在黄河站的极光全天空成像仪观测到了日侧弥散极光对太阳风动压增强的响应。通过2006年1月2日事件观测显示,随着太阳风动压的增强,日侧弥散极光在极光卵赤道向部分首先点亮并逐渐向高纬扩展,同时地磁环境也受到相应扰动影响。我们认为,随着太阳风动压的增强,日侧磁层顶受到压缩,磁层内波粒相互作用导致投掷角散射增强,使得沉降进入极光卵赤道侧电离层的高能粒子数密度增大,进而导致日侧弥散极光强度增强。 相似文献
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本文利用DMSP卫星离子漂移速度测量数据,对高纬顶部电离层离子整体上行进行研究,主要考察平静时和磁暴期间离子上行强度与发生率随MLT(晨昏两侧)分布规律的变化;以及磁暴期间强的离子上行与等离子体对流及其剪切之间的关系。研究发现,磁暴期间强上行事件的发生率比平静期高近2倍,发生率的晨昏不对称性出现逆转,由平静时昏侧发生率较大变为磁暴期间晨侧发生率较大;磁暴期间晨侧离子上行速度的分布向速度高端加权,平均速度大于昏侧,最大上行速度远大于昏侧;强的离子上行往往与强对流剪切或强对流本身相伴随。 相似文献
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本文利用电离层数字测高仪 (DPS - 4)所测的f0 F2和从美国NOAA和DMSP卫星观测估算的半球功率指数和午夜极光区赤道侧边界纬度等资料 ,考察中山站电离层的极区特征。结果表明 ,冬季中山站电离层内的电离生成主要取决于从磁层沉降的粒子。在太阳活动和地磁变化宁静环境下 ,磁正午极隙区内的软粒子是最主要的电离源 ,它能使f0 F2达全天的最大值 ;上、下午各有数小时处于极光带内时 ,高能粒子的电离作用也很重要 ;夜间进入极盖区后 ,电子密度则很低。夏季太阳辐射电离效应使f0 F2值比冬季增加 1- 1 .5MHz,而其日变化的最大值时间也提前了 1- 2hr。发生很大扰动时 ,极隙区和极光带的位置均向低纬方向移动。若中山站日间也处于极盖区内时 ,电子密度会大幅度下降 ,并常接收不到电离层回波的信号。在中等扰动环境下情况更加复杂。由于高纬电离层对流速度很高 ,离子 /中性分子间的碰撞复合系数就很大。热层中性大气全球经向环流对高纬电离层电子密度的增加无显著作用。磁暴期间中午从极隙区向南的等离子体对流对中山站f0 F2的增高也无明显影响。 相似文献
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20 0 0年 7月 ,太阳表面发生了一系列的耀斑与日冕物质抛射事件 ,最大耀斑能级达X5 .7/3 B。地球表面发生相应特大磁暴 ,Dst指数最大负偏达 - 3 0 0 n T。中国南极中山站地处极隙区纬度 ,白天位于磁层极隙区 ,夜间位于极盖区 ,以多种高空大气物理观测设备详细记录了该磁暴过程。对有关数据的分析表明 ,高能粒子引起电离层吸收急剧增加 ,测高仪数据两天多信号空白 ,宇宙噪声吸收显著增加 ;地磁 Pc3 /5脉动增加与行星际磁场南向分量密切对应 ,显示行星际磁流体波对激发磁层脉动的贡献 ;磁暴主相期间 ,Pc3 /5脉动大幅度增加 ;极区地磁水平分量随南向行星际磁场变化 ,但滞后近 8小时 ;Dst指数与南向行星际磁场密切相关 ,磁暴受控于高度负偏的南向行星际磁场 相似文献
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海岸沉积物是记录海-陆-气相互作用下区域古环境变化的重要载体。因短历时古气候事件发生时间短、各物质载体和代用指标都存在一定不足,对华南海岸带沉积物研究多探讨其与海平面波动等长时间尺度上的关系,限制了对粒度信息中可能记录的短期气候事件的深入研究,不利于解译古气候与古人类历史。本研究选取福建霞浦福宁湾FN1钻孔0～8 m部分,以光释光年代标尺为基础,使用粒度作为主要环境代用指标,并通过端元分析、主成分和相关性分析方法,阐明福建东北沿海地区沉积物粒度特征;再结合TOC/TN含量变化,探讨其环境指示意义。结果表明：(1)钻孔0～8 m沉积物以粉砂为主,不同沉积相中各粒级百分比含量波动较大,根据粒径变化趋势和各粒度参数变化曲线分为U1、U2、U3三层。(2)根据BasEMMA方法选取3个端元进行分析。其中,EM1代表低能沉积条件,以粉砂为主,是受冬季风影响的敏感组分,可指示冬季风强度变化;EM2代表中能沉积条件,出现粒级、TOC/TN及沉积速率的突变。受东亚冬季风影响,陆源物质含量增加;EM3代表高能沉积条件,区域水动力增强,沉积物粗颗粒含量增加;高能与低能条件的频繁变化使沉积过程变得复杂,形成... 相似文献
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今年是广东省建成北回归线标志25周年,本文回顾了当年广东省兴建北回归线标志的过程,并对广州从化北回归线标志公园的进一步完善提出建议,以作纪念.北回归线是太阳直射地球表面的最北界限线,又是天文热带和北温带分界线.在北回归线上,每年夏至的晴朗正午,都能观察到"太阳当头照,立竿不见影"的景象.地球上北回归线的位置并非固定不变,而是"漂移"的.在较长的历史时期内,北回归线的位置是逐年向南移动,南移速度逾14 m/a.现在惯称的北回归线纬度为23°26′N,是23°26′21".448N的约数.而23°26′21".448N,只是2000年的北回归线位置,是根据1976年国际天文学联合会的决定,于1984年开始采用. 相似文献
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湖泊植物群落的形成和分布由水文和水质共同决定.以白洋淀台田沟渠内水生植物为研究对象,研究水生植物在不同营养盐含量和与台田边界不同距离条件下的蔓延分布特征.运用野外调查方法,于2012年5月和9月初,对白洋淀20个主要淀区台田沟渠内的水生植物和水质条件进行调查.本次调查在台田沟渠内共发现水生植物14种,占淀区水生植物总种数的40％.沟渠内水生植物对营养盐含量的适应性可以分为3类:金鱼藻(Ceratophyllum demersum)、紫背浮萍(Spirodela polyhiza)、水鳖(Hydracharis dubia)、蓖齿眼子菜(Potamogeton pectinatus)、菹草(Potamogeton crispus)、槐叶萍(Salvinia natans)、莲(Nelumbo nucifera)和芦苇(Phragmites australis适宜于各种水体;狸藻(Utricularia vulgaris)、穗花狐尾藻(Myriophyllum spicatum)和品藻Lemna trisulca)适宜于低氮水体;轮藻(Chara sp.)、光叶眼子菜(Potamo geton lucens)和马来眼子菜(Potamogeton malaianus)适宜于低氮和低磷水体.不同的水生植物分布于台田沟渠的不同位置,菹草、蓖齿眼子菜多分布于台田“外边缘”;轮藻多在台田“内边缘”和“内部水域”分布;浮水植物、浮叶植物和金鱼藻在台田区内分布相对均匀.植物群落物种丰富度沿台田沟渠与台田边界的距离呈单峰曲线关系,在台田入口处达到峰值. 相似文献
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Summary. An existing experimentally verified model for energy dissipation in a processing spherical cavity filled with liquid assumed to be in a semirigidized state except for a viscous Ekman boundary layer is applied to the Earth's liquid core to assess energy dissipation magnitudes. Application of the model to the best available Earth data occurs at the derived energy dissipation maximum for the model. Other existing research showing that the Earth's atmosphere appears to adjust to a state of maximum dissipation led to generic models for systems of maximum dissipation. The maximum dissipation mantle—core model with core motion driven by Earth precession alone, coupled to the mantle only by viscous shear stresses, and with a spherical mantle—core boundary leads to energy dissipation rates on the order of 104 times those necessary for an Earth dynamo. The maximum dissipation model also leads to excessive magnetic field drift rates and to excessive retardation of the Earth's rotation rate. Effects of the mantle—core ellipticity and of magnetic field coupling are briefly discussed and are used to help develop a less than maximum dissipation model also driven by precession alone but using the additional coupling to yield a model more consistent with observed phenomena. 相似文献
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Summary. An exact equation is derived for the magnetic field lines of the general axisymmetric magnetic multipole of arbitrary degree ( n ). This new result has important applications in studies of the possible nature of solarterrestrial physics during geomagnetic polarity reversals. In the limiting case of a magnetic dipole ( n=1 ), the equation for the magnetic field lines of the general axisymmetric magnetic multipole simplifies correctly to the well-known dipolar form, which is used extensively in geomagnetism, magnetospheric physics and cosmic-ray physics as a first-order approximation to the actual configuration of the geomagnetic field.
It is also shown theoretically that suites of similar magnetic field lines of the general axisymmetric multipole attain their maximum radial distances from the origin on a set of circular conical surfaces, with coincident vertices at the centre of the Earth; this set includes the equatorial plane if the degree ( n ) of the multipole is odd. The magnetic field is horizontal everywhere on all these surfaces.
Palaeomagnetic studies have suggested that during some polarity reversals the magnetic field in the inner magnetosphere can be represented approximately either by a single, non-dipolar, low-degree (2 < n < 4), axisymmetric magnetic multipole or by a linear combination of such multipoles. In this situation, the equation for the field lines of an axisymmetric magnetic multipole of low degree (2 < n < 4) would be as fundamental to a proper understanding of magnetospheric, ionospheric and cosmic-ray physics during polarity reversals as is the equation for dipolar field lines in the case of the contemporary geomagnetic field. 相似文献
It is also shown theoretically that suites of similar magnetic field lines of the general axisymmetric multipole attain their maximum radial distances from the origin on a set of circular conical surfaces, with coincident vertices at the centre of the Earth; this set includes the equatorial plane if the degree ( n ) of the multipole is odd. The magnetic field is horizontal everywhere on all these surfaces.
Palaeomagnetic studies have suggested that during some polarity reversals the magnetic field in the inner magnetosphere can be represented approximately either by a single, non-dipolar, low-degree (2 < n < 4), axisymmetric magnetic multipole or by a linear combination of such multipoles. In this situation, the equation for the field lines of an axisymmetric magnetic multipole of low degree (2 < n < 4) would be as fundamental to a proper understanding of magnetospheric, ionospheric and cosmic-ray physics during polarity reversals as is the equation for dipolar field lines in the case of the contemporary geomagnetic field. 相似文献
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Activity rhythms of captive-bred reintroduced houbara bustards (Chlamydotis undulata macqueenii) were studied in the Mahazat as-Sayd reserve in Saudi Arabia. Birds were radio tagged with solar powered transmitters and activity was recorded with an automatic recording station over several weeks in the summer of 1993. Peaks of diurnal activity were observed at dawn and dusk. Daytime activity was negatively related to solar radiation and soil surface temperature. Nocturnal activity was triggered by moonlight. Food consumption, the duration of night-time activity and the minimum distance moved at night by houbara were positively correlated to the duration of moonlight. 相似文献
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Day-side aurora phenomena are examined by using TV image data obtained at Ny-Alesund in Svalbard, Godhavn in Greenland and Zhongshan Station,Antarctica. Results are summarized as follows. During the quiet period, in the pre-and post-noon sectors. (1) Weak arc (Sun-aligned arc), (2) Corona aurora and (3) Band aurora are observed in these stations. During disturbed period,Corona aurora and Band aurora are also observed in the pre- and post-noon sectors. However. bright discrete aurora. instead of weak arc (Sun-aligned arc). develops from thc night side oval in the dawn and dusk sectors. Pre-noon corona and post-noon band aurora are observed in the lower latitude as compared with the location of those auroras during the quiet period. 相似文献
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Archana Bhattacharyya 《Geophysical Journal International》1998,132(1):181-190
A region of enhanced conductivity at the base of the mantle is modelled by an infinitesimally thin sheet of uniform effective conductance adjacent to the core–mantle boundary. Currents induced in this sheet by the temporally varying magnetic field produced by the geodynamo give rise to a discontinuity in the horizontal components of the poloidal magnetic field on crossing the sheet, while the radial component is continuous across the sheet. Treating the rest of the mantle as an insulator, the horizontal components of the poloidal magnetic field and their secular variation at the top of the core are determined from geomagnetic field, secular variation and secular acceleration models. It is seen that for an assumed effective conductance of the sheet of 108 S, which may be not unrealistic, the changes produced in the horizontal components of the poloidal field at the top of the core are usually ≤10 per cent, but corrections to the secular variation in these components at the top of the core are typically 40 per cent, which is greater than the differences that exist between different secular variation models for the same epoch. Given the assumption that all the conductivity of the mantle is concentrated into a thin shell, the present method is not restricted to a weakly conducting mantle. Results obtained are compared with perturbation solutions. 相似文献
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Summary. A new closed-form solution is obtained analytically for a B- polarization induction problem of geophysical interest, in which a local region of the Earth is represented by a generalized thin sheet at the surface of and in electrical contact with a uniformly conducting half-space. The generalized sheet, first introduced by Ranganayaki & Madden, is a mathematical idealization of a double layer which consists, in this problem, of two adjacent half-planes with distinct conductances representing a surface conductivity discontinuity such as an ocean—coast boundary, underlain by a uniform sheet of finite integrated resistivity representing the lower crust. The resistive sheet exerts a considerable mathematical influence on the solution causing, under certain conditions, an additional pole to appear in one of the forms of contour integral by which the solution can be expressed; it also weakens or eliminates field singularities that would otherwise occur at the conductance discontinuity. A numerical calculation is made for model parameters typifying an ocean—coast boundary underlain by a highly resistive crust. It is found that the residue of the pole associated with the resistive sheet dominates the solution for this example, the main consequence of which is a huge increase in the horizontal range over which the induced currents adjust themselves between the different 'skin-effect' distributions at infinity on either side of the model. Moreover the solution shows that this 'adjustment distance' has a more complicated dependence on the conductance and integrated resistivity of the sheet than that given simply by the square root of their product which was the length parameter proposed by Ranganayaki & Madden. 相似文献