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1.
利用南北极极隙区与极光带纬度3个台站对电离层F2层峰值电子密度(NmF2)长达1个太阳活动周的观测数据,对国际参考电离层IRI-2016模型在极区的适用性进行系统的定量研究。结果表明,在极光带纬度的北极Troms?站,IRI预测与观测符合最好,大部分季节相对误差在40%以内,在太阳活动高年略好于太阳活动低年。在极隙区纬度的南极中山站和Longyearbyen站,IRI预测精度在太阳活动低年高于太阳活动高年。在中山站和北极Longyearbyen站仅个别月份相对误差在20%以内,大部分月份相对误差超过40%,冬季相对误差接近100%,特别是Longyearbyen站,在太阳活动高年冬季相对误差超过100%。从季节上看,3个台站都是冬季符合最差,夏季符合最好。IRI-2016模型对极区电离层进行预测时,难以如实反映极区等离子体对流和能量粒子沉降等极区特有的物理过程对极区电离层NmF2的影响。 相似文献
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电离层时延为GPS测量中最棘手、最严重的误差源,而极区结构复杂波动较大,电离层延迟极大影响了GPS测量精度,故在极区选取一个简单有效的电离层模型极为重要。将GPS及BDS采用的不同Klobuchar模型以及Ne Quick模型计算的极区总电子含量,以欧洲定轨中心提供的GIM模型电离层产品作为参考标准,研究三种广播电离层模型在北极地区的均方根和模型改正率。选取了2009—2013年共计5年的时间数据进行分析。结果表明,纬度在57.5°以上地区电离层改正GPS系统采用的Klobuchar模型基本不适用,但改正效果依然优于BDS,而Ne Quick模型改正效果弱于中低纬度,改正率整体在40%左右。 相似文献
3.
"极区电急流天线"辐射依赖于低电离层D/E区背景电急流,而高电离层F区极低频调制加热,可产生抗磁性电流,形成极低频波辐射源。利用电离层F区一维时变加热数值模型,采用全波解算法研究高纬Troms(69.59°N,19.23°E)地区电离层F区极低频调制加热。模拟结果表明,极区高电离层激发的极低频波与极区低电离层激发的结果不同。加热泵波的有效辐射功率(effective radiated power,ERP)、调制频率及电离层背景对极低频波强度有着重要影响。 相似文献
4.
基于南极中山站数字式电离层测高仪DPS-4D和GPS-TEC电离层闪烁监测仪的观测数据,比较研究了两者在2013年所得电离层总电子含量(TEC)随太阳辐射和地磁活动的日变化和季节变化特征。比较结果表明,南极中山站上空电离层TEC存在明显的极区电离层变化特性,这种变化特性大体与太阳辐射成正相关关系,而与地磁活动成负相关。尽管电离层TEC变化具有明显的晨昏不对称性,但都能有效地被DPS-4D和GPS TEC监测仪的数据计算获得,且两者相关系数达到0.86。结合中山站所处的极区电离层位置,考虑太阳辐射电离和地磁活动影响下的极区电离层对流以及中性大气成分改变,初步分析了DPS和GPS所得TEC结果有所差异的原因。 相似文献
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极区空间物理学重要的研究方向之一是剖析南北两极的热层、电离层和磁层的耦合问题。本文简明扼要地描述了极区空间物理学的一场革命——即理论框架的革新。这场科学革命是用磁流体力学理论取代电机工程理论,目前进行得比较缓慢,但将在今后的30～50年彻底改变人们对于热层-电离层-磁层的认知。 相似文献
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利用一维自洽的时变极区电离层模型,研究极隙区极光粒子沉降对极区电离层F层电子密度影响的时变过程。假设一维时变电离层模型描述的磁流管中F层等离子体在对流作用下经过极隙区,随对流路径的不同,磁流管在极隙区经历的时间不同,以此考察极光粒子沉降作用下电离层随时间的演化过程。数值计算结果表明,当磁流管在极隙区停留的时间足够长,F层电子密度能显著增大。然而在磁流管经历极隙区实际时间较短的情况下,极隙区极光粒子沉降对F层电子密度的影响并不大。本文还给出了统计对流模型作用下磁流管在经历极隙区时,有沉降粒子作用和没有沉降粒子作用两种情况下,F层等离子体的时间变化过程的差异。 相似文献
9.
极区是研究各种高空大气物理现象和日地关系的理想场所,通过GPS获取的电离层TEC信息具有高精度、全天候、大范围等优势,所以利用GPS研究极区电离层有重要意义。本文所设计的极区电离层信息监测和发布系统,包含数据回传、数据处理、数据发布三个部分。数据回传包括卫星网络回传和格式转换。数据处理是利用每天回传的GPS双频数据,解算单站VTEC,解决了硬件延迟的求解问题,并用二次建模获得测站上空的VTEC,计算结果表明该方法能较好地给出电离层TEC的大小及变化规律。数据发布是通过中国极地科学考察管理信息系统提供实时的查询服务。 相似文献
10.
中国南极中山站位于极隙区纬度,可以观测到丰富的日地能量传输过程的电离层征兆和极光现象,非常适合开展极区空间环境观测研究。自1989年开始建设以来,中山站极区空间环境观测系统经历了观测设备的不断完善和发展,现已建立了涵盖地面极光、电离层和地磁观测多要素、多手段的自主观测体系,实现了极区空间环境的连续监测并建立了数据库。所有观测设备的运行状态可实时监控,地磁、宇宙噪声吸收等数据实现了准实时远程传输。最后展望中国极区空间环境观测研究的发展前景。 相似文献
11.
Summary. The daily variation for the mean of the eight most quiet days of the IGY is represented as a function of latitude, longitude and UT by means of a spherical harmonic model. The most appropriate choice of Sq baseline is investigated, on the assumption that the external electric currents deduced from the model should be negligible at local midnight. The properties of the final model are discussed, particularly with regard to the external current foci, and are compared with those of previous models. 相似文献
12.
J. Arkani-Hamed 《Geophysical Journal International》1979,56(1):63-80
Summary. Equations governing non-linear and finite-amplitude convection in a heterogeneous planetary interior are developed. Using spherical harmonic expressions of variables, together with Green's function of Laplacian operator in a spherical coordinate, the equations are reduced to one-dimensional integro-differential equations and their numerical solutions are obtained by a finite-difference scheme. The theory is then applied to several lunar models and the following conclusions are obtained.
(1) The mean temperatures and velocities of convecting zones of variable viscosity models are higher than those of constant viscosity ones. This is due to the development of lithospheres with 400–500 km thicknesses in the former models, which reduce heat loss considerably.
(2) Molten regions are continuous shells in variable viscosity models whereas they become discontinuous and localized in a constant viscosity model. The continuous molten shells decrease lateral variations of temperature significantly and tend to stabilize convection.
(3) Lateral variations of viscosity have negligible effects on the thermal evolution of the models considered. 相似文献
(1) The mean temperatures and velocities of convecting zones of variable viscosity models are higher than those of constant viscosity ones. This is due to the development of lithospheres with 400–500 km thicknesses in the former models, which reduce heat loss considerably.
(2) Molten regions are continuous shells in variable viscosity models whereas they become discontinuous and localized in a constant viscosity model. The continuous molten shells decrease lateral variations of temperature significantly and tend to stabilize convection.
(3) Lateral variations of viscosity have negligible effects on the thermal evolution of the models considered. 相似文献
13.
We consider the two coupled differential equations of the two radial functions appearing in the displacement components of spheroidal oscillations for a transversely isotropic (TI) medium in spherical coordinates. Elements of the layer matrix have been explicitly written—perhaps for the first time—to extend the use of the Thomson-Haskell matrix method to the derivation of the dispersion function of Rayleigh waves in a transversely isotropic spherical layered earth. Furthermore, an earth-flattening transformation (EFT) is found and effectively used for spheroidal oscillations. The exponential function solutions obtained for each layer give the dispersion function for TI spherical media the same form as that on a flat earth. This has been achieved by assuming that the five elastic parameters involved vary as r p and that the density varies as r p-2 , where p is an arbitrary constant and r is the radial distance. A numerical illustration with p = - 2 shows that, in spite of the inhomogeneity assumed within layers, the results for spherical harmonic degree n , versus time period T , obtained here for the Primary Reference Earth Model (PREM), agree well with those obtained earlier by other authors using numerical integration or variational methods. The results for isotropic media derived here are also in agreement with previous results. The effect of transverse isotropy on phase velocity for the first two modes of Rayleigh waves in the period range 20 to 240 s is calculated and discussed for continental and oceanic models. 相似文献
14.
Genti Toyokuni Hiroshi Takenaka Masaki Kanao Douglas A. Wiens Andrew Nyblade 《Polar Science》2012,6(2):155-164
We have been developing an accurate and efficient numerical scheme, which uses the finite-difference method (FDM) in spherical coordinates, for the computation of global seismic wave propagation through laterally heterogeneous realistic Earth models. In the field of global seismology, traditional axisymmetric modeling has been used widely as an efficient approach since it can solve the 3-D elastodynamic equation in spherical coordinates on a 2-D cross-section of the Earth, assuming structures to be invariant with respect to the axis through the seismic source. However, it has the severe disadvantages that asymmetric structures about the axis cannot be incorporated and the source mechanisms with arbitrary shear dislocation have not been attempted for a long time. Our scheme is based on the framework of axisymmetric modeling but has been extended to treat asymmetric structures, arbitrary moment-tensor point sources, anelastic attenuation, and the Earth center which is a singularity of wave equations in spherical coordinates. All these types of schemes which solve 3-D wavefields on a 2-D model cross-section are classified as 2.5-D modeling, so we have named our scheme the spherical 2.5-D FDM. In this study, we compare synthetic seismograms calculated using our FDM scheme with three-component observed long-period seismograms including data from stations newly installed in Antarctica in conjunction with the International Polar Year (IPY) 2007–2008. Seismic data from inland Antarctica are expected to reveal images of the Earth's deep interior with enhanced resolution because of the high signal-to-noise ratio and wide extent of this region, in addition to the rarity of sampling paths along the rotation axis of the Earth. We calculate synthetic seismograms through the preliminary reference earth model (PREM) including attenuation using a moment-tensor point source for the November 9, 2009 Fiji earthquake. Our results show quite good agreement between synthetic and observed seismograms, which indicates the accuracy of observations in the Antarctica, as well as the feasibility of the spherical 2.5-D modeling scheme. 相似文献
15.
Various methods that take account of the potential nature of the field have been proposed for modelling geomagnetic data on a regional scale. Several of these have been applied to a standard data set based on annual mean values from observatories in Europe. Here, we examine some of the properties of spherical cap harmonic analysis when applied to this data set, and compare the quality of fit with that of the other models. It is found that, for this data set, rectangular polynomial analysis provides a compact fit to main field data, but that in most other cases, for both main field and anomaly data, spherical cap harmonic analysis provides the better fit. Although relatively insensitive to chosen cap size, spherical cap harmonic analysis deteriorates more rapidly than the other methods when the number of coefficients is reduced. 相似文献
16.
ShengKai Zhang DongChen E Fei Li JiFeng Huang YuanSheng Li ZeMin Wang XiaoHong Zhang 《寒旱区科学》2010,2(3):0198-0202
Tidal motion is the source of short-term vertical motion that an ice shelf experiences, and hence has a significant impact on ice shelves. During the 2003/2004 Austral summer season, five days of GPS measurements were carried out on the front of the Amery Ice Shelf （AIS）, East Antarctica, by the 20th Chinese National Antarctica Research Expedition （CHINARE）. The GPS data was processed using GAMIT/GLOBK software with 2-hour static data segment and the vertical precision is less than 0.18 m. To verify our results for the vertical component, we compare the ice shelf GPS tidal signal with a tidal result derived from tide gauge measurements at China＇s Zhongshan Station on Antarctica. Comparison of the GPS results with the tide gauge were in good agreement in amplitude at the few cm level, which indicates that the tide under the front of Amery Ice Shelf is irregular semidiurnal tide, the maximal tidal differences is approximately 2 m. GPS data can be used to validate the ocean tide model around the Antarctic area and such studies are important to improve our knowledge of the Antarctic ice shelf mass balance and dynamical models of ice sheet/ocean interaction. 相似文献
17.
Geomagnetic secular variation since 1901 总被引：3，自引：0，他引：3
Barbara M. Hodder 《Geophysical Journal International》1981,65(3):763-776
Summary. All available annual means, from the world-wide network of magnetic observatories, of north intensity ( X ), east intensity ( Y ) and vertical intensity (Z) from 1901 to 1977 are subjected to spherical harmonic analysis to obtain 38 models of the Earth's geomagnetic field at two-year intervals. These models are differenced to give 37 models of secular variation at two-year intervals from 1903.5 to 1975.5. The results show the decreasing trend of the dipole moment and are analysed for possible information on the westward drift of the magnetic field. 相似文献
18.
D. R. Barraclough J. M. Harwood B. R. Leaton S. R. C. Malin 《Geophysical Journal International》1978,55(1):111-121
Summary. Using a very large body of post-1955 data, a spherical harmonic model of the geomagnetic field and its secular variation is derived for 1965.0. This model is compared with the original International Geomagnetic Reference Field (IGRF) and with individual models used, or proposed for use, in producing the IGRF. Positions of the dip-poles, the geomagnetic poles and the eccentric dipole are derived from the model, together with their rates of change, and comparisons are made with other estimates of these positions. 相似文献
19.
Multilayer, spherically stratified, self-gravitating relaxation models with a large number of layers (more than 100) can be dealt with analytically. Relaxation processes are studied for both Heaviside surface loads and tidal forcings. Simulations of the relaxation process of a realistic earth model with an incompressible Maxwell rheology show that models containing about 30 to 40 layers have reached continuum limits on all timescales and for all harmonic degrees up to at least 150 whenever an elastic lithosphere is present, irrespective of the viscosity profile in the mantle. In particular, fine-graded stratification of the shallow layers proves to be important for high harmonic degrees in these models. The models produce correct long-time (fluid) limits. It is shown that differences in the transient behaviour of the various models are due to the applied volume-averaging procedure of the rheological parameters. Our earlier proposed hypothesis that purported shortcomings in the fundamental physics of (discrete) normal-mode theory are artificial consequences of numerical inaccuracies, theoretical misinterpretations and the use of incomplete sets of normal modes is reinforced by the results presented. We show explicitly that the models produce both continuous behaviour resulting from continuous rheological stratifications and discrete behaviour resulting from sharp density contrasts, as at the outer surface and the core-mantle boundary. The differences between volume-averaged models and fixed-boundary contrast models are outlined. Reducing many-layer models with a volume-averaging procedure before employing a normal mode analysis is both economical and highly accurate on all timescales and for all spherical harmonic degrees. The procedure minimizes the chances of missing contributing modes, while using models with more layers will not result in any substantial increase of accuracy. 相似文献
20.
The geomagnetic power spectrum 总被引：1，自引：0，他引：1
Stefan Maus 《Geophysical Journal International》2008,174(1):135-142
Combining CHAMP satellite magnetic measurements with aeromagnetic and marine magnetic data, the global geomagnetic field has now been modelled to spherical harmonic degree 720. An important tool in field modelling is the geomagnetic power spectrum. It allows the comparison of field models estimated from different data sets and can be used to identify noise levels and systematic errors. A correctly defined geomagnetic power spectrum is flat (white) for an uncorrelated field, such as the Earth's crustal magnetic field at long wavelengths. It can be inferred from global spherical harmonic models as well as from regional grids. Marine and aeromagnetic grids usually represent the anomaly of the total intensity of the magnetic field. Appropriate corrections have to be applied in estimating the geomagnetic power spectrum from such data. The comparison of global and regional spectra using a consistently defined azimuthally averaged geomagnetic power spectrum facilitates quality control in field modelling and should provide new insights in magnetic anomaly interpretation. 相似文献