CHAMP和GRACE-A/B反演大气密度数据评估分析

利用Colorado大学公开发布的2001-2008年CHAMP和GRACE-A/B三颗卫星加速度计反演的400km高度上的大气密度数据,以大气模式NLRMSISE-00为参考,分析反演数据与模式值的误差特点、产生误差的原因、密度的变化及合理性,并通过卫星轨道两行根数（TLE）的反演结果进行验证,主要结论如下.CHAMP密度值整体稍高于GRACE-A/B,CHAMP密度与模式值之间的误差整体小于GRACE-A/B,2007-2008年 GRACE-A/B与模式的相对误差变化起伏较大.2001年CHAMP与模式存在整体偏差,通过相似空间环境条件下的密度变化比对以及利用TLE的反演结果验证,确定2001年的CHAMP反演密度整体偏低.CHAMP及GRACE-A/B密度变化个例显示,卫星密度值会出现一些个性化特征,使用时应根据需求进行分析处理.研究结果可为合理应用该数据提供参考.      

一种全球临近空间大气密度建模方法及应用

基于TIMED/SABER卫星2002—2018年观测的20~100 km大气密度数据,统计获得多年月平均值和标准偏差的全球网格数据。利用网格数据,分析了大气密度的变化特征。以网格数据为基准,计算了USSA76的相对偏差,分析了USSA76相对偏差的分布特征。以网格数据为驱动,将大气密度表征为平均值与大尺度扰动量和小尺度扰动量的加和,大尺度扰动和小尺度扰动分别采用余弦函数和一阶自回归模型表征,初步建立了全球临近空间大气密度模型。通过对比模型仿真值与激光雷达观测值,表明模型仿真值与观测值具有较好的吻合度,验证了建模方法的可行性。利用蒙特卡罗方法可再现给定轨迹上所有可能的大气状态。      

A tentative analysis of mean meridional- and zonal-vertical circulation by using the satellite cloudiness data

The mean meridional and zonal-vertical circulations in Pacific region have been analyzed by using 1965–1973 monthly mean satellite cloudiness. The general patterns are rather similar to the results calculated by using the rawin data. Furthermore over the open seas where the conventional data are lack, the results obtained from satellite data may be better and more detailed for describing the actual atmospheric circulation.     

Some aspects of the diffusion in the upstream region of the earth deduced from ISEE 1 observations

Two and six keV electron and proton data obtained by the FVA detector onboard ISEE 1 and 2 in the upstream region near apogee are analyzed. Tracing back electron and ion fluxes shows that electrons are present in a region of space near the boundary inside the foreshock, and that diffuse and intermediate ions do not directly issue from the bow shock surface. Using the assumptions that they result from the scattering of an initial population with no magnetic moment (μ=0), and that their mean energy is conserved through a diffusion process, we get a clear organisation of the data. Protons are present in a broad region of space inside the foreshock but appear at greater distances from the boundary when the spacecraft is near apogee. It is thought that these protons have their origin in the scattered beam-like distributions produced at the shock surface.     

On the origin of cosmic rays in the spiral galaxy NGC 3310

The problem of cosmic ray production in the spiral galaxy NGC 3310 is addressed by analysing and comparing optical and radio continuum data. Tentative results indicate that on global scales relativistic electrons may be produced in the shock front associated with teh density wave while on local scales extreme population I objects may be producing them. It is inferred that the same conclusions apply to all cosmic rays produced in the disk.     

基于小波分解与重构方法研究电离层偶发E层

电离层不规则体对卫星导航、通信、雷达系统等有重要影响.通过数值模拟及与实测数据的对比,论证基于小波分解与重构方法实现利用掩星数据反演电离层不规则体的可行性.以电离层偶发E层为例,利用国际参考电离层(IRI)模拟背景电离层电子密度分布,利用掩星探测的水平电子密度总含量δht反演不规则体信息,并与模拟数据进行比较.对200...     

Star formation and AGN fuelling

We present new observational data that tackle the issues of the star formation in Seyfert galaxies, the obscuration and fuelling mechanisms of active galactic nuclei, and the connection between these phenomena. New ISOCAM mid-IR images of nearby Seyfert 2 galaxies confirm that these systems are characterized by enhanced star forming activity. In barred systems the star forming activity occurs preferentially along the bar, indicating that these bars have formed recently and are still in the process of transporting gas towards the center. New X-ray data indicate that the gaseous column density absorbing Sy2 nuclei is a function of the bar strength, therefore indicating that stellar bars play an important role in obscuring AGNs. We speculate that non-axisymmetric disturbances (interaction/bars) both enhance the star forming activity in host galaxy and drive gas into the nuclear region to obscure the AGN, thus making the observed starburst-Sy2 connection. On smaller scales (10–100 pc), we report the discovery of a nuclear gaseous bar in the nearby Sy2 Circinus galaxy. The molecular gas kinematics indicates that this bar causes the gas to flow into the nuclear 10 pc. In the nuclear 10 pc we detect a young nuclear stellar cluster. We show that the post-main-sequence mass loss of this young nuclear stellar population could account for the fuelling of the active nucleus.     

强磁暴期间TIEGCM模式与CHAMP卫星热层大气密度的比较分析

利用NCAR-TIEGCM模式计算了2003年11月20—21日强磁暴期间410km高度上的大气密度,并与CHAMP/STAR加速度计反演数据进行对比和分析. 结果表明,模式结果能够准确反映磁暴期间大气密度的分布和变化情况,与实测结果在变化趋势和量级上具有较好的一致性,但在精细结构和数值大小上仍存在一定差异. 模式低估了磁暴期间大气密度的增幅,实测大气密度增幅高达250%～400%,而模式结果为100%～125%. 模式结果与实测数据的偏差在高纬地区高于低纬地区,日侧高于夜侧. 通过模式和实测数据的分析发现,磁暴期间大气密度扰动具有日夜侧和南北半球不对称性. 此外,模式能够准确反映磁暴期间大气密度扰动从高纬向低纬的传播以及大气密度对SYM-H指数响应的延迟特性.      

"神舟二号"大气密度探测器的探测结果Ⅱ.在太阳和地磁扰动期间高层大气密度的变化

选用了Sz—2大气密度探测器在2001年2—4月间的探测数据,进行日照和阴影区域热层大气密度对太阳和地磁活动程度的响应变化的探讨．结果表明,日照区大气密度峰值主要随F10.7值而变,在地磁扰动期间,阴影区大气密度对扰动的响应更明显,通常响应变化开始于高纬度地区,然后向低纬度地区推移．     

Measuring atmospheric density using GPS–LEO tracking data

We present a method to estimate the total neutral atmospheric density from precise orbit determination of Low Earth Orbit (LEO) satellites. We derive the total atmospheric density by determining the drag force acting on the LEOs through centimeter-level reduced-dynamic precise orbit determination (POD) using onboard Global Positioning System (GPS) tracking data. The precision of the estimated drag accelerations is assessed using various metrics, including differences between estimated along-track accelerations from consecutive 30-h POD solutions which overlap by 6 h, comparison of the resulting accelerations with accelerometer measurements, and comparison against an existing atmospheric density model, DTM-2000. We apply the method to GPS tracking data from CHAMP, GRACE, SAC-C, Jason-2, TerraSAR-X and COSMIC satellites, spanning 12 years (2001–2012) and covering orbital heights from 400 km to 1300 km. Errors in the estimates, including those introduced by deficiencies in other modeled forces (such as solar radiation pressure and Earth radiation pressure), are evaluated and the signal and noise levels for each satellite are analyzed. The estimated density data from CHAMP, GRACE, SAC-C and TerraSAR-X are identified as having high signal and low noise levels. These data all have high correlations with anominal atmospheric density model and show common features in relative residuals with respect to the nominal model in related parameter space. On the contrary, the estimated density data from COSMIC and Jason-2 show errors larger than the actual signal at corresponding altitudes thus having little practical value for this study. The results demonstrate that this method is applicable to data from a variety of missions and can provide useful total neutral density measurements for atmospheric study up to altitude as high as 715 km, with precision and resolution between those derived from traditional special orbital perturbation analysis and those obtained from onboard accelerometers.     

The influence of solid rocket motor retro-burns on the space debris environment

The ESA space debris population model MASTER (Meteoroid and Space Debris Terrestrial Environment Reference) considers firings of solid rocket motors (SRM) as a debris source with the associated generation of slag and dust particles. The resulting slag and dust population is a major contribution to the sub-millimetre size debris environment in Earth orbit. The current model version, MASTER-2005, is based on the simulation of 1076 orbital SRM firings which contributed to the long-term debris environment. A comparison of the modelled flux with impact data from returned surfaces shows that the shape and quantity of the modelled SRM dust distribution matches that of recent Hubble Space Telescope (HST) solar array measurements very well. However, the absolute flux level for dust is under-predicted for some of the analysed Long Duration Exposure Facility (LDEF) surfaces. This points into the direction of some past SRM firings not included in the current event database. The most suitable candidates for these firings are the large number of SRM retro-burns of return capsules. Objects released by those firings have highly eccentric orbits with perigees in the lower regions of the atmosphere. Thus, they produce no long-term effect on the debris environment. However, a large number of those firings during the on-orbit time frame of LDEF might lead to an increase of the dust population for some of the LDEF surfaces. In this paper, the influence of SRM retro-burns on the short- and long-term debris environment is analysed. The existing firing database is updated with gathered information of some 800 Russian retro-firings. Each firing is simulated with the MASTER population generation module. The resulting population is compared against the existing background population of SRM slag and dust particles in terms of spatial density and flux predictions.     

非线性磁声波和动力Alfven波的稀疏孤子解及其在低极尖区的应用

详细研究非线性磁声波和动力Ａｌｆｖｅｎ波稀疏型孤子解的性质，发现激发的电磁场在方向和形态上有明显区别，并和低极尖区Ｆｒｅｊａ卫星观测资料作比较，说明低频流密度下凹型更可能是非线性动力Ａｌｆｖｅｎ波所引起。     

Analysis of IRAS data for orbital debris

The Infrared Astronomical Satellite (IRAS) was launched in 1983 for the purpose of surveying the sky in a broad area of the infrared portion of the spectrum. While the primary objects of interest of IRAS were stars and nebulae, other types of space-related objects could also be observed. These include comets, asteroids, and Earth orbiting objects. Theoretical analysis indicates that IRAS could observe objects with a diameter of 1-mm at a range of 100-km and objects with a diameter of 1-cm at a range of 1000-km, while current ground-based observations of particles in low Earth orbit are limited to objects larger than 1-cm. Thus, these data offer a unique opportunity to ascertain the number density of particles below the present observable limit. At NASA/JSC a preliminary analysis of an IRAS data set has been performed to detect and describe this population, and the results of this study are presented.     

Storm-time atmospheric density modeling using neural networks and its application in orbit propagation

Upper atmospheric densities during geomagnetic storms are usually poorly estimated due to a lack of clear understanding of coupling mechanisms between the thermosphere and magnetosphere. Consequently, the orbit determination and propagation for low-Earth-orbit objects during geomagnetic storms have large uncertainties. Artificial neural networks are often used to identify nonlinear systems in the absence of rigorous theory. In the present study, an attempt has been made to model the storm-time atmospheric density using neural networks. Considering the debate over the representative of geomagnetic storm effect, i.e. the geomagnetic indices ap and Dst, three neural network models (NNM) are developed with ap, Dst and a combination of ap and Dst respectively. The density data used for training the NNMs are derived from the measurements of the satellites CHAMP and GRACE. The NNMs are evaluated by looking at: (a) the mean residuals and the standard deviations with respect to the density data that are not used in training process, and (b) the accuracy of reconstructing the orbits of selected objects during storms employing each model. This empirical modeling technique and the comparisons with the models NRLMSIS-00 and Jacchia-Bowman 2008 reveal (1) the capability of neural networks to model the relationship between solar and geomagnetic activities, and density variations; and (2) the merits and demerits of ap and Dst when it comes to characterizing density variations during storms.     

中纬E层临界频率和低电离层的电子密度剖面计算

本文给出了计算中纬E层临界频率(f_0E)和低电离层的电子密度分布与太阳天顶角、太阳黑子数、地方时之间关系的经验公式.由它对不同年、月、日以及午前、午后情况进行计算的结果与实验探测数据符合得较好;将该公式用于长波传播和吸收计算也得到了与实验一致的结果.此外, 它还能由实测的f_0E值算出D区电子密度分布.      

High-fidelity geometry models for improving the consistency of CHAMP,GRACE, GOCE and Swarm thermospheric density data sets

During the last two decades, accelerometers on board of the CHAMP, GRACE, GOCE and Swarm satellites have provided high-resolution thermosphere density data to improve our knowledge on atmospheric dynamics and coupling processes in the thermosphere-ionosphere region. Most users of the data have focused on relative density variations. Scale differences between datasets and models have been largely neglected or removed using ad hoc scale factors. The origin of these scale differences arises from errors in the aerodynamic modelling, specifically in the modelling of the satellite outer surface geometry and of the gas-surface interactions. Therefore, the first step to remove the scale differences is to enhance the geometry modelling. This work forms the foundation for the future improvement of characterization of satellite aerodynamics and gas-surface interactions models at TU Delft, as well as for extending the use of sideways and angular accelerations in the aerodynamic analysis of accelerations and derivation of thermosphere datasets. Although work to improve geometry and aerodynamic force models by other authors has focused on CHAMP and GRACE, this paper includes the GOCE and Swarm satellites as well. In addition, it uses a density determination algorithm that is valid for arbitrary attitude orientations, enabling a validation making use of attitude manoeuvres. The results show an improvement in the consistency of density data between these four missions, and of data obtained before, during and after attitude manoeuvres of CHAMP and Swarm. The new models result in larger densities, compared to the previously used panel method. The largest average rescaling of density, by switching to the new geometry models is reached for Swarm at 32%, the smallest for GRACE at 5%. For CHAMP and GOCE, mean differences of 11% and 9% are obtained respectively. In this paper, an overview of the improvements and comparisons of data sets is provided together with an introduction to the next research phase on the gas-surface interactions.     

电离层等离子体泡的磁场扰动特征与识别

等离子体泡是赤道区电离层常见的密度耗空结构,同时伴随着背景磁场的增强和垂直背景磁场方向上的扰动,这些扰动具有阿尔芬波的特征.本文利用Swarm卫星的标量、矢量磁场以及等离子体观测数据,考察了等离子体泡产生的磁场扰动信号特征,发现磁场强度和平均场向分量的增强均与等离子体泡密度下降有较强的负相关性,说明磁场标量和矢量(平均...     

Taurid complex meteoroids detected near aphelion with Ulysses

Between 3.4 and 4.0 AU the dust detection system aboard the Ulysses spacecraft showed an increase in detection rate for particles with masses greater than 5 × 10⁻¹³ g. The spacecraft meteoroid encounter geometry indicates highly eccentric orbits detected near aphelion. The outer limit of the enhanced flux is imposed as meteoroids on such orbits move outside the aperture of the dust detector. The inner edge of the enhanced flux would be consistent with the aphelion distance acquired by 50-200 μm particles evolving for 10-20 kyr under Poynting-Robertson drag from an Encke type orbit. We propose such meteoroids provide a source population from which collisional fragmentation produces particles in the mass range to which the Ulysses detector is sensitive. Daughter fragments produced away from the aphelia of the parent orbits, a 2.2 AU, e 0.85, enter hyperbolic orbits which are not evident in the Ulysses data. The spatial density of fragments from collisions very near aphelion drops off rapidly as they evolve inward under Poynting-Robertson drag while collisions closer to 3.4 AU leave the subsequent peak density outside that radius for a significant fraction of the fragment's subsequent lifetime. The rapid orbital evolution for these collision fragments implies a recent breakup and probably a large reservoir of parent meteoroids.