Empirical model of cosmic ray spectrum in energy interval 1 MeV–100 GeV during 11-year solar cycle

The galactic cosmic rays (GCR) are the main ionization source at altitude of ∼3–35 km in the atmosphere. For high latitude anomalous cosmic ray (ACR) component has also a significant influence on the atmospheric ionization. We propose an empirical model for differential spectra D(E) of galactic and anomalous cosmic rays in energy interval 1 MeV–100 GeV during solar cycle. In the model data are used which cover three solar cycles: 20, 22 and 23. The LEAP87, IMAX92, CAPRICE94, AMS98 and BESS experimental spectra for protons and alpha particles are fitted to the proposed empirical model. The modulated GCR differential spectra are compared with force-field approximation to the one-dimensional transport equation and with solutions of two-dimensional cosmic ray transport equation. For experimental spectra, the calculation of the model parameters is performed by Levenberg–Marquardt algorithm, applied to the special case of least squares. Algorithm that combines the rapid local convergence of Newton–Raphson method with globally convergent method for non-linear systems of equations is applied for theoretically obtained differential spectra. The described programmes are realized in algorithmic language C++. The proposed model gives practical possibility for investigation of experimental data from measurements of galactic cosmic rays and their anomalous component.     

电大尺寸开口腔体RCS的SBR并行计算

文章利用消息传递协议MPI开发了针对电大尺寸开口腔体单站雷达截面(RCS)的射线弹跳法(SBR)并行计算程序。程序采用按照RCS计算角度间隔分配计算任务的大粒度并行计算方法,取得了较高的并行计算效率,大大减少了电大尺寸开口腔体的RCS计算时间。算例计算结果与文献吻合良好。     

A method to test HF ray tracing algorithm in the ionosphere by means of the virtual time delay

It is well known that a 3D ray tracing algorithm furnishes the ray’s coordinates, the three components of the wave vector and the calculated group time delay of the wave along the path. The latter quantity can be compared with the measured group time delay to check the performance of the algorithm. Simulating a perfect reflector at an altitude equal to the virtual height of reflection, the virtual time delay is assumed as a real time delay. For a monotonic electronic density profile we find a very small relative difference between the calculated and the virtual delay for both analytic and numerical 3D electronic density models.     

Preliminary results from the second flight of CREAM

Launched from McMurdo (Antarctica) in December 2005, the balloon experiment CREAM (cosmic ray energetics and mass) collected about 15 million triggers during its second flight of 28 days. Redundant charge identification, by two pixelated silicon arrays and a time resolved pulse shaping technique from a scintillator system, allowed a clear signature of the primary nuclei. The energy was measured with a tungsten/SciFi calorimeter preceded by a graphite target. Preliminary results from the analysis of the data of the second flight are presented.     

Large geomagnetic storms of extreme solar event periods in solar cycle 23

During extreme solar events such as big flares or/and energetic coronal mass ejections (CMEs) high energy particles are accelerated by the shocks formed in front of fast interplanetary coronal mass ejections (ICMEs). The ICMEs (and their sheaths) also give rise to large geomagnetic storms which have significant effects on the Earth’s environment and human life. Around 14 solar cosmic ray ground level enhancement (GLE) events in solar cycle 23 we examined the cosmic ray variation, solar wind speed, ions density, interplanetary magnetic field, and geomagnetic disturbance storm time index (D_st). We found that all but one of GLEs are always followed by a geomagnetic storm with D_st  −50 nT within 1–5 days later. Most(10/14) geomagnetic storms have D_st index  −100  nT therefore generally belong to strong geomagnetic storms. This suggests that GLE event prediction of geomagnetic storms is 93% for moderate storms and 71% for large storms when geomagnetic storms preceded by GLEs. All D_st depressions are associated with cosmic ray decreases which occur nearly simultaneously with geomagnetic storms. We also investigated the interplanetary plasma features. Most geomagnetic storm correspond significant periods of southward B_z and in close to 80% of the cases that the B_z was first northward then turning southward after storm sudden commencement (SSC). Plasma flow speed, ion number density and interplanetary plasma temperature near 1 AU also have a peak at interplanetary shock arrival. Solar cause and energetic particle signatures of large geomagnetic storms and a possible prediction scheme are discussed.     

C／C复合材料石墨化度的测定和评价

用Ｘ射线衍射方法对不同热处理温度下Ｃ／Ｃ复合材料石墨化度进行了测定，并对衍射峰进行了分峰处理。得出该材料由三种不同组元构成，即树脂炭，碳纤维和热解炭，求出各组元的石墨化度值及所占比例，进而得到试样的加权平均石墨化度。     

Studying characteristics of traveling ionospheric disturbances using U-shaped traces on vertical incidence ionograms

This paper presents a case study when due to the descending additional U-shaped trace on vertical incidence ionograms, increased critical frequency stabilizes. This corresponds to an ionospheric disturbance that moves toward the ionosonde and then stays overhead.Within a 2D model, traveling ionospheric disturbances (TIDs) are superimposed on the inverted background ionosphere. So ray tracing is used to obtain propagation paths through non-stratified ionosphere thus synthesizing the disturbed ionogram traces. Investigated are changes in the cusp shape caused by varying TID parameters. A cusp-fitting method to determine the TID amplitude, spatial scale, and horizontal drift velocity are shown.     

Research on the disturbance of ballistic missile to ionosphere by using 3D ray tracing method

This study uses the 3D ray tracing to analyse ionospheric disturbance generated by a ballistic missile plume (which was simulated in our previous work). Ray tracing results show that the 6 MHz radio waves are completely reflected by the ionosphere and cannot reach the ionospheric disturbance zone. The 8 MHz radio waves partially penetrate the ionospheric disturbance zone, producing a focusing effect. Most of the 10 MHz radio waves pass through the ionosphere and the disturbance zone. The focusing effect and focus height are reduced. In the height range 65̃400 km, the ray absorption loss of reflection is greater than the transmitted ray. When the ray is reflected multiple times in the cavity formed by the plume, ray absorption loss greatly increases.     

固定网格中基于边界描述的CAD模型快速分析方法

固定网格技术避免了沿结构边界繁琐的网格划分过程，在复杂几何结构分析时具有很大优势。建模精度和分析精度是采用固定网格进行结构分析的两大难题。文中针对固定网格分析中的建模精度问题，提出了一种由CAD模型至分析模型的快速转换方法，首先将CAD模型采用边界描述，然后通过射线交点法来区分固定网格中单元的属性，并借助四叉树/八叉树技术实现对边界网格的细分。最后采用加权B样条有限胞元法来保证CAD模型在固定网格中的分析精度。本文建立了一种由结构CAD模型至固定网格仿真分析的设计框架，数值算例表明了该方法的有效性。     

Cosmic ray modulation with a Fisk-type heliospheric magnetic field and a latitude-dependent solar wind speed

The effect of a latitude-dependent solar wind speed on a Fisk heliospheric magnetic field [Fisk, L. A. Motion of the footpoints of heliospheric magnetic field lines at the Sun: implications for recurrent energetic particle events at high heliographic latitudes. J. Geophys. Res. 101, 15547–15553, 1996] was first discussed by Schwadron and Schwadron and McComas [Schwadron, N.A. An explanation for strongly underwound magnetic field in co-rotating rarefaction regions and its relationship to footpoint motion on the the sun. Geophys. Res. Lett. 29, 1–8, 2002. and Schwadron, N.A., McComas, D.J. Heliospheric “FALTS”: favored acceleration locations at the termination shock. Geophys. Res. Lett. 30, 41–1, 2003]. Burger and Sello [Burger, R.A., Sello, P.C. The effect on cosmic ray modulation of a Parker field modified by a latitudinal-dependent solar wind speed. Adv. Space Res. 35, 643–646, 2005] found a significant effect for a simplified 2D version of a latitude-dependent Fisk-type field while Miyake and Yanagita [Miyake, S., Yanagita, S. The effect of a modified Parker field on the modulation of the galactic cosmic rays. In: Proceedings of 30th International Cosmic Ray Conference. Merida, Mexico, vol. 1, 445–448, 2007] found a smaller effect. The current report improves on a previous attempt Hitge and Burger [Hitge, M., Burger, R.A. The effect of a latitude-dependent solar wind speed on cosmic-ray modulation in a Fisk-type heliospheric magnetic field. In: Proceedings of 30th International Cosmic Ray Conference. Merida, Mexico, vol. 1, pp. 449–450, 2007] where the global change in the solar wind speed and not the local speed gradient was emphasized. The sheared Fisk field of Schwadron and McComas [Schwadron, N.A., McComas, D.J. Heliospheric “FALTS”: Favored acceleration locations at the termination shock. Geophys. Res. Lett. 30, 41–1, 2003.) is similar to the current Schwadron–Parker hybrid field. Little difference is found between the effects of a Parker field and a Schwadron–Parker hybrid field on cosmic-ray modulation, in contrast to the results of Burger and Sello and Miyake and Yanagita [Burger, R.A., Sello, P.C. The effect on cosmic ray modulation of a Parker field modified by a latitudinal-dependent solar wind speed. Adv. Space Res. 35, 643–646, 2005 and Miyake, S., Yanagita, S. The effect of a modified Parker field on the modulation of the galactic cosmic rays. In: Proceedings of 30th International Cosmic Ray Conference. Merida, Mexico, vol. 1, pp. 445–448, 2007]. The two-dimensional approximation used by these authors is therefore inadequate to model the complexities of the actual three-dimensional field. We also show that a Fisk-type field with a latitude-dependent solar wind speed (Schwadron–Parker hybrid field) decreases both the relative amplitude of recurrent cosmic ray intensity variations and latitude gradients and yields similar constants of proportionality for these quantities as for the constant solar wind speed case.