空间科学学报

2007 Vol. 27, No. 6

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Study of Energetic Particle's Acceleration Mechanism at Perpendicular Shock With Particle Simulation Results

SUN Peng, QIN Gang, WANG Chi

2007, 27(6): 441-447. doi: 10.11728/cjss2007.06.441

Abstract(2624) PDF 1938KB(1130)

Abstract:
Large amount of test particles＇ trajectories at perpendicular shock with magnetic turbulence are calculated. And the effect of shock strength and particles＇ initial energy to the average energy change per shock-crossing is also studied. Furthermore, the test particle＇s energy gain from Shock Drift Acceleration （SDA） under different conditions is analysed, too. In addition, a theoretical （1） formula △E=arnvivup（1-1/s） is given for SDA, which agrees very well with our simulation results. The results show that, although magnetic turbulence is included, particles would still be accelerated mainly by SDA at perpendicular shock, while the diffusive shock acceleration, based on the guiding center assumption, is not valid.

Prediction of the Onset of Solar Cycle 24 by Similar Cycle Method

MIAO Juan, WANG Jialong, LIU Siqing, GONG Jiancun

2007, 27(6): 448-452. doi: 10.11728/cjss2007.06.448

Abstract(2889) PDF 1436KB(1093)

Abstract:
In this paper, ＂Similar Cycle＂ method is introduced and applied to predict the onset of solar cycle 24. Meanwhile, the smoothed monthly mean sunspot numbers of the last cycle descending phase are predicted. According to the characterestics of cycle 23, six cycles （9, 10, 11, 15, 17 and 20） are selected as the similar cycles of cycle 23 and was used to predict the beginning of cycle 24. The results are：（1） The beginning of cycle 24 will occur in the period from April to June, 2007. The length of cycle 23 may be 11.1 years. （2） The minimum smoothed monthly mean sunspot numbers is 7.1±2.6. Compared with other predictions, the onset time of cycle 24 in this paper is close to that of Ref.[11],
[12] and MSFC. From the discussion on the solar cycle prediction methods, ＂Similar cycle＂ is thought to be an effective method to the prediction of long-term solar cycle evolution. It could be used to predict the ending time of a solar cycle with a leading time of 3-4 years or more soon after the maximum.

On the Prediction of Geomagnetic Storm Following the Eruptive Event on the Solar Disk

XUE Bingsen

2007, 27(6): 453-458. doi: 10.11728/cjss2007.06.453

Abstract(2874) PDF 993KB(1181)

Abstract:
Solar flares are well-known events on the solar disk while most of them being non-geoeffective. The key factors that makes them geo-effective are weather they have CME accompanied and the features of CME as well. But among the hundreds of CME, only few of them could cause significant geomagnetic disturbances, which mainly depends on whether they are towards to the earth. In this work, the relationship between the geomagnetic disturbances and the energetic proton flux （ACE-EPAM） data, together with the parameter of the solar flares that related to the CME was carefully investigated. The preliminary result is that, more than 90% of the enhancement of the particle flux followed by shock could be measured by ACE. But the correlation between flux of the particles and magnitudes of the geomagnetic disturbances was not much clear. Other factors that related to the characteristics of the CME have also to be taken into consideration. The position of the flare, which may affect the direction of the CME, the flare scale, which may decide the velocity, and the duration, which could relate to the magnetic field strength. But through statistical work, it was found that the relationship between the magnitudes of the geomagnetic disturbance Ap index and all those parameters mentioned above was non-liner, so neural network method was introduced to simulate the relation automatically. After the neural work being trained with the historical data range from 1986 to 2002, a model to predict the geomagnetic storms after the solar eruptive events was constructed. Test result showed that the error of the model comparing with the measurement was less than 20%.

Prediction Method of CME Associated Geomagnetic Disturbances Based on Fuzzy Mathematics

WANG Jing, FENG Xueshang

2007, 27(6): 459-466. doi: 10.11728/cjss2007.06.459

Abstract(2687) PDF 2593KB(1174)

Abstract:
Based on the 73 geomagnetic disturbance events caused by coronal mass ejection （CME） associated with interplanetary shock waves and using fuzzy mathematics, here is presented a prediction method for geomagnetic disturbances. According to the solar location of CME, the transit time of the interplanetary disturbance, the geomagnetic disturbance magnitude and the velocity jump observed by IPS at the disturbed front, five membership functions μθ,μT,μM,μ△v are constituted. Based on the five membership functions and fuzzy mathematics, prediction tests for the 73 CME associated geomagnetic disturbance events during 1996--2004 are made by considering the influence of CME velocity on the onset time of geomagnetic disturbances. Main results are：（1） For the prediction of the magnetic disturbance onset time, 91.78% is within the range of relative error △Tpre/Tos≤30% and 12.33% within △Tpre/Tos≤30%; （2） For the prediction of the geomagnetic disturbance amolitudes, 60.27% is within the range of relative error △∑Kp/∑Kpobs≤30% and 12.33% within △∑Kp/∑Kpobs≤50%. These results show that the prediction method has good feasibility for geomagnetic disturbance prediction.

Relations Between Magnetotail BBF and Pi2 Pulsations

CAO Jinbin, DUAN Juntao, MA Yuduan, YANG Dongmei

2007, 27(6): 467-473. doi: 10.11728/cjss2007.06.467

Abstract(2718) PDF 2033KB(1010)

Abstract:
Recent observations show that there is a close correlation between BBFs （bursty bulk flows） and mid-low latitude Pi2 pulsations. However the relation between BBFs and Pi2 pulsations remains an unsettled open question. In this paper, by using the data of Cluster, TC-1/DSP and six ground stations （Dedu, Taian, Kashi from China and Castello Tesino, Ranchio, Nagycenk from Europe）, three BBF events were analyzed that occurred during magnetic quiet times from 1700 UT to 1930UT on October 22, 2004. It is found that two of BBF events can excite Pi2s. The P.i2s appeared simultaneously The Pi2s in H components at six ground stations have almost the same starting time, same period （about 60 s） and same waveform. The characteristics of relevant Pi2s are consistent with those of cavity mode. For the first BBFs, TC-1 inside the plasmasphere observed a Pi2 event. However for the second BBF, TC-1 did not observe any Pi2 signature. During the third BBF event, both ground and space observations show that there are no Pi2s. Thus it can be concluded that not all BBFs can excite Pi2s. What kind of BBFs can excite the Pi2 remains an open question.

Reverting the Distribution of Space Protons and Ions From the Ground Cosmic Ray Neutrons Intensity

LAI Zhijuan, XUE Bingsen

2007, 27(6): 474-480. doi: 10.11728/cjss2007.06.474

Abstract(2682) PDF 3334KB(1164)

Abstract:
By using the method of linear regress, the relation between the cosmic ray intensity of the OULU neutron monitor and the differential fluxes of space energetic proton and ion during quiet time has been studied. The differential spectrum of interplanetary particles with high energy is also calculated through the intensity of neutron at the ground level. On the basis of the energy spectra of proton and ion, a new calculation of the differential fluxes of proton and ion with＇ high energy is suggested by combining the intensity of the neutron measured by OULU neutron monitor. For particular discussion, four channels （350-420 MeV, 420-510 MeV, 510-700 MeV, 〉700 MeV） on the GOES satellite and the element C on the ACE satellite are chosen as examples. Through comparison, it is concluded that the result is well consistent with the measurements. In order to prove the practicability of the method mentioned above in description of the space radiant condition,the differential As a result, it proton fluxes are is concluded that from the intensity of the ground calculated during November and December in 2006 by the method. the differential fluxes of space proton and ion may be well rebuilt neutron with this method.

MF Radar Observations of Phase Relationships Between Tidal Horizontal Wind Components in the Mid-latitude Winter Lower Thermosphere

LIU Renqiang, Lu Daren

2007, 27(6): 481-490. doi: 10.11728/cjss2007.06.481

Abstract(2824) PDF 3885KB(1312)

Abstract:
Wind measurements obtained from Wuhan/China MF radar during winter 2001 are used to study the phase relationships between tidal horizontal winds in lower thermosphere. The tidal initial phases in any time window are uniformly defined in radians. The meridional and zonal initial phases of each tide exhibit a similar time variation trend at each height and this induces a near phase difference at three consecutive heights. However, in most of the 14 days, △φ4 and △φ12 are quasi-quadrature while △φ8 is unexpectedly quasi-in-phase. The appropriate tidal meridional and zonal quadratic phase coupling （QPC） equations are estimated respectively. The supposed terdiurnal phases and those observed agree well. By subtracting the estimated tidal zonal QPC equation from the meridional, a tidal phase difference correlated equation is obtained. The supposed terdiurnal phase differences and those observed again agree with each other. Within the 14th time window, all the three tides are generally elliptically rather than circularly or linearly polarized. However, both △φ24 and △φ12 in this window are quasi-quadrature at all heights while △φ8 are quasi-in-phase at 92.0 and 94.0km. So the estimated tidal QPC equations, the deduced tidal phase difference correlated equation, the observed terdiurnal quasi-in-phase phase differences and the typical tidal polarization plots are all indications of real QPC between the observed 24, 12 and 8 h tides.

Observations of Atmospheric Gravity Waves in Airglow Over Adelaide

JIANG Kui, DING Feng, WAN Weixing, Reid I M, Woithe J M

2007, 27(6): 491-497. doi: 10.11728/cjss2007.06.491

Abstract(2752) PDF 2001KB(1227)

Abstract:
This paper presents the statistical results of the propagation characteristics of largescale gravity waves observed by OH and OI airglow during the years from 1995 to 2001 in Adelaide, Australia （34.5°S, 138.5°E）. The propagation parameters were obtained through the three-channel maximum entropy method. Totally 48 gravity wave events were identified by the OH airglow observation and 29 events were identified by OI. The periods and horizontal phase speeds of these gravity waves peak at about 68 min and 36 m/s, and the gravity waves shows an obvious dominating direction of propagating south-eastward. The mean elevation is 8°- 10°, which shows the nearly horizontal propagation trends. It was also found that an up-going gravity wave event was observed nearly simultaneously by OH and OI. However, in most cases, the gravity waves cannot be observed simultaneously by OH and OI observations, because of the errors of the instruments or the effects of strong wind shears on gravity waves in the mesopause region.

Analysis of Observation Capability of Ground-based Facilities and Stations to Space Debris

FENG Hao, LIU Jing, ZHANG Yao, YU Youcheng

2007, 27(6): 498-504. doi: 10.11728/cjss2007.06.498

Abstract(2432) PDF 2272KB(1089)

Abstract:
When building-up ground-based stations for space debris observations, it is needed first to imitate and analyze the observation capability by numerical simulations. The important criterion of the observation capability of the station is the observational quantity and frequency of space debris observed by the facilities. The observation capability can be improved by using advanced facilities and selecting suitable station positions. In this paper, the software STK and PROOF was used to make numerical simulation and comparison analysis for the observation capability （both passing and detection rate） of radar and optical facilities in different stations. Some preliminary conclusions were gained and might be profitable to the design of the space debris surveillance network. There are a few problems in calculation with existing observation capability evaluating and simulation software, so it is necessary to built new software which is wieldy and convenient and has better and flawless function. Some suggestions were made in the article for the new software. The Performance model of radar and telescope should be optimized. Phased array radar, bistatic radar, scan patterns of both radar and telescope, and hybrid observation of several failities should be easily simulated. Computational efficiency should be advanced to decrease computing time.

Contour Constraint Based Geomagnetic Matching Method

LIU Ying, WU Meiping, HU Xiaoping, XIE Hongwei

2007, 27(6): 505-511. doi: 10.11728/cjss2007.06.505

Abstract(2462) PDF 1912KB(1910)

Abstract:
Geomagnetism Aided Navigation （GAN） is a new branch of the integrated navigation technique. Navigation principle and the development of the GAN system are introduced in the paper. The emphasis is laid on the research of the matching method. Geomagnetic matching is the technique that uses a geomagnetic map to determine the location of the vehicle. The obtained position information can be used to limit error accumulation of the Inertial Navigation System （INS）. An improved correlation matching method based on the contour constraint is proposed. Map contour is used to confine the searching process, changing the uncertainty field to an uncertainty line, which efficiently reduces the computation burden of the system and eliminates the initial position error of INS. A nearest point principle （NPP） is applied in the precision matching part. The NPP technique can bind the error of INS accumulated during the matching process. The simulation results show that the proposed method can greatly improve the efficiency and precision of the whole GAN system. The accuracy of the matching method is less than the unit cell size of the map. In addition, the proposed method is, to some extend, adaptive to the heading error of the INS.

Key Technologies of Autonomous Radio for Deep Space Network

HU Shengbo, MENG Xin, YAO Xiujuan, ZHAO Na, YAN Yi

2007, 27(6): 512-517. doi: 10.11728/cjss2007.06.512

Abstract(2504) PDF 2671KB(1107)

Abstract:
The primary application of autonomous radio for deep space network is relaying communication signals from multiple deep space assets. The advantage of an autonomous radio is that it can communicate to each asset that comes into view, automatically, without having to be reconfigured from Earth for each pass to account for differences in the signal characteristics. The autonomous radio that can meet the need for deep space network is discussed. The fundamental difference between a conventional radio, or even a software-defined radio, and a truly autonomous radio for deep space network is that an autonomous radio has the ability to recognize features of an incoming signal without much a priori knowledge. Using conventional estimation and tracking design, one quickly gets into a chicken and egg problem. In this paper, we overview the architecture of an autonomous radio, define many parameters one might desire to estimate from the signal. Finally, an iterative layered architecture model of parameters estimating in the autonomous radio is presented, message-passing and the interaction of the estimators is analyzed.

Study and Implementation of the New CCSDS Image Compression Algorithm

CHEN Yuhua, GU Xiaodong, ZHANG Zhongwei, CHEN Xiaomin, SUN Huixian

2007, 27(6): 519-522. doi: 10.11728/cjss2007.06.519

Abstract(3303) PDF 1427KB(1133)

Abstract:
The Consultative Committee for Space Data Systems （CCSDS） has recently adopted a new recommendation for image data compression algorithm released in 2005 as a staudard. The purpose of the Recommended Standard is to solve the problem of efficiently compressing the digital image two-dimensional spatial data from payload instruments and to specify how this compressed data will be formatted into segments to enable decompression at the receiving end. This algorithm can reduce the amount of digital data to achieve benefits, so it not only can reduce the transmission channel bandwidth, the buffering and storage requirement, but also can reduce the data-transmission time at a given rate. This algorithm has important significance to space data compression. This paper describes the new CCSDS image compression algorithm and performance and analyzes the feasibility of hardware implement. And the testing results between this algorithm and other image compression algorithm under software implementing are compared. From the results, it is shown that the performance is as good or even better than that of JPEG 2000, SPIHT under low bit-rate compression. It completely conforms to the on-board image compression under the low bit-rate.