空间科学学报

2007 Vol. 27, No. 1

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Extracting of Periodic Components in the Solar Activity Using EMD Method

LI Qiang, WU Jian, XU Zhengwen, WU Jun

2007, 27(1): 1-6. doi: 10.11728/cjss2007.01.001

Abstract(3156) PDF 2423KB(1413)

Abstract:
EMD (Empirical Mode Decomposition) technique has indicated the advantages and potentials in applications related to processing the nonlinear and non-stationary time series. In this paper, EMD method is adopted to study the solar cycles on various time scales. Using the EMD method, the averages of monthly medians of sunspot numbers of 110 years (1894-2003) and 55 years (1949-2003) can be decomposed into a series of modes and a trend respectively, including 1.3～1.4 years periodic component, 25～30 months QBO (Quasi-Biennial Oscillation) component, 11-year solar cycle component and 22 year Hale cycle component. Among those, the ll-year solar cycle mode with the largest amplitude has the high correlations with original sunspot numbers. In a nutshell, the EMD method other than the traditional and conventional methods can bring us the isolated characteristics of the solar variations on various time scales.

Simulation Study of Elements Influence Ring Current Distribution Properties During Main Phase of Storm

WANG Xinyue, LIU Zhenxing, SHEN Chao

2007, 27(1): 7-12. doi: 10.11728/cjss2007.01.007

Abstract(2446) PDF 1947KB(859)

Abstract:
The ring current is an electric current flowing westward around the Earth from 2 to 7 Re. Changes in this current are responsible for global decreases in the Earth＇s surface magnetic field, which are known as geomagnetic storms. The ring current formed primarily through injection driven by strong convective electric fields, E x B drift and subsequent trapping of particles from the plasma sheet into the inner magnetosphere during main-phase of storms. And ions will scattered into atmosphere by precipitation of loss cone. Based on the model of ring current ion distribution given by simulation, the distribution of ions with different energy by varians convective electric fields and ions pitch angle distributions are researched and the physics of these distributions is discussed.

Jointly Study on Flux Transfer Events Using the Data Observed by TC-1 and Cluster Near Dayside Magnetopause

YAO Li, LIU Shaoliang, LIU Kai, JIN Shuping, LIU Zhenxing, SHI Jiankui

2007, 27(1): 13-18. doi: 10.11728/cjss2007.01.013

Abstract(2758) PDF 1297KB(1206)

Abstract:
One of the Double Star satellite TC-1 and Cluster both in the magnetosheath near the dayside magnetopause amount to 25 times from February to April, 2004, when TC-1 in the low latitude and Cluster in the middle or high latitude region. 27 Flux Transfer Events （FTEs） had been detected by these satellite during that interval. This paper analyzed the influence of the transverse component of the Interplanetary Magnetic Field （IMF） on the position at the magnetopause where the reconnection occurs, and searched the evidence of component reconnection. The main results are as follows：（1） when IMF southward component Bz is dominate （｜Bz｜〉｜By｜）, 87.5% of FTEs were detected at low latitude by TC-1, but when IMF ｜Bz｜〈｜By｜, most FTEs （about 84.2%） were observed at middle or high latitude by Cluster; （2） there were a few correlative events （the correlative event means a event was observed by TC-1 and Cluster at low- and high-latitude, successively）, this imply that most of the FTEs which occurred in lower latitude moved along the sides of the magnetosphere toward the magnetotail, only a few of them over the high-latitude; （3） most FTEs detected at middle latitude were not come from the equator, but burn at that region by the mode of component reconnection.

Application of BP Neural Network in Prediction of Proton Events Peak Flux

ZHANG Longfei, XUE Bingsen

2007, 27(1): 19-22. doi: 10.11728/cjss2007.01.019

Abstract(2775) PDF 1467KB(907)

Abstract:
Solar proton events especially those with high fluxes may cause threat to the spacecrafts and satellites round the orbits near the earth, and may cause damage to the sensitive electronic components on the satellites, therefore, accurate short-term prediction of proton events is very meaningful to assure the safety of the space task and coordinate the instruments aboard the satellites. The current research shows that there exist a considerable correlation between proton events and soft X-ray radiation, so in this paper, based on the 1 ～ 8 A and 0.5 ～ 4A band soft X-ray data from GOES database, and choosing some characteristic parameters for our proton prediction model, a BP neural network was designed and used to predict the peak flux of the proton events, with the network input of soft X-ray data. The test result shows that in most cases the prediction error is less than one order.

Study of Method to Compute Ionospheric S4 Index Based on GPS Signal

CHEN Fenghua, YUAN Hong

2007, 27(1): 23-28. doi: 10.11728/cjss2007.01.023

Abstract(3019) PDF 2920KB(1307)

Abstract:
Ionospheric scintillations are rapid variations in the amplitude and phase of radio signals resulting from density irregularities in the ionosphere. Ionospheric scintillations influence adversely the performance of satellite communication system and the precision of navigation system. In this paper, the traditional computational method of ionospheric S4 index based on GPS signal is analyzed. In view of the insufficiency of the primitive S4 index computational method and the correction method, a new correction method is proposed. In order to test these methods, further study which is based on data from GPS receivers has been made. The result indicates that the primitive S4 index computational method and the correction method are feasible and reliable.

MF Radar Observations of Mesospheric Tides Over Wuhan

ZHANG Xiuchuan, YI Fan

2007, 27(1): 29-34. doi: 10.11728/cjss2007.01.029

Abstract(2635) PDF 3790KB(1130)

Abstract:
Data obtained from the MF radar observations in Wuhan have been used to analyzing the tides＇ structure and variability at the mesospheric altitudes. A dynamic power spectra of the horizontal wind with Lomb-Scargle periodogram illustrates that the diurnal tide is the dominant tidal disturbance and persists almost uninterruptedly in time. The mean amplitudes of the diurnal tidal disturbances show an altitude trend of increasing firstly and decreasing later. The corresponding frequency of the tidal spectral peaks often deviates from fixed one. Hodographs of the diurnal tidal wind vector with respect to heights and time indicates that the phase of the meridional component always leads that of the zonal component and the diurnal tides are upward propagating wave with downward phase progression. The meridional and zonal vertical phase velocities are 1.10 and 1.15 km/h.

Study on the Detectability of Typhoon-Generated Acoustic-Gravity Waves

XIAO Saiguan, ZHANG Donghe, XIAO Zuo

2007, 27(1): 35-40. doi: 10.11728/cjss2007.01.035

Abstract(3178) PDF 392KB(1183)

Abstract:
In this paper, the detectability of the ionospheric response to the typhoon-generated acoustic-gravity waves was studied through the statistical analysis of the HF Doppler shift records which come from the corresponding observation station at Peking University （39.4°N, 116.2°E） and a comparison with corresponding typhoon data. It is shown that the HF Doppler frequency sounding can be an effective tool for detecting the acoustic-gravity waves excited by typhoon, and the detectability is as high as up to 22 out of 24 for the present study. The detailed analysis of the HF Doppler records at different stages of the typhoon influenced period was made under the quiet conditions. Then, a comparison was made with the results of Huang （2 out of 12） and the possible causes of the differences between these two studies were analyzed. The non-linear propagation process of the main disturbances is reappeared by the method of numerical simulation, and the simulation results are in good agreement with observation results and the linear theory of acoustic-gravity waves propagated in the atmosphere. This confirmed that the detectability should be high in general. Also it is shown that the differences of detectability may be due to the fact that the detectability keeps a close correlation with the difference of relative locations of the source of typhoon and Doppler observation sites, and the propagation pattern of the medium-scale TIDs in the ionosphere.

Impact of the Ablation of Micro Meteoric Particle on the Metallic Layer in Mesosphere

LI Huabo, YI Fan

2007, 27(1): 41-47. doi: 10.11728/cjss2007.01.041

Abstract(2442) PDF 1650KB(852)

Abstract:
In this paper, the process of the ablation of meteoroid which radius is less than 100 μm is analyzed by adopting a continuous evaporation model of micro meteoroid, and the impact on the metallic layer in mesosphere （80～110 km） is estimated. The observation of radio meteor radar and Lidar suggests that the ablation of meteoroid which radius is lager than 100 μm is not the major source for metallic layer. From momentum equation and energy equation, the ablation profile of meteoroid with different radius in different velocity is calculated, and the variation of the ablating cut-off height is analyzed. According to the long term observation of lidar, it is concluded that the flux of meteoroid with the radius of 10～40 μm is the major impact of the normal metallic layer. Meteoroids with radius larger than 100μm and average velocity of 12km/s ablate around 80km which is lower than peak of the normal metallic layer. The micro meteoroids with different velocity will result in similar ablation cut-off height if they don＇t ablate completely. Meteoroids with radius of 10～40 μm and injection velocity of 14 km/s ablate mainly at the altitude of 80～110 km and their ablation cut-off heights are also near the underside height of the metallic layers.

Vertical Wavenumber Spectra of Temperature From High-Resolution Balloon Soundings Over Beijing

WU Yongfu, XU Jiyao, YUAN Wei, CHEN Hongbin, BIAN Jianchun

2007, 27(1): 47-54. doi: 10.11728/cjss2007.01.047

Abstract(2522) PDF 3007KB(889)

Abstract:
This study utilizes the vertical profiles of temperature with a high resolution of 10 m to examine spectral character of normalized temperature fluctuations in the 2.90～8.01 km and 14.65～19.76 km altitude ranges and to compare them with model spectra. Six vertical wavenumber spectra of normalized temperature fluctuations in the troposphere and six vertical wavenumber spectra of normalized temperature fluctuations in the lower stratosphere are presented. Results indicate that mean spectral slopes in the wavenumber range of 9.8 × 10^-4 ～ 2.5 × 10^-2m^-1 are about -1.9 in the troposphere and about -2.2 in the lower stratosphere. The two mean spectral slopes are diverge significantly from the value of -3.0 predicted by current saturation models and from the value of -2.4 predicted by a ＂universal＂ atmospheric spectrum model as well as are believed to be the shallowest slopes ever measured by balloon-borne radiosonde soundings. Mean spectral amplitudes in the wavenumber range of 9.8 × 10^-4 ～ 2.5 × 10^-2m^-1 are about 24 times in the troposphere and 5 times in the lower stratosphere larger than the predicted saturated spectral amplitudes. The two mean spectral amplitudes are also significantly different from the saturation models and those measurements in current literature. The larger spectral amplitudes, together with the shallowest slopes, show collectively that the observed temperature spectra do not obey current gravity wave saturation models and ＂universal＂ atmospheric spectrum model.

Inversion of Lunar Regolith Layer Thickness Using Microwave Radiance Simulation of Three Layer Model and Clementine UV-VIS Data

FA Wenzhe, JIN Yaqiu

2007, 27(1): 55-65. doi: 10.11728/cjss2007.01.055

Abstract(2718) PDF 3737KB(1524)

Abstract:
A correspondence of the lunar regolith layer thickness to the lunar Digital Elevation Mapping （DEM） is proposed to construct the global distribution of lunar regolith layer thickness. Using Clementine UV-VIS multispectral data, the global spatial distribution of FeO＋TiO2 content on the lunar regolith layer is calculated. Thus, dielectric permittivity of global lunar regolith layer can be obtained. Based on some measurements of physical temperature of the lunar surface, an empirical formula of physical temperature distribution over the lunar surface is presented. Based on aforementioned works, brightness temperature of lunar regolith layer in passive microwave remote sensing, which is planned for Chinese Chang-E lunar project, is numerically simulated by a three layer model using fluctuation dissipation theorem. Taking these simulations with random noise as observations, an inversion approach of the lunar regolith layer thickness is developed. Physical temperature of the top layer and the lower regolith can be inverted by the brightness temperature at high frequency channels using a two-layer model. The regolith layer thickness can be finally inverted by the brightness temperature at low frequency channel. Inversion error is also discussed. Numerical simulation and inversion approach in this paper make an evaluation of the performance for lunar passive microwave remote sensing, and can be applied to future data calibration and validation.

Study on the Simulation Strategy of Lunar Dust/Regolith Environment Effects

SHI Xiaobo, LI Yunze, HUANG Yong, WANG Jun

2007, 27(1): 66-71. doi: 10.11728/cjss2007.01.066

Abstract(2528) PDF 1367KB(1161)

Abstract:
Lunar regolith grains and dust was found to adhere to all surfaces it came into contact with, including radiators, solar cells, space suits and hand tools. Dust coating and contamination may cause more severe problems such as components overheating, clogging of mechanisms, seal failures, material abrasion, and so on. In this paper, study results on the nature of lunar dust, the interaction mechanism between lunar dust and lunar exploration systems, lunar dust environment simulation strategy are reviewed. A conceptual design of small lunar dust environment simulation system is performed accordingly. The system is a necessary tool to experimentally study the nature of lunar dust, and may serve for the test facility of lunar exploration system material chosen tests, mechanical system reliability tests and dust protection strategy verification tests.

Orbit Control Strategies and Implementation for on-Orbit Geostationary Satellites

LI Yuheng, WEI Wei, YI Kechu

2007, 27(1): 72-76. doi: 10.11728/cjss2007.01.072

Abstract(2256) PDF 950KB(1122)

Abstract:
The controls of west-east station keeping, longitude drifting control, north-south station keeping are the main tasks of the orbit control. From the engineering point of view, many practical formulas to calculate the objective and control parameters are presented here. They have been successfully used for a series control of the China FY-2B on-orbit satellite, which is required to move from 104.5°E to 123.5°E for evacuating the position for upcoming FY-2C satellite in Sept., 2004. During the control process, the longitude drift, north-south station keeping, attitude adjusting and spin speed control are made. Their perfect results show the correction of these practical formulas and strategies.

Study for Model of Inter-Frequency Combinations of Galileo and GPS

CHANG Qing, YI Bingxin, ZHANG Qishan, XIAO Zuo

2007, 27(1): 77-82. doi: 10.11728/cjss2007.01.077

Abstract(2293) PDF 639KB(1315)

Abstract:
Based on introducing signals in space of Galileo system and under the condition that the ambiguity is kept as integers, this paper defines the phase combination observations of the 4 Galileo and GPS L2 carriers. The relevant error impact is analyzed and the method for defining the ranges of searching combination coefficients is expatiated. Accordingly two sets of applied interfrequency combination observations with typical characters are also listed. Finally, some valuable inter-frequency combinations are given.

Remote Sensing Satellite RAW Data Format Analysis and Standardization Research

ZHANG Zhiqi, ZHANG Hongqun, LIU Dingsheng

2007, 27(1): 83-88. doi: 10.11728/cjss2007.01.083

Abstract(3093) PDF 1052KB(1527)

Abstract:
The remote sensing satellite RAW data format is not only one of the focus problems during the operation and development in the remote sensing satellite ground station, but also a problem the remote sensing users concern about. At present, the definition of RAW data format is in great confusion both at home and abroad, and no corresponding technical definition has been available so far. It has brought serious limitation to the usage of expensive satellite data and also brought difficulty on deciding how to save the data for long time storage, it has had great influence on the further development in the remote sensing satellite ground station. By analyzing the characteristics of some main existing remote sensing satellite RAW format combined with the operation experience over 20 years in China, a general RAW data format is proposed in this paper. RAW format has been adopted to our prototype system and well operated. Surely it is quite difficult to found a kind of RAW format standard with excellent compatibility and maneuverability.