空间科学学报

2009 Vol. 29, No. 6

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Medium and Short Term Forecasting of Ap Related to Coronal Holes

LiuSiqing, Luo Bingxian, Zhong Qiuzhen, Dou Xiankang

2009, 29(6): 545-551. doi: 10.11728/cjss2009.06.545

Abstract(3185) PDF 590KB(1240)

Abstract:
Ap index is a daily measure of geomagnetic activity. In many reference atmospheric models, geomagnetic storm effects are modeled using Ap index as the driver of global density changes. Ap index is often used in making space mission plans because of the geomagnetic activity effects, and the forecasting of the Ap index plays an important role in space environment prediction. In the present study, the modified autoregressive model is used to forecast the Ap index 27 days ahead. In the modified model, the input data were reconstructed based on the 27-days periodicity of the solar rotation. The average absolute error between the forecasted and observed geomagnetic Ap index is 4.5. For short-term Ap forecasting (3-days ahead in this paper), a new forecasting index Pch derived from the SOHO/EIT EUV images is used. Pch index is a parameter which can reflect both the area and brightness of coronal holes. Because the high speed stream will arrive at the earth orbit and cause geomagnetic disturbances about 3 days later after a coronal hole passes over the center meridian of the solar disk, the parameters of coronal holes can be used to forecast the geomagnetic disturbances. The average absolute error between the forecasted and observed geomagnetic Ap index is 3.7. According to the results of medium term and short term forecasting, the prediction accuracy can be improved by combining the statistical method with the physical analysis above.

Study of Ionospheric Irregularities in the Vicinity of SED Region During a Super Geomagnetic Storm

Huang Li, Yuan Zhigang, Deng Xiaohua, Nie Zhiying, Lin Minhui

2009, 29(6): 552-557. doi: 10.11728/cjss2009.06.552

Abstract(2808) PDF 612KB(1303)

Abstract:
Small-scale ionospheric irregularities can cause strong amplitude and phase scintillations of radio wave signals passing through the ionosphere. In this paper, the phenomena of Storm Enhanced Density (SED) were studied during a super geomagnetic storm in October 2003 by using the TEC data of IGS. Rate of TEC Index (ROTI) is calculated with the observed data of GPS. The ROTI has been used to analyze the spatial and temporal distribution of small scale ionospheric irregularities in the vicinity of SED region. It shows that the irregularities near the SED border were gradually increased with the development of geomagnetic storm during the main phase, and the distribution density reached its maximum value in the latter part of the main phase, and then was reduced during the recovery phase. Initially, the irregularities were mainly distributed in latitudes 40º~45ºN. Subsequently, the irregularities drifted to higher latitude, and were mainly distributed in latitudes 45 º~55ºN. This study provides an important theoretical foundation on revealing the propagation characteristics of radio waves passing through the vicinity of SED region.

Estimating of RCS of AFAS Based on Ionospheric Heating

Lv Libin, Li Qingliang, Yan Yubo

2009, 29(6): 558-562. doi: 10.11728/cjss2009.06.558

Abstract(2834) PDF 398KB(1316)

Abstract:
In the experimental researches of ionospheric heating, an interesting phenomenon was found: irregularities were excited in the heating experiment, which could scatter radio waves in a special way. The scattering is highly sensitive to the direction of geomagnetic field, and it is termed as AFAS (Artificial Field Aligned Scattering). A number of experimental researches were carried out by using the Platteville high power heating facility and other communication equipments. From these researches, people found that the RCS (Radar Cross Section) of AFAS is quite great, which may be as large as 80dB•m2. This is very useful for scattering communication. To study the application of the AFAS in communication, the estimation of RCS is important. A mathematical model was developed, which is based on the theoretical and experimental researches of the ionospheric heating, the characteristics of the scattering on F region and the scattering theory of irregularities. Comparison of the results between model and theory show that the model is applicable. Using the model, the RCS of AFAS in the frequency range of 20 MHz and 100 MHz were calculated, and a RCS of 80dB•m2 was obtained at low-level of VHF. Our calculation supports that the maximum of RCS occurs when the radar beams are in the direction perpendicular to the magnetic field.

Parallel Numerical Model for the Simulation of Three Dimensional Gravity Wave's Propagation

Liu Xiao, Xu Jiyao, Li Wenqiang, Gao Hong

2009, 29(6): 563-572. doi: 10.11728/cjss2009.06.563

Abstract(3066) PDF 755KB(1144)

Abstract:
Based on the control equations which describe the dynamics of three dimensional compressible atmosphere and the MPI (Message Passing Interface) and the idea of domain decomposition, a parallel numerical model is developed in this paper. The model is used to simulate the gravity waves propagation in three-dimensional compressible atmosphere. Firstly, on the basis of domain decomposition in the vertical direction and the characteristics of the staggered grid system, the main grid lines for vertical velocity are regarded as the lower boundary of the child domain, and the main grid lines for the state variables are regarded as the upper boundary of the child domain. Then, the data communication from one child domain to another is completed by MPI. As a result, the parallel computation on the whole computational domain can be completed successfully. Finally, according to the linear theory for small amplitude gravity waves, we simulated the small amplitude gravity waves propagation and the results indicated that, the propagation of small amplitude gravity wave in three-dimensional atmosphere can be simulated well by our model. The amplitude of gravity wave is increased in the form of exponential with its propagation height increased. The simulated results about the energy path, the available perturbative potential energy and the perturbative kinetic energy are well consistent with the gravity wave's linear theory. Additionally, with the number of processes increasing, the computational time decreases dramatically. All of these indicated that, the parallel numerical model developed in this paper not only can simulate the propagation of gravity waves very well, but also the model can save the computational coast effectively.

Effect of the Heating Flow on the Determination of the Field-aligned Currents

Xu Bin, Wu Jian, Cesar La Hoz, Wu Zhensen, Che Haiiqiin, Xue Kun

2009, 29(6): 573-579. doi: 10.11728/cjss2009.06.573

Abstract(2700) PDF 508KB(1207)

Abstract:
The detection of the filed-aligned currents is an important scientific subject for the Europe Incoherent SCATter radar association (EISCAT). Using the different channels, the ion line and the plasma line can be observed synchronously by the incoherent scatter radar, which can be used to deduce the resonance frequency of the ions and electrons, and the filed-aligned current can be determined by these frequencies. The method is reasonable for the plasma with the Maxwellian distribution. However, the heat flow can be caused by the drift velocity in the velocity phase space. The 16-moment distribution function is used to describe the heat flow effect. On this basis, the solutions of the dielectric function and dispersion relation with a complex frequency are presented for an arbitrary velocity distribution, and the results are compared with those of Maxwellian distribution. The effects of the heating flow on the electron velocity distribution function, the real and imaginary parts of dielectric function, the resonance frequency and damping rate of ions and electrons, are discussed. With a positive electron drift velocity, the filed-aligned currents will be overestimated by the measurement of upshifted plasma line, and with a minus electron drift velocity, the filed-aligned currents will be underestimated. For the case that both upshifted and downshifted plasma lines are measured, the filed-aligned currents will be overestimated.

Simulation Studies on Seasonal Variations of the Stratospheric Dynamics and Trace Gases Using Coupled Chemistry-Climate Model WACCM-3

Liu Yi, Liu Chuanxi

2009, 29(6): 580-590. doi: 10.11728/cjss2009.06.580

Abstract(3997) PDF 969KB(1409)

Abstract:
The coupled chemistry-climate model WACCM-3 (Whole Atmosphere Community Climate Model) developed by NCAR is applied to study the seasonal variations of the stratospheric wind, temperature and trace gases such as O3, CH4, N2O, H2O, HCl, HNO3. Comparisons of the ECMWF/ERA-40 dynamics and observed trace gases from HALOE, MLS, CLEAS on UARS satellite show that the WACCM-3 simulation forced by the climatological Sea-Surface Temperature can generally reproduce the observed characteristics in the seasonal cycles of the stratospheric zonal winds, temperatures and chemical tracers. However, some obvious biases exist in model dynamics, which are closely associated with biases in the distributions of trace gases. Especially, the circumpolar westerlies during austral winter (July) and spring (October) in WACCM-3 model are too strong, which can cause a stronger barrier to the poleward transports of warm air and long-lived trace gases (e.g., CH4, N2O, H2O) in Antarctic lower stratosphere. Moreover, this cold bias also enhances the denitrification and dehydration effects during the formation of Polar Stratospheric Cloud (PSC), on the surface of which more HCl are activated through a series of heterogeneous reactions. As a result, the simulated concentrations of chemical tracers (e.g., CH4, N2O, H2O, HCl, HNO3) are prominently lower than observations in the Antarctic lower stratosphere during wintertime and springtime. In addition, there are also biases in the tropical stratospheric easterlies and the meridional transports of stratospheric tracers (e.g., O3, CH4, N2O, H2O), since WACCM-3 does not generate a Quasi-Biennial Oscillation (QBO) in tropical stratospheric winds.

Climatology of the Effective Winds at Millstone

Wen Kunjie, Liu Libo, Wan Weixing, Ning Baiqi

2009, 29(6): 591-598. doi: 10.11728/cjss2009.06.591

Abstract(2913) PDF 743KB(1031)

Abstract:
The ionospheric data observed with the Millstone Hill incoherent scatter radar from 1976 to 2006 were analyzed to deduce the Vertical Equivalent Winds (VEW), which are attributed to both the contributions of neutral wind and electric drifts under different conditions. The results suggest that the Millstone VEW show obvious diurnal, solar activity and seasonal variations. During the nighttime, Millstone VEW are mostly upward and strong, while the daytime VEW are relatively weak, even close to zero. This diurnal variation of Millstone VEW behaves similarly under different solar activities and seasons. Under solar low condition, the nighttime upward VEW are stronger than higher solar activity conditions. These characteristics of the diurnal and solar activity variations of Millstone VEW are closely related to the aurorally driven high-latitude circulation cell and ion drag. The equinoctial symmetry appears for the magnitudes and phase tendencies in spring and autumn are similar. The nighttime drift in winter is relatively weaker than that in summer, and this difference tends to be greater with the increasing solar activity, which shows the important effect of aurorally driven circulation on Millstone Hill ionosphere again. The VEW derived by three methods, i.e., by ion line-of-sight velocities of the F region ionization, servo theory and Ref.[1]'s method are compared. The magnitudes and phase tendencies of the VEW derived by different methods are accorded well with each other at nighttime, while there are larger differences during daytime; this is possibly caused by that the servo constant adopted by the latter two methods plays an important role in modulating the daytime VEW, which has been discussed previously.

Study on Fragmentation Velocity Increments

Wang Ronglan, Liu Jing, Zhang Qingming

2009, 29(6): 599-604. doi: 10.11728/cjss2009.06.599

Abstract(3194) PDF 497KB(1086)

Abstract:
Fragmentation velocity increments were an important character for breakup events intensity which decided the fragmentation debris orbit distribution and breakup nature. In this paper two means were given for the fragmentation velocity increments. One is orbit position propagation means, the other is orbit plane intersection means which was introduced in details. Orbit position propagation means is that velocity increments are computed by orbit velocity changes before and after the breakup; Orbit plane intersection means is that the velocity increments are computed with breakup spherical triangle for the parent and debris, the changes of breakup debris inclination and right ascension of ascending node, and the parent orbit's inclination and argument of perigee at the breakup epoch. The breakup epoch and velocity increment is then obtained. Compared with the two means, orbit position propagation means is suitable to fragmentation events with high quality data and high fragmentation altitude; orbit plane intersection means is suitable even if the fragmentation altitude is low and the orbit data is lagged more. This paper introduced the means and principle of computing breakup velocity increments, compared and discussed the applicability of the two means in detail. Based on the two means, fragmentation epoch and three velocity increments components in space were given for three past breakup events with two-line element data.

Satellites Separation Method With Eccentricity and Inclination Vector

Li Jiancheng, Zhao Haijun, An Jinwen

2009, 29(6): 605-608. doi: 10.11728/cjss2009.06.605

Abstract(2675) PDF 424KB(1227)

Abstract:
With the rapid increasing of application of geostationary satellites, the limited geostationary source is becoming run out. Collocating several satellites within the same longitude/latitude window is proved to be a good way. Successful separation with eccentricity vector of two Chinese geostationary satellites was achieved in 2003. To meet the different collocation requirement, and compensate the drawbacks of the eccentricity vector separation, this paper investigates the collocation strategy with eccentricity vector and inclination vector, which largely increases the relative separation of satellites. East-West Station Keeping (EWSK) and North-South Station Keeping (NSSK) procedures are discussed in the paper; and the separation constraints and implementation for two Chinese satellites are also given. The simulated minimum distance between the satellites within a period is more than 10\,km, and these two Chinese geostationary satellites work in orbit with secure operation.

Experimental Research and Numerical Simulation on Deep Charging for Spacecraft Dielectrics

Quan Ronghui, Han Jianwei, Zhang Zhenlong, Yan Xiaojuan, Huang Jianguo

2009, 29(6): 609-614. doi: 10.11728/cjss2009.06.609

Abstract(3112) PDF 591KB(1220)

Abstract:
Deep charging effect caused by high-energy electron irradiation is one of the key factors threatening spacecraft safety under the environment of space radiation. This paper compares the deep charging progress of different thickness polyimide films under different electron beam intensity, simulates the GEO orbit radiation environment with Sr90 radioactive source, and studies the charging progress of Delrin and Teflon under its radiation. This paper also presents a new model, which simulate the experiment results. It also analyzes the deep charging equilibrium potential and time with different electron intensity and dielectrics resistance. It shows that deep charging effect becomes more serious with increasing electron beam intensity and dielectrics resistance, and the time to reach charging equilibrium is mainly affected by dielectrics resistance.

Algorithm of the Capacity of Repetitive Observation of Remote Sensing Satellite Sensors

Li Ziyang, Li Chuanrong, Hu Jian, Gao Cai Xia

2009, 29(6): 615-619. doi: 10.11728/cjss2009.06.615

Abstract(2757) PDF 495KB(1212)

Abstract:
Capacity of repetitive observation of remote sensing satellite sensors is a key indicator of the system's dynamic monitoring ability. In the paper, the algorithm of orbit computing for realizing repetitive observations was presented based on the analysis of repetitive observation conditions under two imaging modes: nadir and side-looking; selective orbits for repetitive observations in particular areas were also described taking the HJ-1A/1B satellites (the optical satellites of the small satellite constellation for environment and disaster monitoring and forecasting) for example. The work is focused on the orbits of HJ-1A/B satellites. Before computation and analysis of the orbits, the Area of Interest (AOI) should be defined. Considering the optical sensors, in this paper, only the orbits from north to south were computed, yet orbits from south to north were passed over. The capacity of repetitive observation is defined as the overlap of two satellite scenes. By analysis of the nadir imaging and the side-looking imaging mode, the paper draws the conclusion of how to choose the best orbit to realize repetitive observation. Finally, impacts of the satellite constellation consisting of two satellites on the repetitive observations as well as that of latitude were discussed.

Estimate Algorithm for Pseudo-code Phase Delay and its Uncertainty in the Assisted GPS Receiver

Song Cheng, Wang Xuefei, Zhuan Zhaowen

2009, 29(6): 620-626. doi: 10.11728/cjss2009.06.620

Abstract(2735) PDF 622KB(1046)

Abstract:
Quick acquisition of satellites signals is a key technology in the assisted GPS (A-GPS) receiver. Considering that the A-GPS receiver can obtain the valid ephemeris data from the assistance data, a new estimate algorithm for pseudo-code phase delay and its uncertainty are proposed. On the basis of the Taylor approximation for the time of GPS signal transmission function, the estimate equation of pseudo-code phase delay and its uncertainty are proposed by using the assistance data. Simulation and experimental results show that the proposed algorithm can effectively compress the uncertainty of pseudo-code phase delay to the rest satellites, and can accelerate the signal acquiring speed of A-GPS receiver. As for the conventional un-assisted GPS receiver, the pseudo-code phase delay and its uncertainty can also be well estimated by the algorithm proposed in the paper when effective ephemeris data, satellite clock bias and pseudo-range amendment information are pre-stored in the receiver.

Utilization of modified spherical coordinates for satellite to satellite bearings-only tracking

Li Qiang, Shi Lihui, Wang Hongxian, Guo Fucheng

2009, 29(6): 627-634. doi: 10.11728/cjss2009.06.627

Abstract(2800) PDF 261KB(1322)

Abstract:
A new satellite to satellite passive tracking method using Bearings-Only measurements in Modified Spherical Coordinates (MSC) is proposed. The system dynamics and measurement process are presented in three-dimensional MSC, and then the tracking method is deduced in details based on the Cartesian method. Performance of the new method is validated through computer simulations, which proved that the proposed method is effective in terms of the estimation accuracy and convergence time compared with the Cartesian method no matter the Initial State Errors (ISE) and measurement errors are large or small.