2005 Vol. 25, No. 6

Display Method:
Predicting the 1 AU Arrival Times of Interplanetary Shocks
GAO Yuan, FENG Xueshang
2005, 25(6): 495-503. doi: 10.11728/cjss2005.06.495
Abstract(2076) PDF 2425KB(1068)
In order to predict the arrival time at 1AU of interplanetary shocks, a simple model called shock propagation model is established here. In this model, the travel time is assumed to be a function of energy that is released from solar explosives, and pulse longitudinal width, pulse duration, the interaction of interplanetary shock and background solar wind are also taken into account. In order to verify the prediction efficiency, 27 interplanetary shock events from January 1979 to October 1989 and 68 interplanetary shock events from February 1997 to January 2000 are used for testing. Comparing the results of our shock propagation model with those obtained by STOA and ISPM models, we find that our disturbance propagation model is as good as the other two models, and in some cases even better. The shock propagation model can give the prediction for all the 95 shock events, while STOA model works for 89 events and ISPM model for only 72 events. There are 25.26% percentage of all the 95 events with the relative time error less than 10%, 50.53% of all the events with the relative time error less than 20%, 65.26% of all the events with the relative time error less than 30~.
The Influence of Upper Boundary Conditions on the Polar Ionosphere
LIU Shunlin, ZHANG Beichen, LIU Ruiyuan, XU Zhonghua
2005, 25(6): 504-509. doi: 10.11728/cjss2005.06.504
Abstract(2238) PDF 1758KB(1294)
A one-dimensional high-latitude ionospheric model, in which the continuity, momentum and energy equations are solved self-consistently in the altitude range between 110 and 610km, is used to study the ionospheric responses to different upper boundary conditions. It is found that upper boundary conditions may influence significantly profiles of ionospheric quantities at higher altitudes. A larger upward O^+ velocity at the upper boundary results in lower hmF2 and F region electron densities, and consequently higher electron temperatures. The difference in hmF2 between an upper boundary velocity of 0.0 m/s and 200 m/s reaches about 76 km. The altitude profiles of temperatures are quite different from each other corresponding to different upward ion velocities and heat fluxes from the magnetosphere. The Coulomb collisions between electrons and ions play an important role in shaping the electron temperature profiles at altitudes higher than the hmF2. The simulated electron temperature height profiles are similar to the measurements made in earlier studies. The altitude profile of electron temperature above 200 km is influenced by both downward heat fluxes and field-aligned O^+ velocities, while the ion temperature and the electron density have their responses at altitudes higher than 250km. Proposals are given while specifying the upper boundary conditions in the simulation of the high-latitude ionosphere.
Time-Dependent Simulation of Electrical Field Configuration and Optical Emission of Sprite Halo
WU Mingliang, XU Jiyao
2005, 25(6): 510-515. doi: 10.11728/cjss2005.06.510
Abstract(1687) PDF 2024KB(1511)
Using the two-dimensional, time-dependent quasi-electrostatic field (QEF) code, the configuration, time delay, duration and descending motion speed of quasi-static electric field caused by thunderstorm discharge was investigated, and the effects of atmospheric ionization and optical emission in mesosphere and low ionosphere caused by this QEF was also studied. Research show: the sprite halo initiates at 85 km and with a pancake-like shape, then the regions of breakdown and optical emission move downward at speed of 1.5 × 10^7m·s^-1, the regions of breakdown and optical emission gradually become an upward concave shape. Sprite halo lasts about 5.5 ms with a height range of 64-87km, and with a horizontal scale of 80 km. Moreover, simulation results indicate that appearance time of the maximum of optical emission occurs at the time of t = 2.1 ms, which is delayed to thunderstorm discharge. And the QEF does not monotonously decrease with the altitude increasing, it has complicated structure at symmetrical axes. In addition to, the QEF cause atmosphere breakdown ionization and lead to electron density increases (ionization coefficient 〉 attachment coefficeint) or decreases (attachment coefficient 〉 ionization coefficient). At altitude of 70 km, the increased electron density of Ne = 2.178 × l0^8 m^-3 is much bigger than the fair weather electron density of Ne = 6.329 × 10^5 m^-3.
Gravity Wave Activities in the Lower Atmosphere Over Wuhan, China
LIU Yingjie, YI Fan
2005, 25(6): 516-521. doi: 10.11728/cjss2005.06.516
Abstract(2133) PDF 1729KB(1278)
Radiosonde observations provided by Wuhan Center Station of Meteorology (30.5° N, 114.4° E) between January 2001 and December 2003 are used to study the spatial and temporal variations in gravity wave activities in the lower atmosphere over Wuhan, China. Time series of horizontal kinetic energy show an obvious seasonal variation with the maximum in winter when jet is strongest and the mimimum in summer when there doesn't exist the jet. Using a hodograph analysis, it is found that about 46.4% of the waves are propagating upward in the height range of 1-9 km, while roughly 73.8% of the waves are propagating upward in 14-25 km, in agreement with the assumption that gravity waves are generated by the jet stream near 11 km. Further examination reveals that within the height range of 14-25 km gravity waves are mostly propagating upward in summer while quite a portion of gravity waves propagate downward in winter, which might be caused by reflection. The intrinsic frequencies are mostly 1-3 times the inertial frequency. Horizontal wavelengths of several hundred kilometers are inferred. The vertical wave lengths are centered on 3-3.5 km during 1-9km, but 4.5-5.5km during 14-25km.
The Investigation of Gravity Wave Activities on Mesopause Over Wuhan by Sodium Lidar
SONG Juan, CHENG Xuewu, YANG Guotao, CHANG Qihai, GONG Shunsheng
2005, 25(6): 522-528. doi: 10.11728/cjss2005.06.522
The gravity wave activities were investigated based on the data of 26 observation nights from WIPM sodium fluorescence lidar data-base of year 1999 to now. The result shows, the gravity wave activities are very frequent in the mesopause region over Wuhan: in total 185.5 observation hours during 26 nights, 124 gravity wave activities were observed,so that the occurrence frequency of gravity wave activities is about 0.7 activity per hour, and the occurrence has a relationship with local time. The wavelengths of the waves were mainly distributed from 3 km to 7 km, which is consistent with the result reported,and the phase velocities of the waves were maily distributed from 0.1 m/s to 0.5 m/s, which much shower than the reported result. Another feature of the gravity wave activities over Wuhan is that the multiwave activities were much greater than singlewave ones, and the ratio is 3:2. The typical results of the gravity wave propagation and breaking were given through the time and space sequence of relative density disturbence. The gravity wave parameters were also extracted form part of our data throuth the monowave model method.
Radiosonde Observation of Planetary Waves in the Lower Atmosphere Over the Center China
LU Xian, ZHANG Shaodong
2005, 25(6): 529-535. doi: 10.11728/cjss2005.06.529
Abstract(2307) PDF 2473KB(1254)
Wind data by the radiosonde observation from Wuhan, Yichang, and Enshi Meteorological Stations in the period of 2001-2003 are used to analyze the Planetary Waves (PWs) in the lower atmosphere of the center China. L-S periodgrams show that quasi-16-day PWs and quasi-10-day PWs are dominating planetary wave components in the observed period over three sites. The largeamplitude oscillation of PWs can be observed primarily from 5 km to 15 km. The quasi-16-day PWs propagate westward with a zonal wave number of 2 (the horizontal wave length is 17 324.8 km), and the corresponding phase velocity is estimated to be -12.5 m·s^-1 (positive eastward). The vertical wavelength is estimated to be 25-30 km according to the phase variation with height below 10 km. The phases almost keep unchanged around the tropopause which indicates they may be stationary waves. Quasi-10-day PWs propagate eastward with a wave number of 4 (the horizontal wave length is 8627.3 km) and the corresponding phase velocity is estimated to be 10.0 m·s^-1, the vertical wave length is 22-40 km.
Phenomena of Geomagnetic and Ionospheric Anomalies and Their Relation to Earthquakes
DING Jianhai, SUO Yucheng, YU Surong
2005, 25(6): 536-542. doi: 10.11728/cjss2005.06.536
Abstract(2209) PDF 2025KB(1970)
On the basis of data from the geomagnetic network and ionospheric observatories in China, the geomagnetic low point displacement, diurnal variation anomalies of geomagnetic field and ionospheric f0F2 (critical frequency of F2 layer) anomaly phenomena before large earthquakes have been summarized. Anomaly distribution and characteristics of geomagnetic variation field and ionospheric f0F2 before Mani MS 7.5 earthquake on Nov.8, 1997, and Kunlunshan MS 8.1 earthquake on Nov. 14, 2001, have been comparatively studied. The result shows that the temporal spatial characteristics of short term and imminent anomalies of geomagnetic field and ionosphere are consistent. The obvious anomalies of diurnal variation of geomagnetic field near epicentral area and ionospheric f0F2 at Lhasa observation are found. The geomagnetic low point displacements appeared about one month before the two great earthquakes, the boundary lines of sudden change passed through the epicentral area.
In Situ Observation on Generation of Gaseous Inclusions in BBO Crystal
PAN Xiuhong, JIN Weiqing, HONG Yong
2005, 25(6): 543-546. doi: 10.11728/cjss2005.06.543
Abstract(1947) PDF 1127KB(1380)
The inclusions in BBO single crystal can influence the ultimate crystal size as well as crystal properties. In this paper, the generation process of inclusions in BBO crystal by flux method is observed using Schlieren technique coupling with differential interference microscope.Results show that gaseous inclusions usually form at the inner part of perfect crystals and distribute near the interface. These indusions over generated originally from some small hexagonal cells. The formation and distribution of inclusions are significantly influenced by the development of crystal steps. The steps height and width may strongly constrain the develpment of inclusions, which results in the formation of inclusion clusters on the steps. The possible mechanism of inclusion generation is also discussed. It is noted that the main reason caused inclusions is the volatilization of some elements at high temperature.
Close Approach of Walker Constellation Without Orbital Maneuver
WANG Wei, HUANG Wende, FU Xiaofeng, Zhang Jing
2005, 25(6): 547-551. doi: 10.11728/cjss2005.06.547
Abstract(2170) PDF 1255KB(1608)
A spacecraft that have been launched into orbit can fast close approach multiple non- coplane satellites of Walker Constellation without orbital maneuver by orbital design, since Walker Constellation has several special characteristics in construction, such as symmetry. To approach without orbital maneuver, the height of the spacecraft must be as same as that of the Constellation. Aimed at Walker Constellation, this paper presents a search method and a substitution method that on the base of the characteristic of Constellation. For a given Walker Constellation, both method can get a series of orbits with different orbit inclination. Typical orbits derived from the two methods are given. Each orbit can fast (in half of orbit period) close approach (zero distance for Walker) multiple (2 or more) non-coplane satellites of Walker Constellation.
Movement Reliability of Rotation Joint of Umbrella Antenna
HU Taibin, CHEN Jianjun, ZHANG Jianguo, LI Xiaoping
2005, 25(6): 552-557. doi: 10.11728/cjss2005.06.552
Abstract(1970) PDF 1723KB(1403)
Aiming at the rotation joints in deployment mechanism of umbrella antenna used in a certain satellite, the movement reliability has two parallel performance functions: the performance function according to rotation work and that according to rotation moment. Corresponding to the beginning phase, outspreading phase and the phase that the net has pressing force, the expressions of two performance functions were established respectively according to the position relations of all components. Secondly, two-kind reliabilities can be calculated from the two performance functions by means of the random functional moment method and the second moment method for reliability analysis. The movement reliability of one rotation joint can be got from two parallel reliability models. Finally, the change curve of the movement reliability of umbrella antenna outspread mechanism with outspreading angle was analyzed with an example. To the whole outspreading course, the reliability has the trent of first increase and then decrease, and the reliability of the beginning phase was smallest.
A Variable-Structure Controller of Small Satellite Attitude Maneuver With Reaction Wheels
HE Donglei, CAO Xibin
2005, 25(6): 558-563. doi: 10.11728/cjss2005.06.558
Abstract(2055) PDF 1415KB(1376)
Generally speaking, the Euler angle is usually used to describe the attitude of small satellites. In this case, however, singularity exists during large angle maneuver of small satellites. In contrast, such singularity can be avoided when the attitude is described by the quaternion. In this article, with regard to nonlinear properties of small satellite attitude contol systems actuated by reaction wheels, the attitude kinematics is described by the error-quaternion so that the large angle maneuver of the satellite can be converted into the problem of regulation of the error-quaternion. Sliding surfaces were designed on the basis of error-quaternion and an equivalent variable-structure controller introducing angular velocity acceleration feedback term was derived based on Lyapunov theorem. Simulation results show that the the proposed SMC law can improve the convergence rate, reduce the overshoot value of angular volecity during the maneuver and the demand of initial control torquer. In the meanwhile global stability and robustness of the method considering parameter uncerties and external disturbances such as sunlight pressure moment, the surplus magnetism moment of satellite and the pneumatic moment can also be guaranteed.
Bi-Directional Approach for Motion Planning of Dual-Arm Space Robot Systems
GUO Yishen, CHEN Li
2005, 25(6): 565-568. doi: 10.11728/cjss2005.06.565
Abstract(1845) PDF 1265KB(1597)
Based on the bi-directional approach, the paper discusses the motion planning of freeflying dual-arm space robot systems. With the linear and angular momentum conversation, the state equation is established for the system control design. And then applying the Lyapunov method to the state equation, the control input equation of the manipulator joint angles controlling the vehicle attitude and the manipulator joint angles is obtained. Because no continuous trajectory from the start point to the end point in the state space can complete the desired task, the synthesized trajectory is gained to accomplish the desired task through the bi-directional approach. The advantage of the approach is to decrease the fuel consumption for controlling the vehicle attitude and prolong the available life-span of space robot systems. A planar dual-arm space robot system is simulated to verify the proposed approach.