2003 Vol. 23, No. 6
2003, 23(6): 401-412.
Abstract:
In this paper, a new numerical scheme of Total Variation Diminishing （TVD） Mac-Cormack type for MagnetoHydroDynamic （MHD） equations is proposed by taking into account of the characteristics such as convergence, stability, resolution. This new scheme is established by solving the MHD equations with a TVD modified MacCormack scheme for the purpose of developing a scheme of quick convergence as well as of TVD property. To show the validation, simplicity and practicability of the scheme for modelling MHD problems, a self-similar Cauchy problem with the discontinuous initial data consisting of constant states, and the collision of two fast MHD shocks, and two-dimensional Orszag and Tang’s MHD vortex problem are discussed with the numerical results conforming to the existing results obtained by the Roe type TVD, the high-order Godunov scheme, and Weighted Essentially Non-Oscillatory （WENO） scheme. The numerical tests show that this two-step TVD MacCormack numerical scheme for MHD system is of robust operation
In this paper, a new numerical scheme of Total Variation Diminishing （TVD） Mac-Cormack type for MagnetoHydroDynamic （MHD） equations is proposed by taking into account of the characteristics such as convergence, stability, resolution. This new scheme is established by solving the MHD equations with a TVD modified MacCormack scheme for the purpose of developing a scheme of quick convergence as well as of TVD property. To show the validation, simplicity and practicability of the scheme for modelling MHD problems, a self-similar Cauchy problem with the discontinuous initial data consisting of constant states, and the collision of two fast MHD shocks, and two-dimensional Orszag and Tang’s MHD vortex problem are discussed with the numerical results conforming to the existing results obtained by the Roe type TVD, the high-order Godunov scheme, and Weighted Essentially Non-Oscillatory （WENO） scheme. The numerical tests show that this two-step TVD MacCormack numerical scheme for MHD system is of robust operation
2003, 23(6): 413-423.
Abstract:
The agreement between Rankine-Hugnoniot equations and the simulation of interplanetary MHD shock that can arrive 1AU or further is investigated. A method to locate the position of the forward fast shock in the shock pair structure is proposed in this paper. The method is composed of two main steps. First, by analyzing topology of the simulated MHD shock and its evolution during its propagating forward, it is identified that the discontinuity structure in the computational domain is in fact shock pair structure. According to this judgment, a method to locate the shock in the computation domain is developed. The second step is to select the proper time levels where the space between the shock and the grids is minimal, so as to minimize the errors that the shock is not exactly on the grids. By using this method to locate the shock and the method that was proposed in Reference [14] to determine the local parameters of the shock, it is found that the forward fast shock in the shock pair structure matches the Rankine-Hugoniot relations perfectly with the relative difference limited in the scale, when the shock propagates to or farther, and that the discrepancy between them is limited in the scale when the shock propagates to or farther. This result confirms that the finite-difference numerical solutions can describe the shock accurately. And as to clear out the cause of the discrepancy, the relationship between the discrepancy and the evolution of the shock structure as well as the relationship between the discrepancy and the polytropic index is discussed.
The agreement between Rankine-Hugnoniot equations and the simulation of interplanetary MHD shock that can arrive 1AU or further is investigated. A method to locate the position of the forward fast shock in the shock pair structure is proposed in this paper. The method is composed of two main steps. First, by analyzing topology of the simulated MHD shock and its evolution during its propagating forward, it is identified that the discontinuity structure in the computational domain is in fact shock pair structure. According to this judgment, a method to locate the shock in the computation domain is developed. The second step is to select the proper time levels where the space between the shock and the grids is minimal, so as to minimize the errors that the shock is not exactly on the grids. By using this method to locate the shock and the method that was proposed in Reference [14] to determine the local parameters of the shock, it is found that the forward fast shock in the shock pair structure matches the Rankine-Hugoniot relations perfectly with the relative difference limited in the scale, when the shock propagates to or farther, and that the discrepancy between them is limited in the scale when the shock propagates to or farther. This result confirms that the finite-difference numerical solutions can describe the shock accurately. And as to clear out the cause of the discrepancy, the relationship between the discrepancy and the evolution of the shock structure as well as the relationship between the discrepancy and the polytropic index is discussed.
2003, 23(6): 424-429.
Abstract:
Using the method of the eignvalue and eignvector analysis of chemical system to study the chemical lifetime of sodium layer. The results show that the chemical lifetime of sodium layer calculated in this paper is very different with the traditionally defined chemical lifetime. The results indicate that in the region near the peak of sodium layer, the dynamical transportation predominant than the photochemical process. But in the region of the bottom side of sodium layer, the photochemistry is the main process. The Na layer can be regarded as a tracer of dynamical perturbation. The results of this paper provide a theoretical basis for analyzing the Lidar observations of sodium layer.
Using the method of the eignvalue and eignvector analysis of chemical system to study the chemical lifetime of sodium layer. The results show that the chemical lifetime of sodium layer calculated in this paper is very different with the traditionally defined chemical lifetime. The results indicate that in the region near the peak of sodium layer, the dynamical transportation predominant than the photochemical process. But in the region of the bottom side of sodium layer, the photochemistry is the main process. The Na layer can be regarded as a tracer of dynamical perturbation. The results of this paper provide a theoretical basis for analyzing the Lidar observations of sodium layer.
2003, 23(6): 430-435.
Abstract:
Data obtained from the medium-frequency （MF） radar at Wuhan （30°N, 114°E） from 11 to 25 February and from 28 February to 13 March have been used to study the tidal oscillations and their interactions at mesopause （80-98km） region over Wuhan in winter. A dynamic spectral variation of disturbance amplitude illustrates a prominent peak at a period of 24 hours at all heights and almost uninterrupted, and there are occasionally slightly strong semidiurnal and weak terdiurnal tidal disturbances. These indicate that in the mid-latitude regions, the diurnal tide is the dominant tidal disturbance at mesopause in winter. A detailed analysis of tidal amplitudes and their wave kinematical energies implies that there may be significant resonant interaction among the diurnal, semidiurnal and terdiurnal tides. The phase profiles of the diurnal tides show obvious increase trend with the increasing heights in both the zonal and meridional directions, which indicate that the observed diurnal tides are propagating upward. The mean vertical wavelengths of the diurnal tides obtained from the zonal and meridional phases are 45km and 47km, respectively, and the corresponding downward phase velocities are 1.88km/h and 1.97km/h, respectively.
Data obtained from the medium-frequency （MF） radar at Wuhan （30°N, 114°E） from 11 to 25 February and from 28 February to 13 March have been used to study the tidal oscillations and their interactions at mesopause （80-98km） region over Wuhan in winter. A dynamic spectral variation of disturbance amplitude illustrates a prominent peak at a period of 24 hours at all heights and almost uninterrupted, and there are occasionally slightly strong semidiurnal and weak terdiurnal tidal disturbances. These indicate that in the mid-latitude regions, the diurnal tide is the dominant tidal disturbance at mesopause in winter. A detailed analysis of tidal amplitudes and their wave kinematical energies implies that there may be significant resonant interaction among the diurnal, semidiurnal and terdiurnal tides. The phase profiles of the diurnal tides show obvious increase trend with the increasing heights in both the zonal and meridional directions, which indicate that the observed diurnal tides are propagating upward. The mean vertical wavelengths of the diurnal tides obtained from the zonal and meridional phases are 45km and 47km, respectively, and the corresponding downward phase velocities are 1.88km/h and 1.97km/h, respectively.
2003, 23(6): 436-442.
Abstract:
KREEP rocks with high contents of K, REE and P were first recognized in Apollo 12 samples, and confirmed later that there were KREEP rock fragments in all of Apollo samples particularly in Apollo-12 and 14 samples. The distribution of KREEP rocks on the lunar surface is very important not only for studying the evolution of the moon, but also for evaluating the utilization prospect of REE in KREEP rocks. Based on previous studies and lunar exploration data, the authors analyse the chemical and mineral characteristics of KREEP rocks, the abundance of Th on lunar surface, the correlation between Th and REE of KREEP rocks in abundance, study the distribution region of KREEP rocks on the lunar surface, and further evaluate the utilization prospect of REE in KREEP rocks.
KREEP rocks with high contents of K, REE and P were first recognized in Apollo 12 samples, and confirmed later that there were KREEP rock fragments in all of Apollo samples particularly in Apollo-12 and 14 samples. The distribution of KREEP rocks on the lunar surface is very important not only for studying the evolution of the moon, but also for evaluating the utilization prospect of REE in KREEP rocks. Based on previous studies and lunar exploration data, the authors analyse the chemical and mineral characteristics of KREEP rocks, the abundance of Th on lunar surface, the correlation between Th and REE of KREEP rocks in abundance, study the distribution region of KREEP rocks on the lunar surface, and further evaluate the utilization prospect of REE in KREEP rocks.
2003, 23(6): 443-451.
Abstract:
Solar Proton Events （SPE） are one kind of the major, severe space environmental events that induces errors even failure of the satellites on the orbit. In this paper, a model of SPE forecasting employing artificial neural network technology by Space Environment Prediction Center （SEPC） is introduced. The strength of solar event is related with releused from the solar burst. The size of area of the sunspot indicates the maximum strength of local magnetic field. The Mclntosh classification of the sunspot indicates the structure of the root area of the magnetic rope from the sunspot regions. The joint applying of the Mclntosh classification and the magnetic type enable us to describe the structure of the sunspot. In this paper, 10.7cm radio and X-ray fluxes were used, and the Artificial Neural Network （ANN） is employed. The digitized morphology data are then arranged and "feed" into the neural network. Through training the model based on ANN algorithm a forecast model was constructed. With it, the forecast of SPE 1-3 days ahead can be made. Statistics shows that the accuracy of our forecast is about 80%.
Solar Proton Events （SPE） are one kind of the major, severe space environmental events that induces errors even failure of the satellites on the orbit. In this paper, a model of SPE forecasting employing artificial neural network technology by Space Environment Prediction Center （SEPC） is introduced. The strength of solar event is related with releused from the solar burst. The size of area of the sunspot indicates the maximum strength of local magnetic field. The Mclntosh classification of the sunspot indicates the structure of the root area of the magnetic rope from the sunspot regions. The joint applying of the Mclntosh classification and the magnetic type enable us to describe the structure of the sunspot. In this paper, 10.7cm radio and X-ray fluxes were used, and the Artificial Neural Network （ANN） is employed. The digitized morphology data are then arranged and "feed" into the neural network. Through training the model based on ANN algorithm a forecast model was constructed. With it, the forecast of SPE 1-3 days ahead can be made. Statistics shows that the accuracy of our forecast is about 80%.
2003, 23(6): 452-458.
Abstract:
In this paper, Morlet wavelet is applied to analyze the character of cosmic ray intensity of Apatity station （latitude: 67.56°N, longitude: 33.4°E, Russia） and Oulu station （latitude: 65.05°N, longitude: 25.47°E, Finland） respectively during quiet period of geomagnetic field and before geomagnetic storms from 1998 to 2002. Fourteen examples are selected including two examples of quiet period and 12 examples before geomagnetic storms. The level of major storms selected in this paper is that index Dst is less than -100 nT. By Morlet wavelet transform, cosmic ray intensity of different condition shows different variety. Results show that 24 h periodicity exists and is distinct during quiet time, and usually minimum value of cosmic ray intensity appears around about 0200 local time and maximum value appears around about 1400 local time; Twelve examples before geomagnetic storms period show that variety of 24 h periodicity all change. Some minish, some disappear, and some have anomalous 24 h periodicity, and these varieties differ from that of quiet time. These characters before geomagnetic storms may provide a sign that can be used to forecast the coming of geomagnetic storms of coming of geomagnetic storms.
In this paper, Morlet wavelet is applied to analyze the character of cosmic ray intensity of Apatity station （latitude: 67.56°N, longitude: 33.4°E, Russia） and Oulu station （latitude: 65.05°N, longitude: 25.47°E, Finland） respectively during quiet period of geomagnetic field and before geomagnetic storms from 1998 to 2002. Fourteen examples are selected including two examples of quiet period and 12 examples before geomagnetic storms. The level of major storms selected in this paper is that index Dst is less than -100 nT. By Morlet wavelet transform, cosmic ray intensity of different condition shows different variety. Results show that 24 h periodicity exists and is distinct during quiet time, and usually minimum value of cosmic ray intensity appears around about 0200 local time and maximum value appears around about 1400 local time; Twelve examples before geomagnetic storms period show that variety of 24 h periodicity all change. Some minish, some disappear, and some have anomalous 24 h periodicity, and these varieties differ from that of quiet time. These characters before geomagnetic storms may provide a sign that can be used to forecast the coming of geomagnetic storms of coming of geomagnetic storms.
2003, 23(6): 459-466.
Abstract:
Based on a simple formula for calculating the main beam efficiency presented in Ref.[1], the main beam efficiency calculation is performed for multi-band microwave radiometer antenna boarded on "SZ-4" spaceship. The calculation shows that the main beam efficiencies at 6.6, 19.35, 23.8 and 37 GHz are 89%, 91.24%, 92.91% and 94.87%, respectively.
Based on a simple formula for calculating the main beam efficiency presented in Ref.[1], the main beam efficiency calculation is performed for multi-band microwave radiometer antenna boarded on "SZ-4" spaceship. The calculation shows that the main beam efficiencies at 6.6, 19.35, 23.8 and 37 GHz are 89%, 91.24%, 92.91% and 94.87%, respectively.
2003, 23(6): 467-474.
Abstract:
According to the synthetic space satellite applied system, the basic system of weather forecasting operation, and the properties of the system and network of the weather forecasting operation and the technology and method in weather forecasting operation are introduced in this paper.
According to the synthetic space satellite applied system, the basic system of weather forecasting operation, and the properties of the system and network of the weather forecasting operation and the technology and method in weather forecasting operation are introduced in this paper.
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FALANGA Maurizio (Switzerland)
FU Suiyan KANG Qi
LIN Baojun LIN Yangting
SHI Jiancheng YANG Huigen
YANG Zhen ZHANG Shuangnan
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