空间科学学报

2016 Vol. 36, No. 6

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Research Progress and Prospect of Exoplanetary Atmospheres and Habitable Exoplanet Sciences

TIAN Feng, HU Xiong, WU Ji

2016, 36(6): 815-827. doi: 10.11728/cjss2016.06.815

Abstract(1584) PDF 719KB(1400)

Abstract:
The most fundamental question driving the search and characterization of exoplanets is whether life and habitable planets are ubiquitous. More than 3000 exoplanets have been discovered since 1995, about 20 of which are potentially habitable and this number could be increased dramatically in the next decade. Observation of the atmospheres of potentially habitable exoplanets is becoming the hot spot in planetary sciences. In this review we summarize the research progress regarding exoplanetary atmospheres and propose a practical roadmap, the implementation of which could accelerate the development of exoplanetary sciences in China in the near future.

Influence of Convection Effects of Solar Wind Speed on CME Transit Time

SUN Luyuan

2016, 36(6): 828-836. doi: 10.11728/cjss2016.06.828

Abstract(1509) PDF 1148KB(898)

Abstract:
Based on the experiential predicting model, 52 CME events which cause geomagnetic storms Dst< -50nT, and 10 CME events which cause significant geomagnetic storms (Dst< -200nT) in 1996-2007 are selected, and mix with the observation data of interplanetary solar wind and ICME that are collected by ACE satellite at 1AU, convection effects of ambient solar wind speed on the CME transit time from the Sun to the Earth are analyzed. The results show that significant improvement on the predicting transit time of CME events after taking the convection effects into account has been obtained. For the 52 CME events of Dst< -50nT, the prediction standard difference is reduced from 16.5 to 11.4 hours, and the prediction error is less than 15 hours for 68% of these events. For the 10 CME events (Dst< -200nT), the prediction standard difference is reduced from 10.6 to 6.5 hours. Furthermore, the prediction error of 6 events among these 10 events is less than 5 hours. The study identifies the importance of convection effects of solar wind speed on the prediction of CME transit time.

Survey on the Magnetic Structure of the Neutral Sheets in Earth's Magnetotail

XIAO Chao, SHEN Chao, CHENG Guosheng, ZHANG Hua, ZHANG Ting, CARR C M

2016, 36(6): 837-848. doi: 10.11728/cjss2016.06.837

Abstract(1074) PDF 2282KB(887)

Abstract:
Based on the multipoint magnetic observations of Cluster from 2001 to 2004, the magnetic field structure in magnetotail Neutral Sheet (NS) is statistically surveyed. The results are as follows. In NS, a cubic function is selected to reveal the relation between y (GSM) and positional parameter z. The relation between y and magnetic field values indicates that the magnetic field is weak at midnight region and strengthens gradually at the duskside and dawnside. The relation between y and curvature radius is expressed by a quadratic function. And R_c of flattened CS is less than that of the normal CS. B_y determines the orientation of MFLs' configuration. The polar angle of the curvature vector is affected by the NS configuration. In addition, the correlation between the polar angle of the curvature vector and z is higher. The polar angle of the normal of the osculating plane is uncertain in the center area. The relation between the azimuthal angles of the curvature vector (the normal of the osculating plane) and y is negatively correlated. An empirical model applied to yz plane of the three-dimensional structure of the magnetic field lines in the NS are developed, and it is represented as a function of the positional parameter y. Finally, the current density is also statistically surveyed.

Study on Energy Features During a Field-Aligned Electron Events in the Cusp Region

SHI Jiankui, ZHANG Ziying, TORKAR Klaus, WANG Zheng, CHENG Zhengwei, WANG Guojun

2016, 36(6): 849-856. doi: 10.11728/cjss2016.06.849

Abstract(1152) PDF 2238KB(800)

Abstract:
By focusing on an extremely disturbed field-aligned electrons event observed with Cluster in the northern cusp region on 30 September 2001, the energy features of the field-aligned electrons in the event is analyzed and the roles of the field-aligned electrons on the transmission of solar wind energy to the magnetosphere and on the magnetosphere-ionosphere coupling are discussed. The results show that the velocities and densities of the electrons have strong disturbances during the event, and the velocity is a main factor to enhance the electron flux. The electron energy spectrum in 5~200eV and 500~1500eV show that the up-flowing electron flux is higher than that of down-flowing, which means the up-flowing electrons mainly come from the ionosphere and play an active role in this event. The energy features show that the ionospheric electrons have been accelerated during the up-flowing. However, the accelerating physical mechanism still needs to be further studied.

Improvement and Application of Lax-Friderichs Scheme in MHD Numerical Simulation

LIU Qiang, LI Huichao

2016, 36(6): 857-865. doi: 10.11728/cjss2016.06.857

Abstract(1453) PDF 1359KB(756)

Abstract:
Magnetohydrodynamics (MHD) numerical simulation is an important tool for space physics research. In this paper, Lax-Friderchs scheme with TVD property is employed to solve GLM-MHD equations. The diffusion turning coefficient is introduced for scheme optimization. Simulation result of 2D rotor test and magnetic cloud current sheet interaction test demonstrates GLM-MHD method's divergence control capability. The simulation consumes less than half of the computational time comparing with simulation utilizing Poisson correction method. While numerical stability is not damaged, numerical diffusion is reduced by the diffusion tuning coefficient.

Application of Support Vector Machine to the Forecasting of Dst Index During Geomagnetic Storm

PENG Yuxiang, LÜ Jianyong, GU Saiju

2016, 36(6): 866-874. doi: 10.11728/cjss2016.06.866

Abstract(1222) PDF 1045KB(775)

Abstract:
In this study the support vector machine is applied to the forecasting of Dst index during intense geomagnetic storms (Dst≤ -100nT) that occurred from 1995 to 2014. We collect 2662 Dst indices and use the corresponding solar wind data as model input. We also build Neural Network and Linear machine as comparison, and improve the reliability of the predicted results by using K-fold cross validation. For comparison, we calculate the Correlation Coefficient (CC), the RMS errors, the Mean Absolute Error of the minimum Dst (E_m) and the Mean Absolute Error of the time when the minimum Dst occurred (E_t) between the observed Dst data and the predicted one. As a result, we find that SVM shows the best prediction performance for all events: CC is 0.89, RMS is 24.27nT, E_m is 17.35nT and E_t is 3.2 hours respectively. For further comparison, the 80 storm events are divided into two groups depending on the minimum value of Dst index. It is shown that the forecasting performance of SVM is better than other models both in the intense (-200 <Dst_min ≤-100nT) and the super intense geomagnetic storm (Dst_min ≤-200nT) groups.

Study on Observations of Daytime Spread-F-Like Irregularity in Mid-Latitude Region

XIAO Saiguan, XIAO Zuo, SHI Jiankui, ZHANG Donghe, HAO Yongqiang

2016, 36(6): 875-880. doi: 10.11728/cjss2016.06.875

Abstract(1430) PDF 1051KB(794)

Abstract:
Based on the HF Doppler frequency shift observation, daytime spread-F-like phenomenon occurred at mid-latitude region and the relationship between the daytime spread-F-like and other ionospheric disturbance are studied. The results show that the daytime spread-F-like phenomena have the characteristics of large range of occurrence time, long duration time and are accompanied with other ionospheric disturbances. The morphological features are the blurred echo traces which are similar to those of the nighttime spread-F, frequency shifts of these echoes tend to be positive, and sometimes are accompanied by Traveling Ionospheric Disturbances (TIDs). Although the daytime spread echoes phenomenon occasionally occur and the occurrence rate is very low, the temporal and spatial broad distribution of the daytime spread-F-like implies that its effect on the space weather cannot be ignored, and its properties can not be replaced simply by that of spread-F usually occurred at nighttime. Therefore, the study of the daytime spread-F-like has very important significance.

Influence of Solar and Geomagnetic Activity on Sporadic-E Layer over Different Latitude Stations

DU Peng, ZHANG Yabin, HU Yanli, ZHAO Haisheng, XU Tong

2016, 36(6): 881-887. doi: 10.11728/cjss2016.06.881

Abstract(1232) PDF 1701KB(682)

Abstract:
To study the influences of solar and geomagnetic activity on Es layers over high, mid and low latitude stations, the hourly values of parameters of Es layer during four solar cycles (1970-2010) over different latitude stations are considered. It has been suggested that there are relationships between solar and geomagnetic activities with Es layer, and the correlations are different over high, mid and low latitude stations. At low and mid latitude stations, the correlation coefficients of Es layer with solar activity are positive in daytime and negative in nighttime. At high latitude station, the correlation coefficients are all positive. Moreover it is a positive correlation between geomagnetic activity and unusual density Es layers. During the geomagnetic disturbance, the density of Es layers has an increase at the disturbed day over high latitude station, while the increasing happens on the next day after the geomagnetic disturbance in low and mid latitude stations. The reasons for different behavior of Es frequency parameters to geomagnetic activity are also studied.

The Southward and Northward Difference of Proton Flux in South Atlantic Anomaly

YAN Xingya, CHEN Hongfei, YU Xiangqian, ZOU Hong, SHI Weihong

2016, 36(6): 888-896. doi: 10.11728/cjss2016.06.888

Abstract(1701) PDF 1543KB(830)

Abstract:
This paper discusses the southward and northward proton distributions at 800km height of the South Atlantic Anomaly (SAA) according to the data detected by the >6.9MeV channel of the Medium Energy Proton and Electron Detector (MEPED) of NOAA N15, N16, N17 and N18 satellites. The data show that the counting rate of protons satisfies approximately the Gauss distribution with latitudes along a longitude while the number of southward protons is larger than the northward protons. MEPED has two heads on 0° and 90° directions. It can be used to evaluate the pitch-angle distribution of protons, then to eliminate the direction errors of the detectors between detecting the southward and the northward protons. The result shows that the southward protons are 20%~30% more than the northward protons in the latitudes of 13°S about 23°S along 40°W longitude. The phenomenon may be related to the lower mirror position in the southern hemisphere than in the northern hemisphere due to the geomagnetic anomaly. It causes more southward protons precipitating in SAA. Otherwise, the proton flux in SAA presents a local time dependency. The flux in the dayside is about 20% more than that in the nightside. It may be caused by the daily variation of the geomagnetic filed.

Cosmic Ray Observation at Antarctic Zhongshan Station

HUANG Dehong, HU Hongqiao, LIU Yang, LU Hong, ZHANG Dali, ZHANG Jilong

2016, 36(6): 897-903. doi: 10.11728/cjss2016.06.897

Abstract(1545) PDF 3233KB(934)

Abstract:
By the end of 2014, a cosmic ray muon telescope consisting of two detectors which has 0.5m×0.5m area scintillator was installed at Antarctic Zhongshan Station. The observation data is sent to China by satellite link and is released through network, which can be used to monitor and forecast space environment disasters, and provides support for China operational monitoring of space environment and multidisciplinary research of Polar Regions. The Zhongshan Station muon telescope data shows that there is a significant effect of pressure change with negative correlations. The vertical cutoff rigidity of cosmic ray protons at Zhongshan Station is 0.076GV, compared with those observations from Yangbajing and Beijing in China, Zhongshan Station is very conducive to the observation of the solar proton events.

Properties of C-Band Wave Propagation in Plasma Sheath with Different Incidence Angle

LING Yunfei, CHEN Changxing, JIANG Jin

2016, 36(6): 904-908. doi: 10.11728/cjss2016.06.904

Abstract(1223) PDF 715KB(741)

Abstract:
In order to solve the problem of communication blackout in near space, the influence of different incident angles on the electromagnetic wave propagation characteristics of C-wave band (4~8GHz) in plasma sheath is studied. The transmission performance of C-band electromagnetic wave are calculated and compared by using the numerical method with a uniform plasma model and a Gaussian distributed plasma model, respectively. Analysis results show that the increase of the incident wave frequency and the decrease of incidence angle are beneficial to reduce the attenuation value of the C-band, and to increase the transmissivity, which makes the communication electromagnetic wave more effectively in penetrating the plasma sheath. The conclusion provides a theoretical basis for solving the problem of communication blackout in near space.

Motion of Dayside Auroral Arc Observed At Yellow River Station Affected by the Earth's Rotation

QIU Qi, YANG Huigen, LU Quanming, HU Zejun

2016, 36(6): 909-915. doi: 10.11728/cjss2016.06.909

Abstract(1581) PDF 1385KB(898)

Abstract:
By using of the all-sky auroral data detected at Chinese Arctic Yellow River Station, the frame of dayside auroral arc is extracted and mapped to the Magnetic Local Time (MLT)-geomagnetic Latitude (MLAT) coordinate system, and the auroral arc velocity induced by the Earth's rotation is calculated. For any auroral arc, its tilt is the angle between the arc direction and the local geomagnetic east-west direction. The results indicate that the velocity is determined by the distance that the arc departs away from zenith and the arc tilt. The arc tilt determines the velocity orientation, and hence is more important. In order to calculate the arc tilt, over 40000 images of dayside auroral arcs are extracted from 4 years observations of Chinese Arctic Yellow River Station. The calculation results show that arc tilt decreases as MLT increases and reverses at about 10:00MLT. Due to the reversal of arc tilt, the arc motion induced by the Earth's rotation is poleward and equatorward motion at dawn and afternoon respectively. The equatorward motion of the arc is much more obvious than that of poleward motion, and its maximum velocity may exceed 300m·^-1.

Radiation Characteristic Estimation of Chang'E-3 Landing Area

SONG Xin, ZHANG Youwei, LIU Zijun

2016, 36(6): 916-924. doi: 10.11728/cjss2016.06.916

Abstract(1436) PDF 2358KB(829)

Abstract:
Emissivity and solar radiation reflectivity of the lunar surface are very important for mastering the lunar surface status and exploring resource. But it is very difficult to install special equipment on spacecraft to perform measurement near the lunar surface. Therefore until now there is very few direct measurement data. This paper had estimated emissivity and solar radiation reflectivity of the lunar surface based on thermal control coating parameters of topography camera and stepper motor which are mounted on Chang'E-3 Lander. Numerical results show that the reflectivity and solar radiation reflectivity at Chang'E-3 landing area are 0.105 and 0.866 respectively. This data could be consulted by further scientific research work.

Study of Slitless Imaging Technique of Solar Extreme Ultraviolet Spectrometer

SHENG Fangliang, PENG Jilong

2016, 36(6): 925-931. doi: 10.11728/cjss2016.06.925

Abstract(1589) PDF 1360KB(2512)

Abstract:
Solar imaging spectrometer in the extreme ultraviolet band is an important kind of instrument for solar observation. But traditional solar imaging spectrometer cannot observe the Sun in a large field of view simultaneously. Slitless imaging spectrometer allows imaging spectroscopy with high spatial and temporal resolution. Slitless imaging technique is a revolutionary technique for solar research in the extreme ultraviolet band. In this paper, a reconstruction algorithm is studied which has been used in a slitless imaging spectrometer, but it is found that there is a systematic error in the reconstruction result. A new optical design is proposed to solve this problem. By reconstructing the simulated data, the effectiveness of this design is proved. The reconstruction of new design shows better measurement accuracy in Doppler velocity. It will provide more accurate data for space weather studies.

Research on Electron Irradiation Test of Si-PIN Detectors for Space Particle Monitor

SUN Ying, WANG Feng, ZHANG Shenyi, JING Tao, YANG Chuibai, SHEN Guohong, ZHANG Huanxin, YAN Xuemei

2016, 36(6): 932-937. doi: 10.11728/cjss2016.06.932

Abstract(1504) PDF 1334KB(803)

Abstract:
Long term high energy electron irradiation may affect the performance of the Si-PIN Semiconductor Detector (SSD). In order to check the electronic radiation ability of the device, electron irradiation source was used to simulate space electron environment, and the irradiation experiments were carried out on the semiconductor detector. Experiment results show that under the radiation dose of 7.64×10¹⁴, the SSD's energy response capability had not changed, and the counting efficiency slightly decreased. As the radiation dose increased, the leakage current of the SSD increased, but the noise was relatively stable, and the performance of the detector did not affect the work index of the load.

High Energy X-ray Telescope Data Analysis Method

ZHAO Haisheng, LI Chengkui, LI Xiaobo, NIE Jianyin, GE Mingyu, PAN Yuanyue, SONG Liming

2016, 36(6): 938-944. doi: 10.11728/cjss2016.06.938

Abstract(1036) PDF 271KB(1073)

Abstract:
The science analysis of the data from the High Energy X-ray Telescope (HE) on the Hard X-ray Modulation Telescope (HXMT) satellite is organized in three stages: calibration, screening and extraction of high-level scientific products. At the first stage, the raw PHA value of each event is converted to PI value accounting for temporal changes in gain and energy offset. At the second stage, the calibrated events are screened by applying cleaning criteria. At the third stage, scientific products, i.e. spectra, light curves and redistribution matrix files, are extracted. This work will introduce the three stages as well as the screening criteria and the data combining method.