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Featured researches published by Liu Siqing.


Science China-technological Sciences | 2013

Effect of seed electron injection on chorus-driven acceleration of radiation belt electrons

Yan Qi; Shi LiQing; Liu Siqing

Using the hybrid finite difference method, we solve the Fokker-Planck equation to study the effect of seed electron injection on acceleration of radiation belt electrons driven by chorus waves. Numerical results show that in the absence of injection chorus waves can accelerate electrons at large pitch angles (αe>60°), producing enhancements in the phase space density (PSD) of (1–2 MeV) electrons by a factor of 100–1000 within 1–2 days. In the presence of injection, chorus waves yield increase in PSD of electrons by accelerating the injected seed electrons. Meanwhile, the PSD evolution increases as the pitch angle increases but decreases as electron energy increases. Moreover, the PSD evolution can extend to higher energies with a time scale of 1–2 days for 1–2 MeV energies. When the injection increases by a factor of 10 higher than the initial value and remains for about two days, maximum values of PSD for 1 or 2 MeV increase to 6 or 3 times respectively higher than those without injection in two days. The current results suggest that the injected seed electrons play an important role in the evolution of the radiation belt electrons.


Science China-earth Sciences | 2016

Verification of SPE probability forecasts at the Space Environment Prediction Center (SEPC)

Cui Yanmei; Liu Siqing; A ErCha; Zhong Qiuzhen; Luo Bingxian; Ao XianZhi

In space weather forecasting, forecast verification is necessary so that the forecast quality can be assessed. This paper provides an example of how to choose and devise verification methods and techniques according to different space weather forecast products. Solar proton events (SPEs) are hazardous space weather events, and forecasting them is one of the major tasks of the Space Environment Prediction Center (SEPC) at the National Space Science Center of the Chinese Academy of Sciences. Through analyzing SPE occurrence characteristics, SPE forecast properties, and verification requirements at SEPC, verification methods for SPE probability forecasts are identified, and verification results obtained. Overall, SPE probability forecasts at SEPC exhibit good accuracy, reliability, and discrimination. Compared with climatology and persistence forecasts, the SPE forecasts are more accurate. However, the forecasts for SPE onset days are substantially underestimated and need to be considerably improved.


Chinese Science Bulletin | 2017

The measurement of flat fields and polarization offset from the routine observation data of a solar rotation

Bai Xianyong; Deng Yuanyong; Wang Yiran; Liu Siqing; Mao Xinjie

The correction of flat fields and polarization offset is a necessary step in the reduction of the full-disk solar observing data. The general used methods of the measurement of flat fields are summarized as follows. The first one is realized by randomly moving the solar telescope and making an average of thousands of observed images of the quiet region near the disk center, which is adopted by the large aperture solar telescopes with a small field-of-view. The second one is to shift the solar images with slightly different pointings, which is mostly used in the full-disk solar images. The third method is to use a diffuser to generate the uniform light source and it can be used in the full-disk solar images, too. Observing the nearby continuum of the selected working spectral line is generally used to obtain the polarization offset. It is worth to mention that, all these methods need special calibration observing mode and occupy the valuable scientific observation time. In the paper, we propose a new method to derive the flat fields and polarization offset from the routine observing data. Assuming that the flat fields and polarization offset do not change during a solar rotation, we firstly got the formula which can be used in the calculation of flat fields and polarization offset in the case of the ideal and real telescope guiding and pointing accuracy. The core algorithm in the formula is median process. Moreover, we obtained the flat fields and the crosstalk from Stokes I to Q , U and V using the above mentioned formula from series of the routine observed monochromatic image and Stokes Q / I , U / I and V / I images belonging to the Carrington Rotation 2144 observed by Huairou Solar Observing Station. The derived flat fields could not only reflect the small-scale dirty points but also the large-scale non-uniform pattern from the whole telescope system, which can be removed after the flat-fielding process. The distribution of the resulting Stokes V / I offset from Stokes I to V seems to be a Saddle surface, while that of the Stokes Q / I and U / I from I to Q , U is an upside-down bell shape. In order to evaluate the validity of the correction of the polarization offset we choose a quiet region near the solar limb as an example. The averaged value of Stokes V / I , Q / I and U / I in the region after polarization offset correction is −0.8×10−4, 0.9×10−4, 1.3×10−4, while that before correction is −6.8×10−4, 2×10−3, 1.7×10−3, respectively. It is quite clear that the Stokes V / I , Q / I and U / I improved a lot after the correction of the polarization offset. The main disadvantage of the method is that it can only correct the crosstalk from Stokes I to Q , U and V , incapable of the correction of that from Stokes V to Q and U . Some other methods are needed so as to make up the disadvantages. We suggest that the above mentioned method can be considered as one of the calibration methods for the space-borne or remote unattended full-disk solar observing instrument because it only uses the routine observation data without any other special calibration observation.


Chinese Science Bulletin | 2017

Flat-field measuring and correction method for full-disk solar image based on ground glass

Wang Yiran; Bai Xianyong; Liu Siqing; Deng Yuanyong; Sun Yueqiang

Full-disk solar chromosphere and photosphere images are mainly used for monitoring solar activities. Flat-field correction of observation image is a basic work during data processing. In history, it is difficult to obtain uniform area light whose intensity is similar as sun. So flat-field measurement and correction of full-disk solar image usually depend on moving images and mathematical calculation. In order to overcome some disadvantages of traditional methods, such as large calculating quantity, complicated algorithms and difficult to realize automation, we research and design a new flat-field correction method based on ground glass. In this text, sunlight diffused by ground glass in field of view is used as uniform area light for flat-field measuring. We simulated the area light that sun diffused by ground glass, calculated the uniformity of area light in field of view. The uniformity of area light is more than 99%, so it can be used as uniform area light for flat-field measurement directly. We designed flat-field measurement device and formulate steps and methods for flat-field correction. After numerical stimulation and calculation, experiments carried out on solar chromospheres telescope and photosphere telescope separately. The result shows that the flat field obtained in this text could correct high-frequency information such as spots and non-uniformity of light path. Subjected to telescopes limited ability to eliminate stray light, flat-field measurement and correction also causes low-frequency information anamorphous because the angle of diffused light is much larger than normal observation. In order to amend low-frequency information distortion, we use multi-scale morphology filtering and median filtering to extract the low-frequency image from flat-field corrected image. Then the extracted low-frequency image is amended on the basis of theoretical limb darkening image. After flat-field correction and amendment, the correlation coefficient between corrected image and theoretical image is more than 0.99. At last, photosphere image of HMI and chromospheres image of GONG are used as reference images to quantitatively evaluate corresponding result in various field of view. The preprocessing of reference images includes three steps: (1) Centralization and geometric correction of experiment images and reference images; (2) unify reference images’ pixel resolution based on experiment images; (3) according to fitting intensity attenuation of experiment images’ margin, convolve the same Gaussian profile to unify the atmosphere effect on reference images and experiment images. The evaluation result shows that all indexes of corrected image are better than that of origin images. The flat-field measurement and correction method in this text is simple and convenient, and it is easy to realize automation. We suggest that the above mentioned method can be considered as a new method for full-disk solar telescope flat-field measurement and correction. In the future, we need to use diffuser which output angle is smaller during flat-field measurement to shorten exposure time and narrow the exposure time difference between flat-field measurement and normal observation. If a full-disk solar telescope wants to use this method to measure and correct flat-field, the ability of stray light elimination must be considered and optimized during design stage, and the data processing would be more simple and easy.


Chinese Astronomy and Astrophysics | 2010

Modeling Research of the 27-day Forecast of 10.7 cm Solar Radio Flux (I)☆

Liu Siqing; Zhong Qiuzhen; Wen Jing; Dou Xiankang


Archive | 2016

Coronagraph flat field measurement and light intensity calibration device and method

Bai Xianyong; Liu Siqing; Gong Jiancun; Wang Yiran; Cui Yanmei


Chinese Journal of Geophysics | 2015

Statistical analysis of the ionosphere response to the CIR and CME in Mid-latitude regions

Qiu Na; Chen Yanhong; Wang Wenbin; Gong Jiancun; Liu Siqing


Archive | 2013

Alarm short massage service system for space environment disaster incidents

Gong Jiancun; Liu Siqing; Shi Liqin; Cai Yanxia; Zhong Qiuzhen; Liu Fanghua; Chen Zhaofeng; Lu Guorui


Progress in Geophysics | 2010

Property analysis of cosmic rays before and during the great Wenchuan earthquake

Liu Siqing


Archive | 2016

Device used for flat field measurement of solar photospheric or chromospheric telescope and method thereof

Bai Xianyong; Liu Siqing; Gong Jiancun; Cui Yanmei; Wang Yiran

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Gong Jiancun

Chinese Academy of Sciences

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Bai Xianyong

Chinese Academy of Sciences

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Luo Bingxian

Chinese Academy of Sciences

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Wang Yiran

Chinese Academy of Sciences

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Zhong Qiuzhen

Chinese Academy of Sciences

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Cui Yanmei

Chinese Academy of Sciences

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Deng Yuanyong

Chinese Academy of Sciences

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Dou Xiankang

University of Science and Technology of China

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Li Zhitao

Chinese Academy of Sciences

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Miao Juan

Chinese Academy of Sciences

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