PROGRESSES IN IONOSPHERIC RESEARCH,
2000—2002: A BRIEF REVIEW
Peking University, Beijing 100871, China
WAN Weixing and LIU Libo
Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071, China
This brief report reviews the recent developments in ionospheric physics studies made by Chinese scientists. It covers the research areas from the numerical simulations and theoretical study on ionospheric properties, ionospheric disturbances, ionospheric space weather events, and ionospheric observations, to ionosphere and magnetosphere coupling, as well as the study on comparative planetology.
Key words: Ionospheric storm, Ionospheric model, Ionospheric property, I-M coupling, Comparative planetology
During the last two years, achievements have been made on the ionospheric science by many Chinese scientists. The brief review presented here is focused on the main progresses in the following studies: regional ionospheric models, ionospheric properties, ionospheric observations, ionospheric disturbances and ionospheric space weather studies.
II. REGIONAL IONOSPHERIC MODEL
In recent years, great efforts have been made to develop regional theoretical (or first principal) and empirical ionospheric models. A two-dimensional theoretical ionospheric model for low-latitudes was proposed and updated by physicists at Wuhan Ionospheric Observatory for years. One of distinct features of this model is that the ionospheric plasma equations are solved in a fixed geomagnetic coordinate system, at which grids are chosen to be the cross points of magnetic field lines and their perpendicular directions. It has been used to study the response of low latitude ionosphere to a solar eclipse, the dynamic control effects of electric fields and winds on low latitude ionosphere, and the low latitude nighttime enhancements in f0F2. It was also applied to simulate the evolution of the Equatorial Anomaly Trough (EAT) and to analyze the factors contributing to the variations of the EAT location. EAT has considerable local time, seasonal and longitude variations. The simulations indicate that the seasonal and longitudinal variations of the EAT location are caused mainly by neutral winds, rarely by seasonal variations in photoionization productions as well as longitudinal difference of magnetic declination and the displacement between geographical and magnetic equators. The scheme of this model was later adopted by Shang to simulate the effects of disturbed electric fields on the ionosphere in a certain meridian plane.
This model is now planned to be reconstructed as a self-consistent model by introducing a theoretical electric field model for mid- and low-latitude ionosphere and a thermospheric circulation model. The electric field model solves the electric potential from the ionospheric dynamo equations, and the modelled electric fields and currents well reproduce the main features of such electrodynamics processes as equatorial electric jets and ionospheric electromagnetic drifts. In the thermospheric model, Navier-Stokes equations are solved to derive horizontal winds driven by neutral atmospheric pressure, which so far is provided by the Mass Spectrometer Incoherent Scatter Radar model (MSIS90). The modelling wind is compared with that obtained from ionospheric measurements at Wuhan, China at a particular case.
A polar ionospheric model was established by Zhang et al. The soft electron precipitation is considered in this model. It is indicated by the simulations that a typical polar ionospheric F layer can be obtained only if the soft electron precipitation ionization is considered, while a distinct E layer will appear if the precipitating electrons with higher characteristic energy have a higher ionization rate at lower altitudes. The effects of precipitating electrons can be applied to interpret the magnetic local noon phenomenon at Zhongshan Station(66.4S, 76.4E; 73S magnetic).
There are increasing requirements to forecast the thermospheric and ionospheric environment. However due to the partial deficiency of models in reproducing the actual situation, data assimilation now becomes an important option to improve the ability of ionospheric models in space weather researches and applications.
Zhang et al. performed an exploratory study which considers the data assimilation question and provides information on what can and cannot be done with the electron density profile fitting approach. Liu et al. and Luan et al. introduced a new method to derive vertical effective drifts from the ionosonde measurements. This technique does not need to determine the no-wind reference height as the traditional servo methods did. Examples of vertical components of effective winds (VEWs) in December 2000 were derived from ionospheric data measured with a DGS-256 Digisonde in Wuhan (114.4°E, 30.6°N, 45.2dip), China. The deduced VEWs show large day-to-day variations during the winter, even in low magnetic activity conditions. The average diurnal pattern of VEWs is more complicated than that predicted by the empirical Horizontal Wind Model (HWM).
A thermospheric circulation model in meridian plane and a physical model of ionosphere are presented by Xiao, Wang and Deng, Wang, Xiao respectively, which can be applied in simulating the large scale thermospheric structures. A case study on the variations in the night side thermosphere caused by energy deposition in auroral oval during a single magnetic substorm is expounded using this model. Reported calculations can reflect the thermospheric thermal status and circulation patterns during storm time.
How to forecast or predict the ionosphere is a focus in recent years. Based on TEC data observed at Wuhan for a solar cycle, Chen et al. developed a regional empirical TEC model. In the model, the solar dependence for TEC is assumed as a linear function of solar 10.7 cm flux index, F10.7. The model prediction of TEC over Wuhan is more accurate than that of the well-known IRI model.
Based on the observed f0F2, artificial neural network is used to predict the monthly mean values. In comparison with conserved data, the error is less than 0.34 MHz. The artificial neural network is also used to predict the ionospheric disturbances. The prediction error of model of Liu and Jiao is less than 20%. To actually apply to real situation, their model needs better physical knowledge.
Zhang et al. developed an ion drift empirical model, MUIDM, based on the drifts measurements from the Japanese MU radar during the years 1986—1997. The diurnal variation is expressed in terms of harmonic 6-, 8-, 12- and 24-hour tidal components, the seasonal dependence in terms of the day of the year, and the solar activity dependence in terms of the yearly sunspot number.
III. IONOSPHERIC PROPERTIES
Spread-F is an ionospheric phenomenon with many effects on radio wave propagation. It is the manifestation of multi-scale irregularity structures in ionospheric F layer. The characteristics of the mechanism of equatorial and mid-latitude Spread-F and relations between them were investigated in numerical simulations done by Zhang and Xiao. It is found that, at different latitudes, the same mechanism can cause rather different structures under different background ionosphere conditions. The bubble in the simulation can be generated first at the topside ionosphere while the bottom side ionosphere is not disturbed much. The irregularities then must be closely connected with the ionospheric plasma instabilities. The existence of both E region Pederson and Hall conductivities and F region Pederson conductivity may play a role in the instabilities at mid and low latitudes. The coupling between different regions is considered by Zhang and Xiao to study the effects of the coupling on the formation and evolution of mid-low latitude ionospheric irregularities. It is found that the development of the gradient-drift instability in the nighttime F region not only depends on the local conditions, but also on the state of E region that connects to F region with the geomagnetic field lines.
Zhang and Xiao analyzed the morphological features of the occurrence rate of Spread-F using ionosonde data from 16 stations. The statistical results indicate the significance of geomagnetic configurations in the formation and evolution of Spread-F. Taking magnetic inclination and declination into account, Xiao and Zhang developed a theoretical model for the linear growth-rate of Spread-F. It was shown that the magnetic configuration greatly affects the occurrence rate, which formed some regional characteristics of Spread-F.
2. Sporadic E
Es occurrences over Chongqing (29.5°N,106.6°E) and Lanzhou (36°N, 103.9°E) are investigated by Tan. He found that the change in Es occurrences is consistent with f0E. Es occurrences over Chongqing are higher than that over Lanzhou in the day time and opposite at night.
After analyzing the global ionospheric network critical frequency of Es layer, f0Es, during three solar cycles (1957—1990) in WDC data CD, Zuo and Wan found that the annually averaged f0Es was correlated with solar activity in daytime and anti-correlated at nighttime. The strong correlation of f0Es with solar activity in daytime is attributed mainly to the regular E layers, which are deeply controlled by solar activities. After eliminating the contribution of regular E layers, the intensity of sporadic E layers is slightly correlated with the yearly averaged sunspot numbers in daytime and anti-correlated at nighttime, and the correlation coefficient has a regular diurnal or semi-diurnal variation pattern.
Besides the well-known wind-shear theory, an electric field theory was developed to explain the formation of sporadic E layers in the high-latitude ionosphere. To investigate the role of the electric field on the formation of Es-layers, Wan et al. focused on the relationship between Es-occurrence and the fluctuating properties of the electric fields. It was suggested that the field fluctuation was also an important factor helping to explain the differences in the Es-occurrence at cusp and polar cap latitudes, which was then confirmed by a simulation that Es were more effectively formed by the steady SW fields than by steady NW fields, and less effectively by fluctuating SW fields than by fluctuating NW fields.
3. Overall Properties
He et al. analyzed the monthly data of DPS-4 to investigate the seasonal properties of the F region at the Antarctic station, Zhongshan. They found that, as in mid-latitudes, the summer ionosphere over Zhongshan was dominated by the solar ultraviolet radiation, and f0F2 varied with local time. While in winter, the diurnal variation of f0F2 lies between LT and MLT, solar radiation is less effective to F region ionization, but affected by particle precipitation as well as plasma convection.
Ma et al. investigated trough-like plasma structures in the high-latitude ionosphere near the polar cap boundary with EISCAT CP3 data and in-situ satellite observations and suggested that ionospheric signatures of cusp processes was caused by magnetic reconnection on the dayside magnetopause. Liu et al. statistically analyzed the morphology of large field-aligned ion up-flows between 200—550 km in the high-latitude F region ionosphere with EISCAT and EISCAT Svalbard radar and found the up-flows are clearly different at these two locations. There is a distinct geomagnetic dependence of the morphology of up-flows in the EISCAT measurements around solar maximum.
IV. TRAVELLING IONOSPHERIC DISTURBANCES
Using Manzhouli, Changchun and Beijing ionosonde data, He and Sun reported the travelling ionospheric disturbances (TIDs) caused by acoustic-gravity wave in the belt of solar eclipse and the motional characteristics of acoustic-gravity wave effects during the total solar eclipse occurring on 9 March 1997.
Tang et al. investigated the large scale traveling ionospheric disturbances (LSTIDs) from the observation of an HF Doppler array located in Central China. The data observed in a high solar activity year (year 1989) were analyzed in detail to obtain the main propagation parameters of LSTIDs such as period, horizontal phase velocity and propagating direction. It is found that most of LSTIDs propagate southward, while others tend to propagate northward, mostly in summer. The dispersion of most LS TIDs is matches that of Lamb pseudo mode, while others have the dispersion of long period gravity wave mode. The horizontal phase velocities of these two modes are about 220 m/s and 450 m/s respectively. Their analysis shows that LSTIDs are strongly pertinent to solar activity and geomagnetic disturbances.
Ding et al. investigated the influence of horizontally inhomogeneous wind on the propagation of internal gravity waves in a dissipative atmosphere. The ray-tracing results show that the refraction caused by wind and wind shear leads to considerable changes of wave propagating parameters. Besides, winds with different directions cause ray paths of gravity wave to be horizontally prolonged, vertically steepened, reflected or critically coupled. And only the waves propagating against wind directions can easily reach ionospheric height with less energy attenuation.
In another paper of Ding et al, the propagation features of medium-scale ducted gravity waves are analyzed by obtaining full-wave solutions of Navier-Stokes Equations in a horizontally stratified atmosphere. The study reveals the existence of several long-distance propagating modes when there are strong background winds blowing against the propagating direction of gravity waves. The distribution of Travelling Ionospheric Disturbances observed at Millstone Hill and Wuhan is statistically analyzed, and the experimental results confirm the existence of these superior gravity wave ducted modes.
With the observation in Millstone Hill Station, Yuan et al studied the statistical dispersion of TIDs and found that the observation matches the theoretical dispersion relations of guided gravity waves. It is very important that some components may interpret as the newly proposed wind reflected guided gravity waves.
V. IONOSPHERIC WEATHER
The response of the global ionosphere to the magnetic storm during May 1998 was investigated by Zhang et al. through calculating the percentage deviation of the daily f0F2 from its monthly median values for more than 40 stations. They reported that the characteristics of the ionospheric disturbance during the active phase of the storm can be explained by the storm circulation theory, but the positive phases in the European region during the late recovery phase could not be attributed to this explanation.
The 23rd solar cycle reaches its peak in 2000—2001, and a series of solar events and geomagnetic storms occurred. The STORM23 project is a cooperative effort among Chinese scientists in the study of space weather effects of the solar activities during this solar cycle. Among those, ionospheric responses at low latitudes to severe geomagnetic storms on April 6, 2000 and July 15, 2000 have been studied [34-38].
Using TEC measurements with GPS networks located in China, Southeast Asia and Australia, Wan et al. studied two very intense ionospheric storms occurred on April and July 2000 around the equatorial anomaly region. It is found that the equatorial anomaly crests were compressed to the magnetic equator and the TEC around the crests was decreased in the first day of the recovery phase, but the crests expanded and the TEC around them increased during the second day. Very strong negative TEC storms appeared at the latitudes outside the crests in the first day, and positive storms occurred at the equatorial trough in the first day and at almost all the equatorial anomaly region in the second day. The symmetrical structure to the geomagnetic equator was found in April storms (occurred in spring-autumn), but the behavior of July storm (in summer-winter) was very asymmetrical. It is speculated that the very complicate behaviors of the ionospheric storms in the ionospheric equatorial anomaly region are controlled by both the disturbed atmospheric circulation and equatorial electrodynamic processes.
Digisonde data from low latitude ionospheric stations at Chungli, Wuhan, and Kokubunji was analyzed to investigate the ionospheric responses of low latitudes near longitude 120°E to this April storm,,. The significant ionospheric responses were near-simultaneous downward and rapid and large upward disturbances in the ionospheric heights after the Sudden Storm Commencement (SSC), which lasted for about 2 hours, and wave like disturbances appeared on daytime of April 7. The near simultaneity of the ionospheric height disturbances in the nighttime ionospheric heights after the SSC suggested that an EXB plasma drift due to the storm related perturbed zonal electric fields. The follow wave like disturbances were suggested to be caused by storm induced traveling atmospheric disturbances (TADs).
Liu et al. reported the ionospheric responses at the low latitudes of 120°E during the geomagnetic storm occurred on July 15/16, 2000. There was a negative storm at low latitudes on July 16. The G condition on the ionograms was seen clearly at the early first day after the geomagnetic storm. While on July 17 and some days thereafter, were positive phases. Anomalous Equatorial Ionization Anomaly(EIA) inhibition and development were observed on July 16 and 17, respectively.
The GPS TEC over Jingzhou (30.4°N, 112.2°E) during three great storms from April to August 2000 was collected by Pei et al. to analyze the time-latitude-dependent features of ionospheric storms. Their results show that the ionospheric storm effects are more apparent in local day time than at night in middle and low latitude, more dominant near the hump of the equatorial anomaly region than in other regions.
Liu et al. investigated responses of the polar ionosphere at Zhongshan Station, Antarctica, to the Bastille Day (14 July, 2000) solar event. The polar ionosphere was highly disturbed, as shown by frequently large deviations of the geomagnetic H-component, large riometer absorption events and strong ULF waves. Associated with the huge solar proton event produced by the X5/3B flare, a Polar Cap Absorption (PCA) was observed. It began at 1040 UT on 14 July and ended at 1940 UT on 17 July. Superposing on it, there was a large absorption event with a peak of 26 dB, started at 0300 UT and ended at 1110 UT on 15 July. This kind of absorption was suggested to be produced by an intense ‘cloud of energetic electrons' during an auroral substorm. The ULF waves were very intense during the main phase and recovery phase of the major magnetic storm on 15 and 16 July. The ionospheric absorption was so strong that the digisonde signal was blackout in most of time. The ionosphere returned to normal in the afternoon on 17 July.
Another simultaneous observation at Zhongshan Station, Antarctica, was presented by Liu et al. for the interval of May 1—7, 1998 to show responses of the polar ionosphere to the April May, 1998 solar events. The polar ionosphere was also highly disturbed during this period. During the storm onset on May 2 the ionospheric F2 layer abruptly increased in altitude, the geomagnetic H component started negative deviation and the spectral amplitude of the ULF wave intensified. Both large isolated riometer absorption and large negative deviation of the geomagnetic H-component occurred at about 0639 UT. There was a time lag of about one hour and ten minutes between the storm onset and the IMF southward turning measured by the WIND satellite. The digisonde is also blackout in most of time. However, the data still showed a substantial decrease of the F2 electron density and oscillation of the F2 layer peak height with an amplitude exceeding 200 km.
Ma et al. found an abnormal anti-sunward intense flow of plasma convection with EISCAT radar in the high-latitude ionosphere near the polar cap boundary during the recovery phase of a moderate magnetic storm. When the IMF Bz was southward, the abnormal flow occurred at MLT morning sector. Liu et al.  and Ma et al.  studied the high-latitude ionospheric response to a major magnetic storm on May 15, 1997 with ESR and EISCAT radar observations[42-44]. Negative ionospheric storm occurred in both the polar cap and the auroral zone, which was suggested to be caused by increased recombination rate of O+ ions due to the strong electric fields in the auroral zone, and the transport effect of strong upward ion flux in the dayside polar cap, respectively. Cai et al. simulated the effects of strong convection electric field on the electron density in the auroral ionospheric F region with a physical model and found the magnitudes of the percentage ionization depletions and their recovery time are dependent not only on the intensity of the electric field, but also on the diurnal phase of background electron density. Case study of magnetic storm effects in the auroral ionosphere was performed by Liu et al. with emphasis on their relationship to the solar wind dynamic pressure and the IMF Bz component. Sudden ionospheric disturbance (SID) phenomenon caused by solar flares is another subject interested by scientists. Zhang and Xiao- and Zhang et al.- reported the Sudden Increment of Total Electron Content (SITEC) from GPS observation. With a local GPS network, Wan et al. studies the SITEC caused by the very intense solar flare on July 14, 2000. According to the well-known Chapman theory of ionization, they first derived the relationship between the temporal variation rate of TEC and the flare parameters. The analyzed results show that the variation rate is inverse proportional to the Chapman function of the zenith angle, as the theory predicted.
VI. IONOSPHERIC OBSERVATION
Wu et al described the design and operational features of the automatic data acquisition system for low latitude ionospheric tomography along the 120°E meridian. Xu et al presented experiments of ionospheric tomography at low latitudes along 120°E meridian. In their reconstruction algorithm, both differential Doppler phase and differential Doppler frequency data are jointly used and the integral phase constants are determined in the reconstruction process. The reconstructed ionospheric equatorial anomaly crests usually show a tilt alignment with the magnetic field lines.
It is a tendency that the networking of ionosonde provides real-time information on ionospheric condition with the development of the Internet. Ning et al. updated the DGS256 digital ionosonde at Wuhan Ionospheric Observatory. After the upgrading, Wuhan ionospheric data can be accessed and published by Internet in real-time, and the Wuhan Digisonde can be controlled through Internet at remote sites.
A new set of sounding system of HF Doppler shift and angle-of-arrival at Wuhan was introduced by Yuan et al. he system is composed of microcomputer, data acquisition unit, HF program-controlled receiver with high frequency stability and antenna array. Computer can control the system to adjust received frequencies, sampling parameters, and the Doppler shift and the angle of arrival of the ionospheric echo wave can be measured and displayed in real time.
Zhang and Xiao provided a formula for calculating Doppler shift for GPS signal and ionospheric TEC by using dual-frequency GPS Doppler observations. It is found that the dynamic Doppler shift of GPS signal is usually between several thousands Hz. The precision of TEC derived from GPS Doppler observations is higher than that from pseudo-range observations but is lower than that from GPS carrier phase observations.
A new analysis method of Digisonde is given by Yuan et al.. The high accurate Doppler ionogram can be acquired with digisonde ionogram mode through converting sixteen Doppler channel data to temporal domain by IDFT and estimating the phase differences, if that ionospheric echoes are of narrow band is taken into account. It will have great use in experimental investigation of ionospheric disturbances. Experimental results with Wuhan Digisonde (DGS256) show that this ionogram with high accurate Doppler information can be acquired.
Ning and Lin presented a conception for developing new ionospheric radio probing technique and equipment based on software radio. As a conventional ionospheric sounding instrument, a new software digital ionosonde is discussed in detail about its system architecture, feature and feasibility.
VII. IONOSPHERE AND MAGNETOSPHERE COUPLING
Some research work on the coupling between ionosphere and magnetosphere has been conducted in the recent 4 years. Using the dynamic equations, Shi and Liu  developed a model for the distribution of the ionospheric ions along the magnetic field line during geomagnetic static state (i.e., the magnetic quiet and slowly changing), the distribution of the ion, including ionospheric O+, H+ and He+ ion, along the field line and the distribution features in the meridian plane are studied. Shi et al.  also studied the ionospheric up-flowing ion transportation from the ionosphere to the magnetosphere during the static state. The variation of density and flux of the up-flowing ions along the field line originating from the ionosphere at different latitude is investigated. Combining the observation results in the ionosphere and the theoretical model, Shi and Liu et al. investigated the distribution of the ions originating from the ionosphere in the Geo-Stationary Orbit Region (GSOR) when the geomagnetic magnetic activity index Kp < 6. The results are agreement with the observation in the GSOR. Shi and Liu developed semi-empirical models for the density and flux distributions of the ionospheric ions in the GSOR for Kp =0 and Kp = 3—5.
Shi and Liu investigated the ionospheric ion distribution and dynamics in the magnetosphere by reviewing the observation for different geomagnetic activaties and solar activities, and some theoretical studies. The results show that that the ionospheric ions take an important role in the inner magnetosphere and the solar wind ions play an important role in the out magnetosphere. Shi et al. investigated the geo-center distance of the geopause and its variation. The result shows that the geopause is influenced by the solar activity.
Shi and Liu theoretically studied induced electrical field during the geo-magnetic field dramatically changing in the magnetotail. Some features of the induced electrical field are given and the results show that the induced electrical field can be as high as 28 mV/m in the magnetotail. To consider the ionospheric ion acceleration in the low altitude, Shi et al. studied the nonlinear waves in the upper ionosphere and discussed its application for the ionospheric ion acceleration. These studies give a base for the ionospheric ions acceleration.
Based on the theoretical study on the induced electrical field and the observation, Shi et al. studied the ion distribution function and its evolution during the geo-magnetic field dipolarization by analyzing the ion dynamic equation. They studied the variation of the O+ and H+ ion velocities including the parallel and the perpendicular velocity components, as well as the variation of the ion energy. Shi et al. consider the condition of the substorm, they studied the ionospheric ions acceleration in the geo-magnetotail. The results show that the ion acceleration mainly occurs in the perpendicular component. They also studied the spatial and temporal variation when the ionospheric ions moves earthward during the substorm in the magnetosheet  and got the result of that the ionospheric ion energy can be as high as 200 –300 keV. This is consistent with the observation in the magnetotail and implies that the ionospheric ions can contribute to the ring current during the substorm.
VIII. STUDY ON COMPARATIVE PLANETOLOGY
In recent years, the comparative study between planet and Earth is established in China. Different spacecraft has a different observation result on the Mars intrinsic moment. Based on the theory of the ion distribution in the Earth's ionosphere and magnetosphere, Shi et al. studied the normalized O+ ion flux and density distribution in the Martian environment in different assumed intrinsic moment[75,76]. The results show that the ion distribution will be different if the Martian intrinsic moment is different. So, they proposed a method to deduce the Martian intrinsic moment according to observed ion distribution data. Then, they studied the influences of the interplanetary condition [77, 78] and the solar wind on the ion distribution in the Martian atmosphere. After that, Shi et al. deduced the intrinsic moment of Mars according to their studying results and the observed ion distribution data. The results show that the Martian intrinsic moment is about 2×1021 Gauss·cm3. This is consistent with the observation data from the instrument MAG/ER on board the USA recent satellite Mars Global Surveyor.
ACKNOWLEDGMENTS We are grateful to Prof. J. K. SHI and M. L. ZHANG of Center for Space Science and Applied Research, Chinese Academy of Sciences, Prof. S. Y. MA of Wuhan University, Prof. R. Y. LIU of Polar Research Institute of China for providing us their papers and help.
 Liu L, Wan W. (2001), The evolution of equatorial trough of ionospheric F-region ionization. Terr. Atmos. Oce. Sci., (3):120-125
 Liu L, Wan W, Tu J, Bao Z. (2000), Modelling of the ionospheric response to the solar eclipse of 24 October 1995. Terr. Atmos. Oce. Sci., (2):543-554
 Liu L, Tu J, Bao Z, Wan W. (2000), Effects of neutral winds and vertical drifts on low-latitude ionosphere. Chin. J. Space Sci., 20 (1):23-31
 Liu L, Wan W, Tu J. (1999), Modelling study of the nighttime enhancements at low-latitude ionosphere. Chin. J. Space Sci., 19 (2):108-113
 Shang Seping (1999). Doctorial Dissertation, Center for Space Science and Applied Research.
 Yu T, Wan W, Liu L. (2002), A theoretical model for ionospheric electric fields at mid- and low-latitudes. Sci. China, 32A (6):1-9
 Lei J, Liu L, Luan X, Wan W. (2002), Model study on neutral winds in the ionospheric F-region and compared with the equivalent winds derived from the Ionosonde data. Terr. Atmos. Oce. Sci., submitted
 Zhang B, Liu R, Liu S. Simulation study on the influences of the precipitating electrons on the polar ionosphere. Chin. J. Geophys., 2001, 44 (3):311-319
 Guo J, Shang S, Zhang M. (2000), Problems on the assimilation of space sounding data. Sci. in China, Series A, 30 (special issue)
 Zhang S, Oliver W, Fukao S, Kawamura S. (2001), Extraction of solar and thermospheric information from the ionospheric electron density profile. J. Geophys. Res., 106 (A7):12\,821-12\,836
 Liu L, Luan X, Wan W, Ning B. (2002), Effective winds over Wuhan derived from ionospheric data. J. Atmos. Solar-Terr. Phys., submitted
 Luan X, Liu L, Lei J, Wan W, Ning B. (2002), Deriving equivalent winds from ionospheric F-layer data. Chin. J. Space Sci., 22(2):119-128
 Xiao Z, Wang J. (2000), Thermospheric circulation model in meridian plane (I)---Storm time variations in thermal status and circulation. Sci. China, 43E(6):464-472
 Dng Y.,Wang J. and Xiao Z. (2002), A physical model for ionospheric vertical profile and a comparison of it and IRI-90. Chinese J. Space Sci. 20(2):103-112
 Chen Y, Wan W, Liu L, Li L. (2002), A statistical TEC model based on the observation at Wuhan Ionospheric Observatory. Chin. J. Space Sci., 22 (1), 27-35
 Liu W, Jiao P. (2000), Prediction the monthly mean values of f_0F_2 by using the artificial neural network. Chin. J. Space Sci., 20 (4):310-317
 Liu W, Jiao P. (2001), Prediction of disturbances in the ionosphere by using the artificial neural network. Chin. J. Geophys., 44 (1):24-30
 Zhang S, Oliver W L, Fukao S. (2001), MU radar ion drift model. Adv. Space Res., 27 (1):115-120
 Zhang T, Xiao Z. (2000), The characteristics and relationships of equatorial and mid-latitude Spread-F. Chin. J. Space Sci., 20 (3):224-232
 Zhang T, Xiao Z. (2000), Effect of the coupling of different ionospheric regions on the night time F region irregularities in mid-latitudes. Chin. J. Geophys., 43 (5):589-597
 Zhang T, Xiao Z. (2001), Global distribution characteristics of Spread-F(II)-Data analysis. Sci. China, 44E (7):597-599
 Xiao Z, Zhang T. A theoretical analysis of global characteristics of spread-F. Chin. Sci. Bull., 46 (19):1593-1595
 Tan H. (2000), Comparison and investigation of Es occurrence of the ionosphere over Chongqing and Lanzhou. Chin. J. Space Sci., 20 (4):371-379
 Zuo X, Wan W. (2002), The correlation between Sporidic E layers and solar activities. Chin. J. Geophys., in press
 Wan W, Liu L, Parkinson M, Liu R, He L, Breed A, Dyson P, Morris R. (2001), The effect of fluctuating ionospheric electric fields on Es-occurrence at cusp and polar cap latitudes. Adv. Space Res., 27 (6/7): 1283-1288
 He L, Liu R, Liu S, Liu Y. (2000), Overall properties of F region around solar minimum at Zhongshan station, Antarctica. Chin. J. Geophys., 43 (3):289-295
 Ma S, Liu P, Schlegel K. (2000), EISCAT observation of a high-latitude ionization trough associated with a reversed westward plasma flow. Geophys. Res. Lett., 27 (20):3269-3272
 Liu H, Ma S, Schlegel K. (2001), Diurnal, seasonal, and geomagnetic variations of large field-aligned ion upflows in the high-latitude ionospheric F region. J. Geophys. Res., 106(A11):24\,651-24\,661
 He Y, Sun H. (2001), The acoustic-gravity wave effects of the solar eclipse. Chin. J. Radio Sci., 16(1):93-99
 Tang Q, Wan W, Ning B, Yuan H. (2001), Properties of large-scale TIDs observed in central China. Sci. China, 31A:133-136
 Ding F, Wan W, Yuan H. The (2001), effect of horizontally inhomogeneous wind on internal gravity wave propagation in a dissipative atmosphere. Chin. J. Geophys., 44(5):580-587
 Ding F, Wan W, Yuan H. (2002), The influence of background winds on the propagation of medium-scale ducted gravity waves. Chin. J. Space Sci., 22 (1):44---51
 Yuan H , Wan W, Liang J, Ding F. (2000), The statistical dispersion characteristics of medium-scale travelling ionospheric disturbances observed at Millstone Hill. Chin. J. Space Sci., 20:324-327
 Zhang M, Shang S, Guo J, Luo X. (2001), The global ionospheric response to the geomagnetic storm event during May 1998. Chin. J. Space Sci., 21 (2):131-140
 Liu L, Wan W, Yuan H, Ning B, Gao Y. (2000), The large nighttime increase in ionospheric heights at Wuhan during the storm of April 2000. Chin. J. Space Sci., 20(4):318-322
 Liu L, Wan W, Lee C C. (2002), Effects of the geomagnetic storm in April 2000 in the low latitude ionosphere near longitude 120E. Adv. Space Res., submitted
 Wan W, Yuan H, Liu L, Ning B. (2001), Ionospheric storms observed with a Local GPS Network. In: Proc. Intern. Beacon Satel. Symp., USA,
 Lee C, Liu J, Reinisch B, Lee Y, Liu L. (2002), The propagation of travelling atmospheric disturbances observed during the April 6-7, 2000 ionospheric storm. Geophys. Res. Lett., 29 (5)
 Liu L, Wan W, Ning B, Yuan H, Liu J. (2001), The ionospheric responses at the low latitudes of 120E during the great geomagnetic storm of July 2000. Sci. China, 31A (special issue):126-132
 Pei X, Yu S, Xu J, Ma S. (2001), Storm-time ionospheric disturbances monitored by GPS beacon measurements. Wuhan Univ. J. Nat. Sci., 6 (3):687-693
 Liu R, Hu H, Liu Y, Xu Z, (2002), Sato N, Fraser B. Responses of the polar ionosphere to the Bastille Day solar event. Solar Phys., 204, in press
 Liu R, Hu H, He L, Liu Y, Liu S, Li S, Sato N, Fraser B. (2001), Multiple ground-based observations at Zhongshan station during the April/May, 1998 solar events. Sci. China, 31A :101-110
 Ma S, Liu P, Liu H, Schlegel K, Xu J. (2001), A reversed plasma convection flow in the polar ionosphere observed with EISCAT radar. Chin. J. Geophys., 44 (4):446-453
 Liu H, Schlegel K, Ma S. (2000), Combined ESR and EISCAT observations of the dayside polar cap and auroral oval during the May 15, 1997 storm. Ann. Geophys., 18:1067-1072
 Ma S, Liu H, Schlegel K. (2002), A comparative study of magnetic storm effects on the ionosphere in the polar cap and auroral oval- F-region negative storm. Chin. J. Geophys., 45 (2):1-10
 Cai H, Mao S, Kirchengast G. (2001), A simulation study of ionization depletion in the auroral ionospheric F-region caused by strong convection electric field. Wuhan Univ. J. Nat. Sci., 6 (3):680-686
 Liu H, Ma S, Schlegel K. (2000), Magnetic storm effects in the auroral ionosphere observed with EISCAT radar-two case studies. Wuhan Univ. J. Nat. Sci., 5 (2):181-186
 Zhang D, Xiao Z. (2000), Study of the ionospheric TEC using GPS during the large solar flare burst on Nov. 6, 1997. Chin. Sci. Bull., 45(6):575-578
 Zhang D, Xiao Z. (2000), The calculating TEC methods by using GPS observations and its applications for ionospheric disturbances. Chin. J. Geophys., 43 (4):451-458
 Zhang D, Xiao Z. (2000), The study of TEC enhancement caused by flare radiation occurred on Nov.22, 1998 by means of GPS methods. Acta Sci. Nat., 36 (3):414
 Zhang D, Xiao Z. (2002), Analysis of correlative ionospheric TEC disturbances during solar flare. Chin. Sci. Bull., 47 (1):96-98
 Zhang D, Xiao Z. (2000), Study of the ionospheric TEC using GPS during the large solar flare burst on Nov. 6, 1997. Chin. Sci. Bull., 45 (19):1749
 Zhang D, Xiao Z, Chang Q. (2002), The correlation of flare's location on solar disc and the sudden increase of total electron content. Chin. Sci. Bull., 47 (1):82-84
 Zhang D, Xiao Z, Chang Q. (2002), The observational study of ionospheric response to solar flare. Progr. Nat. Sci., 12 (2):166-169
 Zhang D, Xiao Z, Chang Q. (2001), The relationship of ionospheric SITEC with the location of solar flare on solar disc. Chin. Sci. Bull., 46 (16):1339-1341
 Wan W, Yuan H, Liu L, Ning B. (2002), The sudden increment of ionospheric total electron content caused by the very intense solar flare on July 14, 2000. Sci. China, Series A., in press
 Wu X, Xu J, Ma S, Tian M, Yeh K. (2001), Data acquisition system and image reconstruction for computerized ionospheric tomography. J. Remote Sensing, 5 (1):22-28
 Xu J, Wu X, Ma S, Tian M, Yu S, Yeh K, Franke J, Tsai W, Lin K. (2000), Tomographic imaging of ionospheric structures and disturbances in the region of east-asian equatorial anomaly. Sci. China, 43E (4):395-404
 Ning B, Lin C, Wang B. (2000), Upgrading and networking of DGS-256 digisonde. Chin. J. Radio Sci., 15 (1):90-96
 Yuan Z, Ning B, Yuan H. (2001), Real-time sounding and analyzing of HF Doppler shift and angle of arrival. J. Chin. Radio Sci., 16 (4):487-492
 Yuan Z, Ning B, Wan W. (2002), Acquirement and analysis of high accurate Dopple ionogram. Chin. J. Space Sci., 22:(3)234-239
 Zhang D, Xiao Z. (2002), Analysis of Doppler effect for GPS signals. Chin. J. Radio Sci., 17 (1):42-46.
 Ning B, Lin C. (2002), Application of software radio in ionospheric radio sounding. J. Chin. Radio Sci., 17 (3):286-290
 Shi J. K., Z. X. Liu, (1999), Theoretical studying on the magnetospheric distribution of up-flowing ions, Adv. Space Res., 24 125.
 Shi Jiankui, Li Chunqiang and Liu Zhenxing, (2002), Transportation of the ionospheric ion along the field line to the magnetosphere, Chinese Journal of Geophys., 45(3)306.
 Shi Jiankui, Liu Zhenxing, et al., (2002), The distribution of the ionospheric ions in theGeo-synchronous Region, Science in China (Series D), 32(10):805.
 Shi Jiankui, Liu Zhenxing, (2002), A semi-emperical model for the distribution of the ionospheric ions in theGeo-synchronous Region, Scientific Technology and Engineering, 2(4):29-31.
 Shi Jiankui, Liu Zhenxing, (2001), Origin of the magnetospheric ion，Advance in Space Physics, Science Press, Beijing, p87-124.
 Shi Jiankui, Chen Zhongsheng and Liu Zhenxing, (1999), The Geo-center distance of the Geopause and its variation, Progress in Geophysics, (14) 101.
 Shi Jiankui, Liu Zhenxing, (1999), Theoretical study on the induced electrical field with mf geo-magnetic model and ion acceleration in the magnetotail, Chinese Journal of Geophys., 42, 12.
 Shi J. K., B. Y. Xu, et al., （2001）， Nonlinear Waves in a Low-βcylindrical Symmetry Magnetic Tube in Ionosphere, Phys. of Plasmas, (8),11:4780.
 Shi Jiankui, Liu Zhenxing, et al., (2000), The ionospheric out-flowing ion acceleration during the geo-magnetism diplarization, I: The evolution of the ion distribution function，Chinese Journal of Geophys., 43,11.
 Shi Jiankui, Liu Zhenxing, et al., (2000), The ionospheric out-flowing ion acceleration during the geo-magnetism diplarization, II: The acceleration and energy variation of the ionospheric ion，Chinese Journal of Geophys., 43,738.
 Shi Jiankui, Liu Zhenxing, et. al., (1999), Acceleration of ionospheric out-flowing ions in the substorm in geo-magnetotail., Chin. Phys. Lett., 16 908.
 Shi, J. K, Z. X. Liu, K. Torkar, T. Zhang, et al., (2002), Temporal variation of the distribution function and acceleration of O ions during sunbstorm dipolarization, Advance in Space Research， 30(10).
 Shi J. K., K. Schwingenschuh, Liu Z. X., et al., (1999), The O+ ion flux and magnetic field in the Martian environment, Science Report, IWF9909, Austrian Academy of Sciences, p1-32.
 Shi J. K., K. Schwingenschuh , T. L. Zhang, et al., (2001), Theoretical Distribution of O+ Ion in Martian Magnetosphere, Adv. Space Res. 26 345.
 Shi Jiankui, Liu Zhenxing, (2000), The O+ ion distribution in Martian atmosphere in different interplanetary condition, Chinese Science Abstract, (Science and Technology Letter), Vol.6, No.8, 1000-1003.
 Shi Jiankui，Liu Zhenxing，et al，(2001), Influence of the Solar Wind on O+ Ion's Distribution in Martian Magnetosphere, Science in China (Series E), 126.
 Shi Jiankui, Liu Zhenxing, and T. L. Zhang，( 2001), The O+ ion flux and intrinsic moment of Mars, Chin. J. Astron. Astrophys., 1, 1