Statistics of GPS ionospheric scintillation and irregularities over polar regions at solar minimum

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1 DOI /s x ORIGINAL ARTICLE Statistics of GPS ionospheric scintillation and irregularities over polar regions at solar minimum Guozhu Li Baiqi Ning Zhipeng Ren Lianhuan Hu Received: 7 November 2008 / Accepted: 15 December 2009 Ó Springer-Verlag 2010 Abstract A statistical study of the occurrence characteristic of GPS ionospheric scintillation and irregularity in the polar latitude is presented. These measurements were made at Ny-Alesund, Svalbard [78.9 N, 11.9 E; 75.8 N corrected geomagnetic latitude (CGMLat)] and Larsemann Hills, East Antarctica (69.4 S, 76.4 E; 74.6 S CGMLat) during It is found that the GPS phase scintillation and irregularity activity mainly takes place in the months 10, 11 and 12 at Ny-Alesund, and in the months 5, 6 at Larsemann Hills. The seasonal pattern of phase scintillation with respect to the station indicates that the GPS phase scintillation occurrence is a local winter phenomenon, which shows consistent results with past studies of 250 MHz satellite beacon measurements. The occurrence rates of GPS amplitude scintillation at the two stations are below 1%. A comparison with the interplanetary magnetic field (IMF) B y and B z components shows that the phase scintillation occurrence level is higher during the period from later afternoon to sunset (16 19 h) at Ny-Alesund, and from sunset to pre-midnight (18 23 h) at Larsemann Hills for negative IMF components. The findings seem to indicate that the dependence of scintillation and irregularity occurrence on geomagnetic activity appears to be associated with the magnetic local time (MLT). Keywords GPS Ionospheric scintillation Polar latitude irregularity IMF G. Li (&) B. Ning Z. Ren L. Hu Beijing National Observatory of Space Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China gzlee@mail.igcas.ac.cn Introduction Sometimes when a radio signal acts on the disturbed ionosphere, the received signal will show rapid fluctuations in amplitude and phase that are not consistent with the source strength or modulation. These fluctuations of the radio signals are known as scintillations. It is well known that ionospheric scintillation has the potential to affect Global Navigation Satellite System (GNSS) receivers in a number of ways, from degradation of accuracy such as the range errors, to the loss of signal tracking. Required levels of accuracy and availability may not be met during the occurrence of scintillation, compromising positioning and navigation applications (Aquino et al. 2005). Since ionospheric scintillation can cause considerable communication hazards on radio systems and is therefore of great practical interest (Banerjee et al. 1992), it is generally recognized that further research about scintillation and irregularity producing scintillation is required. Over the past four decades, a great deal of research has revealed that ionospheric scintillation is most likely to occur in equatorial and auroral regions. At low latitudes, the scintillation is primarily controlled by increasing irregularities over the magnetic equator. After sunset, when the eastward electric field is enhanced, irregular plasma density depletions are generated on the bottom-side of the nighttime equatorial F region and rises to higher altitudes as a result of nonlinear evolution of the generalized Rayleigh Taylor (RT) and E 9 B instabilities (e.g., Basu et al. 1978; Kelley 1989; Fejer et al. 1999). Most lowlatitude ionospheric scintillations and irregularities are observed in the pre-midnight period, and have been statistically studied using ground-based and in situ satellite measurements (Su et al. 2006; Li et al. 2007). In the auroral zone, scintillations mainly occur in the nighttime period

2 and exist at all local time in the polar cap region. A review of the auroral zone F region irregularities has been given by Rino et al. (1983), and a survey of theoretical aspects of irregularity formation is found in Keskinen and Ossakow (1983). Evidence indicates that the dayside auroral oval plays a major role in the formation of large-scale ionization structures (patches) in the polar ionosphere (Weber et al. 1984). These structures convect across the polar cap and cause destabilization of the plasma, then develop intermediate scale irregularities (responsible for scintillation of radio signals) by the action of the gradient drift instability mechanism (Tsunoda 1988). The destabilization process also includes the current convective and the Kelvin Helmholtz instability (Basu et al. 1986). It is established that precipitation of soft particles into the F region may play a direct role in irregularity formation (Basu et al. 1983; Kersley et al. 1988). In addition to patches, which convect into the polar cap, the sheared electric field in the cusp/cleft region is a viable source of localized intermediate scale irregularities (Basu et al. 1988). Since patches are associated with high plasma density, scintillations of satellite signals due to irregularities in the velocity shear region are expected to be weaker than patch-induced scintillations (Basu et al. 1998). When studying the morphology of scintillation and irregularity at polar latitudes, Aarons et al. (1981) investigated the UHF scintillation activity by using 250-MHz satellite beacon scintillation measurements at Thule, Greenland. They reported that the seasonal pattern of the polar cap irregularities shows very high intensity levels during the winter months and lower levels during the summer (sunlit) months. A significant result from this longterm study was the noticeable difference in occurrence depending on solar activity. This seasonal and solar cycle dependence at Thule was confirmed in a study by Basu et al. (1985), who also presented the measurements at Goose Bay, Labrador. By monitoring signals from the HILAT satellite at stations Sondre Stromfjord, Churchill and Tromoso, MacDougall (1990) investigated the distributions of scintillations over the northern polar region. They found two enhanced regions of scintillation occurrence. One enhanced region of phase scintillation activity was under the auroral oval. The other region is revealed most clearly by amplitude scintillations and maximizes in an annular region several degrees poleward of the auroral oval. The polar-orbiting multi-satellites of the Navy Navigation Satellite System (NNSS, 150 and 400 MHz signals) were also used by Kersley et al. (1988) in observations at Kiruna, Sweden. Their results were presented in the form of scintillation occurrence rates and relate to the season, the time of day and to geomagnetic activity, showed a premidnight maximum and more scintillation activity in summer and autumn than in winter and early spring. In a later paper by Kersley et al. (1995), attention was concentrated on measurements from Ny-Alesund, Norway. A marked difference in scintillation and irregularity occurrence with season was found. The seasonal pattern of occurrence shows a winter maximum. In the southern polar region, the amplitude scintillation and TEC measurements at Casey in Antarctica were performed by Beggs et al. (1994) and Tate and Essex (2001) using NNSS signals. The patches were observed in the polar cap region at various locations and times during the April August period of In recent years, observations of GPS scintillations at high latitudes were reported by many authors (e.g., De Franceschi et al. 2006; Meggs et al. 2008). Using GPS observations from 11 high-latitude stations, Aarons (1997) noted that phase fluctuation activity has a daily pattern mainly controlled by the motion of the receiver location into the auroral oval. Mitchell et al. (2005) found GPS amplitude and phase scintillation co-located with steep total electron content (TEC) gradient at the southwest of Svalbard during the Halloween storm of October Later, De Franceschi et al. (2008) examined the observations from a chain of GPS ionospheric scintillation and TEC receivers in Northern Europe, and investigated the dynamics of ionospheric plasma during the storm events of 30 October and 20 November A strong influence of IMF on the formation and movement of patches was reported. As mentioned previously, many studies on scintillation and irregularity occurrence have been performed in the Arctic or Antarctic regions, but little has been done regarding statistical studies of inter-hemispheric observations of GPS ionospheric scintillation, and there is no clear established pattern for the seasonal occurrence of irregularities in the polar cap. In 2007, two GPS receivers were established at Ny-Alesund [78.9 N, 11.9 E; 75.8 N corrected geomagnetic latitude (CGMLat)] and Larsemann Hills (69.4 S, 76.4 E; 74.6 S CGMLat) to study scintillation and irregularity characteristics. The two stations are nearly located at geomagnetic conjugate points. About 1 year data from both stations have been used in this paper to investigate the scintillation and irregularity characteristics with season and magnetic local time. We also analyze the dependence of scintillation occurrence on IMF B y and B z components at solar minimum. Experimental observations Ionospheric scintillation measurement was performed using the GPS Ionospheric Scintillation/TEC Monitor (GISTM), model GSV4004 (Van Dierendonck et al. 1993). The system is NovAtel s Euro4 dual-frequency receiver

3 version of the OEM4 card with special firmware, which was developed to maintain lock even under strong scintillation conditions. The amplitude scintillation was monitored by computing the S4 index, which is defined as the standard deviation of the received signal power normalized to the average signal power. It is calculated for each 1-minute period based on a 50-Hz sampling rate. The GISTM also computes the S4 index due to ambient noise in such a way that a corrected S4 index (without noise effects) can be computed (Van Dierendonck et al. 1993). Phase scintillation computation was accomplished by monitoring the r / index, the standard deviation of the detrended carrier phase and was computed over 1, 3, 10, 30 and 60 s intervals. A high-pass sixth-order Butterworth filter was used for detrending raw phase measurements. In the present paper, the corrected S4 index and the average value of 60-second r / are used in the following analyses. Although these scintillation indices have been widely used to monitor and measure the intensity of scintillation, one should keep in mind that the derivation of the phase scintillation index r / has many problems and its interpretation may be doubtful (Beach 2006). A series of experiments were set up to study the effects of cutoff frequency for amplitude and phase filtering (Forte 2005). Comprehensive discussion about the effects of filtering parameters on scintillation can be found in Forte and Radicella (2002, 2004). In this study, only the measurements of signals coming from satellites with an elevation angle greater than 30 and with a time of lock greater than 180 s were taken into account. The geographical locations of both stations are shown in the left panel of Fig. 1. The right panel is a polar plot of CGMLat against magnetic local time (MLT), in which the diurnal position of Ny-Alesund and Larsemann Hills are shown by solid and dash-solid circles at 75.8 N and 74.6 S CGMLat, respectively. A representation of the average position of Feldstein auroral oval for quiet geomagnetic conditions (Q = 3) is shown superposed on the plot (Feldstein 1963; Holzworth and Meng 1975). It can be seen that around magnetic noon both stations are under the cusp/cleft region, and on the night-side, the observations are within the low-latitude region of the polar cap. We should note that the positions of both stations Ny-Alesund and Larsemann Hills with respect to the auroral oval will change with season and magnetic activity. Cases of GPS ionospheric scintillation Figures 2 and 3 illustrate the scintillation and TEC parameters derived from measurements made at Ny-Alesund. The left panels of Fig. 2 show the variation of amplitude scintillation index S4 and phase scintillation index r / on August 4, From the left panels we can note that no amplitude and phase scintillation were observed. The lower value of scintillation index corresponds to the noise level. The middle and right panels indicate that the phase and amplitude scintillation events were observed on October 4 and November 6, 2007, respectively. The scintillation index is apparently larger than the noise level. The two cases were characterized by phase without amplitude scintillation and amplitude without phase scintillation (Fremouw et al. 1978). More details on the structures possibly causing scintillations are shown in Fig. 3. The left and right panels present the scintillation/tec measurements made by the satellites PRN 3 and 23, respectively. It was observed that the phase scintillation obtained from PRN 3 is co-located with the sudden TEC enhancement. The enhancement is located at Fig. 1 Geographical locations of Ny-Alesund and Larsemann Hills (left panel) and geometry of scintillation observations in the MLT and CGMLat polar coordinate system (right panel). The measurements were made from the Chinese Arctic Yellow River station (located at Ny-Alesund) and the Chinese Antarctic Zhongshan station (located at Larsemann Hills).The bold solid (75.8 N) and dash-solid (74.6 S) circles show the positions of the two stations, respectively. The superposed shadow is the average position of auroral oval (Q = 3; Feldstein 1963; Holzworth and Meng 1975)

4 Fig. 2 Amplitude and phase data from the GPS satellites viewed on August 4, October 4 and November 6, 2007 as recorded at Ny-Alesund. Amplitude and phase fluctuations are in noise level (left), phase scintillation was observed (r / [ 10 and 15 cut off angle middle), amplitude scintillation was observed (S4 [ 0.25 right) Fig. 3 Example of amplitude and phase scintillations measured from the GPS satellites PRN 3 and 23. The phase scintillation is co-located with the sudden TEC enhancements as shown in the left panels. The right panels indicate that there exists amplitude scintillation but no apparent phase scintillation and TEC fluctuations. The red asterisks in the bottom panels mark the scintillation occurrence above the threshold

5 about 75 N CGMLat as shown in the left bottom panel. The bold lines in the bottom panels show the GPS satellite tracks assuming a thin shell ionosphere at 350 km altitude. As Tsunoda (1988) suggested, the high-latitude large-scale plasma structures have been divided into four classes: (1) polar cap patches, (2) boundary blobs, (3) sun-aligned arcs and (4) auroral blobs. Here the increase and decrease of TEC probably signify the transit of polar cap patches across the GPS propagation path. The right panels show that when amplitude scintillation occurs, no apparent TEC fluctuation and phase scintillation exists. These phenomena are probably linked with the irregularity characteristics that produce scintillation. Since the magnitude of amplitude scintillation is dictated by the pffiffiffiffiffiffiffi electron density deviation (DN) of the Fresnel scale ð 2kz Þ; the irregularities are located along the ray path (Basu et al. 1998). For the GPS L1 frequency ( MHz, 0.19 m) and the slant range to an assumed phase screen height of 350 km (z), the Fresnel scale is about 370 m. Thus, the amplitude scintillation is determined by the strength of small-scale irregularities with hundreds to tens of meter in size. However, the phase scintillation is dominated by large-scale irregularity (Basu et al. 1999). The irregularity in anisotropy and the drift of the irregularity also impact the index (Beach 2006). During the period of Oct 4, 2007, no solar flare (X-ray and EUV radiation) event was observed. The present observations of amplitude scintillation without phase scintillation probably indicate that the small-scale irregularities, which produce the amplitude scintillation, transit away from the places of origin, where large-scale irregularities (patches) exist. The dominant mechanisms for patch formation are still unknown. Two of the most prominent mechanisms at present are sporadic chopping of a pre-existing tongue of high density plasma (Valladares et al. 1999), which lead to density depletions in a preexisting tongue of high density plasma entering the polar cap from noon collocated with jets of high plasma velocity, and sporadic injection of high density plasma (Lockwood and Carlson 1992), which lead to density enhancements associated with high plasma velocity flows. In the following paragraphs, we shall focus our attention on the statistics of scintillation and irregularity occurrence. The threshold value of 0.25 for S4 index and 10, 15 for r / index will be used. Scintillation statistics at Ny-Alesund and Larsemann Hills The scintillation measurements started in July 2007 at Ny- Alesund, and in March 2007 at Larsemann Hills. Unfortunately, a failure of power supply for the Larsemann Hills GPS receiver in December 2007 terminated the scintillation measurements. Thus, we used the amplitude and phase data from August 2007 to July 2008 for Ny-Alesund and March to November 2007 for Larsemann Hills in the present statistical study. A contour plot of the percent occurrence of scintillation is shown in Fig. 4. The left panels show the number of total data points (specified on the graph to give an idea of the size of the data base), the Fig. 4 Contour plots of percentage occurrence of amplitude (S4 [ 0.25) and phase scintillation (r / [ 15 and 10 ) as a function of corrected geomagnetic latitude and month for observations made at Ny-Alesund and Larsemann Hills

6 percent occurrence of amplitude and phase scintillation as a function of corrected geomagnetic latitude and month of observation at Ny-Alesund. A maximum occurrence of amplitude scintillation to the north of the station latitude can be seen in months 11 and 12. In view of phase scintillation activity with the threshold (r / [ 15 ), it mainly takes place in the months 10, 11 and 12. For the lower threshold of 10, the left bottom panel also shows that the scintillation is a winter phenomenon. The observations from Larsemann Hills are shown in the right panels of Fig. 4. For amplitude scintillation with the threshold S4 [ 0.25, the right second panel indicates that there is no scintillation activity. A maximum occurrence of phase scintillation activity (r / [ 15 ) exists in the months 5 and 6. The right bottom panel shows a strong maximum occurrence for months 5 and 6, and a moderate one for months 4 and 7 exceeding the threshold r / [ 10. Over all, two features can be noted from Fig. 4. The first one is that the occurrence level of phase scintillation is significantly higher than that for amplitude scintillation. This is consistent with observations at Hammerfest (Geo.Lon/Lat, 23.7 E/70.7 N). Considering every day of year 2002, Rodrigues et al. (2004) found that the GPS amplitude scintillation occurrence rates (S4 [ 0.5) rarely exceed 1%, however, strong phase scintillation above the threshold 0.6 occurred during more than 5% of the time. For auroral regions, Klobuchar (2002) also suggested that amplitude scintillation on the GPS L1 frequency does not seem to be a significant concern. The second notable feature is that phase scintillation mainly occurs in the local winter months for both stations, which are of little or no sunlight. Kersley et al. (1995) reported that there is no clear established pattern for the seasonal occurrence of irregularities in the polar cap. Besides many factors such as geographic location and control of geomagnetic conditions, some of the results with different seasonal pattern may be technique dependent. Similar seasonal dependence in scintillation occurrence with winter maximum has been noted by many authors who used the VHF/UHF signals (e.g., Aarons et al. 1981). Using 250-MHz satellite beacon scintillation measurements from Thule Air Base, Greenland, Aarons et al. (1981) reported that a seasonal pattern of the polar cap irregularities shows very high levels during the winter and lower levels during the summer months. They suggested that the seasonal variation of scintillation may be related to E layer conductivity changes caused by the presence or absence of sunlight at *100 km. The diurnal variation of amplitude and phase scintillation occurrence is illustrated in Fig. 5 and presented in polar form as a function of MLT and CGMLat from 70 to 90. The panels from top to bottom show the number of total data points, percent occurrence of amplitude and phase scintillation. From the left second panel, it can be noted that the occurrence of amplitude scintillation observed at Ny-Alesund maximizes in the magnetic afternoon sector. It shows the presence of 100-meter scale irregularities during daytime at 78 N CGMLat over the time interval of h MLT. For phase scintillation exceeding the threshold r / [ 15, high occurrence is found in the h, h and h MLT sector at Ny-Alesund. While at Larsemann Hills, the occurrence maximizes between h and h MLT. For the lower threshold of phase scintillation r / [ 10, the left bottom panel shows maximum occurrence centered around magnetic noon at Ny-Alesund. Larsemann Hills, the right bottom panel of Fig. 5, shows a band of high occurrence following the auroral oval from early morning to noon sector. Between 18 h and 23 h MLT, strong occurrence can also be noted. It can be seen from Fig. 1 that around magnetic noon Ny-Alesund and Larsemann Hills are under the cusp/cleft region with respect to the Q = 3 auroral oval. This possibly indicates that the observed maximum scintillation occurrence around the noon sector arising from irregularities caused by precipitation into the daytime cusp. The clouds of energetic particles ejected from the sun and carried in the solar wind envelope of the earth s magnetosphere can generate irregularities or increase the frequency of their occurrence in the ionosphere. Mangalev et al. (1994) found that energetic particles precipitating in the cusp region are able to influence the spatial distribution of the ionospheric parameters in the E and F regions. Dependence of scintillation on IMF B y and B z components The dependence of scintillation occurrence on magnetic activity was studied by using the interplanetary magnetic field (IMF) data. Because the lower occurrence level of amplitude scintillation and the IMF data were not yet available for July, 2008, attention is concentrated on phase scintillation up to June For this study, the 15-s IMF data from the ACE satellite are averaged over a 1-minute interval for comparing the scintillation occurrence above the threshold r / [ 15 during the different polarity of B y and B z components of IMF. The statistical dependence of scintillation activity on the polarity of the IMF B y and B z components is shown in Fig. 6. It displays the percentage occurrence seen at Ny-Alesund (left panels) and Larsemann Hills (right panels) on CGMLat versus MLT polar plots. For B z northward conditions B z [ 0, we can note from the top two panels that there is a tendency for Ny-Alesund scintillation to occur more frequently during the noon and midnight sectors. For Larsemann Hills, the scintillation occurrence shows a maximum from the early morning to the noon

7 Fig. 5 Percentage occurrence of amplitude (S4 [ 0.25) and phase scintillation (r / [ 15 and 10 ) as a function of CGMLat and MLT for observations made at Ny-Alesund and Larsemann Hills sector. In comparing the IMF B z northward and southward conditions, the left second panel illustrates that for B z southward conditions, a maximum scintillation occurrence exists during the period from later afternoon to sunset at Ny-Alesund; the associated scintillation occurrence level is apparently higher than that for B z northward conditions. For Larsemann Hills, the right second panel shows the scintillation occurrence is maximized through the evening from 18 h to 23 h MLT. The enhanced scintillation occurrence indicates that the dependence of scintillation on IMF B z shows a correlation with magnetic local time. When considering the scintillation dependence on IMF B y, the bottom four panels of Fig. 6 show clear evidence of significant differences in the occurrence characteristics of scintillation for positive and negative IMF B y. For Ny-Alesund observations, there is a relatively high

8 Fig. 6 Percentage occurrence of phase scintillation (r / [15 ) as a function of CGMLat and MLT for observations made at Ny-Alesund and Larsemann Hills during different IMF B y and B z conditions occurrence during negative IMF B y at later afternoon and post-midnight sectors, about from 16 to 19 h MLT and from 23 to 04 h MLT. There is also a difference shown by the right bottom two panels, for the positive and negative B y at Larsemann Hills. An enhanced scintillation occurrence during negative IMF B y is shown through the evening from 18 to 23 h MLT. Together with the IMF B y and B z components, the observations in the current work (Fig. 6) indicate that the dependence of scintillation occurrence on IMF components appears to be associated with magnetic local time. As Aarons (1997) suggested, phase fluctuation activity has a daily pattern mainly controlled by the motion of the receiver location into the auroral oval. The auroral oval expands equatorward with increasing magnetic

9 activity. Sandholt et al. (1998) have classified the dayside aurora into various types that depend on the IMF orientation and the magnetic local time of observation. For polar cap patches, the irregularities are most likely to occur when the Bz component of the interplanetary magnetic field (IMF) is southward, or when planetary magnetic index Kp [ 4. Here the Ny-Alesund and Larsemann Hills phase scintillations show IMF dependence at different MLT sectors. The difference may be associated with the positions of Ny-Alesund and Larsemann Hills under different geomagnetic conditions. Ny-Alesund is about 1 further polarward of the Larsemann Hills position so that under moderate or strong magnetic conditions, Ny-Alesund may be inside the polar cap a bit more than Larsemann Hills. Conclusions The measurements of GPS ionospheric scintillation and irregularity activities have been conducted at Ny-Alesund and Larsemann Hills, which are located at the daytime cusp and under the polar cap on the night-side with respect to the average position of the auroral oval (Q = 3). This paper focused on the investigations of GPS scintillation occurrence above specified thresholds for season, magnetic local time, and the dependence on polarity of IMF B y and B z components. The latitude/month plot illustrates the maximum occurrence of scintillation during the local winter months (10, 11 and 12 at Ny-Alesund, and 5, 6 at Larsemann Hills). This is shown to be consistent with the 250- MHz satellite beacon scintillation measurements from Thule Air Base, Greenland performed by Aarons et al. (1981). The E layer conductivity change caused by the absence of sunlight at *100 km in the winter months is a possible mechanism. The diurnal variation of phase scintillation occurrence is characterized by the higher occurrence during the h, h and h MLT sector at Ny-Alesund. The observations are similar to the results presented by Kersley et al. (1995). Using radio transmissions from NNSS satellites, they investigated the phase scintillation and irregularities at Ny-Alesund. A noon maximum occurrence that extends in a latitudinal belt into the afternoon and evening, and a highest level of occurrence during the pre-midnight sector in the polar cap was reported. At Larsemann Hills, the present work shows the enhanced scintillation is found in the h and h MLT sectors. The observed noon maximum scintillation occurrence possibly indicates that the irregularities producing scintillation may be caused by precipitation into the daytime cusp/cleft region. Under negative IMF B y and B z conditions, this paper performs a comparison of phase scintillation above the threshold 15 with the positive IMF B y and B z components. 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Adv Space Res 27(8): Tsunoda R (1988) High-Latitude F Region irregularities: a review and synthesis. Rev Geophys 26(4): Valladares CE, Alcaydé D, Rodriguez JV, Ruohoniemi JM, Van Eyken AP (1999) Observations of plasma density structures in association with the passage of traveling convection vortices and the occurrence of large plasma jets. Ann Geophysicae 14:1020 Van Dierendonck AJ, Hua Q, Klobuchar J (1993) Ionospheric scintillation monitoring using commercial single frequency C/A code receivers. In: Proceedings of ION GPS 93, Salt Lake City, UT, September, pp Weber E, Buchau J, Moore J, Sharber J, Livingston R, Winningham J, Reinisch B (1984) F Layer ionization patches in the Polar Cap. J Geophys Res 89(A3): Author Biographies Dr. Guozhu Li was born in September, 1980 in China. He received his BS from Wuhan University in 2002 and PhD degree from the Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences in During , he was a postdoctoral fellow. He devotes his time in studying the ionospheric physics using the VHF radar, Digisonde, GPS receiver, in-situ satellite, etc. Prof. Baiqi Ning was born in April, 1957 in China. He received his BS from Wuhan University in 1981 and PhD degree from the Wuhan Institute of Physics, Chinese Academy of Sciences in He has been researching in ionospheric radio probing and radio wave propagation and has published more than 80 papers. Now he is a fulltime professor in the Institute of Geology and Geophysics, Chinese Academy of Sciences.

11 Dr. Zhipeng Ren was born in October, 1982 in China. He received his BS from University of Science and Technology of China (USTC) in 2004 and PhD degree from the Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences in Now, he is a postdoctoral fellow. He devotes his time in studying the ionospheric/ thermospheric physics. Dr. Lianhuan Hu was born in April, 1982 in China. He received his BS from Wuhan University in 2004 and MS degree from the Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences in He devotes his time in studying the ionospheric physics.