Statistics of GPS Ionospheric Scintillation and Irregularities Over Polar Regions at Solar Minimum

GPS Solut DOI 10.1007/s10291-009-0156-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 charac- Introduction teristic of GPS ionospheric scintillation and irregularity in the polar latitude is presented. These measurements were Sometimes when a radio signal acts on the disturbed ion- made at Ny-Alesund, Svalbard [78.9°N, 11.9°E; 75.8°N osphere, the received signal will show rapid ﬂuctuations in corrected geomagnetic latitude (CGMLat)] and Larsemann amplitude and phase that are not consistent with the source Hills, East Antarctica (69.4°S, 76.4°E; 74.6°S CGMLat) strength or modulation. These ﬂuctuations of the radio during 2007–2008. It is found that the GPS phase scintil- signals are known as scintillations. It is well known that lation and irregularity activity mainly takes place in the ionospheric scintillation has the potential to affect Global months 10, 11 and 12 at Ny-Alesund, and in the months 5, Navigation Satellite System (GNSS) receivers in a number 6 at Larsemann Hills. The seasonal pattern of phase scin- of ways, from degradation of accuracy such as the range tillation with respect to the station indicates that the GPS errors, to the loss of signal tracking. Required levels of phase scintillation occurrence is a local winter phenome- accuracy and availability may not be met during the non, which shows consistent results with past studies of occurrence of scintillation, compromising positioning and 250 MHz satellite beacon measurements. The occurrence navigation applications (Aquino et al. 2005). Since iono- rates of GPS amplitude scintillation at the two stations are spheric scintillation can cause considerable communication below 1%. A comparison with the interplanetary magnetic hazards on radio systems and is therefore of great practical

field (IMF) By and Bz components shows that the phase interest (Banerjee et al. 1992), it is generally recognized scintillation occurrence level is higher during the period that further research about scintillation and irregularity from later afternoon to sunset (16–19 h) at Ny-Alesund, producing scintillation is required. and from sunset to pre-midnight (18–23 h) at Larsemann Over the past four decades, a great deal of research has Hills for negative IMF components. The findings seem to revealed that ionospheric scintillation is most likely to indicate that the dependence of scintillation and irregularity occur in equatorial and auroral regions. At low latitudes, occurrence on geomagnetic activity appears to be associ- the scintillation is primarily controlled by increasing ated with the magnetic local time (MLT). irregularities over the magnetic equator. After sunset, when the eastward electric field is enhanced, irregular plasma Keywords GPS Ionospheric scintillation density depletions are generated on the bottom-side of the Polar latitude irregularity IMF 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 low- latitude ionospheric scintillations and irregularities are G. Li (&) B. Ning Z. Ren L. Hu observed in the pre-midnight period, and have been sta- Beijing National Observatory of Space Environment, tistically studied using ground-based and in situ satellite Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China measurements (Su et al. 2006; Li et al. 2007). In the auroral e-mail: [email protected] zone, scintillations mainly occur in the nighttime period 123 GPS Solut and exist at all local time in the polar cap region. A review later paper by Kersley et al. (1995), attention was con- of the auroral zone F region irregularities has been given by centrated on measurements from Ny-Alesund, Norway. A Rino et al. (1983), and a survey of theoretical aspects of marked difference in scintillation and irregularity occur- irregularity formation is found in Keskinen and Ossakow rence with season was found. The seasonal pattern of (1983). Evidence indicates that the dayside auroral oval occurrence shows a winter maximum. plays a major role in the formation of large-scale ionization In the southern polar region, the amplitude scintillation structures (patches) in the polar ionosphere (Weber et al. and TEC measurements at Casey in Antarctica were per- 1984). These structures convect across the polar cap and formed by Beggs et al. (1994) and Tate and Essex (2001) cause destabilization of the plasma, then develop inter- using NNSS signals. The patches were observed in the mediate scale irregularities (responsible for scintillation of polar cap region at various locations and times during the radio signals) by the action of the gradient drift instability April–August period of 1994–1995. mechanism (Tsunoda 1988). The destabilization process In recent years, observations of GPS scintillations at also includes the current convective and the Kelvin– high latitudes were reported by many authors (e.g., De Helmholtz instability (Basu et al. 1986). It is established Franceschi et al. 2006; Meggs et al. 2008). Using GPS that precipitation of soft particles into the F region may observations from 11 high-latitude stations, Aarons (1997) play a direct role in irregularity formation (Basu et al. noted that phase fluctuation activity has a daily pattern 1983; Kersley et al. 1988). In addition to patches, which mainly controlled by the motion of the receiver location convect into the polar cap, the sheared electric field in the into the auroral oval. Mitchell et al. (2005) found GPS cusp/cleft region is a viable source of localized interme- amplitude and phase scintillation co-located with steep diate scale irregularities (Basu et al. 1988). Since patches total electron content (TEC) gradient at the southwest of are associated with high plasma density, scintillations of Svalbard during the Halloween storm of October 2003. satellite signals due to irregularities in the velocity shear Later, De Franceschi et al. (2008) examined the observa- region are expected to be weaker than patch-induced tions from a chain of GPS ionospheric scintillation and scintillations (Basu et al. 1998). TEC receivers in Northern Europe, and investigated the When studying the morphology of scintillation and dynamics of ionospheric plasma during the storm events of irregularity at polar latitudes, Aarons et al. (1981) inves- 30 October and 20 November 2003. A strong influence of tigated the UHF scintillation activity by using 250-MHz IMF on the formation and movement of patches was satellite beacon scintillation measurements at Thule, reported. Greenland. They reported that the seasonal pattern of the As mentioned previously, many studies on scintillation polar cap irregularities shows very high intensity levels and irregularity occurrence have been performed in the during the winter months and lower levels during the Arctic or Antarctic regions, but little has been done summer (sunlit) months. A significant result from this long- regarding statistical studies of inter-hemispheric observa- term study was the noticeable difference in occurrence tions of GPS ionospheric scintillation, and there is no clear depending on solar activity. This seasonal and solar cycle established pattern for the seasonal occurrence of irregu- dependence at Thule was confirmed in a study by Basu larities in the polar cap. In 2007, two GPS receivers were et al. (1985), who also presented the measurements at established at Ny-Alesund [78.9°N, 11.9°E; 75.8°N cor- Goose Bay, Labrador. By monitoring signals from the rected geomagnetic latitude (CGMLat)] and Larsemann HILAT satellite at stations Sondre Stromfjord, Churchill Hills (69.4°S, 76.4°E; 74.6°S CGMLat) to study scintilla- and Tromoso, MacDougall (1990) investigated the distri- tion and irregularity characteristics. The two stations are butions of scintillations over the northern polar region. nearly located at geomagnetic conjugate points. About They found two enhanced regions of scintillation occur- 1 year data from both stations have been used in this paper rence. One enhanced region of phase scintillation activity to investigate the scintillation and irregularity characteris- was under the auroral oval. The other region is revealed tics with season and magnetic local time. We also analyze most clearly by amplitude scintillations and maximizes in the dependence of scintillation occurrence on IMF By and an annular region several degrees poleward of the auroral Bz components at solar minimum. oval. The polar-orbiting multi-satellites of the Navy Nav- igation Satellite System (NNSS, 150 and 400 MHz signals) were also used by Kersley et al. (1988) in observations at Experimental observations Kiruna, Sweden. Their results were presented in the form of scintillation occurrence rates and relate to the season, the Ionospheric scintillation measurement was performed time of day and to geomagnetic activity, showed a pre- using the GPS Ionospheric Scintillation/TEC Monitor midnight maximum and more scintillation activity in (GISTM), model GSV4004 (Van Dierendonck et al. 1993). summer and autumn than in winter and early spring. In a The system is NovAtel’s Euro4 dual-frequency receiver 123 GPS Solut version of the OEM4 card with special firmware, which 75.8°N and 74.6°S CGMLat, respectively. A representation was developed to maintain lock even under strong scintil- of the average position of Feldstein auroral oval for quiet lation conditions. The amplitude scintillation was moni- geomagnetic conditions (Q = 3) is shown superposed on tored by computing the S4 index, which is defined as the the plot (Feldstein 1963; Holzworth and Meng 1975). It can standard deviation of the received signal power normalized be seen that around magnetic noon both stations are under to the average signal power. It is calculated for each the cusp/cleft region, and on the night-side, the observa- 1-minute period based on a 50-Hz sampling rate. The tions are within the low-latitude region of the polar cap. GISTM also computes the S4 index due to ambient noise in We should note that the positions of both stations such a way that a corrected S4 index (without noise effects) Ny-Alesund and Larsemann Hills with respect to the can be computed (Van Dierendonck et al. 1993). Phase auroral oval will change with season and magnetic activity. scintillation computation was accomplished by monitoring the r/ index, the standard deviation of the detrended car- rier phase and was computed over 1, 3, 10, 30 and 60 s Cases of GPS ionospheric scintillation intervals. A high-pass sixth-order Butterworth filter was used for detrending raw phase measurements. In the pres- Figures 2 and 3 illustrate the scintillation and TEC ent paper, the corrected S4 index and the average value of parameters derived from measurements made at Ny-Ales-

60-second r/ are used in the following analyses. und. The left panels of Fig. 2 show the variation of Although these scintillation indices have been widely amplitude scintillation index S4 and phase scintillation used to monitor and measure the intensity of scintillation, index r/ on August 4, 2007. From the left panels we can one should keep in mind that the derivation of the phase note that no amplitude and phase scintillation were scintillation index r/ has many problems and its interpre- observed. The lower value of scintillation index corre- tation may be doubtful (Beach 2006). A series of experi- sponds to the noise level. The middle and right panels ments were set up to study the effects of cutoff frequency indicate that the phase and amplitude scintillation events for amplitude and phase ﬁltering (Forte 2005). Compre- were observed on October 4 and November 6, 2007, hensive discussion about the effects of ﬁltering parameters respectively. The scintillation index is apparently larger on scintillation can be found in Forte and Radicella (2002, than the noise level. The two cases were characterized by 2004). In this study, only the measurements of signals ‘‘phase without amplitude’’ scintillation and ‘‘amplitude coming from satellites with an elevation angle greater than without phase’’ scintillation (Fremouw et al. 1978). More 30° and with a time of lock greater than 180 s were taken details on the structures possibly causing scintillations are into account. The geographical locations of both stations shown in Fig. 3. The left and right panels present the are shown in the left panel of Fig. 1. The right panel is a scintillation/TEC measurements made by the satellites polar plot of CGMLat against magnetic local time (MLT), PRN 3 and 23, respectively. It was observed that the phase in which the diurnal position of Ny-Alesund and Larse- scintillation obtained from PRN 3 is co-located with the mann Hills are shown by solid and dash-solid circles at sudden TEC enhancement. The enhancement is located at

Fig. 1 Geographical locations of Ny-Alesund and Larsemann Hills Larsemann Hills).The bold solid (75.8°N) and dash-solid (74.6°S) (left panel) and geometry of scintillation observations in the MLT and circles show the positions of the two stations, respectively. The CGMLat polar coordinate system (right panel). The measurements superposed shadow is the average position of auroral oval (Q = 3; were made from the Chinese Arctic Yellow River station (located at Feldstein 1963; Holzworth and Meng 1975) Ny-Alesund) and the Chinese Antarctic Zhongshan station (located at

123 GPS Solut

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

123 GPS Solut about 75°N CGMLat as shown in the left bottom panel. exist. The dominant mechanisms for patch formation are The bold lines in the bottom panels show the GPS satellite still unknown. Two of the most prominent mechanisms at tracks assuming a thin shell ionosphere at 350 km altitude. present are sporadic chopping of a pre-existing tongue of As Tsunoda (1988) suggested, the high-latitude large-scale high density plasma (Valladares et al. 1999), which lead to plasma structures have been divided into four classes: (1) density depletions in a preexisting tongue of high density polar cap patches, (2) boundary blobs, (3) sun-aligned arcs plasma entering the polar cap from noon collocated with and (4) auroral blobs. Here the increase and decrease of jets of high plasma velocity, and sporadic injection of high TEC probably signify the transit of polar cap patches density plasma (Lockwood and Carlson 1992), which lead across the GPS propagation path. The right panels show to density enhancements associated with high plasma that when amplitude scintillation occurs, no apparent TEC velocity flows. fluctuation and phase scintillation exists. These phenomena In the following paragraphs, we shall focus our attention are probably linked with the irregularity characteristics that on the statistics of scintillation and irregularity occurrence. produce scintillation. Since the magnitude of amplitude The threshold value of 0.25 for S4 index and 10°,15° for scintillation is dictated by thepffiffiffiffiffiffiffi electron density deviation r/ index will be used. (DN) of the Fresnel scale ð 2kzÞ; the irregularities are located along the ray path (Basu et al. 1998). For the GPS L1 frequency (1575.42 MHz, 0.19 m) and the slant range Scintillation statistics at Ny-Alesund to an assumed phase screen height of 350 km (z), the and Larsemann Hills Fresnel scale is about 370 m. Thus, the amplitude scintillation is determined by the strength of small-scale irregu- The scintillation measurements started in July 2007 at Ny- larities with hundreds to tens of meter in size. However, the Alesund, and in March 2007 at Larsemann Hills. Unfor- phase scintillation is dominated by large-scale irregularity tunately, a failure of power supply for the Larsemann Hills (Basu et al. 1999). The irregularity in anisotropy and the GPS receiver in December 2007 terminated the scintilla- drift of the irregularity also impact the index (Beach 2006). tion measurements. Thus, we used the amplitude and phase During the period of Oct 4, 2007, no solar flare (X-ray and data from August 2007 to July 2008 for Ny-Alesund and EUV radiation) event was observed. The present observa- March to November 2007 for Larsemann Hills in the tions of amplitude scintillation without phase scintillation present statistical study. A contour plot of the percent probably indicate that the small-scale irregularities, which occurrence of scintillation is shown in Fig. 4. The left produce the amplitude scintillation, transit away from the panels show the number of total data points (specified on places of origin, where large-scale irregularities (patches) 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

123 GPS Solut percent occurrence of amplitude and phase scintillation as a noted that the occurrence of amplitude scintillation function of corrected geomagnetic latitude and month of observed at Ny-Alesund maximizes in the magnetic after- observation at Ny-Alesund. A maximum occurrence of noon sector. It shows the presence of 100-meter scale amplitude scintillation to the north of the station latitude irregularities during daytime at 78°N CGMLat over the can be seen in months 11 and 12. In view of phase scin- time interval of 11–18 h MLT. For phase scintillation tillation activity with the threshold (r/ [ 15°), it mainly exceeding the threshold r/ [ 15°, high occurrence is takes place in the months 10, 11 and 12. For the lower found in the 08–13 h, 16–18 h and 23–02 h MLT sector at threshold of 10°, the left bottom panel also shows that the Ny-Alesund. While at Larsemann Hills, the occurrence scintillation is a winter phenomenon. maximizes between 05–11 h and 19–22 h MLT. For the

The observations from Larsemann Hills are shown in the lower threshold of phase scintillation r/ [ 10°, the left right panels of Fig. 4. For amplitude scintillation with the bottom panel shows maximum occurrence centered around threshold S4 [ 0.25, the right second panel indicates that magnetic noon at Ny-Alesund. Larsemann Hills, the right there is no scintillation activity. A maximum occurrence of bottom panel of Fig. 5, shows a band of high occurrence phase scintillation activity (r/ [ 15°) exists in the months following the auroral oval from early morning to noon 5 and 6. The right bottom panel shows a strong maximum sector. Between 18 h and 23 h MLT, strong occurrence can occurrence for months 5 and 6, and a moderate one for also be noted. It can be seen from Fig. 1 that around months 4 and 7 exceeding the threshold r/ [ 10°. Over all, magnetic noon Ny-Alesund and Larsemann Hills are under two features can be noted from Fig. 4. The first one is that the cusp/cleft region with respect to the Q = 3 auroral the occurrence level of phase scintillation is significantly oval. This possibly indicates that the observed maximum higher than that for amplitude scintillation. This is con- scintillation occurrence around the noon sector arising sistent with observations at Hammerfest (Geo.Lon/Lat, from irregularities caused by precipitation into the daytime 23.7°E/70.7°N). Considering every day of year 2002, cusp. The clouds of energetic particles ejected from the sun Rodrigues et al. (2004) found that the GPS amplitude and carried in the solar wind envelope of the earth’s scintillation occurrence rates (S4 [ 0.5) rarely exceed 1%, magnetosphere can generate irregularities or increase the however, strong phase scintillation above the threshold 0.6 frequency of their occurrence in the ionosphere. Mangalev occurred during more than 5% of the time. For auroral et al. (1994) found that energetic particles precipitating in regions, Klobuchar (2002) also suggested that amplitude the cusp region are able to influence the spatial distribution scintillation on the GPS L1 frequency does not seem to be a of the ionospheric parameters in the E and F regions. 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 Dependence of scintillation et al. (1995) reported that there is no clear established on IMF By and Bz components pattern for the seasonal occurrence of irregularities in the polar cap. Besides many factors such as geographic loca- The dependence of scintillation occurrence on magnetic tion and control of geomagnetic conditions, some of the activity was studied by using the interplanetary magnetic results with different seasonal pattern may be technique field (IMF) data. Because the lower occurrence level of dependent. Similar seasonal dependence in scintillation amplitude scintillation and the IMF data were not yet occurrence with winter maximum has been noted by many available for July, 2008, attention is concentrated on phase authors who used the VHF/UHF signals (e.g., Aarons et al. scintillation up to June 2008. For this study, the 15-s IMF 1981). Using 250-MHz satellite beacon scintillation mea- data from the ACE satellite are averaged over a 1-minute surements from Thule Air Base, Greenland, Aarons et al. interval for comparing the scintillation occurrence above

(1981) reported that a seasonal pattern of the polar cap the threshold r/ [ 15° during the different polarity of By irregularities shows very high levels during the winter and and Bz components of IMF. lower levels during the summer months. They suggested The statistical dependence of scintillation activity on the that the seasonal variation of scintillation may be related to polarity of the IMF By and Bz components is shown in E layer conductivity changes caused by the presence or Fig. 6. It displays the percentage occurrence seen at absence of sunlight at *100 km. Ny-Alesund (left panels) and Larsemann Hills (right pan-

The diurnal variation of amplitude and phase scintilla- els) on CGMLat versus MLT polar plots. For Bz northward tion occurrence is illustrated in Fig. 5 and presented in conditions Bz [ 0, we can note from the top two panels polar form as a function of MLT and CGMLat from 70° to that there is a tendency for Ny-Alesund scintillation to 90°. The panels from top to bottom show the number of occur more frequently during the noon and midnight sec- total data points, percent occurrence of amplitude and tors. For Larsemann Hills, the scintillation occurrence phase scintillation. From the left second panel, it can be shows a maximum from the early morning to the noon 123 GPS Solut

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 Bz northward and southward from 18 h to 23 h MLT. The enhanced scintillation conditions, the left second panel illustrates that for Bz occurrence indicates that the dependence of scintillation on southward conditions, a maximum scintillation occurrence IMF Bz shows a correlation with magnetic local time. exists during the period from later afternoon to sunset at When considering the scintillation dependence on IMF By, Ny-Alesund; the associated scintillation occurrence level is the bottom four panels of Fig. 6 show clear evidence apparently higher than that for Bz northward conditions. of signiﬁcant differences in the occurrence characteris- For Larsemann Hills, the right second panel shows the tics of scintillation for positive and negative IMF By. scintillation occurrence is maximized through the evening For Ny-Alesund observations, there is a relatively high 123 GPS Solut

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 By and Bz conditions

occurrence during negative IMF By at later afternoon and components, the observations in the current work (Fig. 6) post-midnight sectors, about from 16 to 19 h MLT and indicate that the dependence of scintillation occurrence on from 23 to 04 h MLT. There is also a difference shown by IMF components appears to be associated with magnetic the right bottom two panels, for the positive and negative local time. As Aarons (1997) suggested, phase ﬂuctuation

By at Larsemann Hills. An enhanced scintillation occur- activity has a daily pattern mainly controlled by the motion rence during negative IMF By is shown through the evening of the receiver location into the auroral oval. The auroral from 18 to 23 h MLT. Together with the IMF By and Bz oval expands equatorward with increasing magnetic 123 GPS Solut activity. Sandholt et al. (1998) have classiﬁed the dayside The results indicate that the phase scintillation occurrence aurora into various types that depend on the IMF orienta- level is found to be higher during the period from later tion and the magnetic local time of observation. For polar afternoon to sunset (16–19 h MLT) at Ny-Alesund, and cap patches, the irregularities are most likely to occur when from sunset to pre-midnight (18–23 h MLT) at Larsemann the Bz component of the interplanetary magnetic ﬁeld Hills. The enhanced scintillation occurrence indicates that (IMF) is southward, or when planetary magnetic index the dependence of scintillation on IMF components shows Kp [ 4. Here the Ny-Alesund and Larsemann Hills phase a correlation with magnetic local time. This is possibly scintillations show IMF dependence at different MLT linked with the IMF dependence of polar cap patches. sectors. The difference may be associated with the positions of Ny-Alesund and Larsemann Hills under different Acknowledgments This work was supported by the Chinese Arctic geomagnetic conditions. Ny-Alesund is about 1° further and Antarctic Administration (20070209), National Natural Science Foundation of China (40774091, 40574072) and National Important polarward of the Larsemann Hills position so that under Basic Research Project (2006CB806306). The authors acknowledge moderate or strong magnetic conditions, Ny-Alesund may CDAWeb for providing the IMF datasets. be inside the polar cap a bit more than Larsemann Hills.

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Geomagn Aeron SSSR 3:227–239 10.1029/2005JA011330 Forte B (2005) Optimum detrending of raw GPS data for scintillation Tate BS, Essex EA (2001) Investigation of irregularities in the measurements at auroral latitudes. J Atmos Solar-Terr Phys Southern high latitude ionosphere. Adv Space Res 27(8):1385– 67:1100–1109 1389 Forte B, Radicella SM (2002) Problems in data treatment for Tsunoda R (1988) High-Latitude F Region irregularities: a review and ionospheric scintillation measurements. Radio Sci 37(6):1096. synthesis. Rev Geophys 26(4):719–760 doi:10.1029/2001RS002508 Valladares CE, Alcayde´ D, Rodriguez JV, Ruohoniemi JM, Van Forte B, Radicella SM (2004) Geometrical control of scintillation Eyken AP (1999) Observations of plasma density structures in indices: what happens for GPS satellites. Radio Sci 39:RS5014. association with the passage of traveling convection vortices and doi:10.1029/2002RS002852 the occurrence of large plasma jets. 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Radio Sci 23(3):320–330 Author Biographies Kersley L, Russell C, Rice D (1995) Phase scintillation and irregularities in the northern polar ionosphere. Radio Sci Dr. Guozhu Li was born in 30(3):619–629 September, 1980 in China. He Keskinen M, Ossakow S (1983) Theories of high-latitude ionospheric received his BS from Wuhan irregularities: a review. Radio Sci 18(6):1077–1091 University in 2002 and PhD Klobuchar J (2002) Ionospheric research issues for SBAS—A White degree from the Wuhan Institute Paper. SBAS Ionospheric Working Group, Ver 225 of Physics and Mathematics, Li G, Ning B, Liu L, Ren Z, Lei J, Su S-Y (2007) The correlation of Chinese Academy of Sciences longitudinal/seasonal variations of evening equatorial pre-rever- in 2007. During 2007–2009, he sal drift and of plasma bubbles. Ann Geophys 25:2571–2578 was a postdoctoral fellow. He Lockwood M, Carlson HC Jr (1992) Production of polar cap electron devotes his time in studying the density patches by transient magnetopause reconnection. Geo- ionospheric physics using the phys Res Lett 19:1731 VHF radar, Digisonde, GPS MacDougall J (1990) Distribution of irregularities in the northern receiver, in-situ satellite, etc. polar region determined from HILAT observations. Radio Sci 25(2):115–124 Mangalev VS, Krisvilev VN, Mingaleva GI (1994) Precipitating soft Prof. Baiqi Ning was born in corpuscle influence on the parameters of the ionosphere E and F April, 1957 in China. He regions at the cusp region. Geomagn Aeron 34:200–204 received his BS from Wuhan Meggs RW, Mitchell CN, Honary F (2008) GPS scintillation over the University in 1981 and PhD European Arctic during the November 2004 storms. GPS Solut degree from the Wuhan Institute 12:281–287. doi:10.1007/s10291-008-0090-3 of Physics, Chinese Academy of Mitchell CN, Alfonsi L, De Franceschi G, Lester M, Romano V, Sciences in 1993. He has been Wernik AW (2005) GPS TEC and scintillation measurements researching in ionospheric radio from the polar ionosphere during the October 2003 storm. probing and radio wave propa- Geophys Res Lett 32:L12S03. doi:10.1029/2004GL021644 gation and has published more Rino CL, Livingston RC, Tsunoda RT, Robinson RM, Vickrey JF, than 80 papers. Now he is a full- Senior C, Cousins MD, Owen J, Klobuchar JA (1983) Recent time professor in the Institute of studies of the structure and morphology of auroral zone F region Geology and Geophysics, Chi- irregularities. Radio Sci 18:1167–1180 nese Academy of Sciences. Rodrigues FS, Aquino MHO, Dodson A, Moore T, Waugh S (2004) Statistical analysis of GPS ionospheric scintillation and short-

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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 2009. 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 2007. He devotes his time in studying the ionospheric physics.

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