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A case study of ionospheric storm effects in the Chinese sector during the October 2013 geomagnetic storm
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ScienceDirect Advances in Space Research xxx (2015) xxx–xxx www.elsevier.com/locate/asr
A case study of ionospheric storm effects in the Chinese sector during the October 2013 geomagnetic storm Tian Mao a,⇑, Lingfeng Sun b,⇑, Lianhuan Hu b, Yungang Wang a, Zhijun Wang b b
a Key Laboratory of Space Weather, National Center for Space Weather, China Meteorological Administration, Beijing 100081, China Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
Received 5 February 2015; received in revised form 27 May 2015; accepted 30 May 2015
Abstract In this study, we investigate the ionospheric storm effects in the Chinese sector during 2 October 2013 geomagnetic storm. The TEC map over China sector (1° 1°) and eight ionosondes data along the longitude of 110°E are used to show significant positive ionospheric phases (enhancements in TEC and ionospheric peak electron density NmF2) in the high-middle latitude region and the negative effects at the low latitude and equatorial region during the storm. A wave structure with periods about 1–2 h and horizontal speed about 680 m/s, propagating from the high latitudes to the low latitudes is observed in electron densities within the height region from 200 to 400 km, which is caused by the combined effects of neutral wind and the large-scale traveling disturbances (LSTIDs). In the low latitude regions, compared with those in the quiet day, the ionospheric peak heights of the F2 layer (hmF2) in the storm day obviously increase accompanying a notably decrease in TEC and NmF2, which might be as a result of the eastward prompt penetration electric field (PPEF) evidenced by the two magnetometers and the subsequent westward disturbance dynamo electric fields (DDEF). The storm-time TEC enhancement mainly occurs in the topside ionosphere, as revealed from the topside TEC, bottomside TEC and GPS TEC. Ó 2015 COSPAR. Published by Elsevier Ltd. All rights reserved.
Keywords: Ionospheric storm; Neutral wind; LSTIDs; PPEF; DDEF
1. Introduction The ionospheric storm induced by geomagnetic storms is one of the most complicated space weather phenomena. During the geomagnetic storm, the solar wind energy impulsively or continually injects into the polar regions of the earth and leads to large changes in the chemistry and dynamics of the high latitude ionosphere–thermosphere (I–T), which will affect the global ionospheric electron density distribution through various dynamic and electrodynamic processes. According to the increasement ⇑ Corresponding authors at: Key Laboratory of Space Weather, National Center for Space Weather, China Meteorological Administration, No. 46 Zhongguancun South Str., Beijing 100081, China (T. Mao). E-mail addresses: [email protected] (T. Mao), sunlingfeng@mail. iggcas.ac.cn (L. Sun).
or the decreasement of electron density in the storm time relative to those in the quiet time, the ionospheric storms can be classified into positive storms or negative storms. Many researchers have investigated the ionospheric storm characteristics and analyzed the physical mechanism in terms of observations and theoretical models since the conception of ionospheric storm has been convinced (Somayajulu, 1960; Zhao et al., 2005, 2008; Mendillo, 2006; Burns et al., 2007; Lei et al., 2008a,b, 2014; Pedatella et al., 2009; Yuan et al., 2009; Liu et al., 2014). Pro¨lss (1993a,b) proposed that the observed daytime positive storm effects, especially during the initial phase, were caused by traveling atmospheric disturbances (TADs) and suggested that the electrodynamics mechanism was not as important as thermospheric dynamics. Hyosub et al. (2003) investigated the ionospheric response to the
http://dx.doi.org/10.1016/j.asr.2015.05.045 0273-1177/Ó 2015 COSPAR. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Mao, T., et al. A case study of ionospheric storm effects in the Chinese sector during the October 2013 geomagnetic storm. Adv. Space Res. (2015), http://dx.doi.org/10.1016/j.asr.2015.05.045
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magnetic storm using the GPS TEC and DMSP data. They pointed out that negative ionospheric storm and the positive ionospheric storm were dominant in the summer hemisphere and in the winter hemisphere, respectively. Liu et al. (2002, 2004) explored the storm-time electric field and composition changes effects on the low latitude ionosphere during two storms in 2000. Lei et al. (2008b) investigated the thermospheric and ionospheric response to the 14–15 December 2006 geomagnetic storm using the Coupled Magnetosphere Ionosphere Thermosphere (CMIT) 2.0 model. They recognized that the electric fields played a dominant role in generating the observed ionospheric positive storm effect in the American sector during the initial phase. Zhao et al. (2009) analyzed the ionospheric storm effect based on the ionosonde chain and GPS network and GUVI data in the west Pacific area during the intense geomagnetic storm on 13–17 April 2006. They recognized that periodic wave structures in middle-low latitude foF2 in the morning sector on 14 April should be caused by TADs with phase propagation velocities ranging 400–800 m/s, while in the afternoon and nighttime, the positive phase would be most probably caused by the combination effects of the enhanced equatorward winds and disturbed electric fields. Shweta et al. (2012) studied the low latitude ionospheric response during the 24 August 2005 geomagnetic storm using the GPS TEC and ionosondes data. The TEC enhancements were attributed to the prompt penetration electric fields. D’ujanga et al. (2013) discussed the effects of the geomagnetic storm during 24– 25 October 2011 in East Africa. Storm time reductions in the diurnal TEC at the two stations were observed, which had been attributed to the uplift of the ionospheric plasma followed by the poleward transportation from equator region by diffusion along magnetic field lines. Liu et al. (2014) used the observation data from GPS, ionosonde, C/NOFS, magnetometer and GUVI to investigate the ionospheric storm during the 14–17 July 2012 geomagnetic storm event. They concluded that, in the East Asian/Australian sector, the three bands of increments and separated by weak depressions in the equatorial ionospheric anomaly (EIA) crest regions were caused by both disturbance dynamo electric field (DDEF) and equatorward neutral winds. Although many researchers analyzed the ionospheric response to the magnetic storm by case studies and numerical modeling, there are still many questions and contradictions in understanding of some aspects of ionospheric storm. The objective of the present paper is to analyze the altitudinal dependence of ionospheric response to different processes such as electric field, neutral wind changes induced by the 2 October 2013 geomagnetic storm on the basis of observation data in the Chinese sector. The rests of this paper are arranged as follows. Section 2 describes the data sources including the grid TEC with 1° 1° bin, eight ionosondes along the 110°E and two magnetometers located in Da Lat (11.94°N, 108.48°E) and Sanya (18.34°N, 109.62°E). Section 3 shows the ionospheric
storm characteristics. The discussion and the conclusions are given in the last two parts. 2. Data sources The observations from the GPS TEC, ionosondes and magnetometers are used to investigate the ionosphere effects induced by the 2 October 2013 geomagnetic storm. The GPS TEC data are from the ground-based high-resolution TEC tracking network of Chinese Meteorology Administrator. The TEC tracking network consists of about 800 GPS stations in China. Slant TEC observations are used to convert to vertical TEC data of 1° grid via least squares fits and nearest neighbor interpolation method over the China region. An automated technique for processing GPS data from multiple receivers was developed by Mao et al. (2008). The horizontal resolution is 1° and the temporal resolution is an hour. The data observed from the eight ionosondes (Mohe (52.00°N, 122.52°E), Beijing (40.30°N, 116.20°E), Xian (34.08°N, 108.88°E), Wuhan (30.50°N, 114.40°E), Shaoyang (27.1°N, 111.3°E), Nanning (22.70°N, 109.25°E), Fuke (19.40°N, 109.00°E) and Sanya (18.34°N, 109.62°E)) are used in this paper. The ionosonde data at Mohe, Wuhan, and Fuke are obtained from the Data Center of Meridian Project, data at Beijing, Shaoyang and Sanya are downloaded from the Low Digital ionogram Database (Reinisch et al., 2009) and Institute of Geology and Geophysics of Chinese Academy and Sciences (IGGCAS), and data at Nanning and Xian are from the National Center for Space Weather,Chinese Meteorology Administrator. All ionograms are manually scaled by using the SAO Explorer software package. Two magnetometers provide an opportunity to estimate the daytime equatorial electrojet and the intensity of ionospheric F region E B vertical drift (Anderson et al., 2002; Liu et al., 2014). The difference in the geomagnetic horizontal component (dHDLT-SAY) between Da Lat (11.94°N, 108.48°E) and Sanya (18.34°N, 109.62°E) is used for the current analysis (the difference of geographical latitude and magnetic latitude is about 8–11°). The geomagnetic data at Da Lat and Sanya are from INTERMAGNET and IGGCAS, respectively. 3. Observations Fig. 1 illustrates the evolutions of interplanetary solar wind V, magnetic field Bz component, solar wind dynamic pressure Pdyn, the dawn-dusk component of interplanetary electric field (IEF) Ey, the auroral electrojet index AE and the magnetic Dst index during 1–3 October 2013. The solar wind data are obtained from ACE satellite measurement. The IEF Ey is computed by Vx Bz. As illustrated in Fig. 1, IMF Bz, IEF and Pdyn are small and stable, V changes slowly, and the magnetic activity is very weak on 1 October. Thus, the ionogram data, magnetometer data and GPS TEC data on 1 October are used as the
Please cite this article in press as: Mao, T., et al. A case study of ionospheric storm effects in the Chinese sector during the October 2013 geomagnetic storm. Adv. Space Res. (2015), http://dx.doi.org/10.1016/j.asr.2015.05.045
T. Mao et al. / Advances in Space Research xxx (2015) xxx–xxx
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Fig. 1. Variations of interplanetary parameters and geomagnetic indices during 1–3 October 2013. From top to bottom are the solar wind velocity (V), south magnetic field (Bz), interplanetary electric field (IEF), solar wind dynamic pressure (Pdyn), AE and Dst index.
quiet-time reference. The solar wind speed suddenly changes from 400 km/s to above 600 km/s at 01:30 UT on 2 October 2013, which show the interplanetary shock reaching the ACE satellite. Almost simultaneously the IMF Bz component and the IEF experience a marked surge. About 40 min later the shock comes to the earth magnetosphere. The AE index experiences an abrupt increase to the extreme value 1272 nT and the Dst index reach the maximum value 24 nT almost simultaneously. After a storm sudden commencement (SSC), the Bz component oscillates between northward and southward within the range from 30 nT to 25 nT, the solar wind speed rises to a relative high level 600 km/s, and the Dst index attains the minimum value 75 nT at 07:00 UT on 2 October. Then the storm recovers gradually. Figs. 2 and 3 show the difference and relative changes of the GPS TEC between the storm day on 2 October and the undisturbed state on 1 October with 1° 1° grid in the
Chinese sector. The numbers in the left-top corner of each panel give the corresponding time and the pentacles show the location of ionosonde situations at Mohe, Beijing, Xian, Wuhan, Shaoyang, Nanning, Fuke and Sanya from northernmost to southernmost. As described in Figs. 2 and 3, a positive ionospheric storm from middle to low latitude start to increase significantly (30 TECU and the relative change exceeding 100%) after 04:00 UT with the maximum increment appearing at 06:00–08:00 UT and a negative ionospheric storm notably appears at 08:00 UT in the low latitude region (below 30 TECU and the relative change under 50% at 12:00 UT) with the maximum decrement appearing at 10:00–16:00 UT. As shown in Figs. 4–6, a meridional ionosonde chain spanning from northernmost to southernmost in China is used to investigate the ionosphere response features. Fig. 4 displays the vertical distribution of ionospheric electron densities obtained by ionosondes as a function of time.
Please cite this article in press as: Mao, T., et al. A case study of ionospheric storm effects in the Chinese sector during the October 2013 geomagnetic storm. Adv. Space Res. (2015), http://dx.doi.org/10.1016/j.asr.2015.05.045
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Fig. 3. The relative changes of the storm time TEC with respect to the quiet time reference TEC in the Chinese sector.
Please cite this article in press as: Mao, T., et al. A case study of ionospheric storm effects in the Chinese sector during the October 2013 geomagnetic storm. Adv. Space Res. (2015), http://dx.doi.org/10.1016/j.asr.2015.05.045
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Fig. 4. Electron density profile variations as a function of time for the Chinese sector: (left) quiet day 1 October and (right) storm day 2 October 2013 data. The station name and geomagnetic latitude are labeled on the left-lower corner of each panel. The F2 layer peak heights are shown by white solid line for the quiet day and by black solid line for the storm day.
The left panels and the right panels describe the electron densities in the quiet day and the storm day, respectively. The name and geographic latitude of station are labeled on the left-lower corner of each panel. The F2 layer peak heights are denoted by white solid lines for the quiet day and by a black solid line for the storm day. The white regions in Fig. 4 show that there are data gaps during the corresponding time. Note that the electron densities above
the F2 layer peak height are approximated by a matched a-Chapman function (Huang and Reinisch, 2001). As illustrated in Fig. 4, electron density enhancements are obviously observed between 05:00 UT (13:00 LT) and 12:00 UT (20:00 LT) from the middle to low latitude stations at Mohe, Beijing, Xian, Wuhan and Shaoyang and the corresponding peak heights continuously increase to 300–400 km height during the same time. Namely the peak
Please cite this article in press as: Mao, T., et al. A case study of ionospheric storm effects in the Chinese sector during the October 2013 geomagnetic storm. Adv. Space Res. (2015), http://dx.doi.org/10.1016/j.asr.2015.05.045
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Fig. 5. Variations of NmF2 (left) and hmF2 (right) at ionosonde station Mohe, Beijing, Xian, Wuhan, Shaoyang, Nanning, Fuke and Sanya on 2 October 2013. The gray solid lines and the vertical dashed lines describe the reference value in the quiet day and one profound peak of NmF2, respectively. The red circle and the blue circle show the corresponding value in the storm day. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
value region of electron density is raised comparing with that in quiet day, which shows that the southward neutral wind pushes the ionospheric plasma up to higher altitudes with reduced recombination rate. However, there are not pronounced positive or negative storm effects until the electron densities evidently decrease during 08:00 UT to 22:00 UT between Nanning and Sanya. At low latitude region the peak height also is lifted to the higher height after the shock arriving at the magnetosphere, which is induced by the interplanetary electric field penetrating to the low latitude ionosphere (Huang and Foster, 2005; Huang, 2008). After 20:00 UT the ionosphere gradually recovers to normal levels. The quasiperiodic oscillations of electron density propagating from Mohe to Sanya along the meridian chain can be clearly seen between 200 and 400 km altitude during 03:00 UT to 10:00 UT on 2 October.
Fig. 5 describes the variations of NmF2 (left panels) and hmF2 (right panels) at all ionosondes during the storm day. The gray solid lines and the vertical dashed lines describe the corresponding reference value and one profound peak of NmF2, respectively. Through comparing of the time corresponding to the vertical dashed lines at all stations, we can find that there is obviously the time delay of the peak values of NmF2 between Mohe and Nanning and the peak values of hmF2 appear early about 40–60 min than those of NmF2 at the same station. Judging from the peak excursions of NmF2 and hmF2, we can infer that periodical structures with periods of 1–2 h propagating from Mohe to Nanning is about 1.5 h. Divided the distance between the two stations about 3700 km by propagation time, the propagation speed of this disturbance is 680 m/s, which matches the propagating characteristics of large scale traveling ionospheric disturbances
Please cite this article in press as: Mao, T., et al. A case study of ionospheric storm effects in the Chinese sector during the October 2013 geomagnetic storm. Adv. Space Res. (2015), http://dx.doi.org/10.1016/j.asr.2015.05.045
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Fig. 6. Ionosonde bottomside TEC (BTEC, black solid line), topside ionospheric TEC (TTEC, blue solid line) and GPS TEC (red solid line) variations as a function of time for the Chinese sector: (left) the quiet day 1 October and (right) the different value of corresponding parameters between the storm day 2 October and the quiet day 1 October. The station name and geomagnetic latitude are labeled on right-upper corner of each panel. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
(LSTIDs). LSTIDs with horizontal velocities between 400 and 1000 m/s and periods in the range of 30 min to 3 h (Lee et al., 2004; Ding et al., 2007; Borries et al., 2009) may be generated during geomagnetic storm or substorms as a result of large amount of energy deposition at high latitudes (Liu et al., 2014). Simultaneously, the time showed by the vertical lines at Fuke and Sanya appears earlier than that at Nanning, which probably indicates that the penetration electric field play a key role. Also analyzing the last four panels in the right column of Fig. 5, we can find that the peak excursions of hmF2 appear at the same time between Shaoyang and Sanya and the increases at Sanya and Fuke are obviously stronger than those at Saoyang and Nanning. The phenomenon is probably induced by
the penetration electric field. In addition, the positive storm and the negative storm occur at the middle latitude and the low latitude region, which is a good agreement with Figs. 2–4. The topside ionospheric electron density shows obvious increasements during the superstorm (Astafyeva, 2009; Zhao et al., 2012). Using the ground based GPS TEC and the meridian chain of ionosondes along the 280°E longitude, Zhao et al. (2012) analyzed the topside ionospheric variations during super magnetic storm and pointed out that the maximum enhancement of the topside ionospheric electron content was 3.2–7.7 times of the bottomside ionosphere at the mid and low latitudes. In this paper, we investigate the topside ionospheric and bottom
Please cite this article in press as: Mao, T., et al. A case study of ionospheric storm effects in the Chinese sector during the October 2013 geomagnetic storm. Adv. Space Res. (2015), http://dx.doi.org/10.1016/j.asr.2015.05.045
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ionospheric effects during the moderate geomagnetic storm by using the ground based GPS TEC and eight ionosondes along the longitude of 110°E. Fig. 6 describes the changes of the GPS TEC (red solid line), bottomside ionospheric TEC (BTEC, blue solid line) and topside ionospheric TEC (TTEC = GPS TEC-BTEC, black solid line) during quiet day 1 October (left column) and the difference of corresponding parameters between the quiet day and the storm day (right column). The GPS TEC is the total electron content observed by GPS which is vertically integrated from ground to the height of GPS satellites (about 20,200 km). We calculate the BTEC by the Romberg integration from the profile curve within boundary of 100 km to hmF2 (Zhao et al., 2012). It can be seen from the left panels that the TTEC is approximately 2–3 times of BTEC during the quiet day at all ionosondes. In the right panels the GPS TEC, TTEC and BTEC increase obviously comparing with those in the quiet day. The maximum increasements of DGPS TEC between 1 and 2 October reach 7.9, 29.6, 24.2, 21.7, 22.2, 21.2, 15.6 and 11.3 TECU at Mohe, Beijing, Xian, Wuhan, Shaoyang, Nanning, Fuke and Sanya, the maximum increases of DBTEC reach 8.5, 7.9, 4.8, 7.7, 5.6, 5.1, 7.9 and 5.3 TECU, the maximum increases of DTTEC are 5.4, 24.1, 22.3, 20.0, 19.4, 21.9, 19.2 and 14.9 TECU, and the DTTEC/DBTEC values are 0.64, 3.05, 4.65, 2.60, 3.46, 4.29, 2.43 and 2.81 at corresponding ionosondes. The results show that the increasement of the electron content in the topside ionosphere is more evident than that in the bottomside ionosphere, the change of topside electron density is in a good agreement with that of GPS TEC, and the enhancement of electron density mainly occurs in the topside ionosphere during the storm day. As shown in the right panels of Fig. 6, the values of DGPS TEC are obviously decrease during 08:00–18:00 UT at Nanning, Fuke and Sanya. And through comparing the values ofDTTEC and DBTEC with DGPS TEC, we can find that the decrease of DTTEC is almost consistent with those in DGPS TEC and the change of DBTEC is very small. The result shows that the decreasement of the electron density mainly occurs in the topside ionosphere of low latitude and equatorial region during the negative ionospheric storm. 4. Discussions As illustrated from Figs. 1–6, the strong ionospheric storm occurs in the Chinese sector on 2 October 2013. The main features of the ionospheric storm are the strong positive storm in the high-middle latitude region and the strong negative storm in the low latitude and equatorial region. The remarkable daytime TEC increases, the relative change of TEC more than 100%, are seen in China, which is the strongest positive ionospheric storm occurred over China Mainland in the current solar activity period. The AE index shows that the strong solar wind energy inputs the Earth atmosphere after the interplanetary shock wave arrives at the earth magnetosphere during the geomagnetic
storm. The heated earth thermosphere will expand and create the equatorward neutral winds which generate the quasiperiodic oscillations of electron density (Lin et al., 2005; Lei et al., 2008a). The equatorward wind pushes the ionospheric plasma upward along magnetic field lines into the higher height where the plasma recombination rate is lower than that in the lower height. In addition, the large-scale traveling ionospheric disturbances (LSTIDs) induced by solar wind also transfer the energy into the ionosphere through the heat conductivity effect and the viscosity effect in the neutral atmosphere. As illustrated in Figs. 4 and 5, the vertical distributions of electron density and the strong wave-like disturbances of NmF2 show that the obvious LSTIDs propagate from the middle-high latitude to low latitudes. Besides the neutral wind and the LSTIDs, the penetration electric field derived from the interplanetary solar wind electric fields also plays an important role during the ionospheric storm. Fig. 7 displays the variations of IEF and dHDLT-SAY on 2 October 2013. The top panel describes the IEF (blue solid line) and dHDLT-SAY (green solid line). The bottom panel shows the dHDLT-SAY in the quiet day (blue solid line) and in the storm day (green solid line), respectively. The IEF is shifted by 40 min given the time lag of solar wind propagation from L1 point to the magnetosphere. In the top panel the IEF is consistent with the dHDLT-SAY between 02:00 UT and 05:00 UT. The eastward penetration electric field uplift the low latitude ionospheric F2 layer for about 100 km (Figs. 3 and 4) during 02:00– 06:00 UT. The strong PPEF pushes the equatorial ionospheric plasma into the high altitude region, which induces the electron density along the magnetic line fall into the low latitude region. As a result, the electron density increases in the middle latitude region and decreases in the equatorial region. Until about 06:00 UT the dHDLT-SAY changes from positive value to negative value, which shows the direction of electric field alters from easterward to westward though the IEF is still positive. We attribute this to the obvious enhancement of the disturbance dynamo electric field (DDEF) and the decrease of the PPEF. At this stage of the storm the DDEF play a primary role in restructuring the storm-time ionosphere and the PPEF play a secondary role. Namely the PPEF immerges into the DDEF (Maruyama et al., 2005). As illustrated in Figs. 2–6, there is the strong TEC depletion in the low and equatorial region after 12:00 UT, whcih is probably induced by the westward DDEF during the night time (Fejer and Scherliess, 1995). Under the effects of the westward DDEF an inverted fountain phenomenon takes place and the ionospheric electron density distinctly decreases in the equatorial region ionosphere. Zhao et al. (2012) studied the ionospheric storm effects at Latin America longitude during 20–22 November 2003 and pointed out that the maximum enhancement of electron content occurred in the topside ionosphere region, not in the bottomside ionosphere. As shown in Fig. 6, the observed positive storm over the Chinese sector is
Please cite this article in press as: Mao, T., et al. A case study of ionospheric storm effects in the Chinese sector during the October 2013 geomagnetic storm. Adv. Space Res. (2015), http://dx.doi.org/10.1016/j.asr.2015.05.045
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Fig. 7. The time sequence of the IEF and dHDLT-SAY during the storm day. The top panel describes the IEF (blue solid line) and dHDLT-SAY (green solid line) on 2 October 2013. The bottom panel shows the dHDLT-SAY on the quiet day 1 October (blue solid line) and on stome day 2 October (green solid line). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
mainly the consequence of the changes of the topside ionosphere. Simultaneously we also can find that the electron content of the topside ionosphere obviously decreases during the negative storm in the low and equatorial latitude, which is not be mentioned by Zhao et al. (2012). The above results show that the increase and the decrease of electron density mainly occur in the topside ionosphere during the 2 October 2013 geomagnetic storm. The phenomenon is probably induced by the electric field. The stronger eastward electric field induces a fountain effect in the equatorial region and moves the ionospheric plasma upward into the higher height then downward along the magnetic line in the middle and low latitude region. The westward electric field causes an inverted fountain effect and pushes the topside ionospheric plasma downward into the lower height in the low latitude and equatorial region. 5. Conclusions In this article we analyze the ionospheric response to a geomagnetic storm on the basis of the regional TEC maps and eight ionosondes along the same longitude and two magnetometers, in the Chinese sector on 2 October 2013. It is the first time that the region characteristic of ionospheric storm is investigated using eight ionosondes data along the same longitude. In future we will further study the physical mechanism of ionospheric storm using the observations such as the wind field measured by FPI. The results are of benefit to researching and predicting the region ionospheric storms and deepen the application of data of Meridian Project and the National Center for Space Weather in China Meteorological Administration. The main conclusions are listed as follows:
(1) Strong increasements in TEC and NmF2 over China are observed by TEC maps and ionosondes along the 110°E meridian during the period of 05:00–10:00 UT. The positive ionospheric storm is induced by the combined effects of the neutral wind, LSTIDs and PPEF. (2) An obvious negative ionospheric storm occurs in the southern of equatorial ionization anomaly during the period of 10:00–16:00 UT, which is mostly produced by the westward DDEF. (3) The electron density in the topside has a much stronger enhancement than that in the bottomside of the ionosphere at Beijing, Xian, Wuhan and Shaoyang during the geomagnetic storm. And the decreases of the topside ionosphere are also observed at Mohe, Nanning, Fuke and Sanya. (4) The PPEF plays an important role in the first 3 h after SSC in the equatorial and low latitude regions.
Acknowledgments The authors thank the National Center for Space Weather, China Meteorological Administration and the Data Centre of Meridian Project in Chinese Academy of Sciences for the data. The authors are also grateful for DIDB and INTERMAGNET for ionograms and geomagnetic data available through the Internet. This research was supported by National High-tech R&D Program of China (863 Program 2014AA123503), and National Natural Science Foundation of China (41231065, 41321003).
Please cite this article in press as: Mao, T., et al. A case study of ionospheric storm effects in the Chinese sector during the October 2013 geomagnetic storm. Adv. Space Res. (2015), http://dx.doi.org/10.1016/j.asr.2015.05.045
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Please cite this article in press as: Mao, T., et al. A case study of ionospheric storm effects in the Chinese sector during the October 2013 geomagnetic storm. Adv. Space Res. (2015), http://dx.doi.org/10.1016/j.asr.2015.05.045
ScienceDirect Advances in Space Research xxx (2015) xxx–xxx www.elsevier.com/locate/asr
A case study of ionospheric storm effects in the Chinese sector during the October 2013 geomagnetic storm Tian Mao a,⇑, Lingfeng Sun b,⇑, Lianhuan Hu b, Yungang Wang a, Zhijun Wang b b
a Key Laboratory of Space Weather, National Center for Space Weather, China Meteorological Administration, Beijing 100081, China Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
Received 5 February 2015; received in revised form 27 May 2015; accepted 30 May 2015
Abstract In this study, we investigate the ionospheric storm effects in the Chinese sector during 2 October 2013 geomagnetic storm. The TEC map over China sector (1° 1°) and eight ionosondes data along the longitude of 110°E are used to show significant positive ionospheric phases (enhancements in TEC and ionospheric peak electron density NmF2) in the high-middle latitude region and the negative effects at the low latitude and equatorial region during the storm. A wave structure with periods about 1–2 h and horizontal speed about 680 m/s, propagating from the high latitudes to the low latitudes is observed in electron densities within the height region from 200 to 400 km, which is caused by the combined effects of neutral wind and the large-scale traveling disturbances (LSTIDs). In the low latitude regions, compared with those in the quiet day, the ionospheric peak heights of the F2 layer (hmF2) in the storm day obviously increase accompanying a notably decrease in TEC and NmF2, which might be as a result of the eastward prompt penetration electric field (PPEF) evidenced by the two magnetometers and the subsequent westward disturbance dynamo electric fields (DDEF). The storm-time TEC enhancement mainly occurs in the topside ionosphere, as revealed from the topside TEC, bottomside TEC and GPS TEC. Ó 2015 COSPAR. Published by Elsevier Ltd. All rights reserved.
Keywords: Ionospheric storm; Neutral wind; LSTIDs; PPEF; DDEF
1. Introduction The ionospheric storm induced by geomagnetic storms is one of the most complicated space weather phenomena. During the geomagnetic storm, the solar wind energy impulsively or continually injects into the polar regions of the earth and leads to large changes in the chemistry and dynamics of the high latitude ionosphere–thermosphere (I–T), which will affect the global ionospheric electron density distribution through various dynamic and electrodynamic processes. According to the increasement ⇑ Corresponding authors at: Key Laboratory of Space Weather, National Center for Space Weather, China Meteorological Administration, No. 46 Zhongguancun South Str., Beijing 100081, China (T. Mao). E-mail addresses: [email protected] (T. Mao), sunlingfeng@mail. iggcas.ac.cn (L. Sun).
or the decreasement of electron density in the storm time relative to those in the quiet time, the ionospheric storms can be classified into positive storms or negative storms. Many researchers have investigated the ionospheric storm characteristics and analyzed the physical mechanism in terms of observations and theoretical models since the conception of ionospheric storm has been convinced (Somayajulu, 1960; Zhao et al., 2005, 2008; Mendillo, 2006; Burns et al., 2007; Lei et al., 2008a,b, 2014; Pedatella et al., 2009; Yuan et al., 2009; Liu et al., 2014). Pro¨lss (1993a,b) proposed that the observed daytime positive storm effects, especially during the initial phase, were caused by traveling atmospheric disturbances (TADs) and suggested that the electrodynamics mechanism was not as important as thermospheric dynamics. Hyosub et al. (2003) investigated the ionospheric response to the
http://dx.doi.org/10.1016/j.asr.2015.05.045 0273-1177/Ó 2015 COSPAR. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Mao, T., et al. A case study of ionospheric storm effects in the Chinese sector during the October 2013 geomagnetic storm. Adv. Space Res. (2015), http://dx.doi.org/10.1016/j.asr.2015.05.045
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magnetic storm using the GPS TEC and DMSP data. They pointed out that negative ionospheric storm and the positive ionospheric storm were dominant in the summer hemisphere and in the winter hemisphere, respectively. Liu et al. (2002, 2004) explored the storm-time electric field and composition changes effects on the low latitude ionosphere during two storms in 2000. Lei et al. (2008b) investigated the thermospheric and ionospheric response to the 14–15 December 2006 geomagnetic storm using the Coupled Magnetosphere Ionosphere Thermosphere (CMIT) 2.0 model. They recognized that the electric fields played a dominant role in generating the observed ionospheric positive storm effect in the American sector during the initial phase. Zhao et al. (2009) analyzed the ionospheric storm effect based on the ionosonde chain and GPS network and GUVI data in the west Pacific area during the intense geomagnetic storm on 13–17 April 2006. They recognized that periodic wave structures in middle-low latitude foF2 in the morning sector on 14 April should be caused by TADs with phase propagation velocities ranging 400–800 m/s, while in the afternoon and nighttime, the positive phase would be most probably caused by the combination effects of the enhanced equatorward winds and disturbed electric fields. Shweta et al. (2012) studied the low latitude ionospheric response during the 24 August 2005 geomagnetic storm using the GPS TEC and ionosondes data. The TEC enhancements were attributed to the prompt penetration electric fields. D’ujanga et al. (2013) discussed the effects of the geomagnetic storm during 24– 25 October 2011 in East Africa. Storm time reductions in the diurnal TEC at the two stations were observed, which had been attributed to the uplift of the ionospheric plasma followed by the poleward transportation from equator region by diffusion along magnetic field lines. Liu et al. (2014) used the observation data from GPS, ionosonde, C/NOFS, magnetometer and GUVI to investigate the ionospheric storm during the 14–17 July 2012 geomagnetic storm event. They concluded that, in the East Asian/Australian sector, the three bands of increments and separated by weak depressions in the equatorial ionospheric anomaly (EIA) crest regions were caused by both disturbance dynamo electric field (DDEF) and equatorward neutral winds. Although many researchers analyzed the ionospheric response to the magnetic storm by case studies and numerical modeling, there are still many questions and contradictions in understanding of some aspects of ionospheric storm. The objective of the present paper is to analyze the altitudinal dependence of ionospheric response to different processes such as electric field, neutral wind changes induced by the 2 October 2013 geomagnetic storm on the basis of observation data in the Chinese sector. The rests of this paper are arranged as follows. Section 2 describes the data sources including the grid TEC with 1° 1° bin, eight ionosondes along the 110°E and two magnetometers located in Da Lat (11.94°N, 108.48°E) and Sanya (18.34°N, 109.62°E). Section 3 shows the ionospheric
storm characteristics. The discussion and the conclusions are given in the last two parts. 2. Data sources The observations from the GPS TEC, ionosondes and magnetometers are used to investigate the ionosphere effects induced by the 2 October 2013 geomagnetic storm. The GPS TEC data are from the ground-based high-resolution TEC tracking network of Chinese Meteorology Administrator. The TEC tracking network consists of about 800 GPS stations in China. Slant TEC observations are used to convert to vertical TEC data of 1° grid via least squares fits and nearest neighbor interpolation method over the China region. An automated technique for processing GPS data from multiple receivers was developed by Mao et al. (2008). The horizontal resolution is 1° and the temporal resolution is an hour. The data observed from the eight ionosondes (Mohe (52.00°N, 122.52°E), Beijing (40.30°N, 116.20°E), Xian (34.08°N, 108.88°E), Wuhan (30.50°N, 114.40°E), Shaoyang (27.1°N, 111.3°E), Nanning (22.70°N, 109.25°E), Fuke (19.40°N, 109.00°E) and Sanya (18.34°N, 109.62°E)) are used in this paper. The ionosonde data at Mohe, Wuhan, and Fuke are obtained from the Data Center of Meridian Project, data at Beijing, Shaoyang and Sanya are downloaded from the Low Digital ionogram Database (Reinisch et al., 2009) and Institute of Geology and Geophysics of Chinese Academy and Sciences (IGGCAS), and data at Nanning and Xian are from the National Center for Space Weather,Chinese Meteorology Administrator. All ionograms are manually scaled by using the SAO Explorer software package. Two magnetometers provide an opportunity to estimate the daytime equatorial electrojet and the intensity of ionospheric F region E B vertical drift (Anderson et al., 2002; Liu et al., 2014). The difference in the geomagnetic horizontal component (dHDLT-SAY) between Da Lat (11.94°N, 108.48°E) and Sanya (18.34°N, 109.62°E) is used for the current analysis (the difference of geographical latitude and magnetic latitude is about 8–11°). The geomagnetic data at Da Lat and Sanya are from INTERMAGNET and IGGCAS, respectively. 3. Observations Fig. 1 illustrates the evolutions of interplanetary solar wind V, magnetic field Bz component, solar wind dynamic pressure Pdyn, the dawn-dusk component of interplanetary electric field (IEF) Ey, the auroral electrojet index AE and the magnetic Dst index during 1–3 October 2013. The solar wind data are obtained from ACE satellite measurement. The IEF Ey is computed by Vx Bz. As illustrated in Fig. 1, IMF Bz, IEF and Pdyn are small and stable, V changes slowly, and the magnetic activity is very weak on 1 October. Thus, the ionogram data, magnetometer data and GPS TEC data on 1 October are used as the
Please cite this article in press as: Mao, T., et al. A case study of ionospheric storm effects in the Chinese sector during the October 2013 geomagnetic storm. Adv. Space Res. (2015), http://dx.doi.org/10.1016/j.asr.2015.05.045
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Fig. 1. Variations of interplanetary parameters and geomagnetic indices during 1–3 October 2013. From top to bottom are the solar wind velocity (V), south magnetic field (Bz), interplanetary electric field (IEF), solar wind dynamic pressure (Pdyn), AE and Dst index.
quiet-time reference. The solar wind speed suddenly changes from 400 km/s to above 600 km/s at 01:30 UT on 2 October 2013, which show the interplanetary shock reaching the ACE satellite. Almost simultaneously the IMF Bz component and the IEF experience a marked surge. About 40 min later the shock comes to the earth magnetosphere. The AE index experiences an abrupt increase to the extreme value 1272 nT and the Dst index reach the maximum value 24 nT almost simultaneously. After a storm sudden commencement (SSC), the Bz component oscillates between northward and southward within the range from 30 nT to 25 nT, the solar wind speed rises to a relative high level 600 km/s, and the Dst index attains the minimum value 75 nT at 07:00 UT on 2 October. Then the storm recovers gradually. Figs. 2 and 3 show the difference and relative changes of the GPS TEC between the storm day on 2 October and the undisturbed state on 1 October with 1° 1° grid in the
Chinese sector. The numbers in the left-top corner of each panel give the corresponding time and the pentacles show the location of ionosonde situations at Mohe, Beijing, Xian, Wuhan, Shaoyang, Nanning, Fuke and Sanya from northernmost to southernmost. As described in Figs. 2 and 3, a positive ionospheric storm from middle to low latitude start to increase significantly (30 TECU and the relative change exceeding 100%) after 04:00 UT with the maximum increment appearing at 06:00–08:00 UT and a negative ionospheric storm notably appears at 08:00 UT in the low latitude region (below 30 TECU and the relative change under 50% at 12:00 UT) with the maximum decrement appearing at 10:00–16:00 UT. As shown in Figs. 4–6, a meridional ionosonde chain spanning from northernmost to southernmost in China is used to investigate the ionosphere response features. Fig. 4 displays the vertical distribution of ionospheric electron densities obtained by ionosondes as a function of time.
Please cite this article in press as: Mao, T., et al. A case study of ionospheric storm effects in the Chinese sector during the October 2013 geomagnetic storm. Adv. Space Res. (2015), http://dx.doi.org/10.1016/j.asr.2015.05.045
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Please cite this article in press as: Mao, T., et al. A case study of ionospheric storm effects in the Chinese sector during the October 2013 geomagnetic storm. Adv. Space Res. (2015), http://dx.doi.org/10.1016/j.asr.2015.05.045
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Fig. 4. Electron density profile variations as a function of time for the Chinese sector: (left) quiet day 1 October and (right) storm day 2 October 2013 data. The station name and geomagnetic latitude are labeled on the left-lower corner of each panel. The F2 layer peak heights are shown by white solid line for the quiet day and by black solid line for the storm day.
The left panels and the right panels describe the electron densities in the quiet day and the storm day, respectively. The name and geographic latitude of station are labeled on the left-lower corner of each panel. The F2 layer peak heights are denoted by white solid lines for the quiet day and by a black solid line for the storm day. The white regions in Fig. 4 show that there are data gaps during the corresponding time. Note that the electron densities above
the F2 layer peak height are approximated by a matched a-Chapman function (Huang and Reinisch, 2001). As illustrated in Fig. 4, electron density enhancements are obviously observed between 05:00 UT (13:00 LT) and 12:00 UT (20:00 LT) from the middle to low latitude stations at Mohe, Beijing, Xian, Wuhan and Shaoyang and the corresponding peak heights continuously increase to 300–400 km height during the same time. Namely the peak
Please cite this article in press as: Mao, T., et al. A case study of ionospheric storm effects in the Chinese sector during the October 2013 geomagnetic storm. Adv. Space Res. (2015), http://dx.doi.org/10.1016/j.asr.2015.05.045
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Fig. 5. Variations of NmF2 (left) and hmF2 (right) at ionosonde station Mohe, Beijing, Xian, Wuhan, Shaoyang, Nanning, Fuke and Sanya on 2 October 2013. The gray solid lines and the vertical dashed lines describe the reference value in the quiet day and one profound peak of NmF2, respectively. The red circle and the blue circle show the corresponding value in the storm day. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
value region of electron density is raised comparing with that in quiet day, which shows that the southward neutral wind pushes the ionospheric plasma up to higher altitudes with reduced recombination rate. However, there are not pronounced positive or negative storm effects until the electron densities evidently decrease during 08:00 UT to 22:00 UT between Nanning and Sanya. At low latitude region the peak height also is lifted to the higher height after the shock arriving at the magnetosphere, which is induced by the interplanetary electric field penetrating to the low latitude ionosphere (Huang and Foster, 2005; Huang, 2008). After 20:00 UT the ionosphere gradually recovers to normal levels. The quasiperiodic oscillations of electron density propagating from Mohe to Sanya along the meridian chain can be clearly seen between 200 and 400 km altitude during 03:00 UT to 10:00 UT on 2 October.
Fig. 5 describes the variations of NmF2 (left panels) and hmF2 (right panels) at all ionosondes during the storm day. The gray solid lines and the vertical dashed lines describe the corresponding reference value and one profound peak of NmF2, respectively. Through comparing of the time corresponding to the vertical dashed lines at all stations, we can find that there is obviously the time delay of the peak values of NmF2 between Mohe and Nanning and the peak values of hmF2 appear early about 40–60 min than those of NmF2 at the same station. Judging from the peak excursions of NmF2 and hmF2, we can infer that periodical structures with periods of 1–2 h propagating from Mohe to Nanning is about 1.5 h. Divided the distance between the two stations about 3700 km by propagation time, the propagation speed of this disturbance is 680 m/s, which matches the propagating characteristics of large scale traveling ionospheric disturbances
Please cite this article in press as: Mao, T., et al. A case study of ionospheric storm effects in the Chinese sector during the October 2013 geomagnetic storm. Adv. Space Res. (2015), http://dx.doi.org/10.1016/j.asr.2015.05.045
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Fig. 6. Ionosonde bottomside TEC (BTEC, black solid line), topside ionospheric TEC (TTEC, blue solid line) and GPS TEC (red solid line) variations as a function of time for the Chinese sector: (left) the quiet day 1 October and (right) the different value of corresponding parameters between the storm day 2 October and the quiet day 1 October. The station name and geomagnetic latitude are labeled on right-upper corner of each panel. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
(LSTIDs). LSTIDs with horizontal velocities between 400 and 1000 m/s and periods in the range of 30 min to 3 h (Lee et al., 2004; Ding et al., 2007; Borries et al., 2009) may be generated during geomagnetic storm or substorms as a result of large amount of energy deposition at high latitudes (Liu et al., 2014). Simultaneously, the time showed by the vertical lines at Fuke and Sanya appears earlier than that at Nanning, which probably indicates that the penetration electric field play a key role. Also analyzing the last four panels in the right column of Fig. 5, we can find that the peak excursions of hmF2 appear at the same time between Shaoyang and Sanya and the increases at Sanya and Fuke are obviously stronger than those at Saoyang and Nanning. The phenomenon is probably induced by
the penetration electric field. In addition, the positive storm and the negative storm occur at the middle latitude and the low latitude region, which is a good agreement with Figs. 2–4. The topside ionospheric electron density shows obvious increasements during the superstorm (Astafyeva, 2009; Zhao et al., 2012). Using the ground based GPS TEC and the meridian chain of ionosondes along the 280°E longitude, Zhao et al. (2012) analyzed the topside ionospheric variations during super magnetic storm and pointed out that the maximum enhancement of the topside ionospheric electron content was 3.2–7.7 times of the bottomside ionosphere at the mid and low latitudes. In this paper, we investigate the topside ionospheric and bottom
Please cite this article in press as: Mao, T., et al. A case study of ionospheric storm effects in the Chinese sector during the October 2013 geomagnetic storm. Adv. Space Res. (2015), http://dx.doi.org/10.1016/j.asr.2015.05.045
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ionospheric effects during the moderate geomagnetic storm by using the ground based GPS TEC and eight ionosondes along the longitude of 110°E. Fig. 6 describes the changes of the GPS TEC (red solid line), bottomside ionospheric TEC (BTEC, blue solid line) and topside ionospheric TEC (TTEC = GPS TEC-BTEC, black solid line) during quiet day 1 October (left column) and the difference of corresponding parameters between the quiet day and the storm day (right column). The GPS TEC is the total electron content observed by GPS which is vertically integrated from ground to the height of GPS satellites (about 20,200 km). We calculate the BTEC by the Romberg integration from the profile curve within boundary of 100 km to hmF2 (Zhao et al., 2012). It can be seen from the left panels that the TTEC is approximately 2–3 times of BTEC during the quiet day at all ionosondes. In the right panels the GPS TEC, TTEC and BTEC increase obviously comparing with those in the quiet day. The maximum increasements of DGPS TEC between 1 and 2 October reach 7.9, 29.6, 24.2, 21.7, 22.2, 21.2, 15.6 and 11.3 TECU at Mohe, Beijing, Xian, Wuhan, Shaoyang, Nanning, Fuke and Sanya, the maximum increases of DBTEC reach 8.5, 7.9, 4.8, 7.7, 5.6, 5.1, 7.9 and 5.3 TECU, the maximum increases of DTTEC are 5.4, 24.1, 22.3, 20.0, 19.4, 21.9, 19.2 and 14.9 TECU, and the DTTEC/DBTEC values are 0.64, 3.05, 4.65, 2.60, 3.46, 4.29, 2.43 and 2.81 at corresponding ionosondes. The results show that the increasement of the electron content in the topside ionosphere is more evident than that in the bottomside ionosphere, the change of topside electron density is in a good agreement with that of GPS TEC, and the enhancement of electron density mainly occurs in the topside ionosphere during the storm day. As shown in the right panels of Fig. 6, the values of DGPS TEC are obviously decrease during 08:00–18:00 UT at Nanning, Fuke and Sanya. And through comparing the values ofDTTEC and DBTEC with DGPS TEC, we can find that the decrease of DTTEC is almost consistent with those in DGPS TEC and the change of DBTEC is very small. The result shows that the decreasement of the electron density mainly occurs in the topside ionosphere of low latitude and equatorial region during the negative ionospheric storm. 4. Discussions As illustrated from Figs. 1–6, the strong ionospheric storm occurs in the Chinese sector on 2 October 2013. The main features of the ionospheric storm are the strong positive storm in the high-middle latitude region and the strong negative storm in the low latitude and equatorial region. The remarkable daytime TEC increases, the relative change of TEC more than 100%, are seen in China, which is the strongest positive ionospheric storm occurred over China Mainland in the current solar activity period. The AE index shows that the strong solar wind energy inputs the Earth atmosphere after the interplanetary shock wave arrives at the earth magnetosphere during the geomagnetic
storm. The heated earth thermosphere will expand and create the equatorward neutral winds which generate the quasiperiodic oscillations of electron density (Lin et al., 2005; Lei et al., 2008a). The equatorward wind pushes the ionospheric plasma upward along magnetic field lines into the higher height where the plasma recombination rate is lower than that in the lower height. In addition, the large-scale traveling ionospheric disturbances (LSTIDs) induced by solar wind also transfer the energy into the ionosphere through the heat conductivity effect and the viscosity effect in the neutral atmosphere. As illustrated in Figs. 4 and 5, the vertical distributions of electron density and the strong wave-like disturbances of NmF2 show that the obvious LSTIDs propagate from the middle-high latitude to low latitudes. Besides the neutral wind and the LSTIDs, the penetration electric field derived from the interplanetary solar wind electric fields also plays an important role during the ionospheric storm. Fig. 7 displays the variations of IEF and dHDLT-SAY on 2 October 2013. The top panel describes the IEF (blue solid line) and dHDLT-SAY (green solid line). The bottom panel shows the dHDLT-SAY in the quiet day (blue solid line) and in the storm day (green solid line), respectively. The IEF is shifted by 40 min given the time lag of solar wind propagation from L1 point to the magnetosphere. In the top panel the IEF is consistent with the dHDLT-SAY between 02:00 UT and 05:00 UT. The eastward penetration electric field uplift the low latitude ionospheric F2 layer for about 100 km (Figs. 3 and 4) during 02:00– 06:00 UT. The strong PPEF pushes the equatorial ionospheric plasma into the high altitude region, which induces the electron density along the magnetic line fall into the low latitude region. As a result, the electron density increases in the middle latitude region and decreases in the equatorial region. Until about 06:00 UT the dHDLT-SAY changes from positive value to negative value, which shows the direction of electric field alters from easterward to westward though the IEF is still positive. We attribute this to the obvious enhancement of the disturbance dynamo electric field (DDEF) and the decrease of the PPEF. At this stage of the storm the DDEF play a primary role in restructuring the storm-time ionosphere and the PPEF play a secondary role. Namely the PPEF immerges into the DDEF (Maruyama et al., 2005). As illustrated in Figs. 2–6, there is the strong TEC depletion in the low and equatorial region after 12:00 UT, whcih is probably induced by the westward DDEF during the night time (Fejer and Scherliess, 1995). Under the effects of the westward DDEF an inverted fountain phenomenon takes place and the ionospheric electron density distinctly decreases in the equatorial region ionosphere. Zhao et al. (2012) studied the ionospheric storm effects at Latin America longitude during 20–22 November 2003 and pointed out that the maximum enhancement of electron content occurred in the topside ionosphere region, not in the bottomside ionosphere. As shown in Fig. 6, the observed positive storm over the Chinese sector is
Please cite this article in press as: Mao, T., et al. A case study of ionospheric storm effects in the Chinese sector during the October 2013 geomagnetic storm. Adv. Space Res. (2015), http://dx.doi.org/10.1016/j.asr.2015.05.045
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Fig. 7. The time sequence of the IEF and dHDLT-SAY during the storm day. The top panel describes the IEF (blue solid line) and dHDLT-SAY (green solid line) on 2 October 2013. The bottom panel shows the dHDLT-SAY on the quiet day 1 October (blue solid line) and on stome day 2 October (green solid line). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
mainly the consequence of the changes of the topside ionosphere. Simultaneously we also can find that the electron content of the topside ionosphere obviously decreases during the negative storm in the low and equatorial latitude, which is not be mentioned by Zhao et al. (2012). The above results show that the increase and the decrease of electron density mainly occur in the topside ionosphere during the 2 October 2013 geomagnetic storm. The phenomenon is probably induced by the electric field. The stronger eastward electric field induces a fountain effect in the equatorial region and moves the ionospheric plasma upward into the higher height then downward along the magnetic line in the middle and low latitude region. The westward electric field causes an inverted fountain effect and pushes the topside ionospheric plasma downward into the lower height in the low latitude and equatorial region. 5. Conclusions In this article we analyze the ionospheric response to a geomagnetic storm on the basis of the regional TEC maps and eight ionosondes along the same longitude and two magnetometers, in the Chinese sector on 2 October 2013. It is the first time that the region characteristic of ionospheric storm is investigated using eight ionosondes data along the same longitude. In future we will further study the physical mechanism of ionospheric storm using the observations such as the wind field measured by FPI. The results are of benefit to researching and predicting the region ionospheric storms and deepen the application of data of Meridian Project and the National Center for Space Weather in China Meteorological Administration. The main conclusions are listed as follows:
(1) Strong increasements in TEC and NmF2 over China are observed by TEC maps and ionosondes along the 110°E meridian during the period of 05:00–10:00 UT. The positive ionospheric storm is induced by the combined effects of the neutral wind, LSTIDs and PPEF. (2) An obvious negative ionospheric storm occurs in the southern of equatorial ionization anomaly during the period of 10:00–16:00 UT, which is mostly produced by the westward DDEF. (3) The electron density in the topside has a much stronger enhancement than that in the bottomside of the ionosphere at Beijing, Xian, Wuhan and Shaoyang during the geomagnetic storm. And the decreases of the topside ionosphere are also observed at Mohe, Nanning, Fuke and Sanya. (4) The PPEF plays an important role in the first 3 h after SSC in the equatorial and low latitude regions.
Acknowledgments The authors thank the National Center for Space Weather, China Meteorological Administration and the Data Centre of Meridian Project in Chinese Academy of Sciences for the data. The authors are also grateful for DIDB and INTERMAGNET for ionograms and geomagnetic data available through the Internet. This research was supported by National High-tech R&D Program of China (863 Program 2014AA123503), and National Natural Science Foundation of China (41231065, 41321003).
Please cite this article in press as: Mao, T., et al. A case study of ionospheric storm effects in the Chinese sector during the October 2013 geomagnetic storm. Adv. Space Res. (2015), http://dx.doi.org/10.1016/j.asr.2015.05.045
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Please cite this article in press as: Mao, T., et al. A case study of ionospheric storm effects in the Chinese sector during the October 2013 geomagnetic storm. Adv. Space Res. (2015), http://dx.doi.org/10.1016/j.asr.2015.05.045