- Email: [email protected]
An investigation of ionospheric F region response in the Brazilian sector to the super geomagnetic storm of May 2005
Available online at www.sciencedirect.com
Advances in Space Research 48 (2011) 1211–1220 www.elsevier.com/locate/asr
An investigation of ionospheric F region response in the Brazilian sector to the super geomagnetic storm of May 2005 A.J. de Abreu a,⇑, Y. Sahai a, P.R. Fagundes a, R. de Jesus a, J.A. Bittencourt b, V.G. Pillat a a
Departamento de Fı´sica e Astronomia, Universidade do Vale do Paraı´ba (UNIVAP), Av. Shishima Hifumi, 2911, Sa˜o Jose´ dos Campos, Sa˜o Paulo, Brazil b Instituto Nacional de Pesquisas Espaciais (INPE), Av. dos Astronautas, 1758, Caixa, Postal 515, Sa˜o Jose´ dos Campos, Sa˜o Paulo, Brazil Received 3 March 2011; received in revised form 23 May 2011; accepted 30 May 2011 Available online 12 June 2011
Abstract In this paper, we have investigated the responses of the ionospheric F region at equatorial and low latitude regions in the Brazilian sector during the super geomagnetic storm on 15–16 May 2005. The geomagnetic storm reached a minimum Dst of 263 nT at 0900 UT on 15 May. In this paper, we present vertical total electron content (vTEC) and phase fluctuations (in TECU/min) from Global Positioning System (GPS) observations obtained at Bele´m, Brası´lia, Presidente Prudente, and Porto Alegre, Brazil, during the period 14–17 May 2005. Also, we present ionospheric parameters h’F, hpF2, and foF2, using the Canadian Advanced Digital Ionosonde (CADI) obtained at Palmas and Sa˜o Jose´ dos Campos, Brazil, for the same period. The super geomagnetic storm has fast decrease in the Dst index soon after SSC at 0239 UT on 15 May. It is a good possibility of prompt penetration of electric field of magnetospheric origin resulting in uplifting of the F region. The vTEC observations show a trough at BELE and a crest above UEPP, soon after SSC, indicating strengthening of nighttime equatorial anomaly. During the daytime on 15 and 16 May, in the recovery phase, the variations in foF2 at SJC and the vTEC observations, particularly at BRAZ, UEPP, and POAL, show large positive ionospheric storm. There is ESF on the all nights at PAL, in the post-midnight (UT) sector, and phase fluctuations only on the night of 14–15 May at BRAZ, after the SSC. No phase fluctuations are observed at the equatorial station BELE and low latitude stations (BRAZ, UEPP, and POAL) at all other times. This indicates that the plasma bubbles are generated and confined on this magnetically disturbed night only up to the low magnetic latitude and drifted possibly to west. Ó 2011 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: Geomagnetic storm; Ionosphere; Equatorial ionospheric irregularities
1. Introduction The ionospheric storms associated with geomagnetic storms represent an extreme form of space weather which has a growing importance at present and can have significant, adverse effects on increasingly sophisticated groundand space-based technological systems (Buonsanto, 1999). Several investigators have studied the space weather distur-
⇑ Corresponding author. Tel.: +55 12 39471146; fax: +55 12 39471149.
E-mail addresses: [email protected] (A.J. de Abreu), [email protected] (Y. Sahai), [email protected] (P.R. Fagundes), [email protected] (R. de Jesus), [email protected] (J.A. Bittencourt), [email protected] (V.G. Pillat).
bances in the ionosphere–thermosphere system (Schunk and Sojka, 1996; Buonsanto, 1999; Jansen and Pirjola, 2004; Klimenko et al., 2011; Sahai et al., 2011). The response of the ionosphere–thermosphere system at equatorial and mid-low latitudes regions during intense/super geomagnetic storms has been recently provided by Becker-Guedes et al. (2007), Sahai et al. (2007a, 2009a,b), de Jesus et al. (2010), and de Abreu et al. (2010a). During the periods of intense/super geomagnetic storms, the equatorial and low latitude regions can have severe modifications in the ionospheric F region height and peak electron density. These modifications are related to the electric fields, winds, and composition changes (Werner et al., 1999; Sastri et al., 2002; Fejer et al., 2007). The
0273-1177/$36.00 Ó 2011 COSPAR. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.asr.2011.05.036
1212
A.J. de Abreu et al. / Advances in Space Research 48 (2011) 1211–1220
responsible for the behavior of the equatorial and low latitude ionospheric electric fields are the prompt equatorward penetration of magnetospheric/high latitude electric fields (period less than one hour) and the ionospheric disturbance dynamo (period of several hours) generated by the global winds circulation due to the Joule heating in the high latitude atmosphere in consequence the particles of precipitation (Maruyama et al., 2005). During the periods of intense geomagnetic disturbances, occurs the injection/transport of energy from high latitudes to low latitudes and changes in the global winds circulation via Joule heating (Nicolls et al., 2004). In addition, this energy injection and changes in the global winds can drive the propagation of atmospheric gravity waves equatorward in the form of traveling atmospheric disturbances (TADs). These TADs when interact with the ionosphere can produce traveling ionospheric disturbances (TIDs) of high speeds (Hines and Hooke, 1960; Killeen et al., 1984; Fagundes et al., 1995; Afraimovich et al., 2001; Lima et al., 2004). Also, during geomagnetic disturbances can occur increase or decrease of the ionospheric electron density as compared with quiet periods, which are called positive ionospheric storm (positive phase) and negative ionospheric storm (negative phase), respectively (Danilov and Morozova, 1985; Prolss, 1993; Bauske and Prolss, 1998). As discussed out by Namgaladze et al. (2000), positive phase are often related the large-scale wind circulation. The generation or suppression of equatorial ionospheric irregularities or equatorial spread-F (ESF) in the equatorial and low latitude regions during geomagnetic disturbances is other important aspect to be investigated (Whalen, 2002; Martinis et al., 2005; Sahai et al., 2009c). In this paper, we present and discuss the response of the ionospheric F region at equatorial and low latitude regions in the Brazilian sector during the super geomagnetic storm that occurred on 15–16 May 2005. The main objectives have been to study the storm-time electrodynamics and generation or inhibition of equatorial ionospheric irregularities (ESF) (Martinis et al., 2005) in the Brazilian sector during this super storm. The ionospheric response during geomagnetic storms in different latitudinal and longitudinal sectors have been studied by Sahai et al. (2005), Lei et al. (2008), Dashora et al. (2009), Paznukhov et al. (2009), and de Abreu et al. (2010b). Lei et al. (2008) observed a pronounced positive ionospheric storm effect in the American sector to the December 2006 geomagnetic storm. Dashora et al. (2009) have reported a large enhancement in low latitude total electron content during the 15 May 2005 super geomagnetic storm in the Indian sector during few hours in the daytime. de Abreu et al. (2010b) have observed positive ionospheric storm phase in the equatorial and low latitude regions in the Brazilian sector to the April 2000 super geomagnetic storm using GPS measurements. The results of this investigation were obtained using ionospheric sounding and Global Positioning System (GPS) observations, from equatorial to low latitude regions in Brazilian sector. To the authors’ knowledge, this is the first
investigation of the response of the ionospheric F region during this strong geomagnetic disturbance in the Brazilian sector. 2. Observations The Global Positioning System (GPS) observations were obtained from several GPS receiving stations in the Brazilian sector in the standard “Receiver Independent Exchange format (RINEX)” with temporal resolution of 15 s from 4 receiving stations during the super storm in May 2005. The GPS observations were used to obtain the measures of the vertical total electron content (vTEC) calculated in units of TEC (1 TECU = 1016 electrons/m2) (Wanninger, 1993; Yizengaw et al., 2009) and the measures of the phase fluctuations (rate of change of TEC) calculated in TECU/min (Aarons et al., 1996, 1997). The GPS observations used for measurements of the vTEC and phase fluctuations were obtained for the satellites above 30° elevations angle. The GPS stations used in the present investigation are from Bele´m (hereafter referred as BELE; 01.4°S, 48.4°W, dip lat. 1.8°N), Brası´lia (hereafter referred as BRAZ; 15.9°S, 47.9°W, dip lat. 11.3°S), Presidente Prudente (hereafter referred as UEPP; 22.12°S, 51.4°W, dip lat. 14.4°S), and Porto Alegre (hereafter referred as POAL; 30.1°S, 51.1°W, dip lat. 20.5°S), Brazil and the stations belong to the “Rede Brasileira de Monitoramento Contı´nuo (RBMC; Brazilian Network for Continuous GPS Monitoring)” operated by the “Instituto Brasileiro de Geografia e Estatı´stica (IBGE; Brazilian Institute of Geography and Statistics)”. All these stations are located in the Brazilian sector and cover equatorial to low latitude regions. Fig. 1 and Table 1 provide the details of the GPS sites used in the present study. The ionospheric sounding observations presented here from the “Universidade do Vale do Paraı´ba (UNIVAP)” network are from Palmas (hereafter referred as PAL; 10.2°S, 48.2°W, dip lat. 6.1°S, a near equatorial station) and Sa˜o Jose´ dos Campos (hereafter referred as SJC; 23.2°S, 45.9°W, dip lat. 18.0°S; located under the southern crest of equatorial ionospheric anomaly), Brazil. The dip latitudes presented for the GPS and digital ionosonde stations are for an altitude of 300 km, for the year 2005 using IGRF-11 (International Geomagnetic Reference Field 11th Generation is a global model of Earth’s large scale internal magnetic field). Both the ionospheric sounding stations are equipped with the Canadian Advanced Digital Ionosonde (CADI) (Grant et al., 1995; Sahai et al., 2007b; de Jesus et al., 2011). The digital ionosondes were used to obtain the variations of the ionospheric parameters minimum virtual height of the F-region (h’F), peak height of the maximum electron density of the F2-region (hmF2 hpF2), and F2-region critical frequency (foF2). The peak height of electron density of F2 region (hmF2) is usually taken as nearly equal to hpF2 (virtual height at 0.834 foF2) (Piggot and Rawer, 1972; Rama Rao et al., 2006). Sastri et al. (1997) have reported that during the daytime,
A.J. de Abreu et al. / Advances in Space Research 48 (2011) 1211–1220
1213
3. Results and discussion
Fig. 1. Map of South America showing the locations of the GPS and digital ionosonde stations used in the present study. Also, the geographic and magnetic equators are shown.
Table 1 Details of the Global Positioning System (GPS) and digital ionosonde (DI) sites used in the present study. For all the stations LT = UT 3 h. Location (symbol)
Instrumentation
Coordinates
Dip. lat.
Bele´m (BELE) Brası´lia (BRAZ) P. Prudente (UEPP) Porto Alegre (POAL) Palmas (PAL) S. J. dos Campos (SJC)
GPS GPS GPS GPS DI DI
01.4°S, 15.9°S, 22.1°S, 30.1°S, 10.2°S, 23.2°S,
01.8°N 11.3°S 14.4°S 20.5°S 06.1°S 18.0°S
48.4°W 47.9°W 51.4°W 51.1°W 48.2°W 45.9°W
hmF2 or hpF2 could serve the same purpose depending on the temporal evolution of the electric field. The hpF2 could depart from the hmF2 by 650 km during daytime and by 610 km during nighttime (Batista et al., 1991), but the temporal variations will be nearly the same (Sastri et al., 1997). Fig. 1 and Table 1 provide the details of the digital ionosondes sites used in the present study. The geomagnetic indices AE (intensity of the aroral electrojet; every 1-min values) and Dst (intensity of the ring current; hourly values) used in the present investigations were obtained from the website http://swdcwww.kugi. kyoto-u.ac.jp and the geomagnetic index Kp (intensity of storm; 3-hourly values) from the website http://ftp.gwdg. de./pub/geophys/kp-ap/tab/. The total interplanetary magnetic field (IMF) B, IMF Bz component in geocentric solar magnetospheric (GSM) coordinates, solar wind proton bulk velocity Vp, and solar wind ion density Np were obtained from the ACE satellite website http://www.srl.caltech.edu/ace/.
Fig. 2 shows the time variations of the solar, interplanetary, and geomagnetic indices for the period studied (14– 17 May 2005). The black vertical arrow indicates the sudden storm commencement (SSC). The sudden storm commencement (SSC) started at 0239 UT on 15 May (see Fig. 2). At the same time, the IMF-Bz turns southward to a value around 45 nT and there is an abrupt simultaneous increase in solar wind speed from about 400 km/s to about 1000 km/s and ion density from about 4 cm 3 to about 30 cm 3, indicating the arrival of an interplanetary shock structure leading to the formation of an super geomagnetic storm. After the SSC, during the storm main phase, the Kp index reached 8+ on the early morning of 15 May and the Dst index started decreasing from 77 nT at 0700 UT to 263 nT at 0900 UT on 15 May. When rapid changes in the Dst index occur during the storm main phase, prompt penetration of magnetospheric electric field affects the ionospheric dynamics at equatorial and low latitudes on both the dayside and nightside (Abdu et al., 1991; Wygant et al., 1998; Basu et al., 2001). After 0900 UT on 15 May, started a long storm recovery phase, lasting near at 2400 UT on 16 May (Fig. 2). Fig. 2 also shows long and strong fluctuations in the AE index between about 0239 UT on 15 May and 2400 UT on 16 May. It is an important indicator of large energy injection at auroral latitudes due the Joule heating. As observed out by Aksnes et al. (2004), the Joule heating appears to be linearly related with the increase of the AE index. The time variations of the ionospheric parameters h’F, hpF2, and foF2 obtained at PAL and SJC during the period 14–17 May 2005 are shown in Figs. 3–6, respectively. The ionospheric parameters (h’F, hpF2, and foF2) observed during the quiet and disturbed (red lines) periods were obtained every 15 min from the ionograms. The averaged h’F, hpF2, and foF2 (three quiet days viz. 23, 24, and 25 May) variations are shown as green bands and their widths corresponds to ±1 standard deviations. Fig. 3 also shows the horizontal black bars indicating the presence of equatorial spread-F (ESF) in ionograms. Fig. 4 shows the time variations of virtual heights at six fixed reflection frequencies (electron densities), with measurements every 100 s (iso-frequency) obtained at PAL and SJC during the period 15–16 May 2005. Fig. 7 (for Figs. 3 and 7, the black vertical arrow indicates the time of sudden storm commencement (SSC)) shows the time variations of the average vertical total electron content (vTEC) obtained at 4 GPS receiving stations during the period 14–17 May 2005. The observed vTEC variations during the disturbed period are shown in red lines and the green lines are observations on the quiet day (14 May) repeated for all the subsequent days to allow a comparative study between quiet and disturbed days. Fig. 8 shows the phase fluctuations (rate of change of TEC) observed at 4 GPS receiving stations (14–17 May 2005). The black vertical dashed line indicates the
1214
A.J. de Abreu et al. / Advances in Space Research 48 (2011) 1211–1220
Fig. 2. Variations of the total interplanetary magnetic field (IMF) B, z component of IMF Bz in GSM coordinates, solar wind proton bulk velocity Vp, and solar wind ion density Np, obtained from the ACE satellite during the period 14–17 May 2005. Also, the AE, Kp, and Dst geomagnetic indices during the period 14–17 May 2005 are presented. The black vertical arrow indicates the sudden storm commencement (SSC).
Fig. 3. Variations of the ionospheric parameter h’F obtained at Palmas (PAL) and Sa˜o Jose´ dos Campos (SJC) during the period 14–17 May 2005 (red lines). The green bands are ±1 standard deviation of the average quiet day values. Also, the horizontal black bars indicate the presence of equatorial spread-F (ESF). The black vertical arrow indicates the sudden storm commencement (SSC). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
sudden storm commencement (SSC). It should be mentioned that the ionospheric sounding stations are located at different places compared with the GPS receiving stations (Table 1).
3.1. Storm main and recovery phases Figs. 3, 5 and 6 show that the ionospheric parameters h’F, hpF2, and foF2 observed at PAL and SJC, start exhib-
A.J. de Abreu et al. / Advances in Space Research 48 (2011) 1211–1220
1215
Fig. 4. Variations of the ionospheric parameter h’F for six different frequencies (isofrequencies) observed at Palmas (PAL) and Sa˜o Jose´ dos Campos (SJC) during the period 15–16 May 2005. The black vertical arrow indicates the sudden storm commencement (SSC).
Fig. 5. Variations of the ionospheric parameter hpF2 obtained at Palmas (PAL) and Sa˜o Jose´ dos Campos (SJC) during the period 14–17 May 2005 (red lines). The green bands are ±1 standard deviation of the average quiet day values. The black vertical arrow indicates the sudden storm commencement (SSC). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
iting deviations from the quiet day average values after the SSC (0239 UT on 15 May), which continue during storm main and recovery phases (15 and 16 May). Figs. 3 and 4 show very clearly the variations of h’F at PAL and SJC. Soon after the SSC there is uplifting of the F region at PAL and SJC on the night of 14–15 May (Figs. 3 and 6), possibly due to prompt penetration of eastward electric field immediately after SSC. As mentioned earlier, soon after SSC during the fast decrease (about 90 nT/h) of
the Dst index (Fig. 2) there is a good possibility of prompt penetration of electric field of magnetospheric origin resulting in uplifting of the F region (Abdu et al., 1991; Wygant et al., 1998; Basu et al., 2001). However, this post-midnight uplifting during storm-time resulted in plasma bubbles (at PAL and BRAZ) only up to the low magnetic latitude and drifted possibly to west. The variations in foF2 at PAL and SJC (Fig. 6) present fairly different behavior after the SSC on 15 and 16 May,
1216
A.J. de Abreu et al. / Advances in Space Research 48 (2011) 1211–1220
Fig. 6. Variations of the ionospheric parameter foF2 obtained at Palmas (PAL) and Sa˜o Jose´ dos Campos (SJC) during the period 14–17 May 2005 (red lines). The green bands are ±1 standard deviation of the average quiet day values. The black vertical arrow indicates the sudden storm commencement (SSC). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Fig. 7. Variations of the average vertical total electron content (vTEC) from GPS observations at 4 receiving stations (Table 1) during the period 14–17 May 2005. The black vertical arrow indicates the sudden storm commencement (SSC).
particularly during the daytime. The foF2 and hpF2 (Fig. 5) variations observed at SJC on 15 and 16 May show large storm time fluctuations, fairly similar to that reported by Vijaya Lekshmi et al. (2008) for Okinawa, Japan. The foF2 variations observed at SJC (mostly positive phase), possibly the daytime equatorward wind produced by high latitude heating reaches only up to low latitude region and does not each near the equatorial region. Lin et al. (2005) have suggested that the storm time equatorward wind is important is producing positive storm effect. Vijaya
Lekshmi et al. (2008) have mentioned that at low latitudes, the occurrence of positive or negative phase depends also on the latitudinal extent of the equatorward wind. The ionospheric sounding station SJC is not very far from the GPS receiving station UEPP and foF2 variations during the daytime observed at SJC are very similar to vTEC variations observed at UEPP on 15 and 16 May (see Fig. 7). The variations in foF2 on the night of 14–15 May at SJC after SSC are fairly similar to the quiet day average values, except a small peak close to about 0600 UT. On the night
A.J. de Abreu et al. / Advances in Space Research 48 (2011) 1211–1220
1217
Fig. 8. The phase fluctuations or rate of change of TEC (in TECU/min) from GPS observations presented in Fig. 6 for each GPS station. The black vertical dashed line indicates the sudden storm commencement (SSC).
of 15–16 May both h’F (Fig. 3) and hpF2 (Fig. 5) observed at SJC show unusual large height rise at centered at about 0400 UT. This could be possibly due to altered dynamo effect of wind circulation with upward drift at night (Fuller-Rowell et al., 2002). Fig. 7 shows the variations of vTEC data obtained at the equatorial and low latitude stations in the Brazilian sector during the period 14–17 May 2005. Soon after SSC a trough is observed at BELE and a crest is above UEPP indicating strengthening of nighttime equatorial anomaly. The large positive storm effects during the daytime on 15 and 16 May (particularly at BRAZ, UEPP, and POAL; away from the magnetic equator) are possibly associated again with strengthening of daytime equatorial anomaly. The variations in foF2 for the SJC and vTEC for the UEPP and POAL are fairly similar during the daytime on 15 and 16 May. There are enhancements close to 1200 UT and 1700 UT on 15 May (after the main phase) and doublepeaked enhancements close to 1400 UT and 1800 UT on 16 May (recovery phase). No similar enhancements in foF2 were observed at PAL on 15 and 16 May. On 15 May, it appears that during the daytime, the variations in foF2 are controlled by both ionospheric dynamo electric fields and meridional neutral wind (Lu et al., 2008). Whereas on 16 May, a careful look at vTEC variations, when a positive phase is observed during the daytime up to BELE (an equatorial station) from equatorial ionospheric anomaly region, it appears that meridional wind plays an important role. This is possibly due to neutral composition change (increase in atomic oxygen density). Balan et al. (2009) (see also Vijaya Lekshmi et al., 2008) mention that direct effects of the equatorward neutral wind without effects of electric field can be the main driver of stronger positive phase in foF2 and vTEC observed at low-mid latitudes.
3.2. Equatorial ionospheric irregularities Fig. 3 shows presence of equatorial spread-F (ESF) at PAL for the nights of 14–15, 15–16, and 16–17 May. Fig. 8 shows a short period of phase fluctuations observed at BRAZ for the night of 14–15 May (satellite number 24). As pointed out by Aarons et al. (1997), the phase fluctuations indicate large-scale ionospheric irregularities of the order of kilometers-size. In contrast to the ionospheric sounding observations, there are no phase fluctuations observed on the nights of 15–16 and 16–17 May. As discussed out by Abdu (2001), the occurrence of ESF has seasonal and day-to-day variability (Burke et al., 2004; Makela and Miller, 2008). In the Brazilian sector, Sahai et al. (2000) observed by the OI 630 nm all-sky imaging system, that the seasonal occurrence of ESF is maximum between October and March and minimum between May and August. Considering the ionospheric pierce point (IPP) to be located at an altitude of 350 km (Kaplan and Hegarty, 2006), the magnetic latitude for BRAZ will be 15.9°S. Therefore, the present observations (on the night of 14–15 May, the ionospheric observations at PAL and GPS observations at BRAZ) show that possibly on this night the plasma bubbles extended only up to low magnetic latitude where the phase fluctuations (irregularities of only few km scale-size) was observed. During the super geomagnetic storm main phase occurring during the postmidnight period, the F-region drifted quickly upwards (Fig. 3) resulting in the generation of any ESF of largescale (plasma bubbles), possibly east of PAL and moved towards west on this magnetically disturbed night (Abdu et al., 2003). Since the ESF and the phase fluctuations were not observed at the low latitude stations (SJC, UEPP, and POAL), the present ESF observations at PAL and phase fluctuations at BRAZ possibly indicate
1218
A.J. de Abreu et al. / Advances in Space Research 48 (2011) 1211–1220
that the plasma bubbles were limited to low magnetic latitude. 4. Conclusions In this paper, we have analyzed and presented the ionospheric sounding and GPS observations in the equatorial and low latitude regions in the Brazilian sector during the super geomagnetic storm of 15 May 2005. Some of the salient features related to these observations are summarized below. 1. The super geomagnetic storm had fast decrease in the Dst index soon after SSC at 0239 UT on 15 May. There is a good possibility of prompt penetration of electric field of magnetospheric origin that resulted in uplifting of the F region observed by ionospheric sounding at PAL and SJC. 2. The vTEC observations showed a trough at BELE and a crest above UEPP, soon after SSC, indicating strengthening of nighttime equatorial anomaly. 3. During the daytime on 15 and 16 May, in the recovery phase, the variations in foF2 at SJC and the vTEC observations, particularly at BRAZ, UEPP, and POAL, showed large positive ionospheric storm. 4. There was ESF on all the nights at PAL, in the postmidnight (UT) sector, and phase fluctuations only on the night of 14–15 May (for a short period) at BRAZ, after the SSC. No phase fluctuations were observed at the equatorial station BELE and low latitude stations (BRAZ, UEPP, and POAL) at all other times. This indicates that the plasma bubbles were generated and confined on this magnetically disturbed night only up to the low magnetic latitude and drifted possibly to west.
Acknowledgements The authors thank the authorities of the “Rede Brasileira de Monitoramento Contı´nuo de GPS (RBMC)”, Brazil, for kindly allowing us to use the data obtained by the RBMC. The authors also thank the Brazilian funding agencies “CNPq” and “FAPESP” for kindly providing the partial financial support. References Aarons, J., Mendillo, M., Yantosca, R. GPS phase fluctuations in the equatorial region during the MISETA 1994 campaign. J. Geophys. Res. 101 (A8), 26851–26862, 1996. Aarons, J., Mendillo, M., Yantosca, R. GPS phase fluctuations in the equatorial region during sunspot minimum. Radio Sci. 32, 1535–1550, doi:10.1029/97RS00664, 1997. Abdu, M.A., Sobral, J.H.A., de Paula, E.R., Batista, I.S. Magnetospheric disturbance effects on the equatorial ionization anomaly (EIA): an overview. J. Atmos. Terr. Phys. 53, 757–771, 1991. Abdu, M.A. Outstanding problems in the equatorial ionosphere–thermosphere electrodynamics relevant to spread F. J. Atmos. Solar-Terres. Phys. 63, 869–884, 2001.
Abdu, M.A., Batista, I.S., Takahashi, H., MacDougall, J., Sobral, J.H., Medeiros, A.F., Trivedi, N.B. Magnetospheric disturbance induced equatorial plasma bubble development and dynamics: a case study in Brazilian sector. J. Geophys. Res. 108 (A12), 1449, doi:10.1029/ 2002JA009721, 2003. Afraimovich, E.L., Kosogorov, E.A., Lesyuta, O.S., Ushakov, I.I., Yakovets, A.F. Geomagnetic control of the spectrum of traveling ionospheric disturbances based on data from a global GPS network. Ann. Geophys. 19, 723–731, 2001. Aksnes, A., Stadsnes, J., Lu, G., Østgaard, N., Vondrak, R.R., Detrick, D.L., Rosenberg, T.J., Germany, G.A., Schulz, M. Effects of energetic electrons on the electrodynamics in the ionosphere. Ann. Geophys. 22, 475–496, 2004. Balan, N., Alleyne, H., Otsuka, Y., Lakshmi, D.V., Fejer, B.G., McCrea, I. Relative effects of electric field and neutral wind on positive ionospheric storms. Earth Planets Space 61, 439–445, 2009. Basu, S., Basu, Su., Valladares, C.E., Yeh, H.C., Su, S.Y., Mackenzie, E., Sultan, P.J., Aarons, J., Rich, F.J., Doherty, P., Groves, K.M., Bullet, T.W. Ionospheric effects of major magnetic storms during the International Space Weather Period of September and October 1999: GPS observations, VHF/UHF scintillations, and in situ density structures at middle and equatorial latitudes. J. Geophys. Res. 106 (A12), 30389–30413, 2001. Batista, I.S., de Paula, E.R., Abdu, M.A., Trivedi, N.B. Ionospheric effects of the March 13, 1989 magnetic storm at low and equatorial latitudes. J. Geophys. Res. 96, 13943–13952, 1991. Bauske, R., Prolss, G.W. Numerical simulation of long-duration positive ionospheric storm effects. Adv. Space Res. 22 (1), 117–121, 1998. Becker-Guedes, F., Sahai, Y., Fagundes, P.R., Espinoza, E.S., Pillat, V.G., Lima, W.L.C., Basu, Su., Basu, Sa., Otsuka, Y., Shiokawa, K., Mackenzie, E.M., Pi, X., Bittencourt, J.A. The ionospheric response in the Brazilian sector during the super geomagnetic storm on 20 November 2003. Ann. Geophys. 25, 863–873, 2007. Buonsanto, M.J. Ionospheric storms – a review. Space Sci. Rev. 88, 563– 601, 1999. Burke, W.J., Huang, C.Y., Gentile, L.C., Bauer, L. Seasonal–longitudinal variability of equatorial plasma bubbles. Ann. Geophys. 22, 3089– 3098, 2004. Danilov, A.D., Morozova, L.D. Ionospheric storms in the F2 region: morphology and physics (review). Geomagn. Aeron. 25, 593–605, 1985. Dashora, N., Sharma, S., Dabas, R.S., Alex, S., Pandey, R. Large enhancements in low latitude total electron content during 15 May 2005 geomagnetic storm in Indian zone. Ann. Geophys. 27, 1803–1820, 2009. de Abreu, A.J., Fagundes, P.R., Sahai, Y., de Jesus, R., Bittencourt, J.A., Brunini, C., Gende, M., Pillat, V.G., Lima, W.L.C., Abalde, J.R., Pimenta, A.A. Hemispheric asymmetries in the ionospheric response observed in the American sector during an intense geomagnetic storm. J. Geophys. Res. 115, A12312, doi:10.1029/2010JA015661, 2010a. de Abreu, A.J., Sahai, Y., Fagundes, P.R., Becker-Guedes, F., de Jesus, R., Guarnieri, F.L., Pillat, V.G. Response of the ionospheric F-region in the Brazilian sector during the super geomagnetic storm in April 2000 observed by GPS. Adv. Space Res. 45, 1322–1329, doi:10.1016/ j.asr.2010.02.003, 2010b. de Jesus, R., Sahai, Y., Guarnieri, F.L., Fagundes, P.R., de Abreu, A.J., Becker-Guedes, F., Brunini, C., Gende, M., Cintra, T.M.F., de Souza, V.A., Pillat, V.G., Lima, W.L.C. Effects observed in the ionospheric Fregion in the South American sector during the intense geomagnetic storm of 14 December 2006. Adv. Space Res. 46, 909–920, doi:10.1016/ j.asr.2010.04.031, 2010. de Jesus, R., Sahai, Y., Guarnieri, F.L., Fagundes, P.R., de Abreu, A.J., Pillat, V.G., Lima, W.L.C. F-region ionospheric parameters observed in the equatorial and low latitude regions during medium solar activity in the Brazilian sector and comparison with the IRI-2007 model results. Adv. Space Res. 47, 718–728, doi:10.1016/j.asr.2010.10.020, 2011.
A.J. de Abreu et al. / Advances in Space Research 48 (2011) 1211–1220 Fagundes, P.R., Aruliah, A.L., Rees, D., Bittencourt, J.A. Gravity-wave generation and propagation during geomagnetic storms over Kiruna (67.8°N, 20.4°E).. Ann. Geophys. 13 (4), 358–366, 1995. Fejer, B.G., Jensen, J.W., Kikuchi, T., Abdu, M.A., Chau, L. Equatorial ionospheric electric fields during the November 2004 magnetic storm. J. Geophys. Res. 112, A10304, doi:10.1029/2007JA012376, 2007. Fuller-Rowell, T.J., Millward, G.H., Richmond, A.D., Codrescu, M.V. Storm-time changes in the upper atmosphere at low latitudes. Atmos. Solar-Terres. Phys. 64, 1383–1391, 2002. Grant, I.F., McDougall, J.W., Ruohoniemi, J.M., Bristow, W.A., Sofko, G.J., Koehler, J.A., Danskin, D., Andre, D. Comparison of plasma flow velocities determined by the ionosonde Doppler drift technique, SuperDARN radars, and patch motion. Radio Sci. 30, 1537–1549, 1995. Hines, C.O., Hooke, W.H. Discussion of ionization effects on the propagation of acoustic-gravity waves in the ionosphere. J. Geophys. Res. 75, 2563–2567, 1960. Kaplan, E.D., Hegarty, C.J. Understanding GPS: Principles and Applications, second ed Artech House, Inc., 2006. Killeen, T.J., Hays, P.B., Carignan, G.R., Heelis, R.A., Hanson, W.B., Spencer, N.W., Brace, L.H. Ion-neutral coupling in the high-latitude F-region: evaluation of ion heating terms from Dynamics Explorer 2. J. Geophys. Res. 89, 7495–7508, 1984. Klimenko, M.V., Klimenko, V.V., Ratovsky, K.G., Goncharenko, L.P., Sahai, Y., Fagundes, P.R., de Jesus, R., de Abreu, A.J., Vesnin, A.M. Numerical modeling of ionospheric effects in the middle- and lowlatitude F region during geomagnetic storm sequence of 9-14 September 2005. Radio Sci. 46, RS0D03, doi:10.1029/2010RS004590, 2011. Jansen, F., Pirjola, R. Space weather research elucidates risks to technological infrastructure. EOS, Transactions, American Geophysical Union, no. 85, pp. 241–245, 2004. Lei, J., Burns, A.G., Tsugawa, T., Wang, W., Solomon, S.C., Wiltberger, M. Observations and simulations of quasiperiodic ionospheric oscillations and large-scale traveling ionospheric disturbances during the December 2006 geomagnetic storm. J. Geophys. Res. 113, A06310, doi:10.1029/2008JA013090, 2008. Lima, W.L.C., Becker-Guedes, F., Sahai, Y., Fagundes, P.R., Abalde, J.R., Growley, G., Bittencourt, J.A. Response of the equatorial and low-latitude ionosphere during the space weather events of April 2002. Ann. Geophys. 22, 3211–3219, 2004. Lin, C.H., Richmond, A.D., Heelis, R.A., Bailey, G.J., Lu, G., Liu, J.Y., Yeh, H.C., Su, S.Y. Theoretical study of the low and mid latitude ionospheric electron density enhancement during the October 2003 super storm: relative importance of the neutral wind and the electric field. J. Geophys. Res. 110, A12312, doi:10.1029/2005JA011304, 2005. Lu, G., Goncharenko, L.P., Richmond, A.D., Roble, R.G., Aponte, N. A dayside ionospheric positive storm phase driven by neutral winds. J. Geophys. Res. 113, A08304, doi:10.1029/2007JA012895, 2008. Makela, J.J., Miller, E.S. Optical observations of the growth and day-today variability of equatorial plasma bubbles. J. Geophys. Res. 113, A03307, 2008. Martinis, C.R., Mendillo, M.J., Aarons, J. Toward a synthesis of equatorial spread F onset and suppression during geomagnetic storms. J. Geophys. Res. 110, A07306, 2005. Maruyama, N., Richmond, A.D., Fuller-Rowell, T.J., Codrescu, M.V., Sazykin, S., Toffoletto, F.R., Spiro, R.W., Millward, G.H. Interaction between direct penetration and disturbance dynamo electric fields in the storm-time equatorial ionosphere. J. Geophys. Res. 32, L17105, doi:10.1029/2005GL023763, 2005. Namgaladze, A.A., Forster, M., Yurik, R.Y. Analysis of the positive ionospheric response to a moderate geomagnetic storm using a global numerical model. Ann. Geophys. 18, 461–477, 2000. Nicolls, M.J., Kelley, M.C., Coster, A.J., Gonzalez, S.A., Makela, J.J. Imaging the structure of a large-scale TID using ISR and TEC data. Geophys. Res. Lett. 31, L09812, doi:10.1029/2004GL019797, 2004. Paznukhov, V.V., Altadill, D., Reinisch, B.W. Experimental evidence for the role of the neutral wind in the development of ionospheric storms in midlatitudes. J. Geophys. Res. 114, A12319, doi:10.1029/ 2009JA014479, 2009.
1219
Piggot, R., Rawer, K. (Eds.), U.R.S.I. Handbook of Ionogram Interpretation and Reduction, Rep. UAG-23, second ed., World Data Cent. for Sol.-Terr. Phys., Boulder, Colo, p. 21, 1972. Prolss, G.W. Common origin of positive ionospheric storms at middle latitudes and the geomagnetic activity effect at low latitudes. J. Geophys. Res. 98 (A4), 5981–5991, 1993. Rama Rao, P.V.S., Niranjan, K., Prasad, D.S.V.V.D., Gopi Krishna, S., Uma, G. On the validity of the ionospheric pierce point (IPP) altitude of 350 km in the Indian equatorial and low-latitude sector. Ann. Geophys. 24, 2159–2168, 2006. Sahai, Y., Fagundes, P.R., Bittencourt, J.A. Transequatorial F-region ionospheric plasma bubbles: solar cycle effects. J. Atmos. Solar-Terres. Phys. 62, 1377–1383, 2000. Sahai, Y., Fagundes, P.R., Becker-Guedes, F., Bolzan, M.J.A., Abalde, J.R., Pillat, V.G., de Jesus, R., Lima, W.L.C., Crowley, G., Shiokawa, K., MacDougall, J.W., Lan, H.T., Igarashi, K., Bittencourt, J.A. Effects of the major geomagnetic storms of October 2003 on the equatorial and low-latitude F region in two longitudinal sectors. J. Geophys. Res. 110, A12S91, doi:10.1029/2004JA010999, 2005. Sahai, Y., Becker-Guedes, F., Fagundes, P.R., Lima, W.L.C., Otsuka, Y., Huang, C. –S., Espinoza, E.S., Pi, X., de Abreu, A.J., Bolzan, M.J.A., Pillat, V.G., Abalde, J.R., Pimenta, A.A., Bittencourt, J.A. Response of nighttime equatorial and low latitude F-region to the geomagnetic storm of August 18, 2003, in the Brazilian sector. Adv. Space Res. 39, 1325–1334, 2007a. Sahai, Y., Becker-Guedes, F., Fagundes, P.R., Lima, W.L.C., de Abreu, A.J., Guarnieri, F.L., Candido, C.M.N., Pillat, V.G. Unusual ionospheric effects observed during the intense 28 October 2003 solar flare in the Brazilian sector. Ann. Geophys. 25, 2497–2502, 2007b. Sahai, Y., Becker-Guedes, F., Fagundes, P.R., de Jesus, R., de Abreu, A.J., Paxton, L.J., Goncharenko, L.P., Brunini, C., Gende, M., Ferreira, A.S., Lima, N.S., Guarnieri, F.L., Pillat, V.G., Bittencourt, J.A., Candido, C.M.N. Effects observed in the Latin American sector ionospheric F region during the intense geomagnetic disturbances in the early part of November 2004. J. Geophys. Res. 114, A00A19, 2009a. Sahai, Y., Becker-Guedes, F., Fagundes, P.R., de Abreu, A.J., de Jesus, R., Pillat, V.G., Abalde, J.R., Martinis, C.R., Brunini, C., Gende, M., Huang, C.S., Pi, X., Lima, W.L.C., Bittencourt, J.A., Otsuka, T. Observations of the F-region ionospheric irregularities in the South American sector during the October 2003 ‘Halloween Storms’. Ann. Geophys. 27 (12), 4463–4477, 2009b. Sahai, Y., Becker-Guedes, F., Fagundes, P.R., de Jesus, R., de Abreu, A.J., Otsuka, Y., Shiokawa, K., Igarashi, K., Yumoto, K., Huang, C.S., Lan, H.T., Saito, A., Guarnieri, F.L., Pillat, V.G., Bittencourt, J.A. Effects observed in the ionospheric F region in the east Asian sector during the intense geomagnetic disturbances in the early part of November 2004. J. Geophys. Res. – Space Phys., 114, doi:10.1029/ 2008JA013053 (Art. No. A00A18), 2009c. Sahai, Y., Fagundes, P.R., de Jesus, R., de Abreu, A.J., Crowley, G., Kikuchi, T., Huang, C.-S., Pillat, V.G., Guarnieri, F.L., Abalde, J.R., Bittencourt, J. Studies of ionospheric F-region response in the Latin American sector during the geomagnetic storm of 21–22 January 2005. Ann. Geophys. 29, 919–929, doi:10.5194/angeo-29-1-2011, 2011. Sastri, J.H., Abdu, M.A., Sobral, J.H.A. Response of equatorial ionosphere to episodes of asymmetric ring current activity. Ann. Geophys. 15, 1316–1323, 1997. Sastri, J.H., Niranjan, K., Subbarao, K.S.V. Response of the equatorial ionosphere in the Indian (midnight) sector to the severe magnetic storm of July 15, 2000. Geophys. Res. Lett. 29 (13), 1651, doi:10.1029/ 2002GL015133, 2002. Schunk, R.W., Sojka, J.J. Ionosphere-thermosphere space weather issues. J. Atmos. Terres. Phys. 58 (14), 1527–1574, 1996. Vijaya Lekshmi, D., Balan, N., Vaidyan, V.K., Alleyne, H., Bailey, G.J. Response of the ionosphere to super geomagnetic storms: observations and modeling. Adv. Space Res. 41, 548–555, 2008. Wanninger, L. Effects of the equatorial ionosphere on GPS. GPS World pp. 48–54, July 1993.
1220
A.J. de Abreu et al. / Advances in Space Research 48 (2011) 1211–1220
Werner, S., Bauske, R., Prolss, G.W. On the origin of positive ionospheric storms. Adv. Space Res. 24 (11), 1485–1489, 1999. Whalen, J.A. Dependence of equatorial bubbles and bottom-side spread F on season, magnetic activity, and E B drift velocity during solar maximum. J. Geophys. Res. 107 (A2), 2002. Wygant, J., Rowland, D., Singer, H.J., Temerin, M., Mozer, F., Hudson, M.K. Experimental evidence on the role of the large spatial scale
electric field in creating the ring current. J. Geophys. Res. 103, 29527– 29544, 1998. Yizengaw, E., Moldwin, M.B., Sahai, Y., de Jesus, R. Strong postmidnight equatorial ionospheric anomaly observations during magnetically quiet periods. J. Geophys. Res. 114, A12308, doi:10.1029/ 2009JA014603, 2009.
Advances in Space Research 48 (2011) 1211–1220 www.elsevier.com/locate/asr
An investigation of ionospheric F region response in the Brazilian sector to the super geomagnetic storm of May 2005 A.J. de Abreu a,⇑, Y. Sahai a, P.R. Fagundes a, R. de Jesus a, J.A. Bittencourt b, V.G. Pillat a a
Departamento de Fı´sica e Astronomia, Universidade do Vale do Paraı´ba (UNIVAP), Av. Shishima Hifumi, 2911, Sa˜o Jose´ dos Campos, Sa˜o Paulo, Brazil b Instituto Nacional de Pesquisas Espaciais (INPE), Av. dos Astronautas, 1758, Caixa, Postal 515, Sa˜o Jose´ dos Campos, Sa˜o Paulo, Brazil Received 3 March 2011; received in revised form 23 May 2011; accepted 30 May 2011 Available online 12 June 2011
Abstract In this paper, we have investigated the responses of the ionospheric F region at equatorial and low latitude regions in the Brazilian sector during the super geomagnetic storm on 15–16 May 2005. The geomagnetic storm reached a minimum Dst of 263 nT at 0900 UT on 15 May. In this paper, we present vertical total electron content (vTEC) and phase fluctuations (in TECU/min) from Global Positioning System (GPS) observations obtained at Bele´m, Brası´lia, Presidente Prudente, and Porto Alegre, Brazil, during the period 14–17 May 2005. Also, we present ionospheric parameters h’F, hpF2, and foF2, using the Canadian Advanced Digital Ionosonde (CADI) obtained at Palmas and Sa˜o Jose´ dos Campos, Brazil, for the same period. The super geomagnetic storm has fast decrease in the Dst index soon after SSC at 0239 UT on 15 May. It is a good possibility of prompt penetration of electric field of magnetospheric origin resulting in uplifting of the F region. The vTEC observations show a trough at BELE and a crest above UEPP, soon after SSC, indicating strengthening of nighttime equatorial anomaly. During the daytime on 15 and 16 May, in the recovery phase, the variations in foF2 at SJC and the vTEC observations, particularly at BRAZ, UEPP, and POAL, show large positive ionospheric storm. There is ESF on the all nights at PAL, in the post-midnight (UT) sector, and phase fluctuations only on the night of 14–15 May at BRAZ, after the SSC. No phase fluctuations are observed at the equatorial station BELE and low latitude stations (BRAZ, UEPP, and POAL) at all other times. This indicates that the plasma bubbles are generated and confined on this magnetically disturbed night only up to the low magnetic latitude and drifted possibly to west. Ó 2011 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: Geomagnetic storm; Ionosphere; Equatorial ionospheric irregularities
1. Introduction The ionospheric storms associated with geomagnetic storms represent an extreme form of space weather which has a growing importance at present and can have significant, adverse effects on increasingly sophisticated groundand space-based technological systems (Buonsanto, 1999). Several investigators have studied the space weather distur-
⇑ Corresponding author. Tel.: +55 12 39471146; fax: +55 12 39471149.
E-mail addresses: [email protected] (A.J. de Abreu), [email protected] (Y. Sahai), [email protected] (P.R. Fagundes), [email protected] (R. de Jesus), [email protected] (J.A. Bittencourt), [email protected] (V.G. Pillat).
bances in the ionosphere–thermosphere system (Schunk and Sojka, 1996; Buonsanto, 1999; Jansen and Pirjola, 2004; Klimenko et al., 2011; Sahai et al., 2011). The response of the ionosphere–thermosphere system at equatorial and mid-low latitudes regions during intense/super geomagnetic storms has been recently provided by Becker-Guedes et al. (2007), Sahai et al. (2007a, 2009a,b), de Jesus et al. (2010), and de Abreu et al. (2010a). During the periods of intense/super geomagnetic storms, the equatorial and low latitude regions can have severe modifications in the ionospheric F region height and peak electron density. These modifications are related to the electric fields, winds, and composition changes (Werner et al., 1999; Sastri et al., 2002; Fejer et al., 2007). The
0273-1177/$36.00 Ó 2011 COSPAR. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.asr.2011.05.036
1212
A.J. de Abreu et al. / Advances in Space Research 48 (2011) 1211–1220
responsible for the behavior of the equatorial and low latitude ionospheric electric fields are the prompt equatorward penetration of magnetospheric/high latitude electric fields (period less than one hour) and the ionospheric disturbance dynamo (period of several hours) generated by the global winds circulation due to the Joule heating in the high latitude atmosphere in consequence the particles of precipitation (Maruyama et al., 2005). During the periods of intense geomagnetic disturbances, occurs the injection/transport of energy from high latitudes to low latitudes and changes in the global winds circulation via Joule heating (Nicolls et al., 2004). In addition, this energy injection and changes in the global winds can drive the propagation of atmospheric gravity waves equatorward in the form of traveling atmospheric disturbances (TADs). These TADs when interact with the ionosphere can produce traveling ionospheric disturbances (TIDs) of high speeds (Hines and Hooke, 1960; Killeen et al., 1984; Fagundes et al., 1995; Afraimovich et al., 2001; Lima et al., 2004). Also, during geomagnetic disturbances can occur increase or decrease of the ionospheric electron density as compared with quiet periods, which are called positive ionospheric storm (positive phase) and negative ionospheric storm (negative phase), respectively (Danilov and Morozova, 1985; Prolss, 1993; Bauske and Prolss, 1998). As discussed out by Namgaladze et al. (2000), positive phase are often related the large-scale wind circulation. The generation or suppression of equatorial ionospheric irregularities or equatorial spread-F (ESF) in the equatorial and low latitude regions during geomagnetic disturbances is other important aspect to be investigated (Whalen, 2002; Martinis et al., 2005; Sahai et al., 2009c). In this paper, we present and discuss the response of the ionospheric F region at equatorial and low latitude regions in the Brazilian sector during the super geomagnetic storm that occurred on 15–16 May 2005. The main objectives have been to study the storm-time electrodynamics and generation or inhibition of equatorial ionospheric irregularities (ESF) (Martinis et al., 2005) in the Brazilian sector during this super storm. The ionospheric response during geomagnetic storms in different latitudinal and longitudinal sectors have been studied by Sahai et al. (2005), Lei et al. (2008), Dashora et al. (2009), Paznukhov et al. (2009), and de Abreu et al. (2010b). Lei et al. (2008) observed a pronounced positive ionospheric storm effect in the American sector to the December 2006 geomagnetic storm. Dashora et al. (2009) have reported a large enhancement in low latitude total electron content during the 15 May 2005 super geomagnetic storm in the Indian sector during few hours in the daytime. de Abreu et al. (2010b) have observed positive ionospheric storm phase in the equatorial and low latitude regions in the Brazilian sector to the April 2000 super geomagnetic storm using GPS measurements. The results of this investigation were obtained using ionospheric sounding and Global Positioning System (GPS) observations, from equatorial to low latitude regions in Brazilian sector. To the authors’ knowledge, this is the first
investigation of the response of the ionospheric F region during this strong geomagnetic disturbance in the Brazilian sector. 2. Observations The Global Positioning System (GPS) observations were obtained from several GPS receiving stations in the Brazilian sector in the standard “Receiver Independent Exchange format (RINEX)” with temporal resolution of 15 s from 4 receiving stations during the super storm in May 2005. The GPS observations were used to obtain the measures of the vertical total electron content (vTEC) calculated in units of TEC (1 TECU = 1016 electrons/m2) (Wanninger, 1993; Yizengaw et al., 2009) and the measures of the phase fluctuations (rate of change of TEC) calculated in TECU/min (Aarons et al., 1996, 1997). The GPS observations used for measurements of the vTEC and phase fluctuations were obtained for the satellites above 30° elevations angle. The GPS stations used in the present investigation are from Bele´m (hereafter referred as BELE; 01.4°S, 48.4°W, dip lat. 1.8°N), Brası´lia (hereafter referred as BRAZ; 15.9°S, 47.9°W, dip lat. 11.3°S), Presidente Prudente (hereafter referred as UEPP; 22.12°S, 51.4°W, dip lat. 14.4°S), and Porto Alegre (hereafter referred as POAL; 30.1°S, 51.1°W, dip lat. 20.5°S), Brazil and the stations belong to the “Rede Brasileira de Monitoramento Contı´nuo (RBMC; Brazilian Network for Continuous GPS Monitoring)” operated by the “Instituto Brasileiro de Geografia e Estatı´stica (IBGE; Brazilian Institute of Geography and Statistics)”. All these stations are located in the Brazilian sector and cover equatorial to low latitude regions. Fig. 1 and Table 1 provide the details of the GPS sites used in the present study. The ionospheric sounding observations presented here from the “Universidade do Vale do Paraı´ba (UNIVAP)” network are from Palmas (hereafter referred as PAL; 10.2°S, 48.2°W, dip lat. 6.1°S, a near equatorial station) and Sa˜o Jose´ dos Campos (hereafter referred as SJC; 23.2°S, 45.9°W, dip lat. 18.0°S; located under the southern crest of equatorial ionospheric anomaly), Brazil. The dip latitudes presented for the GPS and digital ionosonde stations are for an altitude of 300 km, for the year 2005 using IGRF-11 (International Geomagnetic Reference Field 11th Generation is a global model of Earth’s large scale internal magnetic field). Both the ionospheric sounding stations are equipped with the Canadian Advanced Digital Ionosonde (CADI) (Grant et al., 1995; Sahai et al., 2007b; de Jesus et al., 2011). The digital ionosondes were used to obtain the variations of the ionospheric parameters minimum virtual height of the F-region (h’F), peak height of the maximum electron density of the F2-region (hmF2 hpF2), and F2-region critical frequency (foF2). The peak height of electron density of F2 region (hmF2) is usually taken as nearly equal to hpF2 (virtual height at 0.834 foF2) (Piggot and Rawer, 1972; Rama Rao et al., 2006). Sastri et al. (1997) have reported that during the daytime,
A.J. de Abreu et al. / Advances in Space Research 48 (2011) 1211–1220
1213
3. Results and discussion
Fig. 1. Map of South America showing the locations of the GPS and digital ionosonde stations used in the present study. Also, the geographic and magnetic equators are shown.
Table 1 Details of the Global Positioning System (GPS) and digital ionosonde (DI) sites used in the present study. For all the stations LT = UT 3 h. Location (symbol)
Instrumentation
Coordinates
Dip. lat.
Bele´m (BELE) Brası´lia (BRAZ) P. Prudente (UEPP) Porto Alegre (POAL) Palmas (PAL) S. J. dos Campos (SJC)
GPS GPS GPS GPS DI DI
01.4°S, 15.9°S, 22.1°S, 30.1°S, 10.2°S, 23.2°S,
01.8°N 11.3°S 14.4°S 20.5°S 06.1°S 18.0°S
48.4°W 47.9°W 51.4°W 51.1°W 48.2°W 45.9°W
hmF2 or hpF2 could serve the same purpose depending on the temporal evolution of the electric field. The hpF2 could depart from the hmF2 by 650 km during daytime and by 610 km during nighttime (Batista et al., 1991), but the temporal variations will be nearly the same (Sastri et al., 1997). Fig. 1 and Table 1 provide the details of the digital ionosondes sites used in the present study. The geomagnetic indices AE (intensity of the aroral electrojet; every 1-min values) and Dst (intensity of the ring current; hourly values) used in the present investigations were obtained from the website http://swdcwww.kugi. kyoto-u.ac.jp and the geomagnetic index Kp (intensity of storm; 3-hourly values) from the website http://ftp.gwdg. de./pub/geophys/kp-ap/tab/. The total interplanetary magnetic field (IMF) B, IMF Bz component in geocentric solar magnetospheric (GSM) coordinates, solar wind proton bulk velocity Vp, and solar wind ion density Np were obtained from the ACE satellite website http://www.srl.caltech.edu/ace/.
Fig. 2 shows the time variations of the solar, interplanetary, and geomagnetic indices for the period studied (14– 17 May 2005). The black vertical arrow indicates the sudden storm commencement (SSC). The sudden storm commencement (SSC) started at 0239 UT on 15 May (see Fig. 2). At the same time, the IMF-Bz turns southward to a value around 45 nT and there is an abrupt simultaneous increase in solar wind speed from about 400 km/s to about 1000 km/s and ion density from about 4 cm 3 to about 30 cm 3, indicating the arrival of an interplanetary shock structure leading to the formation of an super geomagnetic storm. After the SSC, during the storm main phase, the Kp index reached 8+ on the early morning of 15 May and the Dst index started decreasing from 77 nT at 0700 UT to 263 nT at 0900 UT on 15 May. When rapid changes in the Dst index occur during the storm main phase, prompt penetration of magnetospheric electric field affects the ionospheric dynamics at equatorial and low latitudes on both the dayside and nightside (Abdu et al., 1991; Wygant et al., 1998; Basu et al., 2001). After 0900 UT on 15 May, started a long storm recovery phase, lasting near at 2400 UT on 16 May (Fig. 2). Fig. 2 also shows long and strong fluctuations in the AE index between about 0239 UT on 15 May and 2400 UT on 16 May. It is an important indicator of large energy injection at auroral latitudes due the Joule heating. As observed out by Aksnes et al. (2004), the Joule heating appears to be linearly related with the increase of the AE index. The time variations of the ionospheric parameters h’F, hpF2, and foF2 obtained at PAL and SJC during the period 14–17 May 2005 are shown in Figs. 3–6, respectively. The ionospheric parameters (h’F, hpF2, and foF2) observed during the quiet and disturbed (red lines) periods were obtained every 15 min from the ionograms. The averaged h’F, hpF2, and foF2 (three quiet days viz. 23, 24, and 25 May) variations are shown as green bands and their widths corresponds to ±1 standard deviations. Fig. 3 also shows the horizontal black bars indicating the presence of equatorial spread-F (ESF) in ionograms. Fig. 4 shows the time variations of virtual heights at six fixed reflection frequencies (electron densities), with measurements every 100 s (iso-frequency) obtained at PAL and SJC during the period 15–16 May 2005. Fig. 7 (for Figs. 3 and 7, the black vertical arrow indicates the time of sudden storm commencement (SSC)) shows the time variations of the average vertical total electron content (vTEC) obtained at 4 GPS receiving stations during the period 14–17 May 2005. The observed vTEC variations during the disturbed period are shown in red lines and the green lines are observations on the quiet day (14 May) repeated for all the subsequent days to allow a comparative study between quiet and disturbed days. Fig. 8 shows the phase fluctuations (rate of change of TEC) observed at 4 GPS receiving stations (14–17 May 2005). The black vertical dashed line indicates the
1214
A.J. de Abreu et al. / Advances in Space Research 48 (2011) 1211–1220
Fig. 2. Variations of the total interplanetary magnetic field (IMF) B, z component of IMF Bz in GSM coordinates, solar wind proton bulk velocity Vp, and solar wind ion density Np, obtained from the ACE satellite during the period 14–17 May 2005. Also, the AE, Kp, and Dst geomagnetic indices during the period 14–17 May 2005 are presented. The black vertical arrow indicates the sudden storm commencement (SSC).
Fig. 3. Variations of the ionospheric parameter h’F obtained at Palmas (PAL) and Sa˜o Jose´ dos Campos (SJC) during the period 14–17 May 2005 (red lines). The green bands are ±1 standard deviation of the average quiet day values. Also, the horizontal black bars indicate the presence of equatorial spread-F (ESF). The black vertical arrow indicates the sudden storm commencement (SSC). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
sudden storm commencement (SSC). It should be mentioned that the ionospheric sounding stations are located at different places compared with the GPS receiving stations (Table 1).
3.1. Storm main and recovery phases Figs. 3, 5 and 6 show that the ionospheric parameters h’F, hpF2, and foF2 observed at PAL and SJC, start exhib-
A.J. de Abreu et al. / Advances in Space Research 48 (2011) 1211–1220
1215
Fig. 4. Variations of the ionospheric parameter h’F for six different frequencies (isofrequencies) observed at Palmas (PAL) and Sa˜o Jose´ dos Campos (SJC) during the period 15–16 May 2005. The black vertical arrow indicates the sudden storm commencement (SSC).
Fig. 5. Variations of the ionospheric parameter hpF2 obtained at Palmas (PAL) and Sa˜o Jose´ dos Campos (SJC) during the period 14–17 May 2005 (red lines). The green bands are ±1 standard deviation of the average quiet day values. The black vertical arrow indicates the sudden storm commencement (SSC). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
iting deviations from the quiet day average values after the SSC (0239 UT on 15 May), which continue during storm main and recovery phases (15 and 16 May). Figs. 3 and 4 show very clearly the variations of h’F at PAL and SJC. Soon after the SSC there is uplifting of the F region at PAL and SJC on the night of 14–15 May (Figs. 3 and 6), possibly due to prompt penetration of eastward electric field immediately after SSC. As mentioned earlier, soon after SSC during the fast decrease (about 90 nT/h) of
the Dst index (Fig. 2) there is a good possibility of prompt penetration of electric field of magnetospheric origin resulting in uplifting of the F region (Abdu et al., 1991; Wygant et al., 1998; Basu et al., 2001). However, this post-midnight uplifting during storm-time resulted in plasma bubbles (at PAL and BRAZ) only up to the low magnetic latitude and drifted possibly to west. The variations in foF2 at PAL and SJC (Fig. 6) present fairly different behavior after the SSC on 15 and 16 May,
1216
A.J. de Abreu et al. / Advances in Space Research 48 (2011) 1211–1220
Fig. 6. Variations of the ionospheric parameter foF2 obtained at Palmas (PAL) and Sa˜o Jose´ dos Campos (SJC) during the period 14–17 May 2005 (red lines). The green bands are ±1 standard deviation of the average quiet day values. The black vertical arrow indicates the sudden storm commencement (SSC). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
Fig. 7. Variations of the average vertical total electron content (vTEC) from GPS observations at 4 receiving stations (Table 1) during the period 14–17 May 2005. The black vertical arrow indicates the sudden storm commencement (SSC).
particularly during the daytime. The foF2 and hpF2 (Fig. 5) variations observed at SJC on 15 and 16 May show large storm time fluctuations, fairly similar to that reported by Vijaya Lekshmi et al. (2008) for Okinawa, Japan. The foF2 variations observed at SJC (mostly positive phase), possibly the daytime equatorward wind produced by high latitude heating reaches only up to low latitude region and does not each near the equatorial region. Lin et al. (2005) have suggested that the storm time equatorward wind is important is producing positive storm effect. Vijaya
Lekshmi et al. (2008) have mentioned that at low latitudes, the occurrence of positive or negative phase depends also on the latitudinal extent of the equatorward wind. The ionospheric sounding station SJC is not very far from the GPS receiving station UEPP and foF2 variations during the daytime observed at SJC are very similar to vTEC variations observed at UEPP on 15 and 16 May (see Fig. 7). The variations in foF2 on the night of 14–15 May at SJC after SSC are fairly similar to the quiet day average values, except a small peak close to about 0600 UT. On the night
A.J. de Abreu et al. / Advances in Space Research 48 (2011) 1211–1220
1217
Fig. 8. The phase fluctuations or rate of change of TEC (in TECU/min) from GPS observations presented in Fig. 6 for each GPS station. The black vertical dashed line indicates the sudden storm commencement (SSC).
of 15–16 May both h’F (Fig. 3) and hpF2 (Fig. 5) observed at SJC show unusual large height rise at centered at about 0400 UT. This could be possibly due to altered dynamo effect of wind circulation with upward drift at night (Fuller-Rowell et al., 2002). Fig. 7 shows the variations of vTEC data obtained at the equatorial and low latitude stations in the Brazilian sector during the period 14–17 May 2005. Soon after SSC a trough is observed at BELE and a crest is above UEPP indicating strengthening of nighttime equatorial anomaly. The large positive storm effects during the daytime on 15 and 16 May (particularly at BRAZ, UEPP, and POAL; away from the magnetic equator) are possibly associated again with strengthening of daytime equatorial anomaly. The variations in foF2 for the SJC and vTEC for the UEPP and POAL are fairly similar during the daytime on 15 and 16 May. There are enhancements close to 1200 UT and 1700 UT on 15 May (after the main phase) and doublepeaked enhancements close to 1400 UT and 1800 UT on 16 May (recovery phase). No similar enhancements in foF2 were observed at PAL on 15 and 16 May. On 15 May, it appears that during the daytime, the variations in foF2 are controlled by both ionospheric dynamo electric fields and meridional neutral wind (Lu et al., 2008). Whereas on 16 May, a careful look at vTEC variations, when a positive phase is observed during the daytime up to BELE (an equatorial station) from equatorial ionospheric anomaly region, it appears that meridional wind plays an important role. This is possibly due to neutral composition change (increase in atomic oxygen density). Balan et al. (2009) (see also Vijaya Lekshmi et al., 2008) mention that direct effects of the equatorward neutral wind without effects of electric field can be the main driver of stronger positive phase in foF2 and vTEC observed at low-mid latitudes.
3.2. Equatorial ionospheric irregularities Fig. 3 shows presence of equatorial spread-F (ESF) at PAL for the nights of 14–15, 15–16, and 16–17 May. Fig. 8 shows a short period of phase fluctuations observed at BRAZ for the night of 14–15 May (satellite number 24). As pointed out by Aarons et al. (1997), the phase fluctuations indicate large-scale ionospheric irregularities of the order of kilometers-size. In contrast to the ionospheric sounding observations, there are no phase fluctuations observed on the nights of 15–16 and 16–17 May. As discussed out by Abdu (2001), the occurrence of ESF has seasonal and day-to-day variability (Burke et al., 2004; Makela and Miller, 2008). In the Brazilian sector, Sahai et al. (2000) observed by the OI 630 nm all-sky imaging system, that the seasonal occurrence of ESF is maximum between October and March and minimum between May and August. Considering the ionospheric pierce point (IPP) to be located at an altitude of 350 km (Kaplan and Hegarty, 2006), the magnetic latitude for BRAZ will be 15.9°S. Therefore, the present observations (on the night of 14–15 May, the ionospheric observations at PAL and GPS observations at BRAZ) show that possibly on this night the plasma bubbles extended only up to low magnetic latitude where the phase fluctuations (irregularities of only few km scale-size) was observed. During the super geomagnetic storm main phase occurring during the postmidnight period, the F-region drifted quickly upwards (Fig. 3) resulting in the generation of any ESF of largescale (plasma bubbles), possibly east of PAL and moved towards west on this magnetically disturbed night (Abdu et al., 2003). Since the ESF and the phase fluctuations were not observed at the low latitude stations (SJC, UEPP, and POAL), the present ESF observations at PAL and phase fluctuations at BRAZ possibly indicate
1218
A.J. de Abreu et al. / Advances in Space Research 48 (2011) 1211–1220
that the plasma bubbles were limited to low magnetic latitude. 4. Conclusions In this paper, we have analyzed and presented the ionospheric sounding and GPS observations in the equatorial and low latitude regions in the Brazilian sector during the super geomagnetic storm of 15 May 2005. Some of the salient features related to these observations are summarized below. 1. The super geomagnetic storm had fast decrease in the Dst index soon after SSC at 0239 UT on 15 May. There is a good possibility of prompt penetration of electric field of magnetospheric origin that resulted in uplifting of the F region observed by ionospheric sounding at PAL and SJC. 2. The vTEC observations showed a trough at BELE and a crest above UEPP, soon after SSC, indicating strengthening of nighttime equatorial anomaly. 3. During the daytime on 15 and 16 May, in the recovery phase, the variations in foF2 at SJC and the vTEC observations, particularly at BRAZ, UEPP, and POAL, showed large positive ionospheric storm. 4. There was ESF on all the nights at PAL, in the postmidnight (UT) sector, and phase fluctuations only on the night of 14–15 May (for a short period) at BRAZ, after the SSC. No phase fluctuations were observed at the equatorial station BELE and low latitude stations (BRAZ, UEPP, and POAL) at all other times. This indicates that the plasma bubbles were generated and confined on this magnetically disturbed night only up to the low magnetic latitude and drifted possibly to west.
Acknowledgements The authors thank the authorities of the “Rede Brasileira de Monitoramento Contı´nuo de GPS (RBMC)”, Brazil, for kindly allowing us to use the data obtained by the RBMC. The authors also thank the Brazilian funding agencies “CNPq” and “FAPESP” for kindly providing the partial financial support. References Aarons, J., Mendillo, M., Yantosca, R. GPS phase fluctuations in the equatorial region during the MISETA 1994 campaign. J. Geophys. Res. 101 (A8), 26851–26862, 1996. Aarons, J., Mendillo, M., Yantosca, R. GPS phase fluctuations in the equatorial region during sunspot minimum. Radio Sci. 32, 1535–1550, doi:10.1029/97RS00664, 1997. Abdu, M.A., Sobral, J.H.A., de Paula, E.R., Batista, I.S. Magnetospheric disturbance effects on the equatorial ionization anomaly (EIA): an overview. J. Atmos. Terr. Phys. 53, 757–771, 1991. Abdu, M.A. Outstanding problems in the equatorial ionosphere–thermosphere electrodynamics relevant to spread F. J. Atmos. Solar-Terres. Phys. 63, 869–884, 2001.
Abdu, M.A., Batista, I.S., Takahashi, H., MacDougall, J., Sobral, J.H., Medeiros, A.F., Trivedi, N.B. Magnetospheric disturbance induced equatorial plasma bubble development and dynamics: a case study in Brazilian sector. J. Geophys. Res. 108 (A12), 1449, doi:10.1029/ 2002JA009721, 2003. Afraimovich, E.L., Kosogorov, E.A., Lesyuta, O.S., Ushakov, I.I., Yakovets, A.F. Geomagnetic control of the spectrum of traveling ionospheric disturbances based on data from a global GPS network. Ann. Geophys. 19, 723–731, 2001. Aksnes, A., Stadsnes, J., Lu, G., Østgaard, N., Vondrak, R.R., Detrick, D.L., Rosenberg, T.J., Germany, G.A., Schulz, M. Effects of energetic electrons on the electrodynamics in the ionosphere. Ann. Geophys. 22, 475–496, 2004. Balan, N., Alleyne, H., Otsuka, Y., Lakshmi, D.V., Fejer, B.G., McCrea, I. Relative effects of electric field and neutral wind on positive ionospheric storms. Earth Planets Space 61, 439–445, 2009. Basu, S., Basu, Su., Valladares, C.E., Yeh, H.C., Su, S.Y., Mackenzie, E., Sultan, P.J., Aarons, J., Rich, F.J., Doherty, P., Groves, K.M., Bullet, T.W. Ionospheric effects of major magnetic storms during the International Space Weather Period of September and October 1999: GPS observations, VHF/UHF scintillations, and in situ density structures at middle and equatorial latitudes. J. Geophys. Res. 106 (A12), 30389–30413, 2001. Batista, I.S., de Paula, E.R., Abdu, M.A., Trivedi, N.B. Ionospheric effects of the March 13, 1989 magnetic storm at low and equatorial latitudes. J. Geophys. Res. 96, 13943–13952, 1991. Bauske, R., Prolss, G.W. Numerical simulation of long-duration positive ionospheric storm effects. Adv. Space Res. 22 (1), 117–121, 1998. Becker-Guedes, F., Sahai, Y., Fagundes, P.R., Espinoza, E.S., Pillat, V.G., Lima, W.L.C., Basu, Su., Basu, Sa., Otsuka, Y., Shiokawa, K., Mackenzie, E.M., Pi, X., Bittencourt, J.A. The ionospheric response in the Brazilian sector during the super geomagnetic storm on 20 November 2003. Ann. Geophys. 25, 863–873, 2007. Buonsanto, M.J. Ionospheric storms – a review. Space Sci. Rev. 88, 563– 601, 1999. Burke, W.J., Huang, C.Y., Gentile, L.C., Bauer, L. Seasonal–longitudinal variability of equatorial plasma bubbles. Ann. Geophys. 22, 3089– 3098, 2004. Danilov, A.D., Morozova, L.D. Ionospheric storms in the F2 region: morphology and physics (review). Geomagn. Aeron. 25, 593–605, 1985. Dashora, N., Sharma, S., Dabas, R.S., Alex, S., Pandey, R. Large enhancements in low latitude total electron content during 15 May 2005 geomagnetic storm in Indian zone. Ann. Geophys. 27, 1803–1820, 2009. de Abreu, A.J., Fagundes, P.R., Sahai, Y., de Jesus, R., Bittencourt, J.A., Brunini, C., Gende, M., Pillat, V.G., Lima, W.L.C., Abalde, J.R., Pimenta, A.A. Hemispheric asymmetries in the ionospheric response observed in the American sector during an intense geomagnetic storm. J. Geophys. Res. 115, A12312, doi:10.1029/2010JA015661, 2010a. de Abreu, A.J., Sahai, Y., Fagundes, P.R., Becker-Guedes, F., de Jesus, R., Guarnieri, F.L., Pillat, V.G. Response of the ionospheric F-region in the Brazilian sector during the super geomagnetic storm in April 2000 observed by GPS. Adv. Space Res. 45, 1322–1329, doi:10.1016/ j.asr.2010.02.003, 2010b. de Jesus, R., Sahai, Y., Guarnieri, F.L., Fagundes, P.R., de Abreu, A.J., Becker-Guedes, F., Brunini, C., Gende, M., Cintra, T.M.F., de Souza, V.A., Pillat, V.G., Lima, W.L.C. Effects observed in the ionospheric Fregion in the South American sector during the intense geomagnetic storm of 14 December 2006. Adv. Space Res. 46, 909–920, doi:10.1016/ j.asr.2010.04.031, 2010. de Jesus, R., Sahai, Y., Guarnieri, F.L., Fagundes, P.R., de Abreu, A.J., Pillat, V.G., Lima, W.L.C. F-region ionospheric parameters observed in the equatorial and low latitude regions during medium solar activity in the Brazilian sector and comparison with the IRI-2007 model results. Adv. Space Res. 47, 718–728, doi:10.1016/j.asr.2010.10.020, 2011.
A.J. de Abreu et al. / Advances in Space Research 48 (2011) 1211–1220 Fagundes, P.R., Aruliah, A.L., Rees, D., Bittencourt, J.A. Gravity-wave generation and propagation during geomagnetic storms over Kiruna (67.8°N, 20.4°E).. Ann. Geophys. 13 (4), 358–366, 1995. Fejer, B.G., Jensen, J.W., Kikuchi, T., Abdu, M.A., Chau, L. Equatorial ionospheric electric fields during the November 2004 magnetic storm. J. Geophys. Res. 112, A10304, doi:10.1029/2007JA012376, 2007. Fuller-Rowell, T.J., Millward, G.H., Richmond, A.D., Codrescu, M.V. Storm-time changes in the upper atmosphere at low latitudes. Atmos. Solar-Terres. Phys. 64, 1383–1391, 2002. Grant, I.F., McDougall, J.W., Ruohoniemi, J.M., Bristow, W.A., Sofko, G.J., Koehler, J.A., Danskin, D., Andre, D. Comparison of plasma flow velocities determined by the ionosonde Doppler drift technique, SuperDARN radars, and patch motion. Radio Sci. 30, 1537–1549, 1995. Hines, C.O., Hooke, W.H. Discussion of ionization effects on the propagation of acoustic-gravity waves in the ionosphere. J. Geophys. Res. 75, 2563–2567, 1960. Kaplan, E.D., Hegarty, C.J. Understanding GPS: Principles and Applications, second ed Artech House, Inc., 2006. Killeen, T.J., Hays, P.B., Carignan, G.R., Heelis, R.A., Hanson, W.B., Spencer, N.W., Brace, L.H. Ion-neutral coupling in the high-latitude F-region: evaluation of ion heating terms from Dynamics Explorer 2. J. Geophys. Res. 89, 7495–7508, 1984. Klimenko, M.V., Klimenko, V.V., Ratovsky, K.G., Goncharenko, L.P., Sahai, Y., Fagundes, P.R., de Jesus, R., de Abreu, A.J., Vesnin, A.M. Numerical modeling of ionospheric effects in the middle- and lowlatitude F region during geomagnetic storm sequence of 9-14 September 2005. Radio Sci. 46, RS0D03, doi:10.1029/2010RS004590, 2011. Jansen, F., Pirjola, R. Space weather research elucidates risks to technological infrastructure. EOS, Transactions, American Geophysical Union, no. 85, pp. 241–245, 2004. Lei, J., Burns, A.G., Tsugawa, T., Wang, W., Solomon, S.C., Wiltberger, M. Observations and simulations of quasiperiodic ionospheric oscillations and large-scale traveling ionospheric disturbances during the December 2006 geomagnetic storm. J. Geophys. Res. 113, A06310, doi:10.1029/2008JA013090, 2008. Lima, W.L.C., Becker-Guedes, F., Sahai, Y., Fagundes, P.R., Abalde, J.R., Growley, G., Bittencourt, J.A. Response of the equatorial and low-latitude ionosphere during the space weather events of April 2002. Ann. Geophys. 22, 3211–3219, 2004. Lin, C.H., Richmond, A.D., Heelis, R.A., Bailey, G.J., Lu, G., Liu, J.Y., Yeh, H.C., Su, S.Y. Theoretical study of the low and mid latitude ionospheric electron density enhancement during the October 2003 super storm: relative importance of the neutral wind and the electric field. J. Geophys. Res. 110, A12312, doi:10.1029/2005JA011304, 2005. Lu, G., Goncharenko, L.P., Richmond, A.D., Roble, R.G., Aponte, N. A dayside ionospheric positive storm phase driven by neutral winds. J. Geophys. Res. 113, A08304, doi:10.1029/2007JA012895, 2008. Makela, J.J., Miller, E.S. Optical observations of the growth and day-today variability of equatorial plasma bubbles. J. Geophys. Res. 113, A03307, 2008. Martinis, C.R., Mendillo, M.J., Aarons, J. Toward a synthesis of equatorial spread F onset and suppression during geomagnetic storms. J. Geophys. Res. 110, A07306, 2005. Maruyama, N., Richmond, A.D., Fuller-Rowell, T.J., Codrescu, M.V., Sazykin, S., Toffoletto, F.R., Spiro, R.W., Millward, G.H. Interaction between direct penetration and disturbance dynamo electric fields in the storm-time equatorial ionosphere. J. Geophys. Res. 32, L17105, doi:10.1029/2005GL023763, 2005. Namgaladze, A.A., Forster, M., Yurik, R.Y. Analysis of the positive ionospheric response to a moderate geomagnetic storm using a global numerical model. Ann. Geophys. 18, 461–477, 2000. Nicolls, M.J., Kelley, M.C., Coster, A.J., Gonzalez, S.A., Makela, J.J. Imaging the structure of a large-scale TID using ISR and TEC data. Geophys. Res. Lett. 31, L09812, doi:10.1029/2004GL019797, 2004. Paznukhov, V.V., Altadill, D., Reinisch, B.W. Experimental evidence for the role of the neutral wind in the development of ionospheric storms in midlatitudes. J. Geophys. Res. 114, A12319, doi:10.1029/ 2009JA014479, 2009.
1219
Piggot, R., Rawer, K. (Eds.), U.R.S.I. Handbook of Ionogram Interpretation and Reduction, Rep. UAG-23, second ed., World Data Cent. for Sol.-Terr. Phys., Boulder, Colo, p. 21, 1972. Prolss, G.W. Common origin of positive ionospheric storms at middle latitudes and the geomagnetic activity effect at low latitudes. J. Geophys. Res. 98 (A4), 5981–5991, 1993. Rama Rao, P.V.S., Niranjan, K., Prasad, D.S.V.V.D., Gopi Krishna, S., Uma, G. On the validity of the ionospheric pierce point (IPP) altitude of 350 km in the Indian equatorial and low-latitude sector. Ann. Geophys. 24, 2159–2168, 2006. Sahai, Y., Fagundes, P.R., Bittencourt, J.A. Transequatorial F-region ionospheric plasma bubbles: solar cycle effects. J. Atmos. Solar-Terres. Phys. 62, 1377–1383, 2000. Sahai, Y., Fagundes, P.R., Becker-Guedes, F., Bolzan, M.J.A., Abalde, J.R., Pillat, V.G., de Jesus, R., Lima, W.L.C., Crowley, G., Shiokawa, K., MacDougall, J.W., Lan, H.T., Igarashi, K., Bittencourt, J.A. Effects of the major geomagnetic storms of October 2003 on the equatorial and low-latitude F region in two longitudinal sectors. J. Geophys. Res. 110, A12S91, doi:10.1029/2004JA010999, 2005. Sahai, Y., Becker-Guedes, F., Fagundes, P.R., Lima, W.L.C., Otsuka, Y., Huang, C. –S., Espinoza, E.S., Pi, X., de Abreu, A.J., Bolzan, M.J.A., Pillat, V.G., Abalde, J.R., Pimenta, A.A., Bittencourt, J.A. Response of nighttime equatorial and low latitude F-region to the geomagnetic storm of August 18, 2003, in the Brazilian sector. Adv. Space Res. 39, 1325–1334, 2007a. Sahai, Y., Becker-Guedes, F., Fagundes, P.R., Lima, W.L.C., de Abreu, A.J., Guarnieri, F.L., Candido, C.M.N., Pillat, V.G. Unusual ionospheric effects observed during the intense 28 October 2003 solar flare in the Brazilian sector. Ann. Geophys. 25, 2497–2502, 2007b. Sahai, Y., Becker-Guedes, F., Fagundes, P.R., de Jesus, R., de Abreu, A.J., Paxton, L.J., Goncharenko, L.P., Brunini, C., Gende, M., Ferreira, A.S., Lima, N.S., Guarnieri, F.L., Pillat, V.G., Bittencourt, J.A., Candido, C.M.N. Effects observed in the Latin American sector ionospheric F region during the intense geomagnetic disturbances in the early part of November 2004. J. Geophys. Res. 114, A00A19, 2009a. Sahai, Y., Becker-Guedes, F., Fagundes, P.R., de Abreu, A.J., de Jesus, R., Pillat, V.G., Abalde, J.R., Martinis, C.R., Brunini, C., Gende, M., Huang, C.S., Pi, X., Lima, W.L.C., Bittencourt, J.A., Otsuka, T. Observations of the F-region ionospheric irregularities in the South American sector during the October 2003 ‘Halloween Storms’. Ann. Geophys. 27 (12), 4463–4477, 2009b. Sahai, Y., Becker-Guedes, F., Fagundes, P.R., de Jesus, R., de Abreu, A.J., Otsuka, Y., Shiokawa, K., Igarashi, K., Yumoto, K., Huang, C.S., Lan, H.T., Saito, A., Guarnieri, F.L., Pillat, V.G., Bittencourt, J.A. Effects observed in the ionospheric F region in the east Asian sector during the intense geomagnetic disturbances in the early part of November 2004. J. Geophys. Res. – Space Phys., 114, doi:10.1029/ 2008JA013053 (Art. No. A00A18), 2009c. Sahai, Y., Fagundes, P.R., de Jesus, R., de Abreu, A.J., Crowley, G., Kikuchi, T., Huang, C.-S., Pillat, V.G., Guarnieri, F.L., Abalde, J.R., Bittencourt, J. Studies of ionospheric F-region response in the Latin American sector during the geomagnetic storm of 21–22 January 2005. Ann. Geophys. 29, 919–929, doi:10.5194/angeo-29-1-2011, 2011. Sastri, J.H., Abdu, M.A., Sobral, J.H.A. Response of equatorial ionosphere to episodes of asymmetric ring current activity. Ann. Geophys. 15, 1316–1323, 1997. Sastri, J.H., Niranjan, K., Subbarao, K.S.V. Response of the equatorial ionosphere in the Indian (midnight) sector to the severe magnetic storm of July 15, 2000. Geophys. Res. Lett. 29 (13), 1651, doi:10.1029/ 2002GL015133, 2002. Schunk, R.W., Sojka, J.J. Ionosphere-thermosphere space weather issues. J. Atmos. Terres. Phys. 58 (14), 1527–1574, 1996. Vijaya Lekshmi, D., Balan, N., Vaidyan, V.K., Alleyne, H., Bailey, G.J. Response of the ionosphere to super geomagnetic storms: observations and modeling. Adv. Space Res. 41, 548–555, 2008. Wanninger, L. Effects of the equatorial ionosphere on GPS. GPS World pp. 48–54, July 1993.
1220
A.J. de Abreu et al. / Advances in Space Research 48 (2011) 1211–1220
Werner, S., Bauske, R., Prolss, G.W. On the origin of positive ionospheric storms. Adv. Space Res. 24 (11), 1485–1489, 1999. Whalen, J.A. Dependence of equatorial bubbles and bottom-side spread F on season, magnetic activity, and E B drift velocity during solar maximum. J. Geophys. Res. 107 (A2), 2002. Wygant, J., Rowland, D., Singer, H.J., Temerin, M., Mozer, F., Hudson, M.K. Experimental evidence on the role of the large spatial scale
electric field in creating the ring current. J. Geophys. Res. 103, 29527– 29544, 1998. Yizengaw, E., Moldwin, M.B., Sahai, Y., de Jesus, R. Strong postmidnight equatorial ionospheric anomaly observations during magnetically quiet periods. J. Geophys. Res. 114, A12308, doi:10.1029/ 2009JA014603, 2009.