Ionospheric response to the 2009 sudden stratospheric warming over the equatorial, low, and middle latitudes in the South American sector

The present study investigates the ionospheric total electron content (TEC) and F-layer response in the Southern Hemisphere equatorial, low, and middle latitudes due to major sudden stratospheric warming (SSW) event, which took place during January-February 2009 in the Northern Hemisphere. In this study, using 17 ground-based dual frequency GPS stations and two ionosonde stations spanning latitudes from 2.8°N to 53.8°S, longitudes from 36.7°W to 67.8°W over the South American sector, it is observed that the ionosphere was significantly disturbed by the SSW event from the equator to the midlatitudes. During day of year 26 and 27 at 14:00 UT, the TEC was two times larger than that observed during average quiet days. The vertical TEC at all 17 GPS and two ionosonde stations shows significant deviations lasting for several days after the SSW temperature peak. Using one GPS station located at Rio Grande (53.8°S, 67.8°W, midlatitude South America sector), it is reported for the first time that the midlatitude in the Southern Hemisphere was disturbed by the SSW event in the Northern Hemisphere.Fil: Fagundes, P. R.. Universidade do Vale do Paraíba; BrasilFil: Goncharenko, L. P.. Massachusetts Institute of Technology; Estados UnidosFil: De Abreu, A. J.. Universidade do Vale do Paraíba; BrasilFil: Venkatesh, K.. Universidade do Vale do Paraíba; BrasilFil: Pezzopane, M.. Istituto Nazionale Di Geofisica E Vulcanologia; ItaliaFil: De Jesus, R.. Universidade do Vale do Paraíba; BrasilFil: Gende, Mauricio Alfredo. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Coster, A. J.. Massachusetts Institute of Technology; Estados UnidosFil: Pillat, V. G.. Universidade do Vale do Paraíba; Brasi

Multifractal analysis of vertical total electron content (VTEC) at equatorial region and low latitude, during low solar activity

This paper analyses the multifractal aspects of the GPS data (measured during a period of low solar activity) obtained from two Brazilian stations: Belém (01.3° S, 48.3° W) and São José dos Campos (SJC) (23.2° S, 45.9° W). The results show that the respective geographic sites show important scaling differences as well as similarities when their multifractal signatures for vertical total electron content (VTEC) are compared. The <I>f</I>(&alpha;) spectra have a narrow shape for great scales, which indicates the predominance of deterministic phenomena, such as solar rotation (27 days) over intermittent phenomena. Furthermore, the <I>f</I>(&alpha;) spectra for both sites have a strong multifractality degree at small scales. This strong multifractality degree observed at small scales (1 to 12 h) at both sites is because the ionosphere over Brazil is a non-equilibrium system. The differences found were that Belém presented a stronger multifractality at small scales (1 h to 12 h) compared with SJC, particularly in 2006. The reason for this behaviour may be associated with the location of Belém, near the geomagnetic equator, where at this location the actions of X-rays, ultraviolet, and another wavelength from the Sun are more direct, strong, and constant throughout the whole year. Although the SJC site is near ionospheric equatorial anomaly (IEA) peaks, this interpretation could explain the higher values found for the intermittent parameter μ for Belém compared with SJC. Belém also showed the presence of one or two flattening regions for <I>f</I>(&alpha;) spectra at the same scales mentioned before. These differences and similarities also were interpreted in terms of the IEA content, where this phenomenon is an important source of intermittence due the presence of the VTEC peaks at ±20° geomagnetic latitudes

Ionospheric response to the 2009 sudden stratospheric warming over the equatorial, low, and middle latitudes in the South American sector

The present study investigates the ionospheric total electron content (TEC) and F-layer response in the Southern Hemisphere equatorial, low, and middle latitudes due to major sudden stratospheric warming (SSW) event, which took place during January-February 2009 in the Northern Hemisphere. In this study, using 17 ground-based dual frequency GPS stations and two ionosonde stations spanning latitudes from 2.8°N to 53.8°S, longitudes from 36.7°W to 67.8°W over the South American sector, it is observed that the ionosphere was significantly disturbed by the SSW event from the equator to the midlatitudes. During day of year 26 and 27 at 14:00 UT, the TEC was two times larger than that observed during average quiet days. The vertical TEC at all 17 GPS and two ionosonde stations shows significant deviations lasting for several days after the SSW temperature peak. Using one GPS station located at Rio Grande (53.8°S, 67.8°W, midlatitude South America sector), it is reported for the first time that the midlatitude in the Southern Hemisphere was disturbed by the SSW event in the Northern Hemisphere.Facultad de Ciencias Astronómicas y Geofísica

Hemispheric asymmetries in the ionospheric response observed in the American sector during an intense geomagnetic storm

The main purpose of this investigation is to study the ionospheric F region response induced by the intense geomagnetic storm that occurred on 7-8 September 2002. The geomagnetic index Dst reached a minimum of -181 nT at 0100 UT on 8 September. In this study, we used observations from a chain of 12 GPS stations and another chain of 6 digital ionosonde stations. It should be mentioned that, soon after the sudden commencement (SC) at 1637 UT on 7 September, the TEC variations at midlatitude stations in both hemispheres showed an F region positive storm phase. However, during the recovery phase, a strong hemispheric asymmetry was observed in the ionospheric response. While a TID type soliton was observed to propagate in the Southern American sector, no TID activity was seen in the Northern American sector. Also, in the Southern Hemisphere, the TEC variations were less affected by the geomagnetic storm. The Northern Hemisphere observations showed a strong and long-lasting negative F region storm phase starting at about 1000 UT on 8 September (lasting for about 24 h). A perusal of TEC phase fluctuations and equatorial spread-F (ESF) ionospheric sounding data indicates that, on the disturbed night of 7-8 September, some stations showed the occurrence of ESF starting at about 0000 UT (2000 LT) on 8 September, whereas other stations showed that the ESF occurrence started much later, at about 0800 UT (0500 LT). This hemispheric asymmetric response of the ionospheric F region possibly indicates the presence of different mechanisms for the generation of ESF along the various latitudinal regions during the disturbed period.Facultad de Ciencias Astronómicas y Geofísica

Studies of ionospheric F-region response in the Latin American sector during the geomagnetic storm of 21&ndash;22 January 2005

In the present investigation, we have studied the response of the ionospheric F-region in the Latin American sector during the intense geomagnetic storm of 21–22 January 2005. This geomagnetic storm has been considered "anomalous" (minimum Dst reached −105 nT at 07:00 UT on 22 January) because the main storm phase occurred during the northward excursion of the B_z component of interplanetary magnetic fields (IMFs). The monthly mean <i>F</i>_10.7 solar flux for the month of January 2005 was 99.0 sfu. The F-region parameters observed by ionosondes at Ramey (RAM; 18.5° N, 67.1° W), Puerto Rico, Jicamarca (JIC; 12.0° S, 76.8° W), Peru, Manaus (MAN; 2.9° S, 60.0° W), and São José dos Campos (SJC; 23.2° S, 45.9° W), Brazil, during 21–22 January (geomagnetically disturbed) and 25 January (geomagnetically quiet) have been analyzed. Both JIC and MAN, the equatorial stations, show unusually rapid uplifting of the F-region peak heights (<i>hp</i>F2/<i>hm</i>F2) and a decrease in the <i>Nm</i>F2 coincident with the time of storm sudden commencement (SSC). The observed variations in the F-region ionospheric parameters are compared with the TIMEGCM model run for 21–22 January and the model results show both similarities and differences from the observed results. Average GPS-TEC (21, 22 and 25 January) and phase fluctuations (21, 22, 25, 26 January) observed at Belem (BELE; 1.5° S, 48.5° W), Brasilia (BRAZ; 15.9° S, 47.9° W), Presidente Prudente (UEPP; 22.3° S, 51.4° W), and Porto Alegre (POAL; 30.1° S, 51.1° W), Brazil, are also presented. These GPS stations belong to the RBMC/IBGE network of Brazil. A few hours after the onset of the storm, large enhancements in the VTEC and <i>Nm</i>F2 between about 20:00 and 24:00 UT on 21 January were observed at all the stations. However, the increase in VTEC was greatest at the near equatorial station (BELE) and enhancements in VTEC decreased with latitude. It should be pointed out that no phase fluctuations or spread-F were observed in the Latin American sector during the post-sunset pre-reversal time in the geomagnetic disturbance (21 January). The disturbance dynamo electric field possibly resulted in downward drift of the F-region plasma and inhibited the formation of spread-F

Hemispheric asymmetries in the ionospheric response observed in the American sector during an intense geomagnetic storm

The main purpose of this investigation is to study the ionospheric F region response induced by the intense geomagnetic storm that occurred on 7-8 September 2002. The geomagnetic index Dst reached a minimum of -181 nT at 0100 UT on 8 September. In this study, we used observations from a chain of 12 GPS stations and another chain of 6 digital ionosonde stations. It should be mentioned that, soon after the sudden commencement (SC) at 1637 UT on 7 September, the TEC variations at midlatitude stations in both hemispheres showed an F region positive storm phase. However, during the recovery phase, a strong hemispheric asymmetry was observed in the ionospheric response. While a TID type soliton was observed to propagate in the Southern American sector, no TID activity was seen in the Northern American sector. Also, in the Southern Hemisphere, the TEC variations were less affected by the geomagnetic storm. The Northern Hemisphere observations showed a strong and long-lasting negative F region storm phase starting at about 1000 UT on 8 September (lasting for about 24 h). A perusal of TEC phase fluctuations and equatorial spread-F (ESF) ionospheric sounding data indicates that, on the disturbed night of 7-8 September, some stations showed the occurrence of ESF starting at about 0000 UT (2000 LT) on 8 September, whereas other stations showed that the ESF occurrence started much later, at about 0800 UT (0500 LT). This hemispheric asymmetric response of the ionospheric F region possibly indicates the presence of different mechanisms for the generation of ESF along the various latitudinal regions during the disturbed period.Facultad de Ciencias Astronómicas y Geofísica

Effects observed in the Latin American sector ionospheric F region during the intense geomagnetic disturbances in the early part of November 2004

The Sun was very active in the early part of November 2004. During the period of 8-10 November 2004, intense geomagnetic disturbances with two superstorms were observed. In this paper, we have investigated the generation and suppression of equatorial ionospheric irregularities and the daytime changes in the F region electron density in the Latin American sector during the period of intense geomagnetic disturbances. We present the ionospheric sounding observations carried out at Manaus and Sao Jose dos Campos, Brazil, during this geomagnetically disturbed period. Also, GPS observations obtained from several stations in Brazil, Argentina, and St. Croix, U.S. Virgin Islands, during the disturbed period are presented. During the main phase of the first superstorm, around the prereversal enhancement time (night of 7-8 November), prompt penetration of electric field was observed and the presence of equatorial ionospheric irregularities was detected from St. Croix, U.S. Virgin Islands (in the northern hemisphere) to Bahia Blanca, Argentina (in the southern hemisphere). The ionospheric sounding observations at Manaus indicate inhibition of prereversal enhancement on the nights of 9-10 and 10-11 November, possibly due to the disturbed thermospheric winds or disturbance electric fields. Virtually no phase fluctuations on the nights of 9-10 and 10-11 November were observed in the Latin American sector. During the daytime on 8 November, the vertical total electron content (VTEC) observations show a negative storm phase at Porto Alegre (Brazil) and Bahia Blanca (Argentina). Again during the daytime on 10 November, the VTEC observations show a negative storm phase from Brasilia (Brazil) to Bahia Blanca. These negative storm phases are associated with a decrease in the O/N2 ratio. During the daytime on 9 November, the VTEC observations show a positive storm phase extending from St. Croix to Porto Alegre, and again on 10 November, VTEC observations show a positive storm phase. These positive storm phases observed are possibly due to changes in large-scale wind circulation and an increase in the O/N2 ratio.Facultad de Ciencias Astronómicas y Geofísica

Effects observed in the Latin American sector ionospheric F region during the intense geomagnetic disturbances in the early part of November 2004

The Sun was very active in the early part of November 2004. During the period of 8-10 November 2004, intense geomagnetic disturbances with two superstorms were observed. In this paper, we have investigated the generation and suppression of equatorial ionospheric irregularities and the daytime changes in the F region electron density in the Latin American sector during the period of intense geomagnetic disturbances. We present the ionospheric sounding observations carried out at Manaus and Sao Jose dos Campos, Brazil, during this geomagnetically disturbed period. Also, GPS observations obtained from several stations in Brazil, Argentina, and St. Croix, U.S. Virgin Islands, during the disturbed period are presented. During the main phase of the first superstorm, around the prereversal enhancement time (night of 7-8 November), prompt penetration of electric field was observed and the presence of equatorial ionospheric irregularities was detected from St. Croix, U.S. Virgin Islands (in the northern hemisphere) to Bahia Blanca, Argentina (in the southern hemisphere). The ionospheric sounding observations at Manaus indicate inhibition of prereversal enhancement on the nights of 9-10 and 10-11 November, possibly due to the disturbed thermospheric winds or disturbance electric fields. Virtually no phase fluctuations on the nights of 9-10 and 10-11 November were observed in the Latin American sector. During the daytime on 8 November, the vertical total electron content (VTEC) observations show a negative storm phase at Porto Alegre (Brazil) and Bahia Blanca (Argentina). Again during the daytime on 10 November, the VTEC observations show a negative storm phase from Brasilia (Brazil) to Bahia Blanca. These negative storm phases are associated with a decrease in the O/N2 ratio. During the daytime on 9 November, the VTEC observations show a positive storm phase extending from St. Croix to Porto Alegre, and again on 10 November, VTEC observations show a positive storm phase. These positive storm phases observed are possibly due to changes in large-scale wind circulation and an increase in the O/N2 ratio.Facultad de Ciencias Astronómicas y Geofísica

Observations of the F-region ionospheric irregularities in the South American sector during the October 2003 "Halloween Storms"

The response of the ionospheric F-region in the South American sector during the super geomagnetic storms on 29 and 30 October 2003 is studied in the present investigation. In this paper, we present ionospheric sounding observations during the period 29-31 October 2003 obtained at Palmas (a near equatorial location) and Sao Jose dos Campos (a location under the southern crest of the equatorial ionospheric anomaly), Brazil, along with observations during the period 27-31 October 2003 from a chain of GPS stations covering the South American sector from Imperatriz, Brazil, to Rio Grande, Argentina. Also, complementary observations that include sequences of all-sky images of the OI 777.4 and 630.0 nm emissions observed at El Leoncito, Argentina, on the nights of 28-29 (geomagnetically quiet night) and 29-30 (geomagnetically disturbed night) October 2003, and ion densities observed in the South American sector by the DMSP F13, F14 and F15 satellites orbiting at about 800 km on 29 and 30 October 2003 are presented. In addition, global TEC maps derived from GPS observations collected from the global GPS network of International GPS Service (IGS) are presented, showing widespread and drastic TEC changes during the different phases of the geomagnetic disturbances. The observations indicate that the equatorial ionospheric irregularities or plasma bubbles extend to the Argentinean station Rawson (geom. Lat. 33.1° S) and map at the magnetic equator at an altitude of about 2500 km.Facultad de Ciencias Astronómicas y Geofísica