Unusual topside ionospheric density response to the November 2003 superstorm (original) (raw)
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Journal of Geophysical Research, 2005
The GPS-derived total electron content (TEC), ion drift measurements from the ROCSAT-1 spacecraft at around 600 km altitude, and far-ultraviolet airglow measured by the Global Ultraviolet Imager (GUVI) carried on board the NASA TIMED satellite are utilized for studying large disturbances of the low-latitude ionosphere during the October-November 2003 superstorm period. Two chains of GPS receivers, one in the American sector ($70°W) and the other in the Asian/Australian sector ($120°E), are used to simultaneously observe the daytime equatorial ionization anomaly (EIA) during the entire storm period. It is found from the GPS-TEC measurements that the EIA expanded to very high latitudes with large increases of TEC right after the storm started. The large expansion of the EIA was associated with strong upward E Â B drifts measured from the Ionospheric Plasma and Electrodynamics Instrument (IPEI) on board the ROCSAT-1, providing evidence of a penetration electric field and a strong plasma fountain effect. Suppression of the EIA was observed during the storm recovery, associated with downward E Â B drifts that were observed by the ROCSAT-1. Significant negative storm effects in the southern hemisphere were also observed in the GPS-TEC during the first day of the recovery phase. The areas of negative storm effects are in good agreement with reductions in the [O]/[N 2 ] density ratio inferred from the ratio of OI (135.6 nm) to LBH emissions measured from GUVI. An enhancement of the EIA was observed on the day, 1 November, that the storm was about to fully recover.
Annales Geophysicae, 2005
The effects of the 31 March 2001 severe magnetic storm on the Southern Hemisphere ionosphere have been studied using ground-based and satellite measurements. The prime goal of this comprehensive study is to track the ionospheric response from high-to-low latitude to obtain a clear understanding of storm-time ionospheric change. The study uses a combination of ionospheric Total Electron Content (TEC) obtained from GPS signal group delay and phase advance measurements, ionosonde data, and data from satellite in-situ measurements, such as the Defense Metrological Satellite Program (DMSP), TOPographic EXplorer (TOPEX), and solar wind data from the Advanced Composition Explorer (ACE). A chain of Global Positioning System (GPS) stations near the 150 E meridian has been used to give comprehensive latitude coverage extending from the cusp to the equatorial region. A tomographic inversion algorithm has been applied to the GPS TEC measurements to obtain maps of the latitudinal structure of the ionospheric during this severe magnetic storm period, enabling both the spatial and temporal response of the ionosphere to be studied. Analysis of data from several of the instruments indicates that a strong density enhancement occurred at mid-latitudes at 11:00 UT on 31 March 2001 and was followed by equatorward propagating large-scale Travelling Ionospheric Disturbances (TIDs). The tomographic reconstruction revealed important features in ionospheric structure, such as quasiwave formations extending finger-like to higher altitudes. The most pronounced ionospheric effects of the storm occurred at high-and mid-latitudes, where strong positive disturbances occurred during the storm main phase, followed by a long lasting negative storm effect during the recovery phase. Relatively minor storm effects occurred in the equatorial region.
Ionospheric spatial and temporal variations during the 29–31 October 2003 storm
Journal of Atmospheric and Solar-Terrestrial Physics, 2005
A prominent large-scale ionospheric disturbance was observed in the European mid-latitude sector during the recent extreme space weather event in October 2003. Measurements of the horizontal component of the geomagnetic field H, the critical frequency of the F 2 layer foF2, and the vertical total electron content (TEC) from the European network of observational sites are used to describe the temporal and spatial storm evolution process. It is found that the ionospheric F region storm morphology was dominated by negative disturbances over high mid-latitudes and positive disturbance at low mid-latitudes during the initial phase and by overall negative disturbances during the main phase. Although a good agreement between the two independent measurements was detected by comparing the storm-time behaviour of foF2 and TEC during the main phase of the storm, some irregularities have been recognised in TEC variations at high mid-latitudes. The relative merit of real-time observational solar-terrestrial data for accurate specification of the geomagnetically disturbed ionospheric F region during the extreme space weather conditions is discussed. r
Annales Geophysicae, 2002
TEC data, obtained from over 60 GPS stations, were used to study the ionospheric effects of the 12-16 September 1999 magnetic storm over Europe. The spatial and temporal changes of the ionosphere were analysed as a time series of TEC maps, which present 15 min averages of TEC. The data set consisting of GPS observations, collected by a dense network of European stations, with sampling rate of 30 s, enable the creation of TEC maps with high spatial and temporal resolution. The storm included the positive as well as the negative phase. The positive phase took place during the first storm day of 12 September 1999. The short-lived daytime TEC enhancement was observed at all latitudes. The maximal enhancement reached a factor of 1.3-1.5. On the second and third days, the negative phase of the storm developed. The TEC decrease was registered regardless of time of the day. The TEC depression exceeded 70% relative to quiet days. On the following days (15 and 16 September), a significant daytime enhancement of TEC was observed once again. The complex occurrence of the ionospheric storm was probably related to the features of development of the magnetic storm. We found out that during the storm the large and medium-scale irregularities developed in the high-latitude ionosphere. The multi-stations technique, employed to create TEC maps, was particularly successful while studying the mid-latitude ionospheric trough. We found out that the essential changes of TEC during the storm, which were registered at the auroral and sub-auroral ionosphere, were connected with the effect of the trough and its dynamics, which depends on geomagnetic activity.
Extreme changes in the dayside ionosphere during a Carrington-type magnetic storm
Journal of Space Weather and Space Climate, 2012
It is shown that during the 30 October 2003 superstorm, dayside O + ions were uplifted to DMSP altitudes (~850 km). Peak densities were~9 · 10 5 cm À3 during the magnetic storm main phase (peak Dst = À390 nT). By comparison the 1-2 September 1859 Carrington magnetic storm (peak Dst estimated at À1760 nT) was considerably stronger. We investigate the impact of this storm on the low-to mid-latitude ionosphere using a modified version of the NRL SAMI2 ionospheric code. It is found that the equatorial region (LAT = 0°± 15°) is swept free of plasma within 15 min (or less) of storm onset. The plasma is swept to higher altitudes and higher latitudes due to E · B convection associated with the prompt penetration electric field. Equatorial Ionization Anomaly (EIA) O + density enhancements are found to be located within the broad range of latitudes~± (25°-40°) at~500-900 km altitudes. Densities within these peaks are~6 · 10 6 oxygen ions-cm À3 at~700 km altitude, approximately +600% quiet time values. The oxygen ions at the top portions (850-1000 km) of uplifted EIAs will cause strong low-altitude satellite drag. Calculations are currently being performed on possible uplift of oxygen neutrals by ion-neutral coupling to understand if there might be further significant satellite drag forces present.
Study of the March 31, 2001 magnetic storm effects on the ionosphere using GPS data
Advances in Space Research, 2005
Despite the fact that much has been learned about the Sun-Earth relationship during disturbed conditions, understanding the effects of magnetic storms on the neutral and ionized upper atmosphere is still one of the most challenging topics remaining in the physics of this atmospheric region. In order to investigate the magnetospheric and ionospheric-thermospheric coupling processes, many researchers are taking advantage of the dispersive nature of the ionosphere to compute total electron content (TEC) from Global Positioning System (GPS) dual-frequency data. Even though there are currently a large number of GPS receivers in continuous operation, they are unevenly distributed for ionosphere study purposes, being situated mostly in the Northern Hemisphere. The relatively smaller number of GPS receivers located in the Southern Hemisphere and, consequently, the reduced number of available TEC measurements, cause ionospheric modelling to be less accurate in this region. In the work discussed in this paper, the University of New Brunswick Ionospheric Modelling Technique (UNB-IMT) has been used to describe the local time and geomagnetic latitude dependence of the TEC during the March 31, 2001 magnetic storm with an emphasis on the effects in the Southern Hemisphere. Data collected from several GPS networks worldwide, including the Brazilian Network for Continuous Monitoring, have been used along with ionosonde measurements to investigate the global ionospheric response to this severe storm. Data analysis revealed interesting ionospheric effects, which are shown to be dependent on the local time at the storm commencement and the magnetic conditions previous to and during the storm period. The southward turning of the interplanetary magnetic field during the recovery phase of the storm began a process of substorm activity and development and intensification of electrojet activity over broad regions. Observed effects on the ionosphere during that storm are analysed and the mechanisms that gave rise to the ionospheric behaviour are discussed.
Global ionospheric TEC variations during January 10, 1997 storm
Geophysical Research Letters, 1998
The ionospheric storm evolution process was monitored during the January 10, 1997 magnetic cloud event, through measurements of the ionospheric total electron content (TEC) from 150 GPS stations. The first significant response of the ionospheric TEC to the geomagnetic storm was at 0300 UT as an auroral/subauroral enhancement around the Alaskan evening sector. This enhancement then extended to both noon and midnight. Around 0900 UT, the enhancement at noon broke from the subauroral band and moved to lower latitudes. This dayside northern hemisphere enhancement also corresponded to a conjugate geomagnetic latitude enhancement in the southern hemisphere and lasted about 5 hours. At 1500 UT a large middle latitude enhancement appeared over Mexico and the southern US, and persisted until 2200 UT. The enhancement was probably caused by the equatorward neutral wind which pushed the plasma up. On the basis of this assumption, the kinetic energy of the neutral wind which caused the middle latitude enhancement is estimated as-4.1x109 Joules. This is about 0.03% of solar wind energy impinging on the magnetosphere and about 3% of the energy deposited on polar cap ionosphere. After 2000 UT, a negative phase gradually became stronger (especially in the southern hemisphere), although the northern subauroral enhancement persisted one more day. The entire ionosphere gradually recovered to normal on January 12. Thus, large middle latitude enhancement, equatorward motion of the dayside enhancement (probably related to a TID), the persistence of the subauroral enhancement, and the conjugate features at both hemispheres are the main characteristics of this storm.
Superposed epoch analysis of the dayside ionospheric response to four intense geomagnetic storms
Journal of Geophysical Research, 2008
Prompt daytime ionospheric responses are presented for the following four intense geomagnetic storms: 29 October 2003, 30 October 2003, 20 November 2003, and 7 November 2004. We perform a superposed epoch analysis of the storms by defining the start time of the epoch when the Kan-Lee interplanetary electric field (proportional to the reconnection electric field) first reaches 10 mV/m during a period of continuously southward Bz. Measurements from the GPS receiver onboard the CHAMP satellite at 400 km altitude indicate significant low- to middle-latitude daytime total electron content (TEC) increases above the satellite within 1-2 h of the defined start time for three of the storms (˜1400 local solar time). The 20 November 2003 data follow a different pattern: the largest TEC increases appear several hours (˜5-7) following the interplanetary magnetic field Bz event onset. TEC data obtained from ground-based GPS receivers for the November 2003 storm tend to confirm a "late" TEC increase for this storm at ˜1400 LT. Estimates of vertical plasma uplift near the equator at Jicamarca longitudes (˜281 E) using the dual-magnetometer technique suggest that variability of the timing of the TEC response is associated with variability in the prompt penetration of electric fields to low latitudes. It is also found that for the November 2003 magnetic storm the cross-correlation function between the SYM-H index and the interplanetary electric field reached maximum correlation with a lag time of 4 h. Such a large lag time has never been noted before. The long delays of both the ionosphere and magnetosphere responses need to be better understood.
Journal of Geophysical Research, 2012
Ionospheric storms represent large global disturbances of the ionospheric F region electron density in response to geomagnetic storms. In this study, we use a combination of ionospheric total electron content (TEC) global maps and data from in-situ satellite measurements, such as solar wind data from the Advanced Composition Explorer (ACE), the Defense Meteorological Satellite Program (DMSP), and TOPographic EXplorer (TOPEX) and JASON-1 satellites, to investigate the ionospheric response during the geomagnetic storm event on 24-27 July 2004. A chain of ground-based Global Positioning System (GPS) stations and ionosonde measurements across South Africa have been used to give a comprehensive coverage over this midlatitude location. The most pronounced ionospheric effects of the storm occurred at low-and midlatitudes in the Southern hemisphere, with the most significant enhancements, observed on 25 and 27 July, presented here. The DMSP F15 satellite observed a sharp density enhancement over the midlatitudes. Over South Africa, the enhancement on 25 July was about twice as large as that observed on 27 July. The positive storm enhancements on 25 and 27 July both lasted over 7 hours, and can be classified as long-duration positive storm effects. Also, IMF Bz had southward orientation for an extended number of hours (exceeding 9 hours) and could have been the means by which energy was continuously fed into the magnetosphere and ionosphere. In addition, the F region critical frequency (foF2) values observed at two ionosonde stations showed marked positive responses that were associated with an increase in the ionospheric peak height (hmF2).
Responses of the low-latitude ionosphere to very intense geomagnetic storms
Journal of Atmospheric and Solar-Terrestrial Physics, 2001
In this work, we investigate the ionospheric responses to exceptionally high-intensity and long-duration magnetic storms over Brazil. Disturbed ionospheric F-region vertical drifts and peak electron density changes observed at the equatorial station Fortaleza-Fz (3 • 55 S; 38 • 25 W; dip − 3:5 •) and the low-latitude station Cachoeira Paulista-CP (22 • 41 S; 45 • 00 W; dip 24 • S), for three magnetospheric storm events that occurred in December 1980, April 1981 and September 1982, are analyzed. These storms had minimum Dst indexes −240; −311 and −289 nT, respectively. The interplanetary magnetic ÿeld (Bz) data from the ISEE-3 satellite, the auroral activity index AE, and the ring current index Dst are used as indicators of the magnetospheric conditions. The ionospheric response features are analyzed using the F-layer critical parameters h'F, hpF2 and foF2, from ionograms obtained at Fz and CP. The Bz and the AE index variations were much higher than those in many previous studies. Therefore, many of the observations reported here either have not been observed or are not readily explained by current models for predicting the penetration=dynamo disturbance electric ÿelds. The altitude of the nocturnal ionospheric F-layer at low latitudes may undergo signiÿcant variations during storm-time, caused by magnitude variations on the local zonal component of the F-region electric ÿeld intensity. During the period studied here, clear association of the F-layer rise (vertical velocity and altitude) and spread-F occurrence is observed. It is shown that the storm-time layer rise has a dominant role on the equatorial spread-F. An attempt is made to identify the origin of electric ÿelds responsible for the disturbed F-layer alterations. The main conclusions of this study are that (a) some e ects on the F-layer height and peak electron concentrations are consistent with model predictions. Some others are in discrepancy or have not been either predicted by model studies or experimentally detected, (b) the F-layer rise over Fz played a major role in the generation of spread-F, (c) the maximum disturbance electric ÿeld intensity observed was about 1:09 mV m s −1 , (d) in some cases, foF2 increases (decreases) over CP were seen to be related to increases (decreases), in the fountain e ect mechanism, (e) storm-time-induced h'F post-sunset height rise inhibitions over Fz may extend for at least 4 days, as observed, (f) daytime foF2 depressions of amplitude up to −9 MHz are observed over Fz, (g) in particular, a rather unexpected disturbance rise in h'F over Fortaleza, on September 8 at 08 LT, does not seem directly associated with either disturbance winds or penetration electric ÿelds with origin at high latitude, where the convection remained low during the preceding 10 h.