Study of Ionospheric Variability During Super Substorms (original) (raw)
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Geomagnetism and Aeronomy, 2007
The interval 0000-1400 UT of the superstorm of November 20, 2003, has been studies based on the ACE/WIND data and the MIT2 magnetogram inversion technique. The distributions of the electric potential and currents, field-aligned currents, and Joule heat in the ionosphere have been calculated. The variable magnetotail length and powers coming into the magnetosphere, ionosphere and ring current have been estimated. The selected superstorm intervals, when it became possible to identify the disturbance mode produced by the interaction between the variable solar wind dynamic pressure and IMF effects, have been described. Spontaneous substorms, two types of driven responses to changes in IMF or in the solar wind dynamic pressure ( P d ), zero events at simultaneous jumps of IMF and P d , and a previously unknown mode of saturation of the ionospheric electric field at a redistribution of the energy coming into the magnetosphere between the ionosphere and ring current are among the selected modes. PACS numbers: 94.30.Lr
Journal of Atmospheric and Solar-Terrestrial Physics, 2010
We present a study of ionospheric and thermospheric response during a November 9-10, 2004 major geomagnetic storm event (DsT $À300 nT). We utilize the North American sector longitude chain of incoherent scatter radars at Arecibo, Millstone Hill, and Sondrestrom, operating as part of a coordinated international mesosphere/lower thermosphere coupling study experiment. Total electron content (TEC) determinations from global positioning system (GPS) ground receivers, ground magnetometer traces from the Canadian CANOPUS array, Defense Meteorological Satellite Platform (DMSP) topside data, and global convection patterns from the SuperDARN radar network are analyzed to place the detailed radar data in proper mesoscale context. The plasmaspheric boundary layer (PBL) expanded greatly in the dusk sector during ring current intensification to span more than 251 of magnetic latitude, reaching as far south as 301 invariant latitude. Strong sub-auroral polarization stream velocities of more than 1 km/s were accompanied by large upwards thermal O+ fluxes to the overlying magnetosphere. The large PBL expansion subsequently exposed both Millstone Hill and Sondrestrom to the auroral convection pattern, which developed a complex multicell and reverse convection response under strongly northward IMF conditions during a period of global interplanetary electric field penetration. Large traveling atmospheric and ionospheric disturbances caused significant neutral wind and ion velocity surges in the mid-latitude and tropical ionosphere and thermosphere, with substorm activity launching equatorward neutral wind enhancements and subsequent mid-latitude dynamo responses at Millstone Hill. However, ionosphere and thermosphere observations at Arecibo point to significant disturbance propagation modification in the post-dusk sector PBL region.
Journal of Geophysical Research, 2009
In this paper, we study the local time response of the low-latitude ionosphere during the sequence of geomagnetic storms occurring on 7, 9, and 10 November 2004. Three distinct storm main phases leading to peak negative Dst index of at least À250 nT occur during this period. We analyze total electron content (TEC) measurements from the global network of GPS receivers available from the International Global Navigation Satellite Systems (GNSS) Service. Average TEC within the geomagnetic latitude band ±25°is computed as a function of local time for several hours following storm commencement. We find that significant TEC increases are observed on 7 November (increase of 100%) and 9 November (50%). During 7 November, the increases tend to occur during solar local times 1200-1600 LT. During 9 November, the largest TEC increases tend to occur at earlier local times ($1000-1200 LT). No daytime TEC increase is observed on 10 November, although the K p index suggests that this storm is comparable in intensity to the 7 November storm. Vertical drift measurements from the Jicamarca radar (Peruvian sector) for the 7 and 9 November storm periods suggest large (2-3 mV/m) low-latitude ''prompt penetration'' eastward electric fields (PPEF), consistent with observed increases in TEC. For the 10 November storm, published estimates of electric fields using the dual-magnetometer technique near the Japanese sector, which is near $1400 LT at storm onset, suggest the absence of eastward directed electric fields during daytime. A time series analysis of TEC in the Japanese sector throughout the 7-11 November period reveals significant daytime TEC reduction of 33% relative to quiet conditions. Reduced TEC occurs coincident with the onset of the 10 November storm period, persisting into the 11th. Global Ultraviolet Imager (GUVI) retrievals of thermospheric atomic oxygen to nitrogen ratio suggest depleted oxygen in the southern hemisphere that may contribute to the TEC reduction on 10 November. Solar rotation reduces solar X-ray and EUV fluxes from 10 through 12 November, which may be a contributing factor to reduced TEC on 10 and 11 November. In conclusion, we postulate that an additional source of electric field is present on 10 November during daytime that counteracts the PPEF of magnetospheric origin.
Journal of Geophysical Research, 1996
Model calculations of the electrodynamics of the high-latitude ionosphere are compared to measurements made by the Viking satellite during July-August 1986. The model calculations are based on the IZMEM procedure, where the electric field and currents in the ionosphere are given as functions of the interplanetary magnetic field. The events chosen correspond to the growth, the expansion, and the recovery phases of substorms. During the growth and expansion phases the correlation between the model results and the satellite data is rather good. During recovery phase the correlation is not as good. The correlation between modeled and observed quantities suggest that during growth and expansion phase the magnetosphere is mainly directly driven by the solar wind, whereas during recovery phase it is mainly driven by internal processes, i.e., loading-unloading. Best fit is obtained when averaging the measured quantities over a few minutes, which means adjusting the spatial resolution of the measurements to the resolution of the model. Different time delays between the interplanetary magnetic field observations and those of Viking were examined. Best agreement was obtained, not surprisingly, for time delays corresponding to the estimated information transit time from the solar wind spacecraft to the ionosphere. In the geospace environment modeling (GEM) program, two models are considered for synthesis of sparse high-latitude data [Lotko, 1993]. Both models allow the computation of nearly instantaneous snapshots of electric field and potential distribution in the entire auroral region. The assimilative mapping of ionospheric electrodynamics (AMIE) model is used for calculation of high-latitude electric fields and currents from sets of localized observational data [Richmond and Kamide, 1988; Richmor•d et al., 1988; Richmor•d, 1992]. A similar model has also been used by Marklund et al. [1988]. See also Marklund arid Blomberg [1991] and Blomberg arid Marklur•d [1993]. The Inetitute of Terrestrial Mag-Copyright 1996 t)y the American Geophysical Union. Paper number 96JA00514. 0148-0227 / 96 / 96 J A-00514509.00 netism Electrodynamical Model (IZMEM)is another model for calculating the same parameters, but the input data are the interplanetary magnetic field (IMF) magnitude and direction [Levitir• et al., 1984; Feldsteir• arid Levitire, 1986; Papitashvili et al., 1994]. The influence of the IMF on the upper atmosphere electrodynamics is crucial also in the models of Friis-Christer•ser• et al. [1985] and Mishir• [1990]. The latter two models are used by their respective authors only, whereas the IZMEM model is publicly available through the World Data Center A for Rockets and Satellites [Bilitza, 1990]. The IZMEM model is here used to determine the global convection pattern and its temporal evolution during a number of passes of the Swedish satellite Viking over the northern high-latitude region. The model electric field is compared to the satellite observations along the trajectory, and the global convection pattern and its temporal evolution is estimated in the entire highlatitude region. The sensitivity to averaging of the correlation between the modeled and measured values is discussed. The averaging interval selected influences the sensitivity of the correlation to changes in the model, and it is of interest to determine to what extent the correlation coefficient is dependent on the correct timing of the changes between gross features of the convection system during the period studied. 19,921 19,922 FELDSTEIN ET AL.: HIGH-LATITUDE IONOSPHERE There is today a consensus that there are two processes responsible for the solar wind energy input to the magnetosphere during sUbstorms. These are direct driving and loading-unloading processes. Some fraction of the energy input is directly dissipated in the ionosphere by Joule heating and particle precipitation related to enhanced convection and enhanced ionospheric currents. This power dissipation is directly correlated with the solar wind parameters and is thus a driven process [Akasofu, 1981]. The remaining part of the power transfeted into the magnetosphere is stored temporarily in the Earth's magnetosphere and subsequently released at substorm breakup. The latter is known as loading-unloading process [Baker et al., 1984, 1993]. The delay time between a change in the IMF and the related effects in the ionosphere is different for the two processes. For the directly driven process it is 10-20 min due to the inductance of the magnetosphereionosphere system. For the loading-unloading process it is typically 40-60 min. Which one of these .processes dominates remains an open question.
Empirical modelling of ionospheric storms at midlatitudes
Advances in Space Research, 1998
The reaction of the F-layer to geomagnetic storms is studied between 35' and 55" (dipole latitude) with as indicator the relative deviation of foF2 to its monthly median. A longitude/UT Fourier development yields the longitudinally averaged offset, the diurnal and the semkiiurnal wave. These are evaluated in terms of the total energy input into the aurora1 thermosphere ("Power Index". P) as solutions of a continuity equation written for this ionospheric characteristic. Production, loss and drift terms are introduced in the equation, representing the main physical processes controlling the ionospheric disturbances during storms. The ionospheric characteristic is presented as the sum of the average offset and the slowly rotating standing wave. The expression matches the data satisfactorily for storms in the summer hemisphere, while in winter there is significant discrepancy, possibly as a consequence of interhemispheric influences. 01998 COSPAR.
Space Weather, 2018
An assessment of the ionosphere perturbations can be made through the construction of the global instantaneous maps of the foF2 critical frequency (GIM-foF2) and the ionospheric weather index maps GIM-Wf. These maps can offer a potentially useful tool to provide users with a proper selection of the best radio wave propagation conditions over a certain area and also be used to help mitigate the effects of the disturbances on HF (High Frequency) communication and Global Navigation Satellite System positioning. This paper presents results of reconstruction of the ionospheric weather during five of the most intense superstorms observed since International Geophysical Year, IGY (1957, 1958, 1959, 1989, and 2003) with the instantaneous global maps of the F2 layer critical frequency, GIM-foF2, and the ionospheric weather index maps, GIM-Wf. The intensity of the ionospheric superstorm is characterized by the planetary Wfp index derived from GIM-Wf maps. Superposed epoch analysis of the extreme superstorms is made during 24 hr before the Wfp peak (time zero t 0 = 0 hr) and 48 hr afterwards. Model relationship is established between mean Wfp profile and geomagnetic superstorm profiles demonstrating saturation of the ionospheric storm activity toward the peak of geomagnetic storm. Time lag of Wfp max is found equal to 9 hr after AE max , 6 hr after ap max and aa max , and 2 hr after Dst min , which allows model forecast of ionospheric superstorm when geomagnetic superstorm is captured with one or more of geomagnetic indices.
Analysis of the solar wind IMF Bz and auroral electrojet index during supersubstorms
Russian Journal of Earth Sciences, 2021
This work examines the coupling between solar wind interplanetary magnetic field (IMF) and auroral electrojet () index during supersubstorms (SSSs) of 11 April 2001 and 24 November 2001. The SSSs are particularly intense substorms with the value of < −2500 nT; < −2500 nT. For the detail analysis, the data set of 1 min time resolution of IMF and index in the geocentric solar magnetospheric (GSM) coordinate system are used. The spectral characteristics of SSSs events are studied using continuous wavelet transforms (CWT) and global wavelet spectrum (GWS). The cross-correlation analysis also has been applied to study the correlation and time lag between IMF and index. The spectrum identified the main periodicities of the IMF and index during these events. The short-lived periodicity of high-frequency signals are identified between 70 to 256 minutes and 80 to 256 minutes during 11 April 2001 and 24 November 2001, respectively. The global wavelet spectrum (GWS) identifies the most energetic periods are present during the SSSs. Cross-correlation analysis shows that the index correlates (correlation coefficient ∼ −0.6) with IMF at time lag of approximately zero. These results support the previously existing facts that the magnetic reconnection between southward directed IMF and the northward pointed Earth's magnetic field at the dayside magnetopause is the primary mechanism for transferring solar wind energy into magnetosphere and ionosphere during the SSSs events.
Ionospheric disturbances induced by substorm associated electric fields in the low-latitude F-region
Journal of geomagnetism and geoelectricity, 1987
Based on the observation of low latitude ionosphere around 600 km altitude by the Hinotori satellite, well-defined signatures of the ionospheric disturbances associated with substorm activities are found. In the wide area of the nightside equatorial region, a remarkable enhancement of local electron density takes place in response to the enhancement of the AE index, with a time delay shorter than the revolution period of the satellite (97 min). The enhanced region is usually accompanied by several signatures which indicate the dynamical effects acting on the events, i.e. the development of the equatorial anomaly, longitudinal substructures and formation of the plasma bubbles. These signatures can be interpreted by dynamical uplift of the equatorial ionosphere. On the other hand, the equatorial anomaly is suppressed in dayside. Both of the nightside enhancement and the dayside suppression of the equatorial anomaly are induced simultaneously, although they are followed by rather different time sequential developments. The basic signatures of the ionospheric disturbance can be reasonably explained by dynamical effects of the disturbance electric field which is induced by substorm activities. The polarity of the disturbance electric field should be eastward in nightside and westward in dayside, and duration of the disturbance field is estimated to be about one hour or less.
Unusual topside ionospheric density response to the November 2003 superstorm
Journal of Geophysical Research, 2006
1] We use observations from a variety of different ground-and space-based instruments, including ionosonde, ground-and space-based Global Positioning System (GPS) receivers, magnetometers, and solar wind data from the Advanced Composition Explorer (ACE), to examine the response of the ionospheric F2-layer height during the November 2003 superstorm. We found that the topside ionosphere responded unusually to the 20 November 2003 severe storm compared to behavior observed in a number of previous storms. While ground-based GPS receivers observed a large enhancement in dayside TEC, the low-Earth orbiting ($400 km) CHAMP satellite did not show any sign of dayside TEC enhancement. The real-time vertical density profiles, constructed from ground-based GPS TEC using a tomographic reconstruction technique, clearly revealed that the ionospheric F2-layer peak height had been depressed down to lower altitudes. Ionospheric F-layer peak height (hmF2) from the nearby ionosonde stations over Europe also showed that the dayside F2-layer peak height was below 350 km, which is below the orbiting height of CHAMP. The vertical E Â B drift (estimated from ground-based magnetometer equatorial electrojet delta H) showed strong dayside downward drifts, which may be due to the ionospheric disturbance dynamo electric field produced by the large amount of energy dissipation into high-latitude regions. This storm demonstrates that data from LEO satellites varies widely among different superstorms.