Magnetospheric Convection Electric Field Research Articles

Variability of the Magnetospheric Convection Electric Field (MCEF) Under Shock Activity During the Solar Cycle 24

In the present work, we have analyzed the statistical variability of the MCEF under shock activity during solar cycle 24 as a function of the different phases of solar cycle 24 and as a function of the seasons. We compared the MCEF under shock periods with that under quiet periods. Solar cycle 24 recorded an average MCEF value of 0.28816888 mV/m, i.e. an average value of 0.26399935 mV/m for the ascending phase, 0.2961038 mV/m for the maximum phase and 0.28652747 mV/m for the descending phase. The minimum quantitative deviation from quiet activity observed is 59%. Seasonally, the highest MCEF values were recorded in Summer and Winter, and the lowest in Autumn and Spring. The corresponding mean values are 0.32707785 mV/m, 0.30966472 mV/m, 0.27061512 mV/m and 0.27020401 mV/m respectively. The minimum quantitative deviation from quiet activity observed is 66 %. This study showed that in most cases magnetic reconnection occurs on the night side between 1800 UT and 2400 UT.

Numerical modelling of the IMF influence on the large-scale structure of the ionosphere, including the poles displacement

The interplanetary magnetic field (IMF), frozen into the solar wind plasma, determines the level of geomagnetic activity and significantly affects the large-scale structure of the high-latitude ionosphere. Variations in the IMF components lead to non-stationarity of the magnetospheric convection electric field, causing changes in the spatio-temporal distribution of charged particles in the ionosphere. The situation is complicated by the fact that the geographic and geomagnetic poles do not coincide, which leads to universal time control (UT control) of the parameters of the high-latitude ionosphere. The effect of the poles displacement is most manifest in winter. Therefore, in this work, within the framework of a nonstationary mathematical model of the F-region of the ionosphere in Euler variables, taking into account the displacement between the geographic and geomagnetic poles, we study the influence of the interplanetary magnetic field components on the large-scale structure of the high-latitude ionosphere in winter. For this, the Weimer model of high-latitude electric potentials, which depends on the IMF, was used. As a result, of numerical modelling, it is shown that the IMF components affect the shape, size and spatio-temporal location of the main structural features of the high-latitude ionosphere depending on universal time. The obtained effect of ionisation tongue separation requires experimental confirmation. The obtained results demonstrate that the developed non-stationary three-dimensional model of the ionosphere in Euler variables can be applied to the study of ionospheric disturbances, including ionospheric disturbances associated with changes in the IMF components.

Variability of Ionosphere Over Indian Longitudes to a Variety of Space Weather Events During December 2006

AbstractThis paper highlights the impact of intense solar events over India during 3–20 December 2006. Ionospheric effects of a major solar flare (X9) on December 5 (10:35 UT) have been investigated by using dayside and nightside magnetometer data, dayside ionosondes, and dayside GPS vTEC observations. On the next day, a stream of fast solar wind hits the magnetosphere, causing a HILDCAA (High Intensity Long Duration Continuous Auroral Activity) preceded by moderate geomagnetic storm. The origin and characteristics of a positive ionospheric storm which occurred over Tirunelveli (TIR, geomagnetic latitude: −0.18°N) in the recovery phase of storm due to simultaneous presence of enhanced O/N2 and WEJ or weakened EEJ during the HILDCAA (7th and 8th of December) is investigated. Subsequently, on December 14, the most powerful CME since the Halloween event impacts the Earth, and three SSCs are recorded on December 14, 16, and 18. The variability of the ionosphere over the Indian longitude sector due to these intense space weather fluctuations is presented by utilizing the magnetometers, ionosonde, GPS vTEC, and satellite‐based observations in the same region. This study reports the influence of prompt penetration of the magnetospheric convection electric field and the disturbance dynamo on several key ionospheric and magnetic parameters within the Indian longitude sector.

Ionospheric Response to the Coronal Hole Activity of August 2020: A Global Multi‐Instrumental Overview

AbstractWe have studied the ionospheric response to a coronal hole event of August 2020 using the data from global ionospheric maps, ground magnetometers and parameters from the instruments onboard SWARM and thermosphere, ionosphere, mesosphere energetics and dynamics satellites. The role of different physical drivers, responsible for observed ionospheric disturbance, has been identified. On the storm day (2 August), a steady southward directed interplanetary magnetic field Bz caused the penetration of magnetospheric convection electric field and positive storm effect in daytime sectors. As a result of prompt penetration electric field (PPEF) on 2 August, a polar‐ward expansion of day‐side ionospheric plasma. On 3 August, the signatures of both disturbance dynamo electric field (DDEF) caused by disturbed thermospheric winds and PPEF have been observed. The westward PPEF and eastward disturbance DDEF on the night‐side caused a strong enhancement in ionospheric plasma parameters at the corresponding sectors. The effect of disturbed thermospheric winds and resultant electric field persisted till the end of 7 August. The large decrease in O/N2 ratio at northern mid‐latitudes which is a consequence of the seasonal impact resulted in the negative storm effects at corresponding latitudinal regions. This study has shown that although the storm of August 2020 was a minor one, the associated high speed solar wind streams emanating from a coronal hole resulted in drastic changes in ionospheric parameters including global electron content, in situ electron density and total electron content at the equatorial ionization anomaly and equatorial electric field.

Investigating the Development of Distinctive Subauroral Flow Channels During the November 7–8, 2004 Superstorm

AbstractWe investigate the development of large (∼3,000 m/s) subauroral flows occurring during the November 7–8, 2004 Superstorm by utilizing multisatellite and multiinstrument measurements from the Magnetosphere (M), topside Ionosphere (I), and Thermosphere (T). We present eight scenarios (Sc‐1–Sc‐8) depicting the development of large SubAuroral Polarization Streams (SAPS) in the initial phase (Sc‐1–Sc‐3) and recovery phase (Sc‐5), and structured SAPS (Sc‐4, Sc‐6–Sc‐7) and Double‐peak SubAuroral Ion Drifts (DSAID) in the recovery phase (Sc‐8). Magnetospheric observations reveal dayside magnetopause reconnection increasing both the magnetospheric convection electric field and the large‐scale Field‐Aligned Currents (FACs), long‐lasting (∼5 h) secondary dipolarizations during the initial phase, and a series of dipolarization events during the recovery phase. Ionospheric observations reveal the development of these large subauroral flows (i) during forward and reverse plasma convections—when the topside ionosphere received earthward energy from the magnetosphere and when the diversion of cross‐tail currents in the stretched magnetotail activated the Substorm Current Wedge (SCW)—and (ii) in a short‐circuited system that acted as a voltage generator. Thermospheric observations reveal earthward energy deposition from the ionosphere that drove wind surges—implying the presence of Atmospheric Gravity Waves (AGWs) and Traveling Ionospheric Disturbances (TIDs)—propagating equatorward/poleward and passing through the trough region, and further enhancing the subauroral flows by deepening the trough. From these results we conclude that the strong M‐I‐T coupling occurring under superstorm conditions played a significant role in the enhancement of the subauroral flows investigated.

On the historical origins of the CEJ, DP2, and Ddyn current systems and their roles in the predictions of ionospheric responses to geomagnetic storms at equatorial latitudes

AbstractIn this short letter, we recall the differences between the counter electrojet (CEJ), which is a phenomenon observed on the magnetically quiet days and the disturbance dynamo (Ddyn), which can be observed during and after a geomagnetic storm. The CEJ is well known to occur near the geomagnetic dip equator. It can be identified by a reversal in the horizontal component (H) of the geomagnetic field daily regular variations. In contrast to equatorial electrojet (EEJ) that flows eastward in the daytime, the CEJ is considered to flow westward. The magnetic signatures of the reversed solar quiet (Sq) current at the low latitude during magnetic storms are due to the Ddyn. This disturbance (Ddyn) is produced by current systems that are driven by thermospheric storm winds originating from the Joule heating of enhanced high‐latitude currents. The DP2 is the magnetic effect of current systems at high latitudes. These currents are associated with the coupling of magnetosphere and ionosphere through geomagnetic field lines. They are associated to the magnetospheric convection. During intense magnetic storms these high‐latitude currents are enhanced and their magnetic effects can extend toward the low latitudes. This work shows that the study of magnetic perturbations makes it possible to understand the disturbances of the ionospheric electric currents. The use of an efficient treatment of the magnetic signals makes it possible to separate the magnetic effects of the different perturbations prompt penetration of the magnetospheric convection electric field and disturbance dynamo electric field. This was performed in the paper Nava et al. (2016).

Middle‐ and low‐latitude ionosphere response to 2015 St. Patrick's Day geomagnetic storm

AbstractThis paper presents a study of the St Patrick's Day storm of 2015, with its ionospheric response at middle and low latitudes. The effects of the storm in each longitudinal sector (Asian, African, American, and Pacific) are characterized using global and regional electron content. At the beginning of the storm, one or two ionospheric positive storm effects are observed depending on the longitudinal zones. After the main phase of the storm, a strong decrease in ionization is observed at all longitudes, lasting several days. The American region exhibits the most remarkable increase in vertical total electron content (vTEC), while in the Asian sector, the largest decrease in vTEC is observed. At low latitudes, using spectral analysis, we were able to separate the effects of the prompt penetration of the magnetospheric convection electric field (PPEF) and of the disturbance dynamo electric field (DDEF) on the basis of ground magnetic data. Concerning the PPEF, Earth's magnetic field oscillations occur simultaneously in the Asian, African, and American sectors, during southward magnetization of the Bz component of the interplanetary magnetic field. Concerning the DDEF, diurnal magnetic oscillations in the horizontal component H of the Earth's magnetic field exhibit a behavior that is opposed to the regular one. These diurnal oscillations are recognized to last several days in all longitudinal sectors. The observational data obtained by all sensors used in the present paper can be interpreted on the basis of existing theoretical models.

Response of ionospheric disturbance dynamo and electromagnetic induction during geomagnetic storm

During geomagnetic storms, the direct penetration of magnetospheric convection electric field and the ionospheric disturbance dynamo (IDD) take place in the ionosphere. In this paper, we studied variability of IDD and electromagnetic induction (EMI) at different latitudinal sectors during the geomagnetic storms on 7 and 8 September 2002 and 20 and 21 November 2003 with high solar wind speed due to coronal mass ejection. This investigation employs geomagnetic field components (H and Z), the geomagnetic indices (Dst, AL, and AU), solar wind speed (Vx), and interplanetary magnetic field (Bz). It was observed that the H component of geomagnetic field decreases across latitudes, and varies with Vx, Bz, Dst, AL, and AU indices throughout the difference phases of the storm. Our result demonstrated the dominance of the IDD during the nighttime compared to the daytime. This implies that neutral dynamic wind is greater at night than during the day. Higher ratio ΔZ/ΔH is observed at nighttime because of the reduction on the E region conductivity, which allowed F region electric fields to dominate.

Modeling of properties of the plasmasphere under quiet and disturbed conditions

Based on theoretical models of the ionosphere and the plasmasphere, the ion composition variations in the plasmasphere and the plasmapause structure were studied depending on the choice of the distribution model of the magnetospheric convection electric field at low and high geomagnetic activity at the equinox and the December solstice. Based on the model calculations performed, the plasmapause shape and size during an increase and decrease in geomagnetic activity were studied. It was revealed that the size of the plasmasphere mainly depends on the magnetic local time (MLT) sector and the level of geomagnetic activity, and it greatly depends on the maximum universal time during the equinox. The Earth’s plasmasphere asymmetry is manifested in the noon-midnight and morning-evening directions. The analysis results of daily and seasonal variations in the ionic composition of the Earth’s plasmasphere at a moderate solar activity level show that there is a certain increase in the ion concentrations of H+ and He+ in the winter period probably due to an increase in the exospheric density at the summer to winter transition. The data obtained are in good agreement with satellite observations which makes it possible to use the model proposed to study the plasmasphere under different geophysical conditions.

Solar wind density controlling penetration electric field at the equatorial ionosphere during a saturation of cross polar cap potential

The most important source of electrodynamic disturbances in the equatorial ionosphere during the main phase of a storm is the prompt penetration electric field (PPEF) originating from the high‐latitude region. It has been known that such an electric field is correlated with the magnetospheric convection or interplanetary electric field. Here we show a unique case, in which the electric field disturbance in the equatorial ionosphere cannot be interpreted by this concept. During the superstorm on Nov. 20–21, 2003, the cross polar cap potential (CPCP) saturated at least for 8.2 h. The CPCP reconstructed by Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure suggested that the PPEF at the equatorial ionosphere still correlated with the saturated CPCP, but the CPCP was controlled by the solar wind density instead of the interplanetary electric field. However, the predicted CPCPs by Hill‐Siscoe‐Ober (HSO) model and Boyle‐Ridley (BR) model were not fully consistent with the AMIE result and PPEF. The PPEF also decoupled from the convection electric field in the magnetotail. Due to the decoupling, the electric field in the ring current was not able to comply with the variations of PPEF, and this resulted in a long‐duration electric field penetration without shielding.

Disturbance dynamo, prompt penetration electric field and overshielding in the Earth’s ionosphere during geomagnetic storm

This paper presents a result of model calculation of the disturbance dynamo electric field, prompt penetration, overshielding and their ionospheric effects during geomagnetic storm on December 14–15, 2006. The calculations were carried out with use of the Global Self-Consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP model) developed in WD IZMIRAN. Simulations were performed for quiet and disturbed conditions with took into account the magnetospheric convection electric field with and without took into account dynamo electric field. It has allowed to neglecting thermospheric and ionospheric effects of the disturbance dynamo electric field. The analysis of model calculation results was carried out. We have made conclusions about the role of the disturbance dynamo electric field, prompt penetration electric field and overshielding effects in thermospheic and ionospheric parameters during geomagnetic storm.

Numerical modeling of ionospheric effects in the middle‐ and low‐latitude F region during geomagnetic storm sequence of 9–14 September 2005

This study presents the Global Self‐Consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) numerical simulations of the 9–14 September 2005 geomagnetic storm effects in the middle‐ and low‐latitude ionosphere. Recent modifications to the GSM TIP model include adding an empirical model of high‐energy electron precipitation and introducing a high‐resolution (1 min) calculation of region 2 field‐aligned currents and a cross‐cap potential difference. These modifications resulted in better representation of such effects as penetration of the magnetospheric convection electric field to lower latitudes and the overshielding. The model also includes simulation of solar flare effects. Comparison of model results with observational data at Millstone Hill (42.6°N, 71.5°W, USA), Arecibo (18.3°N, 66.8°W, Puerto Rico), Jicamarca (11.9°S, 76.9°W, Peru), Palmas (10.2°S, 48.2°W, Brazil), and San Jose Campos (23.2°S, 45.9°W, Brazil) shows good agreement of ionospheric disturbances caused by this storm sequence. In this paper we consider in detail the formation mechanism of the additional layers in an equatorial ionosphere during geomagnetic storms. During geomagnetic storms, the nonuniform in height zonal electric field is generated at the geomagnetic equator. This electric field forms the additional layers in the F region of equatorial ionosphere.

Direct measurements of the Poynting flux associated with convection electric fields in the magnetosphere

Observations of Poynting fluxes associated with onset of convection electric fields are essential for understanding of electromagnetic energy transport from the solar wind toward the magnetosphere leading to changes in the convection electric field, which is one of the most fundamental parameters in the magnetosphere‐ionosphere coupled system. We present Cluster multispacecraft observations of Poynting fluxes associated with abrupt changes in large‐scale electric fields during sudden commencements and southward turning of the interplanetary magnetic field (IMF). The Cluster spacecraft detected Poynting fluxes dominated by the field‐aligned upward component during the preliminary impulse of sudden commencements and in the initial period after southward turning of the IMF. The upward Poynting flux indicates existence of Alfvén waves transporting electromagnetic energy from the ionosphere toward the magnetosphere leading to magnetospheric convection changes. The waveguide model and global magnetohydrodynamic (MHD) simulation calculating evolution of the Poynting flux following solar wind pressure enhancements also show upward Poynting fluxes propagating from the ionosphere toward the magnetosphere faster than the propagation of compressional waves. We conclude that the ionosphere acts as a channel to transmit electromagnetic energy supplied as field‐aligned currents toward a wide region in the magnetosphere‐ionosphere system instantaneously, leading to changes in magnetospheric convection electric fields.

Long‐lasting goodshielding at the equatorial ionosphere

During magnetic storm times, a dawnward electric field may build up at the Alfven layer in the inner magnetosphere to cancel an enhanced duskward magnetospheric convection electric field. This effect is known as “shielding” because the dawnward electric field prevents the duskward electric field from penetrating into the inner magnetosphere. The term “goodshielding” refers to the perfect shielding status, in which the penetration electric field is almost completely canceled by shielding electric field. Observational evidence of goodshielding has rarely been reported before. Here we present two long‐lasting (16 and 23 min) goodshielding cases as unambiguous evidence. Both cases show similar historical patterns of shielding status: long‐duration electric field penetration (undershielding), goodshielding, and then overshielding. The goodshielding time periods, featuring quiet‐level ionospheric electric field at the dayside equator, are not directly related to the changes of interplanetary magnetic field (IMF) BZ, but the transitions from goodshielding to overshielding coincide with reduction of convection electric field. Both cases show that the equatorial electric field does not significantly respond to convection electric field enhancements during goodshielding, indicating that the shielding electric field may quickly adjust to shield newly enhanced convection electric fields. The quick shielding is possibly attributed to the fact that the ring current has become stronger and has been brought closer to the Earth. These new features may provide some clues to understand the magnetosphere‐ionosphere coupling processes during storm times.

Latitudinal profile of the ionospheric disturbance dynamo magnetic signature: comparison with the DP2 magnetic disturbance

Abstract. During magnetic storms, the auroral electrojets intensification affects the thermospheric circulation on a global scale. This process which leads to electric field and current disturbance at middle and low latitudes, on the quiet day after the end of a storm, has been attributed to the ionospheric disturbance dynamo (Ddyn). The magnetic field disturbance observed as a result of this process is the reduction of the H component amplitude in the equatorial region which constitutes the main characteristic of the ionospheric disturbance dynamo process, associated with a westward electric current flow. The latitudinal profile of the Ddyn disturbance dynamo magnetic signature exhibits an eastward current at mid latitudes and a westward one at low latitudes with a substantial amplification at the magnetic equator. Such current flow reveals an "anti-Sq" system established between the mid latitudes and the equatorial region and opposes the normal Sq current vortex. However, the localization of the eastward current and consequently the position and the extent of the "anti-Sq" current vortex changes from one storm to another. Indeed, for a strong magnetic storm, the eastward current is well established at mid latitudes about 45° N and for a weak magnetic storm, the eastward current is established toward the high latitudes (about 60° N), near the Joule heating region, resulting in a large "anti-Sq" current cell. The latitudinal profile of the Ddyn disturbance as well as the magnetic disturbance DP2 generated by the mechanism of prompt penetration of the magnetospheric convection electric field in general, show a weak disturbance at the low latitudes with a substantial amplification at the magnetic equator. Due to the intensity of the storm, the magnitude of the DP2 appears higher than the Ddyn over the American and Asian sector contrary to the African sector.

Eastward electric field enhancement and geomagnetic positive bay in the dayside low‐latitude ionosphere caused by magnetospheric substorms during sawtooth events

Substorms cause significant disturbances in the magnetosphere and ionosphere. Although many substorm‐induced phenomena have been relatively well understood, a serious controversy arises as to how the magnetospheric and ionospheric convection responds to the expansion onset. In this paper, we present the observations of the low‐latitude ionospheric electric field and geomagnetic field at substorm onsets during sawtooth events when the interplanetary magnetic field (IMF) remains steady southward, so the ionospheric disturbances are attributed solely to the substorm effects. In the substorm events we have analyzed, the dayside equatorial ionospheric electric field shows an eastward enhancement at the onset, and the geomagnetic field northward component at middle and low latitudes shows an increase (positive bay) on both the dayside and nightside. We suggest that the magnetospheric convection is enhanced at substorm onset and that the enhanced magnetospheric convection electric field penetrates to the low‐latitude ionosphere. The penetration electric field driven by substorm onset causes the eastward ionospheric electric field enhancement and geomagnetic positive bay on the dayside, and the substorm current wedge causes the geomagnetic positive bay on the nightside. Our findings are significantly different from the results of most previous studies and provide new insight into the substorm dynamic process.

Variations of the Auroral Electrojet Belt During Substorms

AbstractEnhancement of auroral activity and intensification of auroral electrojet are the most important manifestations of the magnetosphere‐ionosphere coupling. Both aurora and electrojet result from the same mechanism‐charged particle precipitation, however, they have rather different behaviors and AE‐dependences. In this paper, the dynamic characteristics of the auroral electrojet belt are studied by using equivalent current systems deduced from ground‐based magnetic records. The results show that the auroral electrojet belt is divided by the Harang discontinuity into two parts: the afternoon‐dusk section with minor eastward electrojet and the midnight‐morning section with major westward electrojet, the latter is divided into two subsections: the midnight section and the morning section. Along with AE increasing in substorm expansion phase, the whole auroral oval expanses equatorward, however, the different sections of the auroral electrojet exhibit different dynamic behaviors: the afternoon‐dusk and morning sections drifts equatorward, just as the auroral oval does, while the midnight section drifts poleward. A study on electrodynamics responsible for these differences reveals that the principal controlling factor is different for different sections of the electrojet: the afternoon‐dusk eastward electrojet and the morning westward electrojet are mainly controlled by the magnetospheric convection electric field, corresponding to DP2 currents of the directly driven process, while the midnight westward electrojet largely depends on the ionospheric conductivities, corresponding to DP1 currents of the unloading process.

Comparison between two theoretical mechanisms for the formation of the plasmapause and relevant observations

The plasmapause formation physical mechanisms are recalled: (i) the MHD convection mechanism, based on the original idea that the plasmapause coincides with the last closed equipotential (LCE) of the magnetospheric convection electric field or with the last closed streamline (LCS) of the equatorial plasma, and (ii) the interchange mechanism, which is based on peeling off the plasmasphere as a result of substorm associated enhancements of the night side convection velocity, leading to an enhanced centrifugal acceleration in the outermost layers of the plasmasphere. The plasmapause positions, predicted by these alternative theories, were numerically determined for two different magnetospheric empirical electric field models: (i) the Volland-Stern-Maynard-Chen (VSMC) and (ii) McIlwain E5D models, both of which are Kp-dependent. The predicted positions and overall shape of the equatorial plasmapause cross-sections are confronted to those derived from decades of whistler and satellite observations including the EUV observations during the substorm of June 27, 2001. It is found that the VSMC electric field model and the LCS plasmapause formation theory less correspond to whistler measurements and in-situ satellite observations than the E5D model and the interchange plasmapause formation mechanism.

Numerical modeling of the light ion trough and heat balance of the topside ionosphere in quiet geomagnetic conditions

The results from the numerical calculations of the global distribution of topside ionospheric parameters such as H + ions and ion and electron temperatures up to 1500 km height are presented for equinoctial conditions at solar minimum. Calculations are carried out using the Global Self-consistent Model of Thermosphere, Ionosphere and Protonosphere (GSM TIP) developed in WD IZMIRAN, and using a new calculation block for electric fields due to dynamo and of magnetospheric origin. A comparison of two sets of calculations of magnetospheric convection electric field for a given potential difference is carried out, one through polar caps and other through field aligned currents of first zone. It is shown that the distribution of the electric potential obtained through field aligned currents of first zone is more self-consistent than that through polar caps. The light ion trough in H + ions is deeper and occupies larger region for the potential difference through polar cap. For a given potential difference through field aligned current, at 1500 km, the maximum ion temperature is 150 K higher, minimum ion temperature is 200 K lower and maximum electron temperature is 100 K higher than those obtained for the same potential difference through polar caps. It is concluded that for modeling the electric field of magnetospheric origin, it is necessary to use the potential difference through field aligned current of first zone instead of through polar caps.

Analysis Of Interplanetary Phenomenon, Geomagnetic And Ionospheric Response Associated With The Storm Of July 8, 1975, In The East Asian Sector

A study is made of the moderate geomagnetic storm of July 8, 1975 (Dstmin =-60 nT) and its associated ionospheric storm using solar wind parameters and foF2 data obtained from ionosonde stations in East Asian longitudinal sector. The storm was found to be a double step storm with the first Dstmin resulting mainly from ring current injection due to increase in solar wind density while magnetospheric convection electric field played the leading role in the development of the second Dstmin . The analysis of the interplanetary and foF2 data show that the appearance of positive storm before the beginning of the geomagnetic disturbance in the mid-latitudes and the occurrence of strong negative phase at the low latitude station of Manila is due to the penetration of interplanetary electric field. Furthermore, available results presented ionospheric response features that bear similarity in form and magnitude with those that are due to intense storms. This suggests that a moderate storm is capable of generating ionospheric storms which are of comparable magnitude with those resulting from intense geomagnetic storms. Keywords: Geomagnetic storm, solar wind, plasma sheet density, ring current, ionospheric storm. Nigerian Journal of Physics Vol. 19 (1) 2007: pp. 63-74