IMF Bz Research Articles

Study of the Long-Lasting Daytime Field-Aligned Irregularities in the Low-Latitude F-Region on 13 June 2022

The unusual daytime F-region Field-Aligned Irregularities (FAIs) were observed by the HCOPAR and the satellites at low latitudes on 13 June 2022. These irregularities survived from night-time to the following afternoon at 15:00 LT. During daytime, they appeared as fossil structures with low Doppler velocities and narrow spectral widths. These characteristics indicated that they drifted along the magnetic field lines without apparent zonal velocity to low latitudes. Combining the observations of the ICON satellite and the Hainan Digisonde, we derived the movement trails of these daytime irregularities. We attributed their generation to the rapid ascent of the F-layer due to the fluctuation of IMF Bz during the quiet geomagnetic conditions. Subsequently, the influence of the substorm on the low-latitude ionosphere was investigated and simulated. The substorm caused the intense Joule heating that enhanced the southward neutral winds, carrying the neutral compositional disturbances to low latitudes and resulting in a negative storm effect in Southeast Asia. The negative storm formed a low-density circumstance and slowed the dissipation of the daytime FAIs. These results may provide new insights into the generation of post-midnight irregularities and their relationship with daytime fossil structures.

The Nighttime Horizontal Neutral Winds at Mohe Station in Response to the Temporal Oscillations of Interplanetary Magnetic Field Bz

Temporal oscillations in the IMF Bz associated with Alfvén waves occur frequently in solar wind, with a duration ranging from minutes to hours. Using Swarm observations, Fabry–Pérot interferometer measurements at Mohe station, and Thermosphere–Ionosphere–Electrodynamic General Circulation Model simulations, the perturbations of zonal (ΔUN) and meridional (ΔVN) winds due to temporal oscillations in the IMF Bz on 23–24 April 2023 are explored in the following work. ΔUN is strong westward with a speed of greater than 100 m/s at pre-midnight on 23–24 April. This phenomenon is primarily driven by the pressure gradient, offsetting by the ion drag and Coriolis force. On 23 April, ΔVN is weak northward at the pre-midnight and strong southward at a speed of ~200 m/s at pre-dawn. On 24 April, ΔVN is strong (weak) northward at pre-midnight (pre-dawn). It is mainly controlled by a balance between the pressure gradient, ion drag, and Coriolis force.

IMF Bx, By, and Bz dependence of energetic particle precipitation in the magnetosphere

The orientation of Interplanetary Magnetic Field (IMF B) components plays a major role in magnetospheric Energetic Particles Precipitation (EPP). This is because the IMF B components in the Geocentric Solar Magnetospheric (GSM) coordinate system control magnetic reconnection at the subsolar magnetopause. This study intends to unravel the dependence of the preceding conditions of the orientations of IMF B components that drove geomagnetic storms on the EPPs produced in the Van Allen radiation belt. We classified the geomagnetic storms based on their drivers and IMF Bz orientations prior to the storms’ onset. Energetic particle fluxes, IMF B, and solar wind data were used. The study showed that electrons are more reactive to solar wind speed than protons. Additionally, storms with southward IMF Bz orientation caused more EPP enhancement than with northward orientation. Our results also showed that protons are more influenced by magnetospheric compression than electrons at the northward orientation of IMF Bz. In fact, at this point, the proton’s motion violates adiabatic invariants. As particles interact with electric fields, a significant population of EPPs is produced by pitch angle diffusion. Generally, IMF Bx and IMF By are often anticorrelated. The preceding conditions of orientations of the IMF Bx indicated weaker dependence on auroral indices, and invariably on energetic particles precipitation than the IMF By.

Morphology of equatorial F-region irregularities over the Indian longitude sector using GPS-derived ROTI observations

The occurrence characteristics of Equatorial F-region Irregularities (EFIs) along the Indian longitude sector are investigated using GPS-derived ROTI observations from 2010 to 2023, under both quiet and disturbed geomagnetic conditions. The analysis of the results emphasizes a strong dependence of EFIs occurrence on solar cycle variation. Additionally, the EFIs are more intense at the EIA regions under maximum solar activity periods attributed to the high ambient electron density in the F-layer. The occurrence of EFIs is found to be severe and frequently observed in equinox seasons in contrast to solstice seasons. Also, the occurrence of EFIs exhibits equinoctial asymmetry with more intense EFIs in the spring equinox than autumn equinox during the peak and declining periods of the solar cycle. Conversely, severe EFIs are observed during autumn equinox than spring equinox in the ascending phase of the solar cycle. The seasonal occurrence probability of EFIs is highest in the equinox seasons, following the winter solstice, and summer solstice in high solar activity conditions. Investigations of EFIs during two prominent geomagnetic storm events (17 March 2015 and 08 September 2017) during the study period show that the storm-induced Prompt Penetration Electric Fields (PPEFs) modulated the regular intensity of dusk time Pre-Reversal Enhancement (PRE), resulting in poleward expansion of ionospheric irregularities up to mid-latitude regions with spatial time lag. However, storm-induced westward electric fields and oscillating IMF Bz created Counter Electrojet (CEJ) like conditions, suppressing the dusk time ionospheric irregularities over dip equatorial and low-latitude regions on 17 March 2013. This study provides a comprehensive understanding of how ionospheric irregularities manifest under varying conditions, thereby supporting further research on substantiating the spatiotemporal EFIs characteristics and their predictions over the region.

Magnetotail Variability During Magnetospheric Substorms

AbstractIn this work, we present a statistical study of substorms covering a five‐year period 2016–2020. Substorm phases were identified from time series of the SuperMAG AL (SML) index using a list of 5,077 previously identified substorm onsets, the SML peak value marking transition from expansion to recovery phase, and the recovery identified as return to activity less than −100 nT in the SML index. Magnetic field observations from THEMIS, RBSP, and MMS missions were used to study the magnetotail characteristics during the substorm evolution. A superposed epoch analysis indicates that the substorm onset occurs almost simultaneously with a few minutes of uncertainty throughout the magnetotail, ranging from geostationary orbit to 20 RE. The onset in the transition region precedes the ground onset by a few minutes. The peak SML time coincides with the peak of the outer transition region ΔBZ, which suggests that the field‐aligned currents driving the SML activity arise from the outer transition region. Analysis of 2D maps of the tail magnetic field shows that the magnetotail current changes are limited to the center of the tail within |Y| < 10RE. The substorm recovery is fastest in the inner transition region and lasts longer when moving further out. We did not find major asymmetries in the substorm signatures associated with IMF BY or BZ.

Multi-process driven unusually large equatorial perturbation electric fields during the April 2023 geomagnetic storm

The low latitude ionosphere and thermosphere are strongly disturbed during and shortly after geomagnetic storms. We use novel Jicamarca radar measurements, ACE satellite solar wind, and SuperMAG geomagnetic field observations to study the electrodynamic response of the equatorial ionosphere to the 23, 24 April 2023 geomagnetic storm. We also compare our data with results from previous experimental and modeling studies of equatorial storm-time electrodynamics. We show, for the first time, unusually large equatorial vertical and zonal plasma drift (zonal and meridional electric field) perturbations driven simultaneously by multi storm-time electric field mechanisms during both the storm main and recovery phases. These include daytime undershielding and overshielding prompt penetration electric fields driven by solar wind electric fields and dynamic pressure changes, substorms, as well as disturbance dynamo electric fields, which are not well reproduced by current empirical models. Our nighttime measurements, over an extended period of large and slowly decreasing southward IMF Bz, show very large, substorm-driven, vertical and zonal drift fluctuations superposed on large undershield driven upward and westward drifts up to about 01 LT, and the occurrence of equatorial spread F irregularities with very strong spatial and temporal structuring. These nighttime observations cannot be explained by present models of equatorial storm-time electrodynamics.

Quantifying Uncertainties in the Quiet‐Time Ionosphere‐Thermosphere Using WAM‐IPE

AbstractThis study presents a data‐driven approach to quantify uncertainties in the ionosphere‐thermosphere (IT) system due to varying solar wind parameters (drivers) during quiet conditions (Kp < 4) and fixed solar radiation and lower atmospheric conditions representative of 16 March 2013. Ensemble simulations of the coupled Whole Atmosphere Model with Ionosphere Plasmasphere Electrodynamics (WAM‐IPE) driven by synthetic solar wind drivers generated through a multi‐channel variational autoencoder (MCVAE) model are obtained. Applying the polynomial chaos expansion (PCE) technique, it is possible to estimate the means and variances of the QoIs as well as the sensitivities of the QoIs with regard to the drivers. Our results highlight unique features of the IT system's uncertainty: (a) the uncertainty of the IT system is larger during nighttime; (b) the spatial distributions of the uncertainty for electron density and zonal drift at fixed local times present 4 peaks in the evening sector, which are associated with the low‐density regions of longitude structure of electron density; (c) the uncertainty of the equatorial electron density is highly correlated with the uncertainty of the zonal drift, especially in the evening sector, while it is weakly correlated with the vertical drift. A variance‐based global sensitivity analysis suggests that the IMF Bz plays a dominant role in the uncertainty of electron density. A further discussion shows that the uncertainty of the IT system is determined by the magnitudes and universal time variations of solar wind drivers. Its temporal and spatial distribution can be modulated by the average state of the IT system.

Solar Plasma Structures and Solar Wind Plasma Turbulences in Relation with Geomagnetic Disturbances during Decline Phase of Solar Cycle 24 and Rising Phase of Solar Cycle 25

We have studied the effect of solar structures and turbulences in solar wind plasma on the Earth's magnetosphere during the decline phase of solar cycle 24 and the rising phase of solar cycle 25. Most CMEs are geoeffective, cause geomagnetic storms, and are associated with C-class and M-class solar flares (S.F.s). It is also observed that these geomagnetic storms are associated with disturbances in solar wind plasma parameters. We have determined a large positive correlation with a correlation coefficient of 0.68, 0.58, 0.65, and 0.63 between the magnitude of the extensive geomagnetic storms and the peak value of IMF Btotal, the magnitude of IMF Btotal, the peak value of disturbances in the southward component of interplanetary magnetic fields (IMF Bz), and magnitude of disturbances in the southward component of interplanetary magnetic fields (IMF Bz). The correlation coefficient of 0.61 is higher between the magnitude of Dst and the magnitude of SWPT, as compared with the magnitude of flow pressure (0.39). From the present work, we have concluded that solar plasma structures and solar wind turbulences are mainly responsible for generating extensive geomagnetic storms.

The nature of the mesoscale field-aligned currents in the auroral oval for positive IMF BZ: More frequent occurrence in the dawnside sector than in the duskside sector

To understand the similarities and differences between the duskside mesoscale quasistatic field-aligned currents (FACs) and the dawnside mesoscale FACs, we examined the magnetic field data obtained through the constellation measurements of Swarm satellites for a four-year period. The automatic event identification method developed in the previous study (Yokoyama Y et al., 2021) identified events of quasistatic mesoscale FACs, which are embedded in the diminished dawnside and duskside Region 1/2 current systems, in 774 passes out of 4001 passes on the dawnside, and 443 out of 3755 passes on the duskside, respectively. The dawnside and duskside mesoscale FACs have similar occurrence tendencies such that both have a relatively high occurrence ratio for positive IMF BZ, occur regardless of sunlight conditions, and have the current density increasing with the solar wind proton density. On the other hand, one notable difference was found; the occurrence ratio of the dawnside mesoscale FACs is approximately 1.7 times higher than that of the duskside mesoscale FACs. This difference is discussed in terms of the dawn–dusk asymmetry of the occurrence of Kelvin Helmholtz instabilities on the magnetopause.

25-26 Ağustos 2018 Jeomanyetik Fırtına Sırasında Afrika Bölgesi Üzerindeki Manyetik Eşlenik Çiftleri Üzerindeki TEC Değişikliklerinin İncelenmesi

In this study, the electron transport process resulting from electromagnetic drift between two magnetic conjugate pairs over the African region during the August 25-26 2018 geomagnetic storm was investigated. The effects of geomagnetic conditions presented with Dst index and IMF Bz values on Total Electron Content (TEC) values at conjugate stations were compared separately for stormy and quiet periods. During the storm period, the effect of TEC values at stations in the northern hemisphere (Haifa and Djibouti) on the TEC values at stations in the southern hemisphere (Ambalavao and Malindi) is greater than the effect of TEC values in the southern hemisphere on TEC values in the northern hemisphere. According to this result, it can be said that the south-directed electromagnetic convection was more than the north-directed convection in the examined dates. When the coefficients are examined, it can be said that the interaction is more in the magnetic conjugate pair that is closer to the equator during the storm period, and the interaction is more in the magnetic conjugate pair that is far from the equator during the silent period. Considering the coefficients calculated for Dst and IMF Bz, it is seen that the TEC values are very small compared to their coefficients. From this it can be concluded that the effect of Dst and IMF Bz is much smaller than the effect of TEC values at a station on TEC values at its magnetic conjugates.

Multipoint Cluster Observations of Kinetic Alfvén Waves, Electron Energization, and O+ Ion Outflow Response in the Mid‐Altitude Cusp Associated With Solar Wind Pressure and/or IMF BZ Variations

AbstractWe report the properties of low frequency (LF) electromagnetic fluctuations (≤11 Hz) in relation to input electron and ion outflow response observed by Cluster in the mid‐altitude cusp during high solar wind dynamic pressure PSW and active magnetospheric conditions (Kp = 4+). The multipoint observations reveal the dynamic interplay between the spatial‐temporal properties of the wave and electron inputs and the ion outflow response enabling an assessment of causal connections. The LF waves are identified as ingoing traveling Alfvén waves that become dispersive at the ion gyroradius scale (i.e., kinetic Alfvén waves KAWs). The KAWs are collocated with ingoing field‐aligned electrons and ion outflow at keV energies and below. The KAWs are associated with earthward directed Poynting fluxes and energy densities with peak amplitudes occurring at multiple energy enhancements (“step‐ups”) exhibited in the electrons and ions, attributed to IMF BZ and/or PSW variations. Indicative of a causal connection, KAW Poynting fluxes and energy densities are strongly correlated with precipitating electron energy fluxes and outflowing O+ energies and energy fluxes. These yield mid‐altitude cusp empirical relationships that can be incorporated into or constrain cusp transport models. These results demonstrate the important role played by KAWs in enhancing electron precipitation into the cusp ionosphere and subsequent O+ energization upward along the magnetic field into the mid‐altitude cusp and beyond. The results also suggest the importance of PSW and/or IMF BZ variations in driving/controlling the reconnection source Alfvén wave and electron inputs into the cusp that significantly impact the ion outflow process.

Latituditual Structure of Dayside Polar Cusp Precipitation

The results of observations of low-altitude spacecraft crossing the daytime sector of the auroral zone and of high-apogee spacecraft in the equatorial plane of the magnetosphere were analyzed in order to identify the main processes leading to the formation of dayside polar cusps. Observations from the DMSP F7 spacecraft were used to analyze the latitudinal characteristics of ion precipitation in the cusp region and to study the latitudinal profile of ion pressure in the cusp depending on the IMF parameters. A significant difference was found in identifying the cusp boundaries using an automated data processing system and direct analysis of spacecraft observations. It is shown that for small negative values of the Bz-component of the IMF (〈Bz〉 = –3.0 nT), an ordinary feature of the cusp is the latitudinal profile of the ion pressure (Pi) with a width of ~1° of latitude with two maxima, one of which is located in the equatorward and the other in the poleward of the cusp. For large negative Bz values (–6, –8 nT), the polar maximum in the latitudinal profile Pi disappears; only the equatorial maximum remains, the Pi level at the maximum increases, and the width of the cusp decreases to ~0.7°. For Bz IMF 0, the most characteristic is the Pi profile with a maximum ion pressure in the polar part of the cusp. The cusp for Bz 0 is located at higher latitudes than for Bz 0, and its average latitudinal width increase to ~1.4° of latitude. In the prenoon sector MLT, the most typical for periods with a large negative By-component of the IMF (〈By〉 = –6.3 nT, 〈Bz〉 = –1.7 nT) is a cusp with a width of ~1.4° of latitude with a flat top in the latitudinal Pi profile. Comparison of the pressure distributions observed at low heights with data from high-apogee satellites confirmed the possibility of describing the formation of the cusp as a diamagnetic cavity and using observations in the cusp to determine the ion pressure in the magnetosheath.

The Growth of Ring Current/SYM‐H Under Northward IMF Bz Conditions Present During the 21–22 January 2005 Geomagnetic Storm

AbstractThe total energy transfer from the solar wind to the magnetosphere is governed by the reconnection rate at the magnetosphere edges as the Z‐component of interplanetary magnetic field (IMF Bz) turns southward. The geomagnetic storm on 21–22 January 2005 is considered to be anomalous as the SYM‐H index that signifies the strength of ring current, decreases and had a sustained trough value of −101 nT lasting more than 6 hr under northward IMF Bz conditions. In this work, the standard WINDMI model is utilized to estimate the growth and decay of magnetospheric currents by using several solar wind‐magnetosphere coupling functions. However, it is found that the WINDMI model driven by any of these coupling functions is not fully able to explain the decrease of SYM‐H under northward IMF Bz. A dense plasma sheet along with signatures of a highly stretched magnetosphere was observed during this storm. The SYM‐H variations during the entire duration of the storm were only reproduced after modifying the WINDMI model to account for the effects of the dense plasma sheet. The limitations of directly driven models relying purely on the solar wind parameters and not accounting for the state of the magnetosphere are highlighted by this work.

Dependence of Electron Flux Dropouts in the Earth's Outer Radiation Belt on Energy and Driving Parameters During Geomagnetic Storms

AbstractUsing 5‐year of measurements from Van Allen Probes, we present a survey of the statistical dependence of the Earth's outer radiation belt electron flux dropouts during geomagnetic storms on electron energy and various driving parameters including interplanetary magnetic field Bz, PSW, SYM‐H, and AE. By systematically investigating the dropouts over energies of 1 keV–10 MeV at L‐shells spanning 4.0–6.5, we find that the dropouts are naturally divided into three regions. The dropouts show much higher occurrence rates at energies below ∼100 keV and above ∼1 MeV compared to much smaller occurrence rate at intermediate energies around hundreds of keV. The flux decays more dramatically at energies above ∼1 MeV compared to the energies below ∼100 keV. The flux dropouts of electrons below ∼100 keV strongly depend on magnetic local time (MLT), which demonstrate high occurrence rates on the nightside (18–06 MLT), with the highest occurrence rate associated with northward Bz, strong PSW and SYM‐H, and weak AE conditions. The strongest flux decay of these dropouts is found on the nightside, which strongly depends on PSW and SYM‐H. However, there is no clear MLT dependence of the occurrence rate of relativistic electron flux dropouts above ∼1 MeV, but the flux decay of these dropouts is more significant on the dayside, with stronger decay associated with southward IMF Bz, strong PSW, SYM‐H, and AE conditions. Our statistical results are crucial for understanding of the fundamental physical mechanisms that control the outer belt electron dynamics and developing future potential radiation belt forecasting capability.

Reply to “Comment on ‘‘Unraveling the Role of IMF Bx in Driving Geomagnetic Activity’’” by Lauri Holappa et al.

AbstractWe thank Lauri Holappa, Jone Peter Reistad and Anders Ohma for their interest in our research and for having published their comments, referred hereafter as HEA2023. Here we present our counterarguments to the points presented in HEA2023. We explain the observed excess of AL values for different polarities of IMF By over different IMF Bx polarities by an additional negative IMF Bz, which exist due to the 7.25‐degree tilt of the solar equatorial plane to the ecliptic plane. We emphasize again that the AL index strongly depends on the dipole tilt, so that under the same driving conditions <AL> is more than twice larger during non‐tilted dipole periods than at solstices. The IMF Bx component, depending on its polarity, moves the magnetotail plasma sheet away from or toward the equatorial plane, and thus changes the effective dipole tilt angle. That change may be a cause of the asymmetric response of the AL‐index to positive or negative values of the IMF Bx.

Effect of strong geomagnetic storms and their association with solar wind plasma temperature and IMF during solar cycles 23 and 24.

Strong interaction of CMEs with Earth’s environment causes serious space weather effect through the coupled magnetosphere system. A geomagnetic storm is a global disruption of the earth’s magnetic field, and usually occurs in response to abnormal conditions in the IMF and solar wind. In this paper we present the consequences on interplanetary causes of strong geomagnetic storms (Dst ≤ -200nT), that occurred during solar cycle 23 and 24. It was found that the positive correlation with correlation coefficient (0.46) between the magnitude of strong geomagnetic storm and magnitude of solar wind plasma temperature, (0.54) between the magnitude of strong geomagnetic storm and magnitude of solar wind plasma velocity, (.58) between the magnitude of strong geomagnetic storm and magnitude of southward component of interplanetary magnetic field (IMF Bz) and (0.54) between strong geomagnetic storm and magnitude of interplanetary magnetic field (IMF Btotal).The correlation between magnitude of strong geomagnetic storm and magnitude of interplanetary magnetic field (with positive correlation coefficient 0.58) is higher, as compared with magnitude of strong geomagnetic storm and magnitude of solar wind plasma temperature (0.46). It has been verified that strong geomagnetic storm intensity is correlated well with the interplanetary magnetic field IMF (Btotal and Bz) better than with its solar parameters.

Transport and Acceleration of O+ Ions in Upstream Solar Wind Due To Impact of an IMF Discontinuity: 3D Global Hybrid Simulation

AbstractBased on the predictions of global 3D hybrid simulations, we present a new transport/acceleration path for escaped O+ ions in the upstream solar wind region resulting from the impact of a particular IMF tangential discontinuity (TD) with negative (positive) IMF Bz on the discontinuity's anti‐sunward (sunward) side. For O+ ions escaping to the duskside magnetosheath and with gyro‐radii larger than the TD thickness, when they encounter the TD, they can first go sunward into the upstream solar wind. They then gyrate clockwise to the pre‐noon side and get accelerated within the solar wind region and circulate back to the dawnside magnetosphere. These ions may be accelerated to well within the ring current energy range depending on the solar wind electric field strength. This new transport/acceleration path can bring some of the escaped ions into the inner magnetosphere, thus providing a new mechanism for generating an O+ ring current population.

Statistical Properties of Long‐Period Plasmapause Surface Waves From Van Allen Probes Observations

AbstractRecent work revealed the existence of plasmapause surface waves (PSWs) with Van Allen Probes observations, which are characterized by the periodic modulations of both magnetic/electric fields and plasma densities, and suggested to be the driver of giant undulations (GUs). In this study, six years data from Van Allen Probes were used to investigate the spatial distributions and occurrence conditions of PSWs in the period of 5–30 min. PSWs are found to be mainly distributed at L = 3.5–7 and their occurrence rate is increasing with larger L shells. In the azimuth direction, the spatial distribution of PSWs exhibits an obvious dawn‐dusk asymmetry with highest occurrence rates at MLT = 15–21, which is consistent with the spatial distribution of GUs revealed in the previous study. This further demonstrates that PSWs and GUs are connected, and indicates that PSWs differ from Ps6 waves which have a similar wave period and irregular waveform but mainly concentrate in the dawnside and connect with Ω bands. PSWs preferentially occur under the condition of high solar wind velocities (VSW > 500 km/s) and high dynamic pressures (Pdyn > 5 nPa), and their occurrence rate has a negative correlation with IMF Bz, SYMH and AL. Statistical results also reveal that PSWs preferentially occur around the peak of both magnetic storms and substorms. These findings may shed new lights on the further understanding of PSWs' generation and propagation.

SuperDARN Observations of the Two Component Model of Ionospheric Convection

AbstractWe use a 20 years database of Super Dual Auroral Radar Network (SuperDARN) observations to investigate the two component model of ionospheric convection. A convection pattern is included in the database if it is derived from at least 250 radar vectors and has a distribution of electric potential consistent with Dungey‐cycle twin vortex flow (a negative potential peak in the dusk cell and a positive potential peak in the dawn cell). We extract the locations of the foci of the convection cells from the SuperDARN convection patterns, and compare their dependencies on the north‐south component of the interplanetary magnetic field, IMF BZ, and the SuperMAG auroral electrojet index, SML. We use these parameters to define intervals of expected dayside or nightside dominated reconnection. Our results show that, under conditions favorable for dominant dayside reconnection, the dawn and dusk foci are shifted toward the dayside and that, under conditions favorable for dominant nightside reconnection, the dawn and dusk foci are shifted toward the nightside.

Ionospheric irregularities observed during the geomagnetic storm of March 2015 and June 2015 over Ethiopia

In this paper we studied the occurrence of ionospheric irregularities over Ethiopia as the consequence of the intense geomagnetic storm of March 2015 and June 2015. Total Electron Content (TEC) data obtained from six Ethiopian GPS reciever stations and those data were used to derive the ionospheric irregularities proxy indices, e.g.,rate of change of TEC (ROT) and ROT index (ROTI). These indices were used to characterize the intensity of the fluctuation of total electron content. ROTI was used as a criterion of ionospheric irregularities that took place during the storm. These indices were characterized along side with the disturbance storm time (Dst),the Interplanetary Electric Field (IEFy) and the SYM-H index (high resolution version of Dst) from ground-based magnetometers to see the effect of geomagnetic storm on horizontal component of geomagnetic field. Irregularities manifested in the form of fluctuations in TEC. Prompt penetration of electric field (PPEF) modulated the behaviour of irregularities during the initial and recovery phases of the geomagnetic storms. As a result,it was observed that the irregularities in the ionosphere of Ethiopia was in the range from weak to moderate. These irregularities generally occurred during the initial and recovery phases of the storm at all selected stations. The effect of electric field is found to depend on the local time at which the IMF Bz turned into southward. Therefore,east - west fluctuating Ey in March storm main phase is associated with suppression of irregularities in all stations and eastward Ey in the main phase of June 2015 is associated with small scale irregularity formation. The generation (inhibition) of irregularities is related to the effect of eastward (westward) storm time electric field disturbance dynamo electric fields and prompt penetration electric fields that created favourable (unfavourable) conditions for the generation of irregularities by uplifting (lowering) the F region.