IMF Bz Research Articles

Связь индекса ASY-H с параметрами межпланетной среды и авроральной активностью на главных фазах магнитных бурь во время событий CIR и ICME

In this study, we examine the relationship of the ASY-H index characterizing the partial ring current intensity with interplanetary medium parameters and auroral activity during the main phase of magnetic storms, induced by the solar wind (SW) of different types. Over the period 1979–2017, 107 magnetic storms driven by CIR and ICME (MC + Ejecta) events have been selected. We consider magnetic storms with Dstmin≤ – 50 nT. The average ASY-H index (ASYaver) during the magnetic storm main phase is shown to increase with increasing SW electric field and southward IMF Bz regardless of SW type. There is no relationship between ASYaver and SW velocity. For the CIR and ICME events, the average AE (AEaver) and Kp (Kp aver) indices have been found to correlate with ASYaver. The highest correlation coefficient between AEaver and ASYaver (r = 0.74) is observed for the magnetic storms generated by CIR events. A closer relationship between Kp aver and ASYaver (r = 0.64) is observed for the magnetic storms induced by ICME events. The ASYaver variations correlate with Dstmin. The relationship between ASYaver and the rate of storm development is weak.

Performance evaluation of neural network TEC forecasting models over equatorial low-latitude Indian GNSS station

Global Positioning System (GPS) services could be improved through prediction of ionospheric delays for satellite-based radio signals. With respect to latitude, longitude, local time, season, solar cycle and geomagnetic activity the Total Electron Content (TEC) have significant variations in both time and space. These temporal and spatial TEC variations driven by interplanetary space weather conditions such as solar and geomagnetic activities can degrade the communication and navigation links of GPS. Hence, in this paper, performance of TEC forecasting models based on Neural Networks (NN) have been evaluated to forecast (1-h ahead) ionospheric TEC over equatorial low latitude Bengaluru (12.97∘N,77.59∘E), Global Navigation Satellite System (GNSS) station, India. The VTEC data is collected for 2009–2016 (8 years) during current 24th solar cycle. The input space for the NN models comprise the solar Extreme UV flux, F10.7 proxy, a geomagnetic planetary A index (AP) index, sunspot number (SSN), disturbance storm time (DST) index, solar wind speed (Vsw), solar wind proton density (Np), Interplanetary Magnetic Field (IMF Bz). The performance of NN based TEC forecast models and International Reference Ionosphere, IRI-2016 global TEC model has evaluated during testing period, 2016. The NN based model driven by all the inputs, which is a NN unified model (NNunq) has shown better accuracy with Mean Absolute Error (MAE) of 3.15 TECU, Mean Square Deviation (MSD) of 16.8 and Mean Absolute Percentage Error (MAPE) of 19.8% and is 1–25% more accurate than the other NN based TEC forecast models (NN1, NN2 and NN3) and IRI-2016 model. NNunq model has less Root Mean Square Error (RMSE) value 3.8 TECU and highest goodness-of-fit (R2) with 0.85. The experimental results imply that NNunq/NN1 model forecasts ionospheric TEC accurately across equatorial low-latitude GNSS station and IRI-2016 model performance is necessarily improved as its forecast accuracy is limited to 69–70%.

Comparison of Multiple and Logistic Regression Analyses of Relativistic Electron Flux Enhancement at Geosynchronous Orbit Following Storms

AbstractMany factors influence relativistic outer radiation belt electron fluxes, such as waves in the ultralow frequency (ULF) Pc5, very low frequency (VLF), and electromagnetic ion cyclotron (EMIC) frequency bands, seed electron flux, Dst disturbance levels, substorm occurrence, and solar wind inputs. In this work we compared relativistic electron flux poststorm versus prestorm using three methods of analysis: (1) multiple regression to predict flux values following storms, (2) multiple regression to predict the size and direction of the change in electron flux, and (3) multiple logistic regression to predict only the probability of the flux rising or falling. We determined which is the most predictive model and which factors are most influential. We found that a linear regression predicting the difference in prestorm and poststorm flux (Model 2) results in the highest validation correlations. The logistic regression used in Model 3 had slightly weaker predictive abilities than the other two models but had the most value in providing a prediction of the probability of the electron flux increasing after a storm. Of the variables used (ULF Pc5 and VLF, seed electrons, substorm activity, and EMIC waves), the most influential in the final model were ULF Pc5 waves and the seed electrons. IMF Bz, Dst, and solar wind number density, velocity, and pressure did not improve any of the models, and were deemed unnecessary for effective predictions.

IpsDst of Dst Storms Applied to Ionosphere‐Thermosphere Storms and Low‐Latitude Aurora

AbstractConventionally, the minimum value of Dst (DstMin) and maximum values of Kp and AE (Kpmaxand AEmax) representing the geomagnetic storm intensities have been used for investigating space weather in Earth's environment. The present paper uses the derived parameters (IpsDst, IpsKp, and IpsAE) giving the mean values of Dst, Kp, and AE during the main phase (MP) of Dst storms for investigating ionosphere‐thermosphere storms and low‐latitude (630 nm) aurora. The derived parameters (IpsDst, IpsKp, and IpsAE) representing the impulsive strength of geomagnetic storms seem to have more systematic dependence among themselves than among the intensities (DstMin, Kpmax, and AEmax). The ionosphere‐thermosphere storms observed by the CHAMP (Challenging Minisatellite Payload) satellite and low‐latitude auroras observed by optical imagers are much more intense during high impulsive storms than high intensity storms. In a statistical sense, over 175 positive ionospheric storms (△NmF2) observed in 1985–2005 and the intensity of 20 red auroras observed in 1989–2004 at midlatitudes correlate better with the impulsive parameters than the intensity parameters, with the best correlation being with IpsDst. The mechanism of the impulsive action (high‐energy input over a short duration) leading to large IpsDst arises from the impact of fast solar storms (interplanetary coronal mass ejections) with large IMF Bz southward at their front (or shock). The impulsive action results in bright low‐latitude auroras and strong ionosphere‐thermosphere storms.

Wavelet analysis of the magnetotail response to solar wind fluctuations during HILDCAA events

Abstract. In this work a study of the effects of the high-intensity long-duration continuous AE activity (HILDCAAs) events in the magnetotail was conducted. The aim of this study was to search the main frequencies during HILDCAAs in the Bx component of the geomagnetic field in the magnetotail, as well as the main frequencies, at which the magnetotail responds to the solar wind during these events. In order to conduct this analysis the wavelet transform was employed during nine HILDCAA events that coincided with Cluster spacecraft mission crossing through the tail of the magnetosphere from 2003 to 2007. The most energetic periods for each event were identified. It was found that 76 % of them have periods ≤4 h. With the aim to search the periods that have the highest correlation between the IMF Bz (OMNI) component and the Cluster Bx geomagnetic field component, the cross wavelet analysis technique was also used in this study. The majority of correlation periods between the Bz (IMF) and Bx component of the geomagnetic field observed also were ≤4 h, with 62.9 % of the periods. Thus the magnetotail responds stronger to IMF fluctuations during HILDCCAS at 2–4 h scales, which are typical substorm periods. The results obtained in this work show that these scales are the ones on which the coupling of energy is stronger, as well as the modulation of the magnetotail by the solar wind during HILDCAA events.

Ion Pressure at the Auroral Precipitation Boundaries and Its Relationship with the Solar Wind Dynamic Pressure

The data from the DMSP F7 satellite for 1986 are used to study the behavior of ion pressure at the boundaries of auroral precipitation. The study is based on 7489 satellite passages in the nightside sector of the auroral zone, including over 5000 passages in the 2100–2400 MLT sector. Ion pressure is determined as the average for 5 s of observations, which corresponds to a distance of ~40 km in the satellite trajectory portions adjacent to the precipitation boundaries. It is shown that the plasma pressure at the boundaries of auroral precipitation almost linearly increases at all levels of magnetic activity with an increase in the solar wind dynamic pressure (Psw). The pressure distribution as a function of MLT indicates that the precipitation boundaries, including the isotropy boundary, are not isobars, even at a low level of geomagnetic activity. The plasma pressure is maximal in the 22–24 MLT sector and decreases both in the morning and evening sides. The latitudinal position of the precipitation boundaries and the plasma pressure at the boundaries are found during all the phases of a typical substorm with an intensity of AL = –410 nT at its maximum. The latitudinal profile of ion pressure is constructed with respect to the isotropy boundary (IB) at the beginning of substorm. It is shown that, with an increase in dynamic pressure, there is not only a substantial increase in plasma pressure at the auroral precipitation boundaries but also a change in the latitudinal position of the boundaries themselves. As Psw grows, the latitude of the polarward boundary of the oval increases, while that of the equatorward boundary decreases. Despite the considerable expansion of the precipitation region, the latitudinal pressure gradient between the oval boundaries increases, even during quiet periods (average AL = –18 nT, IMF Bz = +1.4 nT) without any disturbances in the auroral zone, by approximately a factor of 2, from 0.06 to 0.12 nPa/deg.

Analysis of the Steady State Available Energy Budget in the High‐Latitude Lower Thermosphere

AbstractWe evaluate the budgets of available energy (AE) production, transport, and loss under steady state forcing of the high‐latitude lower thermosphere during the southern summer time for weak or strong southward interplanetary magnetic field (IMF, Bz = −2.0 or −10.0 nT), using the National Center for Atmospheric Research Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model. The AE below 150‐km altitude is partitioned into commensurable reservoirs of kinetic energy (KE) and available potential energy (APE). KE density is larger than APE density above 123 km, but they are comparable below 123 km. Whereas Pedersen ion drag generates strong winds and KE, vertical winds and adiabatic cooling above 123 km tend to offset temperature perturbations caused by Joule heating, thereby reducing APE. Below 123 km Hall ion drag and associated vertical motions are important for creating temperature perturbations and APE. With increasingly negative IMF Bz values APE density intensifies more significantly than KE density above about 123 km, while KE density intensifies more significantly than APE density below. KE is generated primarily where the ion‐drag force associated with plasma convection accelerates the neutral gas and is destroyed primarily where the ion‐drag force opposes the wind. APE is generated primarily where Joule heat is deposited in regions of elevated temperatures and destroyed where the heat is deposited in regions of reduced temperatures. Ion drag is generally more important than Joule heating for generating AE for steady‐state conditions, but the relative contribution of the ion‐drag forcing compared with heating decreases with descending altitude. AE generation by Joule heating intensifies more significantly than generation by ion drag with increasingly negative IMF Bz values. Transport of AE by horizontal and vertical winds is a significant component of the AE budget. Conversion of APE to KE, and of KE to APE, constitutes an important part of their budgets.

Longitudinal variability of occurrence of ionospheric irregularities over the American, African and Indian regions during geomagnetic storms

This study presents the longitudinal variabilities of occurrence of ionospheric irregularities over the equatorial/low-latitude region of America, Africa and Indian sectors. Five major geomagnetic storms of the equinoctial months of the year 2012–2013 were analyzed for this study. Total Electron Content (TEC) data obtained from Global Navigation Satellite Systems (GNSS) over American, African and Indian longitudinal sectors were used to derive, the rate of change of TEC index (ROTIave), the ionospheric irregularities proxy. Longitudinal variability of occurrence of irregularities were discussed with respect to the local time when the maximum negative of SYM-H index occurs and polarity of IMF Bz in the dusk hours. Almost all of the storms under investigation inhibited the occurrence of irregularities in Indian sector. Out of five storms, two and three storm periods revealed inhibition in the generation of irregularities over the American and African sectors, respectively. Most of the generation of ionospheric irregularities observed in this study were related to post-midnight local time occurrence of the maximum negative excursion of SYM-H index. There were also cases where irregularities are observed when the minimum value of SYM-H occurred in the pre-midnight and daytime period. It appears that the local time at which minimum SYM-H occur is not a sufficient condition to explain the effect of storms on generation/inhibition of ionospheric irregularities. Significant longitudinal variability in the generation of irregularities were also observed over wide longitudinal ranges (South America, Africa and India) during 09 March 2012 and 17 March 2013 storm events. Difference in longitudinal variation of storm-time electric field were a suggested reason.

Characteristic of the Disturbed Days Ionospheric Current System in the 180-Degree Magnetic Meridian

The behavior of the ionospheric current during disturbed days using 10 geomagnetic observatories along 180-degree magnetic meridian was analysed. Separation of external and internal current during geomagnetic storm on 12 April until 15 April 2012 data was carried out using spherical harmonic analysis method. The contour of day to day variation of total current, external current and internal current were distinguished based on geomagnetic storm phase. These current then were correlate with the solar wind parameter, IMF Bz, and geomagnetic indices in order to identify their relationship. The results reveal that these current intensities were found higher during the initial phase. This due to the enhancement of the magnetic field during the initial phase caused by the increment of solar wind dynamic pressure and southward IMF Bz. Hence, the induced current identified in the internal current. This study demonstrated that the electric current induction can be obtained from the weak geomagnetic storm.

Supersubstorms during strong magnetic storm on 7 September 2017

We analyzed the appearance of two supersubstorms observed during storm on September 07, 2017. Supersubstorms (SSS) are called substorms with SML index < - 2500 nT. The storm on September 07, 2017 is famous event which was studied already in many papers. There were two several geomagnetic storms on 7 and 8 September 2017, which associated with two consecutive solar wind structures: SHEATH with EJECTA and SHEATH with magnetic cloud (MC). Because the first SHEATH have a positive IMF Bz on their front edge the substorm activity absent in this time. The main phase of the first magnetic storm began with arriving the second SHEATH with the strong negative IMF Bz. During this period the first night-side supersubstorm (up to ~ 3500 nT) developed. The second magnetic storm was caused by MC with the negative IMF Bz and the severe night-side supersubstorm (up to ~ 3500 nT) were registered in this time. Thus, during the 7-8 September 2017 storms, two supersubstorms were generated, these supersubstorms caused by the SHEATH and MC impact have demonstrated the global scale distribution.

Signatures of Sudden Storm Commencement on the equatorial thermospheric dayglow

It has been observed that the OI 630.0 nm dayglow emission over a dip equatorial station, Trivandrum (8.5° N, 77° E, dip 0.5° N), India registered an abrupt increase of ~ 2000 R during the compression phase of the magnetosphere as dictated by a sudden increase in solar wind ram pressure. Furthermore, an unusual depletion of these emissions has been observed during the eastward interplanetary electric field (IEF), concomitant with southward excursion of IMF Bz. The ionosonde and magnetometer observations confirmed the effects of prompt penetration electric field (PPEF). Associated with the eastward PPEF, formation of F3 layers were also noticed. These unique results, which emphasize the effect of Sudden Storm Commencement/IEF on these equatorial daytime airglow emissions are discussed in context of changes in the equatorial zonal electric field and F region height variations associated with polar/auroral activities due to the magnetosphere-ionosphere coupling.

PC index as a proxy of the solar wind energy that entered into the magnetosphere: 4. Relationship between the solar wind dynamic pressure (PSW) impulses and PC, AL indices

The solar wind dynamic pressure (PSW) impulses impacting on the magnetosphere were separated on the basis of solar wind parameters measured in the point of libration L1 in 1998–2017. Comparison of the “estimated” PSW impulses reduced to the Earth's magnetopause with the appropriate sudden impulses (SI), revealed in the ground-based 1-min SymH index, showed that features of the really observed sudden impulses (moment of beginning, time evolution, intensity) can be significantly different from characteristics of the estimated PSW impulses. Because of this the preference was given to the real SI events over the estimated PSW impulses. Only the events with sudden impulses starting against the background of steady quiet pressure levels were taken for the analysis (N = 143). Relationship between the positive (leaps) and negative (drops) SI events, on the one hand, and PC and AL indices, on the other hand, were examined under the various solar wind conditions, such as: growing and steady solar wind speed at negative and positive values of the IMF BZ component, fluctuating BZ and solar wind speed, steady solar wind speed and BZ = 0. Analysis of SI events showed that the solar wind dynamic pressure impulses themselves are not promote (or insignificantly promote) the solar wind energy input into the magnetosphere, which is controlled by the interplanetary electric field EKL = Vsw*(BY2+BZ2)1/2 and is displayed by the polar cap magnetic activity PC index. When the PSW impulses (leaps or drops) are accompanied by the corresponding changes in EKL field, the PC index correlates (increases or decreases) with the PSW changes. Inconsistency between the PSW and PC behavior becomes evident as soon as the EKL and PSW courses start to diverge. Development of magnetic disturbances (AL index) is governed only by the EKL field and PC index increase irrespective of the PSW impulses magnitude and time evolution.

Characteristics of storm time ion composition in the near-Earth plasma sheet using Geotail and RBSP measurements

Solar wind particles and ionospheric O+ ions influence the near-Earth plasma sheet and inner magnetospheric composition. We studied the behavior of H+, O+ and He+ ions (9–210 keV) for intense and moderate geomagnetic storms of solar cycle 23 and 24. An average energy density < ε > of ions over a given interval and flux enhancement is estimated using observations from satellites at different L values, namely STICS sensor on-board Geotail spacecraft and HOPE spectrometer on-board Radiation Belt Storm Probes. It provides a comprehensive understanding of the energy density variation of H+, O+ and He+ ions with the strength of IMF Bz, Psw, intensity of storms and L value. Statistically, we observed that (1) In the plasma sheet region, during main phase of the intense geomagnetic storm, < εO+/H+ > and < εHe+/H+ > enhances, (2) < εO+/H+ > is well correlated with Psw (CC = 0.86) and IMF Bz (CC = 0.85), (3) < εO+/H+ > shows higher correlation (CC = 0.73) with Kp than < εHe+/H+ > (CC = 0.65), indicating a fairly good dependence on the strength of geomagnetic activity, (4) < εO+/H+ > and < εHe+/H+ > dependence on L value indicates that O+/H+ and He+/H+ is more pronounced near L = 3. It is a cumulative extension of the previous studies on ion composition change which is in accordance with the existing picture of the plasma sheet and inner magnetosphere.

Magnetotail boundary crossings at lunar distances: ARTEMIS observations

We compare results from a preliminary analysis of two years of ARTEMIS magnetopause boundary crossings at lunar distances with available empirical models. We remove the effects of variable solar wind flow directions and aberration angles to study the magnetotail cross-section as a function of solar wind conditions. The average magnetopause distance from the central axis is 26 RE, but this distance ranges from 10 RE for high solar wind dynamic pressures and strong northward IMF orientations to 39 RE for low solar wind dynamic pressures and weak southward IMF orientations compared to the nominal solar wind conditions. The time-independent Howe and Binsack (1972) model describes the average location of the crossings very well. For high solar wind dynamic pressures, the Lu et al., (2011) model performs best, while for low pressures the Petrinec and Russell (1996) model gives the closest prediction. As predicted by theory and seen in past studies, the magnetotail cross-section is suggestive of prolate during intervals of strong IMF By, but oblate during intervals of strong IMF Bz. Any asymmetric variation of the tail boundary with respect to the sign of IMF By was not observed. The decreasing size of boundary with the increasing dynamic pressure was found when dynamic pressures are smaller than 2 nPa. Although the scatter is larger, the tail size for pressures larger than 2 nPa suggests a constant radius. The tail boundary size decreases as the strength of IMF Bz increases regardless of its polarity. However, it was also observed that an even stronger southward IMF Bz can cause larger magnetopause size in the presence of large dynamic pressures.

Observation of equatorial plasma bubbles by the airglow imager on ISS-IMAP

Using 630 nm airglow data observed by an airglow imager on the International Space Station (ISS), the occurrence of equatorial plasma bubbles (EPBs) is studied. In order to examine the physical mechanisms in the boundary region between the Earth and the outer space, an ionosphere, mesosphere, upper atmosphere, and plasmasphere mapping (IMAP) mission had been conducted onboard the ISS since October 2012. The visible light and infrared spectrum imager (VISI) is utilized in the ISS-IMAP mission for nadir-looking observation of the earth’s atmospheric airglow. In this study, we automatically select EPBs according to the criterion for extracting the tilted dark lines from VISI data. Using the selected events, the dependence of the occurrence rate of EPBs is examined. There is no other report of the occurrence rate of EPBs using downward-looking visible airglow data (630 nm). In this result, the occurrence rate is high at all longitudes in the equinoctial seasons. In the solstice seasons, in contrast, the occurrence rate is very small especially in the Pacific and American sectors. This result is basically consistent with previous studies, e.g., those determined by plasma density data on DMSP satellites.During the June solstice in 2013, EPBs were observed in association with geomagnetic storms that occurred due to a southward turning of the IMF Bz. Using these events, we examined the storm-time features of the occurrence of EPBs in the Pacific-American sectors during the June solstice. In these sectors, where the occurrence rate of EPBs is very small during solstice seasons, some EPBs were observed in the peak and recovery phases of the storms. This result shows that the prompt penetration of electric fields causes the development of EPBs, in the data we analyzed, the geomagnetic storms did not inhibit the generation of EPB in the Pacific–American sectors.

Response of Relativistic Electron Microbursts to the Arrival of High‐Speed Solar Wind Streams and its Relation to Flux Variation of Trapped Radiation Belt Electrons

AbstractRelativistic electron microbursts are frequently observed during high‐speed solar wind stream (HSS) events. However, solar wind parameters, which are important for enhanced microburst precipitation, have not been well understood. We perform a superposed epoch analysis of microburst occurrence frequency during HSS events, considering the north/south component of the interplanetary magnetic field (IMF Bz) and solar wind speed. The IMF Bz dependence is investigated considering the Russell‐McPherron effect following the method used by Miyoshi and Kataoka (2008, https://doi.org/10.1029/2007JA012506). We find that microbursts are most frequently observed during faster (&gt;500 km/s) solar wind speed streams with the IMF Bz shifted southward (fast SBZ‐HSS events), indicating that both fast solar wind speed and the southward IMF Bz are important for enhanced microburst precipitation. The occurrence frequency of chorus waves during the HSS events is investigated to gain an understanding of the different behavior of microburst activity in response to the HSS events. We show that relativistic electron microbursts are not always a good proxy for chorus waves, but a proxy for a subset of chorus that can resonate with MeV electrons. We also show that electron fluxes with energies from hundreds of keV to several MeV preferentially increase during the fast SBZ‐HSS events. These results indicate that observation of an enhanced occurrence of relativistic electron microbursts could be used as a proxy for the direct observation of the acceleration of MeV electrons by chorus waves in the heart of the outer radiation belt, not just a proxy for chorus wave activity in general.

Auroras in the cusp and its poleward vicinity: a case study

Summary We present a case study of the dayside aurora observed simultaneously with optical instruments from the ground and with auroral particle spectrometers aboard the DMSP F16 and F17 satellites. Optical observations were carried out with an all-sky camera at the Polar Geophysical Institute (PGI) observatory Barentsburg on Svalbard. The aurora as a whole moved equatorward in response to negative turning of the IMF Bz component and then the distinct faint rayed arc intensified, moved to the north and faded. Satellite DMSP F17 crossed the cusp twenty minutes after Bz turned southward. Joint analysis of optical and satellite data showed that faint auroral structures are embedded into the cusp precipitations and correspond to the bursts of electron precipitations with energy below 100 eV. The next satellite crossed the camera field-of-view ten minutes later and the data showed that the source of the faded poleward moving rayed arc was located, most probably, on the non-closed magnetic field lines. This finding and the presence of ion-energy dispersion in the DMSP data allows us to make the conclusion that the dayside reconnection may be considered as the reason for this kind of aurora activity. In this study we also estimated the altitude and horizontal scale of auroral rays in the cusp.

Effect of geomagnetic storms on VHF scintillations observed at low latitude

A geomagnetic storm affects the dynamics and composition of the ionosphere and also offers an excellent opportunity to study the plasma dynamics. In the present study, we have used the VHF scintillations data recorded at low latitude Indian station Varanasi ($$\hbox {Geomag. latitude}\,=\,14^{^{\circ }}55^{\prime }$$N, long. = $$154^{^{\circ }}\hbox {E}$$) which is radiated at 250 MHz from geostationary satellite UFO-02 during the period 2011–2012 to investigate the effects of geomagnetic storms on VHF scintillation. Various geomagnetic and solar indices such as Dst index, Kp index, IMF Bz and solar wind velocity (Vx) are used to describe the geomagnetic field variation observed during geomagnetic storm periods. These indices are very helpful to find out the proper investigation and possible interrelation between geomagnetic storms and observed VHF scintillation. The pre-midnight scintillation is sometimes observed when the main phase of geomagnetic storm corresponds to the pre-midnight period. It is observed that for geomagnetic storms for which the recovery phase starts post-midnight, the probability of occurrence of irregularities is enhanced during this time and extends to early morning hours.

Geomagnetic storm effects on the occurrences of ionospheric irregularities over the African equatorial/low-latitude region

The study investigated the effects of intense geomagnetic storms of 2015 on the occurrences of large scale ionospheric irregularities over the African equatorial/low-latitude region. Four major/intense geomagnetic storms of 2015 were analyzed for this study. These storms occurred on 17th March 2015 (−229 nT), 22nd June 2015 (−204 nT), 7th October 2015 (−124 nT), and 20th December 2015 (−170 nT). Total Electron Content (TEC) data obtained from five African Global Navigation Satellite Systems (GNSS) stations, grouped into eastern and western sectors were used to derive the ionospheric irregularities proxy indices, e.g., rate of change of TEC (ROT), ROT index (ROTI) and ROTI daily average (ROTIAVE). These indices were characterized alongside with the disturbance storm time (Dst), the Y component of the Interplanetary Electric Field (IEFy), polar cap (PC) index and the H component of the Earth’s magnetic field from ground-based magnetometers. Irregularities manifested in the form of fluctuations in TEC. Prompt penetration of electric field (PPEF) and disturbance dynamo electric field (DDEF) modulated the behaviour of irregularities during the main and recovery phases of the geomagnetic storms. The effect of electric field over both sectors depends on the local time of southward turning of IMF Bz. Consequently, westward electric field inhibited irregularities during the main phase of March and October 2015 geomagnetic storms, while for the June 2015 storm, eastward electric field triggered weak irregularities over the eastern sector. The effect of electric field on irregularities during December 2015 storm was insignificant. During the recovery phase of the storms, westward DDEF suppressed irregularities.

Superposed Epoch Analysis of High Latitude Ionospheric Joule Heating during Major Geomagnetic Storms over three Solar Cycles

AbstractSuperposed epoch analysis (SPEA) is commonly used to determine some basic structure in a collection of geophysical time series. The present study tries to analyze ionospheric Joule heating response at high latitudes, to the prevailing solar wind and IMF conditions on the basis of SPEA. Major geomagnetic storms (CME driven) over three consecutive solar cycles (SC 22, 23 and 24) have been selected. Ascending phase, solar maximum, and declining phase are investigated separately, for each solar cycle, to find out crucial controlling parameters for the generation of high-latitude ionospheric Joule heating. SPEA results show that, IMF parameters such as IMF By, IMF Bz, IMF clock angle and solar wind parameters such as dynamic pressure and proton density influence Joule heating production rate significantly. Meanwhile, the relentlessness of the other parameters such as IMFBt and solar wind bulk speed show that they have poor impact on Joule heating.