Intense Magnetic Storms Research Articles

How Solar Wind Controls the Recovery Phase Morphology of Intense Magnetic Storms

AbstractGeomagnetic storms are critical space weather phenomena resulting from the interaction between the solar wind and the Earth's magnetosphere. However, most studies focus on the main phase of magnetic storms, leaving the morphology of the recovery phase an open question. In this study, we analyze 82 intense magnetic storms with the minimum Dst index ≤ −100 nT between 1995 and 2018, finding that these storms can be classified into two distinct types: one‐stage recovery storms that exhibit a single rapid exponential recovery and two‐stage recovery storms that are characterized by a rapid exponential recovery in the early recovery phase and a slow linear recovery in the later recovery phase. We find that the two‐stage recovery storms are dominant, accounting for approximately 60% of the events. Interestingly, the proportion of two‐stage recovery storms peaks during solar minimum. The two‐stage recovery storms tend to be accompanied by more Alfvén waves with long‐duration and intense southward interplanetary magnetic fields. In addition, we find that the decay rate of the Dst index in the later recovery phase is correlated with the average BZ of the interplanetary magnetic field when the solar wind has a high degree of Alfvénicity. Overall, our results shed new light on the recovery phase morphology of intense magnetic storms and highlight the role of Alfvén waves in this process.

First Results From REPTile‐2 Measurements Onboard CIRBE

AbstractCIRBE (Colorado Inner Radiation Belt Experiment), a 3U CubeSat, was launched on 15 April 2023 into a sun synchronous orbit (97.4° inclination and 509 km altitude). The sole science payload onboard is REPTile‐2 (Relativistic Electron and Proton Telescope integrated little experiment—2), an advanced version of REPTile which operated in space between 2012 and 2014. REPTile‐2 has 60 channels for electrons (0.25–6 MeV) and 60 channels for protons (6.5–100 MeV). It has been working well, capturing detailed dynamics of the radiation belt electrons, including several orders of magnitude enhancements of the outer belt electrons after an intense magnetic storm, multiple “wisps”‐ an electron precipitation phenomenon associated with human‐made very low frequency (VLF) waves in the inner belt, and “drift echoes” of 0.25–1.4 MeV electrons across the entire inner belt and part of the outer belt. These new observations provide opportunities to test the understanding of the physical mechanisms responsible for these features.

Magnetic Storm Effects on the Occurrence and Characteristics of Plasma Bubbles

AbstractThe Communications/Navigation Outages Forecast System satellite mission was designed to investigate the ionospheric conditions that lead to the formation of irregularities. Here, we have studied the effect of magnetic storms on the formation and evolution of plasma bubbles during the satellite's lifetime (2008–2015). During this period encompassing solar minimum and maximum conditions, many magnetic storms of varying intensity developed, producing a unique and rich data set of 248 storms (14 intense, 69 moderate, and 165 weak) that occurred during the same timeframe to examine the role of external magnetospheric drivers in the production and dynamics of equatorial plasma bubbles. We have used the Planar Langmuir Probe and Ion Velocity Meter instruments to elucidate the role of magnetic storm intensity on the bubble's depth, internal speed, width, occurrence, and lifetime. The pre‐reversal enhancement (PRE) tends to increase during the main phase and when BZ is southward. New bubbles occur during large excursions of the PRE value. The bubble lifetime extends and remains active during the main and part of the recovery phase. The plasma velocity within the bubbles increases and typically becomes over 100 m/s during significant PRE and BZ negative times. The depth of bubbles reaches values close to 100% during intense storms. In general, the intensity of the storms seems to control and augment the plasma bubbles' depth, width, and internal velocity.

The record of the magnetic storm on 15 May 1921 in Stará Ďala (present-day Hurbanovo) and its compliance with the global picture of this extreme event

Abstract. This paper deals with the most intense magnetic storm of the 20th century, which took place on 13–15 May 1921. Part of this storm was observed in the magnetic declination and vertical intensity at Stará Ďala, currently known as Hurbanovo. However, the sensitivity of the magnetometer was not determined there in the years when the storm occurred. Here, we estimated the sensitivity scale values on the basis of data from before and after the studied event. The resulting digitized Stará Ďala’s data for 13–15 May 1921 are the main contribution of this work. The data were also put into the context of the records from other observatories. The overall picture of the geomagnetic field variations compiled from the observations by worldwide observatories, including Stará Ďala, suggests that the auroral oval got close to Stará Ďala and other European mid-latitude observatories in the morning hours on 15 May 1921.

A class of Bayesian machine learning model for forecasting Dst during intense geomagnetic storms

In this paper we apply a class of Bayesian machine learning model, Gaussian Process Regression, to the prediction of Dst index by using 80 intense geomagnetic storms data (Dst⩽-100nT) from 1995 to 2014. The purpose of this paper is to compare the performance of Gaussian process regression model with Support Vector Machine model combined together with Distance Correlation (DC-SVM) and Neural Network model combined together with Distance Correlation (DC-NN) (Lu et al., 2016). For comparison, we estimate the correlation coefficients (CC), the RMS errors, the absolute value of difference in minimum Dst (ΔDstmin) and the absolute value of difference in minimum time (ΔtDst) between observed Dst and predicted one.In order to compare the prediction effects and the generalizability of the three models to magnetic storm events, we combined 70 intense magnetic storm events and 10 super large magnetic storm events into one group. It is shown that DC-GPR model exhibits the better forecasting performance than by DC-SVM model and DC-NN model in magnetic storm. The CC, the RMS errors, the ΔDstmin , and the ΔtDst of GPR are 0.65, 35.45 nT, 16.12 nT and 1.16 h, respectively.

Delayed response of low latitudes TEC during thirty-six geomagnetic storms from 2014 to 2017

Ionospheric response to the onset of geomagnetic storms is an important aspect for developing models towards better understanding and prediction of ionospheric parameters, particularly over the equatorial and low latitude sectors that are associated with several complexities. Our paper discusses the time response of the ionosphere (Δtiono), where Δtiono is the time elapsed from the onset of sudden storm commencement (SSC) of a magnetic storm to the absolute maximum value of DVTEC (TEC: total electron content). Over the period 2014 to 2017, thirty-six storms are reviewed, and their Δtiono are analyzed along with the magnetic and solar parameters. We defined a threshold value of TEC to be 8 TECU. Three storms are studied in detail as a reference for the entire range of storms (March 2015, June 2015, and September 2015). The stations used are Kourou (KOUR; 5.25°N/52.80°W) in the American longitude sector, Addis Ababa (AAE; 9.03N°/38.76°E) in the African longitude, Port Blair (PBRI; 11.63°N/92.71°E) and Patumwan (CUSV; 13.73°N/100.53°E) in the Asian longitude sector. In the Asian and American sectors, for all storms combined, there is no significant correlation (0.44 for the Asian sector and 0.22 for the American sector) between the delay (SSC time/time of maximum DVTEC) and the minimum of the Dst as found by previous studies. Instead, we considered geomagnetic storms satisfying the criteria: a) SSC occurs on the day side, and b) the origin of the magnetic storm on the solar disk must be far from the limb or does not belong to the far side, to obtain a much better correlation. The highest correlation value is observed at Thailand (0.84), followed by India (0.79) and South America (0.759), and the minimum value at Africa (0.641). The average response time in our study was found to be about 27.2 h. We observed positive and negative ionospheric storms, five negative storms in South America followed by two in Asia and a single negative storm in Africa from which it is realized that the most negative storms are in the time range of 9–15 LT. Nevertheless, there is hardly any relationship between the strength of DVTEC amplitude and the intensity of magnetic storms irrespective of longitude sectors.

Solar events and solar wind conditions associated with intense geomagnetic storms

Intense magnetic storms pose a systemic threat to the electric power grid. In this study we examined the solar/interplanetary causes of such storms, their peak theoretical and observed intensities, and their occurrence frequency. Using coronal mass ejection (CME) and solar wind data, we selected the 18 intense magnetic storms from 1996 to 2021 with disturbance storm time (Dst) index of less than – 200 nT and analyzed solar events and solar wind conditions associated with them. Approximately 83% of the CMEs associated with the storms were full halo type and more than 83% of the flares associated with the storms were located within 30 degrees in longitude of solar central meridian. The integrated dawn-to-dusk electric field in the solar wind (Ey) showed a good correlation with |min. Dst| of the storms and the peak Ey (Eyp) and the peak southward interplanetary magnetic field showed next good correlations with |min. Dst|. We obtained the Eyp of 236 mV/m for |min. Dst| of 2500 nT of the expected upper limit of Earth’s magnetosphere using the empirical equations from the correlations between |min. Dst| and solar wind parameters and showed that this value of Ey is possible according to the past observations. The Eyp of 54 mV/m for the 13 March 1989 storm and that of 165/79 mV/m for the Carrington storm (|min. Dst|= 1760/850 nT) were also obtained. The analysis using the complimentary cumulative distribution function suggested the probabilities of Ey of 100, 200, 250, and 340 mV/m over the next 100 years to be 0.563, 0.110, 0.060 and 0.026, respectively.Graphical

Investigation of Dynamical Complexity in Swarm-Derived Geomagnetic Activity Indices Using Information Theory

In 2023, the ESA’s Swarm constellation mission celebrates 10 years in orbit, offering one of the best ever surveys of the topside ionosphere. Among its achievements, it has been recently demonstrated that Swarm data can be used to derive space-based geomagnetic activity indices, similar to the standard ground-based geomagnetic indices monitoring magnetic storm and magnetospheric substorm activity. Recently, many novel concepts originating in time series analysis based on information theory have been developed, partly motivated by specific research questions linked to various domains of geosciences, including space physics. Here, we apply information theory approaches (i.e., Hurst exponent and a variety of entropy measures) to analyze the Swarm-derived magnetic indices from 2015, a year that included three out of the four most intense magnetic storm events of the previous solar cycle, including the strongest storm of solar cycle 24. We show the applicability of information theory to study the dynamical complexity of the upper atmosphere, through highlighting the temporal transition from the quiet-time to the storm-time magnetosphere, which may prove significant for space weather studies. Our results suggest that the spaceborne indices have the capacity to capture the same dynamics and behaviors, with regards to their informational content, as traditionally used ground-based ones.

Investigation of the Geomagnetically Induced Current Index Levels in the Mediterranean Region During the Strongest Magnetic Storms of Solar Cycle 24

AbstractGeomagnetically induced currents (GICs) constitute an integral part of space weather research and are a subject of ever‐growing attention for countries located in the low and middle latitudes. A series of recent studies highlights the importance of considering GIC risks for the Mediterranean region. Here, we exploit data from the HellENIc GeoMagnetic Array, which is deployed in Greece, complemented by magnetic observatories in the Mediterranean region (Italy, France, Spain, Algeria, and Turkey), to calculate values of the GIC index, that is, a proxy of the geoelectric field calculated entirely from geomagnetic field variations. We perform our analysis for the most intense magnetic storms (Dst < −150 nT) of solar cycle 24. Our results show that GIC index increases are well correlated with storm sudden commencements. However, the GIC indices do not exceed “low” activity levels despite the increases in their values, at all magnetic stations/observatories under study during the selected storm events.

Analysis of the Occurrence of the First Most Intense Geomagnetic Storm (G4) to Hit the Earth in Solar Cycle 25; A Multiple-Step Geomagnetic Storm

A study of the occurrence of the first intense Geomagnetic storm (G4) to hit the Earth since the start of the Solar Cycle 25 is carried out. This study analyzed the Geomagnetic Storm that occurred between the 28th of October and the 7th of November 2021. The values of the Disturbance storm time (Dst) index of the storm reach -115 nT (G4) which occurred on the 4th of November at 1300UT. The storm is the first intense magnetic storm that occurred in the solar cycle 25. It is also a multiple-step storm with moderate two-step storm occurrence which occurred on the 5th and 6th of November at 1500UT and 0600UT respectively towards the recovery phase after the intense storm. The interplanetary magnetic field (IMF) Bz (nT) during these storm events decreases. Our analysis shows that the rise in solar wind speed, temperature and the enhancement of pressure plays a significant role in the occurrence of the first intense Geomagnetic storm of Solar Cycle 25.

Проявления геомагнитной активности (солнечные вспышки и магнитные бури) в изменении электротеллурических потенциалов по данным измерений на Южно-Сахалинском геофизическом полигоне

The results of the analysis of changes in electrotelluric potentials (ETP) during the observation of intense solar flare events and intense magnetic storms on Sakhalin are presented. The data were studied in the period from July 20 to October 12, 2023. The absence of characteristic changes in the ETP (integral amplification or attenuation of noise in the low-frequency region) depending on the presence or absence of a solar flare event is shown. At the same time, in some cases, the strongest flashes were found to coincide with the appearance of signals of the GUV type (Geyser type ULF Variation). For almost three months of observations, five cases of quasi-periodic GUV series have been identified, four of which coincide completely or partially with the times of solar flares and magnetic storms. It should be noted that earlier in the literature, the appearance of these signals was not correlated with any physical process. At the same time, the identification of such patterns is an integral part of extensive work on identifying predictive signs of earthquake preparation in the ETP.

Ionospheric Oscillations With a Quasi‐Period of ∼6 hr During Intense Magnetic Storms

AbstractWe study the variations of the topside ionospheric ion density measured by Defense Meteorological Satellite Program satellites during the intense magnetic storm on 7–10 November 2004. It is found for the first time that quasi‐periodic enhancements in the ion density with a period of ∼6 hr occur nearly simultaneously at 0630, 0830, and 0930 local time in the dawn sector during the storm main phase with southward interplanetary magnetic field (IMF). The quasi‐periodic density enhancements extend from the southern subauroral latitudes to the northern subauroral latitudes. In the dusk sector, the topside ion density during the storm main phase is increased at middle latitudes for ∼12 hr but shows decrease or relatively small increase over the magnetic equator, indicating that penetration electric fields dominate the ion density redistribution. Similar quasi‐periodic enhancements in the topside ion density are also observed in the dawn sector during other intense magnetic storms. The solar wind and IMF do not have quasi‐periodic variations in this storm case. Periodic processes in geospace, such as periodic substorms in the magnetosphere, waves and tides in the atmosphere, and traveling ionospheric disturbances, cannot explain the observed periodic enhancements of the ionospheric ion density. We suggest that the magnetosphere‐ionospheric‐thermospheric system may have an intrinsic period of ∼6 hr and that oscillations of the magnetosphere‐ionospheric‐thermospheric system with this period can be excited during intense magnetic storms, although the mechanisms for the generation of the long‐periodic oscillations are not understood.

A Statistical Analysis of Multiple Characteristics of Subauroral Polarization Streams During 15 Intense Magnetic Storms

AbstractSubauroral polarization streams (SAPS) are persistent westward plasma drift equatorward of the auroral oval in the dusk‐midnight sector during geomagnetic storms. Past research has studied the dependence of SAPS latitude on Dst and the seasonal and diurnal variations of SAPS. However, other characterizations of the SAPS structure are largely unexplored. In this study, a new method is developed for SAPS determination which does not require manual analysis. The method is then applied to 15 intense magnetic storms between 2000 and 2015 using data measured by the Defense Meteorological Satellite Program satellites, and the SAPS are characterized at every hour of the storm by (a) magnetic latitude, (b) peak velocity, (c) average velocity, and (d) the integration of velocity over the width of the SAPS, denoted Area. The following statistical analysis of these results demonstrates that all four characteristics have strong correlations with Dst and weak‐to‐moderate correlations with the interplanetary magnetic field. SAPS local time dependence and main phase dependence are derived as well. Finally, a qualitative observation is discussed wherein Area varies with IMF Bz before Dst even begins to show evidence of a magnetic storm. These relationships provide new insight into SAPS evolution and its dependence on solar wind and magnetic activity.

Continuous Enhancements of Electron Temperature in the Subauroral Ionosphere Over Eight Days During the 2015 St. Patrick’s Day Storm

AbstractWe have used measurements of the Defense Meteorological Satellite Program (DMSP) satellites to study variations of electron temperature in the subauroral ionosphere during the magnetic storm on 17–25 March 2015. This magnetic storm had a long recovery phase of 7 days, and the ionospheric behavior over the entire storm time was seldom investigated. In this study, we find that the electron temperature at subauroral latitudes was continuously enhanced for 8 days, from the storm onset to the end of the recovery phase. The maximum electron temperature during the storm times was 1000–4000 K higher than the maximum electron temperature during quiet times. This long‐lasting enhancement of subauroral electron temperature was attributed to energy transfer among the solar wind, magnetosphere, ring current, plasmasphere, and ionosphere driven by high‐speed solar wind streams and fluctuating interplanetary magnetic field during the entire 8‐day period of the storm. The electron temperature enhancements were quite symmetric in the post‐midnight sector but became strongly asymmetric near dawn between the southern and northern hemispheres. The asymmetric enhancements of electron temperature near dawn may be related to the magnetic declination and the daytime midlatitude trough in the southern hemisphere. Large daily variations of maximum electron temperature in the post‐midnight sector were observed and may be related to the offset between geomagnetic and geographic latitudes. These DMSP observations provide new insight on ionospheric response to intense magnetic storms.

Analyzing Dominant 13.5 and 27 day Periods of Solar Terrestrial Interaction: A New Insight into Solar Cycle Activities

Our analysis presents an explanation of the Sun–Earth coupling mechanism during declining phase of a solar cycle, and how the dominant 13.5 and 27 day periods play roles in the coupling mechanism which led to intense terrestrial magnetic storms during this declining phase compared to the rising phase of a solar cycle. Moreover, it is observed that while the 27 day period gets strongly modulated in the rising phase, the 13.5 day period modulation is more prominent during the declining phase. It is suggested that out of the 27 and 13.5 day periods of Sun–Earth interaction, the preferred period of modulation happens to be the one which is more dominant for the less random or quieter system participating in the coupling. It is reported for the first time that the 13.5 day period is more prominent in the Sun–Earth interaction during the declining phase of a solar cycle, as it is the most dominant period of Earth’s magnetic system, which happens to be more persistent as a dynamical system and hence quieter or more receptive than the Sun.

Sensitivity of Ground Magnetometer Array Elements for GIC Applications I: Resolving Spatial Scales With the BEAR and CARISMA Arrays

AbstractGeomagnetically induced currents (GICs) can be driven in terrestrial electrical power grids as a result of the induced electric fields arising from geomagnetic disturbances (GMD) resulting from the dynamics of the coupled magnetosphere‐ionosphere‐ground system. However, a key issue is to assess an optimum spacing for the magnetometer stations in order to provide appropriate monitoring of the GIC‐related GMD. Here we assess the vector correlation lengths of GMD and related amplitude occurrence distribution of the variations of horizontal magnetic field dBH/dt. Specifically, we study the GMD response to two storm‐time substorms using data from two magnetometer arrays, the Baltic Electromagnetic Array Research Project in Scandinavia and the Canadian Array for Realtime Investigations of Magnetic Activity array in North America, so as to determine the appropriate magnetometer spacing in latitude and longitude, for monitoring and assessing GIC risk. We find that although magnetic disturbances are well‐correlated up to distances of several hundred kilometers at mid‐latitudes, the vector correlation length rapidly drops off for station separations of less than 100 km within the auroral oval. In general geomagnetic fluctuations are stronger and more localized in the auroral zone. Since the auroral oval is pushed equatorward during intense magnetic storms, we highlight that networks using a station separation of ∼200 km should provide an excellent basis for monitoring both small and large scale geomagnetic disturbances. A monitoring network with this station spacing is recommended as being appropriate for assessing the role of GMD in driving GICs in the electric power grid.

Prestorm ionospheric disturbances: Precursors or Q-disturbances?

• The foF2 deviations from quiet conditions during prestorm days are, most probably, precursors of magnetic storms. • They depend on the parameters of the following magnetic storm. • The deviations are not Q-dependences. The problem of disturbances in the parameters of the F 2 layer and upper ionosphere during the days preceding onset of a magnetic storm is known already for many decades. Many publications have been dedicated to analysis of these disturbances both in the critical frequency and height of the F2 layer and in the total electron content. The majority of researchers have drawn a conclusion that such disturbances are observed prior almost to every storm, positive events (an excess of the values in the prestorm period over the corresponding values on a geomagnetically quiet day) prevailing. Moreover, some authors claimed that the aforementioned disturbances could be considered as precursors of the coming magnetic storm. A concept of the so-called Q-disturbances, according to which the disturbances during the prestorm days are not related to the coming storm but are a result of several processes (meteorological influence on the ionosphere, changes in the magnetosphere-ionosphere interaction) which sometimes cause deviations of ionospheric parameters is an alternative to the precursor concept. Arguments are presented in favor of the precursor concept. These arguments are, first of all, based on the existence of a dependence of parameters of the prestorm disturbances on parameters of the coming storm. The dependencies on the magnetic storm intensity, local time of the storm onset SO, and time from the disturbance to SO present the strongest arguments against the Q-disturbance concept. Numerous examples of these dependencies are presented. The recent publications with new experimental data on the foF 2 and TEC behavior in the prestorm period are discussed. Arguments in favor of the prestorm concept presented in these publications are briefly considered.

Middle and low latitudes hemispheric asymmetries in ∑O/N2 and TEC during intense magnetic storms of solar cycle 24

We have investigated the global hemispheric differences in thermospheric ∑O/N 2 and its impact on the ionospheric total electron content (TEC) at mid- and low-latitudes. Four intense storms of solar cycle 24 (SC-24) have been considered, three of them occurred in Spring equinox and one in Summer solstice season. It is found that the mid-latitudes region has exhibited a large decrease in ∑O/N 2 during all the phases of the storms under consideration, which corresponds well to the observed negative storm effects. This decrease is directly related with the storm intensity. The maximum reduction in the ∑O/N 2 is observed for the St. Patrick day storm of 2015 (which was the most intense geomagnetic storm of SC-24), whereas the respective minimum decrease is found for the storm of April 2012. Strong hemispheric asymmetries, in ∑O/N 2 variation, have been observed at the mid-latitudes sector, and can be associated with the asymmetric energy input as indicated by polar cap (PC) indices. The high speed solar winds streams (HSSWs) during the recovery phases of March 2013 and 2015 storms have caused a significant reduction in ∑O/N 2 at mid-latitudes, which could not be reproduced by the coupled thermosphere-ionosphere-plasmasphere electrodynamics (CTIPe) model. On the other hand the low-latitudes region depicts an enhancement in ∑O/N 2 during all the storms except for the early recovery phases. The positive storm effect at low-latitudes agrees well with this ∑O/N 2 increase, thus indicating that the composition change is one of the major drivers of TEC enhancement at low-latitudes. The CTIPe model showed discrepancies in reproducing the satellite data for all the considered storms, especially during the recovery phases. Furthermore, the model is failed to replicate the hemispheric asymmetries at low and mid-latitudes during the main and early recovery phases.

Energy Inflow into the Magnetosphere and Its Distribution During Magnetic Storm

The energy inflow from the solar wind into the magnetosphere and its dissipation in the circular current and auroral ionosphere during maximums of magnetic storm intensity are considered. All magnetic storms with Dst intensities from –18 nT to –422 nT for the period from 1996 to 2014 were divided into groups. For each group, the mean contribution of energy from the solar wind to the magnetosphere and subsequent characteristics of the energy dissipation in the auroral ionosphere and circular current were determined by the superposed epoch analysis method. The nonlinearity of the dependence of the intensity of magnetic storms on the energy coming from the solar wind into the magnetosphere was revealed. Anomalous behavior of magnetic storms with intensity |Dst| > 200 nT was detected. A discussion of the results is given.

Low‐Latitude Zonal Ion Drifts and Their Relationship With Subauroral Polarization Streams and Auroral Return Flows During Intense Magnetic Storms

AbstractWe analyze horizontal plasma drifts measured by the Defense Meteorological Satellite Program satellites during two intense magnetic storms. It is found, for the first time, that westward plasma flows associated with subauroral polarization streams (SAPS) in the dusk‐evening sector penetrate continuously to equatorial latitudes. The westward ion drifts between subauroral and equatorial latitudes occur nearly simultaneously. The latitudinal profile of the westward ion drifts at low latitudes (approximately within ±30° magnetic latitude [MLat]) is relatively flat, and the westward ion drifts at the magnetic equator reach 200–300 m s−1. In the dawn‐morning sector, eastward ion drifts at subauroral latitudes are also SAPS. The storm‐time dawnside auroral boundary moves to ∼±55° MLat, and the dawnside SAPS penetrate to ∼±20° MLat at 0930 local time. A dawnside SAPS flow channel appears to exist, although it is not as well defined as the duskside SAPS flow channel. Thermospheric wind data measured by the Challenging Minisatellite Payload satellite are analyzed, and zonal disturbance winds are derived. Disturbance winds can reach equatorial latitudes rapidly near midnight but are limited to ±40° geographic latitude or higher near noon. The effects of disturbance winds on the zonal ion drifts at middle and low latitudes are discussed. It is suggested that both the westward ion drifts at middle and low latitudes in the dusk‐evening sector and the eastward ion drifts at middle and lower latitudes in the dawn‐morning sector are caused primarily by penetration of the SAPS and auroral electric fields.