Pedersen Currents Research Articles

Modeling the Post‐Midnight Equatorial Plasma Bubbles With SAMI3/SD‐WACCM‐X: Large‐Scale Wave Structure

AbstractThis study investigates the relative significance of gravity wave and gravity dynamo effects in large‐scale wave structure (LSWS) development using the coupled Sami3 is Also a Model of the Ionosphere (SAMI3) and Specified Dynamics Whole Atmosphere Community Climate Model with thermosphere‐ionosphere eXtension (SD‐WACCM‐X). Simulations show significant vertical E × B drift perturbations associated with gravity waves in the F region after ∼1700 LT, leading to LSWS near midnight. Notably, LSWS can occur independently of gravity‐driven dynamo current, emphasizing the significance of the gravity wave wind dynamo mechanism. However, LSWS exhibits more pronounced vertical E × B drift perturbations, indicating the involvement of background wind fields. Both gravity wave and background wind dynamo effects cause LSWS to grow vertically by ∼20 km and extend to ±10° in latitude. Gravity‐driven Pedersen current, therefore, plays a role in amplifying the upwelling growth and equatorial plasma bubble development. Furthermore, simulations demonstrate the emergence of predawn ionospheric irregularities in the bottomside F layer, even without gravity‐driven currents, attributed to concentric gravity waves over the magnetic equator. A comparison between FORMOSAT‐7/COSMIC2 and SAMI3 ion density is also conducted. These findings emphasize the significant influence of gravity waves and background wind fields on the formation of LSWS and irregularities.

On the Formation of Auroral Spirals

AbstractThe paper contains a detailed analysis of the formation of an auroral spiral based on hitherto not published observations by the all‐sky camera in Kilpisjärvi, Northern Finland. We conclude that spirals appearing during a substorm form by a modification of the interface between tail and magnetosphere, the location of the generator current of the westward electrojet. Driven by the arriving flow bursts, this current is subject to ruptures by the appearance of a sequence of hook‐like structures. These structures can move eastward with speeds up to 3 km/s. The propagation is attributed to a constructive magnetic fracture process driven from behind by the power of the arriving flow bursts. Poleward bending and extension of a hook‐like structure, followed by a turning to the west and then equatorward, is the first step in spiral formation. It becomes the primary spiral arm, if a poleward arm grows out of weaker auroral structures, poleward and eastward of it. We suggest that the upward field‐aligned currents related to the bright spiral arms are largely balanced by adjacent downward currents. The electric fields associated with the connecting Pedersen currents are consistent with the counter‐clockwise motion. An important additional ingredient in the observed configuration is an eastward directed flow field, which is the generator of an additional upward current and possibly crucial for the spiral formation. Electric field data from literature throw confusing light on the propagation of a spiral, whether like a vessel in the ocean or by incorporating the magnetic flux ahead of it.

Asymmetric Ionospheric Jets in Jupiter's Aurora

AbstractSimultaneous infrared observations of and H2 emissions from Jupiter's northern aurora using the Near Infrared Spectrograph at Keck Observatory were used to measure the ionospheric and thermospheric wind velocities. ions supercorotate near the dawn auroral oval and subcorotate across the dusk sector and in the dawn polar region relative to the planetary rotation rate, broadly in agreement with past observations and models. An anticyclonic vortex is discovered in H2 flows, closely matching the mean magnetospheric subcorotation when the observed magnetospheric flows are averaged azimuthally. In comparing ion and neutral winds, we measure the line‐of‐sight effective ion drift in the neutral reference frame for the first time, revealing two blue‐shifted sunward flows of ∼2 km/s. Observed and H2 emissions overlap with predictions of the Pedersen conductivity layer, suggesting two different regions of the ionosphere: (a) a deep layer, where neutral forces dominate the thermosphere and symmetric breakdown‐in‐corotation currents can close, and (b) a higher layer, where the observed effective ion drift allows dawn‐to‐dusk Pedersen currents within the upper atmosphere, in turn closing asymmetric currents within the magnetosphere. This ionospheric structure aligns well with recent Juno observations of Jupiter's aurora. The detected thermospheric vortex implies the driving of neutral flows by the momentum from the magnetosphere within the thermosphere and deeper in the atmosphere to potentially 20 mbar. Jovian neutral thermosphere might bridge the gap between current observations and modelings and perhaps be significant to the dynamics of aurora on Earth and other outer planets.

Parallel electric fields produced by ionospheric injection

Abstract. It is well known that there exists a thin layer in the lower boundary of the ionosphere between altitudes of 80 and 140 km in which collisional ions and collisionless electrons mix. Local breakdown of charge neutrality may be initiated in this layer by electric fields from the magnetosphere as well as by electric fields generated there by the local neutral winds. The breakdown may be momentarily canceled by Pedersen currents, but complete neutralization is prevented because some ionospheric plasmas are released as outflows by parallel electric fields. Those parallel electric fields are produced by inherent plasma processes in the polar ionosphere and act as auroral drivers. A new scenario creating parallel potential gradients is proposed.

The evolving paradigm of the subauroral geospace

An assessment of the status quo of fast subauroral flows—subauroral ion drifts (SAID) and subauroral polarization streams (SAPS), is presented. For a few decades, their development has been interpreted in terms of the voltage and current magnetospheric generators based largely on the drift motion of test particles. Recent multispacecraft observations revealed serious flaws in the generator paradigm and called for a new generation mechanism of fast-time subauroral flows and ring current (RC) injections. A novel model includes them in the overarching problem of the penetration of magnetotail plasma flow bursts (MPFs) into the plasmasphere and the substorm current wedge (SCW) development. SAID are created near the plasmapause, where inbound MPFs are short-circuited by the cold plasma. This stops the MPF’s electrons and forms the “dispersionless” plasma sheet (PS) boundary. The SAID electric field—the inherent part of the short-circuiting loop—stops the inward-moving MPF’s ions. In turn, SAPS are an integral part of the two-loop SCW system, or SCW2L, where the downward (R2) current emerges in response to the upward (R1) current in the SCW’s “head.” The meridional Pedersen current, which connects the R1 and R2 currents, leads to SAPS that ultimately drive the fast-time RC injections on the duskside.

Influences of various space current systems on the geomagnetic field in near-Earth space

Ground and space-based observations of the geomagnetic field are usually a superposition of different sources from the Earth’s core, lithosphere, ocean, ionosphere, and magnetosphere, and also from field-aligned currents coupling the ionosphere and magnetosphere—the meridional currents that connect the two hemispheres and the induced currents due to the variations of fields over time. The fluctuation of magnetic fields generated by these highly dynamic space currents greatly limits the accuracy of the geomagnetic models. In order to better accomplish the scientific objectives of Macau Science Satellite-1 (MSS-1), and to improve existing geomagnetic field models, we present here for the first time a self-consistent coupling of solar wind, magnetosphere, and ionosphere, which represents the most developed numerical simulation method for space physics research so far, making it possible to quantify the contribution of different current systems to the total observed magnetic field (<italic><bold>B</bold></italic>). The results show that numerical simulation can capture main magnetic disturbance characteristics with significant precision. Partial ring current is a major contributor to the latitudinal magnetic perturbation near the equator. Magnetopause and magnetotail currents affect the radial magnetic perturbation around the mid-latitudes. Field-aligned and Pedersen currents produce significant longitudinal and latitudinal magnetic perturbations at high latitudes.

Instantaneous Achievement of the Hall and Pedersen–Cowling Current Circuits in Northern and Southern Hemispheres During the Geomagnetic Sudden Commencement on 12 May 2021

The present article aims at a consistent understanding of observation, theoretical model, and simulation with the geomagnetic sudden commencement (SC) observed in the morning and afternoon at high and middle latitudes in the northern and southern hemispheres and at the noontime equator on 12 May 2021. The SC in Bx- and By-components of the geomagnetic field, SCx,y, was composed of the positive/negative preliminary (PI) and main impulses (MI) as SCx (+ -) and SCy (- +) in the morning and SCx (- +) and SCy (+ -) in the afternoon at middle latitudes in the northern hemisphere. SCx in the southern hemisphere is in the same polarity as those in the northern hemisphere, except for SCx (+ +) in the morning. SCy in the southern hemisphere has reverse polarity to those in the northern hemisphere. The PIx in the northern hemisphere matches the well-established two-cell Hall current vortices with anti-clockwise and clockwise directions in the morning and afternoon, respectively, and the MIx matches reverse Hall current vortices. The PIx and MIx in the southern hemisphere meet the Hall currents that are mirror images of those in the northern hemisphere with respect to the equator except for the positive MI in the morning. The PIy in the northern hemisphere is shown to meet the northward and southward Pedersen currents in the morning and afternoon, respectively, and the MIy meets reverse Pedersen currents. The PIy and MIy in the southern hemisphere are found to meet the Pedersen currents that are mirror images of those in the northern hemisphere. At the equator, typical SCx (- +) is observed, meeting the Cowling currents that should be supplied by the Pedersen currents responsible for the observed midlatitude SCy in the northern and southern hemispheres. The electric fields of the PI and MI observed by the HF Doppler sounders at the middle latitudes in the northern hemisphere are westward and eastward, respectively, in both the morning and afternoon, meeting the conventional dusk-to-dawn PI and dawn-to-dusk MI electric fields. The onset of the PI is found to be simultaneous with the resolution of a few seconds from high latitude to the equator in both the northern and southern hemispheres, indicating instantaneous achievement of the Pedersen–Cowling currents from high latitude to the equator. The instantaneous achievement of the energy-consuming Pedersen–Cowling currents is explained by the TM0/TEM mode wave in the Earth-ionosphere waveguide/transmission line rather than the compressional waves in the magnetosphere and F-region ionosphere. REPPU (REProduce Plasma Universe) global simulation model equipped with a potential solver at the inner boundary of the model magnetosphere reproduces the PI and MI electric fields at middle latitudes and SCx (- +) at the dayside equator. The simulation results are found to be consistent with most features of observations, such as the time scale of PI and MI, direction of the midlatitude electric field and generation of the Cowling currents. The simulation proves that the electric fields and FACs are generated in the outer magnetosphere, transmitted to the polar ionosphere and then to the equator in the Pedersen–Cowling current circuit.

Middle Latitude Geomagnetic Disturbances Caused by Hall and Pedersen Current Circuits Driven by Prompt Penetration Electric Fields

The prompt penetration electric field (PPEF) drives the DP2 currents composed of the two-cell Hall current vortices surrounding the Region-1 field-aligned currents (R1FACs), and the zonal equatorial electrojet (EEJ, Cowling current) at the dayside equator, which is connected to the R1FACs by the Pedersen currents at middle latitudes. The midlatitude H- and D-components of the disturbance magnetic field are caused by the DP2 currents, as well as by the magnetospheric currents, such as magnetopause currents, FACs, ring currents, and so on. If the DP2 current is the major source for the midlatitude geomagnetic disturbances, H and D are supposed to be caused by the Hall and Pedersen currents, respectively. The H-D correlation would be negative in both morning and afternoon sectors, and H/D-EEJ correlation would be negative/positive in the morning and positive/negative in the afternoon. We picked out 39 DP2 events in the morning and 34 events in the afternoon from magnetometer data at Paratunka, Russia (PTK, 45.58° N geomagnetic latitude (GML)), which are characterized by negative H–D correlation with correlation coefficient (cc) &lt; −0.8. We show that the midlatitude H/D is highly correlated with EEJ at Yap, Micronesia (0.38° S GML) in the same local time zone, meeting the Pedersen–Cowling current circuit between midlatitude and equator in the DP2 current system. Using the global simulation, we confirmed that the ionospheric currents with north–south direction at midlatitude is the Pedersen currents developing concurrently with the Cowling current. We suggest that the negative H-D correlation provides a clue to detect the PPEF when magnetometers are available at middle latitudes.

Effects of Solar Illumination and Substorms on Auroral Electrojets Based on CHAMP Observations

AbstractWe investigate the effects of solar illumination and the substorm process on the auroral electrojets using CHAMP high‐resolution magnetic field data obtained over a period of 10 years. The eastward electrojet was found to be proportional to the ionospheric conductance induced by solar irradiation over the whole day. More notably, a stronger westward current was detected in times of lower fluxtube‐integrated conductance in both hemispheres. The relative spatial distribution and evolution of the westward electrojet and field‐aligned current (FAC) during the substorm periods were also investigated. The position of the westward current coincided with that of the upward FAC in 2000–2200 magnetic local time (MLT), in keeping with the structure of a westward traveling surge. Furthermore, the upward FAC in the local time sector of the poleward of the westward electrojet was supplied mostly by the remote closure current. The downward FACs in the poleward and upward FACs in the equatorward of the westward electrojet existed in the MLT sectors after 2200 h. Finally, the ratio of the peak intensity of the westward electrojet to that of the meridional Pedersen current, in the 2000–2200 MLT sector increased by about 250%, and the value in the 2200–0200 MLT increased by about 10%–20%. These results provide observational evidence of the increased efficiency of the Cowling channel in the night‐time during substorm periods and contribute to our understanding of the formation mechanism of the auroral electrojet.

Conductance Model for Extreme Events: Impact of Auroral Conductance on Space Weather Forecasts

AbstractIonospheric conductance is a crucial factor in regulating the closure of magnetospheric field‐aligned currents through the ionosphere as Hall and Pedersen currents. Despite its importance in predictive investigations of the magnetosphere‐ionosphere coupling, the estimation of ionospheric conductance in the auroral region is precarious in most global first‐principles‐based models. This impreciseness in estimating the auroral conductance impedes both our understanding and predictive capabilities of the magnetosphere‐ionosphere system during extreme space weather events. In this article, we address this concern, with the development of an advanced Conductance Model for Extreme Events (CMEE) that estimates the auroral conductance from field‐aligned current values. CMEE has been developed using nonlinear regression over a year's worth of 1‐min resolution output from assimilative maps, specifically including times of extreme driving of the solar wind‐magnetosphere‐ionosphere system. The model also includes provisions to enhance the conductance in the aurora using additional adjustments to refine the auroral oval. CMEE has been incorporated within the Ridley Ionosphere Model (RIM) of the Space Weather Modeling Framework (SWMF) for usage in space weather simulations. This paper compares performance of CMEE against the existing conductance model in RIM, through a validation process for six space weather events. The performance analysis indicates overall improvement in the ionospheric feedback to ground‐based space weather forecasts. Specifically, the model is able to improve the prediction of ionospheric currents, which impact the simulated dB/dt and ΔB, resulting in substantial improvements in dB/dt predictive skill.

Reproduction of Ground Magnetic Variations During the SC and the Substorm From the Global Simulation and Biot‐Savart's Law

AbstractIn this paper, currents causing the sudden commencement (SC), the AU/AL indices, and the positive bay during the substorm are identified from the global simulation and Biot‐Savart's law. Candidate currents assumed as causes of these ground magnetic variations are the ionospheric Hall current, the ionospheric Pedersen current, the field‐aligned current (FAC), and other magnetospheric currents than the FAC. In general, FAC effect and Pedersen current effect cancel out each other under the restriction of Fukushima's theorem. During the SC, for instance, the midlatitude preliminary positive impulse appears in the prenoon and midlatitude preliminary reverse impulse (PRI) appears in the postnoon, due to the remaining effect of the Hall current. However, violations of the Fukushima's theorem are also common such as in the cases of the equatorial PRI, the auroral electrojet, and the positive bay. The equatorial PRI caused by the Pedersen current appears both in the prenoon and postnoon regions. In the auroral region, the Hall current effect prevails over other currents so much and determines the AU/AL indices only from it regardless other currents. The midlatitude positive bay on the nightside is generated by the effect of the FAC. From these diverse reproduction of ground magnetic variations, a further verification is given for the global simulation in reproductions of the magnetosphere‐ionosphere coupling process.

Identification of potential precursors for the occurrence of Large-Scale Traveling Ionospheric Disturbances in a case study during September 2017

Traveling Ionospheric Disturbances (TIDs) reflect changes in the ionospheric electron density which are caused by atmospheric gravity waves. These changes in the electron density impact the functionality of different applications such as precise navigation and high-frequency geolocation. The Horizon 2020 project TechTIDE establishes a warning system for the occurrence of TIDs with the motivation to mitigate their impact on communication and navigation applications. This requires the identification of appropriate indicators for the generation of TIDs and for this purpose we investigate potential precursors for the TID occurrence. This paper presents a case study of the double main phase geomagnetic storm, starting from the night of 7th September and lasting until the end of 8th September 2017. Detrended Total Electron Content (TEC) derived from Global Navigation Satellite System (GNSS) measurements from more than 880 ground stations in Europe was used to identify the occurrence of different types of large scale traveling ionospheric disturbances (LSTIDs) propagating over the European sector. In this case study, LSTIDs were observed more frequently and with higher amplitude during periods of enhanced auroral activity, as indicated by increased electrojet index (IE) from the International Monitor for Auroral Geomagnetic Effects (IMAGE). Our investigation suggests that Joule heating due to the dissipation of Pedersen currents is the main contributor to the excitation of the observed LSTIDs. We observe that the LSTIDs are excited predominantly after strong ionospheric perturbations at high-latitudes. Ionospheric parameters including TEC gradients, the Along Arc TEC Rate (AATR) index and the Rate Of change of TEC index (ROTI) have been analysed for their suitability to serve as a precursor for LSTID occurrence in mid-latitude Europe, aiming for near real-time indication and warning of LSTID activity. The results of the presented case study suggest that the AATR index and TEC gradients are promising candidates for near real-time indication and warning of the LSTIDs occurrence in mid-latitude Europe since they have a close relation to the source mechanisms of LSTIDs during periods of increased auroral activity.

Estimation of the contributions of conductance and electric field to the intensity of field-aligned currents in the night polar ionosphere during substorm expansion phase

Based on the output data of the magnetogram inversion technique, we analyze the dynamics of the Pedersen ionospheric currents and field-aligned currents (FACs) in the night mesoscale cells of the three main large-scale Iijima and Potemra Regions (R1, R2 and R0) during the expansion phase of the summer and winter substorms. FACs play a key role in the ionosphere-magnetosphere interaction. The continuity equation for the electric current density contains two types of possible feedback within the electric circuit parts that connect Pedersen currents and FACs in each cell. Pedersen ionospheric conductivity is dominant to Type 1, and the electric field dominates in Type 2 feedback. This paper studies both types of physical feedback in mesoscale cells of downward and upward FACs on the night side of the polar ionosphere from the data of two selected substorms of the summer and winter seasons in the northern hemisphere.

Relative role of the azimuthal Pedersen current component in the substorm global electric circuit

In the early, well-known model of the substorm current wedge (SCW) circuit, the azimuthal Pedersen current in the ionosphere closes a pair of the down- and up-ward field-aligned currents connecting the magnetosphere's generator with the ionosphere. In an alternative SCW model, the Pedersen currents flow through the ionosphere in the meridional direction. In this paper, we describe the dynamics of electric currents during the expansion phase of two selected, winter and summer substorms to compare the relative role of the meridional and azimuthal Pedersen currents at the expansion phase peak.

Coordinated observations of postmidnight irregularities and thermospheric neutral winds and temperatures at low latitudes

AbstractWe investigated a postmidnight field‐aligned irregularity (FAI) event observed with the Equatorial Atmosphere Radar at Kototabang (0.2°S, 100.3°E, dip latitude 10.4°S) in Indonesia on the night of 9 July 2010 using a comprehensive data set of both neutral and plasma parameters. We examined the rate of total electron content change index (ROTI) obtained from GPS receivers in Southeast Asia, airglow images detected by an all‐sky imager, and thermospheric neutral winds and temperatures obtained by a Fabry‐Perot interferometer at Kototabang. Altitudes of the F layer (h′F) observed by ionosondes at Kototabang, Chiang Mai, and Chumphon were also surveyed. We found that the postmidnight FAIs occurred within plasma bubbles and coincided with kilometer‐scale plasma density irregularities. We also observed an enhancement of the magnetically equatorward thermospheric neutral wind at the same time as the increase of h′F at low‐latitude stations, but h′F at a station near the magnetic equator remained invariant. Simultaneously, a magnetically equatorward gradient of thermospheric temperature was identified at Kototabang. The convergence of equatorward neutral winds from the Northern and Southern Hemispheres could be associated with a midnight temperature maximum occurring around the magnetic equator. Equatorward neutral winds can uplift the F layer at low latitudes and increase the growth rate of Rayleigh‐Taylor instabilities, causing more rapid extension of plasma bubbles. The equatorward winds in both hemispheres also intensify the eastward Pedersen current, so a large polarization electric field generated in the plasma bubble might play an important role in the generation of postmidnight FAIs.

A two‐dimensional global simulation study of inductive‐dynamic magnetosphere‐ionosphere coupling

AbstractWe present the numerical methods and results of a global two‐dimensional multifluid‐collisional‐Hall magnetohydrodynamic (MHD) simulation model of the ionosphere‐thermosphere system, an extension of our one‐dimensional three‐fluid MHD model. The model solves, self‐consistently, Maxwell's equations, continuity, momentum, and energy equations for multiple ion and neutral species incorporating photochemistry, collisions among the electron, ion and neutral species, and various heating sources in the energy equations. The inductive‐dynamic approach (solving self‐consistently Faraday's law and retaining inertia terms in the plasma momentum equations) used in the model retains all possible MHD waves, thus providing faithful physical explanation (not merely description) of the magnetosphere‐ionosphere/thermosphere (M‐IT) coupling. In the present study, we simulate the dawn‐dusk cross‐polar cap dynamic responses of the ionosphere to imposed magnetospheric convection. It is shown that the convection velocity at the top boundary launches velocity, magnetic, and electric perturbations propagating with the Alfvén speed toward the bottom of the ionosphere. Within the system, the waves experience reflection, penetration, and rereflection because of the inhomogeneity of the plasma conditions. The reflection of the Alfvén waves may cause overshoot (stronger than the imposed magnetospheric convection) of the plasma velocity in some regions. The simulation demonstrates dynamic propagation of the field‐aligned currents and ionospheric electric field carried by the Alfvén waves, as well as formation of closure horizontal currents (Pedersen currents in the E region), indicating that in the dynamic stage the M‐I coupling is via the Alfvén waves instead of field‐aligned currents or electric field mapping as described in convectional M‐I coupling models.

Localized field‐aligned currents in the polar cap associated with airglow patches

AbstractAirglow patches have been recently associated with channels of enhanced antisunward ionospheric flows propagating across the polar cap from the dayside to nightside auroral ovals. However, how these flows maintain their localized nature without diffusing away remains unsolved. We examine whether patches and collocated flows are associated with localized field‐aligned currents (FACs) in the polar cap by using coordinated observations of the Swarm spacecraft, a polar cap all‐sky imager, and Super Dual Auroral Radar Network (SuperDARN) radars. We commonly (66% of cases) identify substantial FAC enhancements around patches, particularly near the patches' leading edge and center, in contrast to what is seen in the otherwise quiet polar cap. These FACs have densities of 0.1–0.2 μA/m−2 and have a distribution of width peaking at ~75 km. They can be approximated as infinite current sheets that are orientated roughly parallel to patches. They usually exhibit a Region 1 sense, i.e., a downward FAC lying eastward of an upward FAC. With the addition of Resolute Bay Incoherent Scatter radar data, we find that the FACs can close through Pedersen currents in the ionosphere, consistent with the locally enhanced dawn‐dusk electric field across the patch. Our results suggest that ionospheric polar cap flow channels are imposed by structures in the magnetospheric lobe via FACs, and thus manifest mesoscale magnetosphere‐ionosphere coupling embedded in large‐scale convection.

Distribution of the field−aligned currents in the ionosphere: dawn–dusk asymmetry and its relation to the asymmetry between the two hemispheres

The dynamics of the system of field-aligned currents (FACs) and closing ionospheric Pedersen currents is considered with the use of original processing methods and the data from four substorms of different types. The total current system comprises of two parts. One is the well-known substorm current wedge (SCW) system, in which the zonal (westward ) current closes FACs in the R1 zone (region). The component 2 consists of two pairs of meridional currents flowing equatorward and poleward in the R1 region and creating regions R0 and R2 (according to the classification of Iijima and Potemra). It is shown that the total FAC of the disturbed magnetosphere–ionosphere system is dominated by the contribution of component 2, which contradicts the original version of the SCW model but is consistent with new data. The quantitative characteristics of the dawn–dusk asymmetry are determined for the FAC distribution in the ionosphere for each substorm. It is shown that the ratio of the average intensities of FACs in the regions R0 and R2 was IR0/IR2 ≥ 0.4, which contradicts the popular opinion that there are no FACs in the polar cap. In addition, a relatively rare event of the simultaneous start of the substorm explosive phase and the SSC caused by the dynamic impact of the solar wind when the polar cap expands (rather than compresses as usual) is considered.

North-south asymmetry of geomagnetic activity and solar wind electric field

Geomagnetic activity asymmetry in the Northern and Southern hemispheres is studied. It is shown that the higher is the level of magnetic activity the greater is the asymmetry. It is found that the asymmetry in the hemispheres manifests itself in the 06–18-hour component of magnetic activity diurnal variation, while the asymmetry in the 00–12-hourly component is completely absent. The cause of geomagnetic north-south asymmetry is supposed to be meridional Pedersen current between high and middle latitudes in the ionosphere. A qualitative model of formation of asymmetry connected with the solar wind electric field is proposed.

Transmission of the electric fields to the low latitude ionosphere in the magnetosphere-ionosphere current circuit

The solar wind energy is transmitted to low latitude ionosphere in a current circuit from a dynamo in the magnetosphere to the equatorial ionosphere via the polar ionosphere. During the substorm growth phase and storm main phase, the dawn-to-dusk convection electric field is intensified by the southward interplanetary magnetic field (IMF), driving the ionospheric DP2 currents composed of two-cell Hall current vortices in high latitudes and Pedersen currents amplified at the dayside equator (EEJ). The EEJ-Region-1 field-aligned current (R1 FAC) circuit is completed via the Pedersen currents in midlatitude. On the other hand, the shielding electric field and the Region-2 FACs develop in the inner magnetosphere, tending to cancel the convection electric field at the mid-equatorial latitudes. The shielding often causes overshielding when the convection electric field reduces substantially and the EEJ is overcome by the counter electrojet (CEJ), leading to that even the quasi-periodic DP2 fluctuations are contributed by the overshielding as being composed of the EEJ and CEJ. The overshielding develop significantly during substorms and storms, leading to that the mid and low latitude ionosphere is under strong influence of the overshielding as well as the convection electric fields. The electric fields on the day- and night sides are in opposite direction to each other, but the electric fields in the evening are anomalously enhanced in the same direction as in the day. The evening anomaly is a unique feature of the electric potential distribution in the global ionosphere. DP2-type electric field and currents develop during the transient/short-term geomagnetic disturbances like the geomagnetic sudden commencements (SC), which appear simultaneously at high latitude and equator within the temporal resolution of 10 s. Using the SC, we can confirm that the electric potential and currents are transmitted near-instantaneously to low latitude ionosphere on both day- and night sides, which is explained by means of the light speed propagation of the TM0 mode waves in the Earth-ionosphere waveguide.