Solar Wind Magnetosphere Ionosphere Coupling Research Articles

Earth’s magnetotail variability during supersubstorms (SSSs): A study on solar wind–magnetosphere–ionosphere coupling

Supersubstorm (SSS) events are associated with extremely intense westward auroral electrojet currents (the minimum SuperMAG AL or SML <-2500nT) resulting from the solar wind-magnetosphere coupling. We present, for the first time, variability of the Earth’s magnetotail and coupling from the solar wind to magnetotail, geosynchronous orbit and auroral ionosphere during the SSS events. Five intervals with multiple SSSs were identified when the Cluster spacecraft was well inside the inner magnetotail. The SSS events are found to be characterized by turbulent magnetotail plasma sheet and injection of energetic (∼100eV to ∼100keV) electrons and protons. Injection of energetic protons from the plasma sheet causes electromagnetic ion cyclotron waves that lead to pitch angle scattering of the outer radiation belt MeV electrons and loss to the atmosphere during the SSSs. The SSS events are found to be associated with interplanetary magnetic clouds characterized by slowly varying interplanetary magnetic fields. An overall increase in the turbulence is recorded from the solar wind to the inner magnetosphere-ionosphere system during the SSSs. From the wavelet and cross-wavelet analyses, the inner magnetosphere and ionosphere are found to respond quasi-periodically at ∼1.5-4hours, and sporadically at shorter timescales of ∼0.5-1.5hours.

Classification and Distribution of the Dayside Ion Upflows Associated with Auroral Particle Precipitation

Two important phenomena of the solar wind–magnetosphere–ionosphere coupling are auroral particle precipitation and the formation of ions flowing upward from the ionosphere. They have opposite transport directions of energy and substance. Based on the observations of particle precipitation and ion drift from the DMSP F13 satellite in January and July 2005, the ionospheric ion upflows in dayside auroral oval (0600–1800 MLT) can be divided into five types according to the velocity of ion upflows and the spectrum characteristics of auroral particle precipitation, and the distribution for different types of ion upflows is studied. The results show that the ion upflows mainly occur in the geomagnetic latitude (MLAT) range of 70–80°.The main magnetospheric source region of ion upflows (type A and D) caused by the accelerated electron (mainly the soft electron) corresponds to Low Latitude Boundary Layer (LLBL) and Cusp, and ion upflows of type B and C (related to the process of ambipolar diffusion caused by electron acceleration) mainly occur in LLBL and Boundary Plasma Sheet (BPS), while ion upflows of type E without electron acceleration mainly occur in the central plasma sheet (CPS).The dawn–dusk asymmetry is obvious in the winter season, with the ion upflows mainly occurring on the dawn/dusk side ionosphere. However, the ion upflows in summer mainly occur at the magnetic noon, with a symmetric distribution centered at the magnetic noon. The occurrence of ion upflow in winter is significantly higher than that in summer, and it is significantly enhanced during the period of moderate geomagnetic activity. The upward region expands to the lower latitude when the geomagnetic activity is enhanced. The effect of interplanetary magnetic field (IMF) components has also been studied in this paper. When IMF Bx is negative, the upflow occurrence increases in the region of 1500–1800 MLT and 0600–0900 MLT, with the MLAT range below 70°. The direction of IMF By may lead to the high-incidence area reverse at the prenoon or postnoon region. The occurrence of ion upflows with the MLAT range below 75° increases significantly when IMF is southward. Type A ion upflow has the highest velocity of ion upflows, followed by type E, and type D has the lowest. The average velocity of ion upflows in winter is significantly higher than that in summer.

Geoeffectiveness of Interplanetary Alfvén Waves. I. Magnetopause Magnetic Reconnection and Directly Driven Substorms

In particular during the descending phase of the solar cycle, Alfvén waves in the high-speed solar wind streams are a major form of interplanetary disturbances. The fluctuating southward interplanetary magnetic field (IMF) of Alfvén waves has been suggested to induce geomagnetic activities through intermittent magnetic reconnection at the magnetopause. In this study, we provide in situ observational evidence for dayside magnetopause reconnection induced by such interplanetary Alfvén waves. Using multipoint conjunction observations, we show that the IMF B z from interplanetary Alfvén waves is transmitted through and amplified by the Earth’s bow shock. Associated with the intensified southward B z to the magnetopause, in situ signatures of magnetic reconnection are detected. Repetitively, interplanetary Alfvén waves transmit the intensified B z to the magnetosheath, leading to intervals of large magnetic shear angles across the magnetopause and magnetopause reconnection. Such intervals are promptly followed by hundreds of nanoTesla (nT) increases in the auroral electrojet indices (AE and AU) within 10–20 minutes. These observations are confirmed in multiple events in corotating interaction region-driven geomagnetic storms. To put the observations into context, we propose a phenomenological model of a strongly driven substorm. The substorm electrojet is linked to the enhanced magnetopause reconnection in the short timescale of re-establishing the ionosphere electric field and the two-cell convection. These results provide insights on the temporal patterns of solar wind magnetosphere–ionosphere coupling, especially during the descending phase of the solar cycle.

A statistical study of space hurricanes in the Northern Hemisphere

The space hurricane is a newly discovered large-scale three-dimensional magnetic vortex structure that spans the polar ionosphere and magnetosphere. At the height of the ionosphere, it has a strong circular horizontal plasma flow with a nearly zero-flow center and a coincident cyclone-shaped aurora caused by strong electron precipitation associated with intense upward magnetic field-aligned currents. By analyzing the long-term optical observation onboard the Defense Meteorological Satellite Program (DMSP) F16 satellite from 2005 to 2016, we found that space hurricanes in the Northern Hemisphere occur in summer and have a maximum occurrence rate in the afternoon sector around solar maximum. In particular, space hurricanes are more likely to occur in the dayside polar cap at magnetic latitudes greater than 80°, and their MLT (magnetic local time) dependence shows a positive relationship with the IMF (interplanetary magnetic field) clock angle. We also found that space hurricanes occur mainly under dominant positive IMF By and Bz and negative Bx conditions. It is suggested that the stable high-latitude lobe reconnection, which occurs under the conditions of a large Earth’s dipole tilt angle and high ionosphere conductivity in summer, should be the formation mechanism of space hurricanes. The result will give a better understanding of the solar wind–magnetosphere–ionosphere coupling process under northward IMF conditions.

A new technique for understanding magnetosphere–ionosphere coupling using directional derivatives of SuperDARN convection flow

The purpose of this paper is to present and evaluate a new technique to better understand ionospheric convection and it’s magnetospheric drivers using convection maps derived from the Super Dual Auroral Radar Network (SuperDARN). We postulate that the directional derivative of the SuperDARN ionospheric convection flow can be used as a technique for understanding solar wind–magnetosphere–ionosphere coupling by identifying regions of strong acceleration/deceleration of plasma flow associated with drivers of magnetospheric convection such as magnetic reconnection. Thus, the technique may be used to identify the open–closed magnetic field line boundary (OCB) in certain circumstances. In this study, directional derivatives of the SuperDARN ionospheric convection flow over a four and a half hour interval on Nov. 04, 2001, is presented during which the interplanetary magnetic field was predominantly southward. At each one-minute time point in the interval the positive peak in the directional derivative of flow is identified and evaluated via comparison with known indicators of the OCB including the poleward boundary of ultraviolet emissions from three FUV detectors onboard the IMAGE spacecraft as well as the SuperDARN spectral widths. Good comparison is found between the location of the peak in the directional derivative of SuperDARN flow and the poleward boundary of ultraviolet emissions confirming that acceleration of ionospheric plasma flow is associated with magnetic reconnection and the open–closed boundary.

Multi-wavelength and multi-scale aurora observations at the Chinese Zhongshan Station in Antarctica

The Chinese Antarctic Zhongshan Station (ZHS) is located in a unique geographical and geomagnetic site that is suitable for observations on the cusp and of the post-noon dayside aurora and the poleward boundary of the nightside auroral oval. Since 2010, a unique, advanced synthetically auroral observation system has been deployed at ZHS, composed of a multi-wavelength all-sky imager, a multi-scale imager, a spectrum imager, and a radio imager. This system can record auroral forms from large (∼100 km) to small scales (∼10 m), auroral spectral lines from 400 to 730 nm, and auroral characteristics in the radio spectrum. Using this system, we have investigated the visible characteristics of UV ‘bright spots,’ the variation characteristics of the dayside shock auroras and convection, and the methodology for the quiet-day curve (QDC), among others. These investigations have enhanced our understanding of the solar wind–magnetosphere–ionosphere coupling process.

Identification of the different magnetic field contributions during a geomagnetic storm in magnetospheric and ground observations

Abstract. We used the empirical mode decomposition (EMD) to investigate the time variation of the magnetospheric and ground-based observations of the Earth's magnetic field during both quiet and disturbed periods. We found two timescale variations in magnetospheric data which are associated with different magnetospheric current systems and the characteristic diurnal orbital variation, respectively. On the ground we identified three timescale variations related to the solar-wind–magnetosphere high-frequency interactions, the ionospheric processes, and the internal dynamics of the magnetosphere. This approach is able to identify the different physical processes involved in solar-wind–magnetosphere–ionosphere coupling. In addition, the large-timescale contribution can be used as a local index for the identification of the intensity of a geomagnetic storm on the ground.

Role of IMF Bx in the solar wind‐magnetosphere‐ionosphere coupling

As far as the role of the interplanetary magnetic field (IMF) in the solar wind‐magnetosphere‐ionosphere (SMI) coupling is concerned, the role of the IMF Bx has more or less been ignored. Recent studies have shown that the IMF Bx plays an important role in the geometry of the bow shock under low Alfvén Mach numbers. Using global MHD simulations, this paper presents a further examination of the effects of the IMF Bx on the geometry of the magnetopause, the ionospheric transpolar potential, and the magnetopause reconnection rate, which quantify the SMI coupling process, under low Alfvén Mach numbers. The role of the IMF Bx manifests itself in three aspects: (1) the magnetopause shifts toward either north or south, depending on whether the Bx · Bz is negative or positive, whereas the bow shock expands in the opposite direction; (2) during southward IMF, the magnetic merging line shifts northward (southward) on the day side and southward (northward) on the night side for Bx &gt; 0 (Bx &lt; 0); (3) both the ionospheric transpolar potential and the magnetopause reconnection rate decrease with increasing Bx, and the relative reduction may reach as high as 20% under extreme cases. The physical mechanism for this reduction is attributed to the change in the width of the magnetosheath, which is sensitive to the variation of Bx under low Alfvén Mach numbers.

Transpolar potential and reconnection voltage of the Earth from global MHD simulations

[1] The ionospheric transpolar potential (Vpc) and the magnetospheric reconnection voltage (Vr) of the Earth are investigated in terms of global MHD simulations of the solar wind-magnetosphere-ionosphere (SMI) system. A spherical shell approximation is used for the ionosphere with a uniform Pedersen conductance and a zero Hall conductance, the interplanetary magnetic field is due southward, and quasi-steady solutions are obtained for the system. Each solution is characterized by the following four parameters: the ionospheric Pedersen conductance ΣP, the solar wind electric field Esw, ram pressure Psw, and Alfven Mach number MA. More than 100 cases are treated separately and Vpc and Vr are calculated in each case. It is found that both Vpc and Vr increase monotonically with increasing Psw and decreasing MA regardless of the magnitude of Esw. The simulation results are well organized by a combined parameter f = EswPswMA−1/2 and approximately fitted by functions of f and ΣP. When the units are S for ΣP, kV for Vpc and Vr, mV/m for Esw, and nPa for Psw, the functions are found to be Vpc = 2.3 × 103 (f + 0.8)(ΣP + 2)−1/(f + 8.2) and Vr = 1.8 × 103[f + 0.45(ΣP1/2 + 1.2)] (ΣP1/2 + 0.45)−1/(f + 15.5). Three conclusions are made as follows: (1) Both Vpc and Vr saturate with respect to the increase of f; any variation of the interplanetary conditions in favor of the increase of f may cause the saturation. (2) The saturation point is found to be fc = 6.6 for Vpc and fc = 14.4 − 0.9ΣP1/2 for Vr, whereas the value of ΣP controls the saturation levels. (3) The two potentials, Vpc and Vr, stem from the SMI coupling and exhibit similar saturation behaviors. They are positively correlated because of sharing the same driving source and the close coupling between the ionosphere and the magnetosphere.

A Science Mission for QSAT Project: Study of FACs in the Polar and Equatorial Regions

Kyushu University, Kyushu Institute of Technology and Fukuoka Institute of Technology are now designing, developing and building a micro-satellite called “QSAT”. The primary objective of QSAT is understanding the mechanism of spacecraft charging, which can be achieved with the onboard magnetometer, high-frequency probe (HP) and Langmuir probe (LP). The magnetometer measures the magnetic field variations caused by field-aligned currents (FACs) in the polar and equatorial regions. Polar FACs are well understood, while equatorial FACs are not. The science goals are as follows: (1) to better understand FACs in the polar region, (2) to compare the FACs observed in orbit with ground-based MAGDAS observations, (3) to investigate spatial distribution of FACs in the equatorial region. FACs play a crucial role in the coupling between solar wind, magnetosphere and ionosphere in terms of energy transfer. Also if we understand the relationship between the space and ground-based FACs data, then we can conduct long-term study on the solar wind–magnetosphere–ionosphere coupling in the future by mainly using data from ground-based magnetometer arrays.

The magnetosphere–ionosphere system from the perspective of plasma circulation: A tutorial

This tutorial review examines the role of O + in the dynamics of magnetosphere–ionosphere coupling. The life cycle of an O + plasma element is considered as it circulates from the mid- to high-latitude ionosphere. Energization and diversion of the convecting plasma element into outflows involves Alfvénic turbulence at the low-altitude base of the cusp and plasmasheet boundary layer and in downward-current “pressure cookers.” Observational evidence indicating that O + dominates the plasmasheet and ring current during extreme storm intervals is reviewed. The impacts of an O +-enriched plasma on solar wind–magnetosphere–ionosphere coupling are considered at both the micro and global scales. A synthesis of results from observation, theory and simulations suggests that the presence of O + in the magnetosphere is both a disruptive and a moderating agent in maintaining the balance between dayside and nightside magnetic merging.

Real‐time Earth magnetosphere simulator with three‐dimensional magnetohydrodynamic code

We developed a real‐time numerical simulator for the solar wind–space–magnetosphere–ionosphere coupling system, adopting the three‐dimensional (3‐D) magnetohydrodynamic (MHD) simulation code developed by Tanaka. By using the real‐time solar wind data, which is available from the ACE spacecraft every minute, as the upstream boundary conditions for density, temperature, flow speed, and interplanetary magnetic field, our MHD simulation system can numerically reproduce the global response of the magnetosphere and ionosphere at the same time as in the real world. We achieved real‐time 3‐D simulations of the solar wind–magnetosphere–ionosphere coupling system with a 44 × 56 × 60 mesh size by adapting high‐performance FORTRAN language with eight CPUs on a supercomputer system located at the National Institute of Information and Communications Technology (NICT). Simulated plasma temperature and density in geostationary orbit were also plotted as an index to predict satellite charging. In addition, we present real‐time virtual AE indices obtained from simulation results that directly compare with geomagnetic field activities as well as real‐time plasma temperature and density in geostationary orbit. Our real‐time MHD simulator now runs routinely on NICT's supercomputer system. We will present a detailed configuration of the real‐time simulator system in this paper. Some examples are presented from system output to show how solar wind variations result in geomagnetic disturbances.

Diurnal, semiannual, and solar cycle variations of solar wind–magnetosphere–ionosphere coupling

Using the Km index, the F10.7 index, and solar wind data from 1965 to 1996, we have examined the variations for the efficiency of solar wind–magnetosphere–ionosphere (SMI) coupling. It is found that the efficiency of SMI coupling depends on the total solar zenith angle, which is defined by the sum of cosine of the solar zenith angles at the northern and southern corrected geomagnetic (CGM) poles. This result suggests that the diurnal and semiannual variations of the coupling efficiency are explained by the variations of the total solar zenith angle. Further, we find that the coupling efficiency during the period of high solar activity (F10.7) tends to be lower than that during the period of low solar activity. This suggests that the efficiency of SMI coupling has a dependence on the solar activity. Our interpretation of these characteristics is that the total Pedersen conductivity on both northern and southern polar caps controls the efficiency of SMI coupling. We find that the variations of the coupling efficiency can be reproduced when our empirical conductivity model is applied in the Siscoe‐Hill model. This suggests that the ionospheric conductivity plays a significant role in SMI coupling and produces diurnal, semiannual, and solar cycle variations of geomagnetic activity.

Space- and ground-based investigations of solar wind–magnetosphere–ionosphere coupling

This paper provides a brief review of the understanding of the coupled solar wind–magnetosphere–ionosphere system that can be attained from observations of the size of the ionospheric polar caps from space and the ground. These measurements allow the occurrence and rate of dayside and nightside reconnection to be deduced. The former can be correlated with upstream interplanetary magnetic field observations to give an estimate of the effective length of the dayside reconnection X-line. The latter allows a preliminary statistical study of flux closure during substorms and other, smaller nightside reconnection events.

Solar wind-magnetosphere–ionosphere coupling at Jupiter

A fundamental property of planetary magnetospheres, which varies from planet to planet, is the dynamical influence of either the solar wind and its embedded interplanetary magnetic field (IMF) or of the rotation of the planet. Jovian magnetospheric dynamics are mainly dominated by the combination of rapid planetary rotation and the outflow of material originating from the moon Io, orbiting deep within the magnetospheric cavity. The main auroral oval in Jupiter’s polar ionosphere appears fixed with respect to the planet, an indication of planetary control, and is understood to be associated with large-scale magnetosphere–ionosphere coupling, and the transfer of angular momentum from the ionosphere to the middle magnetosphere plasma. We will first discuss the origin of this main auroral oval, and the theoretical model which followed. We will also summarise recent developments of the theoretical model to include the effects of precipitation-induced enhancements of the ionospheric Pedersen conductivity in regions of upward field-aligned currents. Jupiter’s polar auroral emissions, which include all auroral emission lying poleward of the main auroral oval, are ordered by magnetic local time, indicating potential external control by the solar wind. We have recently considered from a theoretical standpoint what the effects of pulsed dayside magnetic reconnection will be at Jupiter. This will generate a twin-vortical flow pattern in the ionosphere across the open-closed field line boundary, associated with a bi-polar (i.e. upward and downward) field-aligned current pair. Here, we discuss the conditions under which such currents may be carried in either magnetospheric or cusp plasmas, and summarise the consequences for auroral emissions at UV and X-ray wavelengths.

Solar wind—magnetosphere–ionosphere coupling: an event study based on Freja data

Freja data are used to study the relative contributions from the high-latitude (reconnection/direct entry) and low-latitude (viscous interaction) dynamos to the cross-polar potential drop. Convection streamlines which are connected to the high-latitude dynamo may be identified from dispersed magnetosheath ions not only in the cusp/cleft region itself but also several degrees poleward of it. This fact, together with Freja's orbital geometry allows us to infer the potential drop from the high-latitude dynamo as well as to obtain a lower limit to the potential drop from the low-latitude dynamo for dayside Freja passes. All cases studied here are for active magnetospheric conditions. The Freja data suggest that under these conditions at least one third of the potential is generated in the low-latitude dynamo. These observations are consistent with earlier observations of the potential across the low-latitude boundary layer if we assume that the low-latitude dynamo region extends over several tens of Earth radii in the antisunward direction along the tail flanks, and that the majority of the potential drop derives from the sun-aligned component of the electric field rather than from its cross-boundary component, or equivalently, that the centre of the dynamo region is located quite far down tail. A possible dynamo geometry is illustrated.

A model of solar wind–magnetosphere–ionosphere coupling for due northward IMF

A solar wind–magnetosphere–ionosphere coupling model for due northward IMF is proposed. The magnetosphere couples with the solar wind through reconnection nightside of the cusps. Other than the two small regions where reconnection takes place, the magnetosphere is closed. There are three plasma regions in the magnetosphere. The inner core is dominated by corotation. The outer magnetosphere contains two convection cells, and maps to the ionospheric viscous cells and Region I currents. The boundary layer and magnetotail region consists of a pair of flow channels, and maps to the ionospheric reverse cells. The three regions are separated by separatrix surfaces. Energy coupling across the surfaces can be facilitated by non-ideal-MHD processes such as ionospheric coupling, viscous and diffusive interactions, and waves and instabilities, although only the ionospheric coupling is essential to the model. This model is consistent with most established characteristics from observations and MHD computer simulations in both the ionosphere and magnetosphere. There are two specific features that need to be further confirmed from observations. The model expects that the ionospheric NBZ currents and reverse cells are maximized in the region sunward of the pole near the dayside cusps, and that in the tail there is a region which separates the earthward and tailward flows although the field and plasma characteristics are magnetospheric on both sides.