Solar Wind Electric Field Research Articles

Spatially Highly Resolved Solar-wind-induced Magnetic Field on Venus

Abstract The current work investigates the Venusian solar-wind-induced magnetosphere at a high spatial resolution using all Venus Express (VEX) magnetic observations through an unbiased statistical method. We first evaluate the predictability of the interplanetary magnetic field (IMF) during VEX’s Venusian magnetospheric transits and then map the induced field in a cylindrical coordinate system under different IMF conditions. Our mapping resolves structures on various scales, ranging from the ionopause to the classical IMF draping. We also resolve two recently reported structures, a low-ionosphere magnetization over the terminator, and a global “looping” structure in the near magnetotail. In contrast to the reported IMF-independent cylindrical magnetic field of both structures, our results illustrate their IMF dependence. In both structures, the cylindrical magnetic component is more intense in the hemisphere with an upward solar wind electric field (E SW) than in the opposite hemisphere. Under downward E SW, the looping structure even breaks, which is attributable to an additional draped magnetic field structure wrapping toward −E SW. In addition, our results suggest that these two structures are spatially separate. The low-ionosphere magnetization occurs in a very narrow region, at about 88°–95° solar zenith angle and 185–210 km altitude. A least-squares fit reveals that this structure is attributable to an antisunward line current with 191.1 A intensity at 179 ± 10 km altitude, developed potentially in a Cowling channel.

Plasma Waves in the Distant Martian Environment: Implications for Mars' Sphere of Influence

AbstractWe identify magnetic waves in the initial insertion orbits of the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission spacecraft far upstream of the Martian bow shock. Overall, the majority of the observed magnetic waves are elliptically polarized and more perpendicular than parallel relative to the mean magnetic field. We find and analyze numerous waves near 1 Hz. The handedness of these 1 Hz waves tends toward left‐handed as the angle between the solar wind velocity and the magnetic field decrease. Similar waves are not seen in the Juno cruise data when it passed Mars' orbit (while Mars was more than 1 AU away). The presence of these waves out to distances of 14 Mars radii as observed by MAVEN and their absence in the Juno cruise data suggests the 1 Hz waves are amplified and/or created by the Martian environment. We also find a second, separate class of intermittent waves with frequencies near the proton cyclotron gyrofrequency. These waves are primarily right‐handed polarized in the spacecraft frame. The spatial distribution of the waves suggests no clear association with the well‐known plume of escaping ions that flows in the direction of the solar wind electric field. There are no obvious correlations between the wave amplitudes and the direction of the local interplanetary magnetic field or on their proximity to Mars. These characteristics lead us to conclude that the majority of these near‐proton cyclotron gyrofrequency waves are likely whistler‐mode waves that are not directly associated with Mars.

Magnetospheric chaos and dynamical complexity response during storm time disturbance

Abstract. In this study, we examine the magnetospheric chaos and dynamical complexity response to the disturbance storm time (Dst) and solar wind electric field (VBs) during different categories of geomagnetic storm (minor, moderate and major geomagnetic storm). The time series data of the Dst and VBs are analysed for a period of 9 years using non-linear dynamics tools (maximal Lyapunov exponent, MLE; approximate entropy, ApEn; and delay vector variance, DVV). We found a significant trend between each non-linear parameter and the categories of geomagnetic storm. The MLE and ApEn values of the Dst indicate that chaotic and dynamical complexity responses are high during minor geomagnetic storms, reduce at moderate geomagnetic storms and decline further during major geomagnetic storms. However, the MLE and ApEn values obtained from VBs indicate that chaotic and dynamical complexity responses are high with no significant difference between the periods that are associated with minor, moderate and major geomagnetic storms. The test for non-linearity in the Dst time series during major geomagnetic storm reveals the strongest non-linearity features. Based on these findings, the dynamical features obtained in the VBs as input and Dst as output of the magnetospheric system suggest that the magnetospheric dynamics are non-linear, and the solar wind dynamics are consistently stochastic in nature.

Concurrent Empirical Magnetic Reconstruction of Storm and Substorm Spatial Scales Using Data Mining and Virtual Spacecraft

Data mining (DM) has ushered in a new era of empirical magnetic reconstructions of the magnetosphere via application of the k-nearest neighbors (kNN) method. In this approach, the combined magnetosphere storm-substorm state is characterized by the Sym-H and AL indices, their time derivatives, and the solar wind electric field vBzIMF. However, using the DM reconstructions to account for the substorm contributions to the ring current as well as describing storm-time substorms remains a problem. The inner region r ≤ 12RE, where the ring current develops, has a much higher density of data than the tail region 12RE ≤ r ≤ 22RE, where substorms operate. This results in two models inconsistent in their scales dictated by the corresponding data densities. The inner model reconstructs storm time dynamics, including the formation of the westward and eastward ring current and pressure distributions. The outer model captures substorm features, including the thinning and rapid dipolarization of the tail sheet during the growth and expansion phases, respectively. However, the substorm model is insufficient to reconstruct the eastward ring current while the storm model cannot fully reproduce substorm effects because it overfits in the tail region. This issue is addressed by constructing a hybrid model which is fit using virtual magnetic field observations generated by sampling the other two models. The resulting merged resolution model concurrently captures the spatial scales associated with both storms in the inner region and substorms in the near-tail region. Hence it is particularly useful for investigation of the storm-substorm relationship, including storm-time substorms and the impact of individual substorm injections to the buildup of the storm-time ring current.

Dayside Cusp Aurorae and Ionospheric Convection Under Radial Interplanetary Magnetic Fields

AbstractDayside cusp aurorae are created from particles precipitating into the cusp, and ionospheric convection is driven by solar wind electric fields. In this study, we coordinated the observations obtained from the all‐sky camera on Svalbard, the Super Dual Auroral Radar Network, SuperMAG magnetometer data, and far ultraviolet imagers on board the Defense Meteorological Satellite Program satellites for the event January 4, 2014 to examine the morphology of aurorae and the patterns of ionospheric convection for radial interplanetary magnetic field (IMF). During the event, a poleward‐moving auroral form and antisunward ionospheric convection were observed when the IMF turned into almost purely radial. Moreover, both types of antisunward and sunward convection were simultaneously observed near the footprint of the cusp at different times during the radial IMF period. The antisunward convection and sunward convection are typically an indicator of the dayside reconnection for the southward IMF and the lobe reconnection for the northward IMF, respectively. All those observations support the concept of low‐latitude dayside and high‐latitude lobe reconnection for the radial IMF. This study further shows that the coexistence of the two types of reconnection for radial IMF, resulting in an interplay of repetitive antisunward and sunward convection.

Dependence of Great Geomagnetic Storm ($\Delta $SYM-H$\le -200$ nT) on Associated Solar Wind Parameters

We use $\Delta$SYM-H to capture the variation in the SYM-H index during the main phase of a geomagnetic storm. We define great geomagnetic storms as those with $\Delta$SYM-H $\le$ -200 nT. After analyzing the data that were not obscured by solar winds, we determined that 11 such storms occurred during solar cycle 23. We calculated time integrals for the southward interplanetary magnetic field component I(B$_s$), the solar wind electric field I(E$_y$), and a combination of E$_y$ and the solar wind dynamic pressure I(Q) during the main phase of a great geomagnetic storm. The strength of the correlation coefficient (CC) between $\Delta$SYM-H and each of the three integrals I(B$_s$) (CC = 0.74), I(E$_y$) (CC = 0.85), and I(Q) (CC = 0.94) suggests that Q, which encompasses both the solar wind electric field and the solar wind dynamic pressure, is the main driving factor that determines the intensity of a great geomagnetic storm. The results also suggest that the impact of B$_s$ on the great geomagnetic storm intensity is much more significant than that of the solar wind speed and the dynamic pressure during the main phase of associated great geomagnetic storm. How to estimate the intensity of an extreme geomagnetic storm based on solar wind parameters is also discussed.

Average cometary ion flow pattern in the vicinity of comet 67P from moment data

ABSTRACT Average flow patterns of ions around comet 67P detected by the RPC-ICA instrument onboard Rosetta are presented both as a time series and as a spatial distribution of the average flow in the plane perpendicular to the comet – Sun direction (Y–Z plane in the coordinate systems used). Cometary ions in the energy range up to 60 eV flow radially away from the nucleus in the Y–Z plane, irrespective of the direction of the magnetic field, throughout the mission. These ions may however be strongly affected by the spacecraft potential, the uncertainty due to this is briefly discussed. Inside the solar wind ion cavity and in the periods just before and after, the cometary pick up ions moving antisunward are deflected against the inferred solar wind electric field direction. This is opposite to what is observed for lower levels of mass-loading. These pick up ions are behaving in a similar way to the solar wind ions and are deflected due to mass-loading. A spatial asymmetry can be seen in the observations of deflected pick up ions, with motion against the electric field primarily within a radius of 200 km of the nucleus and also in the negative electric field hemisphere. Cometary ions observed by RPC-ICA typically move in the antisunward direction throughout the mission. These are average patterns, full-resolution data show very much variability.

Dependence of Major Geomagnetic Storm Intensity ($\mathrm{Dst}\le -100$ nT) on Associated Solar Wind Parameters

A geomagnetic storm is the result of sustained interaction between solar wind with a southward magnetic field and the magnetosphere. To investigate the influence of various solar wind parameters on the intensity of major geomagnetic storm, 67 major geomagnetic storms that occurred between 1998 and 2006 were used to calculate the correlation coefficients (CCs) between the intensities of major geomagnetic storms and the time integrals of southward interplanetary magnetic field $B_s$, solar wind electric field ($E_y$) and injection function (Q) during the main phase of the associated geomagnetic storms. SYM-H$_{min}$ was used to indicate the intensity of the associated major geomagnetic storm, while I($B_z$), I($E_y$) and I(Q) were used to indicate the time integrals of $B_z$, $E_y$ and Q during the main phase of associated major geomagnetic storm respectively. The derived CC between I($B_z$) and SYM-H$_{min}$ is 0.33, while the CC between I($E_y$) and SYM-H$_{min}$ is 0.57 and the CC between I(Q) and SYM-H$_{min}$ is 0.86. The results provide statistical evidence that solar wind dynamic pressure or solar wind density plays a significant role in transferring solar wind energy into the magnetosphere, in addition to the southward magnetic field and solar wind speed. Solar wind that has a strong geoeffectiveness requires solar wind dynamic pressure $>$3 nPa or solar wind density $>3$ nPa$/V_{sw}^2$. Large and long duration $B_s$ alone cannot ensure a major geomagnetic storm, especially if the solar wind dynamic pressure is very low, as large and long duration Bs is not a full condition, only a necessary condition to trigger a major geomagnetic storm.

The relationship between geomagnetic indices and the interplanetary medium parameters in magnetic storm main phases during CIR and ICME events

This paper is a continuation of research (Boroyev and Vasiliev, 2018), in which the relationship of substorm indices both with the rate of storm development and electric field of the solar wind (SW) during the main phase of magnetic storms induced by CIR and ICME events for the 1979 to 2000 period was considered. In this paper on the basis of OMNI data for 1979–2017, the correlations between substorm indices and Dst variations, as well as with parameters of the interplanetary medium during the main phase of magnetic storms induced by CIR and ICME events, is analyzed. The obtained results confirm the dependence of substorm index variations on the type of interplanetary source and high efficiency of the SW electric field.

RELATIONSHIP OF THE ASY-H INDEX WITH INTERPLANETARY MEDIUM PARAMETERS AND AURORAL ACTIVITY IN MAGNETIC STORM MAIN PHASES DURING CIR AND ICME EVENTS

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.

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.

A Third Generation Field‐Aligned Current Model

AbstractA new empirical model of field‐aligned currents in the Earth's ionosphere has been developed. This model is derived using magnetometer data from the CHAallenging Minisatellite Payload, Ø rsted, and Swarm satellite missions, which has created a database that spans more than 15 years. These data have been associated with solar wind conditions using the Advanced Composition Explorer satellite, as well as the , , , and solar indices. With the wealth of data and associated driving conditions, this model has been developed to reproduce field‐aligned current maps of the ionosphere based on solar wind electric field, interplanetary magnetic field clock angle, dipole tilt angle, solar index, and geographic hemisphere. This model was constructed using a series of spherical cap harmonic analysis fits based on small selections of the overall database. The coefficients of these fits were then used to develop a model that would reproduce these coefficients based on the previously described driving conditions. One of the most notable improvements demonstrated by this model is the ability to show distinct current regions in the ionosphere, particularly with respect to Region 0 currents during northward and highly positive or negative .

Signatures of Nonideal Plasma Evolution During Substorms Obtained by Mining Multimission Magnetometer Data

AbstractSubstorm‐type evolution of the Earth's magnetosphere is investigated by mining more than two decades (1995–2017) of spaceborne magnetometer data from multiple missions including the first two years (2016‐2017) of the Magnetospheric MultiScale mission. This investigation reveals interesting features of plasma evolution distinct from ideal magnetohydrodynamics (MHD) behavior: X‐lines, thin current sheets, and regions with the tailward gradient of the equatorial magnetic field Bz. X‐lines are found to form mainly beyond 20 RE, but for strong driving, with the solar wind electric field exceeding ∼5mV/m, they may come closer. For substorms with weaker driving, X‐lines may be preceded by redistribution of the magnetic flux in the tailward Bz gradient regions, similar to the magnetic flux release instability discovered earlier in PIC and MHD simulations as a precursor mechanism of the reconnection onset. Current sheets in the growth phase may be as thin as 0.2 RE, comparable to the thermal ions gyroradius, and at the same time, as long as 15 RE. Such an aspect ratio is inconsistent with the isotropic force balance for observed magnetic field configurations. These findings can help resolve kinetic mechanisms of substorm dipolarizations and adjust kinetic generalizations of global MHD models of the magnetosphere. They can also guide and complement microscale analysis of nonideal effects.

Ion Composition Boundary Layer Instabilities at Mars

AbstractThe ion composition boundary layer that separates solar wind from ionospheric plasma at Mars typically contains a smooth compositional transition. However, ~10% of boundary crossings display large nonmonotonic variations in density, indicating an instability. We find that most of these instabilities occur on the flanks or downstream of the planet, and many fall into two distinct classes, which occur in different locations, under different preferred conditions. Plume events, which occur where the solar wind electric field points outward, likely represent the motion of the escaping ion plume across the spacecraft. Snowplow events, which occur where the electric field points inward, likely represent the escape of discrete parcels of plasma, which could account for ~10% of the total ion loss from Mars. Snowplow events occur under conditions that favor the development of ionospheric irregularities, which could form a seed for the snowplow mechanism that detaches and accelerates ionospheric plasma downstream.

Extremely High Plasma Densities in the Mars Ionosphere Associated With Cusp‐Like Magnetic Fields

AbstractThe Martian crustal magnetic field modifies the structure of the ionosphere, the loss of atmosphere to space, and the interactions of the upper atmosphere with the solar wind. The Mars Advanced Radar for Subsurface and Ionosphere Sounding topside sounder on Mars Express has regularly observed oblique echoes from magnetically controlled plasma structures in regions of strong and vertical crustal magnetic fields. Here we present 11 observations of oblique echoes with unusually high plasma densities and compare them to more common oblique echoes with typical ionospheric densities. In two cases, the density is at least 3.6×105 cm−3, perhaps the highest recorded in the Mars ionosphere. We find that high‐density features occur only where the magnetic inclination angle is nearly vertical and the magnetic field is sufficiently strong (>200 nT at 150 km). Additionally, the more frequently the magnetic field is open at a given location, the greater the probability that a high‐density echo is found there. Oblique echoes with typical densities, in contrast, are found at a wider range of magnetic geometries and strengths and are coherent and stable across as much as 45° in longitude (−53° latitude and 165–210°E longitude) and 5.5 years of observation. Based upon these findings, we suggest that these high‐density features occur where the magnetic field is open and interactions with the solar wind, such as plasma instabilities arising from heating by the solar wind electric field, have increased ionospheric plasma densities. The more common oblique echoes with typical densities are more likely to be created by transport along closed field lines in response to pressure gradients and winds.

Epoch‐Based Model for Stormtime Plasmapause Location

AbstractThe output of a plasmapause test particle (PTP) code is used to formulate a new epoch‐based plasmapause model. The PTP simulation is run for an ensemble of 60 storms spanning 3 September 2012 to 28 September 2017 and having peak Dst of −60 nT or less, yielding over 7 million model plasmapause locations. Events are automatically identified and epoch times calculated relative to the respective storm peaks. Epoch analysis of the simulated plasmapause is demonstrated to be an effective method to reveal the dynamical phases of plume formation and evolution. The plasmapause radius is found to be strongly correlated with positive solar wind electric field. The epoch‐binned PTP data are used to create the first analytical model of the plasmapause that explicitly includes plumes. We obtain this result by employing as basis functions our derived exact solutions for the Volland‐Stern convection potential. The analytical plasmapause model depends on epoch time, for moderate and strong storms, and is specified by three main parameters: the duskside plasmapause radius and two tuning coefficients. The epoch‐based analytical model is shown to agree to within 0.5 RE with nightside in situ plasmapause crossings by the Van Allen Probes on 17 March 2015. Compared to dayside plume crossings on 26 June 2000, the model agrees within 0.7 RE of radius and 0.8 RE azimuthal distance. This level of agreement is comparable to that achieved by the full dynamic PTP simulation.

Does the Solar Wind Electric Field Control the Reconnection Rate at Earth's Subsolar Magnetopause?

AbstractWe demonstrate that the reconnection rate at the subsolar magnetopause is strongly controlled by the solar wind electric field and depends weakly on the local properties of the dissipation region. Our approach is to match the solar wind and magnetospheric states in an internal boundary layer described by the Cassak and Shay (2007, https://doi.org/10.1063/1.2795630) expression for two‐dimensional asymmetric reconnection. Faraday's law along the Sun‐Earth line determines the variation of the solar wind electric field from the bow shock to the magnetopause. While the magnetospheric plasma exerts some control over the reconnection rate, magnetic flux pileup in the sheath partially compensates for any local reduction in the reconnection rate. For a fixed magnetospheric state, the reconnection rate is shown to be directly proportional to the solar wind electric field, thus explaining why the solar wind electric field correlates well with geomagnetic indices.

The Magnetic Local Time Distribution of Storm Geomagnetic Field Disturbance Under Different Conditions of Solar Wind and Interplanetary Magnetic Field

AbstractThe magnetic local time (MLT) distributions of the horizontal geomagnetic disturbance (∆H) are investigated with the SuperMAG data set during 330 magnetic storms from 2000 to 2015. Then the MLT distributions of ∆H are verified and interpreted with the SuperMAG‐based partial ring current indices (SMR indices) and the Burton equation. It is shown that the ∆H is positive at most MLTs and slightly stronger on the dayside during the initial phase. Such distribution might be mainly attributed to the global positive impact of the magnetopause currents, while the ring current (RC) only produces weak negative disturbances, which are slightly stronger on the duskside. In the main phase, the ∆H decreases prominently with the peak on the duskside. The RC particles injection plays a major role, especially for large solar wind electric field (ESW). The region with ∆H larger than −20 nT is concentrated on the dawnside for small ESW, which might be attributed to earthward bursty bulk flows. Besides, larger solar wind dynamic pressure might cause stronger disturbances under the same magnitude of ESW. In the recovery phase, the ∆H is weaker and more uniform distributed than in the main phase for negative ESW. For positive ESW, similar dawn‐dusk asymmetry occurs as that in the main phase, but the peak of strongest disturbance tends to weaken and move toward the dayside. Based on the dawn‐dusk asymmetric decay rate derived from the Burton equation, it is speculated that the contribution of partial RC might be no less than the FACs.

Solar Rotation Period Driven Modulations of Plasmaspheric Density and Convective Electric Field in the Inner Magnetosphere

AbstractThis paper presents the first analysis of Van Allen Probes measurements of the cold plasma density and electric field in the inner magnetosphere to show that intervals of strong modulation at the solar rotation period occur in the locations of the outer plasmasphere and plasmapause (~0.7 RE peak‐to‐peak), in the large‐scale electric field (~0.24 mV/m peak‐to‐peak), and in the cold plasma density (~250 to ~70 cm−3 peak‐to‐peak). Solar rotation modulation of the inner magnetosphere is more apparent in the declining phase of the solar cycle than near solar maximum. The periodicities in these parameters are compared to solar extreme ultraviolet irradiance, solar wind dawn‐dusk electric field, and Kp. The variations in the plasmapause location at the solar rotation period anticorrelate with solar wind electric field, magnetospheric electric field, and Kp, but not with extreme ultraviolet irradiance, indicating that convective erosion is the dominant physical process controlling the plasmapause at these timescales.

Relationship between the low-latitude coronal hole area, solar wind velocity, and geomagnetic activity during solar cycles 23 and 24

In order to statistically investigate the relationship between the low-latitude coronal holes (CHs), the solar wind speed, and the geomagnetic activity in solar cycles 23 (1996–2008) and 24 (2009–2016), we conducted a superposed epoch analysis of the variations in CH area, solar winds, the interplanetary magnetic field (IMF), and geomagnetic indices (AL, AU, and SYM-H) for the period from 1996 to 2016. We further divided the temporal variations of the IMF into four types and then investigated the variations in solar winds, the IMF, and the geomagnetic indices before and after the corotating interaction region (CIR) reached Earth’s magnetosphere in each case. As a result, we observed a north–south asymmetry in the CH area, which shows that the CH area was much larger in the southern hemisphere than in the northern hemisphere during solar cycles 23 and 24. In addition, the CH area for solar cycle 24 tended to appear in a wider latitude region compared with that for solar cycle 23. The maximum values of the CH area and the solar wind speed in solar cycle 24 tended to be smaller than those in solar cycle 23. The relationship between these maximum values showed a positive correlation for both solar cycles. The distribution was larger for solar cycle 23 than for solar cycle 24. The variations in solar wind speed and the geomagnetic indices (AE and SYM-H) associated with CIRs in solar cycle 24 tended to be smaller than those in solar cycle 23. We conclude that the geomagnetic activity for solar cycle 24 associated with CIRs was slightly lower compared with that for solar cycle 23. This decrease in geomagnetic activity was due to a decrease in the dawn-to-dusk solar wind electric field intensity, which is obtained as the product of the solar wind speed and the north–south component of the solar wind magnetic field.