Solar Wind Electric Field Research Articles

Investigation of a rare event where the polar ionospheric reverse convection potential does not saturate during a period of extreme northward IMF solar wind driving

AbstractA variety of statistical studies have shown that the ionospheric polar potential produced by solar wind‐magnetosphere‐ionosphere coupling is linear for weak to moderate solar wind driving but becomes nonlinear during periods of very strong driving. It has been shown that this applies to the two‐cell convection potential that develops during southward interplanetary magnetic field (IMF) and also to the reverse convection cells that develop during northward IMF. This has been described as polar potential saturation, and it appears to begin when the driving solar wind electric field becomes greater than 3 mV/m. Utilizing measurements from the Resolute Incoherent Scatter Radar (RISR‐N), we examine ionospheric data near local noon within the reverse convection cells that developed during a period of very strong northward interplanetary magnetic field (IMF) on 12 September 2014. During this period we measure the electric field within the throat of the reverse convection cells to be near 150 mV/m at a time when the IMF is nearly 28 nT northward. This is far in excess of the 30–40 mV/m expected for polar potential saturation of the reverse convection cells. In fact, the development of the electric field responds linearly to the IMF Bz component throughout this period of extreme driving. The conditions in the solar wind show the solar wind velocity near 600 km/s, number density near 20 ions/cm3, and the Alfvén velocity about 75 km/s giving an Alfvén Mach number of 8. A search of several years of solar wind data shows that these values occur together 0.035% of the time. These conditions imply a high plasma β in the magnetosheath. We believe that condition of high β along with high mass density and a strong merging electric field in the magnetosheath are the significant parameters that produce the linear driving of the ionospheric electric field during this unusual period of extreme solar wind conditions. A discussion of current theories to account for cross‐polar cap potential saturation is given with the conclusion that theories that utilize magnetosheath parameters as they affect the reconnection rate appear to be the most relevant to the cross‐polar cap potential saturation solution.

The integrated dayside merging rate is controlled primarily by the solar wind

AbstractAn argument is presented to support the view that the rate of merging between the geomagnetic field and the interplanetary magnetic field across the dayside magnetosphere is controlled primarily by the solar wind parameters. The controlling parameters are the solar wind electric field in the Earth's frame of reference and the solar wind magnetosonic fast mode Mach number. These factors control to first order the total amount of magnetic flux that is carried by the magnetosheath flow to the dayside merging region. We argue that the global dayside merging rate is governed by the amount of flux that is delivered to the dayside merging line by the magnetosheath flow. The ionospheric conductance also plays an important role by modulating the shape of the magnetospheric obstacle around which the magnetosheath flow is deflected. The local conditions at the magnetopause, especially changes in magnetospheric plasma density will affect the local reconnection rate, but not the global dayside merging rate because to change the global merging rate the entire pattern of magnetosheath flow must be changed. The conceptual model presented here can explain how dayside merging depends on solar wind values, including both linear and nonlinear dependencies, through the application of a single, unifying perspective, without the need for ad hoc mechanisms that limit the dayside merging rate.

Intensity of the auroral electrojets during a recovery phase of magnetic storm

In this work, the effect of solar wind velocity on the development of magnetospheric and ionospheric disturbances is studied. It is shown that at high velocity of the solar wind during a recovery phase of magnetic storm the strong auroral activity characterized by the AE index is observed. In some cases during a recovery phase of magnetic storm the value of AE index is practically comparable with the value of AE index observed during the main phase of magnetic storm. When comparing time intervals of two magnetic storms during which the values of solar wind electric fields are approximately equal to each other, it is found that auroral electrojet intensity is stronger in that storm in which the solar wind velocity is higher.

Universal time effect in the response of the thermosphere to electric field changes

AbstractUnderstanding the dynamics of the thermospheric mass density is of paramount importance for predicting drag on low‐altitude satellites, particularly during geomagnetic storms. Transient enhancements in ion velocities, which frequently occur as a result of storm‐driven solar wind electric field fluctuations, cause increases in neutral density and temperature. Since the Earth's quasi‐dipolar magnetic field is tilted and offset from the center of the planet, it is hypothesized that hemispheric asymmetries arise, altering the thermospheric response to energy input based upon the time of day. This study used the Global Ionosphere‐Thermosphere Model (GITM) to investigate this phenomenon via a series of 22 idealized simulations, where the convective electric field was enhanced for 1 h of the day. Two configurations of the Earth's magnetic field were considered, the International Geomagnetic Reference Field (IGRF) and a centered dipole. These runs were conducted at March equinox when the amount of sunlight falling on the two hemispheres was the same. Two additional sets of runs were conducted at the June and December solstices for comparison. It was found that the most geoeffective times were those times when the geomagnetic poles were pointed toward the Sun. This orientation maximizes the photoionization colocated with the high‐latitude potential pattern, leading to more in Joule heating.

Северо-южная асимметрия геомагнитной активности и электрическое поле солнечного ветра

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 asymmetry. It is found, that the asymmetry of hemispheres shows itself in the 06–18-hourly component of magnetic activity daily variation, while the asymmetry in the 00–12-hourly component is completely absent. The cause of geomagnetic north-south asymmetry is supposed to be Pedersen meridional current between high and low latitudes in the ionosphere. The qualitative model of formation of asymmetry connected with the solar wind electric field is proposed.

Mass loading at 67P/Churyumov‐Gerasimenko: A case study

AbstractWe study the dynamics of the interaction between the solar wind ions and a partially ionized atmosphere around a comet, at a distance of 2.88 AU from the Sun during a period of low nucleus activity. Comparing particle data and magnetic field data for a case study, we highlight the prime role of the solar wind electric field in the cometary ion dynamics. Cometary ion and solar wind proton flow directions evolve in a correlated manner, as expected from the theory of mass loading. We find that the main component of the accelerated cometary ion flow direction is along the antisunward direction and not along the convective electric field direction. This is interpreted as the effect of an antisunward polarization electric field adding up to the solar wind convective electric field.

A statistical study of plasmaspheric plumes and ionospheric outflows observed at the dayside magnetopause

AbstractWe present a statistical study of plasmaspheric plumes and ionospheric outflows observed by the Cluster spacecraft near the dayside magnetopause. Plasmaspheric plumes are identified when the low‐energy ions (<1 keV) with ∼90° pitch angle distributions are observed by the Cluster Ion Spectrometer/Hot Ion Analyzer instrument. The ionospheric outflows are characterized by unidirectional or bidirectional field‐aligned pitch angle distributions of low‐energy ions observed in the dayside magnetosphere. Forty‐three (10%) plasmaspheric plume events and 32 (7%) ionospheric outflow events were detected out of the 442 times that C3 crossed the dayside magnetopause between 2007 and 2009. The occurrence rate of plumes at duskside is significantly higher than that at dawnside. The occurrence rate of outflows shows a weak dawn‐dusk asymmetry. We investigate the dependence of the occurrence rates of plumes and ionospheric outflows on geomagnetic activity and on solar wind/interplanetary magnetic field (IMF) conditions. The plume events tend to occur during southward IMF (duskward solar wind electric field) and moderate geomagnetic activity (Kp = 3,−30≤Dst <− 10 nT). However, the ionospheric outflow events tend to occur during northward IMF (dawnward solar wind electric field). The ionospheric outflows do not occur when Kp = 0, and the occurrence rate of the ionospheric outflows does not have a clear Dst dependence. Seventy‐five percent (46%) of the outflows are observed in the duskside for negative (positive) IMF By. Conversely, 54% (25%) of the outflows are observed in the dawnside for positive (negative) IMF By. Finally, the occurrence rates of both plumes and outflows increase with solar wind dynamic pressure.

MAVEN SupraThermal and Thermal Ion Compostion (STATIC) Instrument

The MAVEN SupraThermal And Thermal Ion Compostion (STATIC) instrument is designed to measure the ion composition and distribution function of the cold Martian ionosphere, the heated suprathermal tail of this plasma in the upper ionosphere, and the pickup ions accelerated by solar wind electric fields. STATIC operates over an energy range of 0.1 eV up to 30 keV, with a base time resolution of 4 seconds. The instrument consists of a toroidal “top hat” electrostatic analyzer with a $360^{\circ} \times 90^{\circ}$ field-of-view, combined with a time-of-flight (TOF) velocity analyzer with $22.5^{\circ}$ resolution in the detection plane. The TOF combines a $-15~\mbox{kV}$ acceleration voltage with ultra-thin carbon foils to resolve $\mathrm{H}^{+}$ , $\mathrm{He}^{++}$ , $\mathrm{He}^{+}$ , $\mathrm{O}^{+}$ , $\mathrm{O}_{2}^{+}$ , and $\mathrm{CO}_{2}^{+}$ ions. Secondary electrons from carbon foils are detected by microchannel plate detectors and binned into a variety of data products with varying energy, mass, angle, and time resolution. To prevent detector saturation when measuring cold ram ions at periapsis ( $\sim10^{1 1}~\mbox{eV/cm}^{2}\,\mbox{s}\,\mbox{sr}\,\mbox{eV}$ ), while maintaining adequate sensitivity to resolve tenuous pickup ions at apoapsis ( $\sim10^{3}~\mbox{eV/cm}^{2}\,\mbox{s}\,\mbox{sr}\,\mbox{eV}$ ), the sensor includes both mechanical and electrostatic attenuators that increase the dynamic range by a factor of $10^{3}$ . This paper describes the instrument hardware, including several innovative improvements over previous TOF sensors, the ground calibrations of the sensor, the data products generated by the experiment, and some early measurements during cruise phase to Mars.

A model of high‐latitude thermospheric density

AbstractWe present an empirical model of the high‐latitude air density at 450 km, derived from accelerometer measurements by the CHAllenging Minisatellite Payload and Gravity Recovery and Climate Experiment satellites during 2002–2006, which we call HANDY (High‐Latitude Atmospheric Neutral DensitY). HANDY consists of a quiet model and disturbance model. The quiet model represents the background thermospheric density for “zero geomagnetic activity” conditions. The disturbance model represents the response of the thermospheric density to solar wind forcing at high latitudes. The solar wind inputs used are the following: (1) solar wind electric field ESW, (2) interplanetary magnetic field (IMF) clock angle CSW, and (3) solar wind dynamic pressure PSW. Both quiet and disturbance models are constructed on the basis of spherical harmonic function fitting to the data. Magnetic coordinates are used for the disturbance model, while geographical coordinates are used for the quiet model. HANDY reproduces main features of the solar wind influence on the high‐latitude thermospheric density, such as the IMF By effect that produces a hemispheric asymmetry in the density distribution.

Observation of charged nanograins at comet 67P/Churyumov‐Gerasimenko

AbstractSoon after the Rosetta Orbiter rendezvoused with comet 67P/Churyumov‐Gerasimenko at a solar distance of ~3.5 AU and began to fly in triangular‐shaped trajectories around it, the Ion and Electron Sensor detected negative particles at energies from about 100 eV/q to over 18 keV/q. The lower energy particles came from roughly the direction of the comet; the higher‐energy particles came from approximately the solar direction. These particles are interpreted as clusters of molecules, most likely water, which we refer to as nanograins because their inferred diameters are less than 100 nm. Acceleration of the grains away from the comet is through gas drag by the expanding cometary atmosphere, while acceleration back to the vicinity of the comet is caused partly by solar radiation pressure but mainly by the solar wind electric field. These observations represent the first measurements of energetic charged submicron‐sized dust or ice grains (nanograins) in a cometary environment.

DRIFT-INDUCED DECELERATION OF SOLAR ENERGETIC PARTICLES

We investigate the deceleration of Solar Energetic Particles (SEPs) during their propagation from the Sun through interplanetary space, in the presence of weak to strong scattering in a Parker spiral configuration, using relativistic full orbit test particle simulations. The calculations retain all three spatial variables describing particles' trajectories, allowing to model any transport across the magnetic field. Large energy change is shown to occur for protons, due to the combined effect of standard adiabatic deceleration and a significant contribution from particle drift in the direction opposite to that of the solar wind electric field. The latter drift-induced deceleration is found to have a stronger effect for SEP energies than for galactic cosmic rays. The kinetic energy of protons injected at 1 MeV is found to be reduced by between 35 and 90% after four days, and for protons injected at 100 MeV by between 20 and 55%. The overall degree of deceleration is a weak function of the scattering mean free path, showing that, although adiabatic deceleration plays a role, a large contribution is due to particle drift. Current SEP transport models are found to account for drift-induced deceleration in an approximate way and their accuracy will need to be assessed in future work.

The flapping motion of the Venusian magnetotail: Venus Express observations

AbstractWith a newly developed technique and magnetic field measurements obtained by the magnetometer on Venus Express, we study the flapping motion of the Venusian magnetotail. We find that the flapping motion generally comprises contributions both from a nonpropagating steady flapping and a propagating kink‐like flapping. The flapping motion tilts the current sheet normal significantly in the plane perpendicular to the Venus‐Sun line. The kink‐like flapping waves traveling along solar wind electric field or its antidirection can be found in either magnetotail hemisphere where solar wind electric field pointing toward/away. The traveling behaviors suggest that the locations of the triggers for kink‐like flappings are near the boundaries between magnetotail current sheet and magnetosheath, not near the central region of magnetotail as is for the Earth's magnetotail.

Statistical characterization of the foremoon particle and wave morphology: ARTEMIS observations

AbstractAlthough the zeroth‐order picture of the Moon‐solar wind interaction involves no upstream perturbation, the presence of the Moon does affect the upstream plasma in a variety of ways. In this paper, a large volume of data obtained by the dual‐probe Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun (ARTEMIS) mission are used to characterize the large‐scale morphology of the “foremoon,” which is defined as the region upstream of the Moon and its wake that contains Moon‐related particles and waves. Solar wind ions reflected from the unshielded surface and by crustal magnetic fields, together with heavy ions of lunar surface/exospheric origin, are picked up by the solar wind magnetic and electric fields. Partially coinciding with populations of these Moon‐related ions, ∼0.01 Hz and ∼1 Hz magnetic field fluctuations are observed. The morphology of the Moon‐related ion and wave distributions is well organized by the upstream magnetic field direction. In addition, the low‐frequency wave distributions depend on the upstream Alfvén Mach numbers, suggesting that propagation effects also play a role in determining the wave foremoon morphology. Occurrence of modified electron velocity distributions and higher‐frequency, electromagnetic, and electrostatic waves is primarily controlled by magnetic connection to the Moon and its wake. These statistical results observationally demonstrate the large‐scale properties of the foremoon and upstream‐parameter control thereof.

Estimating the solar wind conditions during an extreme geomagnetic storm: a case study of the event that occurred on March 13–14, 1989

The solar wind conditions of an extreme geomagnetic storm were examined using magnetic field observations obtained from geosynchronous satellites and the disturbance storm-time (Dst) index. During geosynchronous magnetopause crossings (GMCs), magnetic field variations at the magnetosheath, which is the modulated interplanetary magnetic field (IMF), were observed by geosynchronous satellite. The dawn to dusk solar wind electric field (VBS) was estimated from the Dst index by using an empirical formula for Dst prediction; these data were then used to estimate the IMF and solar wind speed. This method was applied in the analysis of an extreme geomagnetic storm event that occurred on March 13–14, 1989, for which no direct solar wind information was available. A long duration of the GMC was observed after the second storm sudden commencement (SSC) of this event. The solar flare possibly associated with the second SSC of this storm event was identified as the March 12 M7.3/2B flare. The IMF B z was estimated to be about −50 nT with a solar wind speed of about 960 km/s during the 5 h in which the main phase of the storm rapidly developed, assuming an Alfvén Mach number (M A) during this period of more than 2.

Solar wind effect on Joule heating in the high‐latitude ionosphere

AbstractThe effect of solar wind on several electrodynamic parameters, measured simultaneously by the European Incoherent Scatter (EISCAT) radars in Tromsø (TRO, 66.6° cgmLat) and on Svalbard (ESR, 75.4° cgmLat), has been evaluated statistically. The main emphasis is on Joule heating rate QJ, which has been estimated by taking into account the neutral wind. In addition, a generally used proxy QE, which is the Pedersen conductance times the electric field squared, has been calculated. The most important findings are as follows. (i) The decrease in Joule heating in the afternoon‐evening sector due to winds reported by Aikio et al. (2012) requires southward interplanetary magnetic field (IMF) conditions and a sufficiently high solar wind electric field. The increase in the morning sector takes place for all IMF directions within a region where the upper E neutral wind has a large equatorward component and the F region plasma flow is directed eastward. (ii) At ESR, an afternoon hot spot of Joule heating centered typically at 14–15 magnetic local time (MLT) is observed during all IMF conditions. Enhanced Pedersen conductances within the hot spot region are observed only for the IMF Bz + /By− conditions, and the corresponding convection electric field values within the hot spot are smaller than during the other IMF conditions. Hence, the hot spot represents a region of persistent magnetospheric electromagnetic energy input, and the median value is about 3 mW/m2. (iii) For the southward IMF conditions, the MLT‐integrated QE for By− is twice the value for By+ at TRO. This can plausibly be explained by the higher average solar wind electric field values for By−.

Morphology of magnetic field in near‐Venus magnetotail: Venus express observations

AbstractKnowledge of the magnetic field morphology in the near‐Venus wake is essential to the studies of magnetotail dynamics and the planetary plasma escape. In this study we use the magnetic field measurements made by Venus Express during the period of April 2006 to December 2012 to investigate the global magnetic field morphology in the near‐Venus magnetotail (0–3 Venusian radii, RV, down tail) in the frame of solar wind electric field coordinates. The hemisphere with electric field pointing toward/away is indicated as ±E hemisphere. It has been reported that the cross‐tail field component has a hemispheric asymmetry in the Venusian magnetotail. We report here that this asymmetry should have been formed at the terminator and would transport tailward. In addition, we find that the draped magnetic field lines near both hemispheric flanks are directed equatorward in the region 0–1.5 RV down tail as it looks like “sinking” into Venus umbra. We estimate the thickness of the magnetotail current sheet and the current density at the sheet center. We find that the average half thickness of central current sheet near +E hemispheric flank (~460 km) is almost twice as thick as that near magnetic equatorial plane (~200 km), but the corresponding current densities at the sheet center are comparable (~6.0 nA/m2). As a result, the larger cross‐tail field component found near the +E hemispheric flank suggests a stronger tailward j × B force, i.e., the more efficient tailward acceleration of plasma in this region, showing the agreement with previous observations of heavy ion outflow from Venus. In contrast, the average magnetic field structure near −E hemispheric flank is irregular, which suggests that dynamic activities, such as magnetic reconnection and magnetic field turbulence, preferentially appear there.

Substorm occurrence during quiet solar wind driving

AbstractWe examine the OMNI database and International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometer chain records to study the substorm occurrence and characteristics during quiet solar driving periods, especially during the solar minimum period in 2009. We define substorm‐like activations as periods where the hourly average AL is below −200 nT. Using the OMNI data set, we demonstrate that there are limiting solar wind speed, interplanetary magnetic field magnitude, and driving electric field values below which substorm‐like activations (AL < 200 nT, intensification and decay of the electrojet) do not occur. These minimum parameter values are V < 266 km/s, B < 1.4 nT, and E < 0.025 mV/m; such low values are observed less than 1% of the time. We also show that for the same level of driving solar wind electric field, the electrojet intensity is smaller (by few tens of nT), and the electrojet resides farther poleward (by over 1°) during extended quiet solar driving in 2009 than during average solar activity conditions. During the solar minimum period in 2009, we demonstrate that substorm‐like activations can be identified from the IMAGE magnetometer chain observations during periods when the hourly average IL index is below −100 nT. When the hourly IL activity is smaller than that, which covers 87% of the nighttime observations, the electrojet does not show coherent behavior. We thus conclude that substorm recurrence time during very quiet solar wind driving conditions is about 5–8 h, which is almost double that of the average solar activity conditions.

Solar wind control of auroral Alfvénic power generated in the magnetotail

The effects of solar wind driving conditions on the polar distribution of large‐scale, nondispersive Alfvénic Poynting flux at low altitude during steady magnetosphere convections are studied using three‐dimensional global simulations of the solar wind‐magnetosphere‐ionosphere interaction. Results from 18 test simulations driven by steady upstream solar wind (SW) and interplanetary magnetic field (IMF) conditions are used to investigate the relationship between SW/IMF driving and low‐altitude signatures of large‐scale Alfvénic Poynting flux. When the IMF is southward, the intensity of the Alfvénic Poynting flux increases, and the hemispheric integrated Alfvénic Poynting flux exhibits a linear relation with the SW electric field. When the IMF has a By component, the simulated hemispheric Alfvénic power does not fit to the same linear relation. During steady IMF By driving conditions, the low‐altitude regions with enhanced Alfvénic Poynting flux are magnetically connected with magnetospheric dynamo regions on both open and closed field lines. The physical origin of low‐altitude Alfvénic Poynting flux connecting to the closed field line region is similar with that during southward IMF Bz driving. However, the Alfvénic Poynting flux flowing from the open field line dynamo region may be related to the physical process on the magnetopause, and only shear‐mode waves are generated.

The solar wind electric field does not control the dayside reconnection rate

AbstractWorking toward a physical understanding of how solar wind/magnetosphere coupling works, four arguments are presented indicating that the solar wind electric field vsw × Bsw does not control the rate of reconnection between the solar wind and the magnetosphere. Those four arguments are (1) that the derived rate of dayside reconnection is not equal to solar wind electric field, (2) that electric field driver functions can be improved by a simple modification that disallows their interpretation as the solar wind electric field, (3) that the electric field in the magnetosheath is not equal to the electric field in the solar wind, and (4) that the magnetosphere can mass load and reduce the dayside reconnection rate without regard for the solar wind electric field. The data are more consistent with a coupling function based on local control of the reconnection rate than the Axford conjecture that reconnection is controlled by boundary conditions irrespective of local parameters. Physical arguments that the solar wind electric field controls dayside reconnection are absent; it is speculated that it is a coincidence that the electric field does so well at correlations with geomagnetic indices.

Interplanetary magnetic field By control of prompt total electron content increases during superstorms

Large magnitude increases in ionospheric total electron content (TEC) that occur over 1–3h on the dayside are a significant manifestation of the main phases of superstorms. For the largest superstorms of solar cycle 23 (based on the Dst index), ground networks of GPS receivers measured peak total electron content increases greater than a factor of 2 relative to quiet time TEC averaged over the broad latitude band ±40° for local times 1200–1600LT. Near 30° latitude, the Halloween storms of October 29–30, 2003 appeared to produce storm-time TEC exceeding quiet time values by a factor of 5 within 2–3h of storm onset, at 1300LT. The physical cause of these large positive phase ionospheric storms is usually attributed to prompt penetration electric fields (PPEFs) initiated by Region 1 current closure through the ionosphere (Nopper and Carovillano, 1978 mechanism). An unresolved question is what determines variation of the TEC response for different superstorms. It has been suggested that the cross polar cap potential and Region 1 currents are significant factors in determining PPEF in the equatorial ionosphere, which are related to the solar wind reconnection electric field estimated by Kan–Lee and others. In this paper, we show evidence that suggests By may be a significant factor controlling the TEC response during the main phase of superstorms. We analyzed the interplanetary conditions during the period that TEC was increasing for eight superstorms. We find that increasing daytime TEC during superstorms only occurs for large reconnection electric fields when By magnitude is less than Bz. The data suggest that Bz is a far more important factor in the TEC response than the reconnection electric field. We also find that TEC decreases following its peak storm-time value for two superstorms, even though Bz remains large and By magnitudes are less than Bz. Such decreases during the geomagnetic disturbance may indicate the role of magnetospheric shielding currents, or of changes in the thermosphere that have developed over the prolonged period of large solar wind electric field. Further analysis is warranted covering a wider range of storm intensities on the role of By in affecting the daytime TEC response for a range of storm intensities.