Convection Electric Field Research Articles

Solar wind density controlling penetration electric field at the equatorial ionosphere during a saturation of cross polar cap potential

The most important source of electrodynamic disturbances in the equatorial ionosphere during the main phase of a storm is the prompt penetration electric field (PPEF) originating from the high‐latitude region. It has been known that such an electric field is correlated with the magnetospheric convection or interplanetary electric field. Here we show a unique case, in which the electric field disturbance in the equatorial ionosphere cannot be interpreted by this concept. During the superstorm on Nov. 20–21, 2003, the cross polar cap potential (CPCP) saturated at least for 8.2 h. The CPCP reconstructed by Assimilative Mapping of Ionospheric Electrodynamics (AMIE) procedure suggested that the PPEF at the equatorial ionosphere still correlated with the saturated CPCP, but the CPCP was controlled by the solar wind density instead of the interplanetary electric field. However, the predicted CPCPs by Hill‐Siscoe‐Ober (HSO) model and Boyle‐Ridley (BR) model were not fully consistent with the AMIE result and PPEF. The PPEF also decoupled from the convection electric field in the magnetotail. Due to the decoupling, the electric field in the ring current was not able to comply with the variations of PPEF, and this resulted in a long‐duration electric field penetration without shielding.

Saturn's inner magnetospheric convection pattern: Further evidence

Observations of the radial locations of satellite absorption microsignatures in energetic particle data at Saturn have suggested the existence of an average convection pattern, fixed in local time, that is superimposed on the dominant near‐corotation of the inner magnetosphere. Such a pattern should have additional observational consequences, and we use several different Cassini data sets to test these expectations. These include day/night asymmetries in the A‐ring absorption signature of high‐energy particles and total electron density, day/night asymmetries in plasma ion and electron temperatures, and day/night asymmetries in energetic‐particle phase‐space densities. For L > 4, the observations are found to be consistent with expectations based on the suggested convective drifts in a global noon‐to‐midnight electric field, such that particles drift outward on the dawn side of the magnetosphere and inward on the dusk side, resulting in drift orbits with an outward offset toward noon. The different data sets yield similar estimates of the required radial offsets, ∼0.5–1 Rs in the region inside L = 10. The corresponding convection electric field appears to decrease with increasing radial distance, from ∼0.3 mV/m near Tethys to ∼0.1 mV/m beyond Dione. The source of such an electric field remains a puzzle, but whatever the source, it appears to be a dominant factor in the circulation of plasma in Saturn's inner magnetosphere. For L < 4, the observations are not fully consistent with such a global convection field, and other explanations for A‐ring absorption asymmetries are needed.

Reflection of solar wind protons on the Martian bow shock: Investigations by means of 3‐dimensional simulations

The reflection of solar wind protons on the Martian bow shock (BS) is investigated by means of three‐dimensional simulation models. A two steps approach is adopted to allow a detailed analysis of the reflected population. Firstly, the 3‐dimensional hybrid model of Modolo et al. (2005) is used to compute a stationary state of the interaction of the solar wind (SW) with Mars. Secondly, the motion of test particles is followed in the electromagnetic field computed by the hybrid simulation meanwhile detection criteria defined to identify reflected protons are applied. This study demonstrates some effects of the large curvature of a planetary BS on the structure of the foreshock. Reflected protons encounter the BS in a region encompassing parts of the quasi‐perpendicular and quasi‐parallel shocks, and exit the shock mainly from the quasi‐parallel region. The energy spectrum of all reflected protons extends from 0 to almost 15keV. A virtual omnidirectional detector (VOD) is used to compute the local omnidirectional flux of reflected protons at various locations upstream of the BS. Spatial variations of this omnidirectional flux indicate the location and spatial extent of the proton foreshock and demonstrate its shift, increasing with the distance downstream, in the direction opposite to the motional electric field of the SW. Local energy spectra computed from the VOD observations demonstrate the existence of an energy gradient along the direction of the convection electric field.

Magnetic latitude and local time distributions of ionospheric currents during a geomagnetic storm

In order to clarify the global distribution of ionospheric currents during a geomagnetic storm, we analyzed ground magnetic disturbances from high latitudes to the magnetic equator for the storm on September 7–8, 2002, with the minimum SYM‐H value of –168 nT. In this analysis, we investigated magnetic field deviations in the northward component from the SYM‐H, as functions of the dipole magnetic latitude (DMLAT) and the magnetic local time (MLT). During the main phase of the storm, the deviations at the low latitudes (10°−35° in DMLAT) were positive/negative in the dawn/dusk (0–9/11–24 h MLT) sector. On the other hand, the deviations at the dayside middle latitudes (35°–55° in DMLAT) were negative/positive in the morning/afternoon (6–12/13–15 h MLT) sector. The local time distribution at the low latitudes may represent the dawn‐dusk asymmetry of the storm time ring current, while that at the dayside middle latitudes coincides with the DP2 currents due to the convection electric field associated with the Region 1 field‐aligned currents (R1 FACs). All over the nightside middle latitude, the deviations were positive. This implies the direct effect of the R1 FACs through the Biot‐Savart's law. At the geomagnetic equator, the eastward and westward electrojets were intensified on the day and nightside, respectively, being caused by the penetrated dawn‐to‐dusk convection electric field. We found that the MLT distribution of the magnetic deviations during the recovery phase was in opposite sense to that during the main phase at the dayside middle latitudes. The reversed magnetic disturbances must be due to the overshielding electric field associated with the Region 2 field‐aligned currents (R2 FACs). Similarly, the deviations at the dayside and nightside equator were reversed, indicating penetration of the dusk‐to‐dawn overshielding electric field into the equatorial ionosphere. Based on the above results, we propose a current system including the ionospheric currents at middle latitudes caused by the R1/R2 FACs, equatorial EEJ/CEJ, and asymmetric ring current, during the main/recovery phase of the geomagnetic storm.

Activation of the tail open part during the magnetospheric storm

In each polar cap (PC) we mark out “old PC” observed during quiet time before the event under consideration, and “new PC” that emerges during the substorm framing the old one and expanding the PC total area. Old and new PCs are the areas for the magnetosphere old and new tail lobes, respectively. The new lobe variable magnetic flux Ψ1 is usually assumed to be active, i.e. it provides the electromagnetic energy flux (Poynting flux) ɛ′ transport from solar wind (SW) into the magnetosphere. The old lobe magnetic flux Ψ2 is supposed to be passive, i.e. it remains constant during the disturbance and does not participate in the transporting process which would mean the old PC electric field absolute screening from the convection electric field created by the magnetopause reconnection. In fact, screening is observed, but far from absolute. We suggest a model of screening and determine its quantitative characteristics in the selected superstorm. The coefficient of a screening is the β = Ψ2/Ψ02, where Ψ02 = const is open magnetic flux through the old PC measured prior to the substorm, and Ψ2 is variable magnetic flux through the same area measured during the substorm. We consider three various regimes of disturbance. In each, the coefficient β decreased during the loading phase and increased at the unloading phase, but the rates and amplitudes of variations exhibited a strong dependence on the regime. We interpreted decrease in β as a result of involving the old PC magnetic flux Ψ2, which was considered to be constant earlier, in the Poynting flux ɛ′ transport process from solar wind into the magnetosphere. Transport process weakening at the subsequent unloading phase creates increase in β. Estimates showed that coefficient β during each regime and the computed Poynting flux ɛ′ varied manifolds. In general, unlike the existing substorm conception, the new scenario describes an unknown earlier of tail lobe activation process during a substorm growth phase that effectively increases the accumulated tail energy for the expansion and recovery phases.

Analysis of Cassini magnetic field observations over the poles of Rhea

We analyze Cassini magnetic field observations from the only two polar flybys of Saturn's largest icy satellite Rhea (R2 on 02 March 2010 and R3 on 11 January 2011) which are scheduled between Saturn Orbit Insertion and the end of the mission in 2017. For the interpretation of these data, we apply estimations from simple analytical models as well as results from numerical hybrid simulations (kinetic ions, fluid electrons) of Rhea's interaction with the incident magnetospheric plasma. In‐situ observations of exospheric neutral gas and pick‐up ions suggest Rhea to be embedded in a tenuous gas envelope. However, the interaction of this gas with the magnetospheric flow does not make any measurable contributions to the magnetic field perturbations detected above the poles of the moon. Instead, the field perturbations observed in these regions mainly arise from the absorption of magnetospheric particles with large field‐aligned velocities, impinging on the north and south polar surface of Rhea. In addition to numerous interaction features known from preceding Cassini flybys of Saturn's plasma‐absorbing moons, the magnetic field data acquired above Rhea's poles reveal perturbations of the flow‐aligned field component, corresponding to a draping/Alfvén wing pattern. Based on our hybrid simulations, we suggest that these signatures arise from the finite extension of Rhea's wakeside plasma void along the corotational flow direction, yielding a density gradient in corotation direction, and thereby generating a diamagnetic current from the Saturn‐facing into the Saturn‐averted hemisphere of the moon. This transverse current is responsible for generating a weak Alfvén wing pattern at Rhea which has been detected by the Cassini spacecraft during the R2 and R3 flybys. Due to the large gyroradii of the incident magnetospheric ions, this structure features a pronounced asymmetry with respect to the direction of the convective electric field. Results of our simulation, considering only plasma absorption on the moon, are in good agreement with Cassini magnetometer data from both flybys. At Saturn's icy satellites Tethys and Dione, the low value of the magnetospheric plasma beta most likely prevents the formation of similar currents and measurable flow‐aligned magnetic field distortions.

Nongyrotropic electron velocity distribution functions near the lunar surface

We have analyzed nongyrotropic electron velocity distribution functions (VDFs) obtained near the lunar surface. Electron VDFs, measured at ∼10–100 km altitude by Kaguya in both the solar wind and the Earth's magnetosphere, exhibit nongyrotropic empty regions associated with the ‘gyroloss’ effect; i.e., electron absorption by the lunar surface combined with electron gyromotion. Particle‐trace calculations allow us to derive theoretical forbidden regions in the electron VDFs, thereby taking into account the modifications due to nonuniform magnetic fields caused by diamagnetic‐current systems, lunar‐surface charging, and electric fields perpendicular to the magnetic field. Comparison between the observed empty regions with the theoretically derived forbidden regions suggests that various components modify the characteristics of the nongyrotropic electron VDFs depending on the ambient‐plasma conditions. On the lunar nightside in the magnetotail lobes, negative surface potentials slightly reduce the size of the forbidden regions, but there are no distinct effects of either the diamagnetic current or perpendicular electric fields. On the dayside in the solar wind, the observations suggest the presence of either the diamagnetic‐current or solar wind convection electric field effects, or both. In the terrestrial plasma sheet, all three mechanisms can substantially modify the characteristics of the forbidden regions. The observations imply the presence of a local electric field of at least 5 mV/m although the mechanism responsible for production of such a strong electric field is unknown. Analysis of nongyrotropic VDFs associated with the gyroloss effect near solid surfaces can promote a better understanding of the near‐surface plasma environment and of plasma–solid‐surface interactions.

Identification of electron field‐aligned current systems in Saturn's magnetosphere

Based on the analysis of 7 years of Cassini electron plasma spectrometer data near Saturn's equatorial plane, we computed the average directional electron current in the Northern and the Southern hemispheres separately. We determined the net current density by subtracting the downward electron current density (equator to the ionosphere) from the upward electron current density (ionosphere to the equator). From the symmetric analysis (no separation in local time), we identified: (1) layers of net upward current carried by the thermal electrons (1–10 eV) in both hemispheres inside 5–8 RS (Saturn Radius = 60,268 km) (region A) and (2) layers of net downward current carried by a population of warmer electrons (10–400 eV) inside 8–10 RS (region B). From the analysis of the currents organized by local time (dayside and nightside parsing), new features were identified such as (1) a day‐night asymmetry of the current carried by the warm and hot (400 eV–26,000 eV) electrons beyond 10 RS (region C), and (2) the possible existence of inter‐hemispheric currents directed from the Southern to the Northern hemisphere inside 4 RS (region A) and oppositely directed at about 13–15 RS (region C). Our interpretation is that the observed current system results from the superimposition of (1) a current system associated with the corotation enforcement, (2) a current system linked to the presence of the newly identified noon‐to‐midnight convection electric field and (3) a system of inter‐hemispheric currents driven by the thermosphere‐ionosphere. We finally discuss the relation of the observed currents with the newly identified Saturn's secondary auroral emissions.

Incoherent scatter spectrum of ionospheric plasma with an anisotropic temperature ion distribution

The expression of anisotropic temperature ion distribution function under the 13-moment approximation is obtained by solving a set of moment equations based on the Boltzmann equation for a relaxation collision model and with consideration of the anisotropic temperature ion distribution. And the incoherent scatter spectrum with an anisotropic temperature ion distribution is simulated in different directions based on the electromagnetic radiation theory of Sheffield. The effects of different electrical field strengths, ratios of electron temperature to ion temperature, and ion-neutral collision frequencies on the incoherent scatter spectrum are all discussed. Finally, the value of theoretical simulation is compared with the measured value of incoherent scattering spectrum. The result show that the incoherent scatter spectrum of ions seriously deviates from the form of the Maxwellian distribution in the equilibrium state. This phenomenon can be attributed to the effects of anisotropic temperature ion distribution, the larger convection electric field, and other factors in high latitude ionosphere.

Electric field structure inside the secondary island in the reconnection diffusion region

Secondary islands have recently been intensively studied because of their essential role in dissipating energy during reconnection. Secondary islands generally form by tearing instability in a stretched current sheet, with or without guide field. In this article, we study the electric field structure inside a secondary island in the diffusion region using large-scale two-and-half dimensional particle-in-cell (PIC) simulation. Intense in-plane electric fields, which point toward the center of the island, form inside the secondary island. The magnitudes of the in-plane electric fields Ex and Ez inside the island are much larger than those outside the island in the surrounding diffusion region. The maximum magnitudes of the fields are about three times the B0VA, where B0 is the asymptotic magnetic field strength and VA is the Alfvén speed based on B0 and the initial current sheet density. Our results could explain the intense electric field (~100 mV/m) inside the secondary island observed in the Earth’s magnetosphere. The electric field Ex inside the secondary island is primarily balanced by the Hall term (j × B)/ne, while Ez is balanced by a combination of (j × B)/ne, −(vi × B), and the divergence of electron pressure tensor, with (j × B)/ne term being dominant. This large Hall electric field is due to the large out-of-plane current density jy inside the island, which consists mainly of accelerated electrons forming a strong bulk flow in the –y direction. The electric field Ey shows a bipolar structure across the island, with negative Ey corresponding to negative Bz and positive Ey corresponding to positive Bz. It is balanced by (j × B)/ne and the convective electric field. There are significant parallel electric fields, forming a quadrupolar structure inside the island, with maximum amplitude of about 0.3B0VA.

Hot flow anomalies at Venus

We present a multi‐instrument study of a hot flow anomaly (HFA) observed by the Venus Express spacecraft in the Venusian foreshock, on 22 March 2008, incorporating both Venus Express Magnetometer and Analyzer of Space Plasmas and Energetic Atoms (ASPERA) plasma observations. Centered on an interplanetary magnetic field discontinuity with inward convective motional electric fields on both sides, with a decreased core field strength, ion observations consistent with a flow deflection, and bounded by compressive heated edges, the properties of this event are consistent with those of HFAs observed at other planets within the solar system.

Disturbance dynamo, prompt penetration electric field and overshielding in the Earth’s ionosphere during geomagnetic storm

This paper presents a result of model calculation of the disturbance dynamo electric field, prompt penetration, overshielding and their ionospheric effects during geomagnetic storm on December 14–15, 2006. The calculations were carried out with use of the Global Self-Consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP model) developed in WD IZMIRAN. Simulations were performed for quiet and disturbed conditions with took into account the magnetospheric convection electric field with and without took into account dynamo electric field. It has allowed to neglecting thermospheric and ionospheric effects of the disturbance dynamo electric field. The analysis of model calculation results was carried out. We have made conclusions about the role of the disturbance dynamo electric field, prompt penetration electric field and overshielding effects in thermospheic and ionospheric parameters during geomagnetic storm.

Perpendicular flow deviation in a magnetized counter-streaming plasma

Charged dust exists in various regions in the Solar System. How this charged dust interacts with the surrounding plasma is not well understood. In this study we neglect the charging process and treat the charged dust as a fluid interacting with the ambient magnetized plasma fluid. The model reproduces the expected plasma deceleration with both positively charged and negatively charged dust, but a new effect arises. Negatively charged dust causes the magnetic field to bend in the direction of the convection electric field, while positively charged dust causes the opposite magnetic field bending. Consequently, the interaction does not only result in a perpendicular shift in the downstream current system, but also a rotation in these currents. We present quantitative results using the multi-fluid MHD code BATSRUS for both subsonic and supersonic interactions. We find that the same perpendicular bending exists for all counter-streaming interaction problems, independent of the shape of the dust cloud. The new model can be applied to plasma interaction studies including, but not limited to, charged dust particles in the solar wind, cometary plasma, the Enceladus plume, and active plasma releases, such as the Active Magnetospheric Particle Tracer Experiment (AMPTE) mission. The predicted behavior is consistent with observations at Enceladus.

Hybrid simulations of proton precipitation patterns onto the upper atmosphere of Mars

We study the dependence of proton precipitation patterns onto the Martian upper atmosphere on altitude, proton energy, proton origin, and in a lesser extent, solar zenith angle, using the HYB-Mars model, a 3D quasineutral hybrid model. We find that the flux of precipitating protons has a strong altitude dependence: on the dayside, the flux of precipitating protons decreases substantially when the altitude over Mars decreases. We also find that the contribution of exospheric protons to the deposition is significant and its spatial distribution is not identical to that of the solar wind protons. In addition, the low energy proton population comes mainly from the newborn planetary protons. The energized pick-up protons and solar wind protons contribute to the higher energy proton population. The study also confirms that the proton precipitation is highly asymmetric with respect to the direction of the convection electric field in the solar wind. The study implies that the Martian induced magnetosphere protects the upper atmosphere effectively against proton precipitation.

Onset of collisionless magnetic reconnection in two-dimensional current sheets and formation of dipolarization fronts

[1] The onset of reconnection in 2-D current sheet equilibria that include an X line separating tail-like regions with magnetized electrons is simulated with a full-particle code. The onset is driven by a finite convection electric field applied outside the current sheet. In the case of tearing stable tails with no accumulated magnetic flux, the convection electric field penetrates the sheet near the X line. In contrast, in multiscale equilibria where the X line is framed by local areas of enhanced flux, the electric field avoids the X line, directly penetrates the areas of increased flux, and ejects them downstream. The ejecta form dipolarization fronts (DFs), sharp magnetic pileups with a thickness on the order of the ion inertial length, much smaller than the mesoscales of the initial flux increase regions. The DFs move with the reconnection outflows in the direction opposite the magnetic field stretching, while behind them new X lines, distinct from the original, form. Simulations with a reduced driving field suggest that DF formation shares properties with the ion tearing instability, which is consistent with its potential destabilization in multiscale equilibria. Weak driving of equilibria with tearing stable tails first forms flux accumulation regions, which then rapidly transform into DFs, making 2-D equilibria inherently metastable. The results are compared with observations of DFs, the statistical visualization of Earth's magnetotail during substorm onset, and the bubble-blob pair formation model.

Dayside midlatitude ionospheric response to storm time electric fields: A case study for 7 September 2002

[1] With the storm of 7–8 September 2002 as a study case, we demonstrate that an ionospheric model driven by a suitable storm time convection electric field can reproduce the F region dayside density enhancements associated with the ionospheric storm positive phase. The ionospheric model in this case is the Utah State University Time Dependent Ionospheric Model (TDIM); the electric field model is the University of Michigan's Hot Electron and Ion Drift Integrator (HEIDI). Extensive ground truth is available throughout the study period from two independent sources: ground-based vertical TEC and ionosonde stations; our simulation results are in good agreement with these observations. We address the question of what is the source of the high-density plasma that is seen during the positive storm phase and show that in this case a magnetospheric electric field with an eastward component that penetrates to midlatitudes increases local production on the dayside to a degree that is sufficient to account for the storm time density increases that have been observed.

Interhemispheric observations of dayside convection under northward IMF

[1] The reverse convection potential and electric field under northward interplanetary magnetic field (IMF) has been shown to saturate at a larger value in the summer than in the winter. Previous studies of reverse convection under northward IMF have suggested that in the winter hemisphere, much of the reconnection involves “internal reconnection” with over-draped field lines from the summer hemisphere. We present a case study in which reverse convection was simultaneously visible in the northern and southern hemispheres near the northern winter solstice. We use SuperDARN radar velocity measurements to demonstrate that the sunward (reverse) convection along the noon meridian is significantly faster in the summer hemisphere. We also use DMSP energetic particle data to demonstrate that in the winter hemisphere, some of the convection circulates on closed field lines, which is a signature of internal reconnection. These results suggest that internal reconnection is much less effective in transmitting the interplanetary electric field (IEF) into the ionosphere.

Polar-equatorial ionospheric currents driven by the region 2 field-aligned currents at the onset of substorms

[1] The dawn-to-dusk convection electric field increases during the growth phase of substorms, driving DP2 currents composed of two-cell current vortices in high latitude and leading to an increase in the eastward electrojet at the dayside dip equator (EEJ). During the expansion phase of substorms, electric field and currents are often reversed in direction to the normal DP2 currents at subauroral to equatorial latitudes when the convection electric field reduces abruptly. The reversed current at the dayside dip equator appears as a counterelectrojet (CEJ) and causes an equatorial enhancement of the negative bay in the afternoon sector. Conversely, the convection electric field increases during substorms as deduced from sawtooth events, causing an increase in the EEJ. In this study, by analyzing isolated substorms with magnetometer array data and SuperDARN (Super Dual Auroral Radar Network) convection maps, we deduce that the reversed electric field and currents develop at the subauroral-to-equatorial latitudes at the onset of substorms, while the convection electric field increases at auroral latitudes. These observations imply that both the region 1 and region 2 field aligned currents (R1 and R2 FACs) develop on the dayside concurrently with the current wedge responsible for the midlatitude positive bay at midnight. The substorm-associated R2 FACs are strong enough to cause the reversed current at the subauroral latitude and the CEJ at the equator. We also deduce that the dayside equatorial CEJ begins simultaneously with or even earlier than the midlatitude positive bay at midnight while the midlatitude positive bay onset is delayed by several minutes as the station departs from the midnight meridian. These observations suggest that the substorm begins with the intensification of the R2 FACs responsible for the equatorial CEJ.

O+outflow channels around Venus controlled by directions of the interplanetary magnetic field: Observations of high energy O+ions around the terminator

[1] Using the plasma and the magnetic field data measured by the ASPERA-4 (Analyzer of Space Plasma and Energetic Atoms) and the magnetometer (MAG) onboard Venus Express between June 2006 and December 2008, positions of high energy O+ fluxes (>100 eV) near the Venus terminator are examined for two different interplanetary magnetic field (IMF) configurations: IMF nearly perpendicular to the Venus-Sun line (perpendicular IMF case) and IMF nearly parallel to it (parallel IMF case). In most of the perpendicular IMF case, the high energy O+ fluxes are observed only near the magnetic poles. In contrast, they are observed regardless of a convection electric field around the terminator in most of the parallel IMF case. Energy of the flux depends on the convection electric field direction in the former case. In contrast, it has no dependence on the field direction in the latter case. We attribute these results to more complicated draping pattern of IMF around the ionosphere in the parallel IMF case than for that of the perpendicular IMF case. In the perpendicular IMF case, the IMF drapes around the ionosphere, forming a single plasma sheet. In contrast, in the parallel IMF case, the IMF drapes complicatedly, creating many antiparallel configuration of local magnetic field. Such multiple antiparallel configuration results in a local acceleration of O+ and more outflow channels. Thus, the ion acceleration region and its mechanism can be essentially different between the perpendicular IMF case and the parallel IMF case.

The efficiency of mechanisms driving Subauroral Polarization Streams (SAPS)

Abstract. We have investigated the seasonal and diurnal variation of SAPS (Subauroral Polarization Streams) occurrence based on 3663 SAPS events identified in DMSP ion drift observations in the Northern Hemisphere during July 2001 and June 2003. Their relationships with high latitude convection electric field, substorm, and ionospheric conductivity have been addressed. SAPS occurrences show a clear seasonal and diurnal variation with the occurrence rates varying by a factor of 5. It is found that the convection electric field might play a dominant role in association with SAPS occurrence. Peak convection electric fields mark the occurrence maximum of SAPS. Substorm might play a secondary role related to SAPS occurrence. It account for the secondary maximum in SAPS occurrence rate during December solstice. Our work demonstrates that the substorm induced electric field can develop SAPS during relatively low global convection. Somewhat low fluxtube-integrated conductivity is favorable for SAPS to develop. Another topic is the temporal relationship between SAPS and substorm phases. SAPS can occur at substorm onset, substorm expansion and recovery phases. Most probably SAPS tend to occur 60 min/45 min after substorm onset during quiet/more disturbed geomagnetic activity, respectively. This indicates that enhanced global convection helps SAPS to develop quicker during substorms. The peak plasma velocity of SAPS is increased on average only by 5–10 % by the substorm process.