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We statistically investigate convective earthward fast flows using data measured by the Magnetospheric Multiscale mission in the tail plasma sheet during 2017–2021. We focus on "frozen in" fast flows and investigate the importance of different electric field components in the Sun‐Earth (V⊥x) and dusk‐dawn (V⊥y) velocity components perpendicular to the magnetic field. We find that a majority of the fast flow events (52% of 429) have the north‐south electric field component (Ez) as the most relevant or dominating component whereas 26% are so‐called conventional type fast flows with Ey and Ex as the relevant components. The rest of the flow events, 22%, fall into the two 'mixed' categories, of which almost all these fast flows, 20% of 429, have Ey and Ez important for V⊥x and V⊥y, respectively. There is no Y‐location preference for any type of the fast flows. The conventional fast flows are detected rather close to the neutral sheet whereas the other types can be measured farther away. Typical total speeds are highest in the mixed category. Typical perpendicular speeds are comparably high in the conventional and mixed categories. The slowest fast flows are measured in the Ez category. Most of the fast flow events are measured in the substorm recovery phase. Prevailing interplanetary magnetic field By conditions influence the V⊥y direction and the influence is most efficient for the Ez‐dominated fast flows. Key Points: Most of the "frozen in" perpendicular bursty bulk flows (BBFs) detected in the 2017–2021 Magnetospheric Multiscale tail seasons have Ez as the most important E‐field componentTypically, the BBFs have fastest total speeds when Ey and Ez are important for V⊥x and V⊥y, respectivelyThe interplanetary magnetic field By influence on BBF plasma is most efficient when Ez is the most important E‐field component [ABSTRACT FROM AUTHOR]

The physical magnetospheric cause for geomagnetically induced currents (GICs) are rapid time‐varying magnetic fields (dB/dt), which occur mainly during magnetic substorms and storms. When, where and why exactly such rapid dB/dt may occur is insufficiently understood. We investigated all storms since 1980 and analyzed the negative and positive dB/dt spikes (>|500| nT/min) in the north and east component using a worldwide coverage (SuperMAG). Our analysis confirmed the existence of two dB/dt spikes "hotspots" located in the pre‐midnight and in the morning magnetic local time sector, independently of the geographic location of the stations. The associated physical phenomena are probably substorm current wedge onsets and westward traveling surges (WTS) in the evening sector, and wave‐ or vortex‐like current flows in the morning sector known as Omega bands. We observed a spatiotemporal evolution of the negative northern dB/dt spikes. The spikes initially occur in the pre‐midnight sector, and then develop in time toward the morning sector. This spatiotemporal sequence is correlated with bursts in the AE index, and can be repeated several times throughout a storm. Finally, we investigated the peak value of Dst and AE during the storm period in comparison with the dB/dt spike occurrence frequency, we did not find any correlation. This result implies that a moderate storm with many spikes can be as (or more) dangerous for ground‐based infrastructures than a major storm with fewer dB/dt spikes. Our findings regarding the physical causes and characteristics of dB/dt spikes may help to improve the GIC forecast for the affected regions. Plain Language Summary: Space weather prognosis is similar to meteorological weather but for predicting space events that can potentially damage humans technologies. One phenomenon are the geomagnetically induced currents or commonly called GICs. They are created by rapid fluctuations in the Earth's magnetic field, which can lead to power black outs and damages in communication systems. These rapid fluctuations are measured by worldwide magnetometers and defined as the time derivative of the magnetic field. In this study, we investigate the spikes in the time derivative for the two horizontal components, namely the northern and eastern component with a threshold of ±500 nT/min. Our first result shows that these rapid fluctuations mainly occur in the magnetic local time (MLT) pre‐midnight and morning sectors. We identified the possible physical phenomena that could caused the fluctuations. We also found that the spikes develop in space and time from the evening toward the morning MLT sectors. Finally, we found that a major geomagnetic storm does not necessary cause more spikes then a less intense one. Our findings concerning the physical nature of fast intense magnetic variations may help to improve the forecast of GICs. Key Points: During storms, dB/dt spikes follow a general spatiotemporal development starting in the pre‐midnight toward the morning sectorConfirmation of 2 dB/dt hotspots (pre‐midnight and morning sector) with different component characteristics independent of station locationThe peak value of Dst and AL indices during the entire storm is not correlated with the dB/dt spikes occurrence frequency of the storm [ABSTRACT FROM AUTHOR]

Previous studies have shown that the average dawn‐dusk component of the perpendicular plasma flow in the plasma sheet (V⊥) can vary depending on the distance relative to the neutral sheet and the dawn‐dusk component of the interplanetary magnetic field (IMF By). In this study, we combined 33 years of data from the Geotail, Time History of Events and Macroscale Interactions during Substorms, Cluster, and magnetospheric multiscale missions to study the slow (<200 km/s) ion flows perpendicular to the magnetic field. We find that IMF By has a hemispheric dependent influence on both the tail By and tail V⊥. Particularly, the influence is more prominent in the midnight sector (compared to both the pre‐ and post‐midnight sectors) and at distances far from the neutral sheet (compared to the distances close to the neutral sheet). However, at distances close to the neutral sheet, there is an increased dominance of duskward flows which dominates over the systematic influence of IMF By on tail V⊥. Our results indicate that IMF By has a major influence on the magnetic flux transport in the magnetotail, mainly at distances far from the neutral sheet. The influence is weaker at distances close to the neutral sheet. Plain Language Summary: The dawn‐dusk component of the interplanetary magnetic field (IMF By) can "penetrate and induce" the magnetic field (of same direction) in the magnetotail's plasma sheet. Consequently, IMF By can cause a dawn‐dusk asymmetry in the plasma sheet flow. Recently, it has been found that the dawn‐dusk asymmetry of the plasma sheet flow can also depend on the distance with respect to the neutral sheet. These two factors present a competing effect on the dawn‐dusk asymmetry of the plasma sheet flows. In this study, we will analyze these two competing factors (i.e., IMF By and distance to the neutral sheet) on the plasma sheet flows. We find that IMF By only has a hemispheric dependent influence on tail V⊥ at distances far from the neutral sheet. At distances close to the neutral sheet, duskward flows become more dominant and IMF By does not have a clear influence on tail V⊥. Our results indicate that IMF By has a major influence on the direction of the magnetic flux transport in the magnetotail, only at distances far from the neutral sheet. Key Points: IMF By has a systematic interhemispheric influence on the By and V⊥y in the magnetotail's plasma sheetThe influences are more prominent in the midnight sectors and at distances far from the neutral sheetAt distances close to the neutral sheet, duskward diamagnetic drift dominates over the influence of IMF By on tail V⊥y [ABSTRACT FROM AUTHOR]

We utilized 33 years of data obtained by the Geotail, THEMIS, Cluster and MMS missions to investigate the slow (<200 km/s) ion flows perpendicular to the magnetic field in Earth's magnetotail plasma sheet. By using plasma β as a proxy of distance to the neutral sheet, we find that the ion flow patterns vary systematically within the plasma sheet. Particularly, in regions farther from the neutral sheet, earthward (tailward) flows exhibit a strong tendency to diverge (converge) quasi‐symmetrically, with respect to the midnight meridional plane. As the distance becomes closer toward the neutral sheet, this tendency to diverge and converge gradually weakens. Moreover, duskward flows become the dominant components in both the earthward and tailward flows. These variations in ion flow patterns with distance to neutral sheet are hemispherically independent. We suggest that the spatial profiles of the electric and diamagnetic drift vary with distance to the neutral sheet and are therefore responsible for the varying ion flow patterns. Plain Language Summary: The plasma sheet can be visualized as "layers" stacking on top of each other where the middle layer represents the neutral sheet. In this study, we investigate the plasma convection patterns in these various plasma sheet "layers" in terms of their location relative to the neutral sheet. Our study finds that the plasma convection patterns in the plasma sheet are different depending on their distance from the neutral sheet. Farther from the neutral sheet, earthward and tailward flows converge and diverge quasi‐symmetrically, respectively, with respect to the midnight plane. As distance becomes closer to the neutral sheet, the degree of convergence and divergence weakens. At distance closest to the neutral sheet, duskward flows become the dominant components. We suggest that the spatial profiles of the electric and diamagnetic drift vary with distance to the neutral sheet and are therefore responsible for the varying ion flow patterns. Key Points: Slow plasma sheet ion flows (<200 km/s) perpendicular to the magnetic field vary systematically with distance to the neutral sheetFarther from the neutral sheet, earthward (tailward) flows exhibit stronger flow divergence (convergence) with the midnight meridional planeCloser to the neutral sheet, the diverging/converging tendency weakens, and the flows are dominated by duskward flow components [ABSTRACT FROM AUTHOR]

In Earth's magnetotail plasma sheet, the sunward-tailward Bx component of the magnetic field is often used to separate the region above and below the cross-tail current sheet. Using a threedimensional magneto-hydrodynamic simulation, we show that high-speed flows do not only affect the north-south magnetic field component (causing dipolarization fronts), but also the sunward-tailward component via the formation of a magnetic dent. This dent is such that, in the Northern Hemisphere, the magnetic field is tailward while in the Southern Hemisphere, it is earthward. This is opposite to the expected signatures where Bx > 0 (Bx < 0) above (below) the neutral sheet. Therefore, the direction of the magnetic field cannot always be used to identify in which hemisphere an in situ spacecraft is located. In addition, the cross-tail currents associated with the dent is different from the currents in a tail without a dent. From the simulation, we suggest that the observation of a dawnward current and a tailward magnetic tension force, possibly together with an increase in the plasma beta, may indicate the presence of a magnetic dent. To exemplify, we also present data of a high-speed flow observed by the Cluster mission, and we show that the changing sign of Bx is likely due to such a dent, and not to the spacecraft moving across the neutral sheet. [ABSTRACT FROM AUTHOR]

We present a statistical study of magnetotail flows that change direction from earthward to tailward using Cluster spacecraft. More precisely, we study 318 events of particle flux enhancements in the O+ data for which the pitch angle continuously changes with time, either from 0° to 180° or from 180° to 0°. These structures are called "Pitch Angle Slope Structures" (PASSes). PASSes for which the pitch angle changes from 0° to 180° are observed in the Northern Hemisphere while those for which the pitch angle changes from 180° to 0° are observed in the Southern Hemisphere. These flux enhancements result in a reversal of the flow direction from earthward to tailward regardless of the hemisphere where they are observed. Sometimes, several PASSes can be observed consecutively which can therefore result in oscillatory velocity signatures in the earth‐tail direction. The PASS occurrence rate increases from 1.8% to 3.7% as the AE index increases from ∼0 to ∼600 nT. Also, simultaneously to PASSes, there is typically a decrease in the magnetic field magnitude due to a decrease (increase) of the sunward component of the magnetic field in the Northern (Southern) Hemisphere. Finally, based on the 115 (out of 318) PASSes that show energy‐dispersed structures, the distance to the source from the spacecraft is estimated to be typically <25RE along the magnetic field line. This study is important as it sheds light on one of the causes of tailward velocities in Earth's magnetotail. Key Points: Flow reversals from earthward to tailward can be due to an enhanced flux of earthward moving particles which move tailward after mirroringFlow reversals can be flux enhancements for which the pitch angle changes from 0° (180°) to 180° (0°) in the Northern (Southern) HemisphereThe particles forming the flow reversals have typically traveled <25RE from the apparent source to the spacecraft [ABSTRACT FROM AUTHOR]

We investigate the heavy ion density and velocity in the Venusian upper ionosphere near the North Pole, using the Ion Mass Analyzer, a part of the Analyzer of Space Plasmas and Energetic Atoms 4, together with the magnetic field instruments on Venus Express. The measurements were made during June–July 2014, covering the aerobraking campaign with lowered altitude measurements (~130 km). The plasma scale heights are ~15 km below 150‐km altitude and ~200 km at 150–400‐km altitude. A clear trend of dusk‐to‐dawn heavy ion flow across the polar ionosphere was found, with speeds of ~2–10 km/s. In addition, the flow has a significant downward radial velocity component. The flow pattern does not depend on the interplanetary magnetic field directions nor the ionospheric magnetization states. Instead, we suggest a thermal pressure gradient between the equatorial and polar terminator regions, induced by the decrease in density between the regions, as the dominant mechanism driving the ion flow. Plain Language Summary: We have calculated the ion density and velocities in the Venusian polar ionosphere using measurements from the Ion Mass Analyzer on board the Venus Express spacecraft. During June–July 2014 the periapsis was lowered to ~130 km, which allowed for measurements down to low altitudes of the ionosphere near the North Pole. The plasma scale heights are ~15 km below 150‐km altitude and ~200 km at 150–400 km, which is similar to what was found near the equatorial region by the Pioneer Venus mission. In addition, there is a clear trend of dusk‐to‐dawn flow, along the terminator, for the heavy ions. This is surprising, as a general flow from day‐to‐night is expected for the Venusian ionosphere due to the long nights and significant heating of the dayside upper atmosphere. The interplanetary magnetic field direction does not appear to affect the ion flow pattern. Instead, we propose a thermal pressure gradient as the dominant accelerating mechanism, induced by the decrease in density from the equator toward the pole. Key Points: A net dusk‐to‐dawn heavy ion flow across the polar region was found, with high speeds inside the collisional region of the ionosphereThe heavy ion flow pattern does not depend on the external interplanetary field directions or the magnetization state of the upper ionosphereWe suggest a thermal pressure gradient between the polar and equatorial terminator regions as an accelerating mechanism toward the pole [ABSTRACT FROM AUTHOR]