Two collections of substorms are created: 28,464 substorms identified with jumps in the SuperMAG AL index in the years 1979–2015 and 16,025 substorms identified with electron injections into geosynchronous orbit in the years 1989–2007. Substorm occurrence rates and substorm recurrence‐time distributions are examined as functions of the phase of the solar cycle, the season of the year, the Russell‐McPherron favorability, the type of solar wind plasma at Earth, the geomagnetic‐activity level, and as functions of various solar and solar wind properties. Three populations of substorm occurrences are seen: (1) quasiperiodically occurring substorms with recurrence times (waiting times) of 2–4 h, (2) randomly occurring substorms with recurrence times of about 6–15 h, and (3) long intervals wherein no substorms occur. A working model is suggested wherein (1) the period of periodic substorms is set by the magnetosphere with variations in the actual recurrence times caused by the need for a solar wind driving interval to occur, (2) the mesoscale structure of the solar wind magnetic field triggers the occurrence of the random substorms, and (3) the large‐scale structure of the solar wind plasma is responsible for the long intervals wherein no substorms occur. Statistically, the recurrence period of periodically occurring substorms is slightly shorter when the ram pressure of the solar wind is high, when the magnetic field strength of the solar wind is strong, when the Mach number of the solar wind is low, and when the polar‐cap potential saturation parameter is high.
The Swarm mission represents a strong new tool to survey polar cap patches and plasma structuring inside the polar cap. In the early commissioning phase, the three Swarm satellites were operated in a pearls‐on‐a‐string configuration making noon‐midnight transpolar passes. This provides an unparalleled opportunity to examine the potential role of the gradient drift instability (GDI) process on polar cap patches by systematically calculating GDI growth times during their transit across the pole from day to night. Steep kilometer‐scale gradients appeared in this study as initial structures that persisted during the approximate 90 min it took a patch to cross the polar cap. The GDI growth times were calculated for a selection of the steep density gradients on both the dayside and the nightside. The values ranged from 23 s to 147 s, which is consistent with recent rocket measurements in the cusp auroral region and provides a template for future studies. Growth times of the order of 1 min found both on the dayside and on the nightside support the existing view that the GDI may play a dominant role in the generation of radio wave scintillation irregularities as the patches transit the polar cap from day to night.
To more fully monitor the elements of the magnetosphere‐ionosphere system and its activity, indices are created to quantify the rate of substorm onset occurrence, the rate of substorm activations, the intensity of the 130 keV substorm‐injected electrons and the intensity of the 1.2 MeV radiation‐belt electrons. The reactions of these various indices to the onset of isolated substorms are examined, and the behaviors of the indices are explored before and during high‐speed‐stream‐driven storms and during solar wind rarefactions after high‐speed streams. Autocorrelation functions of the indices are analyzed and compared with autocorrelation functions of solar wind parameters and geomagnetic indices. Lagged‐time correlations between the indices and solar wind variables and geomagnetic indices are surveyed. These 1 h resolution indices are available to the research community.
We use Super Dual Auroral Radar Network data to study polar cap ionospheric flow under strongly dominant positive interplanetary magnetic field Bz component. We show that the near‐noon flow along the magnetic meridian is predominantly sunward in summer. The sunward velocity increase with intensification of the external driver (the reverse convection electric field) is also faster in summer, and the rate of the increase is slightly larger for the Southern Hemisphere. The sunward flows simultaneously detected in both hemispheres are faster in the summer hemisphere. In addition, while sunward flows are aligned with the midnight‐noon line in a winter hemisphere, they are oriented toward earlier magnetic local hours in a summer hemisphere.
The Super Dual Auroral Radar Network Hokkaido HF radar often detects periodically reoccurring E region echoing regions propagating toward or away from it. In this work, we consider 117 of such events identified for [2008][2009][2010][2011][2012]. These are shown to occur at nighttime, preferentially during summer, although significant number for events was found for winter. Statistics for the local time of occurrence, magnitude of the speed and polarity of progressions, and temporal and spatial periodicities are presented. We show that the power of echoes is linearly related to their Doppler velocity which makes it possible to identify the events on both power and Doppler velocity plots. Other peculiar characteristics of echoes are discussed. The onset of events is associated with gravity waves propagation through the radar field of view.
Statistical characteristics of short‐range coherent echoes observed by the Hokkaido Super Dual Auroral Radar Network (SuperDARN) high‐frequency (HF) radar (geographic/geomagnetic latitude = 43.5°N/37.3°N) at midlatitudes are investigated. We show that the echo occurrence is increased during nighttime and, especially strongly, during winter and summer. During summer, the occurrence rates are still large during morning‐prenoon hours; for these periods, strong sporadic E layers are observed by the Wakkanai ionosonde (geographic/geomagnetic latitude = 45.2°N/39.1°N) located in the vicinity of the radar field of view. Echo occurrence rate does not increase with the planetary magnetic activity characterized by the Kp and Dst magnetic indices and, seasonally, anticorrelates with variations of the Ap index. With respect to the magnetic L shells, echoes are seen more frequently in beams oriented almost perpendicular to L shells during summer, in beams at intermediate angles during equinoxes and winter, and sometimes in beams at the smallest available angles (~45°) during winter. Midlatitude echoes are of about the same power as at high latitudes but narrower by a factor of ~5. Power and spectral width of nighttime echoes increases with Doppler velocity, consistent with high‐latitude observations. The Doppler velocity shows a clear semidiurnal variation. The local time of these maxima changes with season. It is hypothesised that many Hokkaido echoes are received at high magnetic aspect angles of several degrees, and they are coming from the lower part of the E region where the irregularity phase velocity is affected by both E × B plasma drifts and neutral winds.
The advanced beam-driven FRC is a field reversed configuration (FRC) with the addition of neutral beam (NB) injection, electrode biasing, and magnetic expander divertors. The resulting configuration has novel features that make it necessary to revisit many key results in FRC theory. Three of these features include (i) a large energetic ion population, (ii) in-principle capability to adjust the electric field and rotation profiles, and (iii) a combination of magnetic and electrostatic confinement of electrons in the SOL. In some fueling scenarios the electron density profile may exhibit a significant peak outside of the separatrix. To explore these features a hybrid fluid/kinetic equilibrium model has been used to reconstruct typical experimental profiles of the C-2W experiment. Results indicate that the energetic ions provide at least 50% of the total plasma pressure. These equilibrium profiles have been used as initial conditions for global, cross-separatrix, turbulent transport simulations using the 3D electrostatic particle-in-cell code ANC. Electrostatic fluctuations were found to nonlinearly saturate at an amplitude which is an order magnitude lower than that observed previously. The tokamak turbulence code GTC code has also been extended to handle FRC physics in the new GTC-X version, which has been used to perform simulations of turbulent transport in the SOL relevant to electrode biasing. It is found that equilibrium E × B flow shear significantly decreases ion temperature gradient saturation amplitude and ion heat transport. Also in the SOL, a 1D2V continuum code has been developed and applied to parallel electron heat transport. Results show the formation of pre-sheath potential and reduction of parallel electron heat loss close to the ideal ambipolar limit, a result which has been validated by experimental diagnostics. These transport modifications caused by the three novel configuration features help to explain the remarkable plasma performance of the C-2W experiment.
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