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We present ionospheric observational results obtained over Ukrainian Antarctic Akademik Vernadsky station. Ionospheric parameters (peak electron density and height, electron density and electron and ion temperatures in the topside) during the period near the local winter solstice in the Southern Hemisphere (June 28—29, 2019) are considered. The main objective is to show distinctive features of variations in ionospheric parameters during a prolonged period with very low solar and magnetic activities, and minimal daily insolation. Methods. F2 layer peak electron density and height were calculated from ionograms obtained with ionosonde installed at the station with subsequent profile inversion. Defense Meteorological Satellite Program (DMSP) and Swarm data acquired over the station are used as well. Diurnal variations of electron density, and electron and ion temperatures at the altitude of the satellites’ orbits were calculated using a set of sub-models of the International Reference Ionosphere-2016 (IRI-2016) model. Results. We found a very good agreement between the observed and model variations of F2 layer peak electron density. Significant (by ~2 times) nighttime enhancement of electron density was observed on June 29. Electron density models show the similar increase of the density at the same time interval but this enhancement is much more smoothed comparing with the observations. Peak height values obtained using ionosonde are very close to ones calculated with the IRI-2016 sub-models. Satellite data are in a good consistency with the IRI model predictions, especially for electron density obtained by Swarm satellite. Conclusions. Multi-instrumental observations revealed a number of unique features of the ionosphere over Antarctic Peninsula under minima of solar and magnetic activities, and daily insolation.

This study exploits the volumetric sampling capabilities of the Resolute Bay Incoherent Scatter Radar (RISR-N) in collaboration with all-sky imagery and in-situ measurements (DMSP) to examine the i...

Following the St. Patrick's Day (17 March) geomagnetic storm of 2013, the interplanetary magnetic field had near-zero clock angle for almost two days. Throughout this period multiple cusp-aligned a...

We provide high-resolution maps of quasi-static Poynting flux (PF) in each hemisphere based on nine-satellite years of Defense Meteorological Satellite Program (DMSP) data. Conjugate comparisons fr...

In this study, a new high-latitude empirical model is introduced, named for Auroral energy Spectrum and High-Latitude Electric field variabilitY (ASHLEY). This model aims to improve specifications ...

We propose a mechanism for the formation of the horse-collar auroral configuration common during periods of strongly northwards interplanetary magnetic field, invoking the action of dual-lobe reconnection (DLR). Auroral observations are provided by the Imager for Magnetopause-to-Auroras Global Exploration (IMAGE) satellite and spacecraft of the Defense Meteorological Satellite Program (DMSP). We also use ionospheric flow measurements from DMSP and polar maps of field-aligned currents (FACs) derived from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE). Sunward convection is observed within the dark polar cap, with antisunwards flows within the horse-collar auroral region, together with the NBZ FAC distribution expected to be associated with DLR. We suggest that newly-closed flux is transported antisunwards and to dawn and dusk within the reverse lobe cell convection pattern associated with DLR, causing the polar cap to acquire a teardrop shape and weak auroras to form at high latitudes. Horse-collar auroras are a common feature of the quiet magnetosphere, and this model provides a first understanding of their formation, resolving several outstanding questions regarding the nature of DLR and the magnetospheric structure and dynamics during northwards IMF. The model can also provide insights into the trapping of solar wind plasma by the magnetosphere and the formation of a low-latitude boundary layer and cold, dense plasma sheet. We speculate that prolonged DLR could lead to a fully closed magnetosphere, with the formation of horse-collar auroras being an intermediate step.

In previous work (Hairston et al., GRL doi 10.1029/2018GL077381, 2018) we showed the topside F-layer (~850 km) electron temperatures measured by two DMSP spacecraft as they flew through the Moon’s ...

We propose a mechanism for the formation of the horse-collar auroral configuration during periods of strongly northward interplanetary magnetic field (IMF), invoking the action of dual-lobe reconnection (DLR). Auroral observations are provided by the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite and spacecraft of the Defense Meteorological Satellite Program (DMSP). We also use ionospheric flow measurements from DMSP and polar maps of field-aligned currents (FACs) derived from the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE). Sunward convection is observed within the dark polar cap, with antisunward flows within the horse-collar auroral region, together with the NBZ FAC distribution expected to be associated with DLR. We suggest that newly closed flux is transported antisunward and to dawn and dusk within the reverse lobe cell convection pattern associated with DLR, causing the polar cap to acquire a teardrop shape and weak auroras to form at high latitudes. Horse-collar auroras are a common feature of the quiet magnetosphere, and this model provides a first understanding of their formation, resolving several outstanding questions regarding the nature of DLR and the magnetospheric structure and dynamics during northward IMF. The model can also provide insights into the trapping of solar wind plasma by the magnetosphere and the formation of a low-latitude boundary layer and cold, dense plasma sheet. We speculate that prolonged DLR could lead to a fully closed magnetosphere, with the formation of horse-collar auroras being an intermediate step. publishedVersion

We present a multi‐instrument multiscale study of a channel of enhanced, inhomogeneous flow in the cusp ionosphere occurring on November 30, 2014. We provide evidence that strong Global Navigation Satellite System (GNSS) phase scintillations indices (σϕ>0.5 rad) can arise from such events, indicating that they are important in the context of space weather impacts on technology. We compare in detail two‐dimensional maps of ionospheric density, velocity, and temperatures obtained by the European Incoherent Scatter Scientific Association Svalbard Radar with scintillation indices detected from a network of four GNSS receivers around Svalbard and examine the different sources of free energy for irregularity creation. We observe that the strongest phase scintillations occur on the poleward side of the flow channel in a region of sheared plasma motion and structured low‐energy particle precipitation. As inhomogeneous plasma flows are evident in our observations, we perform a quantitative, nonlinear analysis of the Kelvin–Helmholtz instability (KHI) and its impact on phase scintillations using numerical simulations from the first principles‐based Geospace Environment Model of Ion‐Neutral Interactions and Satellite‐beacon Ionospheric‐scintillation Global Model of the upper Atmosphere. Using representative values consistent with the radar data, we show that KHI can efficiently create density structures along with considerable scintillations and is thus likely to contribute significantly under similar conditions, which are frequent in the cusp. publishedVersion

A statistical study of ion upflow and field‐aligned currents (FACs) has been performed in the topside ionosphere of both hemispheres for magnetic quiet and disturbed times by using DMSP satellite observations from 2010–2013. Distributions in MLT/MLat reveal that ion upflow occurrence shows a dawn‐dusk asymmetry distribution that matches well with the Region 1 FACs. In addition, there are highest occurrence regions near noon and within the midnight auroral disturbance area, corresponding to dayside cusp and nightside auroral disturbance regions, respectively. Both the ion upflow occurrence and FAC regions expand equatorward to a wider area during disturbed times. publishedVersion

The expanding/contracting polar cap (ECPC) model, or the time-dependent Dungey cycle, provides a theoretical framework for understanding solar wind-magnetosphere-ionosphere coupling. The ECPC describes the relationship between magnetopause reconnection and substorm growth phase, magnetotail reconnection and substorm expansion phase, associated changes in auroral morphology, and ionospheric convective motions. Despite the many successes of the model, there has yet to be a rigorous test of the predictions or nowcasts made regarding ionospheric convection, which remains a final hurdle for the validation of the ECPC. In this study we undertake a comparison of ionospheric convection, as measured in situ by ion drift meters on board DMSP (Defense Meteorological Satellite Program) satellites and from the ground by SuperDARN (Super Dual Auroral Radar Network), with motions nowcasted by a theoretical model. The model is coupled to measurements of changes in the size of the polar cap made using global auroral imagery from the IMAGE FUV (Imager for Magnetopause to Aurora Global Exploration Far Ultraviolet) instrument, as well as the dayside reconnection rate, estimated using the OMNI data set. The results show that we can largely nowcast the magnitudes of ionospheric convection flows using the context of our understanding of magnetic reconnection at the magnetopause and in the magnetotail.

Previous studies have demonstrated that the high-latitude ionospheric convection is strongly influenced by the interplanetary magnetic field (IMF) direction. However, the temporal details of how the convection transitions from one state to another is still not understood completely. In this study, we analyze an interval on September 12, 2014 which provided a rare opportunity to examine dynamic variations in the dayside convection throat as the IMF transitioned from strong By+ to strong Bz+. Between 18:00 - 20:00 UT the northward face of the Resolute Bay Incoherent Scatter Radar (RISR-N) rotated through the noon sector and directly measured strengthening reverse convection flows in the dayside throat region that peaked at ∼2800m/s. Near-simultaneous measurements from DMSP satellites confirm the magnitude of the reverse convection and its proximity to the cusp. Time-series comparison of the RISR-N north-south flows with the IMF Bz component shows a remarkably high correlation, suggestive of strong linear coupling, with no sign of velocity saturation. Likewise, the east-west flow variations were highly correlated with the changes in IMF By. However, time-lagged correlation analysis reveals that the IMF By influence acted on a time-scale 10 minutes shorter than that of the Bz component. As a consequence, the manner in which the convection transitioned from the strong By+ condition to the strong Bz+ condition is inconsistent with either the anti-parallel and component reconnection models. Instead, we suggest that these particular observations are consistent with two separate reconnection sites on the magnetopause driven independently by the IMF By and Bz components.

The magnetic storm of 22-23 June 2015 was one of the largest in the current solar cycle. We present in situ observations from the Magnetospheric Multiscale Mission (MMS) and the Van Allen Probes (VAP) in the magnetotail, field-aligned currents from AMPERE (Active Magnetosphere and Planetary Electrodynamics Response), and ionospheric flow data from Defense Meteorological Satellite Program (DMSP). Our real-time space weather alert system sent out a "red alert," correctly predicting Kp indices greater than 8. We show strong outflow of ionospheric oxygen, dipolarizations in the MMS magnetometer data, and dropouts in the particle fluxes seen by the MMS Fast Plasma Instrument suite. At ionospheric altitudes, the AMPERE data show highly variable currents exceeding 20 MA. We present numerical simulations with the Block Adaptive Tree-Solarwind - Roe - Upwind Scheme (BATS-R-US) global magnetohydrodynamic model linked with the Rice Convection Model. The model predicted the magnitude of the dipolarizations, and varying polar cap convection patterns, which were confirmed by DMSP measurements.

We investigate the existence of a specific field-aligned current (FAC) system predicted by numerical magnetohydrodynamic simulations in a past study. The FAC system is expected to occur when a drifting θ aurora is formed in response to a stepwise transition of interplanetary magnetic field (IMF) By during strongly northward IMF periods. When the IMF By changes from positive to negative, a crossbar forms in the Northern Hemisphere that moves dawnward, while in the Southern Hemisphere the crossbar moves in the opposite direction. The crossbar motion reverses when the IMF By changes from negative to positive. The FAC system appears on the trailing side of the drifting crossbar of the θ aurora as it moves either dawnward or duskward. When the θ aurora is drifting dawnward, the FACs flow into the ionosphere. The FAC polarity reverses when the θ aurora is drifting duskward. Using low-altitude satellite data, we confirmed the real existence of the above model-predicted FAC system.

Previous investigations of ionospheric storm-enhanced density (SED) and tongue of ionization (TOI) focused mostly on the behavior of TOI during intense geomagnetic storms. Little attention has been paid to the spatial and temporal variations of TOI during weak to moderate geomagnetic disturbed conditions. In this paper we investigate the source and development of TOI during a moderate geomagnetic storm on 14 October 2012. Multi-instrumental observations including GPS total electron content (TEC), Defense Meteorological Satellite Program (DMSP) in situ measured total ion concentration and ion drift velocity, SuperDARN measured polar ion convection patterns, and electron density profiles from the Poker Flat Incoherent Scatter Radar (PFISR) have been utilized in the current analysis. GPS TEC maps show salient TOI structures persisting for about 5 h over high latitudes of North America on 14 October 2012 in the later recovery phase of the storm when the magnitudes of IMF By and Bz were less than 5 nT. The PFISR electron density profiles indicate that the extra ionization for TEC enhancements mainly occurred in the topside ionosphere with no obvious changes in the bottomside ionosphere and vertical plasma drifts. Additionally, there were no signatures of penetration electric fields in the equatorial electrojet data and upward ion drifts at high latitudes. At the same time, strong subauroral polarization streams with ion drift speeds exceeding 2.5 km/s carried sunward fluxes and migrated toward lower latitudes for about 5° based on the DMSP cross-track drift measurements. Based on those measurements, we postulate that the combined effects of initial build-up of ionization at midlatitudes through daytime production of ionization and equatorward (or less poleward than normal daytime) neutral wind reducing downward diffusion along the inclined filed lines, and an expanded polar ion convection pattern and its associated horizontal plasma transport are important in the formation of the TOI.

We use a set of ground-based instruments (Global Positioning System receivers, ionosondes, magnetometers) along with data of multiple satellite missions (Swarm, C/NOFS, DMSP, GUVI) to analyze the equatorial and low-latitude electrodynamic and ionospheric disturbances caused by the geomagnetic storm of 22-23 June 2015, which is the second largest storm in the current solar cycle. Our results show that at the beginning of the storm, the equatorial electrojet (EEJ) and the equatorial zonal electric fields were largely impacted by the prompt penetration electric fields (PPEF). The PPEF were first directed eastward and caused significant ionospheric uplift and positive ionospheric storm on the dayside, and downward drift on the nightside. Furthermore, about 45 min after the storm commencement, the interplanetary magnetic field (IMF) Bz component turned northward, leading to the EEJ changing sign to westward, and to overall decrease of the vertical total electron content (VTEC) and electron density on the dayside. At the end of the main phase of the storm, and with the second long-term IMF Bz southward turn, we observed several oscillations of the EEJ, which led us to conclude that at this stage of the storm, the disturbance dynamo effect was already in effect, competing with the PPEF and reducing it. Our analysis showed no significant upward or downward plasma motion during this period of time; however, the electron density and the VTEC drastically increased on the dayside (over the Asian region). We show that this second positive storm was largely influenced by the disturbed thermospheric conditions.

On 21 January 2005, a moderate magnetic storm produced a number of anomalous features, some seen more typically during superstorms. The aim of this study is to establish the differences in the space environment from what we expect (and normally observe) for a storm of this intensity, which make it behave in some ways like a superstorm. The storm was driven by one of the fastest interplanetary coronal mass ejections in solar cycle 23, containing a piece of the dense erupting solar filament material. The momentum of the massive solar filament caused it to push its way through the flux rope as the interplanetary coronal mass ejection decelerated moving toward 1 AU creating the appearance of an eroded flux rope (see companion paper by Manchester et al. (2014)) and, in this case, limiting the intensity of the resulting geomagnetic storm. On impact, the solar filament further disrupted the partial ring current shielding in existence at the time, creating a brief superfountain in the equatorial ionosphere—an unusual occurrence for a moderate storm. Within 1 h after impact, a cold dense plasma sheet (CDPS) formed out of the filament material. As the interplanetary magnetic field (IMF) rotated from obliquely to more purely northward, the magnetotail transformed from an open to a closed configuration and the CDPS evolved from warmer to cooler temperatures. Plasma sheet densities reached tens per cubic centimeter along the flanks—high enough to inflate the magnetotail in the simulation under northward IMF conditions despite the cool temperatures. Observational evidence for this stretching was provided by a corresponding expansion and intensification of both the auroral oval and ring current precipitation zones linked to magnetotail stretching by field line curvature scattering. Strong Joule heating in the cusps, a by-product of the CDPS formation process, contributed to an equatorward neutral wind surge that reached low latitudes within 1–2 h and intensified the equatorial ionization anomaly. Understanding the geospace consequences of extremes in density and pressure is important because some of the largest and most damaging space weather events ever observed contained similar intervals of dense solar material.

During a large geomagnetic storm, the electric field from the polar ionosphere can expand far enough to affect the mid-latitude and equatorial electric fields. These changes in the equatorial zonal electric field, called the penetration field, will cause changes in the meridional ion flows that can be observed by radars and spacecraft. In general this E × B ion flow near the equator caused by the penetration field during undershielding conditions will be upward on the dayside and downward on the nightside of the Earth. Previous analysis of the equatorial meridional flows observed by CINDI instrument on the C/NOFS spacecraft during the 26 September 2011 storm showed that all of the response flows on the dayside were excess downward flows instead of the expected upward flows. These observed storm-time responses are compared to a prediction from a physics-based coupled model of thermosphere–ionosphere–inner-magnetosphere in an effort to explain these observations. The model results suggest that the equatorial downward flow could be attributed to a combined effect of the overshielding and disturbance dynamo processes. However, some discrepancy between the model and observation indicates a need for improving our understanding of how sensitive the equatorial electric field is to various model input parameters that describe the magnetosphere–ionosphere coupling processes.

The Ion Velocity Meter (IVM), a part of the Coupled Ion Neutral Dynamic Investigation (CINDI) instrument package on the Communication/Navigation Outage Forecast System (C/NOFS) spacecraft, has made over 5 yr of in situ measurements of plasma temperatures, composition, densities, and velocities in the 400–850 km altitude range of the equatorial ionosphere. These measured ion velocities are then transformed into a coordinate system with components parallel and perpendicular to the geomagnetic field allowing us to examine the zonal (horizontal and perpendicular to the geomagnetic field) component of plasma motion over the 2009–2012 interval. The general pattern of local time variation of the equatorial zonal ion velocity is well established as westward during the day and eastward during the night, with the larger nighttime velocities leading to a net ionospheric superrotation. Since the C/NOFS launch in April 2008, F10.7 cm radio fluxes have gradually increased from around 70 sfu to levels in the 130–150 sfu range. The comprehensive coverage of C/NOFS over the low-latitude ionosphere allows us to examine variations of the topside zonal ion velocity over a wide level of solar activity as well as the dependence of the zonal velocity on apex altitude (magnetic latitude), longitude, and solar local time. It was found that the zonal ion drifts show longitude dependence with the largest net eastward values in the American sector. The pre-midnight zonal drifts show definite solar activity (F10.7) dependence. The daytime drifts have a lower dependence on F10.7. The apex altitude (magnetic latitude) variations indicate a more westerly flow at higher altitudes. There is often a net topside subrotation at low F10.7 levels, perhaps indicative of a suppressed F region dynamo due to low field line-integrated conductivity and a low F region altitude at solar minimum.

Using Poker Flat Incoherent Scatter Radar data from the International Polar Year, we observed unexpected short-lived enhancements of a few 100 K in the F region ion temperature, or “Ti spikes”, in conjunction with sharp F region plasma density drops near the dusk plasmapause. The geomagnetic conditions were moderately to weakly disturbed and the dusk spikes were often the largest Ti values recorded within the day. Taking various other observations into consideration, we conclude that the radar observed ion frictional heating events driven by large ion-neutral relative drifts caused by temporary intensifications in the convection pattern. The heating rate was enhanced through an increase in the size of the convection pattern, causing the neutrals just poleward of the dusk plasmapause to be moving antisunward while ions were moving sunward.

[1] For the first time, equatorial plasma depletions (EPDs) have been imaged in the longitude-altitude plane using radiotomography. High-resolution (~10 km) reconstructions of electron density were derived from total electron content (TEC) measurements provided by a receiver array in Peru. TEC data were obtained from VHF/UHF signals transmitted by the Coherent Electromagnetic Radio Tomography (CERTO) beacon on the C/NOFS satellite. EPDs generated premidnight were observed near dawn. On one night, the bubble densities were highly reduced, 100–1000 km wide, and embedded within a layerlike ionosphere. Three nights later, the EPDs exhibited similar features but were embedded in a locally uplifted ionosphere. The C/NOFS in situ instruments detected a dawn depletion where the reconstruction showed lifted EPDs, implying that the postmidnight electric fields raised sections of ionosphere to altitudes where embedded/reactivated fossil EPDs were detected as dawn depletions. Satellites flying under domelike distortions of the ionosphere may observe these distortions as broad plasma decreases (BPDs).

第6回極域科学シンポジウム[OS] 宙空圏11月16日（月） 国立極地研究所１階交流アトリウム

[1] An all-sky imager (ASI) records atmospheric emissions from zenith to low on the horizon at all azimuths, a region typically spanning millions of square kilometers. Each pixel (with its unique elevation, azimuth, and emission height) can be mapped along B-field lines to the equatorial plane of the magnetosphere. Auroral and subauroral structures and boundaries seen in emission within the ionosphere-thermosphere (I-T) system can thus be related to source regions. For a midlatitude site, this I-T to inner magnetosphere connection typically falls within the L = 2–5 earth radii domain. In this study, we present the first case of a stable auroral red (SAR) arc observed from three widely spaced ASI sites (Europe, North America, New Zealand). SAR arcs are produced during the main and recovery phases of a geomagnetic storm, with emission driven by heat conduction from a very specific location in the magnetosphere—the L value where the plasmapause and the inner edge of the ring current overlap. Using three-site observations, we show that this boundary can be followed for 24 consecutive hours. Simultaneous observations made by three satellites in the Defense Meteorological Satellite Program (DMSP) show that the lowest latitude peak in electron temperature can be used to map the same boundary. A key structure of the inner magnetosphere that cannot be observed continuously from sensors orbiting within the magnetosphere is made continuously visible to ground-based optical systems via effects caused by the drainage of small amounts of ring current energy into the I-T system.

[1] The equatorial ionosphere is generally shielded from outside electrical fields except during large geomagnetic storms. During these storms, the polar region electric fields can temporarily extend to the equatorial regions in what is called a penetration field. During the subsequent recovery period, a disturbance dynamo is produced with an enhanced electric field with the opposite orientation relative to the penetration field. The penetration electric field would be oriented toward the east on the dayside causing an excess upward E × B motion of the equatorial ionospheric ions. The disturbance dynamo electric field would have the opposite orientation, westward on the dayside, producing an excess downward E × B motion of the equatorial ionospheric ions. The moderate storm (minimum Dst = −103 nT) on 26 September 2011 is examined using ion flow data from the Coupled Ion-Neutral Dynamics Investigation (CINDI) thermal plasma instrument package on the Communication/Navigation Outage Forecast System (C/NOFS) spacecraft on the dayside and early evening local times to look for examples of these flows. Despite what should have been a large enough storm to produce penetration fields and upward flows, a detailed examination of the observed flows from this storm shows only enhanced downward flows before the storm, during the main phase, and through the recovery.

[1] When the interplanetary magnetic field (IMF) is dawnward or duskward, magnetic merging between the IMF and the geomagnetic field occurs near the cusp on the dayside flanks of the magnetosphere. During these intervals, flow channels in the ionosphere with velocities in excess of 2 km/s have been observed, which can deposit large amounts of energy into the high-latitude thermosphere. In this study, we analyze an interval on 5 April 2010 where there was a strong dawnward impulse in the IMF, followed by a gradual decay in IMF magnitude at constant clock angle. Data from the Sondrestrom incoherent scatter radar and the Defense Meteorological Satellite Program spacecraft were used to investigate ionospheric convection during this interval, and data from the Active Magnetospheric and Planetary Electrodynamics Response Experiment (AMPERE) were used to investigate the associated Field-Aligned Current (FAC) system. Additionally, data from AMPERE were used to investigate the time response of the dawnside FAC pair. We find there is a delay of approximately 1.25 h between the arrival of the dawnward IMF impulse at the magnetopause and strength of the dawnward FAC pair, which is comparable to substorm growth and expansion time scales under southward IMF. Additionally, we find at the time of the peak FAC, there is evidence of a reconfiguring four-sheet FAC system in the morning local time sector of the ionosphere. Additionally, we find an inverse correlation between the dawn FAC strength and both the solar wind Alfvenic Mach number and the SYM-H index. No statistically significant correlation between the FAC strength and the solar wind dynamic pressure was found.

[1] Large-scale periodic plasma bubbles are often observed by ionospheric radars and satellites. The seeding effect of atmospheric gravity waves has been widely used to explain the generation of periodic plasma bubbles. However, it has not been well understood where the seeding process occurs and how a series of plasma bubbles is triggered. In this study, we present the observations of equatorial plasma bubbles by the Communication/Navigation Outage Forecasting System (C/NOFS) satellite. We show examples of quasiperiodic plasma bubbles in the post-midnight sector, with nearly equal distance of 800–1000 km between adjacent bubbles, in 2008 under deep solar minimum conditions. The bubble chain covered a longitudinal range of ~7000 km between 00:00 and 04:00 LT. Quasiperiodic plasma bubbles were also measured by C/NOFS in the evening sector in 2011 during the ascending phase of the solar activity, and the longitudinal distance between adjacent bubbles was ~500 km. We propose a causal mechanism to explain the generation of quasiperiodic plasma bubbles. In this scenario, atmospheric gravity waves are generated near the sunset terminator and initiate the Rayleigh-Taylor instability there. The spatial (longitudinal) periodicity of plasma bubbles is determined by the temporal periodicity of the seeding gravity waves. A period of 15–30 min of the seeding gravity waves corresponds to a longitudinal separation of 500–1000 km between adjacent bubbles. This mechanism provides a reasonable explanation of the observed quasiperiodic plasma bubbles.

[1] We present a statistical analysis on the plasmaspheric mass density derived from the field line resonance (FLR) observations by the Mid-continent MAgnetoseismic Chain (McMAC). McMAC consists of nine stations in the United States and Mexico along the 330° magnetic longitude, spanning L-values between 1.5 and 3.4. Using the gradient method and an automated procedure for FLR detection, we studied a full year of McMAC observations between July 2006 and June 2007. We find that the rate of FLR detection can reach as high as 56% around local noon at L = 2.7, and the detection rates at higher and lower L-values decline due to the occasional presence of the plasmapause and weaker FLR signals, respectively. At L-values between 1.8 and 3.1, the inferred equatorial plasma mass density follows the L-dependence of L−4. By comparing the mass density with the electron density, we found that the ion mass gradually decreased from 1.7 amu at L = 1.8 to 1 amu at L = 3.1. The plasma mass density exhibits an annual variation that maximizes in January, and at L = 2.4 the ratio between January and July densities is 1.6. Our observations also show a local time dependence of plasmaspheric mass density that stays steady in the morning and rises postnoon, a phenomenon that may be attributed to the equatorial ionization anomaly as a part of the plasma neutral coupling at low latitude.

[1] We report the first observations of long-lasting daytime equatorial plasma bubbles with the Communication/Navigation Outage Forecasting System (C/NOFS) satellite. The most unusual features of the plasma bubbles are the persistence from the post-midnight sector through the afternoon sector and the extremely long lifetime of 12 h. In one case, the plasma bubbles were generated at 02:00–03:00 LT near the end of the main phase of a moderate magnetic storm and detected by C/NOFS over eight successive orbits, and the decrease of the ion density inside the bubbles was still as large as ~30% at 14:00–15:00 LT. In another case, one group of plasma bubbles was generated near the sunset terminator and existed over the entire nighttime until the post-sunrise sector (06:00–08:00 LT), and another group of plasma bubbles was first detected at 04:00–06:00 LT and lasted until ~11:00 LT. The latter group of bubbles occurred following a sharp northward turning of the interplanetary magnetic field (IMF) near the end of the main phase of a weak magnetic storm, and the overshielding electric field caused by the IMF northward turning and the storm time disturbance dynamo might both have contributed to the generation of the bubbles. The plasma bubbles reached 800 km or higher in altitude during daytime. The high altitudes may be critical for the long lifetime of the bubbles: the photo-ionization rate decreases rapidly with altitude. The photo-ionization process may take a long time to produce enough new plasma particles to fill the daytime bubbles at high altitudes.

[1] We describe the introduction of the first all-sky imaging system for low-light-level optical observations of the disturbed ionosphere over mid-latitude Europe. Using 6300 angstrom auroral emissions that come from the 200-400 km altitude range, we demonstrate that sub-visual optical patterns spanning the European continent can be obtained from a single site in Italy. Pilot observations during the 26-27 September 2011 geomagnetic storm show that the diffuse aurora's low latitude boundary can be used to find where the poleward wall of the ionospheric trough is located. This relates directly to regions of radiowave disruptions caused by the precipitation of energetic particles from the magnetospheric plasma sheet that move to lower latitudes during space weather events. Images of stable auroral red (SAR) arcs can be used to track the magnetospheric ring current and plasmapause location, a second region of radiowave interference. Comparisons with ground-based and satellite observations of the ionosphere during the same storm demonstrate how ASI images reveal the lowest energy components of magnetospheric input to the ionosphere-thermosphere system. Such observations can be used, potentially, for both now-casting of storm effects spanning Europe, and for retrospective validation of existing models of space weather impacts at sub-auroral locations. Citation: Baumgardner, J., et al. (2013), Imaging space weather over Europe, Space Weather, 11, 69-78, doi:10.1002/swe.20027.

Broad plasma depletions (BPDs) in the equatorial F region represent plasma depletions whose longitudinal and latitudinal scales are much greater than those of normal plasma bubbles. This study investigates the characteristics and origin of BPDs using the coincident ionospheric observations by the Communication/Navigation Outage Forecasting System, Defense Meteorological Satellite Program, and Swarm satellites during the 2015 St. Patrick's Day (17 March) storm. Two types of BPDs were detected before midnight during the main phase of the storm. One type of BPDs showed a gradual plasma density variation (Type 1), and the other type of BPDs showed a steep density gradient (Type 2) at the walls of BPDs. The Type 1 BPDs were detected with no signature of plasma bubbles nearby, whereas the Type 2 BPDs were accompanied by bubbles. The formation of the Type 1 BPDs is attributed to the uplift of the bottomside of the F region above the satellite altitude by the action of storm-induced electric fields. The steep walls of Type 2 BPDs are associated with the ionospheric uplift and the spatial discontinuity of the ionosphere produced by bubbles. The detection of BPDs that are more than 15° wide in latitude by the polar orbit Swarm satellites arises from the elongation of bubbles along the magnetic field lines and the alignment of the elongation with the plane of the orbit.

We report simultaneous global monitoring of a patch of ionization and in situ observation of ion upflow at the center of the polar cap region during a geomagnetic storm. Our observations indicate strong fluxes of upwelling O+ ions originating from frictional heating produced by rapid antisunward flow of the plasma patch. The statistical results from the crossings of the central polar cap region by Defense Meteorological Satellite Program F16–F18 from 2010 to 2013 confirm that the field-aligned flow can turn upward when rapid antisunward flows appear, with consequent significant frictional heating of the ions, which overcomes the gravity effect. We suggest that such rapidly moving patches can provide an important source of upwelling ions in a region where downward flows are usually expected. These observations give new insight into the processes of ionosphere-magnetosphere coupling.

The newly installed SuperDARN Hokkaido HF radar monitors ionospheric plasma flow between magnetic latitudes of 45° and 65° and thus has a great potential for studies of subauroral polarization streams (SAPS) in combination with another SuperDARN radar located at King Salmon, Alaska as well as the DMSP satellites and ground-based instruments in the Alaskan sector of the Arctic. Preliminary survey shows that although SAPS are often detected with the Hokkaido radar, their velocities are rather low, to the order of 150 m/s in its most suitable central beams. In this study, observations of unusually fast Hokkaido flows of up to 800 m/s are presented. The event of 1 April 2007 is investigated in detail. It is shown that high-velocity echoes appear after substorm onsets over North America with a delay of ~30 min. In terms of latitude, the velocity peaks just outside the auroral oval; signatures of a detached polarization jet are occasional and not pronounced. The King Salmon radar operating concurrently detects SAPS signatures as well but at different times and locations. Simulation with the Comprehensive Ring Current Model for the 1 April event reasonably identifies the period of fast flow occurrence but the velocity is underestimated. The event studied suggests that substorm-injected particle populations may intensify the pre-existing SAPS flow and lead to a mismatch of the predictions and observations.

The global distribution of low-latitude plasma blobs was investigated by in-situ plasma density measurements from the Korea Multi-Purpose Satellite-1 (KOMPSAT-1) and Defense Meteorological Satellite Program (DMSP) F15. In the observations, blobs occurred in the longitude sector where the activity of the equatorial plasma bubble (EPB) was appreciable, and additional blobs were found at the lower (KOMPSAT-1) altitude as in the EPBs. However, several notable differences exist between the distributions of EPBs and blobs. First, KOMPSAT-1 found few blobs around 0°E in March and June, as did DMSP F15 from 30°W to 120°E for every season. Second, the overall occurrences in December and March at the DMSP F15 (840 km) altitude were somewhat lower than expected from those of the EBPs. Third, at the DMSP F15 altitude, the occurrence probability of plasma blobs was less controlled by yearly variations in the solar activity. These results imply that topside ionospheric conditions as well as the existence of EPBs control further development of blobs. Additionally, it was found that the blob latitudes became higher as the yearly solar activity increased. Moreover, most of the blobs were encountered in the winter hemisphere, possibly due to the low ambient density.

Observations have revealed large Poynting flux and soft electron precipitation around the cusp region, which have strong impacts on the polar ionosphere/thermosphere. Simulations also confirmed that Poynting flux and soft electron precipitation significantly change the neutral density and dynamics around the dayside polar cap boundary regions. However, no detailed study has been conducted to show if they should coincide with each other or not. Our analysis of Defense Meteorological Satellite Program (DMSP) satellite data reveals a complex correlation between them. Poynting flux and soft particle precipitation are coincident in some cases (match cases), but a clear displacement between them can also be identified in others (nonmatch cases). In the 29 cusp crossings from F13 we investigated, the ratio between nonmatch and match cases is close to 1:4. In nonmatch cases, the displacement between the Poynting flux enhancement and soft particle precipitation enhancement can be as large as 1° in geomagnetic latitude., Key Points Correlation of Poynting flux and particle precipitationRelative location of two energy inputs in the dayside polar cap boundaryInfluence from the IMF conditions

The two-cell aurora is characterized by azimuthally elongated regions of enhanced auroral brightness over extended local times in the dawn and dusk sectors. Its association with the convection, particle precipitation, and field-aligned currents under various phases of substorms has not been fully understood. With Polar Ultraviolet Imager auroral images in conjunction with Defense Meteorological Satellite Program (DMSP) F12 spacecraft on the dusk-side branch of the two-cell aurora, we are able to investigate an association of the auroral emissions with the electric fields, field-aligned currents, and energy flux of electrons. Results show that the substorm expansion onset does not significantly change the orientation of the dusk-side branch of the two-cell aurora. Also, the orientation of the magnetic deflection vector produced by the region1 field-aligned current changed from 73±1° to the DMSP trajectory during the substorm growth phase, to 44±6° to the DMSP trajectory during the substorm expansion phase. With a comparison between the orientation of the dusk-side branch of the two-cell aurora and the orientation of the magnetic deflection vector, it is found that the angular difference between the two orientations is 28±5° during the substorm growth phase, and 13±6° during the substorm expansion phase.

Cross-track ion drifts measured by the DMSP satellites are compared with line-of-sight SuperDARN HF velocities in approximately the same directions. Good overall agreement is found for a data set comprising of 209 satellite passes over the field of view of nine SuperDARN radars in both the Northern and Southern Hemispheres. The slope of the best linear fit line relating the SuperDARN and DMSP velocities is of the order of 0.7 with a tendency for SuperDARN velocities to be smaller. The agreement implies that the satellite and radar data can be merged into a common set provided that spatial and temporal variations of the velocity as measured by both instruments are smooth. Keywords. Ionosphere (Ionospheric irregularities; Plasma convection; Auroral ionosphere)

During the long-duration steady convection activity on 11 December 1998, the development of a few dozen auroral streamers was monitored by Polar UVI instrument in the dark northern nightside ionosphere. On many occasions the DMSP spacecraft crossed the streamer-conjugate regions over the sunlit southern auroral oval, permitting the investigation of the characteristics of ion and electron precipitation, ionospheric convection and field-aligned currents associated with the streamers. We confirm the conjugacy of streamer-associated precipitation, as well as their association with ionospheric plasma streams having a substantial equatorward convection component. The observations display two basic types of streamer-associated precipitation. In its polewardmost half, the streamer-associated (field-aligned) accelerated electron precipitation coincides with the strong (≥2–7μA/m2) upward field-aligned currents on the westward flank of the convection stream, sometimes accompanied by enhanced proton precipitation in the adjacent region. In the equatorward portion of the streamer, the enhanced precipitation includes both electrons and protons, often without indication of field-aligned acceleration. Most of these characteristics are consistent with the model describing the generation of the streamer by the narrow plasma bubbles (bursty bulk flows) which are contained on dipolarized field lines in the plasma sheet, although the mapping is strongly distorted which makes it difficult to quantitatively interprete the ionospheric image. The convective streams in the ionosphere, when well-resolved, had the maximal convection speeds ∼0.5–1km/s, total field-aligned currents of a few tenths of MA, thicknesses of a few hundreds km and a potential drop of a few kV across the stream. However, this might represent only a small part of the associated flux transport in the equatorial plasma sheet.Key words. Ionosphere (electric fiels and currents). Magnetospheric physics (aurroal phenomena; energetic particles, precipitating)

A -190-nT negative bay in the geomagnetic X component measured at Macquarie Island ( -65° L) showed that an ionospheric substorm occurred during 09:58 to 11:10 UT on 27 February 2000. Signatures of an auroral westward flow channel (AWFC) were observed nearly simultaneously in the backscatter power, LOS Doppler velocity, and Doppler spectral width measured using the Tasman International Geospace Environment Radar (TIGER), a Southern Hemisphere HF SuperDARN radar. Many of the characteristics of the AWFC were similar to those occurring during a polarisation jet (PJ), or subauroral ion drift (SAID) event, and suggest that it may have been a pre-cursor to a fully developed, intense westward flow channel satisfying all of the criteria defining a PJ/SAID. A beam-swinging analysis showed that the westward drifts (poleward electric field) associated with the flow channel were very structured in time and space, but the smoothed velocities grew to ~ 800 ms-1 (47 mVm-1) during the 22-min substorm onset interval 09:56 to 10:18 UT. Maximum west-ward drifts of >1.3 km s-1 (>77 mVm-1) occurred during a ~ 5-min velocity spike, peaking at 10:40 UT during the expansion phase. The drifts decayed rapidly to ~ 300 ms-1 (18 mVm-1) during the 6-min recovery phase interval, 11:04 to 11:10 UT. Overall, the AWFC had a lifetime of 74 min, and was located near -65° L in the evening sector west of the Harang discontinuity. The large westward drifts were confined to a geographic zonal channel of longitudinal ex-tent >20° (>1.3 h magnetic local time), and latitudinal width ~2° L. Using a half-width of ~ 100 km in latitude, the peak electric potential was >7.7 kV. However, a transient velocity of >3.1 km s-1 with potential >18.4 kV was observed further poleward at the end of the recovery phase. Auroral oval boundaries determined using DMSP measurements suggest the main flow channel overlapped the equatorward boundary of the diffuse auroral oval. During the ~ 2-h interval following the flow channel, an ~ 3° L wide band of scatter was observed drifting slowly toward the west, with speeds gradually decaying to ~ 50 ms-1 (3 mVm -1). The scatter was observed extending past the Harang discontinuity, and had Doppler signatures characteristic of the main ionospheric trough, implicating the flow channel in the further depletion of F-region plasma. The character of this scatter was in contrast with the character of the scatter drifting toward the east at higher latitude.Key words. Ionosphere (auroral ionosphere; electric fields and currents; ionosphere-magnetospehere interactions) Magnetospheric physics (storms and substorms)